CN106500127B - Bypass air preheater heat recovery system and method - Google Patents
Bypass air preheater heat recovery system and method Download PDFInfo
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- CN106500127B CN106500127B CN201710009415.9A CN201710009415A CN106500127B CN 106500127 B CN106500127 B CN 106500127B CN 201710009415 A CN201710009415 A CN 201710009415A CN 106500127 B CN106500127 B CN 106500127B
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- bypass
- air
- air preheater
- flue gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L15/00—Heating of air supplied for combustion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L2900/00—Special arrangements for supplying or treating air or oxidant for combustion; Injecting inert gas, water or steam into the combustion chamber
- F23L2900/15043—Preheating combustion air by heat recovery means located in the chimney, e.g. for home heating devices
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E20/00—Combustion technologies with mitigation potential
- Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery
Abstract
The invention discloses a system and a method for recovering heat of a bypass air preheater; the invention arranges a set of bypass air preheater at the part of the air preheater of the tail flue of the common boiler, and the bypass air preheater and the existing air preheater form parallel arrangement, and according to the change of the flue gas volume and the flue gas temperature at the inlet of the air preheater, the flue gas volume is adjusted to pass through the flue gas distribution proportion of the existing air preheater and the bypass air preheater, thereby fully recovering the heat energy of the flue gas of the boiler, reducing the heat loss and improving the boiler efficiency. The invention can change the operation mode of the automatic adjusting system according to the operation condition, so that the waste heat of the flue gas is fully utilized, the heat loss of the flue gas is reduced, and the economical efficiency of the boiler is improved.
Description
Technical Field
The invention relates to a system and a method for recovering heat of a bypass air preheater, in particular to a system and a method for recovering flue gas waste heat of a bypass of a power station boiler air preheater.
Background
The energy is the life pulse of national economy and is the essential material basis for the development of social economy. In recent years, in countries around the world, especially developed countries, improvement of energy utilization efficiency and energy saving have been important targets of energy development strategies. The country continuously puts forward a plurality of energy-saving and emission-reducing policies, encourages and urges the energy-saving and emission-reducing work of all the industries of the whole society, and the power industry is taken as an important energy component and has great significance for developing energy conservation and consumption reduction. The loss of the boiler exhaust smoke of the power station is the main part of the loss of the boiler, the boiler efficiency can be obviously improved by reducing the temperature of the exhaust smoke, and the unit economy is improved.
Therefore, the smoke exhaust temperature is greatly needed to be further reduced, the energy-saving potential is developed, and the unit economy is improved. The measures for reducing the exhaust gas temperature of the boiler mainly comprise: 1. the heat absorption capacity of the heating surface of the boiler is increased through boiler combustion adjustment and deep soot blowing, and the smoke exhaust temperature is reduced; 2. a low-temperature economizer is arranged behind the air (gas) preheater, condensed water is introduced, the waste heat of the flue gas is absorbed, the steam extraction is reduced, and the exhaust temperature is reduced.
The utilization of the waste heat of the boiler flue gas has a plurality of designs and practices at home and abroad, and the type of a flue gas heat exchanger is adopted, and the heat in the flue gas is replaced by other media for utilization through the heat exchanger. The flue gas heat exchanger is called as a low-temperature economizer, a low-pressure economizer, a flue gas cooler, a flue gas water heat exchanger and the like, and the names are the same or similar in nature, except that the arrangement position of the flue gas heat exchanger is different from that of a heat exchange medium.
(1) The tail part of the boiler is arranged, and the condensed water is adopted to absorb the waste heat of the flue gas. For example, the exhaust gas temperature of a certain power plant boiler in China is high, in order to reduce the exhaust gas temperature and improve the operation economy of a unit, a low-temperature economizer is additionally arranged at the outlet of an air preheater at the tail part of the boiler, and condensed water is adopted to absorb the waste heat of the exhaust gas, which is shown in the attached drawing 1.
