JP2019148349A - Boiler system and operating method for boiler system - Google Patents

Abstract

To provide a boiler system enabling efficient operation while improving boiler efficiency.SOLUTION: A boiler system includes: a conveyance air supply line; an exhaust gas discharge line; an air preheater connected to each of the conveyance air supply line and the exhaust gas discharge line for preheating conveyance air flowing in the conveyance air supply line by using exhaust gas flowing in the exhaust gas discharge line; a mill device provided in the conveyance air supply line; an exhaust gas recirculation line branched from a portion between an induction ventilator installed downstream of the air preheater and a desulfurization device in the exhaust gas discharge line and connected to a portion between the air preheater and the mill device in the conveyance air supply line; and exhaust gas recirculation amount control means provided in the exhaust gas recirculation line and capable of controlling a flow rate of recirculation exhaust gas recirculating through the exhaust gas recirculation line.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a boiler system including a boiler, and more particularly, to temperature adjustment of primary air (transport air) for drying and transporting fuel.

  For example, a boiler system including a coal-fired boiler that uses coal as a fuel includes a mill device for pulverizing coal to obtain fine powder such as pulverized coal, and the pulverized fuel generated by the mill device is supplied to the mill device. The primary air (conveyance air) is conveyed to the boiler (burner) through the pulverized coal pipe. Coal contains moisture, and when moisture condensation occurs in the middle of transportation when drying is inadequate, there is a possibility of causing pulverized coal to adhere to and clog the pulverized coal pipe and mill. May affect combustion performance. For this reason, conventionally, the primary air introduced into the mill device is preheated (preheated) by an air preheater (AH) using the heat of the exhaust gas of the boiler, and the fuel is dried by the preheated air ( For example, see Patent Documents 1 and 2). More specifically, a line (duct) for supplying primary air to the mill device includes a line for generating primary air (hereinafter, hot air) preheated by AH, and preheating by AH by bypassing AH. And a line for generating primary air (hereinafter referred to as cold air). And by adjusting the flow rate ratio of hot air and cold air by the opening control of the hot air damper that adjusts the flow rate of hot air and the cold air damper that adjusts the flow rate of cold air, and mixing them The primary air at the required temperature is supplied to the mill device.

  Conventionally, the opening control of each of the cold air damper and the hot air damper described above is performed so that the temperature of the primary air at the outlet or inlet of the mill device (mill outlet temperature, mill The goal was to keep the inlet temperature constant. The temperature of primary air at the outlet and inlet of the mill device varies depending on the amount of moisture in the fuel such as coal described above, the amount of fuel supplied to the mill device, and the amount of primary air supplied. In addition, about the water content in coal, it changes with coal types, and generally the primary air temperature supplied to a mill apparatus becomes high, so that the coal type with much moisture. However, if it is necessary to lower the temperature of the primary air supplied to the mill device, for example, when the moisture in the fuel is reduced, the flow rate of the cold air that bypasses AH if the opening of the cold air damper is increased. Increases, the amount of heat exchange in AH decreases. For this reason, deterioration of boiler efficiency and the temperature rise of the exhaust gas after passing through AH occur. After passing AH, the exhaust gas will pass through the downstream equipment such as the electric dust collector (EP) and the chimney. If the exhaust gas temperature exceeds the design temperature of the downstream equipment, the boiler load will be lowered. This will hinder the efficient operation of the boiler.

  In order to make it possible to use low-grade coal such as modified lignite, Patent Document 1 reduces the oxygen concentration at the pulverized coal machine outlet to reduce the exhaust gas between the desulfurization tower and the chimney. The exhaust gas taken out from the duct (exhaust gas discharge line) is added to the air from the primary air fan (PAF) to make a mixed gas, and then bypasses the GAH (AH) carrier gas duct (carrier air supply line) and GAH. The mixed gas is allowed to flow separately to the bypass carrier gas duct, and then the mixed gas is supplied to the mill. That is, the transportation air containing the exhaust gas is recirculated to the boiler by the exhaust gas recirculation line that connects the desulfurization tower outlet in the exhaust gas discharge line and the upstream side of the detour line in the transportation air supply line.

  In Patent Document 2, while reducing NOx during the operation of the pulverized coal machine, the oxygen concentration in the pulverized coal machine before the start of the high volatile coal coal injection and the stop of the coal injection is reduced. In order to achieve this, the exhaust gas recirculation line is branched from the downstream side of the desulfurization device in the exhaust gas discharge line, and the other end of the exhaust gas recirculation line is connected to the inlet of the pulverized coal machine (mill device).

JP2013-019638A Japanese Patent Laid-Open No. 5-187609

  However, from the viewpoint of improving boiler efficiency, in Patent Document 1, a higher-temperature exhaust gas (recirculated exhaust gas) is mixed with the carrier air before being preheated by AH. For this reason, since the temperature of the conveying air is increased before being preheated by the air preheater, the temperature difference between the preheating side fluid (exhaust gas) and the heat receiving side fluid (primary air) in AH is reduced. Therefore, the improvement of the heat exchange efficiency in AH cannot be expected, and the temperature of the exhaust gas after passing through AH may be higher than that before mixing (before introduction) of the recirculated exhaust gas. In addition, when the desulfurization tower (desulfurization apparatus) is wet, the exhaust gas having a high moisture content after passing through the desulfurization tower is recirculated, and moisture loss in the exhaust gas increases, so that the boiler efficiency deteriorates. . If there is a lot of moisture in the exhaust gas, it may be necessary to increase the temperature of the conveying air supplied to the mill device for drying the fuel, so boiler efficiency can be improved by reducing the flow rate of cold air. Overall improvement in boiler efficiency cannot be expected by offsetting the deterioration in boiler efficiency due to an increase in moisture loss.

  In view of the above circumstances, at least one embodiment of the present invention aims to provide a boiler system capable of efficient operation while improving boiler efficiency.

(1) A boiler system according to at least one embodiment of the present invention includes:
A transfer air supply line for supplying transfer air for transferring fuel to the boiler;
An exhaust gas discharge line for discharging the exhaust gas generated by the combustion of the fuel inside the boiler to the outside;
An air preheater connected to each of the transfer air supply line and the exhaust gas discharge line, for preheating the transfer air flowing through the transfer air supply line with the exhaust gas flowing through the exhaust gas discharge line;
A mill device for pulverizing the fuel to be supplied to the boiler, provided in the air supply line for conveyance;
The air is branched from between the induction ventilator and the desulfurization device installed on the downstream side of the air preheater in the exhaust gas discharge line, and between the air preheater and the mill device in the transfer air supply line. Connected exhaust gas recirculation lines;
Exhaust gas recirculation amount adjusting means provided in the exhaust gas recirculation line and capable of adjusting a flow rate of the recirculated exhaust gas recirculated through the exhaust gas recirculation line.

  According to the configuration of (1) above, the boiler system is an exhaust gas that flows through the exhaust gas exhaust line after passing through the air preheater, and a part of the exhaust gas (recirculated exhaust gas) that has been boosted by the induction fan is used as an exhaust gas. Under the adjustment by the recirculation amount adjusting means, it is configured to recirculate downstream of the air preheater in the transfer air supply line through the exhaust gas recirculation line. That is, the recirculated exhaust gas is recirculated (joined) to a position where it is supplied to the mill device without passing through the air preheater. While the exhaust gas flows on the downstream side of the air preheater in the exhaust gas discharge line, the exhaust gas has a temperature lower than that of the conveying air when supplied to the mill device preheated by the air preheater. Therefore, the temperature of the air for conveyance after joining can be lowered | hung by joining the recirculation exhaust gas which is a low temperature with respect to the air for conveyance at the time of being supplied to a mill apparatus. Therefore, the recirculated exhaust gas can reduce the temperature of the conveying air when supplied to the mill device without increasing the flow rate of the cold air, while avoiding (suppressing) the decrease in boiler efficiency. The temperature of the conveying air at the inlet or outlet of the mill device can be lowered.

  Further, since the pressure of the recirculated exhaust gas is increased by the induction fan, the flow rate of the recirculated exhaust gas can be easily adjusted by the exhaust gas recirculation amount adjusting means, and the exhaust gas recirculation amount adjusting means is reactivated. When a fan that pumps circulating exhaust gas is included, the power of the fan can be reduced because the pressure of the recirculated exhaust gas is increased.

  Further, as described above, when reducing the temperature of the conveying air at the inlet or outlet of the mill device, it is possible to avoid (suppress) the reduction in the amount of air that exchanges heat with the exhaust gas in the air preheater. It is possible to prevent the exhaust gas temperature from exceeding the design temperature of the downstream equipment of the air preheater in the line. Therefore, it is possible to prevent the occurrence of a situation in which the boiler is operated while reducing the load so as not to exceed the design temperature of the latter-stage equipment, and it is possible to efficiently operate the boiler.

