JP2001355806A - Controller for waste heat recovery steam generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller for waste heat recovery steam generator which can prevent the occurrence of cavitation in a high-pressure feed water pump which occurs when the flow rate of hot water in a high-pressure economizer-size pipeline increases due to the load change, etc., of a heat source. SOLUTION: When the valve travel control value (proportionally integrated value PI2) of a recirculating flow rate control valve outputted from a proportional integrator 23 becomes larger due to the valve travel control of the valve based on the temperature T of feed water in the pipeline at the inlet of a low-pressure economizer, the valve travel of the valve is limited so that the suction flow rate of the high-pressure water pump and the flow rate ir of hot water in the recirculation pipeline of a high-pressure economizer may respectively become the suction flow rate limiting value ils of the high-pressure feed water pump outputted from a signal generator 17 and a recirculating flow rate limiting valve ilr outputted from another signal generator 17 or smaller by finding the difference between the smaller one of the difference between the flow rate ih of hot water in the high-pressure economizer-side pipeline and the suction flow rate limiting valve ils and the recirculating flow rate limiting valve outputted from the signal generator 17 and the flow rate ir of the hot water in the recirculating pipeline of the economizer and limiting the valve travel to the valve travel limiting value Rg corresponding to the proportionally integrated value of the difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a waste heat recovery boiler provided with a low-pressure economizer and a high-pressure economizer to supply high-temperature hot water to a high-pressure steam drum and to connect a recirculation pipe from a middle stage of a water supply pump. The present invention relates to a control device of an exhaust heat recovery boiler that recirculates hot water into a feedwater inflow pipe of a low-pressure economizer through a low-pressure economizer.

[0002]

2. Description of the Related Art In order to effectively utilize exhaust heat discharged from a gas turbine or the like, exhaust gas is guided to an exhaust heat recovery boiler,
A boiler device configured to recover heat by using a economizer disposed in an internal exhaust gas passage is well known.
FIG. 3 is a water supply system diagram showing a water supply system of the exhaust heat recovery boiler. The feedwater supplied by the condensate pump 1 is sent to the low-pressure economizer 3 via the low-pressure economizer inlet pipe 2. Low pressure economizer 3
A part of the warmed supply water is recovered to the low-pressure steam drum 4, and the rest is supplied to the high-pressure water pump 6 through the connecting pipe 5.
Sent to Most of the hot water pressurized by the high-pressure water supply pump 6 is flow-regulated by the high-pressure water supply control valve 8, and
The hot water heated to a high temperature by heat recovery is sent to the high-pressure steam drum 9. On the other hand, the hot water sent from the middle stage of the high-pressure water supply pump 6 into the economizer recirculation pipe 10 is flow-regulated by the recirculation flow control valve 11 and joins the low-pressure economizer inlet pipe 2.

When the temperature of the feedwater in the low-pressure economizer inlet pipe 2 decreases, dew condensation occurs near the inlet of the low-pressure economizer 3 from the low-pressure economizer inlet pipe 2, and low-temperature corrosion occurs there. Thus, by thus returning hot water to the low-pressure economizer inlet pipe 2 through the economizer recirculation pipe 10, the feedwater temperature therein is maintained above the dew point. A high pressure side discharge flow meter 13 and a middle stage extraction flow meter 14 are connected to the high pressure water saving pump 7 side of the high pressure water pump 6 and the side of the economizer recirculation pipe 10 respectively, and the hot water flowing in each pipe is connected. The flow rates i _h and _ir are detected. A feedwater thermometer 12 is installed near the inlet of the low-pressure economizer inlet pipe 2 to the low-pressure economizer 3, and detects a feedwater temperature T in the low-pressure economizer inlet pipe 2. The flow rate of the water supplied by the water supply pump 1 directly corresponds to the flow rate required on the suction side of the high-pressure water supply pump 6.

The recirculation flow control valve 11 is provided with a feedwater temperature T in the low-pressure economizer inlet pipe 2 detected by the feedwater thermometer 12, a high-pressure side discharge flowmeter 13 and a high-pressure economizer 7 detected by the middle-stage extraction flowmeter 14. hot water flow rate i _h in the side and economizer recirculation pipe 10 pipe, based on the i _r, are opening control by a not-shown control valve control device.

FIG. 4 is a system diagram showing the flow of recirculation flow control in the regulating valve control device. As shown in the figure, the feedwater temperature T in the low-pressure economizer inlet pipe 2 detected by the feedwater thermometer 12 is input to a subtractor 21, and similarly, a signal generator 22.
Is calculated from the reference water supply temperature T _S, which is set in advance to a value equal to or higher than the dew point. The deviation is input to the proportional integrator 23 and proportionally integrated, and is set as an opening control value Rg of the recirculation flow control valve 11 according to the proportional integral value. That is,
When the proportional integral value calculated by the proportional integrator 23 decreases, the opening control value Rg is controlled to a small value, and when the proportional integral value increases, the opening control value Rg is controlled to a large value. You.