(2) The device is arranged in front of the absorption tower, and the condensed water is adopted to absorb the residual heat of the flue gas. A flue gas cooler is additionally arranged between an electrostatic dust collector and a flue gas desulfurization tower in a 2 x 800MW lignite power generator set of a German power plant Schwarze Pumpe, and condensed water is adopted to absorb the waste heat of flue gas. A smoke-water heat exchanger is also arranged at the same position in a certain domestic power plant, and is shown in an attached figure 2.
The Chinese patent application with the publication number of CN104896503A discloses a boiler flue gas waste heat utilization system, which comprises a main pipeline consisting of a boiler body, an air preheater, a low-temperature heat exchanger and a water supply tank which are sequentially connected, wherein the low-temperature heat exchanger and an outlet pipe of the water supply tank form a loop; the system is respectively communicated with the low-temperature heat exchanger, the air inlet branch of the air preheater and the water supply tank pipeline, the air inlet heating of the air preheater or the water heating in the water supply tank can be selected, and the recovery heat distribution system can adjust the heated condensed water amount of the main pipeline and each branch pipeline according to actual needs to control the heat utilization ratio of the heated air inlet or condensed water of the air preheater. The system is characterized in that two feed water heaters are added at the position of a flue gas outlet of the existing air preheater, one feed water heater is arranged in front of a dust remover after the existing air preheater, the other feed water heater is arranged on a newly added flue after the existing air preheater, two paths of flue gases are converged in front of an induced draft fan, and the waste heat of the flue gases is completely absorbed by the feed water. However, the efficiency of recovering heat is low, and the efficiency of the boiler cannot be improved.
Chinese patent CN204880080U discloses a boiler flue gas waste heat recovery system, including economizer, pump body, first heat exchanger, second heat exchanger, heat supply network water system and condensate system, the economizer the heat transfer medium side of first heat exchanger and the pump body communicates in proper order and forms first circulation circuit, the economizer the heat transfer medium side of second heat exchanger and the pump body communicates in proper order and forms second circulation circuit, the first water side of first heat exchanger with condensate system intercommunication forms first heat exchange circuit, the second water side of second heat exchanger with heat supply network water system intercommunication forms second heat exchange circuit. The utility model discloses an independent heat transfer of heating network water and condensate water has prevented quality of water interference phenomenon effectively, guarantees that the host computer condensate water is not polluted. Meanwhile, an indirect heat exchange mode of heat exchange between a heat exchange medium and boiler flue gas is adopted, so that condensed water and heat supply network water are not in direct contact with the economizer, the pressure resistance requirement of the economizer is reduced, and the manufacturing cost of raw materials can be saved. The patent utilizes the heat absorbed by the water supplied by a low-temperature economizer behind a dust remover, one part of the heat is used for heating condensed water, the other part of the heat is used for heating hot water of a heat supply network, and the heat of the hot water of the heat supply network is used for absorbing heat to reduce the temperature of flue gas.
At present, the method for reducing the exhaust gas temperature of the power station boiler has 3 defects: 1. the heat absorption of the heating surface of the boiler is increased through combustion adjustment and deep soot blowing, the amplitude of reducing the temperature of the exhaust smoke is small, and continuous implementation cannot be realized; 2. the exhaust gas temperature is reduced by absorbing heat through the condensed water, the waste heat of the flue gas enters the low-pressure condensed water part of the regenerative system, and the steam is extracted by a steam turbine, so that the economy is not high; 3. the requirement of continuously reducing the exhaust gas temperature when the factors such as the sulfur content, the moisture content, the ash deposition on the heating surface and the like of the raw coal change is difficult to adapt; 4. the efficiency of recovering heat is low, and the efficiency of the boiler cannot be additionally improved.
