JPH05296401A - Exhaust heat recoverying boiler system and its main steam temperature controller - Google Patents

Abstract

PURPOSE:To restrict an increasing rate of a main steam temperature within an allowable range of a steam turbine without changing a load increasing rate (a feeding amount of fuel) of the gas turbine, and make a minimum consumption of life of a steam turbine without extending a starting time of a plant. CONSTITUTION:High pressure superheaters 18 and 19 are divided in such a manner that a relation between a heating face area of the second high pressure superheater 19 and a heating surface area of the first high pressure superheater 18 may become the most suitable districution. High pressure main steam temperature is controled by the desuperheater 23 provided in the midway of the communicating pipe between the divided superheaters and also mixing the saturated steam branched from the high pressure communicating pipe 17 on directly from the high pressure steam drum 15 into the high pressure main steam pipe 20 by controling the main steam temperature control valve 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a main steam temperature control device for an exhaust heat recovery boiler of a combined cycle thermal power plant.

[0002]

2. Description of the Related Art Recent combined cycle plants are equipped with gas turbines in order to cope with high efficiency and large capacity.
The temperature of the gas at the inlet of the bottle is raised, and the temperature of the exhaust gas is also raised accordingly. Outlet steam temperature (high-pressure main steam temperature) of exhaust heat recovery boiler due to high temperature of gas turbine exhaust
Also tends to be higher. However, since the steam turbine uses high-pressure steam, the casing has a thick wall.
There is an optimum steam condition depending on the output from the condition that the water is also exposed to high temperature steam. At present, the maximum value of the main steam temperature at the steam turbine inlet is about 538 to 566 ° C. Therefore, when an operating state occurs in which the main steam temperature exceeds this value, the steam temperature is controlled by setting the upper limit value of the steam temperature generated by the exhaust heat recovery boiler regardless of the load. Is common. FIG. 4 is a diagram showing components of the exhaust heat recovery boiler and flows of water, steam, and gas, and FIG. 5 is a block diagram showing an example of a control device.

In FIG. 4, the steam that has worked in the steam turbine is cooled in the condenser to become condensed water, which is stored in the condenser hot well. Condensed water stored in the hot well is extracted by a condensate pump and supplied to the low pressure economizer 2 via the low pressure water supply pipe 1. In the low-pressure economizer 2, the entire feedwater is heated by heat exchange between the exhaust gas of the gas turbine and the exhaust gas which has already become low temperature due to heat exchange in other heat exchanger parts. The feed water heated by the low-pressure coal economizer 2 is supplied to the low-pressure drum 8 through the low-pressure connecting pipe 4 with the low-pressure feed water control valve 5 adjusting the low-pressure feed water amount so as to keep the water level of the low-pressure steam drum 8 constant. It

On the other hand, the high-pressure water supply pump 6 is supplied through the high-pressure water supply pump suction pipe 3 branched from the low-pressure communication pipe 4,
The pressure is increased by the high-pressure water supply pump 6. The pressurized water supply supplies high-pressure water supply to the high-pressure economizer 12 via the high-pressure water supply pipe 7. The high-pressure feedwater, which has been heated by exchanging heat with the exhaust gas in the high-pressure economizer 12, is adjusted through the high-pressure connecting pipe 13 by the high-pressure feedwater control valve 14 to adjust the high-pressure feedwater amount so that the water level of the high-pressure steam drum 15 is kept constant. And supply it to the high pressure steam drum.

The feed water previously supplied to the low-pressure steam drum 8 returns to the steam drum 8 while generating heat by exchanging heat with the exhaust gas in the low-pressure evaporator 9. That is, the heat is exchanged between the low-pressure steam drum 8 and the low-pressure evaporator 9 to circulate and generate steam. The steam separated by the low-pressure steam drum 8 is supplied to the low-pressure superheater 11 via the low-pressure steam communication pipe 10, exchanges heat with the exhaust gas, and is supplied to the low-pressure stage of the steam turbine as superheated steam.