(2) In some embodiments, in the configuration of (1) above,
A bypass line for connecting the upstream side and the downstream side of the air preheater in the transfer air supply line, the bypass air for bypassing the air preheater,
The exhaust gas recirculation line is branched from the downstream side of the air preheater in the exhaust gas discharge line, and is connected between the air preheater and the mill device in the transfer air supply line or to the bypass line. The
According to the configuration of (2) above, the exhaust gas recirculation line connects the downstream side of the air preheater in the exhaust gas discharge line and the downstream side or bypass line of the air preheater in the transfer air supply line. While the exhaust gas flows downstream of the air preheater in the exhaust gas discharge line, the carrier air (hot air) preheated in the air preheater and the carrier air that is not preheated by the air preheater by flowing in the bypass line ( The temperature is lower than that of the air for conveyance after merging with (cold air). Therefore, the temperature of the conveyance air when supplied to the mill device can be lowered by merging the recirculated exhaust gas having a lower temperature with respect to the conveyance air after the merging, and (1) Has the same effect as.

(3) In some embodiments, in the configuration of (2) above,
A cold air amount adjusting means provided in the detour line, and capable of adjusting a flow rate of the transfer air flowing through the detour line;
The opening degree of the cold air amount adjusting means is adjusted to the closed side when the recirculated exhaust gas is supplied to the transfer air supply line via the exhaust gas recirculation line by the exhaust gas recirculation amount adjusting means. The

  According to the configuration of (3) above, when the recirculated exhaust gas is introduced into the carrier air supply line, the opening degree of the cold air amount adjusting means is made smaller than that before the recirculated exhaust gas is introduced. Since the temperature of the conveying air when supplied to the mill device by the recirculated exhaust gas can be reduced, the temperature of the conveying air can be lowered even if the flow rate of the cold air is decreased by that amount. Therefore, by reducing the flow rate of cold air in the above case, the temperature of the carrier air when supplying to the mill device is lowered by the recirculated exhaust gas, and the carrier air exchanged with the exhaust gas in the air preheater. The flow rate of can be increased. Accordingly, it is possible to further improve the boiler efficiency and further reduce the temperature of the exhaust gas flowing through the subsequent equipment installed on the downstream side of the air preheater in the exhaust gas discharge line.

(4) In some embodiments, in the above configurations (1) to (3),
An exhaust gas recirculation amount control device for controlling the opening degree of the exhaust gas recirculation amount adjusting means is further provided.
According to the configuration of (4) above, the flow rate of the recirculated exhaust gas passing through the exhaust gas recirculation line is automatically adjusted by controlling the opening degree of the exhaust gas recirculation amount adjusting means by the exhaust gas recirculation amount control device. Can do.

(5) In some embodiments, in the configuration of (4) above,
The exhaust gas recirculation amount control device controls the opening degree of the exhaust gas recirculation amount adjusting means based on the moisture content of the fuel supplied to the mill device.
According to the configuration of (5) above, the opening degree of the exhaust gas recirculation amount adjusting means is adjusted based on the moisture content of the fuel (such as the moisture content per unit weight). That is, when the moisture content of the fuel decreases, it is necessary to lower the mill inlet temperature or the mill outlet temperature of the carrier air in order to prevent ignition or the like due to excessive drying of the fuel F due to the heat of the carrier air G1. This situation is determined based on the moisture content of the fuel. For example, if the exhaust gas recirculation amount adjusting means is opened without increasing the opening degree of the cold air amount adjusting means capable of adjusting the flow rate of the cold air flowing through the bypass line, the exhaust gas recirculation exhaust line is passed through. The recirculated exhaust gas introduced in this manner can reduce the temperature of the conveying air when it is supplied to the mill device without reducing the flow rate of hot air preheated by the air preheater. Therefore, it is possible to prevent a decrease in boiler efficiency and an increase in exhaust gas temperature on the downstream side of the air preheater.

(6) In some embodiments, in the above configurations (4) to (5),
The flow rate of hot air preheated by the air preheater provided between the connection portion of the air supply line for conveyance and the bypass line on the downstream side of the air preheater and the air preheater is adjusted. Possible hot air amount adjusting means;
A cold air amount adjusting means provided in the bypass line and capable of adjusting a flow rate of the transfer air flowing through the bypass line;
Temperature measuring means for detecting the temperature of at least one of the outlet temperature or the inlet temperature of the mill device;
A cooling opening degree determining device for determining opening degrees of the hot air amount adjusting means and the cold air amount adjusting means based on the temperature detected by the temperature measuring means;
The exhaust gas recirculation amount control device controls the opening degree of the exhaust gas recirculation amount adjusting means based on the determined opening degree that is the opening degree of the cold air amount adjusting means determined by the cold heat opening degree determining device.

  According to the configuration of (6) above, the opening degree of the exhaust gas recirculation amount adjusting means is controlled based on the determined opening degree of the cold air amount adjusting means. Specifically, when the determined opening degree of the cold air amount adjusting means is equal to or larger than a predetermined opening threshold value, or the determined opening degree of the cold air amount adjusting means is larger than the predetermined opening degree change threshold value from the immediately preceding opening degree. In such a case, the exhaust gas recirculation amount adjusting means is opened. Thereby, the temperature of the air for conveyance at the time of being supplied to a mill apparatus by recirculation waste gas can be reduced, avoiding that the opening degree (decision opening degree) of a cold air amount adjustment means changes large.

(7) In some embodiments, in the above configurations (4) to (6),
An oxygen sensor installed on the downstream side of a connection portion to which the exhaust gas recirculation line in the transfer air supply line is connected;
The exhaust gas recirculation amount control device controls the opening degree of the exhaust gas recirculation amount adjusting means based on the measured value of the oxygen sensor.

  The oxygen concentration contained in the carrier air when it is supplied to the mill device decreases according to the flow rate of the recirculated exhaust gas, but if the oxygen concentration becomes too low due to the excessive flow rate of the recirculated exhaust gas, May become unstable.

  According to the configuration of (7) above, the flow rate of the recirculated exhaust gas is adjusted based on the measured value measured by the oxygen sensor. Specifically, the flow rate of the recirculated exhaust gas is controlled within a range that does not fall below the lower limit value of the oxygen amount necessary for stable combustion in the burner. As a result, the combustion in the burner can be prevented from becoming unstable, and the combustion can be prevented from becoming unstable, for example, the burner misfires due to insufficient oxygen concentration.

(8) In some embodiments, in the configurations of (1) to (7) above,
A combustion air supply line for supplying combustion air for burning the fuel to the boiler;
A total air amount adjusting means capable of adjusting a flow rate of the total air including the carrier air and the combustion air to be heat-exchanged with the exhaust gas in the air preheater;
An exhaust gas flow rate acquisition means for acquiring the flow rate of the exhaust gas discharged from the boiler to the exhaust gas discharge line,
The flow rate of the total air is adjusted based on the flow rate of the exhaust gas acquired by the exhaust gas flow rate acquisition means.

  Generally, when the amount of gas flowing through the boiler increases, the steam temperature rises. Normally, the boiler is operated so that the steam temperature becomes constant, but when the amount of gas flowing through the boiler increases by the amount of the recirculated exhaust gas, the steam temperature rises accordingly.

  According to the configuration of (8) above, the flow rate of the total air composed of the carrier air and the combustion air exchanged with the exhaust gas in the air preheater is adjusted based on the flow rate of the exhaust gas discharged from the boiler. Therefore, when the flow rate of the carrier air supplied to the mill device is increased by the flow rate of the recirculated exhaust gas, the flow rate of the total air pushed from the total air amount adjusting means (for example, FDF) is reduced by the increase amount. Thus, the steam temperature in the boiler can be controlled to be constant without cooling the steam with a spray device so that the steam temperature in the boiler becomes constant. In addition, the total amount of heat of the exhaust gas can be reduced by reducing the flow rate of the exhaust gas as compared with the case where the amount of gas flowing through the boiler increases by the amount of the recirculated exhaust gas. The temperature of the exhaust gas after heat exchange in can be lowered, and the amount of heat discarded can be reduced. Therefore, boiler efficiency can be improved.

(9) A boiler system operation method according to at least one embodiment of the present invention includes:
A transfer air supply line for supplying transfer air for transferring fuel to the boiler;
An exhaust gas discharge line for discharging the exhaust gas generated by the combustion of the fuel inside the boiler to the outside;
An air preheater connected to each of the transfer air supply line and the exhaust gas discharge line, for preheating the transfer air flowing through the transfer air supply line with the exhaust gas flowing through the exhaust gas discharge line;
A bypass line for connecting the upstream side and the downstream side of the air preheater in the transfer air supply line, and for the transfer air to flow around the air preheater;
A mill device for pulverizing the fuel to be supplied to the boiler, provided in the air supply line for conveyance;
Branching between the induction ventilator and the desulfurization device installed downstream of the air preheater in the exhaust gas discharge line, and between the air preheater and the mill device in the transfer air supply line or An exhaust gas recirculation line connected to the bypass line;
An exhaust gas recirculation amount adjusting means provided in the exhaust gas recirculation line and capable of adjusting a flow rate of the recirculated exhaust gas recirculated through the exhaust gas recirculation line;
The moisture content of the fuel supplied to the mill device, the opening of the cold air amount adjusting means capable of adjusting the flow rate of the transfer air flowing through the bypass line, and the exhaust gas recirculation line in the transfer air supply line The method includes a step of controlling the opening degree of the exhaust gas recirculation amount adjusting means based on at least one of measured values of an oxygen sensor installed on the downstream side of the connecting portion to be connected.

