US20110197831A1

US20110197831A1 - Pulverized Coal Burning Boiler

Info

Publication number: US20110197831A1
Application number: US12/594,997
Authority: US
Inventors: Noriyuki Ohyatsu; Hidehisa Yoshizako; Katsumi Shimohira; Hitoshi Okimura; Seishi Miyake
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 2007-04-13
Filing date: 2008-04-11
Publication date: 2011-08-18
Also published as: EP2143997B1; EP2143997A4; KR101232696B1; WO2008133051A1; CN101663537A; CA2683873C; PL2143997T3; CN101663537B; JP4855518B2; JPWO2008133051A1; EP2143997A1; KR20100003288A; CA2683873A1

Abstract

A pulverized coal burning boiler is provided, which reduces an air-excess ratio thereby to reduce the emission of unburned contents such as CO. The pulverized coal burning boiler includes a pulverized coal feed measuring device for measuring the feeding rates of the pulverized coal to be conveyed through coal feeding pipes, individually, and a control device for calculating the burning air feeding rates to match the pulverized coal feeding rates thereby to send a control command signal to burning air feed adjusting device, so that a burner air ratio set by a burner air ratio setting device may be kept on the basis of both the pulverized coal feeding rate, which is measured by the pulverized coal feed measuring device, and the burning air feeding rate, which is measured by the burning air feeding rate measuring device and fed to a pulverized coal burner connected to the coal feeding pipes.

Description

TECHNICAL FIELD

The present invention relates to a pulverized coal burning boiler such as a power generation boiler apparatus and particularly to a pulverized coal burning boiler in which a plurality of coal feeding pipes are connected to a single milling means such as a roller mill so that pulverized coal generated by the milling means is distributed to the plurality of coal feeding pipes, fed to individual pulverized coal burners and burned.

BACKGROUND ART

(Background Art 1)

Conventionally, a pulverized coal burning boiler uses a two-stage burning method in which air with a smaller ratio than a theoretical air ratio is imported by a burner and low NOx combustion is performed in a reducing atmosphere in order to reduce the amount of emergence of NOx and then additional air is imported from an after airport (hereinafter abbreviated as AAP) as a post-stage in order to burn unburned contents such as CO.
To achieve complete burning at a furnace outlet finally, the amount of air imported into a combustion device as a whole is imported so excessively as to be about 1.2 which is more than the theoretical air ratio of 1.0.
In recent years, there has been an increasing demand for combustion at a ratio as close to the theoretical air ratio of 1.0 as possible, i.e. at a low excess air ratio for the purpose of reducing the amount of combustion gas to thereby attain reduction in size of a furnace and an exhaust gas processing device, etc. following the furnace, reduction in various kinds of fan motive utilities, etc.
With respect to the background art 1, for example, Patent Documents 1 to 3 can be listed.

(Background Art 2)

FIGS. 36 and 37 are views for explaining a variable pressure once-through type pulverized coal burning boiler according to the background art. As shown in FIG. 36, in this type pulverized coal burning boiler according to the background art, multi-stage multi-column pulverized coal burners 702 are disposed for a furnace 701 so that pulverized coal and combustion air are jetted from the pulverized coal burners 702 into the furnace and burned. To reduce production of NOx, this combustion device uses a two-stage combustion method in which a smaller amount of combustion air than the theoretical air amount is imported by the pulverized coal burners 702, low NOx combustion is performed in a reducing atmosphere and then additional air is imported from AAPs 703 as a post-stage to burn an unburned component such as CO.
The amount of this additional air is supplied so that the total amount of air containing the amount of air supplied from the pulverized coal burners 702 exceeds the theoretical air amount. This is for the purpose of compensating for local shortage of air caused by uneven supply of pulverized coal to the pulverized coal burners 702 or the purpose of compensating for imperfect mixing of exhaust gas from the pulverized coal burners 702 and air imported from the AAPs 703 as will be described later.
Accordingly, as the excess ratio of the total air amount to the theoretical air amount, that is, the excess air ratio increases, the concentration of CO in exhaust gas decreases but thermal loss due to exhaust gas increases to cause lowering of boiler efficiency. For this reason, the excess air ratio is generally set to be about 20-30%. Incidentally, there may be a pulverized coal burning boiler using a so-called single-stage combustion method in which all air is supplied from pulverized coal burners without provision of any AAP.
Raw coal is milled by milling means so that pulverized coal is generated and supplied to the respective pulverized coal burners 702. Although the amounts of pulverized coal supplied to the respective pulverized coal burners 702 are adjusted to be equal at the time of trial operation, a deviation may be generated between the supply amounts of pulverized coal in vessel left and right because it is difficult to adjust the amounts of pulverized coal uniformly based on all loads and the supply amounts of pulverized coal may be unbalanced in accordance with aging. The deviation between the supply amounts of pulverized coal in vessel left and right causes a deviation between combustion gas temperatures in the furnace. As a result, a deviation is generated between steam temperatures in the vessel left and right.
As shown in FIG. 36, in the pulverized coal burning boiler according to the background art, when suspension type secondary repeaters are disposed in a flue in reheating steam temperature control, a vessel left side primary reheater 710 is connected to a vessel right side secondary reheater 713 and a vessel right side primary reheater 711 is connected to a vessel left side secondary reheater 712 to thereby reduce the deviation between steam temperatures in the vessel left and right.
FIG. 37 is a characteristic graph showing an example of reheating steam temperature (ROT) deviations based on deviations between the supply amounts of fuel (pulverized coal). In FIG. 37, the solid line shows a state of the vessel left side and the broken line shows a state of the vessel right side. As shown in FIG. 37, when a deviation is generated between the supply amounts of pulverized coal in the vessel left and right at time A for a certain reason, a deviation is generated in a gas temperature distribution, a deviation is lately generated in a reheater metal temperature distribution and a deviation is further lately generated between reheating steam temperatures (ROTs) in the vessel left and right at time B. If there is no countermeasure, the deviation remains forever as shown in FIG. 37.
In Japan, the reheating steam temperature generally must not be increased by 8° C. or higher from a designated steam condition. Accordingly, in the state in which the higher one is 5° C. higher and the lower one is −5° C. lower than the steam condition, tolerance on control is only 3° C., as shown in FIG. 37. Because the limit of 8° C. is provided for the purpose of protecting materials, repeater inlet sprays start immediately when not an average but either of reheating steam temperatures in the vessel left and right is going to be 8° C. higher.

(Background Art 3)

JP-A-6-101806 (Patent Document 4) has described that a deviation between reheating steam temperatures is reduced when the apertures of gas distributing dampers disposed in the rear of a furnace are adjusted to apply biases to the vessel left and right. FIG. 38 is a view showing arrangement of the gas distributing dampers in a flue based on this proposal.
As shown in FIG. 38, a partition wall 801 a is provided in the center between the vessel left and right, and a partition wall 801 b is provided so as to be perpendicular to the partition wall 801 a. Gas distributing dampers 718, 719, 720 and 721 are disposed in respective space portions partitioned by the partition walls 801 a and 801 b and a casing 802. The apertures of the gas distributing dampers 718 to 721 can be adjusted individually.

(Background Art 4)

JP-A-9-21505 (Patent Document 5) has described that a connection pipe 902 connecting the inlet and outlet of a primary reheater 901 is provided and a steam flow rate adjusting valve 903 inserted in an intermediate portion of the connection pipe 902 is operated based on a temperature difference between the vessel left and right systems to adjust the flow rates of steam in the vessel left and right to thereby reduce the deviation between reheating steam temperatures, as shown in FIG. 39.
In FIG. 39, the reference numeral 904 designates a secondary reheater; 905, a primary reheater inlet connection pipe; 906, a reheater inlet spray connection pipe; 907, a reheater inlet spray; 908, a reheater inlet spray adjusting valve; 909, a secondary reheater inlet connection pipe; and 910, a reheater outlet connection pipe.

(Background Art 5)

As shown in FIG. 36, in main steam temperature control, a vessel left side secondary superheater 706 is connected to a vessel right side tertiary superheater 709 and a vessel right side secondary superheater 707 is connected to a vessel left side tertiary superheater 708 to thereby reduce a deviation between left and right steam temperatures.
Alternatively, the amounts of spray water in superheater inlet sprays 723 and 724 shown in FIG. 36 are biased in the vessel left and right to thereby reduce a deviation between main steam temperatures.
In FIG. 36, the reference numeral 704 designates a vessel left side primary superheater; 705, a vessel right side primary superheater; 714, a header; 715 drawn by the arrowed thick line, various kinds of steam piping; and 722, a primary repeater inlet spray.
FIG. 40 is a characteristic graph showing an example of superheating steam temperature (SOT) deviations based on deviations between the supply amounts of fuel (pulverized coal). As shown in FIG. 40, when a deviation is generated between the supply amounts of pulverized coal in the vessel left and right at time A for a certain reason, a deviation is generated in a gas temperature distribution, a deviation is lately generated in a superheater metal temperature distribution and a deviation is further lately generated between superheating steam temperatures (SOTs) in the vessel left and right at time C.

Patent Document 1: JP-A-8-270931
Patent Document 2: JP-A-4-222315
Patent Document 3: JP-A-60-221616
Patent Document 4: JP-A-6-101806
Patent Document 5: JP-A-9-21505

DISCLOSURE OF THE INVENTION

Problems that the Invention is to Solve

(Problem 1)

As described in (Background Art 1), combustion at a low excess air ratio has a demerit that the supply amount of combustion air decreases greatly and production of an unburned component such as CO increases in comparison with the related art.
A pulverized coal burning method for reducing the amount of produced NOx has been disclosed in the Patent Document 1. Specifically, combustion of pulverized coal by an in-flame denitration type pulverized coal burner which forms a reducing flame region short of oxygen takes a point of view that the concentration of NOx in exhaust gas is largely affected by the temperature of the reducing flame region or the air ratio of the reducing flame region.
Configuration is made so that a light extractor is attached to the pulverized coal burner, light of flame in the reducing flame region formed by the burner is detected by the light extractor, the detection signal is led to an emission spectrometer, the intensity of emitted light is detected, the temperature of the reducing flame region or the air ratio of the reducing flame region is calculated, and the amount of pulverized coal or the amount of air supplied to the burner is controlled based on a result of the calculation.
This pulverized coal burning method is effective in reducing NOx but brings a state short of oxygen as a whole. As a result, there is a problem that production of an unburned component such as CO increases.

(Problem 2)

In a structure (see FIG. 36) in which the vessel left side primary reheater 710 is connected to the vessel right side secondary reheater 713 and the vessel right side primary reheater 711 is connected to the vessel left side secondary reheater 712 as described in (Background Art 2), the deviation between the reheating steam temperatures in the vessel left and right is apt to be reduced but quantitative control cannot be performed so that the deviation between the reheating steam temperatures cannot be eliminated surely. Therefore, there is a problem of reliability.

(Problem 3)

In the method in which the deviation between the reheating steam temperatures in the vessel left and right is eliminated by the gas distributing dampers described in (Background Art 3), the gas distributing dampers 718 to 721 are disposed in the respective space portions partitioned as shown in FIG. 38. For example, assume now that the vessel left reheater side gas distributing damper 720 is opened and the vessel right reheater side gas distributing damper 721 is closed to increase the reheating steam temperature on the vessel left reheater side and decrease the reheating steam temperature on the vessel right reheater side. Then, the flow rate of gas on the reheater side increases on the vessel left side and decreases on the vessel right side, whereas the flow rate of gas on the superheater side decreases on the vessel left side and increases on the vessel right side. This is because the flow rates of gas interfere with one another to be balanced at the place where all pressure losses from the inlets of the rear heat-transfer surfaces to the gas distributing dampers 718 to 721 are equalized.
Because the gas distributing dampers 718 to 721 are mechanically slow in operating velocity and a metal thermal capacity is interposed in each of the gas distributing dampers 718 to 721, for example, gas distributing damper reheating steam temperature characteristic exhibits a wasteful time of 1-5 minutes and a time constant of about 3-10 minutes. Finally, because of the interference and the response delay of the gas distributing dampers 718 to 721, response of the gas distributing dampers 718 to 721 to the reheating steam temperature and the main steam temperature is further worsened so that there is a possibility that the deviation between the vessel left and right steam temperatures cannot be eliminated by the gas distributing dampers 718 to 721. In this case, a superheater spray which has a wasteful time of 30 seconds to 2 minutes and a time constant of 2-5 minutes, that is, has rapider response than the gas distributing dampers 718 to 721 is started to keep the steam temperature condition.
To use the reheater spray is to cool superheated steam with spray water. This causes lowering of efficiency of the combustion device. Moreover, when the number of times of importing compressed water into a connection pipe in which superheated steam circulates increases, the spray is damaged by thermal shock so that the lifetime of the spay is shortened.