On the other hand, a high pressure drum heated by the high pressure economizer 12
The feed water supplied to 15 returns to the high pressure steam drum 15 while generating heat by exchanging heat with the exhaust gas in the high pressure evaporator 16. That is, the high pressure steam drum 15 and the high pressure evaporator 16 circulate while exchanging heat to generate steam. The steam separated in the high-pressure steam drum 15 is supplied to the high-pressure first superheater 18 via the high-pressure steam communication pipe 17, exchanges heat with the exhaust gas to become superheated steam, and to bring the main steam temperature to a predetermined temperature. The spray water is supplied to the high pressure section of the steam turbine.

On the other hand, the steam that has worked in the high pressure stage of the steam turbine is heated by heat exchange with the exhaust gas in the reheaters 21 and 22 to be turned into high temperature steam again, and then the medium pressure stage of the steam turbine. Is supplied to. For this reheated steam, the maximum allowable temperature determined by the material of the steam turbine is set, and the reheated steam temperature is controlled below the allowable temperature regardless of changes in operating conditions. This temperature control divides the heat transfer surface of the reheater, installs a desuperheater 26 in the connecting pipe of the divided heat transfer surface, and sprays water to the desuperheater 26 according to the temperature of the reheated steam. The reheat steam control valve 27
It is common to adjust and supply at. However, this reheater may not be installed depending on the scale of the plant.

Further, a low pressure economizer inlet feed water temperature control pipe 28 and a low pressure feed water temperature control valve that branch from the high pressure water supply pipe 7 on the discharge side of the high pressure water supply pump 6 and circulate to the inlet of the low pressure economizer 2.
29 is installed and the inlet temperature of the low pressure economizer 2 is adjusted to be constant.

Generally, the main steam temperature of the exhaust heat recovery boiler is
It is determined by the determinants of characteristics such as exhaust gas inlet temperature, exhaust gas amount, steam amount, and heat transfer area. Generally, the main steam temperature of the steam turbine has an upper limit value.The superheater is divided so that it does not exceed this upper limit, and the temperature is reduced in the middle of the connecting pipe that connects the heat transfer surfaces of the divided superheaters. A system is generally used in which the steam generator 23 is provided and the amount of spray water supplied to the desuperheater 23 is adjusted by the main steam temperature control valve 25 according to the main steam temperature. The water source of the spray water should have a pressure higher than the steam pressure and should be able to cope with changes in the water volume sufficiently. In the example of FIG. 4, a method of branching from the high-pressure water supply pipe 7 is shown.

FIG. 5 shows an example of conventional main steam temperature control. The pressure of the high pressure steam drum 15 is the high pressure second superheater.
The lower limit value of the inlet steam temperature of the high-pressure second superheater 19 corresponding to the pressure of the high-pressure steam drum 15 is calculated by inputting into the function generator 35 for calculating the lower limit value of the inlet steam temperature of 19. This calculated value is input to the opening calculator 36 of the high pressure main steam temperature control spray valve 25 together with the steam flow rate of the high pressure steam pipe 20 and the spray water temperature of the reduced temperature water supply pipe 24, and the high pressure main steam temperature control spray is supplied.
The opening degree of the valve 25 is calculated.

On the other hand, the opening of the high-pressure main steam temperature control spray valve 25 is set so that the deviation becomes zero based on the deviation between the high-pressure steam temperature of the high-pressure steam pipe 20 and its set value. Is calculated by. Then, this calculated value and the opening calculator 36
The low value priority circuit 38 is provided for selecting the smaller one of the calculated values and the output value of the opening command to the high pressure main steam temperature control spray valve 25.

The main steam temperature control according to the conventional example employs a constant value control for keeping the set temperature constant regardless of the load. However, by adopting an operating method in consideration of the large capacity of the gas turbine and environmental measures, the exhaust gas temperature of the gas turbine tends to increase and the temperature rise rate tends to increase. Especially, in an exhaust heat recovery boiler without an auxiliary combustion device, the exhaust gas inlet temperature, the exhaust gas amount, the steam amount,
The outlet steam temperature of the high-pressure second superheater 19 is determined by the determinants such as the heat transfer area. In an operating state where the output of the gas turbine with a small amount of steam generation is low, the temperature change is equivalent to the temperature rise rate of the exhaust gas. In the case of the steam temperature constant value control, the steam temperature control is possible even with the conventional technique. However, if the steam temperature rises at the same rate as the exhaust gas temperature rise rate, it will exceed the allowable temperature rise rate of the steam turbine, and the thermal stress of the steam turbine will become abnormally large, leading to an increase in life consumption. Occurs.

