JPH06229505A - Controlling device for feed water temperature of waste heat recovery heat exchanger - Google Patents

Abstract

PURPOSE:To stabilize feed water temperature and utilize excessive steam effectively by a method wherein when a rise in load is small and relatively sufficient pressure is provided, heating steam is caused to flow into a feed water tank, and when a load has risen and sufficient pressure is not provided, excessive steam is prevented from flowing into the feed water tank. CONSTITUTION:When a load is stabilized, main steam is sufficient, and the opening of a steam pressure control valve 11 is kept constant, a feed water control valve 16 is controlled by a control signal to keep the outlet side temperature of a feed water tank 12 at a specified value, whereby superheated steam is injected into the tank 12 from a steam relief pipe system L6, so that the temperature of stored feed water is kept constant. On the other hand, when the main steam is not sufficient and pressure thereof falls due to changes in load and the opening of the valve 11 becomes below certain value, the feed water control valve 16 is closed until the pressure of a main steam pipe system L5 rises, whereby the amount of steam injection into the tank 12 is limited. As a result, fluctuations in the feed water temperature can be minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed water temperature control device for an exhaust heat recovery heat exchanger that recovers heat from high temperature exhaust gas to generate steam.

[0002]

2. Description of the Related Art FIG. 8 shows a system diagram of conventional feed water temperature control of an exhaust heat recovery heat exchanger.

The waste heat recovery heat exchanger comprises a superheater 1 and an evaporator 2.
And an economizer 3, and an upstream exhaust gas piping system L1a
First, the high-temperature exhaust gas flows into the superheater 1, where it exchanges heat with the exhaust gas, and then heat-exchanges with the exhaust gas in the evaporator 2 and is discharged from the exhaust gas piping system L1b downstream via the economizer 3. It

On the other hand, normal temperature water is supplied from the water supply piping system L3 by the water supply pump 4 and flows into the economizer 3 through the water supply flow rate control valve 5. In the economizer 3, the water whose temperature has risen due to heat exchange between the exhaust gas and the feed water flows into the evaporator 2 through the feed water piping system L3. The heated water exchanges heat with the exhaust gas in the evaporator 2 to become saturated steam, flows into the next superheater 1, and a part of the saturated water is saved from the boiler water circulation piping system L4 by the boiler water circulation pump 6 to save the coal. 3 is returned to the water supply piping system L3 on the inlet side for circulation.

The saturated steam flowing into the superheater 1 exchanges heat with the high temperature exhaust gas to become superheated steam, and the main steam flow control valve 7
Is supplied from the main steam piping system L5 to a predetermined location such as a turbine (not shown) for work.

By the way, a water supply temperature detecting means 8 is arranged in the water supply pipe system L3 near the confluence of the boiler water circulation pipe system L4 and the water supply pipe system L3, and further, the water supply temperature control is carried out in the boiler water circulation pipe system L4. A valve 9 is arranged and the feed water temperature detecting means 8 is connected to the temperature control means 10.

The temperature control means 10 obtains a deviation between the feed water temperature detection signal from the feed water temperature detection means 8 and a preset temperature, controls the deviation, and outputs a control signal to the feed water temperature control valve 9. . As a result, the flow rate of circulating saturated water of the evaporator 2 from the boiler water circulation piping system L4 to the water supply piping system L3 and mixing it is increased or decreased, the inlet temperature of the economizer 3 is kept constant, and the economizer 3 is saved. Economizer 3 due to lower inlet temperature
Prevents low temperature corrosion of piping.

The main steam piping system L5 and the downstream exhaust gas piping system L1b are connected to the escape steam piping system L that connects both pipings.
6 is formed by bypass, and the steam pressure control valve 11 is arranged to keep the outlet pressure of the superheater 1 at a predetermined value.

[0009]

However, in the conventional apparatus shown in FIG. 8, the feed water temperature control is unstable, and
There is a problem that the excess steam of the plant cannot be effectively used.

First, as one of them, the feed water temperature detecting means 8
Is placed in a pipe having a small heat capacity, and therefore, if the flow rate of the water supply piping system L3 changes, the water supply detection temperature signal changes correspondingly and the controlled temperature changes. .

