JPH09280503A - Control for steam pressure in boiler steam supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a plant cost optimum and minimize an operating cost by deciding the load ratio of respective boilers every period so that a predictable mixed steam pressure approaches a set value, controlling the quantity of generation of steam of the respective boilers to optimum values, and most suitably controlling the consumption of respective fuel so as to minimize a fuel cost. SOLUTION: A first optimum calculating part 3 calculates the steam pressure of respective boilers so that a future output value predicted based on an evaluation function 1 showing an operation exponent such as a cost function and a restricted condition 1 such as the upper and lower limits of boiler steam pressure comes near to a set value relative to predicted future mixed steam pressure. Then, the steam pressure of the respective boilers is set by an output part 4. Further, a second optimum calculating part 7 calculates the consumption respective fuel so that future boiler steam pressure predicted based on an evaluation function 2 showing an operating exponent such as a cost function and a restricted condition such as the upper and lower limits of the flow rate of fuel comes nearest to a set value relative to predicted future boiler steam pressure. Then, the consumption of respective fuel is determined by an output part 8.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a steam pressure control method for a boiler steam supply system for supplying mixed steam to a steam load in a process of heating a plurality of boilers with a plurality of fuels.

[0002]

2. Description of the Related Art For example, in a steam turbine power plant, as a boiler steam supply system for supplying steam to a steam turbine for driving a generator, a plurality of boilers B1, B2, B3 are provided as shown in FIG. Fuel A, B,
There is one in which the steam is heated at C, the steam generated from each of the boilers B1, B2, B3 is mixed, and the mixed steam is supplied to a steam turbine.

Conventionally, in order to control the boiler steam pressure of such a boiler steam supply system, the operator sets the steam pressure of each boiler B1, B2, B3 empirically, and based on the set value, each boiler B1, The mixed vapor pressure is controlled by appropriately adjusting the vapor pressures of B2 and B3.

As another boiler steam pressure control method, load distribution is automatically determined in consideration of the efficiency of each boiler, and each boiler B1, B2, B3 is determined according to this load distribution.
The mixed vapor pressure is controlled by appropriately adjusting the vapor pressure of.

In this case, even if the steam pressure of any of the above-mentioned boilers is controlled, each boiler B is controlled at a long time interval (several minutes to several hours) as shown in FIG.
The set values of 1, B2 and B3 are changed. On the other hand, the same applies to the fuel distribution in each of the boilers B1, B2, B3, and the present situation is that the control that minimizes the fuel cost is not necessarily performed.

[0006]

As described above, in the conventional boiler steam pressure control system control method, fine control is not performed in the load distribution of each boiler and the fuel distribution in each boiler, so that it is often optimum. Sometimes I got out of the driving point.

The present invention has been made in view of the above circumstances, and it is possible to control the output of each boiler at an optimum ratio at all times.
Another object of the present invention is to provide a steam pressure control method for a boiler steam supply system, which can realize optimization of plant efficiency or minimization of plant operation cost by consuming the fuel of each boiler at an optimum ratio.

[0008]

In order to achieve the above object, the present invention heats each of a plurality of boilers with a plurality of fuels, mixes steam generated from each boiler, and uses this mixed steam as a steam load. In the boiler steam supply system to be supplied, first, when determining the steam generation amount of each boiler, the future movement of the mixed steam pressure is calculated using a mathematical model of the process showing the relationship between the pressure of the mixed steam and each boiler load. Is predicted by the model predictive control, and the first optimum calculation unit that determines the load ratio of each boiler for each control cycle so that the predicted mixed steam pressure approaches the set value always optimizes the steam generation amount of each boiler. In controlling and then determining multiple fuel consumption for each boiler, the boiler steam pressure generalization is calculated using a mathematical model of the process that describes the relationship between each fuel consumption in the past and boiler steam pressure. Is predicted by model predictive control, and the fuel consumption ratio is controlled for each control cycle so that the predicted boiler steam pressure approaches the set value of the load ratio of each boiler determined by the first optimum calculation unit. It is characterized in that the second optimum calculation unit to be determined optimally controls the consumption of each fuel so that the fuel cost is minimized.

Therefore, in such a steam pressure control method for the boiler steam supply system, when determining the steam generation amounts of the plurality of boilers, the load ratio of each boiler of the first optimum calculation section of the model predictive control is determined. By the function to determine the, the steam generation amount of each boiler is always optimally controlled.
By optimally controlling the consumption of each fuel by the function that determines the consumption ratio of each fuel of the optimum calculation unit, the steam pressure is always generated from each boiler at the optimum ratio, and the fuel of each boiler is optimized to the optimum ratio. It is possible to optimize the plant efficiency or minimize the operating cost of the plant by consuming.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram for explaining a control method of a boiler steam pressure control system according to the present invention.

