JPH0694210A - Vapor temperature controller for boiler - Google Patents

Abstract

PURPOSE:To improve control performance of a fuel flow rate by enhancing a predicting accuracy of an outlet steam temperature of a superheater even by using a furnace physical model parameter which is difficult to be previously set. CONSTITUTION:In order to compensate a delay of a control correcting operation due to steam temperature response delay of a boiler, a predicted value of a steam temperature Ts of an outlet of a secondary superheater in n min to be calculated by sing a predicting model 1 of the superheater with a input steam temperature of the superheater and an outlet steam temperature of the superheater as input values is input to a furnace physical model parameter regulator 3. Optimum parameters F, Fcg, F1 calculated by the regulator 3 are applied to a furnace physical model 2, a furnace outlet gas temperature calculated by the model 2 is input to the model 1 to obtain a predicted value of the Ts in n min. A sum of a signal due to a deviation between the predicted value and a target value obtained from a target temperature setter 4 and a precedent value to be decided from a boiler input command is used as a fuel amount command, and an operation signal of a fuel regulating valve 5 is formed by feeding back a fuel flow rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steam temperature control device for a boiler, and more particularly to a steam temperature control device for a boiler for a thermal power plant having a suitable calculation prediction model.

[0002]

2. Description of the Related Art As a conventional steam temperature control method, a fuel flow rate as a sum of a preceding value determined by predicting a boiler plant profile in advance and a feedback of a deviation between a set value of steam temperature and an actually measured value, The mainstream method is to correct the spray amount. However, high frequency start / stop (DS
S) A control method has been considered in which a physical model of a superheater is incorporated in a control system so as to cope with diversification of operations such as operation, and the value of steam temperature n minutes ahead is predicted (Japanese Patent Laid-Open No. 57- 1
6719).

Further, in a physical model of a superheater, a control method is considered in which the physical temperature of a boiler furnace in which a superheater external gas temperature given as a calculation condition is divided into a burner region and a two-stage combustion region is applied for calculation. (Japanese Patent Application No. 4-8642).

The above-mentioned conventional predictive control method will be described with reference to FIG. The conventional control method uses two-stage combustion air flow rate, fuel flow rate, air flow rate, recirculation gas flow rate, all gas (fuel combustion gas and Sum with circulating gas)
N minutes ahead calculated using the furnace physics model 12 with the input value of the flow rate, and the prediction model 11 of the secondary superheater with the inlet steam temperature of the secondary superheater and the secondary superheater outlet steam temperature as input values The fuel flow rate is corrected in advance based on the predicted value of the steam temperature at the secondary superheater outlet, and the superheater external gas temperature, which is the calculation condition for the secondary superheater prediction model, is calculated from the physical model of the boiler furnace. Is.

A secondary superheater (final superheater) is taken as the superheater to be treated in the physical model, assuming application to the steam temperature control of a constant pressure once-through (UP) boiler. That is, in the prediction model of the secondary superheater, the energy conservation equation for the secondary superheater outlet fluid enthalpy (water / steam enthalpy) Hs and the secondary superheater metal temperature Tm is VRdHs / dt = (Hin-Hs) Fs + Asαs (Tm −Ts) (1) MmCmdTm / dt = −Asαs (Tm−Ts) + Amαm (Tg−Tm) (2) Here, V: Secondary superheater channel volume [m ³ ] R: Secondary superheater fluid specific gravity [kg / m ³ ] Hs: Secondary superheater outlet fluid enthalpy [kcal / k]
g] Hin: Secondary superheater inlet fluid enthalpy [kcal / k
g] Fs: Secondary superheater fluid flow rate [kg / s] As: Secondary superheater fluid side heat transfer area [m ² ] αs: Secondary superheater metal / fluid heat transfer coefficient [kcal / m]
² ℃ s] Ts: Secondary superheater fluid temperature (function of Hs) [℃] Mm: Secondary superheater metal mass [kg] Tm: Secondary superheater metal temperature [℃] Tg: Secondary superheater external gas Temperature [° C] Am: Heat transfer area of the secondary superheater metal side [m ² ] αm: Secondary superheater gas / metal heat transfer coefficient [kcal / m
² ℃ s] Cm: Secondary superheater metal specific heat [kcal / kg ℃] Here, the secondary superheater fluid is the vapor passing through the inside of the secondary superheater pipe, and is the secondary superheater external gas or secondary Superheater gas is combustion gas for heating the secondary superheater.