In order to solve this, it is conceivable to increase the control sensitivity. However, since the temperature is controlled by mixing water at room temperature with a small amount of saturation temperature,
If the control sensitivity is high and the feed water flow rate at room temperature is small, the feed water temperature control valve 9 is extremely narrowed, and rather, the inlet temperature of the economizer 3 is lowered, or hunting occurs, which causes instability.

As described above, when the feed water flow rate fluctuates due to a load change or the like, there is a problem that the inlet temperature of the economizer 3 is lowered and the exhaust gas flowing into the economizer 3 causes low-temperature corrosion of pipes and the like.

Secondly, excess steam is discharged to the outside of the system from the escape steam piping system L6 through the exhaust gas piping system L1b downstream by the opening operation of the steam pressure control valve 11 shown in FIG. However, there is a problem that heat is not efficiently used.

For example, the exhaust heat recovery heat exchanger is applied to a small-scale fuel cell power plant, and the superheated steam supplied from the main steam piping system L5 is used as the steam source of the reformer. Generally, in a fuel cell power plant, the load changes abruptly and largely, and it is possible to supply superheated steam according to the maximum load.Therefore, there is a waste of energy in discharging excess steam to the outside of the system under normal and load conditions. there were.

Therefore, it is an object of the present invention to provide a feed water temperature control device for stabilizing the feed water temperature and effectively utilizing the surplus steam.

[0016]

According to a first aspect of the present invention, there is provided a coal-saving coal which is connected to a water supply pipe and has a built-in heat exchanger for exchanging heat between the water supplied from the water supply pipe and exhaust gas to generate heated water supply. Vessel, a water supply pipe connected to this economizer and a built-in heat exchanger, and an evaporator for exchanging heat with the heated water supply and exhaust gas to generate saturated steam, and a steam pipe connected to this evaporator Steam for exchanging heat with saturated steam and exhaust gas to generate superheated steam and supplying superheated steam from a main steam pipe to a heat demand destination, and steam for discharging excess steam branched from the main steam pipe A relief steam pipe is arranged via a pressure control valve, and the inlet side of the evaporator and the water supply pipe on the inlet side of the economizer are connected to each other through a circulation pump and a main feed water temperature control valve. Exhaust heat recovery heat exchanger configured by arranging water circulation piping Main temperature detecting means for detecting the water supply temperature of the water supply pipe on the inlet side of the charcoal device and outputting a water supply temperature detection signal, and a deviation between the water supply temperature detection signal and the water supply temperature setting signal is control-calculated to control the control signal. In a feed water temperature control device for an exhaust heat recovery heat exchanger, which comprises a main temperature control means for outputting to a feed water temperature control valve and controls the feed water temperature to a predetermined value,
A water supply tank connected to a makeup water pipe for supplying makeup water is provided to store the water supply, the water supply tank is connected to the water supply pipe, and excess superheated steam is supplied from the main steam pipe to the water supply tank. Connected to the main steam pipe through the superheated steam supply pipe in which the feed water temperature control valve is arranged to receive, further, a pressure detector that is arranged in the main steam pipe to detect the main steam pressure and output a pressure detection signal, Pressure control means for controlling and calculating the deviation between the pressure detection signal and the pressure setting signal and outputting a control signal to the steam pressure control valve; and limiting the supply of the surplus superheated steam when the load of the heat demand destination rises. Function setting means for inputting the control signal and outputting a limit signal based on a preset function, and a temperature for outputting a temperature detection signal provided in the water supply pipe on the outlet side of the water tank Output means, temperature control means for controlling and calculating the deviation between the temperature detection signal and the temperature setting signal and outputting a control signal, and inputting the limit signal and the control signal to select a low value signal A low value selecting means for opening and closing the water supply control valve according to this signal is provided.

