JPH07269801A - Method and apparatus for controlling pressurized fluidized-bed boiler - Google Patents

Abstract

PURPOSE:To set a reheating steam temperature and a fluidized-bed temperature within designing plan values by calculating a predicted value of the steam temperature after a predetermined time is elapsed according to a formula for representing dynamic characteristics of the steam temperature and calculating a bed height set value with the calculated value as one of calculating factors. CONSTITUTION:A calculator calculates a predicted reheating steam temperature calculated value and a predicted bed temperature calculated value according to a formula for representing dynamic characteristics. The calculated predicted steam temperature value after a calculated predetermined time lapse is compared with a repeating steam temperature set value after a predetermined time lapse formed by a predetermined function from a load request by a subtracter, its deviation is guided to a regulator 411b to form an operation signal 412b. This is added with an operation signal decided from a bed height leading signal 310 and a deviation between the reheating steam temperature at present time and the set steam temperature value by an adder to form a bed height set value. The bed height is compared with the bed height set value by a subtracter, its deviation is guided to a regulator 307d to form an operation signal 380d, which is allowed to follow up the steam temperature set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling a fluidized bed height of a pressurized fluidized bed boiler.

[0002]

2. Description of the Related Art FIG. 2 is a water / steam flow chart showing an example of a conventional pressurized fluidized bed boiler. This boiler has a twin bed configuration of a first furnace 101 mainly containing a superheater and a second furnace 102 mainly containing a reheater. Feed water heater (not shown) to pump (not shown)
The water pressurized by is introduced into the second furnace 102 via the primary water wall 201 in the first furnace 101, and in the secondary water wall 202 and the evaporator 203 in the second furnace 102. It becomes steam, and water and steam are separated in the brackish water separator 204 outside the furnace, and the steam is again heated by the primary superheater 205 in the first furnace 101, and then branches to the second furnace 10.
Guided to 2. In the second furnace 102, the branched flows are superheated by the secondary superheater 206a and the secondary superheater 206b, respectively, and after the temperature is reduced by the first-stage spray 207a and the first-stage spray 207b, respectively, the tertiary superheaters 208a and 208a are generated. It is superheated by the next superheater 208b, goes out of the second furnace 102 and merges, and then branches to return to the first furnace 101.

In the first furnace 101, the branched flow is cooled by the second-stage spray 209a and the second-stage spray 209b, respectively, and then the quaternary superheater 210a and the quaternary superheater 21.
0b is overheated, exits the furnace and joins, main steam pipe 211
And reaches the high-pressure turbine 212. High pressure turbine 212
The steam that has worked in the second branch 10 after passing through the emergency reheat spray 213 and the low temperature reheat piping 214,
Guided to 2. In the second furnace 102, the branched flows are superheated by the reheater 215a and the reheater 215b, respectively, go out of the furnace and merge, and pass through the high temperature reheat pipe 216 to the condenser (from the middle and low pressure turbine 217) (not shown). Return to ().

Next, for example, a conventional control technique of the fluidized bed temperature and the reheated steam temperature in the second furnace 102 in such a pressurized fluidized bed boiler will be described. Figure 3
It is a flowchart which shows the control technology of the fluidized bed temperature and reheat steam temperature of the conventional pressurized fluidized bed boiler.

The reheat steam temperature is controlled by the fluidized bed height as follows, and the reheat steam temperature set value 304 composed of the function 303a from the load request 302 is compared by the subtractor 305a. , The deviation 306a of the adjuster 3
07a to produce a feedback signal 308a. From the boiler master 309, a bed height preceding signal 310 composed of a function generator 303b is created, and an adder 311a adds it to a feedback signal 308a to create a bed height set value 312. The floor height 313 and the floor height setting value 312 are subtracted by a subtractor 305.
b, the deviation 306b is guided to the controller 307b, a feedback signal 308b is generated, and the reheated steam temperature 301 follows the reheated steam temperature set value 304 in the bed height 313 by the predetermined bed height control equipment 314. To adjust.

