JPH05126301A - Mixed pressure type exhaust heat recovery boiler protection device - Google Patents

Abstract

(57) [Summary] [Purpose] Provide a minimum flow rate control method that can protect the high-pressure water supply pump regardless of the operating state of the plant, and a high-pressure water supply pump minimum flow rate control in the high-pressure water supply pump performing middle-stage water extraction. Integrate steaming prevention control of the economizer as one facility. [Structure] After the water extracted from the condenser by the condensate pump is sequentially supplied to the low-pressure economizer connected to the low-pressure steam drum, the high-pressure feed pump, and the high-pressure economizer connected to the high-pressure steam drum, In the protective device for the mixed pressure type exhaust heat recovery boiler, in which the feed water extracted from the intermediate stage of the high-pressure feed pump is mixed with the inlet feed water of the low-pressure economizer, the minimum flow rate is adjusted only for the high-pressure economizer with the highest feed water temperature. A valve is provided, and the minimum flow rate control valve is controlled by the difference between the suction flow rate of the high-pressure feed water and the feed water amount extracted from the intermediate stage of the high-pressure feed pump.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust heat recovery boiler protection device for a thermal power plant having a mixed pressure type exhaust heat recovery boiler, particularly during startup and low load operation.

[0002]

2. Description of the Related Art In recent thermal power plants, due to problems such as diversification of high-efficiency operation and operation and shortening start-up time,
Combined cycle power plants of the type having steam drums operating at more than one type of pressure are often employed.

That is, FIG. 6 is a schematic system diagram of a plant having a so-called mixed pressure type exhaust heat recovery boiler having a steam drum which operates at the above-mentioned two types of pressures, which is extracted from a condenser (not shown) by a condenser pump. The supplied water is supplied to the low-pressure economizer 2 via the low-pressure water supply pipe 1. A part of the feed water supplied to the low pressure economizer 2 and heated therein is supplied to a low pressure steam drum (not shown) via a low pressure connecting pipe 4 branched from a high pressure feed water pump suction pipe 3, and
The low-pressure feed water control valve 5 provided in the low-pressure communication pipe 4 controls the water level of the low-pressure steam drum to be constant.

On the other hand, the rest of the feed water flowing out from the low-pressure economizer 2 flows through the high-pressure feed pump suction pipe 3 and is boosted by the high-pressure feed pump 6, and then the high-pressure economizer 7 via the high-pressure feed pipe 7. Water is supplied to 8. The low-pressure economizer 2 and the high-pressure economizer 8 are arranged so as to be able to exchange heat with the exhaust gas of a gas turbine (not shown), and are heated by exchanging heat with the exhaust gas of the gas turbine with the high-pressure economizer 8. Water is supplied to a high-pressure steam drum (not shown) via the high-pressure connecting pipe 9.
In this case, the flow rate is controlled by the high pressure water supply control valve 10 provided in the high pressure communication pipe 9 so that the water level of the high pressure steam drum becomes constant.

A low-pressure feed water temperature control pipe 11 connected to the inlet of the low-pressure coal economizer 2 is branched from the middle paragraph of the high-pressure feed pump 6, and is extracted from the middle paragraph of the high-pressure feed pump 6. The opening of the extracted water is controlled by the inlet temperature of the low-pressure economizer 2, the low-pressure economizer inlet temperature control valve 1
The temperature of the feed water mixed with the feed water in the low pressure feed pipe 3 via 2 and flowing into the low pressure economizer 2 is kept constant.

By the way, as an operation protection device for the equipment constituting the above-mentioned system, the temperature of the feed water in the high-pressure feed pump 6 and each of the economizers 2, 8 depends on the internal pressure of each steam drum at that time. The condition of α ≧ (saturation temperature of each drum internal pressure) − (each coal economizer outlet water supply temperature) (1) so that it is kept below the saturation temperature and does not flush on the secondary side of each water supply control valve 5 and 10. Control to satisfy. Here, the value of α is generally given a certain value.

In order to prevent steaming at the outlet of the high-pressure economizer 8, the required flow rate is adjusted by the high-pressure economizer minimum flow control valve 14 provided in the high-pressure economizer dump pipe 13 so as to satisfy the above condition. Then, control is performed to drain a part of the water supply. As for steaming prevention at the outlet of the low-pressure economizer 2, the low-pressure economizer minimum flow rate control valve 16 provided in the low-pressure economizer dump pipe 15 is used as in the case of the high-pressure economizer 8. The required flow rate is adjusted and a part of the water supply is drained to the condenser. On the other hand, as for the minimum flow rate control of the high-pressure water supply pump 6, similar to a general thermal power plant, high-pressure water supply driven by a flow rate control signal based on the flow rate detected by the flow meter 17 provided in the high-pressure water supply pump suction pipe 3. The pump minimum flow rate control valve 18 controls the flow rate of the high-pressure water supply pump through the minimum flow pipe 19 to the condenser, and protects against the temperature rise of the water inside the pump and the reduction of the suction performance during the low water volume operation.