The secondary superheater external gas temperature Tg is calculated by Tg = F (Ff, Fa, Fgr, Fgas) (3) using the physical model of the furnace described later. However, Ff: fuel flow rate [kg / s] Fa: air flow rate [kg / s] Fgr: recirculation gas flow rate [kg / s] Fgas: total gas flow rate [kg / s], and the secondary superheater external gas In addition to this, the temperature Tg is calculated depending on the enthalpies and specific heats of fuel, air and gas, and also depends on the physical model parameters of the furnace described later.

Next, a method for calculating the secondary superheater external gas temperature Tg will be described. First, a physical model of a furnace in which the furnace is divided into a burner area and a two-stage combustion area will be described. The furnace is divided into a burner region and a two-stage combustion region, and the solution of the heat balance equation in both regions is the combustion gas temperature in the burner region and the two-stage combustion region. That is, the heat balance in the burner region is expressed by the following equation. QBin = QBout + QBtr (4) Here, the heat input QBin to the burner region is the amount of heat QBgen generated in the burner region, the sensible heat of air QBair, the sensible heat of fuel Qfuel, and the sensible heat of the recirculated gas QBgr, in. It is the sum of the quantities. That is, QBin = QBgen + QBair + Qfuel + QBgr, in (5). Of these, the heat generation amount QBgen of the fuel is the combustion rate F
It depends on l.

The heat output QBout from the burner region is sensible heat QBgas of combustion gas, sensible heat QBgr of recirculated gas,
It is the sum of the carry-out amounts of out and unburned sensible heat Qubc. That is, QBout = QBgas + QBgr, out + Qubc (6).

Further, the heat transfer amount QBtr from the flame in the burner region to the water wall in the burner region is the sum of the heat transfer amount QBrad due to radiation and the heat transfer amount QBcv due to heat transfer. That is, QBtr = QBrad + QBcv (7). Of these, the heat transfer amount QBrad due to radiation is determined depending on the product F of the emissivity and the form factor and the flame filling rate Fcg.

Thus, both sides of the heat balance equation in the burner region are functions of the combustion gas temperature TGB in the burner region, and the TGB is calculated by solving this equation. That is, TGB is the heat flow rate Ff, the recirculation gas flow rate Fgr,
It is obtained as a function of the two-stage combustion air flow rate Fa. This function includes, as parameters, the combustion rate F1, the product F of the emissivity and the form factor, and the flame filling rate Fcg, and these parameters are hereinafter referred to as "furnace model parameters".

On the other hand, the heat balance in the two-stage combustion region is expressed by the following equation. QYin = QYout + QYtr (8) Here, the heat input QYin to the two-stage combustion area is the heat quantity QYgen of the unburned portion in the burner area, the sensible heat QBout of the inflow gas from the burner area, and the sensible heat QYair of the two-stage combustion air. And the amount of sensible heat QYgr, in of the recirculated gas brought in. That is, QYin = QYgen + QBout + QYair + QYar, in (9).

The heat output QYout from the two-stage combustion region is the sensible heat QYgas of the combustion gas and the sensible heat QYg of the recirculated gas.
This is the sum of the amount of r and out carried out. That is, QYout = QYgas + QYgr, out (10). Of these, the heat generation amount QYgen is determined depending on the combustion rate F1.