From the bed temperature 315 and the load request 302, the function 3 is obtained.
03c and the set value 316 of the bed temperature are subtracted from the subtracter 305.
Then, the deviation 306c is introduced to the controller 307c, and the operation signal 308c is generated. From the boiler master 309, the fuel flow rate advance signal 3 composed of the function generator 303d
17 is made. The operation signal 308c and the fuel flow rate preceding signal 317 are added by the adder 311b to create the fuel flow rate set value 318 to be guided to the second furnace 102. However, in order to stabilize the bed temperature 315 when the bed height changes, the bed height 313 is set. The operation signal 308d is generated by the controller 307d from the deviation 306b between the bed height setting value 312 and the layer height setting value 312, and this is added by the adder 311b.

[0007]

However, in the pressurized fluidized bed boiler, the fuel is supplied in the form of coal / water paste for the purpose of making the bed temperature in the furnace uniform. for that reason,
The combustion delay in the furnace is larger than that in a normal boiler. That is, when the coal / water paste is supplied to the furnace, the lumped paste is diffused in the fluidized bed of the furnace by the fluidizing air, and the moisture in the paste is evaporated in this diffusion process to form pulverized coal and ignite. Leading to. In the conventional reheat steam temperature and bed temperature control technologies described above, this combustion delay is not taken into consideration.Therefore, when the reheat steam temperature or bed temperature hunts when the load changes and deviates from the initial design plan value. There is. Also, if reheat spraying is activated, it will reduce plant efficiency.

The present invention compensates for the combustion delay peculiar to a pressurized fluidized bed boiler, so that the reheat steam temperature and fluidized bed temperature can be kept within the designed design values even when the load changes rapidly. An object of the present invention is to provide a method and apparatus for controlling a pressurized fluidized bed boiler.

[0009]

The first invention for solving the above-mentioned problems is to provide a reheated steam which is an appropriate value of the reheated steam temperature of the boiler in response to a load request to the pressurized fluidized bed boiler. A step of calculating the temperature set value, based on the calculated reheat steam temperature set value, a step of calculating a bed height set value that is an appropriate value of the fluidized bed height of the boiler, and based on this calculated value In the method for controlling a pressurized fluidized bed boiler having a step of adjusting the fluidized bed height, a predictive value of the reheated steam temperature after a predetermined time has elapsed is calculated by an equation showing the dynamic characteristics of the reheated steam temperature. And a step of calculating the bed height setting value, wherein the calculated predicted value is used as one of the calculation elements.

Further, a step of calculating a reheated steam temperature set value which is an appropriate value of the reheated steam temperature of the boiler according to a load request to the pressurized fluidized bed boiler, and the calculated reheated steam temperature. Based on the set value, a step of calculating a bed height setting value that is an appropriate value of the fluidized bed height of the boiler, a step of adjusting the fluidized bed height based on the calculated value, and depending on the load request. A step of calculating a bed temperature set value which is an appropriate value of the fluidized bed temperature of the boiler, and a fuel flow rate of the boiler based on the calculated bed temperature set value and the calculated bed height set value. In a method for controlling a pressurized fluidized bed boiler having a step of calculating a fuel flow rate set value that is an appropriate value and a step of adjusting the fuel flow rate based on the calculated value, the dynamic characteristics of the reheat steam temperature are According to the formula shown, the reheated steam after a predetermined time And a step of calculating a predicted value of the fluidized bed temperature after a lapse of a predetermined time by a formula showing a characteristic of the fluidized bed temperature, the bed height setting value calculation step, The predicted value of the reheated steam temperature calculated above is one of the calculation elements, and the fuel flow rate set value calculation step is characterized in that the predicted value of the fluidized bed temperature calculated above is one of the calculation elements. A method of controlling a pressure fluidized bed boiler is a second invention.