Disclosure of Invention
The invention aims to provide a heat recovery system and a heat recovery method based on a bypass air preheater, which can automatically optimize the operation mode of an adjusting system according to the change of operation conditions, so that the waste heat of boiler flue gas is fully utilized, the loss of smoke discharge is reduced, and the economic maximization of a boiler is realized.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention discloses a bypass air preheater heat recovery system, which comprises:
a main flue;
the main air preheater is arranged on the main flue and is respectively connected with the cold primary air channel and the cold secondary air channel, the flue gas entering the main flue is respectively subjected to heat exchange with the cold primary air in the cold primary air channel and the cold secondary air in the cold secondary air channel through the main air preheater, the cooled flue gas is discharged to a flue at the tail part of the boiler, and the cold primary air and the cold secondary air are heated and respectively changed into hot primary air and hot secondary air to be discharged to the boiler for combustion;
a bypass flue gas channel branched from the main flue, wherein a part of flue gas branched from the main flue enters the bypass flue;
the bypass air preheater is arranged on the bypass flue gas channel and is connected with the cold secondary air channel, so that flue gas entering the bypass air preheater exchanges heat with cold air from the cold secondary air channel, the flue gas cooled in the way is discharged to a flue at the tail part of the boiler, and the cold secondary air is heated and then respectively changed into hot secondary air to be discharged to a main secondary air pipe of the boiler for combustion in the boiler.
The bypass air preheater heat recovery system is characterized in that a bypass flue gas regulating valve is arranged on a bypass flue gas channel before flue gas enters the bypass air preheater;
and a bypass cold secondary air regulating valve is arranged on a channel for the cold secondary air to enter the bypass air preheater.
And the bypass secondary hot air stop valve is arranged on a bypass secondary hot air channel at the air outlet of the bypass air preheater.
And a second flue gas temperature measuring element is arranged on the front flue of the inlet of the main air preheater.
And a ninth flue gas temperature measuring element is arranged in the rear flue of the outlet of the main air preheater before a flue gas mixing point.
And a twenty-first flue gas temperature measuring element is arranged in a flue gas outlet of the bypass air preheater.
And a twenty-third flue gas temperature measuring element is arranged in the flue behind the mixing point of the flue at the outlet of the main air preheater.
And a fourth flue gas temperature measuring element is arranged on the cold primary air channel.
And a seventh flue gas temperature measuring element is arranged on the cold secondary air duct.
And a fourteenth flue gas temperature measuring element is arranged in the primary hot air duct.
Seventeen smoke temperature measuring elements are arranged in the main heat secondary air channel.
And a twentieth flue gas temperature measuring element is arranged in the bypass hot secondary air channel.
The air of the bypass air preheater can be led out from the cold secondary air duct and can also be led out from the cold primary air duct, but only one of the air and the cold primary air duct can be selected and is incompatible.
The invention also provides a heat recovery method of the bypass air preheater, which comprises the following steps:
high-temperature flue gas in a front flue of an inlet of a main air preheater of a main flue flows through the main air preheater and exchanges heat with air flowing through the main air preheater through a cold primary air duct and a cold secondary air duct;
the bypass air preheater is connected with the main air preheater in parallel, high-temperature flue gas in a front flue of an inlet of the bypass air preheater flows through the bypass air preheater and exchanges heat with air flowing through the bypass air preheater through one branch of the cold secondary air;
mixing the main hot secondary air flowing through the main air preheater and the bypass hot secondary air flowing through the bypass air preheater, and then feeding the mixed air into a boiler secondary air main pipe for combustion in a boiler;
and the flue gas flowing through the main air preheater passes through the outlet back flue of the main air preheater and the flue gas flowing through the bypass air preheater and then enters the tail flue of the boiler after being mixed by the outlet back flue of the bypass air preheater.
When the measured temperature at the outlet of the main air preheater is higher than the set temperature value of the outlet of the main air preheater, opening a large bypass flue gas regulating valve to increase the amount of the flue gas flowing through the bypass air preheater; and when the measured temperature at the outlet of the main air preheater is lower than the set temperature of the outlet of the main air preheater, closing the bypass flue gas regulating valve to reduce the amount of the flue gas flowing through the bypass air preheater.