(Problem 4)

In the method (see FIG. 39) in which the connection pipe 902 connecting the inlet and outlet of the primary reheater 901 is provided so that the flow rates of steam in the vessel left and right systems are adjusted as described in (Background Art 4), the amount of absorbed heat is reduced because any primary reheater needs to be bypassed to adjust the flow rates. For this reason, the heat-transfer area needs to increase in accordance with reduction of the amount of absorbed heat to bring increase in device size and increase in construction cost. Moreover, because the reheater outlet steam temperature in a primary reheater in which the flow rate of steam is reduced is too high, a reheat spray is started. Accordingly, lowering of efficiency of the combustion device and damage of the spray by thermal shock occur so that the lifetime of the spray is shortened.

(Problem 5)

In the structure (see FIG. 36) in which the vessel left side secondary superheater 706 is connected to the vessel right side tertiary superheater 709 and the vessel right side secondary superheater 707 is connected to the vessel left side tertiary superheater 708 as described in (Background Art 5), the deviation between the steam temperatures in the vessel left and right is apt to be reduced but quantitative control cannot be performed. For this reason, the deviation between the steam temperatures cannot be eliminated surely, so that there is a problem of reliability.
In the method in which the amounts of spray water put into the secondary superheater inlet spray 723 and the tertiary superheater inlet spray 724 are biased in the vessel left and right as shown in FIG. 36, a function of adjusting the superheating steam temperatures in the vessel left and right is added to the sprays 723 and 724 besides the function of controlling the superheating steam temperatures. For this reason, increase in the amount of superheater inlet spray is unavoidable. Accordingly, there is a demerit such as lowering of efficiency of the combustion device, reduction in controllable range, etc.
A first object of the invention is to provide a pulverized coal burning boiler in which production of an unburned component such as CO is reduced in a pulverized coal burning boiler having a reduced excess air ratio.
A second object of the invention is to provide a pulverized coal burning boiler which is so highly efficient that a deviation between steam temperatures in the vessel left and right can be reduced.

Means for Solving the Problems

A first means of the invention to achieve the first object is a pulverized coal burning boiler including:
milling means such as vertical roller mills which generate pulverized coal by milling supplied coal;
coal feeding pipes which are arranged in such a manner that a plurality of coal feeding pipes are connected to one milling means and through which the pulverized coal is airflow-conveyed by primary air;
pulverized coal burners which are connected to front end sides of the coal feeding pipes respectively and which have pulverized coal nozzles disposed so as to face into a furnace;
combustion air supply means which supply combustion air other than the primary air to the pulverized coal burners individually;
combustion air supply amount measuring means which measure the supply amounts of the combustion air supplied by the combustion air supply means individually;
combustion air supply amount adjusting means which adjust the supply amounts of the combustion air; and
burner air ratio setting means which set burner air ratios;
wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air;
the pulverized coal burning boiler characterized in that there are provided:
pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively; and
air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept.
According to a second means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal supply amount measuring means are attached to the coal feeding pipes of pulverized coal burners or pulverized coal burner groups high in unburned component reducing effect in the pulverized coal burners so that the supply amounts of combustion air are adjusted individually.
According to a third means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal burners are disposed as several stages for the furnace and the pulverized coal supply amount measuring means are attached to the coal feeding pipes of the pulverized coal burners except the pulverized coal burners disposed on the lower stage so that the supply amounts of combustion air are adjusted individually.
According to a fourth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal burners are disposed as several stages for the furnace and the pulverized coal supply amount measuring means are attached to the coal feeding pipes of the pulverized coal burners disposed on at least the uppermost stage so that the supply amounts of combustion air are adjusted individually.
According to a fifth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that a plurality of the pulverized coal burners are disposed side by side to form a burner stage, a plurality of after air ports are disposed side by side on a downstream side of the burner stage in an exhaust gas flow direction,
the amount of combustion air supplied to at least one of the pulverized coal burners is adjusted, and
the amount of combustion air supplied to an after air port near to flame formed by the pulverized coal burner is adjusted.
According to a sixth means of the invention, the pulverized coal burning boiler defined in the fifth means is characterized in that the plurality of pulverized coal burners and the plurality of after air ports are disposed so as to be separated into a vessel front and a vessel back of a furnace,
when the amount of combustion air supplied to the pulverized coal burners disposed in the vessel front is adjusted, the amount of combustion air supplied to the after air ports disposed in the vessel back is adjusted, and
when the amount of combustion air supplied to the pulverized coal burners disposed in the vessel back is adjusted, the amount of combustion air supplied to the after air ports disposed in the vessel front is adjusted.
According to a seventh means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that a plurality of after air ports are dispersively disposed on a downstream side of the pulverized coal burners in an exhaust gas flow direction, concentration distribution detection means such as a concentration measuring meter for detecting a distribution of oxygen concentrations or CO concentrations in exhaust gas is provided in a flue on a downstream side of the after air ports in an exhaust gas flow direction, and
while the amount of combustion air supplied to the pulverized coal burners is adjusted, the amount of combustion air supplied to the after air ports corresponding to a low oxygen concentration or high CO concentration region detected by the concentration distribution detection means is increased.
According to an eighth means of the invention, the pulverized coal burning boiler defined in any one of the fifth to seventh means is characterized in that the pulverized coal burners are disposed as a plurality of stages for a furnace, the pulverized coal burners to adjust the supply amount of combustion air are pulverized coal burners disposed on the uppermost stage.
According to a ninth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that each of the pulverized coal supply amount measuring means has a microwave resonance pipe through which a mixed fluid of the pulverized coal and primary air circulates, and a microwave transmitter and a microwave receiver which are disposed in the microwave resonance pipe so as to be at a predetermined distance from each other along a direction of a flow of the mixed fluid, and
the microwave transmitter transmits microwaves to the microwave receiver to measure a resonance frequency of the microwave resonance pipe to thereby measure the supply amount of the pulverized coal based on the resonance frequency.
According to a tenth means of the invention, the pulverized coal burning boiler defined in the ninth means is characterized in that a part of each of the coal feeding pipes is used as the microwave resonance pipe.
According to an eleventh means of the invention, the pulverized coal burning boiler defined in the ninth or tenth means is characterized in that the microwave transmitter and the microwave receiver protrude into the microwave resonance pipe, and a knocking member such as fluid guiding means which will be described later is disposed on an upstream side of the microwave transmitter in the microwave resonance pipe to unravel a flow of the pulverized coal condensed like a string in the microwave resonance pipe.
According to a twelfth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal supply amount measuring means has a first charge sensor and a second charge sensor which are disposed in each of the coal feeding pipes so as to be at a predetermined distance from each other along an axial direction of the coal feeding pipe, and
movement of electrostatic charges resulting from passage of pulverized coal in the coal feeding pipe is measured by the two charge sensors so that the supply amount of pulverized coal is measured based on the movement of electrostatic charges measured by the two charge sensors.
According to a thirteenth means of the invention, the pulverized coal burning boiler defined in the twelfth means is characterized in that the first charge sensor and the second charge sensor are circular and fluid guiding means is provided on an upstream side of the charge sensors to collect pulverized coal and pour the collected pulverized coal into a central portion side of the coal feeding pipe to thereby reduce the amount of pulverized coal passing through an inner circumferential side of the charge sensors.
A fourteenth means of the invention to achieve the second object is a pulverized coal burning boiler provided with a first reheater system and a second reheater system disposed side by side so that supplied steam circulates while forked into the first and second reheater systems, characterized in that there are provided:
reheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second reheater systems;
reheater outlet steam temperature measuring means which measure reheater outlet steam temperatures of the first and second reheater systems; and
reheating steam distributing amount control means which send control command signals to the reheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means.
A fifteenth means of the invention to achieve the second object is a pulverized coal burning boiler including:
milling means which generate pulverized coal by milling supplied coal;
coal feeding pipes which are arranged in such a manner that a plurality of coal feeding pipes are connected to one milling means and through which the pulverized coal is airflow-conveyed by primary air;
pulverized coal burners which are connected to front end sides of the coal feeding pipes respectively and which have pulverized coal nozzles disposed so as to face into a furnace;
combustion air supply means which supply combustion air other than the primary air to the pulverized coal burners individually;
combustion air supply amount measuring means which measure the supply amounts of the combustion air supplied by the combustion air supply means individually;
combustion air supply amount adjusting means which adjust the supply amounts of the combustion air;
burner air ratio setting means which set burner air ratios; and
a reheater which has a first reheater system and a second reheater system disposed side by side;
wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air; and
steam from a high-pressure turbine is heated by the reheater and supplied to middle-pressure and low-pressure turbines;
the pulverized coal burning boiler characterized in that there are provided:
pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively;
air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept;
reheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second reheater systems;
reheater outlet steam temperature measuring means which measure reheater outlet steam temperatures of the first and second reheater systems; and
reheating steam distributing amount control means which send control command signals to the reheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means.
According to a sixteenth means of the invention, the pulverized coal burning boiler defined in the fourteenth or fifteenth means is characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first reheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second reheater system, and
control command signals are output from the reheating steam distributing amount control means to the reheating steam distributing amount adjusting means based on the deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means and the deviation between the supply amounts of pulverized coal calculated by the pulverized coal supply amount deviation calculating means.
According to a seventeenth means of the invention, the pulverized coal burning boiler defined in the fourteenth or fifteenth means is characterized in that there are provided:
reheating steam temperature deviation prediction means which has reheating steam temperature deviation prediction models and which predicts a reheating steam temperature deviation based on information exerting influence on the reheating steam temperatures; and
correction means which obtain correction signals for correcting control command signals output from the reheating steam distributing amount control means based on the reheating steam temperature deviation value predicted by the reheating steam temperature deviation prediction means.
According to an eighteenth means of the invention, the pulverized coal burning boiler defined in the seventeenth means is characterized in that the information exerting influence on the reheating steam temperatures contains at least one piece of information selected from the group consisting of the supply amount of pulverized coal, the supply amount of water, the flow rate of spray, and the power generator output.
A nineteenth means of the invention to achieve the second object is a pulverized coal burning boiler provided with a first superheater system and a second superheater system disposed side by side so that supplied steam circulates while forked into the first and second superheater systems, characterized in that there are provided:
superheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second superheater systems;
superheater outlet steam temperature measuring means which measure superheater outlet steam temperatures of the first and second superheater systems; and
superheating steam distributing amount control means which send control command signals to the superheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the superheater outlet steam temperatures measured by the superheater outlet steam temperature measuring means.
A twentieth means of the invention to achieve the second object is a pulverized coal burning boiler including:
milling means which generate pulverized coal by milling supplied coal;
coal feeding pipes which are arranged in such a manner that a plurality of coal feeding pipes are connected to one milling means and through which the pulverized coal is airflow-conveyed by primary air;
pulverized coal burners which are connected to front end sides of the coal feeding pipes respectively and which have pulverized coal nozzles disposed so as to face into a furnace;
combustion air supply means which supply combustion air other than the primary air to the pulverized coal burners individually;
combustion air supply amount measuring means which measure the supply amounts of the combustion air supplied by the combustion air supply means individually;
combustion air supply amount adjusting means which adjust the supply amounts of the combustion air;
burner air ratio setting means which set burner air ratios; and
a superheater which has a first superheater system and a second superheater system disposed side by side;
wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air; and
steam is superheated by the superheater and supplied to a high-pressure turbine;
the pulverized coal burning boiler characterized in that there are provided:
pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively; air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept;
superheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second superheater systems;
superheater outlet steam temperature measuring means which measure superheater outlet steam temperatures of the first and second superheater systems; and
superheating steam distributing amount control means which send control command signals to the superheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the superheater outlet steam temperatures measured by the superheater outlet steam temperature measuring means.
According to a twenty-first means of the invention, the pulverized coal burning boiler defined in the nineteenth or twentieth means is characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first superheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second superheater system, and
control command signals are output from the superheating steam distributing amount control means to the superheating steam distributing amount adjusting means based on the deviation between the superheater output steam temperatures measured by the superheater outlet steam temperature measuring means and the deviation between the supply amounts of pulverized coal calculated by the pulverized coal supply amount deviation calculating means.
According to a twenty-second means of the invention, the pulverized coal burning boiler defined in the nineteenth or twentieth means is characterized in that there are provided:
superheating steam temperature deviation prediction means which has superheating steam temperature deviation prediction models and which predicts a superheating steam temperature deviation based on information exerting influence on the superheating steam temperatures; and
correction means which obtain correction signals for correcting control command signals output from the superheating steam distributing amount control means based on the superheating steam temperature deviation value predicted by the superheating steam temperature deviation prediction means.
According to a twenty-third means of the invention, the pulverized coal burning boiler defined in the twenty-second means is characterized in that the information exerting influence on the superheating steam temperatures contains at least one piece of information selected from the group consisting of the supply amount of pulverized coal, the supply amount of water, the flow rate of spray, and the power generator output.

