JP2009156553A - Reheat steam temperature control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To constantly control a temperature of reheat steam with accuracy in a power generating installation such as a thermal power plant. <P>SOLUTION: The power generating installation is equipped with a boiler device 11 with a regulated furnace 12, and superheaters 14, 16 and reheaters 15, 17 arranged in a flue 13 passing combustion exhaust gas of the boiler device. The combustion exhaust gas is recirculated to the furnace by an exhaust gas recirculation duct 24. When controlling the temperature of the reheat steam, first, an opening of a furnace hopper damper 26 is controlled to adjust a recirculation amount of the combustion exhaust gas. If the temperature of the reheat steam drops even when the recirculation amount of the combustion exhaust gas is adjusted, soot blowing is carried out to clean surfaces of the reheaters. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for controlling the steam temperature of a boiler in a thermal power plant, and more particularly to a method for controlling the temperature of reheat steam.

  Generally, in a thermal power plant, a part of combustion exhaust gas generated by combustion of fuel such as oil in a boiler device is passed through an exhaust gas recirculation fan (GRF) and an exhaust gas recirculation amount adjustment damper (furnace hopper damper). Is introduced into the bottom of the furnace specified in the above, and the combustion exhaust gas and fuel are mixed in the furnace. A superheater, reheater, economizer, etc. are arranged in sequence at the outlet side of the furnace, and after the water (condensate) supplied from the condenser is boosted (feed water) with a booster pump, Heat (warm). Thereafter, the feed water passes through the furnace water wall and is given to the superheater, where it becomes superheated steam, which is sent to the high-pressure turbine and works in the high-pressure turbine (drives the high-pressure turbine).

  Steam discharged from the high-pressure turbine is sent to a reheater, reheated by the reheater, sent to an intermediate-pressure turbine, where it works, and further sent to a low-pressure turbine. The generator is driven by the driving of these turbines, and electric power is generated and sent to the transmission line. On the other hand, the combustion exhaust gas is discharged from the chimney through a denitration device, an air preheater, an electrostatic precipitator, and a desulfurization device.

  By the way, particulate matter such as ash contained in the combustion exhaust gas inevitably adheres to the surface of the heat transfer tube of the above-mentioned superheater, reheater, and economizer, so the heat absorption amount Decreases with time. In order to correct such a decrease in heat absorption amount, the boiler device is provided with a soot blower (soot blower), and soot blow periodically removes soot and the like adhering to the surface of the heat transfer tube to reduce the heat absorption performance. I try to prevent it.

When the above-mentioned soot blow is performed, soot and the like on the surface of the heat transfer tube are removed in a short time, the heat absorption amount of the heat transfer tube increases rapidly, and as a result, a phenomenon that the steam temperature rapidly increases may occur. For this reason, the above-mentioned superheater and reheater are arranged in the boiler combustion exhaust gas flow path, and soot blow that removes at least the deposits (such as soot) from the superheater and reheater to the reheater is intermittent. The soot blow to remove deposits on the reheater is performed when the so-called reheat steam temperature control is performed by controlling the flow rate of the combustion exhaust gas to the reheater and superheater by the gas distribution damper. Prior to this, there is a gas distribution damper that reduces the amount of gas passing on the reheater side to reduce the amount of heat absorption (see, for example, Patent Document 1).
JP 2004-264002 A

  By the way, in the conventional reheat steam temperature control, the furnace hopper damper has a lower limit opening for securing the minimum recirculation gas amount and a gas amount in the furnace to limit the upper limit opening to prevent poor combustion and increase in furnace pressure. The degree is set, and in either case, the reheat steam temperature is disturbed. Therefore, the soot blow is intermittently performed to remove the deposits adhering to the reheater, but it is difficult to grasp the change in the opening degree of the furnace hopper damper due to the change in the steam temperature after the soot blow due to the cleaning frequency. In particular, there is a tendency to carry out regular soot blowing.