If the measured temperature at the outlet of the main air preheater is higher than the measured temperature at the outlet of the bypass air preheater, closing the cold secondary air regulating valve to reduce the air quantity of the cold secondary air entering the bypass air preheater; or if the measured temperature at the outlet of the main air preheater is lower than the measured temperature at the outlet of the bypass air preheater, opening the cold secondary air regulating valve to increase the air volume of the cold secondary air entering the bypass air preheater.
When the cold secondary air quantity entering a bypass of the bypass air preheater is larger than a set value, keeping the air channel opening of the hot secondary air of the bypass air preheater in a full-open state; or when the cold secondary air quantity entering the bypass of the bypass air preheater is smaller than a set value, keeping the air channel opening of the hot secondary air of the bypass air preheater in a closed state.
According to the invention, the other bypass air preheater is connected in parallel to the existing air preheater, low-temperature cold air is led out from the outlet of the fan, high-temperature flue gas is led out from the flue gas in front of the air preheater, and the low-temperature cold air and the high-temperature flue gas exchange heat in the bypass air preheater connected in parallel, so that the heat exchange area on the flue gas side is increased, and the flue gas temperature is reduced. The prior art mostly utilizes a water supply heater to absorb the waste heat of the flue gas, but the invention utilizes cold air to absorb the waste heat of the flue gas by connecting a bypass air preheater in parallel, and completely different waste heat utilization modes and system structures achieve the following remarkable technical effects:
(1) the cold air is used for absorbing the waste heat of the flue gas, the waste heat completely enters the boiler to participate in heat exchange, and the utilization efficiency of the recovered heat is over 90 percent and is far higher than the preheating utilization of a common feed water heater.
(2) The cold air can be selected from primary air or secondary air, if the drying capacity of the pulverized coal is insufficient, the primary air can be selected, otherwise, the secondary air is selected, and the boiler can be suitable for different characteristics of boilers.
(3) The bypass air preheater can be put into operation when the unit is in high load, and can be stopped when the unit is in low load, so that the requirement of large-amplitude peak regulation of the current unit can be met.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 schematically illustrates an example of the prior art;
FIG. 2 schematically illustrates another example of the prior art;
fig. 3 schematically illustrates the structure of a preferred embodiment of the bypass air preheater heat recovery system of the present invention.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained below by combining the specific drawings.
As shown in fig. 3, the bypass air preheater heat recovery system provided by the invention comprises: main air preheater 3, bypass air preheater 10, air passageway and flue gas passageway. The air channel comprises an air channel 5 of cold primary air, an air channel 6 of cold secondary air, an air channel 15 of hot primary air, an air channel 15 of main hot secondary air and an air channel 19 of bypass hot secondary air. The air entering the main air preheater 3 from the air duct 5 of the cold primary air and the air duct 6 of the cold secondary air is called cold primary air and cold secondary air; the air which comes out of the main air preheater 3 or the bypass air preheater 10 and enters the air duct 15 of the hot primary air, the air duct 16 of the main hot secondary air and the air duct 19 of the bypass hot secondary air is called hot primary air, main hot secondary air and bypass hot secondary air.
The flue gas channel comprises a main air preheater inlet front flue 1, a main air preheater outlet rear flue 11, a bypass air preheater inlet front flue 12 and a bypass air preheater outlet rear flue 22.
The air channel and the smoke channel are both connected with the main air preheater 3 or the bypass air preheater 10.
The inlet front flue 1 of the main air preheater is connected to the main air preheater 3 and is communicated with the outlet rear flue 11 of the main air preheater. The cold primary air duct 5, the cold secondary air duct 6, the hot primary air duct 15 and the main hot secondary air duct (16) are all connected with the main air preheater (3), so that the cold primary air and the cold secondary air of the cold primary air duct 5 and the cold secondary air duct 6 exchange heat with high-temperature flue gas in the main air preheater (3).