EFFECT OF THE INVENTION

The first means of the invention is configured as described above. Because the flow rates of pulverized coal conveyed through the coal feeding pipes are measured individually so that the supply amounts of combustion air corresponding to the supply amounts of pulverized coal can be calculated and supplied so that burner air ratios set in advance can be kept, production of an unburned component such as CO can be reduced effectively even in the pulverized coal burning boiler in which the excess air ratio is reduced, for example, to 1.1.
The fourteenth, fifteenth, nineteenth and twentieth means of the invention are configured as described above. Because the steam temperature deviation is detected to adjust the flow rates of steam, the steam temperature deviation can be reduced to zero to attain improvement in efficiency.

BEST MODE FOR CARRYING OUT THE INVENTION

Specific contents of the invention will be described below with reference to the drawings.

(1) Configuration of Pulverized Coal Burning Combustion System

FIG. 23 is a schematic configuration view showing an example of a pulverized coal burning combustion system.
As shown in FIG. 23, air A fed in by an air forcing blower 1 is bifurcated to primary air A1 and secondary air A2, and the primary air A1 is bifurcated to air directly fed as cold air to a vertical roller mill 3 by a primary air forcing blower 2 and air heated by an exhaust gas type air preheater 4 and fed as hot air to the vertical roller mill 3. The cold air and the hot air are mixed and adjusted to form mixed air of a suitable temperature to be supplied to the roller mill 3.
After raw coal 5 is put into a coal banker 6, the raw coal 5 is supplied to the vertical roller mill 3 by a coal supply 7 and milled. Pulverized coal milled and generated while dried with the primary air A1 is conveyed by the primary air A1, jetted from pulverized coal nozzles 8 into a pulverized coal burning boiler 9 and ignited/burned. The secondary air A2 is heated by a steam type air preheater 10 and the exhaust gas type air preheater 4, fed to a wind box 11 and after air ports (AAP) 65 and subjected to combustion in the pulverized coal burning boiler 9.
A system for exhaust gas generated by the combustion of the pulverized coal is formed so that dust is removed by a dust collector 12, NOx is reduced by a denitrator 13, the exhaust gas is sucked by an induced blower 14 via the exhaust gas type air preheater 4, a sulfur content is removed by a desulfurizer 15, and the exhaust gas is released from a chimney 16 into the atmospheric air.
Although this example shows the case where the dust collector 12, the denitrator 13 and the exhaust gas type air preheater 4 are disposed in this order from an upstream side in a direction of a flow of the exhaust gas, there may be, for example, the case where the denitrator 13, the exhaust gas type air preheater 4 and the dust collector 12 are disposed in this order.

(2) Configuration of Vertical Roller Mill 3

FIG. 24 is a schematic configuration view showing an example of the vertical roller mill 3.
As shown in FIG. 24, the vertical roller mill 3 mainly includes a milling portion 21, a classifying portion 22, a milling portion driving portion 23, a classifying portion driving portion 24, and a distributing portion 25.
The milling portion 21 includes a housing 26, a milling table 27, milling rollers 28 rolled on the milling table 27, and a throat 29 which is a primary air inlet provided in an outer circumference of the milling table 27.
The classifying portion 22 includes the housing 26, a cyclone type stationary classifier 30 disposed in the inside of the housing 26, and a rotary classifier 31 disposed in the inside of the stationary classifier 30. The stationary classifier 30 has a fixed fin 32, and a recovery cone 33 provided so as to be connected to a lower end of the fixed fin 32. The rotary classifier 31 has a rotary shaft 34, and a rotary vane 35 supported to the rotary shaft 34.
The milling portion driving portion 23 includes a milling portion motor 36 for driving the milling table 27 to rotate, a pedestal 37 on which the milling table 27 is mounted rotatably, pressure frames 38 and brackets 39 for supporting the milling rollers 28, a rod 40, a pressure cylinder 41 for adjusting pressurizing force of each milling roller 28 acting on the milling table 27, etc.
The classifying portion driving portion 24 has a classifier motor 42, an output of which is transmitted to the rotary shaft 34 of the classifying portion 22 through gears. The distributing portion 25 is provided in an upper portion of the vertical roller mill 3 and has one distributing chamber 47 to which coal feeding pipes 43 are connected. In this embodiment, about 4-6 coal feeding pipes 43 are connected. However, only one coal feeding pipe 43 is drawn in FIG. 24 for the sake of simplification of the drawing.
Raw coal 5 supplied by a coal supply pipe 44 drops down into a central portion of the milling table 27 rotating, moves to an outer circumferential side by centrifugal force generated with rotation of the milling table 27 and is clamped between the milling table 27 and each milling roller 28 so as to be milled.
The milled coal grains further move to the outer circumference, become confluent with primary air 45 heated to 150° C.-300° C. led into a milling chamber from the throat 29 provided in the outer circumference of the milling table 27, and are blown up while dried. The blown-up grains are primary-classified according to weight, so that rough coal grains drop down and return to the milling portion 21.
Small coal grains which have reached the classifying portion 22 are classified (secondary-classified) into pulverized coal not larger than a predetermined grain size and roughly-powdered coal larger than the predetermined grain size by the stationary classifier 30 and the rotary classifier 31. The roughly-powdered coal drops along the inner wall of the recovery cone 33 so that the roughly-powdered coal will be milled again. On the other hand, a mixed fluid 46 of pulverized coal not larger than the predetermined grain size and primary air is fed into the distributing chamber 47. In the distributing chamber 47, the mixed fluid 46 is distributed into the coal feeding pipes 43 and conveyed to the pulverized coal nozzles 8 through the coal feeding pipes 43 respectively.
Incidentally, a small number of coal feeding pipes (e.g. about 1-4 pipes) may be connected to the mill so that each of the coal feeding pipes branches halfway and leads to two or more burners. The description “coal feeding pipes connected for one milling means” in Claim 1 includes such a form.
Fine-powdered coal flowmeters 51 are attached to intermediate portions of the coal feeding pipes 43 respectively. The configuration and measuring theory of each pulverized coal flowmeter 51 will be described below.

(3) Configuration and Measuring Theory of Pulverized Coal Flowmeter 51

The pulverized coal flowmeter 51 used in this embodiment is classified into a microwave type flowmeter and an electrostatic charge type flowmeter.
FIG. 25 is a schematic configuration view of a microwave type pulverized coal flowmeter 51 a. The flowmeter 51 a uses the coal feeding pipe 43 as a microwave resonance pipe (waveguide) and has a microwave transmitter 52 and a microwave receiver 53 which are disposed opposite to each other with a predetermined distance in the inside of the coal feeding pipe 43.
Although the transmitter 52 transmits microwaves to the receiver 53, the resonance frequency of the coal feeding pipe 43 (microwave resonance pipe) varies according to dielectric constant ∈r in the inside of the pipe. The dielectric constant ∈r of air is 1 whereas the dielectric constant ∈r of coal is about 4. Frequency characteristic in the case where the coal feeding pipe 43 is empty and frequency characteristic in the case where the mixed fluid 46 of pulverized coal and primary air flows in the coal feeding pipe 43 can be measured based on the difference between the dielectric constants, so that the flow rate of pulverized coal flowing in the coal feeding pipe 43 can be calculated based on the difference between resonance frequencies.
FIG. 26 is a schematic configuration view of an electrostatic charge type pulverized coal flowmeter 51 b. The flowmeter 51 b has two charge sensors 54 a and 54 b which catch static electricity generated by collision of pulverized coal and a flow path wall while the pulverized coal passes through the coal feeding pipe 43. The flowmeter 51 b uses the fact that the amount of electric charges varies according to the concentration of pulverized coal. Movement of electrostatic charges with passage of pulverized coal through the coal feeding pipe 43 is detected by the two charge sensors 54 a and 54 b, so that the flow rate of pulverized coal can be measured.
As shown in FIG. 26, the first charge sensor 54 a and the second charge sensor 54 b are disposed in an intermediate portion of the coal feeding pipe 43 with a predetermined distance L along the axial direction of the pipe.
First, a concentration ρ of pulverized coal passing through the coal feeding pipe 43 is obtained by the charge sensors 54 a and 54 b. Then, a passage time τ of pulverized coal from the first charge sensor 54 a to the second charge sensor 54 b is obtained. The passage time τ can be measured based on a time difference between a fluctuating phenomenon (specific waveform portion) detected when pulverized coal passes through the first charge sensor 54 a and a fluctuating phenomenon (the same specific waveform portion) detected when pulverized coal passes through the second charge sensor 54 b. Then, the flow velocity V of pulverized coal is calculated based on the relational expression V=L/τ. Then, the flow rate Q of pulverized coal can be calculated based on the relational expression Q=ρ×V×S in which ρ is the concentration of pulverized coal, V is the flow velocity of pulverized coal, and S is the flow sectional area of the coal feeding pipe 43.
Incidentally, as shown in FIG. 26, each of the charge sensors 54 a and 54 b is circular and has an inner diameter substantially equal to the inner diameter of the coal feeding pipe 43 so that the charge sensors 54 a and 54 b are prevented as sufficiently as possible from being worn away by pulverized coal.
The flow rate of pulverized coal distributed from the mill to each burner always varies according to the amount of coal supplied to the mill, the deviation on distribution, etc. Incidentally, in the background art, the amount of air supplied to each burner and each downstream-side AAP could not be controlled in real time because there was no means for measuring the flow rate of pulverized coal directly. Therefore, it was necessary to supply excessive air to the furnace combustion region as a whole for complete combustion of unburned parts such as CO, so that it was impossible to obtain combustion at a low excess air ratio as described above.
When the pulverized coal flowmeter 51 is used, the flow rate of pulverized coal distributed from the mill to each burner can be measured accurately. Accordingly, the amount of air supplied to each burner and each AAP can be adjusted/controlled precisely in accordance with the measured flow rate of pulverized coal, so that combustion can be made at an air ratio as close to the theoretical air ratio of 1.0 as possible, that is, at a low excess air ratio.