Depending on the load demand on the pressurized fluidized bed boiler,
A first computing unit that calculates a reheated steam temperature set value that is an appropriate value of the reheated steam temperature of the boiler, and an appropriate fluidized bed height of the boiler based on the calculated reheated steam temperature set value. In the controller of the pressurized fluidized bed boiler, which has a second arithmetic unit for calculating a bed height set value, which is a value, and means for adjusting the fluidized bed height based on the calculated value, the reheat steam temperature A third arithmetic unit for calculating a predicted value of the reheated steam temperature after a predetermined time has passed, by an equation showing the dynamic characteristics of
A third aspect of the present invention is a control device for a pressurized fluidized bed boiler, wherein the second computing unit uses the calculated predicted value as one of the calculation elements.

Depending on the load demand on the pressurized fluidized bed boiler,
A first computing unit that calculates a reheated steam temperature set value that is an appropriate value of the reheated steam temperature of the boiler, and an appropriate fluidized bed height of the boiler based on the calculated reheated steam temperature set value. A second computing unit for calculating a bed height set value, which is a value, a means for adjusting the fluidized bed height based on the calculated value, and an appropriate value of the fluidized bed temperature of the boiler according to the load request. And a fuel flow rate that is an appropriate value of the fuel flow rate of the boiler based on the calculated bed temperature set value and the calculated bed height set value. In a controller of a pressurized fluidized bed boiler having a fourth arithmetic unit for calculating a set value and means for adjusting the fuel flow rate based on the calculated value, an equation showing the dynamic characteristics of the reheat steam temperature. Calculate the predicted value of the reheat steam temperature after a predetermined time by And a sixth calculator that calculates a predicted value of the fluidized bed temperature after a lapse of a predetermined time by an equation indicating the characteristic of the fluidized bed temperature, and the second calculator is the above-mentioned A pressurized fluidized bed, wherein the calculated predicted value of the reheated steam temperature is one of the calculation elements, and the fourth computing unit uses the calculated predicted value of the fluidized bed temperature as one of the calculation elements. A boiler control device is a fourth invention.

[0013]

The predicted value of the reheated steam temperature after the lapse of a predetermined time can be calculated by the equation showing the dynamic characteristics of the reheated steam temperature. Therefore, the predicted value of the reheated steam temperature after a predetermined time has elapsed is calculated, the reheated steam temperature set value is calculated by using the calculated predicted value as one of the calculation elements, and the bed height is adjusted by this ( For example, considering the combustion delay time τ, if the manipulated variable at the present time is held for the time τ, predict the reheat steam temperature after the time τ from the present time, and deviate from the reheat steam temperature set value. The bed height setting value is corrected by the above), and the combustion delay can be compensated to keep the reheat steam temperature within the design plan value even when the load changes rapidly. If the reheat steam temperature can be kept within the design plan value, the reheat spray as an emergency will not work and the efficiency of the pressurized fluidized bed boiler will not be reduced.

When the fuel flow rate is adjusted in order to stabilize the fluidized bed temperature when the bed height changes, the predicted value of the fluidized bed temperature after a lapse of a predetermined time is calculated by an equation showing the characteristics of the fluidized bed temperature. can do. Therefore, the fuel flow rate set value is calculated by using the calculated predicted value of the fluidized bed temperature as one of the calculation elements, and the fuel flow rate is adjusted by this (for example, considering the combustion delay time τ, If the manipulated variable is held for time τ, the fluidized bed temperature after time τ from the present time is predicted, and the fuel flow rate set value is corrected by the deviation from the fuel flow rate set value.), And combustion delay is compensated. Thus, even if the load changes abruptly, the fluidized bed temperature can be kept within the design plan value. If the fluidized bed temperature can be kept within the design plan, NO at the furnace outlet
The x and SOx concentrations can be kept within the designed design values. The reduction of NOx concentration reduces the load on the denitration device,
Ammonia consumption can be reduced.