  In other words, in the conventional reheat steam temperature control, the circulation gas amount is controlled by the furnace hopper damper, and soot blow is periodically performed so as not to reach the upper and lower limits described above.

  Accordingly, an object of the present invention is to provide a reheat temperature control method that can always control the temperature of reheat steam with high accuracy.

  The present invention is driven by a boiler device in which a furnace is defined, a superheater and a reheater disposed in a combustion exhaust gas passage through which the combustion exhaust gas of the boiler device passes, and superheated steam obtained from the superheater. A turbine driven by the reheat steam obtained by reheating the steam obtained after the superheated steam has worked by the reheater, and a generator driven by the driving of the turbine A reheat steam temperature control method used in a system for controlling the temperature of the reheat steam, wherein the power generation system includes a recirculation unit for recirculating the combustion exhaust gas to the furnace, A combustion exhaust gas recirculation amount regulating part for regulating the recirculation amount; and a cleaning means for cleaning the surface of the reheater; and the recirculation amount of the combustion exhaust gas by the combustion exhaust gas recirculation quantity regulating unit. A first step of adjusting and controlling the temperature of the reheat steam, and a control range of the reheat circulation amount in the first step within a range optimal for temperature control. And a second step of cleaning the surface.

  In the reheat steam temperature control method according to the present invention, when the temperature of the reheat steam becomes lower than a predetermined threshold temperature in the first step, the combustion exhaust gas recirculation amount regulating unit controls the combustion exhaust gas to the furnace. The amount of recirculation is increased, and the second step is performed after performing the first step at least once, and when the temperature of the reheat steam again becomes lower than the threshold temperature, the cleaning unit performs the reheat. The surface of the vessel is cleaned.

  The reheat steam temperature control method according to the present invention is a third step in which the recirculation amount of the flue gas is set to a preset recirculation amount by the flue gas recirculation amount regulating unit before the first step. It is characterized by performing. This set recirculation amount is, for example, the recirculation amount when the opening degree of the furnace hopper damper becomes the lower limit opening degree + 10%.

  The reheat steam temperature control method according to the present invention includes a fourth step that is performed after the second step and determines whether or not the temperature of the reheat steam has reached a predetermined temperature. The second step is repeated until the temperature reaches the predetermined temperature, and the predetermined temperature is made substantially equal to the temperature of the reheat steam when the recirculation amount of the combustion exhaust gas is the lower limit recirculation amount. It is characterized by that. The predetermined temperature is, for example, the temperature of the reheat steam when the recirculation amount of the combustion exhaust gas is a set recirculation amount (for example, the recirculation amount corresponding to the opening degree of the furnace hopper damper corresponding to the lower limit opening degree + 10%). The temperature is approximately equal to.

  The reheat steam temperature control method according to the present invention includes a fourth step that is performed after the second step and determines whether or not the temperature of the reheat steam has reached a predetermined temperature. The second step is repeated until the temperature reaches the predetermined temperature.

  The reheat steam temperature control method according to the present invention is characterized in that soot blow is used as the cleaning means.

  In the reheat steam temperature control method according to the present invention, the recirculation unit is connected to the combustion exhaust gas passage downstream of the superheater and the reheater, and the exhaust gas recirculation is performed to recirculate the combustion exhaust gas to the furnace. A duct and an exhaust gas recirculation fan disposed in the exhaust gas recirculation duct, and the combustion exhaust gas recirculation amount regulating unit is disposed between the exhaust gas recirculation fan and the furnace in the exhaust gas recirculation duct. A furnace hopper damper that is disposed and regulates an opening area of the exhaust gas recirculation duct is provided, and the opening degree of the furnace hopper damper is controlled in the first step.

  As described above, according to the present invention, when the recirculation amount of the combustion exhaust gas is adjusted to control the temperature of the reheat steam, even if the recirculation amount of the combustion exhaust gas is adjusted, the recirculation amount of the combustion exhaust gas is adjusted. This prevents the situation where the temperature control of the reheat steam is hindered by the upper and lower limit values, so that the temperature of the reheat steam can always be controlled with high accuracy.