Further, the amount of heat transfer QYtr from the flame in the two-stage combustion region to the water wall in the two-stage combustion region is determined by radiation QYrad and heat transfer Q.
This is the sum of Ycv. That is, QYtr = QYrad + QYcv (11). Of these, the radiation QYrad is determined depending on the product F of the radiation rate and the form factor and the flame filling rate Fcg.

Thus, both sides of the heat balance equation in the two-stage combustion region are functions of the combustion gas temperature TGG in the two-stage combustion region and the combustion gas temperature TGB in the burner region, and the TGB is calculated from the heat balance equation in the burner region. Since it has been calculated, TGY is calculated by solving this equation (11). That is, TGY can be obtained as a function of the fuel flow rate Fl, the air flow rate Fa, the recirculation gas flow rate Fgr, and the total gas flow rate Fgas in the form of the equation (3), but as described above, as a function, the furnace model parameter (emissivity And the product of the form factor F and the flame fill Fcg) are also included. The combustion gas temperature TGY in the two-stage combustion region calculated as described above can be applied as the two-stage superheater external gas temperature Tg.

Since the above equations (1) and (2) are time ordinary differential equations, Tg calculated from Hin (two-stage superheater inlet enthalpy (steam temperature)) and equation (3)
If (2 step superheater external gas temperature) is given, the current Hs
And Tm are integrated as initial conditions, Hs (secondary superheater outlet fluid enthalpy (steam temperature)) and Tm (secondary superheater metal temperature) after n minutes can be calculated and predicted. However, it is assumed that Hin and Tg are constant for n minutes from the present time.

The predicted value of the secondary superheater outlet steam temperature calculated as described above after n minutes and the target temperature setting circuit 13
A feedback signal is created according to the deviation from the target value obtained from (Fig. 3), the sum of this and the preceding value determined from the boiler input command is used as the fuel amount command, and the deviation between the fuel amount command and the fuel flow rate is fed back. By doing so, an operation signal of the fuel control valve 14 is created.

Since the secondary superheater external gas temperature Tg is calculated using such a physical model 12 of the furnace, the secondary superheater outlet steam is set by using this as the calculation condition of the secondary superheater model. The temperature can be calculated and predicted, and the control performance of the fuel flow rate based on the predicted calculation value can be improved.

[0018]

However, when the furnace physics model 12 is applied to calculate the furnace heat transfer and water wall heat absorption, the furnace physics model parameters are determined in advance in order to calculate the radiant heat transfer. There is a need. However, these parameters (combustion rate Fl, emissivity and form factor product F, flame filling rate Fcg) are arbitrary in modeling, and strongly depend on combustion mode, and it is not possible to preset them. It can be difficult.

To solve this, the furnace outlet gas temperature calculated by the furnace physics model 12 as a function of the parameters of the furnace physics model such as the combustion rate Fl, the product F of the emissivity and the form factor, and the flame filling rate Fcg becomes the measured values. The above parameters may be estimated moment by moment so that they match. However, it is often difficult to directly measure the furnace outlet gas temperature. Therefore, an object of the present invention is to improve the accuracy of predicting the superheater outlet steam temperature while improving the fuel flow control performance while using the furnace physical model parameters that are difficult to set in advance.

[0020]

The object of the present invention is achieved by the following constitutions. That is, in the steam temperature control device of the thermal power plant that maintains the secondary superheater outlet steam temperature n minutes ahead at the rated value by the calculation prediction model of the boiler furnace and the secondary superheater, calculation of the boiler furnace and the secondary superheater is performed. It is a steam temperature control device for a boiler that automatically adjusts parameters included in the calculation prediction model to adaptive values according to a deviation between an estimated value of the secondary superheater outlet steam temperature based on the prediction model and an actually measured value thereof. Here, it is desirable to automatically adjust the parameters included in the calculation prediction model to the adaptive values by the steepest descent method. Further, the parameters included in the calculation prediction model may be the combustion rate, the product of the emissivity and the form factor, and the flame filling rate.