An inlet front flue (bypass flue) 12 of the air preheater is connected to the bypass air preheater 10 and communicated with an outlet rear flue 22 of the bypass air preheater, and the cold secondary air duct 6 and the bypass hot secondary duct 18 are connected with the bypass air preheater 10, so that bypass secondary air of the bypass hot secondary duct 18 exchanges heat with bypass flue gas in the bypass air preheater 10.
The bypass air preheater heat recovery system further comprises a bypass cold secondary air regulating valve 8, a bypass hot secondary air stop valve 18 and a bypass flue gas regulating valve 13.
The bypass cold secondary air regulating valve 8 is arranged on a cold secondary air channel through which cold secondary air enters the bypass air preheater 10; the bypass hot secondary air stop valve 18 is arranged on a bypass hot secondary air 19 channel of an air outlet of the bypass air preheater 10; the bypass flue gas regulating valve 13 is arranged on the bypass flue gas channel 12 before the flue gas enters the bypass air preheater 10.
The main hot secondary air duct 16 and the bypass hot secondary air 19 are connected through a three-way air duct interface, and the main air preheater outlet rear flue 11 and the bypass air preheater outlet rear flue 22 are connected through a three-way flue interface.
The second flue gas temperature measuring element 2 is arranged on the inlet front flue 1 of the main air preheater 3, the ninth flue gas temperature measuring element 9 is arranged in front of a flue gas mixing point of the outlet rear flue 11 of the main air preheater 3, the flue gas outlet flue of the bypass air preheater 10 and the flue gas temperature measuring elements 21 and 23 are respectively arranged on the flue gas mixing point rear flue of the main air preheater outlet flue, the cold primary air flue 5, the cold secondary air flue 6, the hot primary air flue 15, the main hot secondary air flue 16 and the bypass hot secondary air flue 19 are respectively provided with the fourth flue gas temperature measuring element 4, the seventh flue gas temperature measuring element 7, the fourteenth flue gas temperature measuring element 14, the seventeenth flue gas temperature measuring element 17 and the twentieth flue gas temperature measuring element 20.
The cold primary air duct 5 and the cold secondary air duct 6 are respectively from a primary fan and a blower, the flow rates of the cold primary air duct 5 and the cold secondary air duct 6 depend on the load and the operating conditions of a boiler, the hot primary air duct 15 is connected with a hot primary air duct main pipe and goes to a powder making system, the main hot secondary air duct 16 and the bypass hot secondary air duct 19 are connected with a hot secondary air duct after being mixed through an air duct tee joint part, and the output air goes to a secondary air box.
The working method of the system comprises the following steps:
high-temperature flue gas in a front flue 1 at the inlet of the main air preheater flows through the main air preheater 3 and exchanges heat with cold primary air and cold secondary air flowing through the main air preheater 3 through a cold primary air duct 5 and a cold secondary air duct 6;
high-temperature flue gas in a front flue 12 at the inlet of the bypass air preheater 10 flows through the bypass air preheater 10 and exchanges heat with cold secondary air of one branch of the cold secondary air duct 6 flowing through the bypass air preheater 10;
the main hot secondary air duct 16 flowing through the main air preheater 3 and the bypass hot secondary air duct (19) flowing through the bypass air preheater 10 are mixed and then enter a boiler secondary air main pipe for combustion in a boiler;
the flue gas flowing through the main air preheater 3 passes through an outlet back flue 11 of the main air preheater 3 and the flue gas flowing through the bypass air preheater 10 passes through an outlet back flue 22 of the bypass air preheater to be mixed and then enters a tail flue of the boiler; and
a second flue gas temperature measuring element 2 is arranged on a front flue 1 at an inlet of a main air preheater 3, a ninth flue gas temperature measuring element 9 is arranged in front of a flue gas mixing point of a rear flue 11 at an outlet of the main air preheater, and a twenty-first flue gas temperature measuring element 21 and a twenty-third measuring element 23 are respectively arranged on a flue gas outlet flue of a bypass air preheater 10 and a rear flue at a mixing point of the flue gas outlet flue of the main air preheater 3. The cold primary air duct 5, the cold secondary air duct 6, the hot primary air duct 15, the main hot secondary air duct 16 and the bypass hot secondary air duct 19 are respectively provided with a fourth flue gas temperature measuring element 4, a seventh measuring element 7, a fourteenth measuring element 14, a seventeenth measuring element 17 and a twenty-second measuring element 20.