The invention of claim 2 is a economizer which is connected to a water supply pipe and has a built-in heat exchanger, which exchanges heat with the exhaust water and exhaust gas from the water supply pipe to generate heated water. An evaporator that is connected to a water supply pipe and has a built-in heat exchanger to exchange heat with the heated water and exhaust gas to generate saturated steam, and a steam pipe connected to this evaporator to heat the saturated steam, exhaust gas and heat. For exchanging superheated steam to supply superheated steam from the main steam pipe to the heat demand destination via the main steam flow control valve, and for discharging excess steam branched from the main steam pipe Of the steam pressure control valve of the escape steam pipe is arranged, and the inlet side of the evaporator and the feed water pipe of the inlet side of the economizer are connected to each other via a circulation pump and a feed water temperature control valve. Exhaust heat recovery heat exchanger configured with boiler water circulation piping Main temperature detecting means for detecting the water supply temperature of the water supply pipe on the inlet side of the economizer and outputting a water supply temperature detection signal, and a control signal by controlling and calculating a deviation between the water supply temperature detection signal and the water supply temperature setting signal. In the feed water temperature control device of the exhaust heat recovery heat exchanger for controlling the feed water temperature to a predetermined value by providing a main temperature control means for outputting to the main feed water temperature control valve, to the makeup water pipe for supplying makeup water. A water supply tank is provided to store connected water supply, the water supply tank is connected to the water supply pipe, and a water supply temperature control valve is arranged to receive supply of excess superheated steam from the main steam pipe to the water supply tank. A pressure detector that is connected to the main steam pipe via a steam pipe and that is arranged in the main steam pipe to detect the main steam pressure and output a pressure detection signal; and a deviation between the pressure detection signal and the pressure setting signal. Pressure control means for performing control calculation and outputting a control signal to the steam pressure control valve, flow rate detection means for detecting a main steam flow rate of the main steam pipe and outputting a main steam detection signal, flow rate setting signal and the main steam A flow rate control means for controlling and calculating a deviation from a detection signal to output a control signal to the main steam flow rate control valve; a differential calculating means for differentially calculating the flow rate setting signal and outputting a change rate signal; Function setting means for inputting the rate-of-change signal and outputting a limiting signal based on a preset function in order to limit the supply of the excess superheated steam when the load on the demand side increases, and the outlet side of the water supply tank Temperature detection means provided in the water supply pipe for outputting a temperature detection signal, temperature control means for controlling and calculating the deviation between the temperature detection signal and the temperature setting signal, and outputting the control signal, the limit signal and the control signal And enter And a low value selecting means for opening and closing the water supply control valve according to this signal.

[0018]

According to the first aspect of the present invention, when the increase in load is small and the pressure is relatively large, the feed water temperature control valve is controlled by the control signal that sets the temperature on the outlet side of the feed water tank to a predetermined value, and superheated steam is generated. It flows into the water tank. On the other hand, when the load increases and the pressure has no margin, the water supply control valve is controlled by the restriction signal, and the inflow of excess steam into the water supply tank is blocked. At this time, since the water supply tank has a large storage amount, there is no large fluctuation in the water supply temperature even if the excess steam does not flow in. As a result, the temperature of the feed water supplied to the inlet side of the economizer is stable, so that the variation of the feed water temperature is small even if the flow rate of the water supplied to the inlet side of the economizer is varied. Therefore, low-temperature corrosion of the economizer can be prevented, and excess steam can be effectively used.

According to the second aspect of the invention, the increase in load is small,
When the flow rate set value is relatively stable, the feed water temperature control valve is controlled by a control signal that sets the temperature on the outlet side of the water feed tank to a predetermined value, and superheated steam flows into the feed water tank. On the other hand, when the load rises and the flow rate set value rises sharply, the rate of change of the flow rate set value is set to a large and low limit signal that controls the feedwater temperature control valve to prevent the superheated steam from flowing into the feedwater tank. It At this time, since the water supply tank has a large storage amount, even if there is no inflow of superheated steam, the temperature of the water supply does not significantly change. As a result, the temperature of the feed water supplied to the inlet side of the economizer is stable, so that the variation of the feed water temperature is small even if the flow rate of the water supplied to the inlet side of the economizer is varied. Therefore, low-temperature corrosion of the economizer can be prevented, and excess steam can be effectively used.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram of a feed water temperature control system of an exhaust heat recovery heat exchanger showing a first embodiment of the present invention. The same reference numerals as those in FIG. 8 showing the prior art indicate the same or corresponding portions, and the difference between them is that a water supply tank 12 is additionally provided in the makeup water piping system L2, and the main steam piping system L5 is added to this water supply tank 12. Is connected to the superheated steam supply pipe system L7, and in order to maintain the temperature on the outlet side of the water supply tank 12 at a predetermined value, the temperature detection means 13, the temperature control means 14, the low value priority means 15, and the superheated steam supply piping system. The water supply control valve 16 arranged at L7 is provided.