That is, in the combined cycle plant having the above-mentioned system, as described above, generally, (a) minimum flow control of the high-pressure feed pump (b) minimum flow control of the high-pressure economizer (c) low-pressure economizer The minimum flow rate control is configured as an independent control element. In this case, these control devices operate independently.

By the way, all such control devices are provided especially when the amount of water supplied to the steam drum at each pressure such as the low-pressure steam drum and the high-pressure steam drum at the time of start-up is small or very small. May work at the same time. That is, when the high-pressure water supply pump minimum flow rate control valve 18 is in operation, the amount of water supplied to the high-pressure water supply pump 6 is equal to the minimum flow rate in the low-pressure economizer 2, the high-pressure water supply pump suction pipe 3, and the high-pressure water supply pump 6. Is flowing. The amount of temperature rise in the low pressure economizer 2 at this flow rate is determined by the gas side temperature and the flow rate condition, and the outlet feedwater temperature of the low pressure economizer 2 is determined. At this time, if the condition shown by the equation (1) is satisfied, the low-pressure economizer minimum flow rate control valve 16 does not open, and therefore, there is no drainage to the condenser via the low-pressure economizer blow pipe 15. .. However, when the condition of the expression (1) is not satisfied, the low-pressure economizer minimum flow rate control valve 16 opens, and drainage to the condenser occurs via the low-pressure economizer blow pipe 15.

On the other hand, in this state, the feed water temperature at the outlet of the high-pressure coal economizer finally reaches the gas temperature, although it depends on the duration of the same operating state when there is no water feed to the high-pressure steam drum.

Generally, the gas inlet temperature of the high pressure economizer 8 is higher than the saturation temperature with respect to the pressure of the high pressure steam drum,
In the state of no water supply to the high-pressure steam drum, the condition of the formula (1) cannot be satisfied, and the high-pressure economizer minimum flow rate control valve 14 operates, and the water is discharged to the condenser via the high-pressure economizer blow pipe.

In this state, the high-pressure economizer minimum flow rate control valve 1
4 and the high-pressure coal economizer blow pipe 13, the high-pressure feed pump minimum flow rate control valve 18 is fully closed when the flow rate discharged to the condenser is higher than the minimum flow rate of the high-pressure water feed pump 6.
The drainage to the condenser via the high-pressure feed pump minimum flow pipe is also eliminated.

[0013]

However, in such a system, the high-pressure economizer minimum flow control valve 14 and the low-pressure economizer minimum flow control valve 1 according to the control signals of the respective control devices.
6. The operation of the high-pressure feed pump minimum flow rate control valve 18 may cause disturbance of the control system.

That is, the flow rate change of the high pressure economizer 8 by the constant temperature difference control of the saturation temperature and the feed water temperature with respect to the pressure of the high pressure steam drum by the high pressure economizer minimum flow rate control valve 14 is the discharge flow rate change of the high pressure water feed pump 6. Therefore, there is a problem that it affects the minimum flow rate control of the high-pressure feed water pump, and thus also controls the constant temperature difference between the saturation temperature and the feed water temperature with respect to the pressure of the low-pressure steam drum of the outlet feed water of the low-pressure coal economizer 2.
On the other hand, from the aspect of system equipment, it is not necessary to install these control devices individually if there is no significant difference in the value of the minimum flow rate of equipment that should secure the minimum flow rate arranged in series in this system. Absent.

Further, when the high-pressure water supply pump 6 has a structure having an intermediate stage water extraction, a problem may occur in controlling the minimum flow rate of the high-pressure water supply pump. That is, the main purpose of ensuring the pump minimum flow rate is for the work of the impeller after the middle stage extraction, and the stage extraction amount is large relative to the design flow rate of the pump,
Moreover, when the flow rate fluctuation is large, a problem occurs in the minimum flow rate control of the high pressure feed pump.

In other words, because of the operating characteristics of the plant, the discharge amount of the high-pressure water supply pump 6 may be zero, and in this case, it is necessary to secure the minimum flow rate for protecting the pump. However, the amount of hot water for low-pressure feed water temperature adjustment that is extracted from the middle stage of the high-pressure water supply pump 6 does not become zero in the entire operation area of the plant, and when this middle-stage water extraction amount is larger than the minimum flow rate of the high-pressure water supply pump 6. In the control based only on the flow rate measurement value of the high-pressure water supply pump suction flow meter, the minimum flow rate of the high-pressure water supply pump 6 cannot be secured.