(4) First Embodiment

FIG. 1 is a schematic plan configuration view of a pulverized coal burning boiler according to a first embodiment.
In this embodiment, for example, four pulverized coal burners 61 a to 61 d are disposed in vessel front of the pulverized coal burning boiler 9 while four pulverized coal burners 61 e to 61 h are disposed in vessel back thereof so as to be opposite to the four pulverized coal burners 61 a and 61 d respectively. Two mills 3 are disposed in vessel front and in vessel back, respectively. Four coal feeding pipes 43 a to 43 d extended from the vessel front mill 3 a are connected to the pulverized coal burners 61 a to 61 d respectively while four coal feeding pipes 43 e to 43 h extended from the vessel back mill 3 b are connected to the pulverized coal burners 61 e to 61 h respectively.
Pulverized coal flowmeters 51 a to 51 h are attached to the coal feeding pipes 43 a to 43 h respectively so that the flow rates of pulverized coal passing through the coal feeding pipes 43 can be measured individually.
FIG. 2 is a schematic configuration view of a pulverized coal burner 61. As shown in FIG. 2, a pulverized coal nozzle 8 is disposed in the central portion of the pulverized coal burner 61. A combustion air supply path 63 for supplying combustion air (secondary air and tertiary air) 62 other than primary air is provided in an outer circumferential portion of the pulverized coal nozzle 8 individually in accordance with each burner 61. Combustion air supply amount adjusting means 64 (see FIG. 4), for example, of a dumper type or a slide type for adjusting the amount of supplied combustion air 62 is provided in an intermediate portion of the combustion air supply path 63. As shown in FIG. 2, while the mixed fluid 46 of pulverized coal and primary air is jetted from the pulverized coal nozzle 8 into the furnace, combustion air 62 of a low excess air ratio is supplied from the combustion air supply path 63 to thereby ignite and burn pulverized coal.
Although this embodiment has been described in the case where the combustion air 62 is supplied to the outer circumference of the pulverized coal nozzle 8, the invention is not limited thereto as long as the combustion air 62 can be supplied so that pulverized coal jetted from the pulverized coal nozzle 8 into the furnace can be burned.
FIG. 3 is a graph showing an example of deviations from an average flow rate in the case where pulverized coal obtained by supplying raw coal at a rate of X(t/h) to one mill 3 and milling the raw coal in the mill 3 is distributed to coal feeding pipes 43 a to 43 d so that the flow rates of pulverized coal are measured by pulverized coal flowmeters 51 a to 51 d respectively.
In this graph, 0% deviation means detection of pulverized coal at the average flow rate (X/4 in this example). This example shows that pulverized coal at flow rates lower than the average flow rate is conveyed to the coal feeding pipes 43 a and 43 b while pulverized coal at flow rates higher than the average flow rate is conveyed to the coal feeding pipes 43 c and 43 d. For example, the deviation of the measured value is caused by a pressure loss difference based on the pipe length difference between the coal feeding pipes 43, the structure of the mill, etc. It is confirmed that the deviation varies according to the operating condition of the mill such as the rotational velocity of the rotary classifier.
In this embodiment, a deviation state of the flow rate of pulverized coal conveyed by each coal feeding pipe 43 is detected, the amount of supplied combustion air corresponding to the amount of supplied pulverized coal is calculated based on the deviation individually for each burner so that the air ratio set by the burner air ratio setting means can be kept, and a control signal is transmitted to each combustion air supply amount adjusting means 64 to thereby adjust the amount of combustion air supplied to each burner 61 individually.
FIG. 4 is a view for explaining a combustion air supply amount control system therefor. A right half of FIG. 4 is a view showing an example of arrangement of pulverized coal burners 61 and AAPs 65 on their downstream sides in the pulverized coal burning boiler 9. Each of vessel front and vessel back is separated into burner stages so that a large number of pulverized coal burners 61 are arranged side by side in accordance with each burner stage. AAPs 65 are provided separately in both vessel front and vessel back so that the AAPs 65 are arranged side by side correspondingly to the respective pulverized coal burners 61.
A left half of FIG. 4 is a view showing a combustion air supply amount control system for the pulverized coal burners 61. The amounts of pulverized coal distributed and supplied from the mill 3 to the respective burners 61 a and 61 b as described above are measured individually by the pulverized coal flowmeters 51 a and 51 b, so that measured values thereof are input to a control circuit 66.
On the other hand, combustion air supply amount adjusting means 64 a and 64 b and air flowmeters 67 a and 67 b are attached individually to intermediate portions of combustion air supply paths 63 a and 63 b provided correspondingly to the burners 61 a and 61 b respectively. Measured values of the amounts of air supplied to the burners 61 a and 61 b and measured individually by the air flowmeters 67 a and 67 b are also input to the control circuit 66. There is a mechanism that the control circuit 66 outputs combustion air supply amount control signals 68 a and 68 b to the combustion air supply amount adjusting means 64 a and 64 b individually.
FIG. 5 is a block diagram showing an example of configuration of the control circuit 66. Values measured by the pulverized coal flowmeters 51 a and 51 b are input to the control circuit 66, so that deviation values from the average flow rate in the respective coal feeding pipes 43 a and 43 b are obtained by an adder 69 and dividers 70.
A supplied coal amount 71, a burner air ratio 72, a theoretical air amount 73, combustion air amounts 74 a and 74 b for the respective burners, etc. are input to the control circuit 66 in advance. In this embodiment, the burner air ratio 72 is set at 0.8 and the AAP air ratio is set at 0.3. Accordingly, the air ratio of the whole boiler is a low excess air ratio of 1.1.
Combustion air supply amounts corresponding to the pulverized coal supply amounts are calculated and output as combustion air amount command values 68 a and 68 b based on the various set values and the deviation values of the pulverized coal amounts in the respective coal feeding pipes 43 a and 43 b so that the aforementioned burner air ratio can be kept. Various multipliers 76, subtracters 77, etc. in the control circuit 66 are used as means for calculating the command values 68 a and 68 b. Limiting items of correction amount limiters 75 a and 75 b provided on the output end side of the control circuit 66 are upper and lower limits of absolute values, change widths, and change ratios.
When the combustion air supply amounts corresponding to the pulverized coal supply amounts in the respective coal feeding pipes are controlled individually as described above, a CO reducing effect is large in combustion at a low excess air ratio.

(5) Second Embodiment

FIG. 6 is a schematic configuration view of a pulverized coal burning boiler according to a second embodiment.
As shown in FIG. 6, mills 3 a to 3 c are disposed. The mills 3 a, 3 b and 3 c are connected to upper-stage, middle-stage and lower-stage burners 61 respectively so that pulverized coal is supplied thereto.
FIG. 7 is a view showing results of an experiment performed for specifying a burner stage large in CO reducing effect. This experiment was performed by use of a combustion analysis model having six burners in each burner stage.
The amount of CO produced when pulverized coal (fuel) was equally distributed to burners in each burner stage was measured and regarded as a reference value (1.00) (see left columns in FIG. 7). A relative value of the amount of CO produced when deviation was given to the fuel supply amount so that the sum of deviation values (see FIG. 3) from the average flow rate of the six burners became 20% was shown in each central column in FIG. 7. As shown in the central columns in FIG. 7, the amount of CO produced in the lower-stage burners little increased in spite of more or less deviation of the fuel supply amount whereas the amount of CO produced in the upper and middle stages increased by about 40% or more when there was deviation of the fuel supply amount. Especially, the increase in the amount of CO produced in the upper-stage burners was remarkable.
Then, the pulverized coal flowmeters 51 were attached to the coal feeding pipes 43 connected to the burners 61 respectively and the combustion air amount was adjusted as described in the first embodiment. Results thereof were shown in right columns in FIG. 7. As is obvious from the results in the right columns in FIG. 7, the CO reducing effect in the upper and middle stages is large, especially the effect in the upper-stage burners is remarkable.
Therefore, this embodiment is configured so that the pulverized coal flowmeters 51, the control circuit 66, etc. are not attached to the lower stage but the pulverized coal flowmeters 51, the control circuit 66, etc. are attached to the upper and middle stages having a CO reducing effect, especially, to at least the upper stage to adjust the combustion air amount.
Although this embodiment has been described in the case where whether the pulverized coal flowmeters 51 and the control circuit 66 are attached or not is determined in accordance with each burner stage, the magnitudes of the CO reducing effect in all burners may be grasped in advance by an experiment or the like so that the pulverized coal flowmeters 51 and the control circuit 66 can be selectively attached to burners having a CO reducing effect.

(6) Third Embodiment A third embodiment will be described below. In the electrostatic charge type pulverized coal flowmeter 51 b shown in FIG. 26, the concentration ρ of pulverized coal passing through the coal feeding pipe 43 and the flow velocity V of the pulverized coal can be obtained as described above. Accordingly, the flow rate of primary air carrying pulverized coal can be calculated based on the concentration ρ and flow velocity V of the pulverized coal, the circulation sectional area S of the coal feeding pipe 43 and the temperature correction value. As the flow velocity V becomes higher, the flow rate of primary air, that is, the flow rate of primary air supplied to the burner 61 increases.

Therefore, this embodiment is configured so that the flow rate of primary air is calculated and the amount of supplied combustion air 62 is adjusted in consideration of the flow rate of primary air, for example, by means of reducing the amount of supplied combustion air 62 when the flow rate of primary air is high. Incidentally, calculation of the flow rate of primary air and adjustment of the amount of supplied combustion air 62 based on the calculation result are performed by the control circuit 66.
This embodiment is particularly effective for a coal type such as subbituminous coal low in theoretical air amount because the rate of the amount of primary air in the coal type is higher than that in another coal type such as bituminous coal. The theoretical air amount of bituminous coal is 7.0 m³N/kg whereas the theoretical air amount of subbituminous coal is 5.5 m³N/kg which is small.

(7) Fourth Embodiment

FIG. 8 is a schematic configuration view of a pulverized coal burning boiler according to a fourth embodiment. FIG. 8( a) is a view showing the correspondence relation between pulverized coal burners 61 and AAPs 65. FIG. 8( b) is a view showing the arrangement of pulverized coal burners 61. FIG. 8( c) is a view showing the arrangement of AAPs 65.
In this embodiment, as shown in FIG. 8( b), pulverized coal burners 61 a to 61 d in vessel front are disposed opposite to pulverized coal burners 61 e to 61 h in vessel back on a plane. As shown in FIG. 8( c), AAPs 65 a to 65 d in vessel front are disposed opposite to AAPs 65 e to 65 h in vessel back on a plane. As shown in FIG. 8( a), the AAPs 65 are disposed just above the pulverized coal burners 61 respectively.
A burner combustion air amount adjustable range in each of the pulverized coal burners 61 a to 61 h is limited in advance from view of burner design. In this embodiment, the adjustable range is limited to 10% of the rating burner combustion air amount.
For example, when the air amount needs to increase by 13% of the rating air amount as a result of calculation based on the output of the pulverized coal flowmeter 51 c shown in FIG. 8( b), configuration is made so that the amount of burner combustion air supplied to the pulverized coal burner 61 c increases by 10% and the amount of AAP air supplied to the AAP 65 g on the opposite side increases by the remaining 3%.
FIG. 9 is a view showing the CO reducing effect in this embodiment. In this experimental example, a fuel deviation of +20% is detected in the pulverized coal burner 61 c in the vessel-front upper stage. On this occasion, the CO relative value is 1.53 (see the upper stage in FIG. 7). Accordingly, when the amount of burner combustion air supplied to the pulverized coal burner 61 c increased by 10%, the relative value of CO decreased to 0.75 (see the right of the upper stage in FIG. 9) so that the amount of CO could be reduced by 25% from the reference value.
The amount of AAP air needs to cover the remaining 10%. The CO reducing effect in the case where the amount of air supplied to the vessel-front AAP 65 c just above the pulverized coal burner 61 c was increased by 10% and the CO reducing effect in the case where the amount of air supplied to the vessel-back AAP 65 g on the side opposite to the pulverized coal burner 61 c was increased by 10% were examined. When the amount of air supplied to the vessel-front AAP 65 c was increased, there was little effect (see the left of the lower stage in FIG. 9). On the other hand, when the amount of air supplied to the vessel-back AAP 65 g was increased, a further CO reducing effect was obtained, so that the amount of CO could be overall reduced by 37% from the reference value (see the right of the lower stage in FIG. 9).

(8) Fifth Embodiment

FIG. 10 is a view showing the correspondence relation between pulverized coal burners 61 and AAPs 65 in a pulverized coal burning boiler according to a fifth embodiment.
In this embodiment, the number of AAPs 65 is larger than the number of pulverized coal burners 61, so that each pulverized coal burner 61 is disposed just below a midpoint between two AAPs 65. For example, when the amount of air supplied to the vessel-front pulverized coal burner 61 b is increased, the amount of air supplied to the vessel- back AAPs 65 g and 65 h substantially opposite to the pulverized coal burner 61 b, that is, nearest to flame formed by the pulverized coal burner 61 b is increased while divided into two equal parts for the vessel- back AAPs 65 g and 65 h. Configuration is made so that when the amount of air supplied to the vessel-front pulverized coal burner 61 c is increased, air is increased while divided into two equal parts for the vessel-back AAPs 65 h and 65 i substantially opposite to the pulverized coal burner 61 c.

(9) Sixth Embodiment

FIG. 11 is a schematic configuration view of a pulverized coal burning boiler according to a sixth embodiment. An economizer 79 is disposed on an outlet side of a furnace 78. An oxygen densitometer (or a CO densitometer) 80 for measuring the concentration of oxygen (or the concentration of CO) in exhaust gas is provided on a downstream side of the economizer 79. A dumper type supply amount adjuster 84 is attached individually to an intermediate portion of each supply path of AAP air 83 supplied to each AAP 65.
A plurality of detection ends 81 (four in this embodiment) of the oxygen densitometer 80 are disposed in a widthwise direction X (see FIG. 12) of a flue 82. The detection ends 81 can be moved vertically so that the position of each detection end 81 can be switched to a plurality of stages (three stages in this embodiment) in a vertical direction Y (see FIG. 12) of the flue 82.
FIG. 12 shows measuring points in the flue 82. An oxygen concentration or CO concentration distribution state of the economizer outlet can be grasped by the measuring points. The measuring points substantially correspond to the positions of the AAPs 65 (vessel front, vessel back, vessel right and vessel left), respectively.
In this embodiment, the total amount of AAP air supplied to all the AAPs 65 is determined to be constant. For example, when the concentration of oxygen measured at the measuring point ⊚ is lower than that measured at any other measuring point or when the concentration of CO measured at the measuring point ⊚ is higher than that measured at any other measuring point, a command signal is output from the control portion to increase the amount of AAP air on the vessel front and vessel left side.
Although this embodiment has been described in the case where the total amount of AAP air supplied to all the AAPs 65 is determined to be constant and then the amounts of AAP air supplied to the AAPs 65 respectively are determined, the total amount of AAP air may be not determined to be constant so that the amount of air supplied to an AAP corresponding to the region where a low oxygen concentration or a high CO concentration is detected can be increased simply. Accordingly, in this case, the total amount of AAP air is increased by the amount.
According to these embodiments, the amount of AAP air can be accurately distributed to a region high in unburned gas concentration.
Incidentally, also in the fifth and sixth embodiments, the amount of burner combustion air is adjusted in accordance with the flow rate of pulverized coal but the amount of air not covered is supplemented as AAP air.