Here, the water supply tank 12 is a storage tank having a large capacity, and while the make-up water is made to flow from the make-up water piping system L2 and made to stay therein, it is mixed with the superheated steam flowing from the superheated steam supply piping system L7 inside. After the temperature is raised, water is supplied from the water supply piping system L3 by the water supply pump 4.

The temperature detecting means 13 detects the temperature at the outlet of the water supply tank 12 and outputs a temperature detection signal. The temperature control means 14 controls and calculates the deviation between the temperature detection signal of the temperature detection means 13 and the temperature setting signal and outputs a control signal. The low value priority means 15 selects one of the control signal of the temperature control means 14 and the limit signal S1 whichever is lower, and outputs the control signal to the water supply control valve 16. The water supply control valve 16 is opened and closed according to a control signal from the low value priority means 15 to increase or decrease the amount of superheated steam flowing into the water supply tank 12 from the superheated steam supply piping system L7.

With the above structure, the water supply at room temperature is introduced into the water supply tank 12 from the makeup water source (not shown) through the makeup water piping system L2. In the water supply tank 12, the superheated steam is supplied from the superheated steam supply pipe system L7, and the water at room temperature is heated and stays therein. The water supply heated by the water supply tank 12 is sent by the water supply pump 4, reaches the confluence point between the water supply pipe system L3 and the boiler water circulation pipe system L4 via the water supply flow rate control valve 5, and then the exhaust heat recovery heat exchanger. Into the economizer 3.

The feed water that has flowed into the economizer 3 exchanges heat with the exhaust gas and flows into the evaporator 2 through the feed water piping system L3.

Here, heat is further exchanged with the exhaust gas to form saturated steam, which is supplied to the superheater 1, and a part of the saturated water is circulated from the boiler water circulation piping system L4 to the water supply piping system L3.
The saturated steam exchanges heat with high-temperature exhaust gas by the superheater 1 to become superheated steam, is supplied from the main steam flow control valve 7 to a predetermined location through the main steam flow control valve 7, and is allowed to work. In this case, the amount of superheated steam supplied is the main steam flow control valve 7
Is maintained at the set flow rate.

Here, the temperature control on the outlet side of the water supply tank 12 will be described.

First, the outlet temperature of the water supply tank 12 is detected by the temperature detection means 13 and the temperature detection signal is sent to the temperature control means 14.
Entered in. In the temperature control means 14, the deviation between the temperature detection signal and the temperature setting signal is controlled and calculated, and the control signal is input to the low value priority means 15.

On the other hand, in order to limit the control signal of the temperature control means 14 when the excess steam is not generated, a preset limit signal is inputted to the low value priority means 15. As a result,
A low value signal is selected by the low value priority means 15 from the limit signal and the control signal of the temperature control means 14, and the water supply control valve 16 is opened and closed.

That is, when the surplus steam is generated, a part of the surplus steam discharged to the outside of the system is supplied from the water supply control valve 16 to the water supply tank 12 in accordance with the control signal of the temperature control means 14, The outlet temperature of the water supply tank 12 is kept constant by controlling the amount of water supply. When the excess steam is not generated, the temperature control means 14 is controlled by the signal limited to the minimum. As a result, even if the amount of water supply greatly changes due to a sudden change in load, or even if there is no excess steam, the temperature of the water supply supplied from the water supply tank 12 to the water supply piping system L3 is increased, and the water supply with a large heat capacity is provided. Because it flows out of the tank 12,
There is little change in the temperature of the water supply.

Next, since the temperature detection signal detected by the feed water temperature detecting means 8 arranged on the inlet side of the economizer 3 is relatively stable, the feed water temperature control valve is controlled by the control signal from the temperature control means 14. 9 is controlled stably.