[0006]

When the load on the exhaust heat supply side of a gas turbine or the like increases, the amount of heat absorbed on the high pressure side of the exhaust heat recovery boiler increases, and the amount of evaporation increases. When the water level at 9 drops, the high-pressure water supply control valve 8 is controlled by the control of the control valve control device so as to increase the opening thereof, so that the hot water flow rate i _h on the high-pressure economizer 7 side.
Increase. For this reason, the flow rate of hot water passing through the connecting pipe 5, that is, the flow rate of feed water supplied by the condensate pump 1 through the low-pressure economizer inlet pipe 2 increases, so that the water supply in the low-pressure economizer inlet pipe 2 increases. Temperature T drops temporarily. Thus, because the recirculation flow rate control valve 11 is open wide, hot water flow i _r in the piping of the economizer recirculation pipe 10 side is increased in accordance with the opening degree control of the recirculation flow rate control valve 11 described above, the high-pressure feed water the rapid increase in hot water flow i _r in overload or economizer recirculation pipe 10 of the high-pressure feed water pump 6 in response to a rapid increase in the suction flow rate of the pump 6, cavitation (cavitation) was sometimes occur .

An object of the present invention is to control an exhaust heat recovery boiler capable of preventing an overload or cavitation of a high pressure feed pump caused by an increase in a flow rate of hot water in a high pressure economizer side pipe due to an increase in a load of a heat source. It is to provide a device.

[0008]

According to the present invention, in order to solve the above-mentioned problems, the flow rate of hot water in the piping on the high-pressure economizer is changed to the hot water warmed by the low-pressure economizer to the high-pressure economizer. With a regulating valve control device that adjusts the opening of the recirculation flow control valve so that the hot water flow rate in the recirculation pipe is equal to or less than the recirculation flow limit value when the suction flow rate of the feed water pump is less than the suction flow rate limit value It is.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a system diagram showing a flow of recirculation flow rate control in the regulating valve control device according to the present embodiment. In the figure, 15 and 17 are signal generators, 1
6, 19 are subtractors, 18 and 24 are low value selectors, and 20 is a proportional integrator. The same reference numerals are given to portions which are the same as or can be regarded as the same as those in the conventional example, and redundant description thereof will be omitted.

[0010] As shown in FIG.
The detected hot water flow rate i _{h in} the pipe on the high pressure economizer 7 side was input to the subtractor 16 and input from the signal generator 15.
The difference from the suction flow rate limiting value i _ls that is the suction flow rate limiting value of the high-pressure water supply pump 6 is calculated. The deviation is determined by the low value selector 1
8 is compared with a recirculation flow rate limiting value i _lr that limits the hot water flow rate i _r in the economizer recirculation pipe 10, which is input from the signal generator 17, and a smaller value is selected. Is output. Low value signal selected by the low value selector 18 is input to the subtracter 19, middle emergent flow meter 14 is the difference between the hot water flow i _r in economizer recirculation pipe 10 detected is calculated.
The deviation is input to the proportional integrator 20 and proportionally integrated.

On the other hand, the low pressure
The feedwater temperature T in the vessel inlet pipe 2 is input to the subtractor 21,
Reference water supply input from signal generator 22 as in the conventional example
Temperature T_S Is calculated. The deviation is proportional integrator 2
3 and is proportionally integrated and proportionally integrated PI_Two Is low price
Selector 24 and output from the proportional integrator 20 described above.
PI₁ And the smaller value is selected.
And the proportional integral PI _i Recirculation flow control valve 11 according to
Is the opening control value Rg.

In this embodiment, since the opening degree control of the recirculation flow control valve 11 is performed by the above-described recirculation flow control,
When the hot water flow rate i _{h in} the pipe on the high pressure economizer 7 side is equal to or less than the suction flow rate limit value i _{ls of the} high pressure feed pump 6, the economizer recirculation pipe 1
As the hot water flow i _r in 0 becomes less recirculation flow limit value i _lr, since the opening of the recirculation flow rate control valve 11 is adjusted, the high pressure economizer 7 side by the load change of the heat source also prevented the hot water flow rate i _h in the piping is increased, the recirculation flow rate control by hot water flow rate i _h, i _r it is possible to suppress the excessive increase in the occurrence of cavitation of the high-pressure feed water pump 6 can do.