  According to the present invention, when the temperature of the reheat steam becomes lower than a predetermined threshold temperature, the recirculation amount of the combustion exhaust gas to the furnace is increased, and even if the recirculation amount is increased in this way, Since the surface of the reheater is cleaned when the temperature is lower than the threshold temperature, the number of times of cleaning the reheater surface is reduced, and there is an effect that the temperature of the reheat steam can always be controlled to a desired temperature with high accuracy. .

  According to the present invention, the recirculation amount of the combustion exhaust gas is initially set to the preset recirculation amount and the reheat steam temperature control is performed. There is an effect that it can be taken widely.

  According to the present invention, since the surface of the reheater is cleaned until the temperature of the reheat steam reaches a predetermined temperature, the recirculation amount of the combustion exhaust gas is set to the predetermined recirculation amount. If the temperature is set to be approximately equal to the temperature of the reheated steam, the recirculation amount of the combustion exhaust gas can be easily returned to the set recirculation amount.

  Next, an example of the reheat steam temperature control method according to the embodiment of the present invention will be described. Referring to FIG. 1, FIG. 1 is a diagram illustrating a main part of a thermal power plant (thermal power plant) in which a reheat steam temperature control method according to an embodiment of the present invention is used. 12 is defined, and a secondary superheater 14, a first reheater 15, a primary superheater 16, and a second superheater 13 are sequentially provided in a flue (combustion exhaust gas passage) 13 continuous with the furnace 12 toward the downstream side. The reheater 17 and the economizer 18 are disposed. The flue 13 is connected to a chimney 23 via a denitration device 19, an air preheater 20, an electrostatic precipitator 21, and a desulfurization device 22.

  On the other hand, an exhaust gas recirculation duct 24 is connected to the flue 13 between the economizer 18 and the denitration device 19, and the exhaust gas recirculation duct 24 is connected to the bottom of the furnace 12. An exhaust gas recirculation fan (GRF) 25 is disposed in the exhaust gas recirculation duct 24, and a furnace hopper damper (furnace damper) 26 is disposed near the bottom of the furnace 12. The exhaust gas recirculation duct 24 and the GRF 25 constitute a recirculation part, and the furnace hopper damper 26 is a combustion exhaust gas recirculation amount regulation part.

  As shown in the figure, a ventilation duct 27 is connected to the furnace 12 through the air preheater 20, and air is sent to the furnace 12 through the ventilation duct 27 by a forced air blower (FDF) 28. Further, on the downstream side of the air preheater 20, the ventilation duct 27 is connected to the exhaust gas recirculation duct 24 via a bypass duct 29. An exhaust gas recirculation booster fan (GRBF) 30 is disposed in the bypass duct 29, and the bypass duct 29 is connected to the exhaust gas recirculation duct 24 between the GRF 25 and the furnace hopper damper 26.

  The aforementioned economizer 18 is supplied with condensate (water) boosted by a water supply pump (not shown) from the condenser, and the economizer 18 is supplied via a furnace water wall (furnace water cooling wall) 31. It is connected to the primary superheater 16. The primary superheater 16 is connected to the secondary superheater 14, and the secondary superheater 14 is connected to a high-pressure turbine (HP) 32. The second reheater 17 is connected to the high pressure turbine 32, the first reheater 15 is connected to the second reheater 17, and the first reheater 15 is connected to the intermediate pressure turbine (IP ) 33.

  The steam that has passed through the intermediate pressure turbine 33 is given to the low pressure turbine 34, and the steam that has passed through the low pressure turbine 34 is cooled by seawater in the condenser 35 to become condensed water (water) (condensed). Then, water (pure water) is separately supplied to the condenser 35, and the condensate is supplied from the condenser 35 to the aforementioned economizer 18. Further, a generator 36 is connected to the turbine shaft, and the generator 36 is driven by the rotational drive of the turbine shaft to generate power.