[0015]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a flow chart of a control device for a pressurized fluidized bed boiler which is an embodiment of the present invention. Members having the same reference numerals as those in FIG.
These are the same members as those in the control device for the conventional pressurized fluidized bed boiler described with reference to FIG.
Further, the pressurized fluidized bed boiler to which the control device of this embodiment is applied is, for example, the pressurized fluidized bed boiler shown in FIG. 2, and the detailed description thereof will be omitted.

A calculator 401 calculates predicted values of the reheat steam temperature and the fluidized bed temperature after the combustion delay time τ of the boiler from the present time. The dynamic characteristics calculation model of the reheat steam temperature and the fluidized bed temperature is as follows and is described by the following equation.

[0017]

[Equation 1]

Where t is time [s] and d / dt is time differential [s to ¹ ], TB (t): fluidized bed temperature [° C] Ts (t): reheated steam temperature [° C] Cs: specific heat of fluidized bed [kcal / kg · ° C.] ρs: density of fluidized bed [kg / m ³ ] x (t): height of fluidized bed [m] VB (x (t)): volume of fluidized bed [m ³ ] Hn : Calorific value of coal [kcal / kg] Gf (t): Burning amount [kg / s] Cg: Specific heat of combustion gas [kcal / kg ° C] α (x (t)): Heat transfer of fluidized bed to water / steam Rate [kcal
/ M ² ° Cs] A (x (t)): Reheater effective heat transfer area [m ² ] ρw: Water / steam density [kg / m ³ ] Vw: Reheater water / steam volume [m ³ ] H (t): Reheater outlet enthalpy [kcal / kg] HSH (t): Reheater inlet enthalpy [kcal / kg] P (t): Pressure [at] J: Unit conversion coefficient [at · m ³ / kcal] and Gf (t) = (1 + τS) to ¹ Gfuel (t) (3) Ts (t) = f (H (t), P (t)) (4) . Here, S: Laplace operator (= d / dt) τ: Combustion delay time in the furnace [s] Gfuel (t): Fuel flow rate [kg / s] f (H, P): From enthalpy H and pressure P This is a function for calculating the temperature [° C]. Further, the bed volume VB (X (t)) is a function determined by the furnace shape that changes with the bed height X (t), and the bed height X
The change in (t) is determined by the following equation.

[0019]

[Equation 2]

Here, GBMin (t): BM input flow rate from the BM tank to the furnace [kg / s] GBMout (t): BM withdrawal flow rate from the furnace to the BM tank [kg / s] CBM: BM in the BM tank Specific heat [kcal / k
g · ° C.] TBM: BM temperature in BM tank [° C.] From the above equations (1) and (2), the manipulated variables for controlling the bed temperature TB (t) are the fuel flow rate Gfuel (t) and the bed height X (t). And
The manipulated variable controlling the reheat steam temperature is the bed height X (t),
Even if the flow rate Gfuel (t) is manipulated at the present time, it has an effect on the bed temperature TB (t + τ) after time τ from the current time. That is, in the equation (1), it is understood that the combustion delay time τ is included in the dynamic characteristic equation of the reheat steam temperature and the bed temperature.

The arithmetic unit 401 calculates the air flow rate Ga (t) at the present time t, the feed water flow rate Gw (t), the fuel flow rate Gfuel (t), 402, the bed height X (t), 313, and the BM according to the above formula. Tank BM temperature TBM, 403, BM input / output flow rate GBM
in (t) and GBMout (t), 404 are held from the current time until after time τ, and the reheat steam temperature Ts (t), 301 and the bed temperature TB (t) 315 at the current time t are held as initial conditions. Give,
Reheat steam temperature prediction calculation value Ts (t +
τ), 405 and the predicted value TB of the layer temperature at time t + τ
(T + τ), 406 is calculated.

