JP2007285553A - Control method of combustion boiler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method of a combustion boiler capable of providing stable combustion without excessively increasing NOx concentration even in output runup and output fall. <P>SOLUTION: In this combustion boiler comprising air supply pipe conduits 11a, 11b, an exhaust gas discharging pipe conduit 19, an exhaust gas recirculation pipe conduit 17 for recirculating a part of exhaust gas to the air supply pipe conduit, a GMF damper 16 disposed on the way of the exhaust gas recirculation pipe conduit for adjusting the amount of recirculation of the exhaust gas, an OFA damper 14 for adjusting the amount of air when a part of the air is injected from the wake of flame, a high-pressure turbine 31 for rotating the generated vapor of high temperature and high pressure, and a reheater 32 for reheating the vapor expanded by the high-pressure turbine 31, an opening of the OFA damper 14 is controlled by performing the correction on the basis of an air flow rate and an opening of the GMF damper 16. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for controlling a combustion boiler, and more particularly to a method for controlling a combustion boiler that suppresses the generation of nitrogen oxides by adjusting the opening of an OFA damper.

  Since exhaust gas discharged from boilers used in thermal power plants and the like contains nitrogen oxides (NOx), NOx using a flue gas denitration facility consisting of a denitration device, ammonia injection device, NOx meter, etc. After removing the exhaust gas, the exhaust gas is released from the chimney to the atmosphere. In addition to the NOx removing means, various combustion methods are employed so that NOx is not generated from the beginning. When burning at high temperatures, a large amount of NOx is generated, and when the combustion temperature is low, the amount of generation is reduced. Therefore, in order to suppress the combustion temperature in the boiler and suppress the generation of NOx, the two-stage combustion method, exhaust gas recirculation method, etc. The combustion method is adopted.

  A two-stage combustion type boiler will be described with reference to FIG. The two-stage combustion boiler is provided with a two-stage combustion air supply pipe 11b for supplying combustion air downstream of the flame in addition to an air supply pipe 11a for supplying combustion air to the vicinity of the burner of the furnace. .

  The two-stage combustion air supply pipe is provided with an OFA (Over Fire Air) damper (also referred to as an over-air port damper or an over-fire port damper) 14 for adjusting the amount of air supplied to the wake of the flame. Generally, the opening degree of the OFA damper 14 is controlled by the opening degree command signal of the OFA damper 14 based on the NOx concentration in the exhaust gas and the amount of air to be supplied.

  Through the two-stage combustion air supply pipe, a part of the combustion air is injected from the wake of the flame, reducing the air ratio around the burner 3 which has a large influence on the generation of NOx, thereby suppressing the generation of NOx, Is recombusted with air injected from the downstream.

  Next, an exhaust gas recirculation boiler will be described with reference to FIG. The exhaust gas recirculation boiler has an exhaust gas recirculation pipe 17 for circulating the exhaust gas into the furnace again, and the exhaust gas recirculation pipe 17 adjusts the amount of the recirculation gas (GMF (Gas Mixing Fan)). A damper 16 is provided.

  The opening of the GMF damper is adjusted mainly to control the reheat steam temperature. When the reheat steam temperature is lowered, the GMF damper is opened and more recirculation gas is supplied into the furnace. Since the exhaust gas has a small amount of oxygen, the oxygen concentration in the combustion air is reduced, and combustion is performed with combustion air with a low oxygen concentration, so there is no localized high temperature range, and the amount of NOx generated is reduced by lowering the flame temperature. can do.

  However, the power generation output of a power plant is not always constant. When the boiler load increases or decreases, the balance between the air and the fuel ratio is lost, the combustion state becomes unstable, and the NOx concentration changes excessively. Even when a feedback control system that corrects the OFA damper opening command signal based on the NOx concentration in the exhaust gas is employed, it is difficult to follow a rapid change in the NOx concentration because a response delay occurs.

  On the other hand, there has been proposed a boiler NOx reduction method that suppresses the rapid increase in the air-fuel ratio even when the output command changes, thereby reducing the NOx concentration (for example, Patent Document 1).

  The technique described in Patent Document 1 is a technique for correcting the opening of the OFA damper from the pressure difference between the pressure of combustion air supplied to the burner and the pressure in the boiler furnace in a two-stage combustion boiler. Nitrogen oxide concentration is reduced by suppressing a sudden rise in the air-fuel ratio of the burner when the output command is changed and fuel supply is started or stopped.

In addition, a boiler that combines a two-stage combustion method and an exhaust gas recirculation method is also in operation in order to further reduce NOx.
JP-A-8-261410

  However, in the case of a boiler that combines a two-stage combustion method and an exhaust gas recirculation method, the OFA damper and the GMF damper are usually controlled separately, and the following problems arise.

  When the load on the boiler rises, the reheat steam temperature tends to rise, and the GMF damper opening degree is in the closing direction. For this reason, as the amount of recirculated gas decreases, there is a problem that the relative air density increases and the NOx concentration rises excessively when the load drops. The generated NOx is removed using a flue gas denitration facility consisting of a denitration device, ammonia injection device, NOx meter, etc., but if the amount of NOx increases rapidly, the burden on the flue gas denitration facility will increase. Has the problem of becoming difficult.

  On the other hand, when the boiler load is lowered, the reheat steam temperature is lowered and the GMF damper is opened. For this reason, as the amount of recirculated gas increases, the air density decreases and the NOx concentration decreases. However, there is a problem that the air density becomes too small and the combustion itself deteriorates.

  Moreover, although the technique described in Patent Document 1 is a technique that can suppress NOx excessively at each load of the boiler in a boiler using a two-stage combustion method, and is effective in reducing the NOx concentration. No mention is made of a boiler that combines a two-stage combustion method and an exhaust gas recirculation method.

  The present invention has been made in view of such circumstances, an air supply pipe, an exhaust gas discharge pipe, an exhaust gas recirculation pipe for recirculating a part of the exhaust gas to the air supply pipe, and an exhaust gas recirculation. A GMF damper that adjusts the recirculation amount of exhaust gas provided in the middle of the pipeline, an OFA damper that adjusts the amount of air injected from the wake of the flame, and the generated high-temperature and high-pressure steam rotate. A combustion boiler that includes a high-pressure turbine and a reheater that reheats the steam expanded in the high-pressure turbine, controls the opening of the OFA damper from the air flow rate, and controls the opening of the GMF damper from the reheat steam temperature. In the control method, the opening of the OFA damper is corrected based on the opening of the GMF damper.

  Further, the present invention is characterized in that when the output of the combustion boiler is increased, the correction based on the GMF damper corrects the OFA damper so as to open more.

  Furthermore, the present invention is characterized in that when the output of the combustion boiler is lowered, the correction based on the GMF damper is performed so as to close the OFA damper.

  In the combustion boiler control method according to the present invention, the OFA damper opening degree suitable for the combustion state in the boiler can be controlled by associating the separately controlled OFA damper and the GMF damper.

  In particular, when the output is increased, excessive NOx generation based on an insufficient amount of recirculated gas can be suppressed with respect to the actual combustion state, and the burden on the denitration device can be reduced. Further, when the output is lowered, deterioration of the combustion state based on the excessive amount of recirculated gas can be avoided with respect to the actual combustion state, and a stable combustion state can be maintained.

  FIG. 1 is a schematic configuration diagram of a combustion boiler that combines a two-stage combustion method and an exhaust gas recirculation method. FIG. 2 is a flowchart showing a method for controlling the opening degree of the OFA damper.

  With reference to FIG. 1, the schematic structure of the combustion boiler which combined the two-stage combustion system and the exhaust gas recirculation system is demonstrated. The boiler is mainly an air supply line that supplies combustion air, an exhaust gas discharge / circulation line that discharges exhaust gas after combustion, and steam that changes its state to water after the steam drives the turbine and is sent to the boiler again It comprises a circulation line, a burner 3 for burning fuel, and a fuel supply line for supplying fuel.

  The air supply line includes an air supply line 11a, a two-stage combustion air supply line 11b, a ventilator 12, and an OFA damper 14. One end of the air supply pipe 11 a is connected to the ventilator 12, and the other end is connected to the vicinity of the burner 3 below the furnace 2. The two-stage combustion air supply pipe 11 b has one end connected to the air supply pipe and the other end connected to the upper portion of the furnace 2. The OFA damper 14 is provided in the middle of the two-stage combustion air supply pipe 11b.

  By the ventilator 12, the combustion air 13 passes through the air supply pipe, is sent to the vicinity of the burner 3, and is combusted together with the fuel 5 injected into the furnace 2 through the fuel supply pipe 4. The opening degree of the OFA damper 14 is normally controlled by detecting the combustion amount of the boiler based on the air flow rate. In order to increase the load on the boiler, it is necessary to increase the supply amount of fuel and air. When the air supply amount is large, the oxygen concentration becomes high and combustion around the burner is improved, but the generation of NOx is also intense. For this reason, in order to reduce the air ratio around the burner 3 that greatly affects the generation of NOx, the OFA damper 14 opens and the combustion air 15b is sent to the upper portion of the furnace 2 to cause incomplete combustion due to excessive fuel. The fuel is completely burned.

  The exhaust gas discharge / circulation line includes an exhaust gas discharge line 19, an exhaust gas recirculation line 17, a GMF damper 16, a recirculation damper 20, a gas mixing damper 10, and a denitration device 6. One end of the exhaust gas discharge pipe 19 is connected to the furnace 2, and the other end is connected to the denitration device 6. One end of the exhaust gas recirculation pipe 17 is connected to the exhaust gas discharge pipe 19, the other end is branched into two branches, one end branched into two branches is connected to the furnace 2, and the other end branched into two branches is supplied with air. It is connected to the pipe line 11a. The exhaust gas recirculation pipeline 17 is provided with a GMF damper 16, a recirculation damper 20, and a gas mixing damper 10.

  The exhaust gas 18 a generated by the combustion is sent to the denitration device 6 through the exhaust gas discharge pipe 19 and then discharged from the chimney (not shown). Part of the exhaust gas is sent again into the furnace 2 through the GMF damper 16 and the recirculation damper 20 provided in the exhaust gas recirculation pipe 17. Further, a part of the exhaust gas sent to the exhaust gas recirculation pipe 17 is sent to the air supply pipe 11a via the GMF damper 16 and the gas mixing damper 10, and mixed with the combustion air 13 to be mixed gas 15a. , 15b and sent again into the furnace 2.

  The GMF damper 16 is normally controlled by the temperature of the reheat steam 43 that drives the low-pressure turbine 33. When the reheat steam temperature decreases due to excessive decrease in the combustion temperature in the furnace 2, the GMF damper 16 opens and more recirculation gas is supplied into the furnace 2. Since the exhaust gas has a small amount of oxygen, the air density in the furnace 2 is reduced, and combustion is performed with combustion air having a low oxygen concentration. For this reason, there is no localized high temperature region, and the amount of NOx generated can be reduced by lowering the flame temperature.

  The steam circulation line mainly includes a high-pressure turbine 31, a reheater 32, a low-pressure turbine 33, a condenser 34, and a feed water pump 35. The high pressure turbine 31 has one end connected to the superheated steam line 22 and the other end connected to the high pressure turbine exhaust steam line 23. The low-pressure turbine 33 has one end connected to the reheat steam line 24 and the other end connected to the low-pressure turbine exhaust steam line 25. The reheater 32 has one end connected to the high pressure turbine exhaust steam line 23 and the other end connected to the low pressure turbine 33. One end of the condenser 34 is connected to the low-pressure turbine exhaust steam line 25, and the other end is connected to the water supply line 26. The water supply pump 35 has one end connected to the water supply pipe 26 and the other end connected to the evaporation pipe 21.

  The superheated steam 41 heated in the evaporation pipe 21 drives the high-pressure turbine 31 and obtains electric power by a generator (not shown) connected to the turbine. The superheated steam 41 that has driven the high-pressure turbine is sent to the reheater 32 through the high-pressure turbine exhaust steam line. The reheat steam 43 heated by the reheater 32 drives the low pressure turbine 33 and is then sent to the condenser 34 as low pressure turbine exhaust steam. The steam sent to the condenser 34 changes its state into water by heat exchange, and is poured into the evaporation pipe through the water supply pump 35.

  Next, a method for controlling the OFA damper 14 implemented in the present invention will be described with reference to FIG.

  A base signal based on the amount of combustion air for controlling the opening degree of the OFA damper 14 is output, and a correction signal based on the opening degree of the GMF damper 16 is output. By opening the opening command signal of the OFA damper 14 from the base signal and the correction signal, the opening of the OFA damper 14 is controlled.

  As described above, the opening degree of the GMF damper 16 is controlled by the temperature of the reheat steam 43 heated by the reheater 32 and discharged.

  When the output of the boiler is increased, the reheat steam temperature is increased, and the opening of the GMF damper 16 is closed. For this reason, the amount of recirculated gas tends to decrease. Therefore, the relative air density in the vicinity of the burner 3 is increased and the combustion state is improved, but the NOx concentration tends to be excessively increased. Therefore, by correcting the OFA damper opening based on the base signal in the opening direction, the relative air density in the vicinity of the burner 3 can be maintained and NOx can be prevented from being excessively generated.

  On the other hand, when the output of the boiler is lowered, the reheat steam temperature is lowered and the GMF damper 16 is opened. For this reason, the amount of recirculated gas tends to increase. Therefore, since the relative air density near the burner 3 becomes small, the NOx concentration decreases. However, the air density becomes too small and the combustion state in the boiler 1 is deteriorated. For this reason, by correcting the opening degree of the OFA damper 14 based on the base signal in the closing direction, it is possible to maintain the relative density near the burner 3 and achieve stable combustion.

It is a figure which shows schematic structure of the combustion boiler which combined the two-stage combustion system and the exhaust gas recirculation system. It is a flowchart which shows the control method of the OFA damper implemented by this invention. It is a figure which shows schematic structure of a two-stage combustion boiler. It is a figure which shows the schematic structure of an exhaust gas recirculation boiler.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Boiler 2 Furnace 3 Burner 4 Fuel supply line 5 Fuel 6 Denitration apparatus 10 Gas mixing damper 11a Combustion air supply line 11b Two-stage combustion air supply line 12 Ventilator 13 Combustion air 14 OFA damper 15a Combustion air Or mixed gas 15b Two-stage combustion air or mixed gas 16 GMF damper 17 Exhaust gas recirculation line 18a Exhaust gas 18b Recirculation gas 19 Exhaust gas discharge line 20 Recirculation damper 21 Evaporation pipe 22 Superheated steam line 24 Reheat steam line 26 Water supply line 31 High pressure turbine 32 Reheater 33 Low pressure turbine 41 Superheated steam 42 High pressure turbine exhaust steam 43 Reheat steam 44 Low pressure turbine exhaust steam 45 Water

Claims (3)

An air supply pipe, an exhaust gas discharge pipe, an exhaust gas recirculation pipe for recirculating a part of the exhaust gas to the air supply pipe, and an exhaust gas recirculation amount provided in the middle of the exhaust gas recirculation pipe A GMF damper that adjusts the pressure, an OFA damper that controls the amount of air that is injected from the wake of the flame, a high-pressure turbine that rotates the generated high-temperature and high-pressure steam, and reheats the steam expanded in the high-pressure turbine A combustion boiler control method for controlling the opening of the OFA damper from the air flow rate and controlling the opening of the GMF damper from the reheat steam temperature.
A combustion boiler control method, comprising: adding a correction based on the opening of the GMF damper to the opening of the OFA damper.   The combustion boiler control method according to claim 1, wherein when the output of the combustion boiler is increased, the correction based on the GMF damper is performed so that the OFA damper is opened more.   The combustion boiler control method according to claim 1, wherein when the output of the combustion boiler is lowered, the correction based on the GMF damper is performed so as to close the OFA damper.

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