JPH01212802A - Steam temperature control device for boiler - Google Patents

Abstract

PURPOSE:To stabilize the main steam temperature-rise control upon starting a boiler, by a method wherein the lowest feed water flow rate of the boiler is set at a feed water flow rate, necessary for the protection of a fire furnace, in the once-through operation, while the same flow rate is set at a value higher than the value, necessary for the protection of the fire furnace, upon starting bypass operation. CONSTITUTION:The time constant Tp of steam temperature responsive characteristic with respect to the change of the flow rate of fuel of an once-through boiler becomes larger when the quantity Q of steam is smaller. The boiler is operated upon starting the boiler with the lowest feed water flow rate, conventionally determined from the protection of a fire furnace upon starting, alphaT/H whereby the response property of steam temperature is improved. An 1SH bypass flow rate B and a 2SH bypass flow rate are reduced in the sequence of the supply of steam to a turbine, parallel running and ramping and the flow rate D of steam in the turbine is increased while the starting bypass operation of the boiler is switched to the once-through operation of the same upon the load of 40%. At this switching point, the setting of the lowest feed water flow rate of the boiler may be switched to the flow rate of feed water, which is necessary for the protection of the fire furnace.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has a thermal power of 9! Regarding boiler automatic control equipment at electric power stations,
In particular, the present invention relates to a boiler steam temperature control device suitable for controlling main steam temperature increase during plant startup.

[Conventional technology]

Conventional equipment is thermal and nuclear power generation VOL, 29°NO, 1
P83 of 2 [Improvement of controllability of subcritical pressure once-through boiler]
(2) Specific measures to improve the startup control method in 3 of pages 86-87 to address the phenomenon of the main steam temperature dropping when switching from the startup bypass system to the once-through system, as described in Improvement of the startup control method. As shown in , based on conventional boiler operation results, a method has been adopted in which the S11 pressure reducing valve is opened one hour before the start of ramping.

[Problem to be solved by the invention]

The above conventional technology does not consider the optimum value of the boiler minimum feed water flow rate during start-up bypass operation, has large temperature fluctuations in the main steam temperature increase control process, and requires manual intervention by the operator (fine adjustment of fuel amount). There was a problem that occurred.

An object of the present invention is to stabilize main steam temperature increase control during startup.

[Means to solve the problem]

The purpose of the above is to set the boiler minimum feed water flow rate to a value necessary for furnace protection during once-through operation, and to set the above feed water flow rate + αT/H (10% of the boiler maximum feed water flow rate) during start-up bypass operation. This is achieved by setting.

[Effect]

During start-up bypass operation, the minimum boiler water supply flow rate is set to be αT/H more than the value required for furnace protection. As a result, the amount of heat retained in the boiler increases, so that main steam temperature increase control can be performed stably.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 2, an overview of a once-through boiler power generation plant will be explained. The power generation plant is composed of a boiler main body 3, a high pressure turbine 2, an intermediate pressure turbine 32, and a generator 33, and the boiler automatic control device 202 controls the load (turbine/generator).
A request from, that is.

The turbine control device 203 adjusts the opening degree of the turbine control valve 41 and controls the fuel amount 17 using the fuel flow control valve 16 to maintain the turbine inlet steam at the rated steam pressure and temperature. ) 6 controls the amount of water supplied, and a forced draft fan (hereinafter abbreviated as FDP) 36 controls the amount of air.

Next, to explain the flow of combustion gas, the gas combusted in the furnace (boiler main body) 3 first passes through the furnace wall water pipe (hereinafter abbreviated as WW) 15, the tertiary superheater (hereinafter abbreviated as 3SH) 2
7. Secondary superheater (hereinafter abbreviated as 2SH) 25, Reheater (hereinafter abbreviated as RH) 42. Primary superheater (hereinafter abbreviated as ISH)
22, a part passes through an economizer (hereinafter abbreviated as ECO) 14, and a part of it is recycled as gas by a gas recirculation fan (hereinafter abbreviated as GRF) 35 and a gas recirculation fan artificial damper (hereinafter abbreviated as GRF input rotor damper) 35. , by adjusting the amount of gas recirculation and injecting it into the furnace, WW15, 3SH27
, 2SH25, RH42°l5H22, and EC014, and the remaining fuel gas is discharged to the atmosphere from the chimney.