  In the above-described thermal power generation system, fuel (for example, crude oil) is supplied from the fuel pipe 37 to the furnace 12, air preheated by the air preheater 20 is supplied from the ventilation duct 27 to the furnace 12, and fuel is supplied to the furnace 12. Burn. The combustion exhaust gas is discharged through the flue 13. At this time, the condensate is superheated by the economizer 18, the primary superheater 16, and the secondary superheater 14 to the high pressure turbine 32 as heated steam. Supplied. That is, the condensate supplied from the condenser 35 is heated by the economizer 18, then passes through the furnace water cooling wall 31, reaches the primary superheater 16, where it is primarily superheated and primary superheated steam. It becomes. The primary superheated steam is sent to the secondary superheater 14 and further heated to be supplied to the high pressure turbine 32 as superheated steam (secondary superheated steam).

  The steam that has passed through the high-pressure turbine 32 is sent to the second reheater 17, where it is reheated and then reheated by the first reheater 15 to be reheated steam as an intermediate pressure turbine. 33. And the steam which passed the intermediate pressure turbine 33 is sent to the low pressure turbine 34, and the generator 36 is driven by the drive of these turbines.

  On the other hand, the combustion exhaust gas that has passed through the economizer 18 is denitrated in the denitration device 19 and then preheats the air that passes through the ventilation duct 27 in the air preheater 20. Then, after dust and the like in the combustion exhaust gas are collected by the electric dust collector 21, desulfurization is performed by the desulfurization device 22 and discharged from the chimney 23.

  Part of the combustion exhaust gas is taken into the exhaust gas recirculation duct 25 by the GRF 25, and sent to the bottom of the furnace 12 while the flow rate is regulated by the furnace hopper damper 26. At this time, the exhaust gas is taken into the combustion air through the bypass duct 29 by the GRBF 30. As described later, the opening degree of the furnace hopper damper 26 is adjusted, that is, the flow rate of the combustion exhaust gas fed to the furnace 12 is regulated, and the reheat steam temperature control is performed.

  By the way, the combustion exhaust gas contains soot such as ash generated as a result of combustion, and this soot is removed by the electric dust collector 21, but is smoked before the electric dust collector 21. When soot adheres to the first and second reheaters 15 and 17 and the like located in the path 13, and the steam tubes (heat transfer tubes) of the first and second reheaters 15 and 17 become dirty, The heat exchange efficiency is reduced, and as a result, the desired reheat steam temperature cannot be obtained. For this reason, the reheat steam temperature control mentioned later is performed.

  Here, with reference to FIG. 2, a control system used in the reheat temperature control method according to the embodiment of the present invention will be described. The temperature of the reheated steam output from the first reheater 15 is measured by temperature measuring means (not shown) such as a temperature measuring sensor, and the temperature of the reheated steam measured by the temperature measuring means is re-measured. It is given to the control device 38 as the heating steam temperature (the temperature of the reheated steam).

  The illustrated control device 38 is, for example, a computer system, and drives and controls a furnace damper motor (for example, a stepping motor) 39 in accordance with the reheated steam temperature as described later, thereby opening the furnace hopper damper 26. (In other words, the opening area of the exhaust gas recirculation duct) is adjusted, and the soot blow group (soot blower: cleaning means) 40 is driven to remove dirt from the first and second reheaters 15 and 17.

  Next, the operation of the control device 38 shown in FIG. 2 will be described with reference to FIG. In a memory (not shown) built in the control device, the lower limit + 10% of the opening degree of the furnace hopper damper 26 is set as a set opening degree (this set opening degree corresponds to the set recirculation amount of the combustion exhaust gas). The control device 38 sets the opening degree of the furnace hopper damper 26 to the set opening degree in the initial state. (Step S1 (third step)).