(10) Seventh Embodiment

FIG. 13 is a view for explaining correction of coal supply amount data according to a seventh embodiment. As described above, raw coal 5 input to the coal banker 6 passes through the coal supply 7 and is milled by the mill 3, so that pulverized coal distributed to each coal feeding pipe 43 is measured by the pulverized coal flowmeter 51. At the time of measurement, coal supply amount data 85 from the coal supply 7 is output to the pulverized coal flowmeter 51 (control circuit 66). However, coal staying time in the mill 3 is generally from 45 seconds to 60 seconds, so that there is actually a time lag until pulverized coal passes through the flowmeter 51.
Therefore, this embodiment is configured so that the coal supply amount data 85 is multiplied by a correction coefficient in consideration of the staying time in the mill so that the corrected coal supply amount data 85 is output to the pulverized coal flowmeter 51 (control circuit 66).
According to this embodiment, the detection accuracy of the pulverized coal flowmeter 51 can be improved. This embodiment is suitable for a system in which the absolute amounts of pulverized coal passing through the respective coal feeding pipes 43 are measured by the pulverized coal flowmeters 51 so that deviations between the respective coal feeding pipes 43 are calculated based on the absolute amounts.

(11) Eighth Embodiment

FIG. 14 is a view for explaining correction of the flow rate of pulverized coal according to an eighth embodiment. In this embodiment, the flow rate of pulverized coal is corrected based on the percentage of moisture contained in raw coal, the coal supply amount, the amount of primary air supplied to the mill and the temperature difference between the inlet and outlet of the mill.
FIG. 15 is a characteristic graph showing the relation between the moisture increasing rate in coal having 3% by weight of moisture and the dielectric constant increasing rate of the coal. As shown in FIG. 15, in the pulverized coal flowmeter 51 which measures the flow rate of pulverized coal based on the dielectric constant as described above, because a difference is generated between dielectric constants when the percentage of moisture in coal changes, the percentage of moisture contained in pulverized coal passing through the pulverized coal flowmeter 51 is estimated to correct the output of the flowmeter 51 so that the accuracy of the measured value can be improved.
Therefore, in this embodiment, as shown in FIG. 14, a mill inlet air thermometer 86 and a mill outlet air thermometer 87 are attached to the inlet and outlet of the mill 3, respectively, so that a mill inlet air temperature T1 and a mill outlet air temperature T2 of primary air A1 supplied to the mill 3 are measured and a temperature difference ΔT (=T1−T2) between the inlet and outlet of the mill 3 is calculated based on the temperatures T1 and T2.
The percentage C of moisture contained in raw coal varies according to the coal type. The percentage C of moisture according to the coal type can be stored in a storage portion (not shown) of the control circuit 66 in advance by analysis or the like. The amount Q of coal supplied to the mill 3 can be obtained based on the rotational speed of the coal supply 7. The flow rate A of primary air A1 supplied to the mill 3 can be obtained based on the rotational speed of the forcing blower 1.
The estimated value of the amount of evaporation of moisture in coal milled in the mill 3 is calculated based on these data in accordance with the following relational expression:
Moisture Evaporation Amount Estimated Value=f(C,Q,A,ΔT)
in which f is a correction coefficient.
The percentage of moisture contained in pulverized coal passing through the pulverized coal flowmeter 51 is estimated based on the thus calculated estimated value of the moisture evaporation amount to thereby correct the output of the pulverized coal flowmeter 51 so that detection accuracy can be improved.

(12) Ninth Embodiment

FIG. 16 is a schematic configuration view showing a ninth embodiment. FIGS. 17 and 18 are views for explaining the function of fluid guiding means used in this embodiment. FIG. 17 is a sectional view. FIG. 18 is a side view of the fluid guiding means from an upstream side.
In this embodiment, fluid guiding means 88 made of an abrasion-resistant material or coated with an abrasion-resistant material is disposed on an upstream side of the pulverized coal flowmeter 51 in order to improve accuracy of the pulverized coal flowmeter 51 and prevent abrasion due to pulverized coal. Specifically as shown in FIGS. 17 and 18, the fluid guiding means 88 includes a separation plate 89 disposed in a substantially central position of the inside of the coal feeding pipe 43 so as to extend along a flow direction of the mixed fluid 46, and a turning plate 90 provided in a leading end portion of the separation plate 89. The side shape of the turning plate 90 is substantially so semicircular as to correspond to an aperture of the coal feeding pipe 43. As shown in FIG. 17, the turning plate 90 can turn around a turning shaft 91 in directions of the arrows.
When the group of pulverized coal flows in the coal feeding pipe 43, pulverized coal is not distributed substantially equally in the pipe but becomes in most cases a flow condensed like an irregularly bent string. The uneven flow has a bad influence on detection accuracy of the pulverized coal flowmeter 51.
In this embodiment, a microwave type pulverized coal flowmeter 51 a having a transmitter 52 and a receiver 53 is disposed in an intermediate portion of the coal feeding pipe 43. Because the transmitter 52 and the receiver 53 are inserted into the coal feeding pipe 43, the transmitter 52 and the receiver 53 are worn out by collision with pulverized coal.
Therefore, in this embodiment, the turning plate 90 is raised as shown in FIGS. 17 and 18 to unravel the flow of pulverized coal condensed like a string by collision with the turning plate 90 to distribute pulverized coal uniformly to thereby attain improvement of detection accuracy.
Moreover, the concentration of pulverized coal flowing on the transmitter 52 side and on the receiver 53 side is reduced by the turning plate 90 so as not to hinder measurement to thereby suppress abrasion of the transmitter 52 and the receiver 53.

(13) Tenth Embodiment

FIGS. 19 and 20 are views for explaining the function of fluid guiding means used in a tenth embodiment. FIG. 19 is a sectional view. FIG. 20 is a side view of the fluid guiding means from an upstream side. The fluid guiding means 88 according to this embodiment has a reduced diameter portion 92, and taper faces 93 and 93 provided in front and back of the reduced diameter portion 92.
FIGS. 21 and 22 are views showing a modification of this embodiment. FIG. 21 is a sectional view. FIG. 22 is a side view of the fluid guiding means from an upstream side. The fluid guiding means 88 according to the modification has a trumpet-shaped member 94 tapered gradually from an upstream side to a downstream side.
As shown in FIGS. 19 and 21, a pulverized coal flowmeter 51 b having a first charge sensor 54 a and a second charge sensor 54 b is disposed on a downstream side of the fluid guiding means 88. The charge sensors 54 a and 54 b are made of circular bodies. Inner circumferential surfaces of the charge sensors 54 a and 54 b are substantially on the same level with the inner circumferential surface of the coal feeding pipe 43.
Pulverized coal in the mixed fluid 46 conveyed by the coal feeding pipe 43 is collected to the central portion side of the coal feeding pipe 43 by the reduced diameter portion 92 or the trumpet-shaped member 94. Accordingly, the amount of pulverized coal passing through the inner circumferential surface side of the charge sensors 54 a and 54 b is reduced so that abrasion of the charge sensors 54 a and 54 b due to pulverized coal can be suppressed.

(14) Eleventh Embodiment

FIG. 27 is a flow path system view of a reheater in a boiler according to an eleventh embodiment. A reheater 100 disposed in a flue on a downstream side of an exhaust gas flow in a furnace includes a primary reheater portion 101 and a secondary reheater portion 102 from view of arrangement and configuration of members. The reheater 100 includes a first reheater system 103 on a vessel left side and a second reheater system 104 on a vessel right side from view of steam flow path system. The first reheater system 103 and the second reheater system 104 are provided side by side.
In this embodiment, the first reheater system 103 has a primary reheater inlet header 105 a, a primary reheater 106 a, a primary reheater outlet header 107 a, a secondary reheater inlet header 108 a, a secondary reheater 109 a, and a secondary reheater outlet header 110 a. The second reheater system 104 has a primary reheater inlet header 105 b, a primary reheater 106 b, a primary reheater outlet header 107 b, a secondary reheater inlet header 108 b, a secondary reheater 109 b, and a secondary reheater outlet header 110 b.
In this embodiment, a first reheating steam distributing valve 111 and a second reheating steam distributing valve 112 are disposed on the inlet side of the first reheater system 103 and the second reheater system 104. A first reheater steam thermometer 113 and a second reheater steam thermometer 114 are disposed on the outlet side of the first reheater system 103 and the second reheater system 104.
Steam supplied from a high-pressure turbine (not shown) is forked into two flow paths via one reheater spray 115. The forked steam is heated while passing through the first and second reheater systems 103 and 104 from the first and second reheating steam distributing valves 111 and 112 respectively, so that the reheated steam is fed from the secondary reheater outlet headers 110 a and 110 b to middle/low-pressure turbines.
Although this embodiment is configured so that the distributing valves 111 and 112 are provided in the first and second reheater systems 103 and 104 respectively to thereby adjust the flow rates of distributed steam, a distributing valve may be provided in one reheater system so that the flow rates of steam distributed to the first and second reheater systems can be adjusted by operation of the distributing valves.
A method of adjusting apertures of the distributing valves 111 and 112 will be described below. First, the reheater outlet steam temperatures 116 and 117 of vessel left and right, that is, of the first and second reheater systems 103 and 104 are measured by the reheater steam thermometers 113 and 114, so that the measured signals are input to a subtracter 118 to obtain a deviation value 119. The signal of the deviation value 119 is input to a PI controller 120, so that aperture adjusting signals 121 and 122 for eliminating the deviation value 119 are output from the PI controller 120 to the distributing valves 111 and 112 respectively. On this occasion, an operation reverse in phase to the distributing valve 111 is performed on the distributing valve 112 through an inverter (“−1”) 123.
FIG. 28 is a characteristic graph showing an example of time-lapse changes of the flow rate of fuel (flow rate of pulverized coal), the aperture of the distributing valve, the flow rate of steam and the reheater outlet steam temperature (ROT) in this embodiment.
As shown in FIG. 28, when a deviation is generated between the amounts of fuel supplied to the burners at time A for a certain reason, a deviation is generated between ROTs of the first and second reheater systems 103 and 104 at time B later than the time A. This deviation is detected by the reheater steam thermometers 113 and 114 to perform an operation of opening the aperture of the distributing valve (e.g. distributing valve 111) of a system high in ROT based on the aperture adjusting signal 121 and contrariwise throttling the aperture of the distributing valve (e.g. distributing valve 112) of a system low in ROT based on the aperture adjusting signal 122 at time C. Accordingly, the flow rate of steam distributed to the system high in ROT, that is, having an increased thermal load increases and the flow rate of steam distributed to the system low in ROT, that is, having a decreased thermal load decreases, so that the deviation between ROTs of the first and second reheater systems 103 and 104 is eliminated.
Although the example has been described in the case where both the apertures of the distributing valves 111 and 112 are adjusted, the same effect can be expected in the case where only the aperture of the distributing valve (e.g. distributing valve 112) on an ROT reduced side, that is, on a side required to reduce the flow rate of distributed steam is throttled.
Although the embodiment has been described in the case where the distributing valves 111 and 112 are disposed on the inlet side of the first and second reheater systems 103 and 104 respectively, a resistor such as an orifice may be provided in place of one distributing valve (e.g. distributing valve 111) so that the flow rates of steam distributed to the first and second reheater systems 103 and 104 can be adjusted when only the aperture of the other distributing valve (e.g. distributing valve 112) is adjusted.
Because ROTs of the first and second reheater systems 103 and 104 are averaged when the maximum temperature limit of ROT is a reference steam condition plus 8° C. or lower, there is a function of keeping tolerance at 8° C. Accordingly, the number of times for starting the reheater spray 115 can be reduced against disturbance due to the load change in the combustion device, stopping of the mill, the start of a soot blower, etc., so that improvement in boiler efficiency and improvement in life of the reheater spray 115 can be attained.