On the other hand, in order to eliminate such inconvenience,
It becomes necessary to change the set temperature at a certain rate of temperature rise to control the steam temperature. Spray this temperature control
When performing only by adjusting the water amount, it is general to limit the injection amount of the spray water so that the water does not become supersaturated so that the spray water does not flow into the superheater in the state of water droplets. The limit value of the amount of spray water is generally 30 to 50 ° C. at the saturation temperature with respect to the steam pressure of the spray injection part.
The amount of water is set so that the temperature does not drop below the temperature that includes the margin. Also, there is a large delay in controlling the main steam temperature in the spray water. For this reason, a state in which the main steam temperature cannot be controlled to the set value occurs, and as a result, the temperature increase rate also becomes higher than the initial target.

[0014]

By the way, in an operating state in which the output of the gas turbine with a small amount of steam generation is low, the temperature change becomes equivalent to the temperature rise rate of the exhaust gas.

In the case of constant steam temperature control, steam temperature control is possible with the prior art. However, if the steam temperature rises at the same rate as the exhaust gas temperature rise rate, it will exceed the allowable temperature rise rate of the steam turbine, and the thermal stress of the steam turbine will become abnormally large, leading to an increase in life consumption. Occurs.

The object of the present invention is to control the increase rate of the main steam temperature within the allowable range of the steam turbine without changing the load increase rate (fuel input amount) of the gas turbine, and prolong the starting time of the plant. Is to minimize the lifetime consumption of steam turbines.

[0017]

[Means for Solving the Problems] The high-pressure superheaters 18, 19 are divided so that the relationship between the heat-transfer area of the high-pressure second superheater 19 and the heat-transfer area of the high-pressure first superheater 18 is optimally distributed. The saturated steam of the high-pressure steam drum 15 is taken out from the high-temperature main steam pipe 20 by branching from the high-temperature steam communication pipe 17 or the branch from the desuperheater 23 and the high-pressure steam communication pipe 17 provided in the middle of the divided heat-transfer surface steam communication pipe. The temperature of the high-pressure main steam is controlled by adjusting and mixing with the main steam temperature control valve 31.

[0018]

[Operation] According to the high-pressure steam temperature control that uses both the spray and steam mixing methods, spray water is supplied to the desuperheater provided in the middle of the steam pipe that connects the heat transfer surfaces of the divided high-pressure superheaters. At the same time as the injection, the saturated vapor mixing control is performed in advance.
Therefore, even in an operating state in which a supersaturated state of spray water occurs, the high-pressure main steam temperature can exhibit sufficient controllability even when the temperature is set within the allowable range of the temperature increase rate.

[0019]

FIG. 1 shows the equipment configuration and system of an embodiment of the present invention.

The equipment configuration and system shown in FIG. 1 is the same as the equipment configuration and system of the prior art shown in FIG.
A superheater bypass steam pipe (30) branching from and joining the high-pressure main steam pipe (20), and a main steam temperature control valve (31) for adjusting the saturated steam flow rate to be mixed are provided in the middle of the superheater bypass steam pipe (30). The main steam temperature control valve 31 is a main steam temperature control device 32.
The opening degree is adjusted based on the control signal.

The internal structure of the main steam temperature control device 32 shown in FIG. 2 is the inlet temperature of the high temperature side heat transfer surface of the superheater divided by the pressure of the high pressure steam drum 15, that is, the high pressure second superheater 19 of FIG. Function generator 35 for calculating the allowable minimum temperature equivalent to the inlet temperature of the, and the allowable minimum temperature, spray water temperature, steam flow rate, etc. of the inlet temperature of the high-pressure side of the superheater calculated by the function generator 35 A calculator 36 that calculates the high-pressure main steam temperature control spray valve opening by inputting the data required for the calculation, and a high-pressure main steam temperature control spray to reduce the deviation between the steam set temperature and the high-pressure main steam temperature. -Main steam temperature controller for calculating valve opening and high-pressure main steam temperature control spray for both of the above-Low value priority circuit 38 that prioritizes and outputs low value of valve opening, steam temperature set value and high pressure main Differentiator 39 that differentiates the deviation from the steam temperature Another main steam temperature controller is provided which outputs the valve opening of the main steam temperature control valve 31 so as to reduce the deviation differentiated by the device 39.