[0021]

The present invention compares the calculated predicted value of the secondary superheater outlet steam temperature with the actual measured value, and the secondary superheater external gas temperature, and therefore the furnace physical model parameter, is adjusted so that the calculated predicted value matches the actual measured value. Product F of a certain emissivity and form factor, burning rate F
By adjusting the flame filling rate Fcg and obtaining the predicted value of the secondary superheater outlet steam temperature n minutes ahead based on the adjustment result, it is possible to set a furnace physical model parameter that is difficult to set in advance. While using it, the prediction accuracy of the superheater outlet steam temperature is increased to improve the control performance of the fuel flow rate.

If the automatic adjustment using the actual measured values of the parameters is performed as described above, the furnace physical model parameters are held at the optimum values in any operating condition or in any combustion condition, so that the secondary superheat is maintained. The accuracy of the calculated prediction value n minutes ahead of the steam outlet temperature is also improved, and the control performance of the fuel flow rate based on the predicted calculation value can be improved as compared with the prior art.

[0023]

Embodiment An embodiment of the present invention will be described below with reference to FIG. Further, FIG. 2 is a diagram showing an entire flow of a boiler to which the boiler steam temperature control method according to this embodiment is applied. In FIG. 1, an outline of a control procedure for compensating the delay of the control correction operation due to the steam temperature response delay of the boiler will be described. Predicted value of steam temperature at the outlet of the secondary superheater n minutes ahead calculated using the prediction model 1 of the secondary superheater with the inlet steam temperature of the secondary superheater and the outlet superheater outlet steam temperature as input values Is input to the furnace physical model parameter adjusting unit 3, and the optimum parameters F, Fcg, and F1 calculated there are adopted as parameters to be applied to the furnace physical model 2. Then, the furnace outlet gas temperature calculated by the furnace physical model 2 using the parameters F, Fcg, and F1 is input to the secondary superheater prediction model 1 to obtain a predicted value n minutes ahead of the secondary superheater outlet steam temperature. Ask.

A feedback signal is created in accordance with the deviation between the predicted value of the secondary superheater outlet steam temperature after n minutes calculated as described above and the target value obtained from the target temperature setting circuit 4. The sum of the preceding value determined from the input command is used as the fuel amount command, and the operation signal of the fuel control valve 5 is created by feedback with the fuel flow rate.

The energy conservation equation for the secondary superheater outlet fluid enthalpy Hs and the secondary superheater metal temperature Tm in the physical model of the secondary superheater of this embodiment is expressed by the following equation (1):
As in (2), this can be transformed into a second-order ordinary differential equation with respect to the enthalpy Hs. d ² Hs / dt ² = 1 / VR ((dHin / dt-dHs / dt) Fs + (Hin-Hs) dFs / dt + Asαs (dTm / dt-dTs / dt)) (1) 'where dTm / dt Is expressed by Expression (2), d ² Hs / dt ² = 1 / VR ((dHin / dt-dHs / dt) Fs + (Hin-Hs) dFs / dt + Asαs [(1 / MmCm) {-Asαs ( Tm−Ts) + Amαm (Tg−Tm)} − dTs / dt] (1) ″. Thus, the second-order differential equation of the enthalpy Hs is obtained.

Therefore, the value Ts (t) at the calculation time t of the secondary superheater outlet steam temperature, the value Ts (t-dt) at the previous step t-dt, the secondary superheater inlet fluid enthalpy H
Tin at the inlet steam temperature of the secondary superheater calculated from the value Hin (t) at the calculation time point t of in and the value Hin (t-dt) at the previous step t-dt, respectively, and Tin at t-dt.
(T), Tin (t-dt), secondary superheater metal temperature T
If m (t) is given, the secondary superheater external steam temperature Tg (t), which is the output value of the furnace physical model, is applied to the secondary superheater outlet temperature at the next step t + dt by applying the equation (1) ". The values Ts and cal (t + dt) can be calculated.