Therefore, in such a case, in general,
It is conceivable that a flow meter is provided on the discharge side of the high-pressure water supply pump 6 and the high-pressure water supply pump minimum flow rate control valve 18 is operated based on the measured flow rate. However, in this case, in addition to the flow meter for controlling the water supply to the high-pressure steam drum, different flowmeters for different purposes are provided in the same pipeline, and a straight pipe length sufficient to install two flow nozzles is required. Physical problems such as difficulty in securing them also occur.

In view of the above points, the present invention simplifies the structure of the minimum flow rate control system, does not cause any disturbance in the control system of the minimum flow rate control valve, and supplies sufficiently high pressure water regardless of the operating state of the plant. An object of the present invention is to obtain a mixed pressure type exhaust heat recovery boiler protection device capable of protecting a pump and the like.

[0019]

According to the present invention, condensed water extracted from a condenser by a condensate pump is connected to a low pressure economizer connected to a low pressure steam drum, a high pressure feed pump, and a high pressure steam drum. In the protective device for the mixed pressure type exhaust heat recovery boiler, in which the supply water extracted from the intermediate stage of the high pressure water supply pump is mixed with the inlet supply water of the low pressure economizer, the supply water temperature is the highest. The minimum flow rate control valve is installed only at the outlet of the high pressure economizer, and the minimum flow rate control valve is controlled by the difference between the suction flow rate of the high pressure water supply pump and the water supply amount extracted from the intermediate stage of the high pressure water supply pump. It is characterized by.

[0020]

The feed water pumped up from the condenser by the condensate pump is partially supplied to the low pressure drum through the low pressure economizer, and the rest is supplied to the high pressure economizer by the high pressure water pump. The feed water heated by the high pressure economizer is supplied to the high pressure drum. On the other hand, part of the feed water is mixed with the inlet feed water of the low pressure economizer from the intermediate stage of the high pressure feed pump, and the inlet feed water temperature is adjusted.

By the way, when the water supply to the high pressure drum is stopped or becomes extremely small, the difference between the outlet water supply flow rate of the high pressure water supply pump, that is, the suction flow rate of the high pressure water supply pump and the water supply amount extracted from the intermediate stage of the high pressure water supply pump. Thus, the opening of the minimum flow rate control valve is controlled, and the required minimum flow rate of the high pressure economizer is secured. In this case, the flow rate of the low-pressure economizer is always higher than that of the high-pressure economizer by the hot water flow rate for temperature adjustment. Therefore, if this amount secures the minimum flow rate of the low-pressure economizer, the minimum flow rate of the system can be reduced simply by draining it to the condenser through the minimum flow control valve provided at the outlet of the high-pressure economizer. Can be secured.

[0022]

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

In FIG. 1, feed water extracted from a condenser (not shown) by a condensate pump is supplied to a low pressure economizer 2 via a low pressure water supply pipe 1. A part of the feed water supplied to the low pressure economizer 2 and heated therein is supplied to a low pressure steam drum (not shown) via a low pressure connecting pipe 4 branched from a high pressure feed water pump suction pipe 3, and The low-pressure feed water control valve 5 provided in the low-pressure communication pipe 4 controls the water level of the low-pressure steam drum to be constant.

On the other hand, the rest of the feed water flowing out of the low-pressure economizer 2 flows through the high-pressure feed pump suction pipe 3 and is boosted by the high-pressure feed pump 6, and then the high-pressure economizer 7 via the high-pressure feed pipe 7. Water is supplied to 8. The low-pressure economizer 2 and the high-pressure economizer 8 are arranged so as to be able to exchange heat with the exhaust gas of a gas turbine (not shown), and are heated by exchanging heat with the exhaust gas of the gas turbine with the high-pressure economizer 8. Water is supplied to a high-pressure steam drum (not shown) via the high-pressure connecting pipe 9.
In this case, the flow rate is controlled by the high pressure feed water control valve 10 provided in the high pressure communication pipe 9 so that the water level of the high pressure steam drum becomes constant.

A low-temperature feedwater temperature control pipe 11 connected to the inlet of the low-pressure coal economizer 2 is branched from the middle paragraph of the high-pressure water supply pump 6 and extracted from the middle paragraph of the high-pressure water supply pump 6. The opening of the extracted water is controlled by the inlet temperature of the low-pressure economizer 2, the low-pressure economizer inlet temperature control valve 1
The temperature of the feed water mixed with the feed water in the low pressure feed pipe 3 via 2 and flowing into the low pressure economizer 2 is kept constant.

Further, a high-pressure economizer dump pipe 13 is branched from the high-pressure connection pipe 9 from the upstream side of the high-pressure water supply control valve 10, and the high-pressure economizer dump pipe 13 has a minimum high-pressure economizer. A flow control valve 14 is provided. On the other hand, the suction side of the high-pressure water supply pump 6 is provided with a high-pressure water supply pump suction flow meter 17, and the low-pressure water supply temperature adjusting pipe 11 is provided with a temperature adjusting hot water flow meter 20.