In FIG. 1, reference numeral 1 is a plant data intake section for taking in mixed steam pressures respectively detected in the turbine steam supply system shown in FIG. 5 and steam pressure of each boiler in real time on-line, and 2 is this plant data intake section. For the steam pressure change and mixed steam pressure change of each boiler taken in No. 1, predict the steam pressure of each boiler using a process model that represents the relationship between past steam pressure change and mixed steam pressure change of each boiler It is a first model predicting unit.

Further, 3 is an index for determining the load distribution ratio of each boiler by the evaluation function 1 with respect to the steam pressure of each boiler predicted by the first model predicting unit 2 and the steam pressure determined from the characteristics of each boiler. The first optimum calculation unit 4 which determines the optimum steam pressure of each boiler to satisfy the required mixed steam pressure based on the constraint conditions such as the upper and lower limit values and the limit value of the pressure change rate is the first optimum calculation unit. This is an output unit that sets the steam pressure of each boiler based on the steam pressure determined by the calculation unit 3.

The first model predicting section 2 and the first optimum calculating section 4 constitute a first stage optimizing section. On the other hand, 5 is a plant data importing unit that captures the steam pressure of each boiler and the consumption of each fuel (fuel flow rate) detected in the turbine steam supply system shown in FIG.
6 is a process model showing the relationship between the change in fuel consumption in each boiler and the change in steam pressure in each boiler with respect to the steam pressure and each fuel consumption of each boiler taken in from the plant data import unit 5. It is a 2nd model prediction part which predicts the consumption of each fuel in each boiler using it.

Numeral 7 is an index for determining the consumption distribution ratio of each fuel by the evaluation function 2 with respect to the fuel consumption of each boiler predicted by the second model predicting unit 6 and constraint conditions such as fuel flow rate upper and lower limits. A second optimal calculation unit for determining the consumption amount of each fuel to satisfy the steam pressure of each boiler (set value obtained by the first stage optimization unit) based on This is an output unit that sets the flow rate of each fuel based on the consumption amount of each fuel determined by the chemical calculation unit 7.

The second model predicting section 6 and the second optimum calculating section 7 constitute a second stage optimizing section. Next, the operation of the control function of the boiler steam supply system configured as described above will be described.

First, the operation of the first stage optimization section will be described with reference to FIG. Now, when the steam pressure of the boiler B1, the steam pressure of the boiler B2, the steam pressure of the boiler B3, and the mixed steam pressure shown in FIG. From the steam pressure (input value) of the boiler, the future mixed steam pressure (output value) of the process is predicted by model predictive control using a process model.

With respect to the future mixed steam pressure predicted by the first model predicting unit 2, the first optimum calculating unit 3 evaluates the operating function such as a cost function 2 and constraints such as upper and lower limits of boiler steam pressure. The steam pressure of each boiler is calculated so that the future output value predicted based on the condition 2 comes closest to the set value. Then, the steam pressure of each boiler is set by the output unit 4.

Next, the operation of the second stage optimizing unit will be described with reference to FIG.
This will be described below. After the steam pressure of each boiler is set in the first stage optimization unit, when the steam pressure of each boiler and the consumption amount of each fuel are taken into the plant data import unit 5,
The second model predicting unit 6 predicts the boiler steam pressure (output value) in the future of the process by model predictive control using the process model from the past fuel consumption amounts (input values) for the process.

With respect to the future boiler steam pressure predicted by the second model predicting unit 6, the second optimum calculating unit 7 evaluates the operating function such as the cost function 2 and the constraint conditions such as the upper and lower limits of the fuel flow rate. Based on 2, the consumption amount of each fuel is calculated so that the predicted boiler steam pressure in the future comes closest to the set value (solution of the first stage optimization unit). And the output unit 4
Set the consumption of each fuel by.

In this way, the steam pressure distribution to each boiler is optimized by the first stage optimization unit, and the fuel distribution is made so as to follow the steam pressure set value of each boiler obtained by the second stage optimization unit. Optimal control can realize optimization of plant efficiency and minimization of plant operating cost.

A specific example of the control function of the boiler steam supply system described in the above embodiment will be described with reference to FIG. The control function of the boiler steam supply system shown in FIG. 4 takes in the mixed steam pressure P on-line and displays a process model [G1 G2 G3] that represents the relationship between the change in each steam amount P1, P2, P3 and the mixed steam pressure P. Model predictive control function used 11
And a model predictive control function 12 using a process model showing the relationship between the changes in the fuel consumption amounts FA, FB, FC and the steam pressure changes P1, P2, P3 of the boilers.