From the above, the necessary information for calculating the secondary superheater outlet steam temperature in the next step is the value Ts (t) at the calculation time t of the secondary superheater outlet steam temperature, the previous step t.
The value Ts (t-dt) at -dt, the secondary superheater inlet steam temperature t, Tin (t) at t-dt, Tin (t-d)
t), the secondary superheater metal temperature Tm (t), and the secondary superheater external steam temperature Tg (t). That is, Ts, cal (t + dt) = F (Ts (t), Ts (t-dt), Tin (t), Tm (t), Tg (t)) (12) This secondary superheater outlet steam temperature calculation Values Ts, cal (t +
dt) is because the secondary superheater external gas temperature Tg (t) includes the uncertainty of the product F of the emissivity and the form factor which are the physical model parameters of the furnace, the flame filling rate Fcg, and the burning rate Fl. Measured value of the steam temperature at the outlet of the next superheater Ts (t +
dt) does not always match.

Therefore, the secondary superheater outlet steam temperature Ts (t
+ Dt) and secondary superheater outlet steam temperature calculated value Ts, cal
(T + dt) is input to the furnace physical model parameter adjustment unit, and the following calculation is performed. First, Ts (t + dt) and T
Calculate the error squared ERR with s, cal (t + dt). ERR = (Ts (t + dt) −Ts, cal (t + dt)) ² (13) This ERR is Ts, cal (t + dt) depends on the parameters F, Fcg, and Fl of the furnace physical model 2, It becomes a function, and ERR = ERR (F, Fcg, Fl) (13) ′. To minimize this error square ERR, F, F
The steepest descent method may be applied to determine cg and Fl. That is, F → F + ηdERR / dF (14) -1 Fcg → Fcg + ηdERR / dFcg (14) -2 F1 → F1 + ηdERR / dF1 (14) -3, the parameters F, Fcg, and Fl are sequentially corrected to obtain the ERR. The correction may be completed at the minimum point.
Where η is a negative real number. Optimal parameters Fopt, Fcgopt, F1op calculated by the above calculation
t is adopted as a parameter applied in the furnace physical model 2.

[0029]

As described above, in the present invention, when calculating the secondary superheater external gas temperature, the product F of the emissivity form factor of the superheater physical model, the flame filling rate Fcg,
Parameters that are not necessarily uniquely determined, such as the burning rate F1, are adjusted to their optimum values moment by moment using the online measurement amount. For this reason, the calculated accuracy of the calculated secondary superheater external gas temperature is high, and by applying this to the secondary superheater model, it is possible to calculate and predict the superheater outlet steam temperature with much higher accuracy than the conventional technology. You can
The steam temperature control performance based on the predicted calculation value can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a boiler steam temperature adaptive control method according to an embodiment of the present invention.

FIG. 2 is a diagram showing an entire flow of a boiler to which a boiler steam temperature control method according to an embodiment of the present invention is applied.

FIG. 3 is a diagram showing a conventional boiler steam temperature control method.

[Explanation of symbols]

1, 11 ... Secondary superheater prediction model, 2, 12 ... Reactor physics model, 3 ... Reactor physics model parameter adjusting unit, 4, 1
3 ... Target temperature setting circuit, 5, 14 ... Fuel control valve

Claims (3)

[Claims] 1. A steam temperature control device for a thermal power plant that maintains a steam temperature at a secondary superheater outlet n minutes ahead at a rated value by a calculation prediction model for a boiler furnace and a secondary superheater. Steam of the boiler characterized by automatically adjusting the parameter included in the calculation prediction model to an adaptive value by the deviation between the estimated value of the secondary superheater outlet steam temperature by the calculation prediction model of the reactor and its measured value Temperature control device. 2. The steam temperature control device for a boiler according to claim 1, wherein the automatic adjustment of the parameter included in the calculation prediction model to the adaptive value is performed by the steepest descent method. 3. The steam temperature control device for a boiler according to claim 1, wherein the parameters included in the calculation prediction model are a combustion rate, a product of an emissivity and a form factor, and a flame filling rate.