As described above, since a large amount of water stored in the water supply tank 12 is maintained at the set temperature and the heat capacity is increased as compared with the conventional method, the water supply temperature is changed even when the water supply flow rate largely changes due to load change or the like. Fluctuations are minimized. Further, since a part of surplus steam discharged to the outside of the system is used to heat the feed water, it is suitable for future small-scale, energy-saving plants.

Next, a second embodiment of the present invention will be described with reference to FIG.

The second embodiment differs from the first embodiment shown in FIG. 1 in that a pressure detector 17, a pressure control means 18 and a function setting means 19 are additionally provided.

Here, the pressure detector 17 detects the pressure on the inlet side of the main steam flow control valve 7 and outputs a pressure detection signal. The pressure control means 18 controls and calculates the deviation between the pressure detection signal of the pressure detector 17 and the pressure setting signal, and outputs a control signal. The function setting means 19 outputs a limit signal according to the function setting described later.

In the above structure, first, the pressure on the inlet side of the main steam flow control valve 7 is detected by the pressure detector 17, and the pressure detection signal is input to the pressure control means 18. A deviation of the pressure detection signal from the pressure setting signal is calculated by the pressure control means 18, the deviation is control-calculated, and the steam pressure control valve 11 is opened / closed by the control signal.

As a result, the pressure on the inlet side of the main steam flow control valve 7 is maintained at a predetermined pressure set value. Then, the control signal of the pressure control means 18 is input to the function setting means 19.

In the function setting means 19, for example, as shown in FIG. 3, the relationship between the control signal and the limit signal is previously obtained by experiment and set, and when the control signal is smaller than the value of α, the limit signal is set to α. = 0% is output and the control signal is α
When it is larger than the value of, the limiting signal α = 100% is given.

On the other hand, the temperature on the outlet side of the water supply tank 12 is
A temperature detection signal detected by the temperature detection means 13 is input to the temperature control means 14. In the temperature control means 14,
The deviation between the temperature detection signal and the temperature setting signal is controlled and calculated, and the control signal is input to the low value priority means 15.

The low value priority means 15 to which the limit signal and the control signal are input selects the low value signal and outputs the selected signal to the water supply control valve 16.

As a result, for example, when the load is stable,
If the main steam has a margin, the control signal is large, and the steam pressure control valve 11 is at a certain opening or more, the function setting means 1
A control signal of 9 to 100% is input to the low value priority means 15. Therefore, the control signal from the temperature control means 14 is output from the low value priority means 15. Therefore, a part of the surplus steam conventionally discharged from the steam pressure control valve 11 is controlled by the temperature control means 14. Thereby, the superheated steam is released by the water supply control valve 16 and is injected into the water supply tank 12 from the steam piping system L6, the water supply is heated, and the stored water supply temperature is kept constant.

On the other hand, when the steam pressure does not have a margin and the pressure drops due to a load change or the like, and the steam pressure control valve 11 becomes less than a certain opening, the function setting means 19 sends a 0% limit signal to the low value priority means 15. Is output to. At this time, the main steam piping system L
Until the pressure of 5 rises, the water supply control valve 16 is closed, and the injection amount of the water supply tank 12 is limited. At this time, the water supply temperature is large because the heat capacity in the water supply tank 12 is large.
Also, since the pressure recovers immediately, the feed water temperature does not drop significantly.

Next, a third embodiment of the present invention will be described with reference to FIG.

The present embodiment differs from the second embodiment shown in FIG. 2 in that the function setting means 20 is replaced by the function setting means 20.
Is provided.

As shown in FIG. 5, the function setting means 20 has a function curve b set as a pressure detection signal on the horizontal axis and a limit signal on the vertical axis, and when the input pressure detection signal is equal to or higher than the pressure value γ. Outputs a 100% limit signal, and 0% is output as the limit signal when the pressure detection signal is less than or equal to the pressure β value. As a result, similarly to the second embodiment shown in FIG. 2, when the pressure decreases due to an increase in the load and the pressure detection signal becomes the pressure value β or less, the limit signal of the function setting means 20 becomes 0%. The low value priority means 15 selects a 0% limit signal from the control signal and the limit signal of the temperature control means 14, and the water supply control valve 16 is closed by this signal. Thus, when the surplus steam is exhausted, the amount of heating steam to the water supply tank 12 is limited.