  When receiving the reheat temperature control start command, the control device 38 starts the reheat temperature control. As described above, the temperature of the reheat steam is given to the control device 38, and it is determined whether or not the temperature of the reheat steam is less than a predetermined threshold temperature (step S2). When the temperature of the reheated steam becomes lower than the threshold temperature, the control device 38 drives and controls the furnace damper motor 39 to increase the opening degree of the furnace hopper damper 26 (increase the opening degree: step S3, step S2 and step S2). S3 is the first step). That is, the recirculation amount of the combustion exhaust gas to the furnace 12 is made larger than the set recirculation amount, and the reheat temperatures of the first and second reheaters 15 and 17 are increased. Then, the control device compares the reheat steam temperature with the threshold value while monitoring the opening degree of the furnace hopper damper 26 (step S4), and even if the opening degree upper limit opening degree of the furnace hopper damper 26 is reached, the reheating is performed. When the steam temperature does not reach the threshold temperature, the soot blow group 40 is activated and the opening degree of the furnace hopper damper 26 is returned to the set opening degree.

  That is, when the reheat steam temperature is lower than the threshold temperature, the control device 38 increases the opening degree of the furnace hopper damper 26 to increase the recirculation amount of the combustion exhaust gas, but the opening degree of the furnace hopper damper 26 is increased. Even if the preset upper limit opening is reached, if the reheat steam temperature is lower than the threshold temperature, the controller 38 causes the heat transfer tube surfaces of the first and second reheaters 15 and 17 to become dirty with soot and the like. It is determined that the heat absorption efficiency is lowered, the soot blow group 40 is driven (step S5), and soot and the like adhering to the first and second reheaters 15 and 17 are removed (steps S4 and S5 are the first) 2 steps).

  Thus, the control device 38 adjusts the recirculation amount of the combustion exhaust gas to control the temperature of the reheat steam to a desired temperature, and the temperature of the reheat steam decreases even if the recirculation amount of the combustion exhaust gas is adjusted. If so, the soot blow is executed. In other words, when the temperature of the reheat steam becomes less than the threshold temperature, the operation of adjusting and controlling the temperature of the reheat steam by opening the opening of the furnace hopper damper 26 is performed at least once. The soot blow is performed only when the temperature of the steam falls below the threshold temperature.

  Although not shown in FIG. 3, after the controller 38 performs the soot blow, the temperature of the reheated steam is a predetermined temperature (this predetermined temperature is, for example, the first and second reheaters 15). In the case where the surfaces of No. 17 and No. 17 are clean, the recirculation amount of the combustion exhaust gas is substantially equal to the temperature of the reheat steam when the recirculation amount is the set recirculation amount, and corresponds to the set opening of the furnace hopper damper 26) When the temperature of the reheat steam is not a predetermined temperature, soot blow is performed again.

  Thereafter, the control device 38 determines whether or not the boiler device 11 is stopped (step S6). If the boiler device 11 is not stopped, the control device 38 returns to step S1.

  In this way, when the temperature of the reheat steam becomes lower than the threshold temperature, the opening degree of the furnace hopper damper 26 is increased. And even if the opening degree of the furnace hopper damper 26 is increased, when the temperature of the reheat steam is lower than the threshold temperature, the surface of the heat transfer tubes of the first and second reheaters 15 and 17 is first cleaned by soot blow. Therefore, there is an effect that the temperature of the reheated steam can be controlled to a desired temperature with high accuracy at all times.

  In the above description, the thermal power generation system using crude oil as the fuel has been described. However, the present invention can be similarly applied to, for example, a thermal power generation system using coal, liquefied natural gas, or liquefied petroleum gas as the fuel.