(15) Twelfth Embodiment

FIG. 29 is a flow path system view of a reheater in a boiler according to a twelfth embodiment of the invention.
An attempt to reduce the excess air ratio to about 10% has been made in order to attain further reduction of NOx and improvement of boiler efficiency in recent years. In the excess air ratio of 10%, there is a possibility that CO will be produced because of local shortage of air even when the amounts of pulverized coal supplied to the burners are slightly uneven. To cope with this, a method of individually measuring the amounts of pulverized coal supplied to the respective burners to thereby dynamically adjust combustion air supplied to the respective burners, that is, individual burner air ratio control has been proposed in the first to tenth embodiments, etc.
In a pulverized coal burning boiler using the individual burner air ratio control, there is a possibility that the deviation between combustion gas temperatures in vessel left and right may become large compared with a pulverized coal burning boiler in which combustion air is equally supplied to the respective burners. In the background art, because air was equally supplied to the vessel left and right, imperfect combustion due to shortage of air occurred in a place where much pulverized coal was supplied so that the deviation between thermal loads in the vessel left and right was suppressed compared with the deviation between the amounts of pulverized coal. However, when just enough air is given to pulverized coal supplied to the vessel left and right with a deviation as in the individual burner air ratio control, the deviation between the amounts of supplied pulverized coal appears directly as a deviation between thermal loads in the vessel left and right.
For example, assume that pulverized coal 15% larger than the average value of the supply amounts is supplied to the vessel right side, that is, pulverized coal 15% smaller than the average value is supplied to the vessel left side in a pulverized coal burning boiler operated at an excess air ratio of 10%. On the other hand, because air is equally supplied to all after air ports, the deviation between the amounts of pulverized coal supplied to the vessel left and right exceeds supplied air tolerance to cause imperfect combustion. For this reason, though fuel (pulverized coal) 15% larger is supplied to the vessel right side, increase in thermal load is reduced to 10%. However, in the pulverized coal burning boiler using the individual burner air ratio control, because air just fit to the deviation between the amounts of supplied pulverized coal is supplied, 15% increase in thermal load equal to the deviation between the amounts of supplied pulverized coal appears in the aforementioned example. The increase in thermal load has a direct influence on the amount of heat exchange in a heat exchanger to bring a deviation between steam temperatures. This embodiment aims at this respect.
In the pulverized coal burning boiler, the deviation between the amounts of pulverized coal supplied to the respective burners appears as a deviation between ROTs with a time lag as described above. This is because a heat exchanger having a large number of heat-transfer pipes has a response delay corresponding to change in gas temperature caused by its metal heat capacity. The time constant sometimes reaches tens of seconds to several minutes.
In this embodiment, like the first embodiment etc., the supply amounts of combustion air corresponding to the supply amounts of pulverized coal are calculated based on the flow rates of pulverized coal measured by the pulverized coal flowmeters 51 a to 51 h and the supply amounts of combustion air measured by the air flowmeters 67 a to 67 h and control command signals are sent to combustion air supply amount adjusting means 64 a to 64 h so that the burner air ratio set by the burner air ratio setting means can be kept.
As shown in FIG. 1, the pulverized coal flowmeters 51 a to 51 h are attached to the coal feeding pipes 43 a to 43 h connecting the roller mills 3 a and 3 b and the respective pulverized coal burners 61 a to 61 h so that the amounts of pulverized coal passing through the coal feeding pipes 43 can be measured individually.
The flows of exhaust gas produced by combustion in the respective pulverized coal burners 61 a to 61 h are substantially directly poured into flues without large disorder and give heat to the repeater 100.
Accordingly, in this embodiment, from the relation between FIGS. 1 and 29, the first reheater system 103 disposed on the vessel left side is heated by exhaust gas produced from the pulverized coal burners 61 c, 61 d, 61 g and 61 h disposed on the vessel left side, whereas the second reheater system 104 disposed on the vessel right side is heated by exhaust gas produced from the pulverized coal burners 61 a, 61 b, 61 e and 61 f.
In this embodiment, in addition to the aforementioned combustion air supply amount individual control, measured values of the flow rates of pulverized coal from the pulverized coal flowmeters 51 a to 51 h are input to a vessel left/right fuel supply amount calculator 124 as shown in FIG. 29. The vessel left/right fuel supply amount calculator 124 calculates the flow rate of pulverized coal supplied to the vessel left side pulverized coal burners 61 c, 61 d, 61 g and 61 h and the flow rate of pulverized coal supplied to the vessel right side pulverized coal burners 61 a, 61 b, 61 e and 61 f. The former is obtained as the sum of the pulverized coal flowmeters 51 c, 51 d, 51 g and 51 h whereas the latter is obtained as the sum of the pulverized coal flowmeters 51 a, 61 b, 51 e and 51 f.
A vessel left/right fuel supply amount calculated value 125 calculated thus is input to a bias calculator 126. The bias calculator 126 obtains a deviation between the flow rate of pulverized coal supplied to the vessel left side pulverized coal burners 61 c, 61 d, 61 g and 61 h and the flow rate of pulverized coal supplied to the vessel right side pulverized coal burners 61 a, 61 b, 61 e and 61 f and calculates bias values 127 and 128 for the aperture adjusting signals 121 and 122 as the PI feedback control signals based on the pulverized coal flow rate deviation value. Incidentally, optimum patterns for the size of the bias (the shape of the feed-forward component) are obtained by dynamic characteristic calculation in advance and the patterns are adjusted at the time of trial operation.
The calculated bias values 127 and 128 are added to the aperture adjusting signals 121 and 122 by adders 129 and 130 respectively to obtain aperture adjusting signals 131 and 131 in consideration of deviations of the flow rate of pulverized coal to thereby adjust the apertures of the distributing valves 111 and 112.
FIG. 30 is a characteristic graph showing an example of time-lapse changes of the flow rate of fuel (flow rate of pulverized coal), the aperture of the distributing valve, the flow rate of steam and ROT in this embodiment.
As shown in FIG. 30, unbalance (deviation) between the flow rates of fuel (flow rates of pulverized coal) causing the deviation between the vessel left and right repeater outlet steam temperatures is detected early at time D and the apertures of distributing valves 104 a and 104 b are adjusted since the time D based on the unbalance (as represented by the hatched portion in FIG. 30) so that feed-forward control can be made. Accordingly, the deviation between the vessel left and right ROTs can be reduced, so that improvement of boiler controllability can be attained.

(16) Thirteenth Embodiment

According to the twelfth embodiment, there is a possibility that the feed-forward component may be so intensive that the temperature reduction is too large or too small in accordance with the occasion because the feed-forward component has a substantially fixed shape.
For example, as shown in FIG. 36, superheaters 706 to 709 are disposed on upstream sides of reheaters 710 to 713 in an exhaust gas flow direction. Sprays 723 and 724 are mainly used in accordance with the transitional temperature change of superheating steam. The sprays 723 and 724 operate to change the amounts of heat exchange of the superheaters 706 to 709 and have influence on the inlet gas temperatures of the reheaters 710 to 713. Accordingly, when the bias of the flow rate of reheating steam is determined only based ion the change of the flow rate of fuel (flow rate of pulverized coal) as in the twelfth embodiment, excess and deficiency may occur due to the effect of the sprays 723 and 724.
This embodiment is accomplished in consideration of this respect. FIG. 31 is a flow path system view of a repeater in a boiler according to the thirteenth embodiment.
In this embodiment, various kinds of reheating steam temperature deviation prediction models 133 for predicting reheating steam temperature deviations based on pieces of information exerting influence on the reheating steam temperature, such as the amount of supplied fuel, the flow rate of boiler supplied water, the amount of superheater inlet spray, the output of a power generator, etc. are prepared so that the reheating steam temperature deviation prediction models 133 are stored in a storage portion (not shown) of reheating steam temperature deviation prediction means 134.
The amount of supplied fuel 135, the flow rate of boiler supplied water 136, the amount of superheater inlet spray 137 and the power generator output 138 in the pulverized coal burning boiler currently operating are input to the reheating steam temperature deviation prediction means 134, so that a predicted reheating steam temperature deviation value 139 is obtained by referring to these input values and the reheating steam temperature deviation prediction models 133.
The predicted reheating steam temperature deviation value 139 is input to reheating steam distributing valve aperture correction means 140. The reheating steam distributing valve aperture correction means 140 generates distributing valve aperture correction signals 141 and 142 based on the predicted reheating steam temperature deviation value 139. The distributing valve aperture correction signals 141 and 142 are added to the aperture adjusting signals 121 and 122 by adders 143 and 144 respectively, so that the apertures of the reheating steam distributing valves 111 and 112 are adjusted based on the corrected aperture adjusting signals 145 and 146 respectively.
FIG. 32 is a characteristic graph showing an example of time-lapse changes of the flow rate of fuel (flow rate of pulverized coal), the aperture of the distributing valve, the flow rate of steam and ROT in this embodiment.
In this embodiment, the apertures of the distributing valves 104 a and 104 b are adjusted at time D (as represented by the hatched portion in FIG. 32) based on the vessel left and right ROT deviations in consideration of pieces of information exerting influence on the reheating steam temperature, such as the amount of supplied fuel, the flow rate of boiler supplied water, the amount of superheater inlet spray, the power generator output, etc. Because feed-forward control can be performed in this manner, further reduction in the vessel left and right ROT deviations can be obtained so that further improvement in boiler controllability can be attained.

(17) Fourteenth Embodiment

In a superheater, when a bias between the vessel left and right is applied to the input amount of superheater spray, the deviation between the vessel left and right superheating steam temperatures can be reduced. However, when the deviation between the vessel left and right superheating steam temperatures is high, it is necessary to increase the flow rate of spray because tolerance of steam temperature control as the original purpose of the superheater spray is reduced, and control follow-up characteristic is worsened because spray control is complicated. As a result, increase in the flow rate of spray means increase in the amount of bypassing the heat-transfer surface halfway, so that boiler efficiency is lowered.
In this embodiment, the flow rates of steam in the vessel left and right of the superheater are adjusted to eliminate the deviation between the vessel left and right main steam temperatures.
FIG. 33 is a flow path system view of a superheater in a boiler according to the fourteenth embodiment.
A superheater 200 disposed from an upper portion of a furnace into a flue on a downstream side in an exhaust gas flow direction thereof includes a primary superheater portion 201 and a secondary superheater portion 202 from view of arrangement and configuration of members. The superheater 200 includes a first superheater system 204 on the vessel left side and a second superheater system 205 on the vessel right side from view of steam flow path systems. The first superheater system 204 and the second superheater system 205 are arranged side by side.
In this embodiment, the first superheater system 204 has a primary superheater inlet header 206 a, a primary superheater 207 a, a primary superheater outlet header 208 a, a secondary superheater inlet header 209 a, a secondary superheater 210 a, a secondary superheater outlet header 211 a, a tertiary superheater inlet header 212 a, a tertiary superheater 213 a, and a tertiary superheater outlet header 214 a. The second superheater system 205 has a primary superheater inlet header 206 b, a primary superheater 207 b, a primary superheater outlet header 208 b, a secondary superheater inlet header 209 b, a secondary superheater 210 b, a secondary superheater outlet header 211 b, a tertiary superheater inlet header 212 b, a tertiary superheater 213 b, and a tertiary superheater outlet header 214 b.
In this embodiment, a first superheating steam distributing valve 215 and a second superheating steam distributing valve 216 are disposed on the inlet side of the first superheater system 204 and the second superheater system 205. A first superheater steam thermometer 217 and a second superheater steam thermometer 218 are disposed on the outlet side of the first superheater system 204 and the second superheater system 205.
In the first superheater system 204, a secondary superheater inlet spray 219 a is attached to a connection pipe which connects the primary superheater outlet header 208 a and the secondary superheater inlet header 209 a. A tertiary superheater inlet spray 220 a is attached to a connection pipe which connects the secondary superheater outlet header 211 a and the tertiary superheater inlet header 212 a. In the second superheater system 205, a secondary superheater inlet spray 219 b is attached to a connection pipe which connects the primary superheater outlet header 208 b and the secondary superheater inlet header 209 b. A tertiary superheater inlet spray 220 b is attached to a connection pipe which connects the secondary superheater outlet header 211 b and the tertiary superheater inlet header 212 b.
Steam supplied from a cage (not shown) is forked into two flow paths via outlet headers 221 a and 221 b. The forked steam is superheated while passing through the first and second superheater systems 204 and 205 from the first and second superheating steam distributing valves 215 and 216 respectively, so that the superheated steam is fed from the tertiary superheater outlet headers 214 a and 214 b to high-pressure turbines.
A method of adjusting the apertures of the distributing valves 215 and 216 will be described below. First, superheater outlet steam temperatures 222 and 223 of vessel left and right, that is, of the first and second superheater systems 204 and 205 are measured by the superheater steam thermometers 217 and 218, so that the measured signals are input to a subtracter 224 to obtain a deviation value 225. The signal of the deviation value 225 is input to a PI controller 226, so that aperture adjusting signals 227 and 228 for eliminating the deviation value 225 are output from the PI controller 226 to the distributing valves 215 and 216 respectively. On this occasion, an operation reverse in phase to the distributing valve 215 is performed on the distributing valve 216 through an inverter (“−1”) 229.
When a deviation is generated between the amounts of fuel supplied to the burners for a certain reason, a deviation is lately generated between superheater outlet steam temperatures (SOTs) 222 and 223 of the first and second superheater systems 204 and 205. This deviation is detected by the superheater steam thermometers 217 and 218 to perform an operation of opening the aperture of the distributing valve (e.g. distributing valve 215) of a system high in SOT based on the aperture adjusting signal 227 and contrariwise throttling the aperture of the distributing valve (e.g. distributing valve 216) of a system low in SOT based on the aperture adjusting signal 228. Accordingly, the flow rate of steam distributed to the system high in SOT, that is, having an increased thermal load increases and the flow rate of steam distributed to the system low in SOT, that is, having a decreased thermal load decreases, so that the deviation between SOTs of the first and second superheater systems 204 and 205 is eliminated.
Although FIG. 28 is a characteristic graph showing an example of time-lapse changes of the flow rate of fuel, the aperture of the distributing valve, the flow rate of steam and the reheater outlet steam temperature (ROT) in the eleventh embodiment, the fourteenth embodiment behaves as if the reheater outlet steam temperature (ROT) in FIG. 28 were replaced by the superheater outlet steam temperature (SOT).