The bypass flue gas regulating valve 13 controls the opening degree thereof according to the load of the unit and the measured temperature of the ninth flue gas temperature measuring element 9: when the measured temperature of the ninth flue gas temperature measuring element 9 is higher than the set outlet temperature value of the main air preheater 3, the opening degree of the bypass flue gas regulating valve 13 is increased; or the temperature measured by the ninth flue gas temperature measuring element 9 is lower than the set value of the outlet temperature of the main air preheater 3, the opening degree of the bypass flue gas regulating valve 13 is reduced.
The bypass cold secondary air regulating valve 8 is synchronously opened after the bypass flue gas regulating valve 13 is opened, and the opening degree of the bypass cold secondary air regulating valve is controlled according to the temperature deviation measured by a ninth flue gas temperature measuring element 9 arranged behind the main air preheater 3 and a flue gas temperature measuring element 21 arranged behind the bypass air preheater 10: if the measured temperature of the ninth flue gas temperature measuring element 9 behind the main air preheater 3 is greater than the measured temperature of the twenty-first flue gas temperature measuring element 21 behind the bypass air preheater 10, the opening degree of the bypass cold secondary air regulating valve 8 is reduced; or if the measured temperature of the ninth flue gas temperature measuring element 9 behind the main air preheater 3 is lower than the measured temperature of the twenty-first flue gas temperature measuring element 21 behind the bypass air preheater 3, the opening degree of the bypass cold secondary air regulating valve 8 is increased.
The bypass hot secondary air stop valve 18 controls the opening thereof according to the opening of the bypass cold secondary air regulating valve 8: when the opening degree of the bypass cold secondary air regulating valve 8 is larger than a set value, the bypass hot secondary air stop valve 18 is kept in a full-open state; alternatively, when the opening degree of the bypass cold secondary air adjusting valve 8 is smaller than the set value, the bypass hot secondary air cut-off valve 18 is closed.
When RB or MFT occurs to the unit, the opening degrees of the bypass cold secondary air regulating valve 8 and the bypass flue gas regulating valve 13 are synchronously reduced until the whole unit is closed, the closing speed depends on the speed of RB or MFT, and after the whole unit is closed, the bypass hot secondary air stop valve 18 is closed.
In addition, the invention can quote the measured value of the sulfur content of the flue gas or the dew point of the acid of the flue gas which is monitored in real time, and automatically correct the initial set values of the temperature of the flue gas at the outlet of the air preheater, the temperature of the air at the inlet of the main air preheater 3 and the like, so as to enhance the adaptability of the unit to the coal for combustion and the operation condition of the equipment. When the measured value of the sulfur content in the flue gas or the dew point of the acid in the flue gas is increased from the initial set value, the deviation is subjected to control operation to output correction values so as to respectively increase the set values of the temperature of the flue gas at the outlet of the air preheater 3 and the temperature of the air at the inlet of the main air preheater 3, and vice versa.
Through the above description, it can be seen that in the invention, another bypass air preheater is connected in parallel to the existing air preheater, low-temperature cold air is led out from the outlet of the fan, high-temperature flue gas is led out from the flue gas in front of the air preheater, and the low-temperature cold air and the high-temperature flue gas exchange heat in the bypass air preheater connected in parallel, so that the heat exchange area on the flue gas side is increased, and the flue gas temperature is reduced. The prior art mostly utilizes a water supply heater to absorb the waste heat of the flue gas, but the invention utilizes cold air to absorb the waste heat of the flue gas by connecting a bypass air preheater in parallel, and is completely different in waste heat utilization mode and system structure, thereby achieving the following remarkable technical effects:
(1) the cold air is used for absorbing the waste heat of the flue gas, the waste heat completely enters the boiler to participate in heat exchange, and the utilization efficiency of the recovered heat is over 90 percent and is far higher than the preheating utilization of a common feed water heater.