  According to the structure of said (9), there exists an effect similar to at least 1 of said (5)-(7).

(10) In some embodiments, in the configuration of (9) above,
The boiler system includes a combustion air supply line for supplying combustion air for burning the fuel to the boiler;
A total air amount adjusting means capable of adjusting a flow rate of the total air including the carrier air and the combustion air to be heat-exchanged with the exhaust gas in the air preheater;
An exhaust gas flow rate acquisition means for acquiring the flow rate of the exhaust gas discharged from the boiler to the exhaust gas discharge line,
The method further includes the step of adjusting the flow rate of the total air based on the flow rate of the exhaust gas acquired by the exhaust gas flow rate acquisition means.

  According to the configuration of the above (10), the same effect as the above (8) is obtained.

  According to at least one embodiment of the present invention, a boiler system capable of efficient operation while improving boiler efficiency is provided.

It is a schematic diagram of a boiler system provided with an exhaust gas recirculation line and exhaust gas recirculation amount adjustment means concerning one embodiment of the present invention. It is a flowchart which shows the operating method of a boiler system provided with the exhaust gas recirculation line and exhaust gas recirculation amount adjustment means which concern on one Embodiment of this invention. It is a flowchart which shows the operating method of a boiler system provided with the exhaust gas recirculation line which concerns on one Embodiment of this invention, and exhaust gas recirculation amount adjustment means, and is a flowchart which adjusts the flow volume of total air based on the flow volume of exhaust gas. .

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.
For example, expressions expressing relative or absolute arrangements such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly In addition to such an arrangement, it is also possible to represent a state of relative displacement with an angle or a distance such that tolerance or the same function can be obtained.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
For example, expressions representing shapes such as quadrangular shapes and cylindrical shapes represent not only geometrically strict shapes such as quadrangular shapes and cylindrical shapes, but also irregularities and chamfers as long as the same effects can be obtained. A shape including a part or the like is also expressed.
On the other hand, the expressions “comprising”, “comprising”, “comprising”, “including”, or “having” one constituent element are not exclusive expressions for excluding the existence of the other constituent elements.

FIG. 1 is a schematic view of a boiler system 1 including an exhaust gas recirculation line Lr and an exhaust gas recirculation amount adjusting unit 6 according to an embodiment of the present invention. The boiler system 1 is a system including a boiler 2, and as shown in FIG. 1, a conveyance air supply line L <b> 1 and an exhaust gas discharge line Le connected to the boiler 2, an air preheater 3, a mill device 4, An exhaust gas recirculation line Lr and an exhaust gas recirculation amount adjusting means 6 are provided. As shown in FIG. 1, the boiler system 1 may further include a detour line Lb. Hereinafter, the boiler 2 is demonstrated as a coal burning boiler (pulverized coal cooking boiler) which uses coal as the fuel F, for example. However, the present invention is not limited to this embodiment. For example, in some other embodiments, the boiler 2 may be a boiler 2 that uses a solid fuel other than coal, such as biomass fuel, as the fuel F.
Hereinafter, the above-described configuration of the boiler system 1 will be described with reference to FIG.

  The conveyance air supply line L1 is a duct for supplying conveyance air G1 (primary air) for conveying the fuel F to the boiler 2, and the conveyance air G1 passes through the inside of the conveyance air supply line L1. Is supplied to the boiler 2. As shown in FIG. 1, combustion air supply for supplying combustion air G <b> 2 (secondary air) for burning the fuel F to the boiler 2 is usually supplied to the boiler 2 together with the conveying air supply line L <b> 1. A line L2 (duct) is connected, and the conveyance air supply line L1 is provided so as to branch from the combustion air supply line L2. The sum of the flow rate of the transfer air G1 (the amount of air per unit time; the same applies hereinafter) and the flow rate of the combustion air G2 (the flow rate of the total air Ga) is the combustion air supply line L2 and the transfer air supply It is controlled by a forced air blower (hereinafter referred to as FDF82: Forced Draft Fan) installed upstream of the branch position with the line L1. Further, the flow rate of the transfer air G1 is controlled by a primary air blower (hereinafter referred to as PAF81: Primary Air Fan) installed in the transfer air supply line L1, and a part of the flow rate of the total air Ga pushed in by the FDF 82. Is guided to the conveying air supply line L1 by the PAF 81.

  In the embodiment shown in FIG. 1, the flow rate of the total air Ga described above is the first oxygen sensor 91 (O 2 sensor) for measuring the air ratio inside the boiler 2 (the ratio of the actual combustion air amount to the theoretical air amount). ) Is controlled by the FDF 82 so that the measured value becomes constant (constant range) (air ratio constant control). In the present embodiment, the first oxygen sensor 91 is installed upstream of the air preheater 3 (described later) in the exhaust gas discharge line Le (described later). In some other embodiments, the first oxygen sensor 91 may be inside the boiler 2, or may be a steel pipe type air preheater that does not leak from the air side to the gas side in the air preheater 3. When employed, it may be downstream of the air preheater 3 (described later) in the exhaust gas discharge line Le.

  In the embodiment shown in FIG. 1, the flow rate of the conveying air G <b> 1 is supplied to the mill device 4 (described later) under the opening degree control of the hot air amount adjusting means 71 and the cold air amount adjusting means 72 described later. It is controlled by the PAF 81 so that the measured value of the flow meter 92 that measures the flow rate can be set to a set value (set range). This set value is determined according to the output command value of the boiler 2. More specifically, the amount of fuel F (fine fuel) supplied to the boiler 2 from the mill device 4 (described later) is determined according to the output command value of the boiler 2, and the amount of fuel F thus determined is determined. The flow rate of the conveying air G1 is also determined according to the amount of the fuel F so that it can be properly conveyed to the boiler 2. In the present embodiment, the flow meter 92 is connected to a connection portion (hereinafter referred to as a cold air confluence portion Ca as appropriate) to which a downstream end portion of a detour line Lb (described later) in the transfer air supply line L1 is connected. It is provided between the mill device 4. In some other embodiments, the flow meter 92 is, for example, a pulverized coal pipe L1a that connects the mill device 4 (described later) and the boiler 2 if the flow rate of the carrier air G1 can be appropriately measured. You may install in another position.

  The exhaust gas discharge line Le is a duct for discharging the exhaust gas Ge generated by the combustion of the fuel F inside the boiler 2 to the outside (outside the system), and the exhaust gas Ge is discharged outside through the inside of the exhaust gas discharge line Le. Is done. As shown in FIG. 1, the exhaust gas discharge line Le usually has an induction fan (hereinafter referred to as IDF 84) and an environmental device (for example, a denitration device that removes nitrogen oxides from exhaust gas, a dust collector that removes soot, and sulfur. By installing a desulfurization device 85 or the like for removing oxides, the exhaust gas Ge is rendered harmless and discharged to the outside from a chimney (not shown).

  In the boiler 2, the mixture of the fuel F (pulverized coal) and the conveying air G <b> 1 via the conveying air supply line L <b> 1 and the combustion air G <b> 2 via the combustion air supplying line L <b> 2 are contained in the boiler 2. Combustion is performed by blowing into the combustion chamber through a burner 22 or the like. Usually, the boiler 2 is provided with heat exchangers (not shown) such as a superheater, a reheater, and a economizer for recovering the heat of the exhaust gas Ge, and is circulated through these. Heat exchange is performed between a fluid such as water and the exhaust gas Ge to generate steam. After that, the exhaust gas Ge is discharged to the outside of the boiler system 1 through the chimney through the exhaust gas discharge line Le.

  The air preheater 3 is connected to each of the transfer air supply line L1 and the exhaust gas discharge line Le, and preheats the transfer air G1 flowing through the transfer air supply line L1 by the exhaust gas Ge flowing through the exhaust gas discharge line Le. It is a heat exchanger. The fuel F (coal in the present embodiment) of the boiler 2 has a property that the amount of water contained varies depending on the type (coal type) and rainfall. And when there is much moisture content, the moisture condensation which arises in the middle of conveyance has a possibility that the pulverized coal pipe L1a and the pulverized coal adhering to the inside of the mill device 4 and clogging may occur, and the combustion performance is affected. there is a possibility. Therefore, the air preheater 3 preheats (preheats) the transport air G1 and dries the fuel F with heat from the transport air G1 whose temperature has been increased. In the embodiment shown in FIG. 1, the air preheater 3 is connected to the combustion air supply line L2 in addition to the transfer air supply line L1 and the exhaust gas discharge line Le, so that the air preheater 3 flows relative to the exhaust gas discharge line Le. In particular, the relatively low temperature carrier air G1 and combustion air G2 are preheated simultaneously by the hot exhaust gas Ge.

  The bypass line Lb is a duct for connecting the upstream side and the downstream side of the air preheater 3 in the transfer air supply line L1 and for the transfer air G1 to flow around the air preheater 3, and the air described above. It is the structure for adjusting the temperature of the conveyance air G1 with the preheater 3. FIG. As described above, the temperature of the carrier air G1 is raised by the air preheater 3, but if the temperature of the carrier air G1 is too high, there is a possibility that ignition will occur due to excessive drying of the fuel F. . Therefore, by providing the bypass line Lb in the transfer air supply line L1, the transfer air G1 (hereinafter, cold air Gb) that is not preheated by the air preheater 3 by passing through the bypass line Lb and the bypass line Lb flows. The flow rate of the transfer air G1 that is preheated by the air preheater 3 by generating the transfer air G1 (hereinafter referred to as hot air Gh) preheated by the air preheater 3 by directly flowing through the transfer air supply line L1. Adjust. And the temperature of the conveyance air G1 is adjusted by making the cold air Gb and the hot air Gh join and mix by said cold air confluence | merging part Ca.

  More specifically, a cold air amount adjusting means 72 (for example, a damper) capable of adjusting the flow rate of the conveying air G1 flowing through the bypass line Lb is provided in the bypass line Lb, and the flow rate of the cold air Gb is adjusted by the cold air amount adjusting means 72. By adjusting, you may adjust the temperature of the conveyance air G1 at the time of being supplied to the mill apparatus 4 (after-mentioned) after the merge after the cold air Gb and the hot air Gh merge. Alternatively, as shown in FIG. 1, together with the cold air amount adjusting means 72, the hot air amount adjusting means 71 (for example, the flow rate of the conveying air G1 and the flow rate of the hot air Gh when being supplied to the mill device 4 can be adjusted. A damper is provided on the upstream side of the mill device 4 in the conveying air supply line L1, and at least one of the opening degrees of the hot air amount adjusting means 71 or the cold air amount adjusting means 72 is adjusted so that the conveying air after merging The temperature of G1 may be adjusted. As a result, the temperature of the conveying air G1 at the inlet side (mill inlet temperature) or the temperature at the outlet side (mill outlet temperature) of the mill device 4 (described later) can be prevented from being abnormal due to moisture condensation or ignition. The temperature of the conveyance air G1 is adjusted so as to be within the range.

  In the embodiment shown in FIG. 1, the hot air amount adjusting means 71 is provided between the cold air merging portion Ca and the air preheater 3 in the conveying air supply line L1, and the inlet of the mill device 4 (described later) or A temperature measuring means 93 (93u, 93d) such as a thermometer is provided at at least one of the outlets, and the above opening degree adjustment is performed based on the measured value (at least one of the mill inlet temperature and the mill outlet temperature) of the temperature measuring means 93. Is called. More specifically, the above-described opening degree adjustment is performed by adjusting the amount of hot air 71 or the amount of cold air with the aim that the cold opening degree determination device 14 described later has a constant measurement value of the temperature measuring means 93. This is done by determining the opening of the means 72.

  The mill device 4 is a device for pulverizing the fuel F supplied to the boiler 2 and is provided in the conveying air supply line L1. The mill apparatus 4 is supplied with coal (fuel F), and the pulverized coal (pulverized powder) pulverized by the mill apparatus 4 is conveyed by the conveying air G1 through the pulverized coal pipe L1a. It is supplied to the boiler 2 (burner 22). The amount of pulverized fuel (fuel F) supplied from the mill device 4 to the boiler 2 is determined according to the output command value of the boiler 2.

  And the boiler system 1 provided with the structure mentioned above controls so that the mill inlet temperature or mill outlet temperature of the conveyance air G1 may be settled in a predetermined temperature range, as mentioned above. For example, since the cold air Gb flowing through the bypass line Lb is not preheated by the air preheater 3, the cold air Gb remains in a low temperature state (for example, normal temperature), and has an effect of cooling the hot air Gh. Therefore, for example, when the moisture content of the fuel F decreases, it is necessary to lower the temperature of the conveying air G1 in order to prevent the fuel F from igniting, and the conveying air can be increased by increasing the flow rate of the cold air Gb. The temperature of the air G1 can be lowered. However, when the flow rate of the cold air Gb is increased by increasing the opening degree of the cold air amount adjusting means 72, the flow rate of the hot air Gh is decreased accordingly. When the flow rate of the hot air Gh is reduced, the heat exchange amount in the air preheater 3 is reduced accordingly, so that the heat recovery amount of the exhaust gas Ge is reduced (increase in heat loss) and the boiler efficiency is deteriorated. I will let you. Further, when the amount of heat recovery is reduced, the temperature of the exhaust gas Ge after passing through the air preheater 3 flows downstream with a correspondingly high temperature. When the design temperature of the downstream equipment (IDF 84, desulfurization device 85, etc.) installed on the downstream side of the air preheater 3 in Le exceeds the design temperature, it is necessary to reduce the load on the boiler 2 and operate the boiler 2 efficiently. It becomes the limitation of the operation control for driving.

  Therefore, the boiler system 1 further includes an exhaust gas recirculation line Lr and an exhaust gas recirculation amount adjusting unit 6 in addition to the above configuration. The exhaust gas recirculation line Lr is branched from between the induction ventilator (IDF 84) installed on the downstream side of the air preheater 3 in the exhaust gas discharge line Le and the desulfurization device 85, and the air in the transport air supply line L1. It is a duct connected between the preheater 3 and the mill device 4 or to the detour line Lb. The exhaust gas recirculation amount adjusting means 6 is a means that is provided in the exhaust gas recirculation line Lr and that can adjust the flow rate of the recirculated exhaust gas Gr that recirculates through the exhaust gas recirculation line Lr. That is, the exhaust gas recirculation line Lr connects between the IDF 84 and the desulfurization device 85 in the exhaust gas discharge line Le and the conveying air supply line L1 or the detour line Lb, and passes through the exhaust gas recirculation line Lr. The flow rate of the exhaust gas Ge (recirculated exhaust gas Gr) introduced (joined) into the transfer air supply line L1 is adjusted by the exhaust gas recirculation amount adjusting means 6.

  Since the pressure of the exhaust gas Ge on the downstream side of the IDF 84 is increased by the IDF 84, the pressure of the recirculated exhaust gas Gr can be increased rather than branching the exhaust gas recirculation line Lr from the upstream side of the IDF 84. Therefore, when the exhaust gas recirculation amount adjusting means 6 includes the GRF 62 described above, the power for pumping the recirculated exhaust gas Gr of the GRF 62 is branched from the upstream side of the IDF 84 to the exhaust gas recirculation line Lr. Even if it is reduced, the recirculated exhaust gas Gr can be appropriately introduced into the carrier air supply line L1.

  Further, as shown in FIG. 1, the exhaust gas recirculation line Lr is branched from between the IDF 84 and the desulfurization device 85 in the transfer air supply line L1, so that the exhaust gas recirculation line Lr is provided from the downstream side of the desulfurization device 85. The high-pressure recirculation exhaust gas Gr can be introduced into the exhaust gas recirculation line Lr as compared with the case of branching. In addition, when the desulfurization apparatus 85 is wet, the exhaust gas Ge having a low water content can be recirculated rather than recirculating the exhaust gas Ge after passing through the wet desulfurization apparatus 85. It becomes possible to prevent deterioration in boiler efficiency due to moisture contained in the exhaust gas Gr.

  More specifically, the exhaust gas recirculation amount adjusting means 6 includes a flow path opening / closing means 61 such as a damper, a manual valve, or an automatic valve. Therefore, if the flow path formed by the exhaust gas recirculation line Lr is closed by closing the exhaust gas recirculation amount adjusting means 6, the recirculated exhaust gas Gr is not introduced into the transfer air supply line L1. To be. Further, if the above-described flow path is opened by opening the exhaust gas recirculation amount adjusting means 6, the recirculation exhaust gas Gr is introduced into the transfer air supply line L1 by a flow rate corresponding to the opening degree. To be done. The closed state of the exhaust gas recirculation amount adjusting means 6 is to minimize the opening degree. For example, when the exhaust gas recirculation amount adjusting means 6 is a damper, the exhaust gas recirculation amount adjusting means 6 is closed even in the closed state. There may be a flow rate passing through the amount adjusting means 6.

  In the embodiment shown in FIG. 1, the exhaust gas recirculation amount adjusting means 6 includes a flow path opening / closing means 61 and a recirculated exhaust gas induction fan (hereinafter referred to as GRF 62) that induces the recirculated exhaust gas Gr. The flow of the recirculated exhaust gas Gr is controlled by the flow path opening / closing means 61, and the flow rate of the recirculated exhaust gas Gr is controlled by the flow path opening / closing means 61 and the GRF 62. Further, the exhaust gas recirculation line Lr is connected between the cold air merging portion Ca and the mill device 4. However, the present invention is not limited to this embodiment. In some other embodiments relating to the exhaust gas recirculation amount adjusting means 6, the exhaust gas recirculation amount adjusting means 6 is composed only of the flow path opening / closing means 61 when the pressure of the recirculated exhaust gas Gr is sufficiently high. Also good. In some other embodiments related to the position where the exhaust gas recirculation line Lr is connected, the exhaust gas recirculation line Lr may be connected between the cold air merging portion Ca and the air preheater 3 or bypassed. It may be connected to the line Lb. In some other embodiments, the above-described embodiments may be combined.

  That is, on the downstream side of the air preheater 3 in the exhaust gas discharge line Le, the temperature of the exhaust gas Ge is lower than the temperature of the transfer air G1 after mixing the hot air Gh and the cold air Gb. For this reason, the recirculated exhaust gas Gr introduced through the exhaust gas recirculation line Lr is merged with the conveying air G1 at the position as described above, so that the recirculated exhaust gas Gr has passed through the cold air confluence portion Ca. It is possible to lower the temperature of the working air G1. In one example, the temperature of the exhaust gas Ge between the IDF 84 and the desulfurization device 85 is around 100 ° C., whereas the temperature of the conveying air G1 after passing through the cold air joining portion Ca is around 300 ° C. By mixing the relatively low temperature recirculated exhaust gas Gr with such a relatively high temperature carrier air G1, the mill inlet temperature of the carrier air G1 can be lowered to around 200 ° C.

  Therefore, when it is necessary to lower the mill inlet temperature or the mill outlet temperature of the conveying air G1, the opening degree of the exhaust gas recirculation amount adjusting means 6 is less than 0, for example, manually or by the recirculation amount control device 12 (described later). If it is opened wide (open state), the recirculated exhaust gas Gr is introduced into the transfer air supply line L1, whereby the mill inlet temperature or the mill outlet temperature of the transfer air G1 can be lowered. Therefore, it is possible to reduce the mill inlet temperature and the mill outlet temperature of the conveying air G1 without increasing the opening of the cold air amount adjusting means 72 and increasing the flow rate of the cold air Gb. Become.

  In addition, even if the recirculated exhaust gas Gr is introduced as described above, the total flow rate of the carrier air G1 and the combustion air G2 exchanged with the exhaust gas Ge in the air preheater 3 does not decrease. Since the flow rate of the transfer air G1 supplied to the mill device 4 is increased by the introduction of the recirculation exhaust gas Gr, the transfer air G1 may be reduced by the PAF 81 by the amount of the introduction flow rate of the recirculation exhaust gas Gr. Therefore, the flow rate reduced by the air flows to the combustion air G2, and is subject to heat exchange in the air preheater 3. As described above, a part of the carrier air G1 pressure-fed by the PAF 81 flows separately from the bypass line Lb, so that not all of it passes through the air preheater 3. However, when such conveying air G1 turns to the combustion air G2, all of it passes through the air preheater 3, so that the amount of air exchanged with the exhaust gas Ge in the air preheater 3 increases conversely. Therefore, the amount of heat exchange by the air preheater 3 is not reduced, and a decrease in boiler efficiency can be prevented. Further, since the amount of heat exchange in the air preheater 3 is not lowered, the temperature of the exhaust gas Ge flowing through the above-mentioned subsequent equipment is not increased.

  According to said structure, the boiler system 1 is the waste gas Ge which flows through the exhaust gas discharge line Le after passing the air preheater 3, Comprising: A part (recirculation waste gas Gr) of the waste gas Ge pressurized by IDF84, Under the adjustment by the exhaust gas recirculation amount adjusting means 6, the exhaust gas recirculation line Lr is configured to recirculate downstream of the air preheater 3 in the transfer air supply line L1 or to the detour line Lb. That is, the recirculated exhaust gas Gr is recirculated (joined) to a position where it is supplied to the mill device 4 without passing through the air preheater 3. While the exhaust gas Ge flows downstream of the air preheater 3 in the exhaust gas discharge line Le, the air preheater flows by flowing the carrier air G1 (hot air Gh) preheated in the air preheater 3 and the bypass line Lb. 3, the temperature becomes lower than that of the conveying air G <b> 1 after merging with the conveying air G <b> 1 (cold air Gb) not preheated. Therefore, the temperature of the transported air G1 after joining can be lowered by joining the recirculated exhaust gas Gr having a lower temperature to the transporting air G1 after joining. Therefore, the recirculated exhaust gas Gr can reduce the temperature of the conveying air G1 when it is supplied to the mill device 4 without increasing the flow rate of the cold air Gb, thereby avoiding a decrease in boiler efficiency ( The temperature of the conveying air G1 at the inlet or the outlet of the mill device 4 can be lowered.

  Further, since the pressure of the recirculated exhaust gas Gr is increased by the induction fan (IDF 84), the flow rate of the recirculated exhaust gas Gr can be easily adjusted by the exhaust gas recirculation amount adjusting means 6, and the exhaust gas recirculation can be facilitated. When the circulation amount adjusting means 6 includes a fan that pumps the recirculated exhaust gas Gr, the power of the fan can be reduced by increasing the pressure of the recirculated exhaust gas Gr.

  Further, as described above, in reducing the temperature of the conveying air G1 at the inlet or the outlet of the mill device 4, it is possible to avoid (suppress) a decrease in the amount of air exchanged with the exhaust gas Ge in the air preheater 3. Therefore, it is possible to prevent a situation in which the exhaust gas temperature exceeds the design temperature of the subsequent equipment installed on the downstream side of the air preheater 3 in the exhaust gas discharge line Le. Therefore, it is possible to prevent a situation in which the boiler 2 is operated while reducing the load so as not to exceed the design temperature of the subsequent equipment, and it is possible to efficiently operate the boiler 2. it can.

  In some embodiments, as shown in FIG. 1, the boiler system 1 further includes the above-described cold air amount adjusting means 72 provided in the detour line Lb. The opening degree of the cold air amount adjusting means 72 is adjusted to the closed side when the exhaust gas recirculation amount adjusting means 6 supplies the recirculated exhaust gas Gr to the transfer air supply line L1 via the exhaust gas recirculation line Lr. Is done. That is, when the recirculated exhaust gas Gr is introduced into the conveying air supply line L1, the opening degree of the cold air amount adjusting means 72 is made smaller than that before the recirculated exhaust gas Gr is introduced. Since the temperature of the conveying air G1 when supplied to the mill device 4 by the recirculated exhaust gas Gr can be reduced, the temperature of the conveying air G1 is lowered even if the flow rate of the cold air Gb is decreased by that amount. be able to. Therefore, by reducing the flow rate of the cold air Gb in the above case, the temperature of the conveying air G1 when being supplied to the mill device 4 is lowered by the recirculated exhaust gas Gr, and the exhaust gas Ge and the heat in the air preheater 3 are reduced. The flow rate of the exchanged transfer air G1 can be increased.

  In general, the flow rate of the conveying air G1 supplied to the mill device 4 is determined so that the fuel supply amount to the boiler 2 determined according to the output command value of the boiler 2 can be appropriately conveyed. When the recirculated exhaust gas Gr is supplied to the conveying air supply line L1 via the exhaust gas recirculating line Lr, the flow rate of the conveying air G1 when supplied to the mill device 4 is increased by the amount of the recirculated exhaust gas Gr supplied. . At this time, in order to set the flow rate of the conveying air G1 to the set value, the conveying air G1 is controlled by controlling the hot air amount adjusting means 71 and the primary air blower (PAF81) installed in the conveying air supply line L1. As described above, the combustion air G2 preheated by the air preheater 3 is increased even if the flow rate of the air is decreased. Therefore, since the heat exchange amount in the air preheater 3 can be increased, the boiler efficiency can be further improved.

  According to said structure, while improving boiler efficiency further, the temperature of the waste gas Ge which flows through the back | latter stage installation installed in the downstream of the air preheater 3 in the waste gas discharge line Le can further be reduced. .

  In some embodiments, as shown in FIG. 1, the exhaust gas recirculation line Lr described above is branched from the downstream side of an induction fan (hereinafter referred to as IDF 84) installed in the exhaust gas discharge line Le. Since the pressure of the exhaust gas Ge on the downstream side of the IDF 84 is increased by the IDF 84, the pressure of the recirculated exhaust gas Gr can be increased rather than branching the exhaust gas recirculation line Lr from the upstream side of the IDF 84. Therefore, when the exhaust gas recirculation amount adjusting means 6 includes the GRF 62 described above, the power for pumping the recirculated exhaust gas Gr of the GRF 62 is branched from the upstream side of the IDF 84 to the exhaust gas recirculation line Lr. Even if it is reduced, the recirculated exhaust gas Gr can be appropriately introduced into the carrier air supply line L1.

  In the embodiment shown in FIG. 1, the exhaust gas recirculation line Lr is branched from between the IDF 84 and the desulfurization device 85 in the transfer air supply line L1. Accordingly, it is possible to introduce the high-pressure recirculation exhaust gas Gr into the exhaust gas recirculation line Lr as compared with the case where the exhaust gas recirculation line Lr is branched from the downstream side of the desulfurization device 85. In addition, when the desulfurization apparatus 85 is wet, the exhaust gas Ge having a low water content can be recirculated rather than recirculating the exhaust gas Ge after passing through the wet desulfurization apparatus 85. It is possible to prevent deterioration in boiler efficiency due to moisture contained in the exhaust gas Gr.

  In some other embodiments, the exhaust gas recirculation line Lr may be branched from the downstream side of the desulfurization device 85 in the transfer air supply line L1. In this case, when the desulfurization apparatus 85 is of a dry type, the pressure of the recirculated exhaust gas Gr is reduced while preventing deterioration of boiler efficiency due to moisture contained in the recirculated exhaust gas Gr, as in the embodiment shown in FIG. Higher pressure can be achieved. Even if the desulfurization device 85 is wet, the temperature of the exhaust gas Ge after passing through the wet desulfurization device 85 is lower than that after passing through the dry desulfurization device 85, so that after the recirculation exhaust gas Gr joins The effect of lowering the temperature of the carrier air G1 can be expected. Therefore, in some other embodiments, the exhaust gas recirculation line Lr may be branched from the downstream side of the wet desulfurization device 85 in the transfer air supply line L1.

  According to the above configuration, the exhaust gas Ge boosted by the induction fan (IDF 84) is recirculated in the exhaust gas recirculation line Lr. Thereby, the adjustment of the flow rate of the recirculated exhaust gas Gr by the exhaust gas recirculation amount adjusting means 6 can be facilitated. Further, when the exhaust gas recirculation amount adjusting means 6 includes a fan (GRF 62) for pumping the recirculated exhaust gas Gr, the pressure of the recirculated exhaust gas is increased, so that the power of the fan can be reduced accordingly. it can.

Next, the recirculation amount control device 12 that controls the opening degree of the exhaust gas recirculation amount adjusting means 6 will be described.
In some embodiments, the above-described boiler system 1 further includes a recirculation amount control device 12 that controls the opening degree of the exhaust gas recirculation amount adjusting means 6 (flow path opening / closing means 61). The recirculation amount control device 12 is configured by a computer, and includes a CPU (processor) (not shown) and a memory (storage device) such as a ROM and a RAM. Then, a command for controlling the opening degree of the exhaust gas recirculation amount adjusting means 6 when the CPU operates (data calculation, etc.) according to the instruction of the program (exhaust gas recirculation amount control program) loaded in the main storage device. Is transmitted to the exhaust gas recirculation amount adjusting means 6 to perform the opening degree control. Specifically, it is confirmed whether or not a control execution condition as will be described later is satisfied, and when the control execution condition is satisfied, the exhaust gas is controlled by feedback control so that the measured value of the temperature measuring means 93 becomes a target value. The opening degree of the recirculation amount adjusting means 6 may be controlled.

  In the embodiment shown in FIG. 1, the recirculation amount control device 12 is the same as another program provided in the boiler system 1, for example, executing control of the hot air amount adjusting means 71 and the cold air amount adjusting means 72. However, in some other embodiments, it may be configured to run independently on another computer that is different from the other programs described above. good.

  According to the above configuration, the flow rate of the hot air Gh passing through the exhaust gas recirculation line Lr can be automatically adjusted by controlling the opening degree of the exhaust gas recirculation amount adjusting means 6 by the recirculation amount control device 12. it can.

Further, the opening degree of the exhaust gas recirculation amount adjusting means 6 described above may be adjusted by the recirculation amount control device 12 or manually based on various information (control execution conditions).
For example, in some embodiments, the recirculation amount control device 12 includes the exhaust gas recirculation amount adjusting means 6 based on the moisture content of the fuel F supplied to the mill device 4 (such as the amount of moisture per unit weight). Control the opening. That is, when the moisture content of the fuel F decreases, the mill inlet temperature or the mill outlet temperature of the carrier air G1 is lowered in order to prevent ignition due to excessive drying of the fuel F due to the heat of the carrier air G1. This situation is determined based on the moisture content. Then, when it is necessary to lower the mill inlet temperature or the mill outlet temperature, the recirculated exhaust gas Gr having a temperature lower than that of the hot air Gh is supplied to the conveying air supply line L1 to be conveyed to the mill device 4. In order to lower the temperature of the working air G1, the exhaust gas recirculation amount adjusting means 6 is opened.

  For example, in some embodiments, the exhaust gas recirculation amount adjustment is performed when the amount of decrease from the immediately preceding water content is equal to or greater than a predetermined water content threshold (the amount of water content decreased ≥ the water content threshold). The means 6 may be opened. In some other embodiments, the water content is equal to or less than a predetermined water content threshold that is determined to require the exhaust gas recirculation amount adjusting means 6 to be in an open state (water content ≦ water content threshold). ), The exhaust gas recirculation amount adjusting means 6 may be opened. At this time, the difference is large depending on the difference (difference) between the amount of decrease in the water content of the fuel F and the above-described threshold value for water decrease, or the difference (difference) between the water content and the above-mentioned water amount threshold value. You may make it an opening degree so large. Conversely, when the amount of decrease in the moisture content of the fuel F is less than the above-described threshold value for reducing the moisture content (the amount of decrease in moisture content <the threshold value for reducing moisture content), or the moisture content is less than the above-described threshold value for moisture content. When exceeding (water content> water content threshold), the exhaust gas recirculation amount adjusting means 6 is closed. Note that the moisture content of the fuel F is measured before the fuel F is supplied to the mill device 4 and the thermal material balance around the mill device 4 is calculated from the operation data of the boiler system 1 measured in real time. To get it.

  According to the above configuration, the opening degree of the exhaust gas recirculation amount adjusting means 6 is adjusted based on the moisture content of the fuel F. That is, when the moisture content of the fuel F decreases, the mill inlet temperature or the mill outlet temperature of the conveying air G1 needs to be lowered. Such a situation is determined based on the moisture content of the fuel F. For example, if the exhaust gas recirculation amount adjusting means 6 is opened without increasing the opening degree of the cold air amount adjusting means 72 capable of adjusting the flow rate of the cold air Gb flowing through the bypass line Lb, the air preheater The temperature of the conveying air G <b> 1 when supplied to the mill device 4 can be reduced without reducing the flow rate of the hot air Gh preheated by 3. Therefore, it is possible to prevent a decrease in boiler efficiency and an increase in the temperature of the exhaust gas Ge on the downstream side of the air preheater 3.

  In some other embodiments, as shown in FIG. 1, the boiler system 1 is provided at least one of the hot air amount adjusting means 71, the cold air amount adjusting means 72, and the inlet or outlet of the mill device 4 described above. The installed temperature measuring means 93 and the cold air opening degree determining device 14 for determining the opening degrees of the hot air amount adjusting means 71 and the cold air amount adjusting means 72 based on the temperature detected by the temperature measuring means 93. Prepare. Then, the recirculation amount control device 12 controls the opening degree of the exhaust gas recirculation amount adjusting means 6 based on the determined opening degree that is the opening degree of the cold air amount adjusting means 72 determined by the cold heat opening degree determining device 14. .

  For example, in some embodiments, when the determined opening is equal to or greater than a predetermined opening threshold (determined opening ≧ opening threshold), the opening of the exhaust gas recirculation amount adjusting means 6 is opened. May be. In some other embodiments, when the determined opening degree of the cold air amount adjusting means 72 is larger than a predetermined opening degree change threshold value from the immediately preceding opening degree (opening degree before calculating the determined opening degree) (determined) The opening degree of the exhaust gas recirculation amount adjusting means 6 may be in an open state such that the opening degree—the opening degree immediately before ≧ the opening degree change threshold value). At this time, depending on the difference (difference) between the determined opening and the opening threshold, or the difference (difference) between the determined opening and the opening difference immediately before and the opening change threshold, the larger the difference, the opening May be increased. Conversely, when the determined opening is less than the above opening threshold or the difference between the determined opening and the immediately preceding opening is less than the opening change threshold (determined opening <opening threshold or determined opening− The exhaust gas recirculation amount adjusting means 6 is closed in the immediately preceding opening degree <opening degree change threshold). Thereby, it is possible to avoid the opening degree (determining opening degree) of the cold air amount adjusting means 72 from becoming larger than a predetermined value. The opening degree change threshold may be 0 or more.

  According to the above configuration, the temperature of the conveying air when being supplied to the mill device by the recirculated exhaust gas is reduced while avoiding a large change in the opening degree (decision opening degree) of the cold air amount adjusting means 72. Can be made.

  In some other embodiments, as shown in FIG. 1, the boiler system 1 is located downstream of the connection portion (exhaust gas merging portion Ce) to which the exhaust gas recirculation line Lr in the transfer air supply line L1 is connected. A second oxygen sensor 95 is further provided. The recirculation amount control device 12 controls the opening degree of the exhaust gas recirculation amount adjusting means 6 based on the measurement value of the second oxygen sensor 95. The oxygen concentration contained in the carrier air G1 when supplied to the mill device 4 decreases according to the flow rate of the recirculated exhaust gas Gr (usually several percent), but the flow rate of the recirculated exhaust gas Gr becomes excessive. If the oxygen concentration is too low, combustion in the burner 22 may become unstable. Therefore, in this embodiment, the amount of recirculated exhaust gas Gr introduced is limited so that the oxygen concentration contained in the carrier air G1 when used for combustion in the burner 22 does not decrease too much.

  In the embodiment shown in FIG. 1, the recirculated exhaust gas Gr is introduced in a range where the measured value by the second oxygen sensor 95 is equal to or higher than the lower limit value of the oxygen concentration necessary for stable combustion in the burner 22. I am doing so. Specifically, an oxygen concentration command value that is equal to or greater than the lower limit value is determined, and the oxygen concentration at the inlet of the mill device 4 is controlled to be constant at the command value (mill inlet oxygen concentration constant control). . When the exhaust gas recirculation amount adjusting means 6 is opened or further opened, the second oxygen sensor 95 is checked so that the value does not fall below the lower limit (measurement by the second oxygen sensor 95). Value ≧ lower limit value), the opening degree of the exhaust gas recirculation amount adjusting means 6 may be gradually opened. Alternatively, based on the oxygen concentration contained in the recirculated exhaust gas Gr (exhaust gas Ge) and the oxygen concentration of the carrier air G1 before the introduction of the recirculated exhaust gas Gr, the possible introduction amount of the recirculated exhaust gas Gr is calculated. The flow rate may be adjusted by providing a restriction so that the flow rate of the recirculated exhaust gas Gr flowing through the recirculation line Lr does not exceed the possible introduction amount. In this case, the mill inlet oxygen concentration constant control may be performed so that the oxygen concentration is constant in a state where the opening degree of the exhaust gas recirculation amount adjusting means 6 is fixed (after control). The opening degree of the exhaust gas recirculation amount adjusting means 6 may be controlled in a state where the oxygen concentration constant control is temporarily stopped.

  In the embodiment shown in FIG. 1, the second oxygen sensor 95 is installed between the exhaust gas merging portion Ce and the mill device 4 in the transfer air supply line L1. However, the present invention is not limited to this embodiment. For example, in some other embodiments, the second oxygen sensor 95 includes the pulverized coal pipe L1a and the mill device 4 as long as the oxygen amount necessary for stable combustion in the burner 22 is ensured. Etc. may be installed.

  According to said structure, the flow volume of the recirculation waste gas Gr is adjusted based on the measured value measured by an oxygen sensor. More specifically, the flow rate of the recirculated exhaust gas Gr is controlled in a range that does not fall below the lower limit value of the amount of oxygen necessary for stable combustion in the burner 22. As a result, it is possible to prevent the combustion in the burner 22 from becoming unstable, and it is possible to prevent the combustion from becoming unstable, such as a misfire of the burner 22 due to insufficient oxygen concentration.

  In some other embodiments, as shown in FIG. 1, the boiler system 1 includes a combustion air supply line L <b> 2 described above, a carrier air G <b> 1 that exchanges heat with the exhaust gas Ge in the air preheater 3, and The total air amount adjusting means (FDF 82 in FIG. 1) capable of adjusting the flow rate of the total air Ga including the combustion air G2, and the exhaust gas flow rate acquiring means 94 for acquiring the flow rate of the exhaust gas Ge discharged from the boiler 2 to the exhaust gas discharge line Le. And further comprising. The flow rate of the total air Ga is adjusted based on the flow rate of the exhaust gas Ge acquired by the exhaust gas flow rate acquisition means 94. In the embodiment shown in FIG. 1, the total air amount adjusting means is the FDF 82, and the total air Ga is composed of the conveying air G1 and the combustion air G2.

  Generally, when the amount of gas flowing through the boiler 2 increases, the steam temperature rises. Therefore, when the recirculated exhaust gas Gr is introduced, the amount of gas flowing through the boiler 2 increases by the flow rate of the recirculated exhaust gas Gr introduced if the amount of air pushed from the FDF 82 does not change, so that the steam temperature increases accordingly. It will be. However, when the steam temperature of the boiler 2 is controlled to be constant (target value) in the boiler system 1, the amount of cooling water sprayed by a spray device (not shown) is increased so that the steam temperature does not rise. For example, the steam temperature is kept constant. That is, the increase in the steam temperature due to the introduction of the recirculated exhaust gas Gr is lowered by moving the other devices correspondingly, so that the boiler efficiency is deteriorated.

  Therefore, in this embodiment, when the flow rate of the exhaust gas Ge acquired by the exhaust gas flow rate acquisition unit 94 increases from a target value (target range) or the like, the amount of pushing in the total air Ga from the total air amount adjustment unit (FDF 82) Is reduced so that the flow rate of the exhaust gas Ge becomes the target value (the flow rate of the exhaust gas Ge = the target value). As a result, the amount of gas in the boiler 2 does not increase, thereby preventing an increase in steam temperature.

  In the embodiment shown in FIG. 1, the exhaust gas flow rate acquisition means 94 is a flow meter capable of measuring the flow rate of the exhaust gas Ge installed upstream of the air preheater 3 in the exhaust gas discharge line Le. However, the invention is not limited to this embodiment. For example, in some other embodiments, the flow rate of the exhaust gas Ge may be acquired by measuring the flow rate of the recirculated exhaust gas Gr and adding it to the flow rate of the exhaust gas Ge before the introduction of the recirculated exhaust gas Gr. .

  According to said structure, the flow volume of the total air Ga which consists of the conveyance air G1 and the combustion air G2 heat-exchanged with waste gas Ge in the air preheater 3 is based on the flow volume of the waste gas Ge discharged | emitted from the boiler 2. Adjusted. Therefore, when the flow rate of the conveying air G1 supplied to the mill device 4 is increased by the flow rate of the recirculated exhaust gas Gr, the total air Ga pushed from the total air amount adjusting means (for example, the FDF 82) by the increased amount. By reducing the flow rate, the steam temperature in the boiler 2 can be controlled to be constant without cooling the steam with a spray device so that the steam temperature in the boiler 2 becomes constant. Further, compared to the case where the amount of gas flowing through the boiler 2 increases by the amount of the recirculated exhaust gas Gr, the total amount of heat of the exhaust gas Ge can be reduced by reducing the flow rate of the exhaust gas Ge. The temperature of the exhaust gas Ge after heat exchange in the air preheater 3 can be lowered, and the amount of heat discarded can be reduced. Therefore, boiler efficiency can be improved.

  In some other embodiments, at least two controls of the above-described embodiment relating to the opening degree control of the exhaust gas recirculation amount adjusting means 6 may be combined. In addition, the above-described moisture reduction threshold, moisture threshold, opening threshold, opening change threshold, steam temperature target value, lower limit of oxygen concentration, and the like are stored in a memory or the like provided in the recirculation amount controller 12. Yes.

  Hereinafter, the operation method of the boiler system 1 provided with the exhaust gas recirculation line Lr and the exhaust gas recirculation amount adjusting means 6 described above will be described with reference to FIGS. FIG. 2 is a flowchart showing an operation method (a control method of the exhaust gas recirculation amount adjusting means 6) of the boiler system 1 including the exhaust gas recirculation line Lr and the exhaust gas recirculation amount adjusting means 6 according to an embodiment of the present invention. is there. FIG. 3 is a flowchart showing an operation method of the boiler system 1 including the exhaust gas recirculation line Lr and the exhaust gas recirculation amount adjusting means 6 according to an embodiment of the present invention. It is a flowchart which adjusts the flow volume of the air Ga. The operation method of the boiler system 1 may be executed by the recirculation amount control device 12 described above or may be executed manually. 2 to 3 are repeatedly executed at a predetermined cycle, for example.

  As shown in FIG. 2, the operation method of the boiler system 1 includes the moisture content of the fuel F supplied to the mill device 4, the opening degree of the cold air amount adjusting means 72 described above, and the downstream side of the exhaust gas merging portion Ce described above. The step of controlling the opening degree of the exhaust gas recirculation amount adjusting means 6 (exhaust gas recirculation amount adjusting step) is provided based on at least one of the measured values of the second oxygen sensor 95 installed in the exhaust gas. More specifically, in the embodiment shown in FIG. 2, whether or not the exhaust gas recirculation amount adjusting step satisfies a control execution condition including at least one condition for executing the open / close control of the exhaust gas recirculation amount adjusting means 6. Monitoring steps (S1 to S2), and control steps (S3 to S4) for controlling the opening degree of the exhaust gas recirculation amount adjusting means 6 when the control execution condition is satisfied. An operation method of the boiler system 1 including these steps will be described in the order of execution of the flow of FIG.

  In steps S1 and S2 of FIG. 2, the above monitoring step is executed. Specifically, in step S1, information necessary for monitoring the control execution condition is acquired. In the embodiment shown in FIG. 2, the control execution conditions include the above-described conditions regarding the moisture content of the fuel F, the determined opening degree of the cold air amount adjusting means 72, and the measured value of the second oxygen sensor 95. In some embodiments, at least one of them may be present. In the embodiment shown in FIG. 1, the moisture content of the fuel F is input after being measured before the fuel F is supplied to the mill device 4. The determined opening degree of the cold air amount adjusting means 72 is acquired from the cold opening degree determining device 14 described above.

  In step S <b> 2, for example, the amount of decrease in the moisture content of the fuel F ≧ the moisture decrease amount threshold, the moisture content ≦ the moisture amount threshold, {the determined opening degree of the cold air amount adjusting unit 72 −the previous cold air amount adjusting unit 72 It is confirmed whether or not any of the conditions defined as the control execution conditions, such as the opening} ≧ the opening change threshold and the determined opening of the cold air amount adjusting means 72 ≧ the opening threshold, is confirmed. Note that the above-described conditions (measured value of the second oxygen sensor 95 ≧ lower limit value) for stabilizing the combustion in the burner 22 are based on the degree of opening when the exhaust gas recirculation amount adjusting means 6 is in the open state. It becomes a condition to decide.

  And control step is performed in following step S3-S4. Specifically, if it is determined in step S2 that the control execution condition is satisfied, the exhaust gas recirculation amount adjusting means 6 is opened in step S3. At this time, if the exhaust gas recirculation amount adjusting means 6 is already open, the open state is maintained. Further, the opening degree of the exhaust gas recirculation amount adjusting means 6 may be made larger or smaller depending on the situation. Conversely, when it is determined in step S2 that the control execution condition is not satisfied, the exhaust gas recirculation amount adjusting means 6 is closed in step S4. At this time, if the exhaust gas recirculation amount adjusting means 6 is already closed, the closed state is maintained.

  According to said structure, it can prevent that a boiler efficiency fall, the temperature rise of the waste gas in the downstream of an air preheater, and the combustion in a burner become unstable.

  In some embodiments, as shown in FIG. 3, the boiler system 1 includes the combustion air supply line L2, the total air amount adjusting means (FDF 82 in FIG. 1), and the exhaust gas flow rate acquiring means 94 described above. 3, the operation method of the boiler system 1 is based on the flow rate of the exhaust gas Ge acquired by the exhaust gas flow rate acquisition means 94, and the total air including the carrier air G1 and the combustion air G2 The method further includes a step of adjusting the flow rate of Ga (total air amount adjusting step).

  In the embodiment shown in FIG. 3, the flow rate of the exhaust gas Ge acquired by the exhaust gas flow rate acquisition means 94 is acquired in step S31. In step S32, when the recirculated exhaust gas Gr is introduced and the flow rate of the exhaust gas Ge is equal to or higher than the target value (maximum value in the target range), the flow rate of the exhaust gas Ge becomes the target value (in the target range). By controlling the FDF 82, the flow rate of the total air Ga is decreased.

  The present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.

DESCRIPTION OF SYMBOLS 1 Boiler system 12 Recirculation amount control apparatus 14 Cooling opening degree determination apparatus 2 Boiler 22 Burner 3 Air preheater 4 Mill apparatus 6 Exhaust gas recirculation amount adjustment means 61 Flow path opening / closing means 62 Recirculation exhaust gas induction fan (GRF)
71 Hot air amount adjusting means 72 Cold air amount adjusting means 81 Primary air blower (PAF)
82 Total air volume adjustment means (FDF: Intrusion blower)
84 Induction fan (IDF)
85 Desulfurizer 91 First oxygen sensor 92 Flow meter 93 Temperature measurement means 94 Exhaust gas flow acquisition means 95 Second oxygen sensor F Fuel G1 Transport air G2 Combustion air Ga Total air Ge Exhaust gas Gb Cold air Gh Hot air Gr Recirculation exhaust gas L1 Transport air supply line L1a Pulverized coal pipe L2 Combustion air supply line Lb Detour line Le Exhaust gas discharge line Lr Exhaust gas recirculation line Ca Cold air confluence (connecting portion between L1 and Lb)
Ce Exhaust gas merging section (connection between L1 and Lr)

Claims (10)

A transfer air supply line for supplying transfer air for transferring fuel to the boiler;
An exhaust gas discharge line for discharging the exhaust gas generated by the combustion of the fuel inside the boiler to the outside;
An air preheater connected to each of the transfer air supply line and the exhaust gas discharge line, for preheating the transfer air flowing through the transfer air supply line with the exhaust gas flowing through the exhaust gas discharge line;
A mill device for pulverizing the fuel to be supplied to the boiler, provided in the air supply line for conveyance;
The air is branched from between the induction ventilator and the desulfurization device installed on the downstream side of the air preheater in the exhaust gas discharge line, and between the air preheater and the mill device in the transfer air supply line. Connected exhaust gas recirculation lines;
A boiler system comprising: an exhaust gas recirculation amount adjusting means provided in the exhaust gas recirculation line, capable of adjusting a flow rate of the recirculated exhaust gas recirculated through the exhaust gas recirculation line. A bypass line for connecting the upstream side and the downstream side of the air preheater in the transfer air supply line, the bypass air for bypassing the air preheater,
The exhaust gas recirculation line is branched from the downstream side of the air preheater in the exhaust gas discharge line, and is connected between the air preheater and the mill device in the transfer air supply line or to the bypass line. The boiler system according to claim 1. A cold air amount adjusting means provided in the detour line, and capable of adjusting a flow rate of the transfer air flowing through the detour line;
The opening degree of the cold air amount adjusting means is adjusted to the closed side when the recirculated exhaust gas is supplied to the transfer air supply line via the exhaust gas recirculation line by the exhaust gas recirculation amount adjusting means. The boiler system according to claim 2.   The boiler system according to any one of claims 1 to 3, further comprising an exhaust gas recirculation amount control device that controls an opening degree of the exhaust gas recirculation amount adjusting means.   The boiler according to claim 4, wherein the exhaust gas recirculation amount control device controls an opening degree of the exhaust gas recirculation amount adjusting means based on a moisture content of the fuel supplied to the mill device. system. The flow rate of hot air preheated by the air preheater provided between the connection portion of the air supply line for conveyance and the bypass line on the downstream side of the air preheater and the air preheater is adjusted. Possible hot air amount adjusting means;
A cold air amount adjusting means provided in the bypass line and capable of adjusting a flow rate of the transfer air flowing through the bypass line;
Temperature measuring means for detecting the temperature of at least one of the outlet temperature or the inlet temperature of the mill device;
A cooling opening degree determining device for determining opening degrees of the hot air amount adjusting means and the cold air amount adjusting means based on the temperature detected by the temperature measuring means;
The exhaust gas recirculation amount control device controls the opening degree of the exhaust gas recirculation amount adjusting means based on a determined opening degree that is an opening degree of the cold air amount adjusting means determined by the cold heat opening degree determining device. The boiler system according to claim 4 or 5, characterized by the above-mentioned. An oxygen sensor installed on the downstream side of a connection portion to which the exhaust gas recirculation line in the transfer air supply line is connected;
The boiler according to any one of claims 4 to 6, wherein the exhaust gas recirculation amount control device controls an opening degree of the exhaust gas recirculation amount adjusting means based on a measurement value of the oxygen sensor. system. A combustion air supply line for supplying combustion air for burning the fuel to the boiler;
A total air amount adjusting means capable of adjusting a flow rate of the total air including the carrier air and the combustion air to be heat-exchanged with the exhaust gas in the air preheater;
An exhaust gas flow rate acquisition means for acquiring the flow rate of the exhaust gas discharged from the boiler to the exhaust gas discharge line,
The boiler system according to claim 1, wherein the flow rate of the total air is adjusted based on the flow rate of the exhaust gas acquired by the exhaust gas flow rate acquisition unit. A transfer air supply line for supplying transfer air for transferring fuel to the boiler;
An exhaust gas discharge line for discharging the exhaust gas generated by the combustion of the fuel inside the boiler to the outside;
An air preheater connected to each of the transfer air supply line and the exhaust gas discharge line, for preheating the transfer air flowing through the transfer air supply line with the exhaust gas flowing through the exhaust gas discharge line;
A bypass line for connecting the upstream side and the downstream side of the air preheater in the transfer air supply line, and for the transfer air to flow around the air preheater;
A mill device for pulverizing the fuel to be supplied to the boiler, provided in the air supply line for conveyance;
Branching between the induction ventilator and the desulfurization device installed downstream of the air preheater in the exhaust gas discharge line, and between the air preheater and the mill device in the transfer air supply line or An exhaust gas recirculation line connected to the bypass line;
An exhaust gas recirculation amount adjusting means provided in the exhaust gas recirculation line and capable of adjusting a flow rate of the recirculated exhaust gas recirculated through the exhaust gas recirculation line;
The moisture content of the fuel supplied to the mill device, the opening of the cold air amount adjusting means capable of adjusting the flow rate of the transfer air flowing through the bypass line, and the exhaust gas recirculation line in the transfer air supply line Operation of a boiler system, comprising a step of controlling the opening degree of the exhaust gas recirculation amount adjusting means based on at least one of measured values of an oxygen sensor installed downstream of a connecting portion to be connected Method. The boiler system includes a combustion air supply line for supplying combustion air for burning the fuel to the boiler;
A total air amount adjusting means capable of adjusting a flow rate of the total air including the carrier air and the combustion air to be heat-exchanged with the exhaust gas in the air preheater;
An exhaust gas flow rate acquisition means for acquiring the flow rate of the exhaust gas discharged from the boiler to the exhaust gas discharge line,
The boiler system operating method according to claim 9, further comprising a step of adjusting the flow rate of the total air based on the flow rate of the exhaust gas acquired by the exhaust gas flow rate acquisition unit.

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