A subtractor 409a calculates the reheated steam temperature predicted value 405 calculated at the time t + τ calculated from the calculator 401 and the reheated steam temperature set value 408 at the time t + τ composed of the function 407a from the load request 302. Comparison, deviation 4
10a is led to the adjuster 411a, which produces an operating signal 412a. This is added by the adder 311a to the layer height preceding signal 310.
And an operation signal 308 determined from a deviation 306a between the reheated steam temperature 301 and the reheated steam temperature set value 304 at the current time t.
It is added to a to create a layer height set value 413. The floor height 313 and the floor height set value 413 are compared by the subtractor 305b, and the deviation 30
6b to the controller 307b to generate the operation signal 308b, and the bed height 313 is adjusted by the predetermined bed height control equipment 314 so that the reheated steam temperature 301 follows the reheated steam temperature set value 304.

Further, the predicted value 406 of the bed temperature calculation at the time t + τ calculated by the arithmetic unit 401 and the set value 4 of the bed temperature at the time t + τ composed of the function 407b from the load request 302.
14 is compared by the subtractor 409b, and the deviation 410b is led to the adjuster 411b to generate the operation signal 412b. This is calculated by the adder 311b and the deviation 30 between the fuel flow rate leading signal 317 and the bed temperature 315 at the current time t and the bed temperature set value 316 is set.
6c is added to the operation signal 308b which is determined from 6c to create a fuel flow rate set value 415, and the fuel flow rate is adjusted by a predetermined fuel flow rate adjusting device based on this.

According to the control device of the present embodiment, the reheat steam temperature after time τ from the current time, when the operation amount of the height control facility 314 at the current time is maintained for the time τ, It is possible to predict and correct the bed height setting value by the deviation from the reheat steam temperature setting value. Also, assuming that the manipulated variable of the fuel flow rate at the current time is held for the time τ, the fluidized bed temperature after the time τ from the current time is predicted, and the fuel flow rate set value is calculated by the deviation from the fuel flow rate set value. Can be corrected.

Therefore, the combustion delay of the boiler can be compensated and the reheat steam temperature and the fluidized bed temperature can be kept within the designed values even when the load changes abruptly. If the reheat steam temperature can be kept within the design plan value,
The emergency reheat spray does not work and the efficiency of the pressurized fluidized bed boiler is not reduced. Also, if the fluidized bed temperature can be kept within the design plan value, NO at the furnace outlet
The x and SOx concentrations can be kept within the designed design values. The reduction of NOx concentration reduces the load on the denitration device,
Ammonia consumption can be reduced.

[0026]

According to the present invention described above, the reheat steam temperature and the fluidized bed temperature at a time point later than the present time are predicted, and the bed height set value and the fuel are set so that they follow the respective set values. Since the flow rate setting value is given, the combustion delay peculiar to the pressurized fluidized bed boiler can be compensated, and the reheat steam temperature and the fluidized bed temperature can be kept within the designed values even when the load changes abruptly.

When the reheat steam temperature is within the design plan value, the reheat spray as an emergency does not operate and the efficiency of the boiler is not reduced. When the fluidized bed temperature is within the design plan value, the NNOx and SOx concentrations at the furnace outlet of the boiler can be kept within the design plan value. When the NOx concentration is within the design plan value, the load on the denitration device can be reduced and the amount of ammonia used can be reduced.

[Brief description of drawings]

FIG. 1 is a flow diagram of a control device for a pressurized fluidized bed boiler that is an embodiment of the present invention.

FIG. 2 is a water / steam flow diagram of a conventional pressurized fluidized bed boiler.

FIG. 3 is a flow chart of a control device for a conventional pressurized fluidized bed boiler.