(2) The cold air can be selected from primary air or secondary air, if the drying capacity of the pulverized coal is insufficient, the primary air can be selected, otherwise, the secondary air is selected, and the boiler can be suitable for different characteristics of boilers.
(3) The bypass air preheater can be put into operation when the unit is in high load, and can be stopped when the unit is in low load, so that the requirement of large-load peak shaving of the current unit can be met.
(4) Because the proper exhaust gas temperature is related to the sulfur content and the moisture content of the coal, the operation rate of the bypass air preheater can be adjusted according to the change of the coal, and the proper exhaust gas temperature is adjusted to meet the requirements of the coal.
(5) The exhaust gas temperature is reduced under high load, the boiler efficiency can be improved, the power consumption of the induced draft fan can be reduced, and the energy-saving effect is remarkable.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (15)
1. A bypass air preheater heat recovery system, comprising:
a main flue (1);
the main air preheater (3) is arranged on the main flue (1), the main air preheater (3) is respectively connected with a primary cold air duct (5) and a secondary cold air duct (6), the flue gas entering the main flue (1) is respectively subjected to heat exchange with the primary cold air of the primary cold air duct (5) and the secondary cold air of the secondary cold air duct (6) through the main air preheater (3), the cooled flue gas is discharged to a flue at the tail part of the boiler, and the primary cold air and the secondary cold air are respectively changed into primary hot air and secondary hot air after being heated and discharged to the boiler for internal combustion;
a bypass flue gas channel (12) branched from the main flue (1), wherein a part of flue gas branched from the main flue (1) enters the bypass flue gas channel; and
a bypass air preheater (10) arranged on the bypass flue gas channel (12), wherein the bypass air preheater (10) is connected with any one of the cold secondary air channels (6), so that flue gas entering the bypass air preheater (10) exchanges heat with cold air from the cold secondary air channels (6), the flue gas cooled in the way is discharged to a flue at the tail part of the boiler, the cold secondary air is heated and respectively changed into hot secondary air to be discharged to a main secondary air pipe of the boiler for combustion in the boiler,
the bypass air preheater heat recovery system is characterized in that a bypass flue gas regulating valve (13) is arranged on a bypass flue gas channel (12) before flue gas enters a bypass air preheater (10), and a ninth flue gas temperature measuring element (9) is arranged in front of a flue gas mixing point of an outlet rear flue (11) of a main air preheater (3).
2. The bypass air preheater heat recovery system of claim 1, wherein a bypass cold secondary air regulating valve (8) is provided on the passage of the cold secondary air into the bypass air preheater (10).
3. The bypass air preheater heat recovery system of claim 1, wherein the bypass hot secondary air shutoff valve (18) is provided on a bypass hot secondary air passage (19) of an air outlet of the bypass air preheater (10).
4. The bypass air preheater heat recovery system according to claim 1, wherein a second flue gas temperature measuring element (2) is provided on the inlet front main flue (1) of the main air preheater (3).
5. The bypass air preheater heat recovery system of claim 1, wherein a twenty-first flue gas temperature measuring element (21) is provided in the flue gas outlet stack of the bypass air preheater (10).
6. The bypass air preheater heat recovery system of claim 1, wherein a twenty-third flue gas temperature measuring element (23) is provided in the flue after the exit flue mixing point of the main air preheater (3).
7. The bypass air preheater heat recovery system according to claim 1, wherein a fourth flue gas temperature measuring element (4) is provided on the cold primary air duct (5).
8. The bypass air preheater heat recovery system according to claim 1, wherein a seventh flue gas temperature measuring element (7) is provided on the cold secondary air duct (6).
9. The bypass air preheater heat recovery system of claim 1 wherein a fourteenth flue gas temperature measuring element (14) is provided in the primary hot air duct (15).