The model predictive control function 11 includes an optimum calculation section 1 for optimum distribution (K1, K2, K3) of steam pressure in consideration of output efficiency and capacity of each boiler.
Further, the model predictive control function 12 optimally allocates the consumed fuel in consideration of the cost of each fuel, the calorie burned, etc. based on the value obtained by converting the required fuel calorie from the steam pressure optimally distributed by the model predictive control function 11. And an optimum calculation unit 2 for outputting the optimum calculation result (fuel A flow rate FA, fuel B flow rate FB, fuel C flow rate FC).

In such a control function of the boiler steam supply system, the mixed steam pressure P of the boiler steam supply system shown in FIG.
Control the steam pressure P of each boiler B1, B2, B3
1, P2, P3 are controlled. In this case, the model predictive control function 11 controls the steam pressures P1, P2, P3 of each boiler by the model control using the process model [G1 G2 G3] representing the change of each steam pressure and the change of the mixed steam pressure (1) below. Determined by the formula.

[0024]

[Equation 1]

Then, the optimum calculation section 1 of the model predictive control function 11 determines the optimum output distribution [P1, P2, P3] in consideration of the efficiency of each boiler. Next, the model predictive control function 11 determines the fuel distribution of each boiler so as to realize the steam pressure obtained by the above optimization.

Considering the boiler B1 as an example, when controlling the steam pressure P1, the fuel consumption FA, F of each fuel is controlled.
Control B and FC. In this case, the model predictive control function 1
In 2, the consumption of each fuel A, B, C FA, FB, FC is calculated by the following equation (2) by the model control using the process model [G1 G2 G3] showing the change of each steam pressure and the change of the mixed steam pressure. decide.

[0027]

[Equation 2]

Then, the optimum calculation unit 2 of the model predictive control function 12 determines the optimum fuel consumption distribution [FA FB FC] in consideration of the cost of each fuel, the calories burned and the like.

In this way, stable control of the mixed vapor pressure and operation cost (fuel cost) are minimized by always controlling the output distribution of each boiler and the consumption distribution of each fuel for heating each boiler optimally. You can

In the above embodiment, the steam pressure control of the boiler steam supply system in the case where the steam turbine driving the generator of the steam turbine power plant is subjected to the steam load has been described. The same can be applied to the boiler steam supply system that supplies steam as described above.

[0031]

As described above, according to the present invention, the output of each boiler can be controlled at an optimum ratio at all times, and the fuel efficiency of each boiler can be optimized by consuming the fuel of each boiler at an optimum ratio. A steam pressure control method for a boiler steam supply system that can realize cost minimization can be provided.

[Brief description of drawings]

FIG. 1 is a functional block diagram for explaining an embodiment of a steam pressure control method for a boiler steam supply system according to the present invention.

FIG. 2 is an operation explanatory diagram of a first stage optimizing unit in the embodiment.

FIG. 3 is an operation explanatory view of a second stage optimization unit in the embodiment.

FIG. 4 is a configuration diagram showing a specific example of a control function of a boiler steam supply system of the same embodiment.

FIG. 5 is a diagram showing a configuration example of a boiler steam supply system.

FIG. 6 is an operation curve diagram showing the relationship between boiler output and time according to a conventional steam pressure control method for a boiler steam supply system.

[Explanation of symbols]

 1, 5 ...... Plant data importing unit 2 ...... First model predicting unit 3 ...... First optimum calculating unit 4,8 ...... Output unit 6 ...... Second model predicting unit 7 ...... Second optimum calculating unit

Claims (1)

[Claims] 1. A boiler steam supply system for heating each of a plurality of boilers with a plurality of fuels, mixing steams generated from the respective boilers, and supplying the mixed steam to a steam load. When determining the amount, the future behavior of the mixed steam pressure is predicted by the model predictive control using the mathematical model of the process showing the relationship between the pressure of the mixed steam and each boiler load, and the predicted mixed steam pressure is predicted. , The load ratio of each boiler is determined for each control cycle so that it approaches the set value, the steam generation amount of each boiler is always optimally controlled by the first optimal calculation unit, and then the consumption amount of multiple fuels of each boiler is determined. When doing
The future behavior of the boiler steam pressure is predicted by model predictive control using a mathematical model of the process that represents the relationship between the past fuel consumption and the boiler steam pressure, and the predicted boiler steam pressure is the first The second optimum calculation unit, which determines the fuel consumption ratio for each control cycle so as to approach the load ratio setting value of each boiler determined by the optimum calculation unit, reduces the fuel cost to the minimum. A steam pressure control method for a boiler steam supply system, characterized by optimally controlling consumption.