[Explanation of symbols]

 302 Load request 401 Calculator 405 Reheat steam temperature prediction calculation value 406 Bed temperature calculation prediction value 408 Reheat steam temperature setting value 413 Bed height setting value 414 Bed temperature setting value

Claims (4)

[Claims] 1. A step of calculating a reheated steam temperature set value which is an appropriate value of the reheated steam temperature of the boiler according to a load request to the pressurized fluidized bed boiler, and the calculated reheated steam temperature. A pressurized fluidized bed boiler having a step of calculating a bed height setting value that is an appropriate value of a fluidized bed height of the boiler based on a set value, and a step of adjusting the fluidized bed height based on the calculated value. In the control method, a step of calculating a predicted value of the reheated steam temperature after a predetermined time has elapsed by an equation showing the dynamic characteristics of the reheated steam temperature, the bed height set value calculation step is the calculation A method for controlling a pressurized fluidized bed boiler, wherein the predicted value is used as one of the calculation elements. 2. A step of calculating a reheated steam temperature set value which is an appropriate value of the reheated steam temperature of the boiler according to a load request to the pressurized fluidized bed boiler, and the calculated reheated steam temperature. Based on the set value, a step of calculating a bed height setting value that is an appropriate value of the fluidized bed height of the boiler, a step of adjusting the fluidized bed height based on the calculated value, and depending on the load request. A step of calculating a bed temperature set value that is an appropriate value of the fluidized bed temperature of the boiler, and a fuel flow rate of the boiler based on the calculated bed temperature set value and the calculated bed height set value. In the method for controlling a pressurized fluidized bed boiler, which comprises a step of calculating a fuel flow rate set value that is an appropriate value of the above, and a step of adjusting the fuel flow rate based on the calculated value, the dynamic characteristics of the reheat steam temperature. The reheated steam temperature after a predetermined time has passed And a step of calculating a predicted value of the fluidized bed temperature after a lapse of a predetermined time by a formula showing the characteristic of the fluidized bed temperature, wherein the bed height set value calculation step is The calculated reheat steam temperature predicted value is one of the calculation elements, and the fuel flow rate set value calculation step is characterized in that the calculated predicted fluidized bed temperature value is one of the calculation elements. Control method of fluidized bed boiler. 3. A first arithmetic unit for calculating a reheated steam temperature set value which is an appropriate value of the reheated steam temperature of the boiler according to a load request to the pressurized fluidized bed boiler, and the calculated value. A second arithmetic unit for calculating a bed height set value that is an appropriate value of the fluidized bed height of the boiler based on the reheated steam temperature set value;
Based on this calculated value, in the control device of the pressurized fluidized bed boiler having means for adjusting the fluidized bed height, the reheated steam after a lapse of a predetermined time by an equation showing the dynamic characteristics of the reheated steam temperature. A control device for a pressurized fluidized bed boiler, comprising a third calculator for calculating a predicted value of temperature, wherein the second calculator uses the calculated predicted value as one of calculation elements. 4. A first arithmetic unit for calculating a reheated steam temperature set value which is an appropriate value of the reheated steam temperature of the boiler according to a load request to the pressurized fluidized bed boiler, and the calculated value. A second arithmetic unit for calculating a bed height set value that is an appropriate value of the fluidized bed height of the boiler based on the reheated steam temperature set value;
A means for adjusting the fluidized bed height based on the calculated value; and a third computing unit for computing a bed temperature set value which is an appropriate value of the fluidized bed temperature of the boiler in response to the load request. A fourth calculator that calculates a fuel flow rate set value that is an appropriate value of the fuel flow rate of the boiler based on the calculated bed temperature set value and the calculated bed height set value, and based on this calculated value In the controller of the pressurized fluidized bed boiler having means for adjusting the fuel flow rate, the predicted value of the reheated steam temperature after a lapse of a predetermined time is calculated by the equation showing the dynamic characteristics of the reheated steam temperature. And a sixth arithmetic unit for calculating a predicted value of the fluidized bed temperature after a lapse of a predetermined time according to an equation indicating the characteristic of the fluidized bed temperature.
The computing unit of the above makes the calculated predicted value of the reheated steam temperature one of the calculation elements, and the fourth computing unit makes the calculated predicted value of the fluidized bed temperature one of the calculation elements. A control device for a pressurized fluidized bed boiler.