When the high pressure main steam temperature rises rapidly,
Spray water is injected by the main steam temperature controller 37,
At the same time, the other main steam temperature controller 40 rapidly increases the temperature deviation differentiated by the differentiator 39, thereby increasing the amount of saturated steam mixed.

At this time, the decrease in suppression of the high-pressure steam temperature rise due to spray water injection causes a considerable delay, but the effect of mixing saturated steam immediately appears, and the high-pressure main steam temperature becomes the steam temperature set value. Acts like.

When the steam temperature change rate such as the main steam temperature rise rate is restricted, there are cases where the change rate limit cannot be satisfied only by spray water control. By adopting a steam temperature control method of mixing saturated steam as described above, and obtaining the mixed amount of saturated steam by the differential value of the temperature deviation, it is possible to suppress the rise in steam temperature,
The desired temperature control is possible even when the rate of change limitation is required.

Next, FIG. 3 shows another embodiment. The internal configuration of the main steam temperature control device 32, the high temperature side heat transfer surface inlet temperature of the superheater divided by the pressure of the high pressure steam drum 15 as an input,
That is, the function generator 35 that calculates the allowable minimum temperature of the inlet temperature of the high-pressure second superheater 19 of FIG. 1, the main steam temperature set value,
Estimating the inlet temperature of the high-temperature side heat transfer surface of the superheater divided by inputting the steam flow rate, exhaust heat recovery boiler inlet gas temperature and other data necessary for calculation, that is, the inlet temperature of the high pressure second superheater 19 in FIG. A high pressure second superheater inlet temperature set point calculation part composed of a calculator 36 for calculating a value and a high value priority circuit 37 for preferentially outputting the high value of the outputs of both, and the set value and the second superheat Dehumidifying spray water amount controller 38 which outputs the drive signal of the high pressure main steam temperature control valve 25 by inputting the deviation of the measured value of the inlet temperature of the reactor, and the main steam temperature controller 39 which further regulates the mixing amount of the saturated steam. Is.

In the case of the embodiment shown in FIG. 3, the estimated value calculated using the related data is compared with the minimum allowable value, and the higher value is set to the second superheater inlet steam temperature set value. Then, the amount of spray water is adjusted by comparison with the measured value. Therefore, when the set value of the inlet temperature of the second superheater is higher than the allowable minimum temperature, the high pressure main steam temperature can be controlled only by this spray water amount control. On the other hand, in the case of this opposite phenomenon, the high-pressure main steam temperature cannot be controlled to the set value, but in the case of the embodiment, since the high-pressure main steam temperature control by further mixing the saturated steam is combined, It is possible to control the set value.

When the steam temperature change rate such as the main steam temperature rise rate is restricted, there are cases where it is impossible to satisfy the change rate limitation only by spray water control. These restrictions can be lifted by adopting a steam temperature control method in which saturated steam is mixed as described above. That is,
The desired temperature control is possible even when the rate of change limitation is required.

Further, regarding the spray water amount control, the set value of the inlet temperature of the high pressure second superheater 19 is the same as in the above-mentioned embodiment, and the high pressure second superheater inlet temperature lower limit function generator
The output of the high temperature 35 and high temperature second superheater inlet steam temperature calculator 36 is set to the high value, but the spray water amount is calculated by inputting this set value and the spray water temperature and steam flow rate, etc. Set the opening of the spray water control valve to control the water volume. The vapor mixing control is the same as in the embodiment shown in FIG.

[0029]

[Effects of the Invention] In combined cycle power generation equipment, it is necessary to control the steam temperature by limiting the rate of temperature rise on the steam turbine side due to the difference in starting characteristics between the gas turbine side and the steam turbine side. In that case, the heat transfer surface of the conventional superheater is divided, a desuperheater is installed in the middle of the connecting pipe that connects the two, and spray water is supplied to this desuperheater to control the steam temperature. The method may not be able to control the steam temperature to the set value of the main steam temperature. However, in the present invention, the steam temperature can be controlled without such a limitation. Therefore, there is an effect that the plant can be started by taking advantage of the quick starting characteristic of the gas turbine.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a main steam temperature control block diagram showing an embodiment of the present invention.

FIG. 3 is a main steam temperature control block diagram showing another embodiment of the present invention.