FIG. 2 is a graph showing the aging of the flow rate in the main pipe, the feedwater temperature T in the low-pressure economizer inlet pipe 2 and the opening control value Rg of the recirculation flow control valve 11 when the load of the gas turbine increases. It is a time-dependent change figure which shows a change. When the load of the gas turbine increases at a certain point in time, the heat source temperature of the exhaust heat recovery boiler increases, and the amount of evaporation on the high pressure side increases, so that the water level of the high pressure steam drum 9 decreases. This in order to compensate for the drawdown, because the high-pressure feed water control valve 8 is opened largely by the control of the regulating valve control device, the high-pressure economizer 7 heat water flow i _h increases. Along with this, the flow rate of hot water passing through the connecting pipe 5 and the flow rate of feed water supplied into the low-pressure economizer inlet pipe 2 by the feed water pump 1 increase. Thus, since the flow rate i _r heat water supplied into the low-pressure economizer inlet pipe 2 via a economizer recirculation pipe 10 is relatively ratio is reduced relative to the feed water flow, low-pressure economizer The feedwater temperature T in the inlet pipe 2 decreases. The opening of the recirculation flow control valve 11 is increased by the opening control of the recirculation flow control valve 11 based on the decrease in the feedwater temperature.

[0014] If these control operations work too strongly,
The flow rate of hot water through the pipe 5 and the recirculation pipe 10 of the economizer
Hot water flow rate i_r Is the suction flow rate limit value i_lsAnd re
Circulating flow rate limit value i_lrHigh pressure as described above
Since cavitation of the water supply pump 6 occurs,
In the embodiment, based on the feedwater temperature T in the low-pressure economizer inlet pipe 2,
By controlling the opening of the recirculation flow control valve 11, the recirculation flow
The opening control value of the control valve 11 (PI_Two) Is larger,
The opening degree is determined by the flow rate of hot water i in the pipe on the high-pressure economizer 7 side._h When
Suction flow rate limit value i of high pressure feed pump 6_lsDeviation and recirculation
Ring flow limit value i _lrThe smaller one of the inside and the economizer recirculation pipe 1
Hot water flow rate i during 0_r And the proportional integral PI
_i To the opening control value Rg corresponding to
Suction flow rate of high-pressure feed pump 6 and recirculation pipe of economizer
Hot water flow rate i in 10_r Is the suction flow rate limit value i_lsYou
And recirculation flow limit i_lrIs restricted to:
(The flow rate in the shaded area in FIG.
).

[0015]

As described above, according to the present invention, the hot water flow rate in the high pressure economizer side pipe is less than the suction flow rate limit value of the feed water pump, and the hot water flow rate in the recirculation pipe is recirculated. Since the opening of the recirculation flow control valve is adjusted so that it is equal to or less than the flow rate limit value, even if the flow rate of hot water in the piping on the high pressure The circulation flow rate control can suppress an excessive increase in the flow rate of hot water in the pipe on the high-pressure economizer side and in the recirculation pipe, and can prevent cavitation of the feedwater pump.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a flow of recirculation flow control according to an embodiment of the present invention.

FIG. 2 is a temporal change diagram showing a temporal change of a flow rate in a main pipe, a feedwater temperature T, and an opening control value Rg of a recirculation flow rate control valve when a load amount increases.

FIG. 3 is a water supply system diagram showing a water supply system of a waste heat recovery boiler according to a conventional example.

FIG. 4 is a system diagram showing a flow of recirculation flow control according to a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 feedwater pump 2 low-pressure economizer inlet pipe 3 low-pressure economizer 5 connecting pipe 6 high-pressure water pump 7 high-pressure economizer 8 high-pressure water supply control valve 9 high-pressure steam drum 10 economizer recirculation pipe 11 recirculation flow control valve 12 Feed water thermometer 13 High-pressure side discharge flow meter 14 Middle stage extraction flow meter 15, 17, 22 Signal generator 16, 19, 21 Subtractor 18, 24 Low value selector 20, 23 Proportional integrator

Claims (1)

[Claims] 1. Hot water warmed by a low-pressure economizer provided in an exhaust heat recovery boiler is fed to a high-pressure economizer by a water supply pump, and further heated to produce high-temperature hot water via a high-pressure water supply control valve. While supplying the high-pressure steam to the high-pressure steam drum, and a flow path for returning hot water from the middle stage of the water supply pump to the low-pressure coal economizer through a recirculation pipe via a recirculation flow control valve. A waste heat recovery boiler configured to perform a recirculation flow rate control for controlling an opening degree of the flow rate control valve so that a difference between a feed water temperature in the feed water inflow pipe and a predetermined reference feed water temperature is not increased. In the control device, the hot water flow rate in the pipe on the high pressure economizer side is equal to or less than the suction flow rate limit value of the feedwater pump, and the hot water flow rate in the recirculation pipe is equal to or less than the recirculation flow rate limit value. Adjustment valve control to adjust the opening of the recirculation flow control valve A control device for an exhaust heat recovery boiler, comprising a device.