Therefore, in such a system, the feed water temperature in the high-pressure feed water pump 6 and each of the economizers 2, 8 is kept lower than the saturation temperature for the internal pressure of each steam drum at that time, and each feed water control valve is controlled. The minimum flow rate of the high-pressure economizer to satisfy the condition of α ≧ (saturation temperature of each drum internal pressure)-(each economizer economizer outlet feed water temperature) so as not to flush (steam) on the secondary side of Nos. 5 and 10. Control valve 14
Is controlled, the required flow rate is adjusted, and a part of the water supply is discharged to the condenser via the high-pressure economizer dump pipe 13.

In this case, the system minimum flow rate setting value is shown in FIG.
It may be determined by the characteristics of the exhaust heat recovery boiler shown in, but the difference between the flow rate measured by the high-pressure water supply pump suction flow meter 17 and the flow rate measured by the temperature adjusting warm water flow meter 20, that is, the high-pressure water supply pump 6 The discharge flow rate controls the high pressure economizer minimum flow rate control valve 14. An example of this control is shown in FIG.

In this way, it is possible to suppress the temperature rise of the feed water in the high-pressure economizer 8, and to secure the feed water in which a predetermined temperature difference is maintained from the saturation temperature with respect to the pressure of the high-pressure steam drum, and moreover, from the outlet of the high-pressure economizer. Since it is the drainage of the feed water and the drainage from the outlet of the final heater, this drainage can reliably ensure a fixed flow rate for the entire system.

FIG. 4 is a view showing another embodiment of the present invention. Instead of the high pressure water supply pump 6 of the example shown in FIG. 1, a high pressure water booster pump 6a and a high pressure water supply pump 6b are used. The feed water for adjusting the low pressure feed water temperature is drawn from between the pumps 6a and 6b. Therefore, also in this case, the same operational effect as that shown in FIG. 1 can be obtained.

Regarding the flow rate control, considering the case where the set value of the minimum flow rate of the high pressure economizer is changed according to the load, as shown in FIG. 5, the high pressure water supply from the flow rate controller 21 is used. Minimum flow rate control signal of pump and flow rate controller 22
The minimum flow rate control signal of the high pressure economizer is applied to the low value priority circuit 23, and the low value signal of both of them (the signal with the larger flow rate) is prioritized to operate the high pressure economizer minimum flow control valve 14. It may be controlled.

[0032]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, a plurality of independently provided protection systems are branched from the portion where the supply water temperature of each equipment arranged in series becomes the highest, and the flow rate is branched. It is possible to protect equipment by ensuring a minimum flow rate by installing only one system that controls the flow rate and drains it to a condenser etc. It is possible to prevent the operation of the control system from disturbing other control systems. Moreover, even when using the high-pressure water supply pump that performs the middle-stage water injection, the discharge amount of the high-pressure water supply pump necessary for surely protecting the equipment can be calculated, and it is necessary to install a flow meter in the high-pressure water supply pipe. Instead, it can be inexpensive.

[Brief description of drawings]

FIG. 1 is a system diagram of a protective device for a mixed pressure type exhaust heat recovery boiler of the present invention.

FIG. 2 is a diagram showing an example of changes in the flow rate of the economizer and the value of α corresponding to the load of the plant.

FIG. 3 is a block diagram of minimum flow rate control according to the present invention.

FIG. 4 is a system diagram in another embodiment of the present invention.

FIG. 5 is a block diagram showing another embodiment of the minimum flow rate control.

FIG. 6 is a system diagram of a conventional mixed pressure type exhaust heat recovery boiler protection device.

[Explanation of symbols]

 1 Low-pressure water supply pipe 2 Low-pressure economizer 5 Low-pressure feedwater control valve 6 High-pressure water supply pump 8 High-pressure economizer 10 High-pressure feedwater control valve 11 Low-pressure feedwater temperature control pipe 12 Low-pressure economizer inlet temperature control valve 14 High-pressure economizer minimum Flow control valve 20 Hot water flow meter for temperature control

Claims (1)

[Claims] 1. Condensate extracted from a condenser by a condensate pump,
While supplying the low-pressure economizer connected to the low-pressure steam drum, the high-pressure water pump, and the high-pressure economizer connected to the high-pressure steam drum in sequence, the feed water extracted from the intermediate stage of the high-pressure water pump is supplied to the low-pressure economizer. In the protective device for the mixed pressure type exhaust heat recovery boiler which is designed to mix with the inlet water supply, the minimum flow rate control valve is installed only at the outlet of the high pressure economizer where the feed water temperature becomes the highest, and the suction flow rate of the high pressure water supply pump and the high pressure water supply pump A protective device for a mixed pressure type exhaust heat recovery boiler, characterized in that the minimum flow rate control valve is controlled according to a difference from the water supply amount extracted from the intermediate stage.