[Fig. 4] System diagram of a conventional example

FIG. 5 is a conventional steam temperature control block diagram.

[Explanation of symbols]

1 ... Low pressure water supply pipe 2 ... Low pressure coal economizer 3 ... High pressure water supply pump suction pipe 4 ... Low pressure connection pipe 5 ... Low pressure water supply control valve 6 ... High pressure water supply pump 7 ... High pressure water supply pipe 8 ... Low pressure steam drum 9 ... Low pressure evaporator 10 Low pressure steam connecting pipe 11 Low pressure superheater 12 High pressure economizer 13 High pressure connecting pipe 14 High pressure water supply control valve 15 High pressure steam drum 16 High pressure evaporator 17 High pressure steam connecting pipe 18 High pressure first superheater 19 ... High-pressure second superheater 20 ... High-pressure main steam pipe 21 ... First reheater 22 ... Second reheater 23 ... High-pressure main steam desuperheater 24 ... Dehumidified water supply pipe 25 ... High-pressure main steam temperature control spray Valve 26 ... Reheat steam desuperheater 27 ... Reheat steam temperature control valve 28 ... Low pressure coal economizer inlet feed water temperature control pipe 29 ... Low pressure feed water temperature control valve 30 ... Superheater bypass steam pipe 31 ... Main steam temperature control valve 32 … Main steam temperature controller 35… Second overheat Inlet steam lower limit function generator 36 ... High-pressure main steam temperature control spray valve opening calculator 37 ... Main steam temperature controller 38 ... Low value priority circuit 39 ... Differentiator 40 ... Main steam temperature controller 41 ... Second superheat Unit inlet temperature calculator 42 ... High price priority circuit 43 ... Dehumidifying spray water amount controller 44 ... Main steam temperature controller

Claims (4)

[Claims] 1. A steam drum that operates feed water at one or more pressures, a economizer that heats the feed water to the steam drum, an evaporator that circulates and heats boiler water to heat and evaporate, and steam generated in the steam drum. In an exhaust heat recovery boiler system that has a superheater that superheats and controls the main steam temperature to a temperature according to the purpose of use of steam, and divides the heat transfer surface of the superheater into multiple parts. Provided with a connecting pipe for connecting the heat transfer surface and a desuperheater, system equipment for adjusting and supplying spray water having appropriate conditions such as discharge of high pressure water supply pump, low temperature of superheater divided from high pressure steam drum Branched from the connecting pipe to the steam inlet of the side superheater or independent from the steam drum, adjust the saturated steam in the steam drum to the outlet pipe (main steam pipe) of the high temperature side superheater of the divided superheater The temperature of the main steam is reduced by mixing with the steam that has passed through Exhaust heat recovery boiler system configured to control the main steam temperature by adjusting the amount of spray water and the mixing amount of steam in the drum. 2. A main steam temperature control device using the exhaust heat recovery boiler system according to claim 1 by adjusting a spray water amount and a saturated steam mixture amount, wherein the spray water amount is a main steam temperature set value and a main steam temperature. The main steam temperature control device is characterized in that it is adjusted to reduce the deviation, and the saturated steam mixing amount is adjusted to decrease the differential value of the deviation between the main steam temperature set value and the main steam temperature. 3. The main steam temperature control device using the exhaust heat recovery boiler system according to claim 1 by adjusting the amount of spray water and adjusting the amount of saturated steam, the temperature of the high temperature side superheater inlet of the divided superheater is -Spray after mixing water-
Mix the steam at the high temperature side superheater and the steam in the steam drum by keeping the temperature above the saturation temperature of the steam pressure in the steam drum in the same part or in the steam drum upstream of the steam so that the water becomes completely steam. The main steam temperature control device is characterized in that it is configured to finally control the main steam temperature by. 4. The main steam temperature control device according to claim 3, wherein an output of a function generator for calculating a saturation temperature with respect to a high-pressure steam drum pressure and a divided low-temperature side superheater outlet or high-temperature side superheater inlet pressure of the superheater, Measure the high temperature side superheater inlet steam temperature by using the high value of the output of the calculator that calculates the high temperature side superheater inlet steam temperature using the main steam temperature set value, steam flow rate and heat transfer characteristics. Main steam temperature controller characterized by adjusting the amount of spray water in comparison with the value.