(18) Fifteenth Embodiment

FIG. 34 is a flow path system view of a superheater in a boiler according to a fifteenth embodiment.
As shown in FIG. 34, measured values of the flow rates of pulverized coal from the pulverized coal flowmeters 51 a to 51 h are input to a vessel left/right fuel supply amount calculator 230. The vessel left/right fuel supply amount calculator 230 calculates the flow rate of pulverized coal supplied to the vessel left side pulverized coal burners 61 c, 61 d, 61 g and 61 h and the flow rate of pulverized coal supplied to the vessel right side pulverized coal burners 61 a, 61 b, 61 e and 61 f. The former is obtained as the sum of the pulverized coal flowmeters 51 c, 51 d, 51 g and 51 h whereas the latter is obtained as the sum of the pulverized coal flowmeters 51 a, 61 b, 51 e and 51 f.
A vessel left/right fuel supply amount calculated value 231 calculated thus is input to a bias calculator 232. The bias calculator 232 obtains a deviation between the flow rate of pulverized coal supplied to the vessel left side pulverized coal burners 61 c, 61 d, 61 g and 61 h and the flow rate of pulverized coal supplied to the vessel right side pulverized coal burners 61 a, 61 b, 61 e and 61 f and calculates bias values 233 and 234 for the aperture adjusting signals 227 and 228 as the PI feedback control signals based on the pulverized coal flow rate deviation value. Incidentally, optimum patterns for the size of the bias (the shape of the feed-forward component) are obtained by dynamic characteristic calculation in advance and the patterns are adjusted at the time of trial operation.
The calculated bias values 233 and 234 are added to the aperture adjusting signals 227 and 228 by adders 235 and 236 respectively to obtain aperture adjusting signals 237 and 238 in consideration of deviations of the flow rate of pulverized coal to thereby adjust the apertures of the distributing valves 215 and 216.
Although FIG. 30 is a characteristic graph showing an example of time-lapse changes of the flow rate of fuel, the aperture of the distributing valve, the flow rate of steam and the reheater outlet steam temperature (ROT) in the twelfth embodiment, the fifteenth embodiment behaves as if the reheater outlet steam temperature (ROT) in FIG. 30 were replaced by the superheater outlet steam temperature (SOT).

(19) Sixteenth Embodiment

FIG. 35 is a flow path system view of a superheater in a boiler according to a sixteenth embodiment.
In this embodiment, various kinds of superheating steam temperature deviation prediction models 240 for predicting superheating steam temperature deviations based on pieces of information exerting influence on the superheating steam temperature, such as the amount of supplied fuel, the flow rate of boiler supplied water, the amount of superheater inlet spray, the power generator output, etc. are prepared so that the superheating steam temperature deviation prediction models 240 are stored in a storage portion (not shown) of superheating steam temperature deviation prediction means 241.
The amount of supplied fuel 242, the flow rate of boiler supplied water 243, the amount of superheater inlet spray 244 and the power generator output 245 in the pulverized coal burning boiler currently operating are input to the superheating steam temperature deviation prediction means 241, so that a predicted superheating steam temperature deviation value 246 is obtained by referring to these input values and the superheating steam temperature deviation prediction models 240.
The predicted superheating steam temperature deviation value 246 is input to superheating steam distributing valve aperture correction means 247. The superheating steam distributing valve aperture correction means 247 generates distributing valve aperture correction signals 248 and 249 based on the predicted superheating steam temperature deviation value 246. The distributing valve aperture correction signals 248 and 249 are added to the aperture adjusting signals 227 and 228 by adders 250 and 251 respectively, so that the apertures of the superheating steam distributing valves 215 and 216 are adjusted based on corrected aperture adjusting signals 252 and 253 respectively.
Although FIG. 32 is a characteristic graph showing an example of time-lapse changes of the flow rate of fuel, the aperture of the distributing valve, the flow rate of steam and the reheater outlet steam temperature (ROT) in the thirteenth embodiment, the sixteenth embodiment behaves as if the reheater outlet steam temperature (ROT) in FIG. 32 were replaced by the superheater outlet steam temperature (SOT).
Although the embodiment has been described in the case where steam distributing valve control for reheater systems and steam distributing valve control for superheater systems are performed separately, steam distributing valve control for reheater systems and superheater systems can be performed in only one pulverized coal burning boiler.
Specific effects of the invention are as follows.
(1) With respect to the problem that the deviation between reheater vessel left and right steam temperatures cannot be eliminated thoroughly by the background-art method of exchanging reheater vessel left and right systems, the effect of reducing the steam temperature deviation to zero is obtained according to this invention because the flow rates of steam are adjusted while the deviation between the reheater vessel left and right steam temperatures is viewed.
(2) With respect to the problem that response is delayed due to the influence of interference and the operating velocity of a gas damper in the background-art method using the gas damper for adjusting the deviation between reheater vessel left and right steam temperatures, the effect of quickening the response characteristic is obtained according to this invention because adjustment of the flow rates of steam supplied to the reheater vessel left and right does not interfere with the superheater and the flow rates of steam supplied to the superheater vessel left and right does not likewise interfere with the reheater.
(3) With respect to the problem that lowering of efficiency due to bypassing, increase in the heat-transfer surface and sudden increase in temperature in the bypassed heat-transfer surface occur in the background-art method in which a connection pipe for connecting the inlet and outlet of the primary reheater is provided to adjust the flow rates of steam in the vessel left and right systems, the problem of lowering of efficiency, increase in the heat-transfer surface and sudden increase in temperature of the bypassed heat-transfer surface does not occur in this invention because bypassing can be avoided when the balance between the flow rates of steam supplied to the repeater vessel left and right is changed.
(4) With respect to the problem that the deviation between superheater vessel left and right steam temperatures cannot be eliminated thoroughly by the background-art method of exchanging superheater vessel left and right systems, the effect of reducing the steam temperature deviation to zero is obtained according to this invention because the flow rates of steam are adjusted while the deviation between the superheater vessel left and right steam temperatures is viewed.
With respect to the problem that the flow rate of spray increases in the background-art method of applying a bias to the flow rate of superheating spray between the vessel left and right, the effect of reducing the flow rate of spray is obtained according to this invention because the deviation between the superheater vessel left and right steam temperatures is adjusted only based on the flow rate of steam led into the superheater so that the spray is used only for adjusting the temperature of superheating steam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A schematic plan configuration view of a pulverized coal burning boiler according to a first embodiment of the invention.
FIG. 2 A schematic configuration view of a pulverized coal burner used in the pulverized coal burning boiler according to the first embodiment.
FIG. 3 A graph showing an example of deviations from an average flow rate in the case where pulverized coal is distributed to four coal feeding pipes and the flow rates of pulverized coal are measured by pulverized coal flowmeters respectively.
FIG. 4 A view for explaining a combustion air supply amount control system according to the first embodiment of the invention.
FIG. 5 A block diagram showing a control circuit used in the combustion air supply amount control system.
FIG. 6 A schematic configuration view of a pulverized coal burning boiler according to a second embodiment of the invention.
FIG. 7 A view showing results of an experiment performed for specifying a burner stage large in CO reducing effect.
FIG. 8 A schematic configuration view of a pulverized coal burning boiler according to a third embodiment of the invention. FIG. 8( a) is a view showing the correspondence relation between pulverized coal burners and AAPs. FIG. 8( b) is a view showing the arrangement of pulverized coal burners. FIG. 8( c) is a view showing the arrangement of AAPs.
FIG. 9 A view showing the CO reducing effect in the third embodiment.
FIG. 10 A view showing the correspondence relation between pulverized coal burners and AAPs in a pulverized coal burning boiler according to a fifth embodiment of the invention.
FIG. 11 A schematic configuration view of a pulverized coal burning boiler according to a sixth embodiment of the invention.
FIG. 12 A view showing measuring points in a flue in the sixth embodiment.
FIG. 13 A view for explaining correction of coal supply amount data according to a seventh embodiment of the invention.
FIG. 14 A view for explaining correction of the flow rate of pulverized coal according to an eighth embodiment of the invention.
FIG. 15 A characteristic graph showing the relation between the moisture increasing rate in coal and the dielectric constant increasing rate of the coal.
FIG. 16 A schematic configuration view showing a ninth embodiment of the invention.
FIG. 17 A sectional view for explaining the function of fluid guiding means used in this embodiment.
FIG. 18 A side view of the fluid guiding means from an upstream side.
FIG. 19 A sectional view for explaining the function of fluid guiding means used in a tenth embodiment of the invention.
FIG. 20 A side view of the fluid guiding means from an upstream side.
FIG. 21 A sectional view for explaining the function of fluid guiding means used in a modification of the tenth embodiment of the invention.
FIG. 22 A side view of the fluid guiding means from an upstream side.
FIG. 23 A schematic configuration view of a pulverized coal burning combustion system according to an embodiment of the invention.
FIG. 24 A schematic configuration view of a vertical roller mill used in an embodiment of the invention.
FIG. 25 A schematic configuration view of a microwave type pulverized coal flowmeter used in an embodiment of the invention.
FIG. 26 A schematic configuration view of an electrostatic charge type pulverized coal flowmeter used in an embodiment of the invention.
FIG. 27 A flow path system view of a reheater in a boiler according to an eleventh embodiment of the invention.
FIG. 28 A characteristic graph showing an example of time-lapse changes of the flow rate of fuel, the aperture of the distributing valve, the flow rate of steam and the reheater outlet steam temperature (ROT) in this embodiment.
FIG. 29 A flow path system view of a reheater in a boiler according to a twelfth embodiment of the invention.
FIG. 30 A characteristic graph showing an example of time-lapse changes of the flow rate of fuel, the aperture of the distributing valve, the flow rate of steam and the reheater outlet steam temperature (ROT) in this embodiment.
FIG. 31 A flow path system view of a reheater in a boiler according to a thirteenth embodiment of the invention.
FIG. 32 A characteristic graph showing an example of time-lapse changes of the flow rate of fuel, the aperture of the distributing valve, the flow rate of steam and the reheater outlet steam temperature (ROT) in this embodiment.
FIG. 33 A flow path system view of a superheater in a boiler according to a fourteenth embodiment of the invention.
FIG. 34 A flow path system view of a superheater in a boiler according to a fifteenth embodiment of the invention.
FIG. 35 A flow path system view of a superheater in a boiler according to a sixteenth embodiment of the invention.
FIG. 36 A view for explaining a variable pressure once-through type pulverized coal burning boiler according to the background art.
FIG. 37 A characteristic graph showing an example of deviation of reheating steam temperature (ROT) based on deviation of the amount of supplied fuel in the pulverized coal burning boiler.
FIG. 38 A view showing arrangement of gas distributing dampers in a fuel based on a proposal according to the background art.
FIG. 39 A view showing a reheating steam system in a boiler proposed according to the background art.
FIG. 40 A characteristic graph showing an example of deviation of superheating steam temperature (SOT) based on deviation of the amount of supplied fuel in a pulverized coal burning boiler according to the background art.

DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS

1: forcing blower, 2: primary air forcing blower, 3: vertical roller mill, 4: exhaust gas type air preheater, 5: raw coal, 6: coal banker, 7: coal supply, 8: pulverized coal nozzle, 9: pulverized coal burning boiler, 10: steam type air preheater, 11: wind box, 12: dust collector, 13: denitrater, 14: induced blower, 15: desulfurizer, 21: milling portion, 22: classifying portion, 23: milling portion driving portion, 24: classifying portion driving portion, 25: distributing portion, 43: coal feeding pipe, 44: coal supply pipe, 45: primary air, 46: mixed fluid, 47: distributing chamber, 51: pulverized coal flowmeter, 51 a: microwave type pulverized coal flowmeter, 51 b: electrostatic charge type pulverized coal flowmeter, 52: microwave transmitter, 53: microwave receiver, 54 a: first charge sensor, 54 b: second charge sensor, 61: pulverized coal burner, 62: combustion air, 63: combustion air supply path, 64: combustion air supply amount adjusting means, 65: AAP, 66: control circuit, 67: air flowmeter, 68: combustion air amount control command value, 69: adder, 70: divider, 71: coal supply amount, 72: burner air ratio, 73: theoretical air amount, 74: combustion air amount, 75: correction amount limiter, 76: multiplier, 77: subtracter, 78: furnace, 79: economizer, 80: oxygen concentration measuring meter, 81: detection end, 82: flue, 83: AAP air, 84: supply amount adjuster, 85: coal supply amount data, 86: mill inlet thermometer, 87: mill outlet thermometer, 88: fluid guiding means, 89: separation plate, 90: turning plate, 91: turning shaft, 92: reduced-diameter portion, 93: taper face, 94: trumpet-shaped member, A: air, A1: primary air, A2: secondary air.
100: reheater, 101: primary reheater portion, 102: secondary reheater portion, 103: first reheater system, 104: second reheater system, 105: primary reheater inlet header, 106: primary reheater, 107: primary reheater outlet header, 108: secondary reheater inlet header, 109: secondary reheater, 110: secondary reheater outlet header, 111: first reheating steam distributing valve, 112: second reheating steam distributing valve, 113: first reheating steam thermometer, 114: second reheating steam thermometer, 115: reheater spray, 116: first reheater outlet steam temperature, 117: second reheater outlet steam temperature, 118: subtracter, 119: deviation value, 120: PI controller, 121, 122: aperture adjusting signal, 123: inverter, 124: vessel left/right fuel supply amount calculator, 125: vessel left/right fuel supply amount calculated value, 126: bias calculator, 127, 128: bias calculated value, 129, 130: adder, 131, 132: aperture adjusting signal, 133: reheating steam temperature deviation prediction model, 134: reheating steam temperature deviation prediction means, 135: fuel supply amount, 136, boiler water supply amount, 137: superheater inlet spray amount, 138: power generator output, 139: predictive reheating steam deviation value, 140: reheating steam distributing valve aperture correction means, 141, 142: distributing valve aperture correction signal, 143, 144: adder, 200: superheater, 201: primary superheater portion, 202: secondary superheater portion, 203: tertiary superheater portion, 204: first superheater system, 205: second superheater system, 206: primary superheater inlet header, 207: primary superheater, 208: primary superheater outlet header, 209: secondary superheader inlet header, 210: secondary superheater, 211: secondary superheater outlet header, 212: tertiary superheater inlet header, 213: tertiary superheater, 214: tertiary superheater outlet header, 215: first superheating steam distributing valve, 216: second superheating steam distributing valve, 217: first superheating steam thermometer, 218: second superheating steam thermometer, 219: secondary superheater inlet spray, 220: tertiary superheater inlet spray, 221: outlet header, 222, 223: superheater outlet steam temperature, 224: subtracter, 225: deviation value, 226: PI controller, 227, 228: aperture adjusting signal, 229: inverter, 230: vessel left/right fuel supply amount calculator, 231: vessel left/right fuel supply amount calculated value, 232: bias calculator, 233, 234: bias calculated value, 235, 236: adder, 237, 238: aperture adjusting signal, 240: superheating steam temperature deviation prediction model, 241: superheating steam temperature deviation prediction means, 242: fuel supply amount, 243: boiler water supply amount, 244: superheater inlet spray amount, 245: power generator output, 246: predictive superheating steam deviation value, 247: superheating steam distributing valve aperture correction means, 248, 249: distributing valve aperture correction signal, 250, 251: adder, 252, 253: aperture adjusting signal.

Claims

1. A pulverized coal burning boiler comprising:

milling means which generate pulverized coal by milling supplied coal;

coal feeding pipes which are arranged in such a manner that a plurality of coal feeding pipes are connected to one milling means and through which the pulverized coal is airflow-conveyed by primary air;

pulverized coal burners which are connected to front end sides of the coal feeding pipes respectively and which have pulverized coal nozzles disposed so as to face into a furnace;

combustion air supply means which supply combustion air other than the primary air to the pulverized coal burners individually;

combustion air supply amount measuring means which measure the supply amounts of the combustion air supplied by the combustion air supply means individually;

combustion air supply amount adjusting means which adjust the supply amounts of the combustion air; and

burner air ratio setting means which set burner air ratios;

wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air;

the pulverized coal burning boiler characterized in that there are provided:

pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively; and

air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept.

2. A pulverized coal burning boiler according to claim 1, characterized in that the pulverized coal supply amount measuring means are attached to the coal feeding pipes of pulverized coal burners or pulverized coal burner groups high in unburned component reducing effect in the pulverized coal burners so that the supply amounts of combustion air are adjusted individually.

3. A pulverized coal burning boiler according to claim 1, characterized in that the pulverized coal burners are disposed as several stages for the furnace and the pulverized coal supply amount measuring means are attached to the coal feeding pipes of the pulverized coal burners except the pulverized coal burners disposed on the lower stage so that the supply amounts of combustion air are adjusted individually.

4. A pulverized coal burning boiler according to claim 1, characterized in that the pulverized coal burners are disposed as several stages for the furnace and the pulverized coal supply amount measuring means are attached to the coal feeding pipes of the pulverized coal burners disposed on at least the uppermost stage so that the supply amounts of combustion air are adjusted individually.

5. A pulverized coal burning boiler according to claim 1, characterized in that a plurality of the pulverized coal burners are disposed side by side to form a burner stage, a plurality of after air ports are disposed side by side on a downstream side of the burner stage in an exhaust gas flow direction,

the amount of combustion air supplied to at least one of the pulverized coal burners is adjusted, and

the amount of combustion air supplied to an after air port near to flame formed by the pulverized coal burner is adjusted.

6. A pulverized coal burning boiler according to claim 5, characterized in that the plurality of pulverized coal burners and the plurality of after air ports are disposed so as to be separated into a vessel front and a vessel back of a furnace,

when the amount of combustion air supplied to the pulverized coal burners disposed in the vessel front is adjusted, the amount of combustion air supplied to the after air ports disposed in the vessel back is adjusted, and

when the amount of combustion air supplied to the pulverized coal burners disposed in the vessel back is adjusted, the amount of combustion air supplied to the after air ports disposed in the vessel front is adjusted.

7. A pulverized coal burning boiler according to claim 1, characterized in that a plurality of after air ports are dispersively disposed on a downstream side of the pulverized coal burners in an exhaust gas flow direction, concentration distribution detection means for detecting a distribution of oxygen concentrations or CO concentrations in exhaust gas is provided in a flue on a downstream side of the after air ports in an exhaust gas flow direction, and

while the amount of combustion air supplied to the pulverized coal burners is adjusted, the amount of combustion air supplied to the after air ports corresponding to a low oxygen concentration or high CO concentration region detected by the concentration distribution detection means is increased.

8. A pulverized coal burning boiler according to claim 5, characterized in that the pulverized coal burners are disposed as a plurality of stages for a furnace, the pulverized coal burners to adjust the supply amount of combustion air are pulverized coal burners disposed on the uppermost stage.

9. A pulverized coal burning boiler according to claim 1, characterized in that each of the pulverized coal supply amount measuring means has a microwave resonance pipe through which a mixed fluid of the pulverized coal and primary air circulates, and a microwave transmitter and a microwave receiver which are disposed in the microwave resonance pipe so as to be at a predetermined distance from each other along a direction of a flow of the mixed fluid, and

the microwave transmitter transmits microwaves to the microwave receiver to measure a resonance frequency of the microwave resonance pipe to thereby measure the supply amount of the pulverized coal based on the resonance frequency.

10. A pulverized coal burning boiler according to claim 9, characterized in that a part of each of the coal feeding pipes is used as the microwave resonance pipe.

11. A pulverized coal burning boiler according to claim 9, characterized in that the microwave transmitter and the microwave receiver protrude into the microwave resonance pipe, and a knocking member is disposed on an upstream side of the microwave transmitter in the microwave resonance pipe to unravel a flow of the pulverized coal condensed like a string in the microwave resonance pipe.

12. A pulverized coal burning boiler according to claim 1, characterized in that the pulverized coal supply amount measuring means has a first charge sensor and a second charge sensor which are disposed in each of the coal feeding pipes so as to be at a predetermined distance from each other along an axial direction of the coal feeding pipe, and

movement of electrostatic charges resulting from passage of pulverized coal in the coal feeding pipe is measured by the two charge sensors so that the supply amount of pulverized coal is measured based on the movement of electrostatic charges measured by the two charge sensors.

13. A pulverized coal burning boiler according to claim 12, characterized in that the first charge sensor and the second charge sensor are circular and fluid guiding means is provided on an upstream side of the charge sensors to collect pulverized coal and pour the collected pulverized coal into a central portion side of the coal feeding pipe to thereby reduce the amount of pulverized coal passing through an inner circumferential side of the charge sensors.

14. A pulverized coal burning boiler provided with a first reheater system and a second reheater system disposed side by side so that supplied steam circulates while forked into the first and second reheater systems, characterized in that there are provided:

reheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second reheater systems;

reheater outlet steam temperature measuring means which measure reheater outlet steam temperatures of the first and second reheater systems; and

reheating steam distributing amount control means which send control command signals to the reheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means.

15. A pulverized coal burning boiler comprising:

milling means which generate pulverized coal by milling supplied coal;

combustion air supply amount adjusting means which adjust the supply amounts of the combustion air;

burner air ratio setting means which set burner air ratios; and

a reheater which has a first reheater system and a second reheater system disposed side by side;

wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air; and

steam from a high-pressure turbine is heated by the reheater and supplied to middle-pressure and low-pressure turbines;

the pulverized coal burning boiler characterized in that there are provided:

pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively;

air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept;

16. A pulverized coal burning boiler according to claim 14, characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first reheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second reheater system, and

control command signals are output from the reheating steam distributing amount control means to the reheating steam distributing amount adjusting means based on the deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means and the deviation between the supply amounts of pulverized coal calculated by the pulverized coal supply amount deviation calculating means.

17. A pulverized coal burning boiler according to claim 14, characterized in that there are provided:

reheating steam temperature deviation prediction means which has reheating steam temperature deviation prediction models and which predicts a reheating steam temperature deviation based on information exerting influence on the reheating steam temperatures; and

correction means which obtain correction signals for correcting control command signals output from the reheating steam distributing amount control means based on the reheating steam temperature deviation value predicted by the reheating steam temperature deviation prediction means.

18. A pulverized coal burning boiler according to claim 17, characterized in that the information exerting influence on the reheating steam temperatures contains at least one piece of information selected from the group consisting of the supply amount of pulverized coal, the supply amount of water, the flow rate of spray, and the power generator output.

19. A pulverized coal burning boiler provided with a first superheater system and a second superheater system disposed side by side so that supplied steam circulates while forked into the first and second superheater systems, characterized in that there are provided:

superheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second superheater systems;

superheater outlet steam temperature measuring means which measure superheater outlet steam temperatures of the first and second superheater systems; and

superheating steam distributing amount control means which send control command signals to the superheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the superheater outlet steam temperatures measured by the superheater outlet steam temperature measuring means.

20. A pulverized coal burning boiler comprising:

milling means which generate pulverized coal by milling supplied coal;

burner air ratio setting means which set burner air ratios; and

a superheater which has a first superheater system and a second superheater system disposed side by side;

steam is superheated by the superheater and supplied to a high-pressure turbine;

the pulverized coal burning boiler characterized in that there are provided:

21. A pulverized coal burning boiler according to claim 19, characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first superheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second superheater system, and

control command signals are output from the superheating steam distributing amount control means to the superheating steam distributing amount adjusting means based on the deviation between the superheater output steam temperatures measured by the superheater outlet steam temperature measuring means and the deviation between the supply amounts of pulverized coal calculated by the pulverized coal supply amount deviation calculating means.

22. A pulverized coal burning boiler according to claim 19, characterized in that there are provided:

superheating steam temperature deviation prediction means which has superheating steam temperature deviation prediction models and which predicts a superheating steam temperature deviation based on information exerting influence on the superheating steam temperatures; and

correction means which obtain correction signals for correcting control command signals output from the superheating steam distributing amount control means based on the superheating steam temperature deviation value predicted by the superheating steam temperature deviation prediction means.

23. A pulverized coal burning boiler according to claim 22, characterized in that the information exerting influence on the superheating steam temperatures contains at least one piece of information selected from the group consisting of the supply amount of pulverized coal, the supply amount of water, the flow rate of spray, and the power generator output.

24. A pulverized coal burning boiler according to claim 15, characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first reheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second reheater system, and

25. A pulverized coal burning boiler according to claim 15, characterized in that there are provided:

26. A pulverized coal burning boiler according to claim 20, characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first superheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second superheater system, and

27. A pulverized coal burning boiler according to claim 20, characterized in that there are provided: