JPH11325408A - Operation control method of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stable circulation/percolation switching characteristics, even when delay of operation timing or change in boiler state occur. SOLUTION: The control method has a steam separator and a re-circulation system provided with a drain tank, for switching between circulation/percolation modes. Here, a fluid temperature detector which detects fluid temperature 9 at appropriate parts between a furnace waterwall outlet and an inlet for the steam separator, and a pressure detector which detects pressure 10 of the drain tank, are provided, and at the switching of circulation/percolation modes, an overheating degree of the fluid is obtained, based on an deviation 8 between the fluid temperature 9 from the fluid temperature detector and a saturation temperature 6 from the pressure detector, while the flow rate of water-supply to the furnace waterwall is corrected (3) based on the overheating degree.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation control system for a Benson boiler, and more particularly to an operation control system suitable for obtaining stable boiler characteristics at the time of switching between circulation and once-through.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a recirculation system around a Benson boiler. The water supplied from the water supply pump 11 (BFP) is supplied to the economizer 13, the furnace water wall 14, and the ceiling wall 1.
5. It is sent to the steam separator 17 through the evaporator 16 and separated into steam and water. The steam is superheated by the superheater 19 (SH) and sent to the turbine. The water is returned from the steam separator 17 to the drain tank 18, and the recirculation pump 12 (BCP) and the recirculation flow rate are adjusted according to the water level. It is recirculated through valve 21 to the inlet of economizer 13.

In the initial stage of the start-up, since the inlet fluid of the steam separator 17 is a two-phase flow of steam and water, a circulation operation is performed by a recirculation system, but the inlet fluid of the steam separator 17 is entirely steam and water. Cycle / through flow switching load (typically 25% -3
After 0% load), all the fluid becomes vapor and is sent to the superheater 19, so that the flow-through operation is performed.

[0004] The control system in the circulation operation is a steam-water separator 17.
Since the inlet fluid is a two-phase flow of saturated steam and saturated water, the main steam pressure is controlled by the amount of fuel and the main steam temperature is controlled by the superheat (SH) spray in the desuperheater 20, as in the drum boiler. The water supply amount is controlled by the minimum water supply amount constant control (generally 25% to 28% MCR).

In the once-through operation, since the inlet fluid of the steam separator 17 is entirely vaporized, the main steam pressure is controlled by a boiler master (water supply amount and fuel amount) as in the once-through boiler. The main steam temperature is controlled by the water-fuel ratio (fuel amount). The switching from the circulation control to the once-through control is performed under the condition that the recirculation flow control valve 21 is fully closed or the recirculation pump 12 is stopped in order to confirm that all of the inlet fluid of the steam separator 17 has been converted to steam. To switch to the flow-through control mode.

[0006] At the time of switching between circulation and once-through, the amount of heat collected in the furnace increases due to an operation for increasing the fuel amount (main steam pressure control by water-fuel ratio) due to a decrease in main steam pressure accompanying an increase in load (steam flow), and the steam-water separator 17 Fluid becomes superheated steam.
Switching from the circulation control to the once-through control is normally performed at the timing when the fully closed recirculation flow control valve 21 or the stop of the recirculation pump 12 is detected, and the switching to the once-through control is delayed. In this case, even if the fuel amount is increased, the main steam pressure does not recover (the specific volume cannot be increased because the feedwater is all steam). As a result, there is a concern that the metal temperature of the furnace water wall 14 exceeds an allowable value.

In the conventional control, a circuit (see FIG. 3) for correcting (increasing) the amount of supplied water by a program control by a load is provided in order to alleviate the operation of increasing the fuel due to the decrease in the main steam pressure at the time of the circulation / through flow switching. I have. As shown in FIG. 4, the feed water flow rate is determined by a function from the boiler input command 1. The feed water flow rate command shown in FIG. As the other input of the high value selector 3, the high value is selected, and the signal selects the high value of the minimum water supply for furnace protection at the time of starting and the water supply correction amount of the boiler input command. It was done.

At this time, as the water supply correction amount, the boiler input command 1 is appropriately converted by the function generator 2b, and this function-converted signal is converted into a change rate limiter 7 (an input signal to the change rate limiter is In the case of a sudden change, the signal is output through a device that takes into account the delay characteristics of the boiler control system and limits the input signal to not necessarily follow the change.

[0009]

The above-mentioned conventional control includes an operation (such as a timing of extracting steam supplied from a boiler to a turbine and starting extraction to a feed water heater) and a state of a boiler (such as a timing of extracting steam supplied from a boiler to a turbine). Since the water supply is corrected only by the load without considering the fuel properties and the degree of fouling of the furnace, the circulation / through flow switching characteristics are unstable due to a shift in operation timing or a change in the state of the boiler. However, there was a problem that the furnace water wall metal temperature increased due to the fuel increase operation.

An object of the present invention is to solve the above-mentioned problems of the conventional control and to provide a control system capable of obtaining a stable circulation / through flow switching characteristic even when the operation timing is shifted or the boiler state changes. is there.

[0011]

In order to solve the above problems, the present invention mainly employs the following configuration.

[0012] In a boiler operation control system which has a recirculation system provided with a steam separator and a drain tank, and switches between circulation and once-through modes, an appropriate portion from the furnace water wall outlet to the steam-water separator inlet is provided. A fluid temperature detector for detecting a fluid temperature, and a pressure detector for detecting a pressure of the drain tank, wherein when the circulation / flow-through mode is switched, the fluid temperature from the fluid temperature detector and the pressure detection A boiler operation control method for obtaining a degree of superheat of a fluid based on a deviation from a saturation temperature from a vessel and correcting a flow rate of water supplied to the furnace water wall based on the degree of superheat.

[0013]

FIG. 1 is a diagram showing a configuration of a water supply amount correction circuit according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of a Benson boiler recirculation system. put it here,
1 is a boiler input command, 2a, 2b and 2c are function generators,
3, 4 are high value selectors, 5 is a signal generator, 6 is a signal switcher, 7 is a rate-of-change limiter, 8 is a subtractor, 9 is a fluid temperature at an appropriate point from the furnace water wall outlet to the brackish water separator inlet. ,
10 is a drain tank pressure of a brackish water separator, 11 is a feed water pump, 12 is a recirculation pump, 13 is a coal saver, 14 is a furnace water wall, 15 is a ceiling wall, 16 is an evaporator, 17 is a brackish water separator,
18 is a drain tank, 19 is a superheater, 20 is a cooler, 2
Reference numeral 1 denotes a recirculation flow control valve.

The feed water flow rate command is an output of the high value selector 3 for controlling the flow rate of the water supply from the water feed pump 11. One input of the high value selector 3 is a boiler input command (B
ID) 1 is the feed water flow rate under program control, and the other input of the high value selector 3 is the feed water flow rate shown in FIG. The feedwater flow rate is calculated based on the minimum feedwater flow rate from the signal generator 5 for furnace protection at the time of startup and the feedwater correction based on the degree of fluid superheat at any point from the furnace water wall outlet to the steam-water separator inlet. The quantity and the high value of are selected.

The pressure 10 in the steam / water separator drain tank 18 is detected, and the saturation temperature of an appropriate portion from the furnace water wall outlet to the steam / water separator inlet is obtained from the function of the detection signal. The fluid temperature at an appropriate portion from the wall outlet to the steam-water separator inlet is determined, and the saturation temperature and the fluid temperature are subtracted by the subtractor 8 to determine the degree of superheat of the fluid. The water supply correction amount is created by a function from By passing the function output of the degree of superheat through the change rate limiter 7, the delay characteristic of the boiler control system is compensated for. It can be set individually.