10. The bypass air preheater heat recovery system of claim 1, wherein a seventeen flue gas temperature measuring element (17) is provided in the primary heat secondary air duct (16).
11. The bypass air preheater heat recovery system of claim 1, wherein a twentieth flue gas temperature measuring element (20) is provided in the bypass hot overfire air duct (19).
12. The bypass air preheater heat recovery system of claim 1, wherein the air of the bypass air preheater (10) can be led out not only from the cold secondary air duct (6) but also from the cold primary air duct (5), but only one of them is selected and incompatible.
13. A heat recovery method of a bypass air preheater is characterized by comprising the following steps:
high-temperature flue gas in a main flue (1) in front of an inlet of a main air preheater (3) flows through the main air preheater (3) and exchanges heat with cold primary air and cold secondary air flowing through the main air preheater (3) in a cold primary air duct (5) and a cold secondary air duct (6);
high-temperature flue gas in a front flue (12) at the inlet of the bypass air preheater (10) flows through the bypass air preheater (10) to exchange heat with air flowing through the bypass air preheater (10) from one branch of the cold secondary air duct (6);
the main hot secondary air flowing through the main hot secondary air channel (16) of the main air preheater (3) and the bypass hot secondary air flowing through the bypass hot secondary air channel (19) of the bypass air preheater (10) are mixed and then enter a boiler secondary air main pipe for combustion in the boiler;
the flue gas flowing through the main air preheater (3) passes through the outlet back flue (11) of the main air preheater and the flue gas flowing through the bypass air preheater (10) passes through the outlet back flue (22) of the bypass air preheater to be mixed and then enters the tail flue of the boiler,
when the measured temperature at the outlet of the main air preheater (3) is higher than the set temperature value at the outlet of the main air preheater (3), opening the bypass flue gas regulating valve to increase the smoke volume flowing through the bypass air preheater (10); when the measured temperature at the outlet of the main air preheater (3) is lower than the set temperature of the outlet of the main air preheater (3), the bypass flue gas regulating valve is closed, so that the smoke quantity flowing through the bypass air preheater (10) is reduced.
14. The bypass air preheater heat recovery method according to claim 13, wherein when the measured temperature at the outlet of the main air preheater (3) is higher than the measured temperature at the outlet of the bypass air preheater, the cold secondary air regulating valve is closed to reduce the amount of cold secondary air entering the bypass air preheater (10); and when the measured temperature at the outlet of the main air preheater (3) is lower than the measured temperature at the outlet of the bypass air preheater, opening the cold secondary air regulating valve to increase the air volume of the cold secondary air entering the bypass air preheater (10).
15. The bypass air preheater heat recovery method according to claim 13, wherein when the amount of cold secondary air entering the bypass of the bypass air preheater (10) is greater than a set value, the duct opening of the hot secondary air of the bypass air preheater (10) is kept fully open; when the cold secondary air quantity entering the bypass of the bypass air preheater (10) is smaller than a set value, the air channel opening of the hot secondary air of the bypass air preheater (10) is kept in a closed state.
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| CN107062194A (en) * | 2017-04-19 | 2017-08-18 | 大唐贵州发耳发电有限公司 | A kind of thermal power plant flue gas waste heat recovery apparatus |
| CN109404958B (en) * | 2018-11-12 | 2024-02-02 | 南京博沃科技发展有限公司 | Energy-saving synergistic anti-blocking method and system based on bypass flue of air preheater |
| CN110594777B (en) * | 2019-09-26 | 2024-04-09 | 中国电建集团河南工程有限公司 | Steam supply system of air heater of boiler air preheater |
| CN110793057B (en) * | 2019-10-18 | 2024-01-30 | 华电电力科学研究院有限公司 | System and method for preventing blockage of air preheater of coal-fired power plant |
| CN114110638B (en) * | 2021-11-26 | 2024-01-19 | 西安热工研究院有限公司 | Automatic regulating system and method for efficient flue gas waste heat utilization of bypass of air preheater |
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