It is a figure which shows an example of the principal part of the thermal power generation system with which the reheat steam temperature control method by embodiment of this invention is used. It is a block diagram which shows an example of the control system used with the reheat steam temperature control method by embodiment of this invention. 3 is a flowchart for explaining the operation of the control device shown in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Boiler apparatus 12 Furnace 13 Flue 14 Secondary superheater 15 1st reheater 16 1st superheater 17 2nd reheater 18 Carbon-saving device 19 Denitration device 20 Air preheater 21 Electric dust collector 22 Desulfurization Equipment 23 Chimney 24 Exhaust gas recirculation duct 25 Exhaust gas recirculation fan (GRF)
26 Furnace hopper damper (furnace damper)
27 Ventilation duct 28 Pushing ventilator (FDF)
29 Bypass duct 30 Exhaust gas recirculation booster fan (GRBF)
31 Furnace water wall (furnace water wall)
32 High-pressure turbine (HP)
33 Medium pressure turbine (IP)
34 Low pressure turbine (LP)
35 Condenser 36 Generator 37 Fuel Pipe 38 Control Device 39 Furnace Damper Motor 40 Soot Blow Group

Claims (7)

A boiler device in which a furnace is defined, a superheater and a reheater disposed in a flue gas passage through which the flue gas of the boiler device passes, and driven by superheated steam obtained from the superheater, It is used in a power generation system having a turbine driven by reheat steam obtained by reheating steam obtained after superheated steam works by the reheater and a generator driven by driving the turbine. A reheat steam temperature control method for controlling the temperature of the reheat steam,
The power generation system includes a recirculation unit that recirculates the combustion exhaust gas to the furnace, a combustion exhaust gas recirculation amount regulation unit that regulates a recirculation amount of the combustion exhaust gas, and a cleaning unit that cleans the surface of the reheater. And
A first step of controlling a temperature of the reheat steam by adjusting a recirculation amount of the flue gas by the flue gas recirculation amount regulating unit;
In order to perform the control range of the recirculation amount in the first step in an optimum range for temperature control, the reheating includes a second step of cleaning the surface of the reheater by the cleaning means. Steam temperature control method. In the first step, when the temperature of the reheat steam becomes less than a predetermined threshold temperature, the combustion exhaust gas recirculation amount regulating unit increases the recirculation amount of the combustion exhaust gas to the furnace,
The second step is performed after the first step is performed at least once, and the surface of the reheater is cleaned by the cleaning means when the temperature of the reheated steam becomes lower than the threshold temperature again. The reheat steam temperature control method according to claim 1.   The third step of performing the third step of setting the recirculation amount of the combustion exhaust gas to a preset recirculation amount set in advance by the combustion exhaust gas recirculation amount regulating unit before the first step. Reheat steam temperature control method. A fourth step is performed after the second step to determine whether or not the temperature of the reheat steam has reached a predetermined temperature;
Repeating the second step until the temperature of the reheated steam reaches the predetermined temperature,
4. The reheat steam temperature control method according to claim 3, wherein the predetermined temperature is substantially equal to a temperature of the reheat steam when the recirculation amount of the combustion exhaust gas is the lower limit recirculation amount. A fourth step is performed after the second step to determine whether or not the temperature of the reheat steam has reached a predetermined temperature;
The reheat steam temperature control method according to any one of claims 1 to 3, wherein the second step is repeated until the temperature of the reheat steam reaches the predetermined temperature.   The reheat steam temperature control method according to any one of claims 1 to 5, wherein a soot blow is used as the cleaning means. The recirculation unit is connected to the combustion exhaust gas passage downstream of the superheater and the reheater, and is disposed in the exhaust gas recirculation duct that recirculates the combustion exhaust gas to the furnace, and the exhaust gas recirculation duct. An exhaust gas recirculation fan,
The combustion exhaust gas recirculation amount regulating unit is provided between the exhaust gas recirculation fan and the furnace in the exhaust gas recirculation duct, and includes a furnace hopper damper that regulates an opening area of the exhaust gas recirculation duct,
The reheat steam temperature control method according to any one of claims 1 to 6, wherein an opening degree of the furnace hopper damper is controlled in the first step.

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