When the water supply correction amount exceeds a predetermined load by the signal switch 6 (for example, the load after circulation / through flow switching> 35%), the water supply correction from the change rate limiter 7 is corrected. The signal is cut, and the zero input from the signal generator 5 is output from the signal switch 6.

According to the present invention, it is possible to appropriately control the transition of the fluid at the outlet of the furnace water wall to the superheated region during the circulation operation, which is a factor of the temperature rise of the metal wall of the furnace water (the feedwater becomes all steam) without delay. The amount of water supply can be corrected. Therefore, it is possible to reduce the fuel input amount due to the increase in the main steam pressure accompanying the correction of the water supply amount, and to reduce the fluid enthalpy at the outlet of the furnace water wall by increasing the water supply amount passing through the furnace water wall. Realizes stabilization of the furnace water wall metal temperature characteristics at the time of the circulation / through flow switching.

As described above, in the embodiment of the present invention, the temperature of any fluid from the outlet of the furnace water wall to the inlet of the steam separator is monitored, and the portion is overheated before switching of the circulation / through flow control. In the case of steam, it is intended to stabilize the boiler characteristics such as the furnace water wall metal temperature by optimizing the feedwater flow rate correction in accordance with the degree of superheat. If any of the fluids up to the separator inlet becomes superheated steam before the circulation / through-flow control is switched, if the water supply amount is increased, the fuel input amount will decrease due to the increase in the main steam pressure accompanying the increase in the boiler evaporation amount ( The main steam pressure of the fuel is controlled) and the flow rate of the feedwater passing through the furnace water wall increases, so that the metal temperature of the furnace water wall tends to decrease, thereby stabilizing the boiler characteristics.

[0019]

According to the present invention, even when the coal output response characteristic of the pulverized coal machine changes due to the change in the number of revolutions of the classifier, the fuel injection amount (BIR) to the furnace at the time of load change can be properly adjusted. Therefore, it is possible to stabilize the boiler characteristics such as the steam temperature and the pressure.

According to the present invention, even when the operation (boiler / turbine bleeding, water supply heater in-service timing, etc.) affecting the main steam pressure characteristic or the boiler state (fuel property, furnace contamination degree, etc.) is changed, Feedback control of the water supply amount corresponding to the boiler state (the degree of fluid superheat from the furnace water wall outlet to the steam-water separator inlet section) is possible, so even if the operation timing shifts or the boiler state changes, the water supply amount correction timing An object of the present invention is to provide a control method capable of obtaining a circulation / through flow switching characteristic with a stable delay.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a water supply amount correction circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a Benson boiler recirculation system.

FIG. 3 is a diagram illustrating a configuration of a water supply amount correction circuit according to the related art.

FIG. 4 is a diagram showing a water supply flow rate command according to the prior art.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 Boiler input command 2 Function generator 3 High value selector 4 Adder 5 Signal generator 6 Signal switch 7 Rate of change limiter 8 Subtractor 9 Fluid temperature from furnace water wall outlet to brackish water separator inlet 10 Steam separator Drain tank pressure 11 Feed water pump 12 Recirculation pump 13 Energy saving device 14 Furnace water wall 15 Ceiling wall 16 Evaporator 17 Steam separator 18 Drain tank 19 Superheater 20 Desuperheater 21 Recirculation flow control valve

Claims (1)

[Claims] An operation control system for a boiler which has a recirculation system provided with a steam / water separator and a drain tank, and switches between a circulation / flow-through mode, wherein a proper flow from a furnace water wall outlet to a steam / water separator inlet is provided. A fluid temperature detector for detecting a fluid temperature in a portion; and a pressure detector for detecting a pressure of the drain tank. When the circulation / flow-through mode is switched, a fluid temperature from the fluid temperature detector, An operation control method for a boiler, wherein a superheat degree of a fluid is obtained from a deviation from a saturation temperature from a pressure detector, and a flow rate of water supplied to the furnace water wall is corrected based on the superheat degree.