Also, to explain the steam system, the intermediate pressure turbine 32
The exhaust gas is cooled by the condenser 4 to become condensed water, this water is pressurized by the BFP 6, the water supply amount is adjusted by the feed water flow control valve 9, and then passed through the high pressure feed water heater 7 and heated by the EC014. , WW15, it is superheated and becomes saturated steam. This steam is superheated to 15H22゜2SH25, 3SH27, and at the same time, a part of the feed water is pumped through the first stage superheater spray valve (hereinafter ISH).
19. Two-stage superheater spray valve (hereinafter referred to as 2S)
The water is injected into the primary superheater attemperator (hereinafter referred to as ISH attemperator) 23 and the secondary superheater attemperator (hereinafter referred to as ZSH attemperator) 26 through the H spray valve (abbreviated as H spray valve) 21, respectively. By doing so, the steam temperature is adjusted. Steam that has been superheated to the rated steam temperature by the time it passes through 38H27 is sent to the high-pressure turbine 2 via the turbine control valve 41.

The steam that has finished its work in high pressure turbine 2 is transferred to RH42
The RF input rotary damper 34 absorbs gas convection heat commensurate with the adjusted gas recirculation amount, reburns the steam to the rated temperature, and sends it to the intermediate pressure turbine 32.

The steam that has completed its work in the intermediate pressure turbine 32 is sent to the condenser 4, where it is condensed and further passed through the deaerator 5 to be used as boiler feed water.

Next, to explain the startup bypass system unique to once-through boilers, once-through boilers rely only on the cooling effect of the internal fluid of WW 15 to prevent burnout of the furnace wall water tube (WW) 15 against the burned high-temperature gas. In any state from startup to maximum output, the amount of internal fluid needs to flow above a specified value (normally 30% of the water supply flow rate at maximum output). Therefore, when the amount of steam flowing to the turbine is less than this specified value, the difference between the amount of water supplied and the amount of steam flowing to the turbine is flowed to the startup bypass system. In other words, the steam is sent from the port of 15H22 to the flash tank 8 through the ISO bypass valve, and after being depressurized in the flash tank, the steam is sent to the heater low pressure stop valve 2.
2 S H25 through 0.

3 S H27 and main steam piping warming, or sent to the high pressure feed water heater 7 through the high pressure feed water heater steam pressure adjustment valve 13, or sent to the deaerator through the deaerator steam pressure adjustment valve 12. Efforts are being made to recover heat.

The steam that still remains will be removed from the flash tank water level adjustment valve 1.
1 to the condenser 4. As mentioned above, a state in which steam is flowing to the startup bypass system is called "startup bypass operation", and a state in which this is not the case is called "throughflow operation".

FIG. 4 shows the behavior of the main processes during conventional plant start-up, from annexation to main steam temperature rise (hereinafter referred to as ramping).

As is clear from this figure, the main steam temperature controllability during ramping is poor, and it can be seen that there is a limit to relying solely on fuel control for temperature fluctuations.

Here, the temperature characteristics of the once-through boiler will be explained, and the correlation with the present invention will be described.

A simple model of a once-through boiler is shown in Figure 6. The relational expression between these variables is: t Here, Cw: specific heat of the tube wall Kcal/'CH; heat transfer coefficient from the tube wall to the fluid in the tube Kcal/℃HV; specific volume of the fluid in the tube rn'/kg (1) ~ (3) can be summarized as follows. (C is a constant) Equation (4) is transformed into Laplace transform.

Equation (5) is the Laplace transform representation of the −th lag element,
The block diagram is as shown in the block diagram of FIG.

From equations (5) to (7), the time constant Tp of the steam temperature response characteristic to a change in fuel amount in the once-through boiler is:

(i) The smaller the steam amount Q is, the larger it becomes.

(it) The larger the intratubular volume V, the larger it becomes.

(iii) The larger the tube heat capacity Cw, the larger it becomes.

It turns out that.

That is, in the present invention, by utilizing the characteristic shown in the above-mentioned item (i) and operating the boiler with the minimum feed water flow rate at startup set to the minimum feed water flow rate determined from conventional furnace protection + αT/H, the steam temperature can be adjusted. This improves the responsiveness (TP can be reduced).

FIG. 5 shows the behavior of the water supply flow rate and bypass flow rate when the present invention is applied, and will be described below.

First, in Figure 5, A...water supply flow rate, B...IS
H bypass flow rate, C...2SH bypass flow rate, D...
・Indicates turbine ventilation flow rate. That is, during startup bypass operation, the furnace protection water supply flow rate +αT/H is operated as the startup water supply flow rate setting. Then, in the order of turbine ventilation, merging, and ramping, 1.3H bypass flow rate B, 2
The SH bypass flow rate is decreased and the turbine ventilation flow rate is increased, and at a load of 40%, the startup bypass operation is switched to the once-through operation.

At this switching point, the boiler minimum feed water flow rate setting is switched to the furnace protection feed water flow rate. This is because it is necessary to widen the boiler load adjustment range. In addition, in the -carrying once-through operation, the boiler condition is stabilized compared to the time of startup, so there is no problem even if the boiler minimum water supply flow rate is lowered.

FIG. 1 shows a control circuit to which the present invention is applied.

1 indicates the range of the control device.

First, a main steam temperature set value signal determined from the main steam temperature 28 signal and the boiler characteristics (startup temperature rise characteristics) set by the function generator 101 based on the generator output signal 29 is sent to the comparison calculator 102. This deviation signal is calculated by a proportional integrator 103 to create a water-fuel ratio correction signal. Next, the function generator 104 creates a boiler output command (based on the water supply flow rate) signal based on the generator output signal 29, and the adder 105 calculates this signal and the water-fuel ratio correction signal to determine the amount of fuel. A comparison calculator 106 calculates the actual fuel amount signal 17 as a command signal, and a proportional integrator 107 calculates this deviation signal to create an operation signal for the fuel flow control valve 16.

Next, a comparison calculator 115 calculates a main steam pressure set value signal determined by the boiler characteristics (startup pressure boost characteristics) set by the function generator 114 based on the main steam pressure signal 38 and the generator output signal 29. Then, this deviation signal is calculated by a proportional integrator 116 to create an operation signal for the SH pressure reducing valve 24. In addition.

The SH pressure reducing valve 24 becomes fully open when switching from startup bypass operation to once-through operation.

Furthermore, the water supply flow rate control circuit will be explained.

First, the water supply flow rate request value (set value) is determined by the generator output signal 2
9 as a base, a boiler output command (feed water flow rate base) signal is created by the function generator 104, and this signal and the signal set by the signal generator 108 during startup bypass operation are combined by the high value selector 111. Calculate and take the higher signal as the water supply flow rate request value. Similarly, during once-through operation, signal generator 1
The signal set in step 09 and the boiler output command signal of the function generator 104 are calculated by the high value selector 111, and the high signal is set as the water supply flow rate request value. Here, the signal switch 110
selects the A side during start-up bypass operation and selects the B side during once-through operation. Next, the water supply flow rate request value selected by the high value selector 111 and the water supply flow rate signal 10 are compared with the calculation unit 112.
This deviation signal is calculated by the proportional integrator 113 to create an operation signal for the water supply flow rate regulating valve 9.

FIG. 8 shows characteristics of main processes during ramping and load increase when the present invention is applied.

As is clear from this figure, stable steam temperature control is possible during ramping during start-up bypass operation.

FIG. 3 shows a functional explanation flow of the present invention.

First, calculation block 301 determines whether the plant is in once-through operation. If once-through operation is in progress, the process advances to calculation block 302.

In calculation block 302, the minimum water supply flow rate of the boiler is set to the minimum value necessary for protecting the furnace, so that the load adjustment range can be widened.

On the other hand, during start-up bypass operation, the process proceeds to calculation block 303, and the minimum feed water flow rate setting for the boiler is set to a value necessary for furnace protection + αT/H, thereby improving main steam temperature controllability during ramping. It shows the function explanation flow.

〔Effect of the invention〕

According to the present invention, in a boiler of a thermal power plant, steam temperature controllability at startup can be improved, and turbine metal thermal stress and boiler thermal stress can be reduced, so that it is possible to improve intermediate load operation of existing base load plants. It has the effect of improving the start-up characteristics of conversion and new plants.

[Brief explanation of the drawing]

Fig. 1 is a control circuit diagram of one embodiment of the present invention, Fig. 2 is a main body system diagram of a typical once-through boiler, Fig. 3 is a flowchart explaining the functions of the present invention, and Fig. 4 is a control circuit diagram of a typical once-through boiler. FIG. 5 is a diagram showing the behavior of the water supply flow rate when the present invention is applied. FIG. 6 is a diagram showing a simple model of a once-through boiler, FIG. 7 is a block diagram of the once-through boiler, and FIG. 8 is a diagram showing the behavior of main processes when the present invention is applied. 9...Water supply flow control valve, 10...Water supply flow rate, 16...
Fuel flow control valve, 28...Main steam temperature, 202...Boiler automatic control device. Agent Patent Attorney Muscle Ogawa (Ku) (--heartζ

Claims (1)

[Claims] 1. In the boiler of a thermal power plant, in order to control the temperature rise of the main steam at the time of plant startup, it consists of a fuel amount detector, a main steam temperature detector, a feed water flow rate detector, a fuel amount control valve, and a feed water flow rate control valve. 1. A steam temperature control device for a boiler, characterized in that the boiler is provided with a control circuit that switches the setting of a boiler minimum feed water flow rate during start-up bypass operation and once-through operation.