Next, a fourth embodiment of the present invention will be described with reference to FIG.

This embodiment differs from the third embodiment shown in FIG. 4 in that the main steam flow control valve 7 and the function setting means 20 are excluded.
Flow rate detecting means 21, flow rate controlling means 22, and differential calculating means 2
3 and the function setting means 20 and the function setting means 24 having a different configuration are additionally provided.

With this configuration, the main steam flow rate is detected by the flow rate detecting means 2
1, the flow rate control means 22 and the main steam flow rate control valve 7 control the flow rate set value s2. Differentiating means 23
Then, the flow rate set value s2 is input, and the set value change rate is obtained by the differential operation. In the function setting means 24, as shown in FIG. 7, the change rate of the flow rate setting value s2 is set on the horizontal axis and the function curve c is set as the limit signal on the vertical axis. here,
When the change rate is larger than δ, the limit signal is 0%, and when the change rate is δ or less, 100% is output as the limit signal. As a result, when the flow rate setting value s2 is increased when the load is increased and the rate of change is equal to or greater than a predetermined value, the output of the function setting means 24 becomes 0%. As a result, the low value priority means 15 outputs 0%, and the water supply control valve 16 is fully closed. Therefore, the amount of steam to be heated to the water supply tank 12 is limited when the load rises where there is a concern that the excess steam will be insufficient.

[0049]

As described above, according to the present invention, since the feed water heated by the feed water and the surplus steam and heated to a predetermined temperature is supplied from the feed tank to the inlet side of the economizer, the feed water flow rate varies. Even so, fluctuations in the water temperature can be minimized. Therefore, low-temperature water is not supplied to the economizer and low-temperature corrosion of the economizer is prevented. In addition, the surplus steam that has been conventionally discharged to the outside of the system is used to raise the temperature of the feed water, and energy can be used efficiently.

[Brief description of drawings]

FIG. 1 is a system diagram of a feed water temperature control system of an exhaust heat recovery heat exchanger showing a first embodiment of the present invention.

FIG. 2 is a system diagram of a feed water temperature control system of an exhaust heat recovery heat exchanger showing a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing setting contents of a function setting unit in FIG.

FIG. 4 is a system diagram of a feed water temperature control system of an exhaust heat recovery heat exchanger showing a third embodiment of the present invention.

5 is an explanatory diagram showing setting contents of a function setting means in FIG.

FIG. 6 is a system diagram of a feed water temperature control system of an exhaust heat recovery heat exchanger showing a fourth embodiment of the present invention.

7 is an explanatory diagram showing setting contents of a function setting unit in FIG.

FIG. 8 is a system diagram of a feed water temperature control system of an exhaust heat recovery heat exchanger showing a conventional example.

[Explanation of symbols]

 1 superheater 2 evaporator 3 economizer 8 feed water temperature detecting means 9 feed water temperature control valve 10 temperature control means 11 steam pressure control valve 12 feed water tank 13 temperature detecting means 14 temperature control means 15 low value priority means 16 feed water control valve 17 Pressure detector 18 Pressure control means 19 Function setting means 20 Function setting means 21 Flow rate detecting means 22 Flow rate controlling means 23 Differentiating operation means 24 Function setting means

Claims (2)

[Claims] 1. A economizer that is connected to a water supply pipe and has a built-in heat exchanger to exchange heat between the water supplied from the water supply pipe and exhaust gas to generate heated water, and a water supply pipe connected to the economizer. An evaporator that has a built-in heat exchanger to exchange heat with the heated feed water and exhaust gas to generate saturated steam, and a steam pipe is connected to this evaporator to exchange heat with the saturated steam and exhaust gas and superheated steam. And a superheater that supplies superheated steam from the main steam pipe to the heat demand destination, and escapes steam pipe through a main steam pressure control valve for discharging excess steam branched from the main steam pipe. The boiler water circulation pipe is arranged by connecting the inlet side of the evaporator and the water supply pipe on the inlet side of the economizer, through the circulation pump and the main water temperature control valve. Water supply temperature of water supply pipe on the inlet side of the economizer of the heat recovery heat exchanger Temperature detecting means for detecting the degree of temperature and outputting a feed water temperature detection signal, and a main temperature control for controlling and calculating a deviation between the feed water temperature detection signal and the feed water temperature setting signal and outputting a control signal to the feed water temperature control valve. And a means for controlling the supply water temperature of the exhaust heat recovery heat exchanger to control the supply water temperature to a predetermined value, the inlet side is connected to a makeup water pipe for supplying makeup water, and the outlet side is the supply water pipe. And a superheated steam supply which is connected to the main steam pipe and is connected to the main water supply tank via a water supply temperature control valve to receive supply of excess superheated steam to the main water supply pipe. A pipe, a pressure detector arranged in the main steam pipe for detecting the main steam pressure and outputting a pressure detection signal, and a control signal for controlling the deviation between the pressure detection signal and the pressure setting signal to output the control signal as the main steam pressure. A pressure control means for outputting to a force control valve, and inputting the control signal for limiting the supply of the surplus superheated steam when the load of the heat demand destination increases, and outputs a limiting signal based on a preset function. Function setting means, temperature detecting means for outputting a temperature detection signal provided in the water supply pipe on the outlet side of the water supply tank, and control operation of the deviation between the temperature detection signal and the temperature setting signal to output the control signal. A discharge control device comprising: a temperature control means; and a low value selection means for inputting the limit signal and the control signal to select a low value signal and opening / closing the feed water temperature control valve according to this signal. Water temperature control device for heat recovery heat exchanger. 2. A economizer that is connected to the water supply pipe and has a built-in heat exchanger to exchange heat between the water supply and the exhaust gas from the water supply pipe to generate heated water, and the water supply pipe is connected to the economizer. An evaporator that has a built-in heat exchanger to exchange heat with the heated feed water and exhaust gas to generate saturated steam, and a steam pipe is connected to this evaporator to exchange heat with the saturated steam and exhaust gas and superheated steam. And a superheater for supplying superheated steam from the main steam pipe to the heat demand destination via the main steam flow control valve, and a steam pressure control valve for discharging excess steam branched from the main steam pipe. The escape water steam pipe is installed through the water supply pipe, and the boiler water circulation pipe is connected through the circulation pump and the feed water temperature control valve by connecting the inlet side of the evaporator and the water supply pipe on the inlet side of the economizer. The inlet of the economizer of the heat recovery heat exchanger Main water temperature detection means for detecting the water supply temperature of the side water supply pipe and outputting a water supply temperature detection signal, and a control signal for controlling the deviation between the water supply temperature detection signal and the water supply temperature setting signal to control the main water temperature control signal. In a feedwater temperature control device for an exhaust heat recovery heat exchanger that controls the feedwater temperature to a predetermined value by including a main temperature control means for outputting to a valve, an inlet side is connected to a makeup water pipe for supplying makeup water. Together with the water supply tank, the outlet side of which is connected to the water supply pipe to store water supply, and the water supply tank that is connected to the main steam pipe to receive the supply of excess superheated steam to the water supply tank via the water supply temperature control valve. A superheated steam supply pipe connected to the main steam pipe, a flow amount detection means for detecting a main steam flow amount of the main steam pipe and outputting a main steam flow amount detection signal, and a deviation between a flow amount setting signal and the main steam flow amount detection signal. A flow rate control means for performing a calculation to output a control signal to the main steam flow rate control valve, a differential operation means for performing a differential operation on the flow rate setting signal and outputting a change rate signal, and the above-mentioned method when the load of the heat demand destination increases. Function setting means for inputting the change rate signal in order to limit the supply of excess superheated steam and outputting a limit signal based on a preset function, and a temperature provided in the water supply pipe on the outlet side of the water supply tank. A temperature detection unit that outputs a detection signal, a temperature control unit that controls and calculates a deviation between the temperature detection signal and the temperature setting signal, and outputs a control signal, and a low value by inputting the limit signal and the control signal. And a low value selecting means for opening and closing the water supply control valve in response to the signal, the supply water temperature control device for the exhaust heat recovery heat exchanger.