Power plant boiler water supply system

Abstract

The utility model belongs to the technical field of power plant auxiliary machine operation systems, and particularly discloses a power plant boiler water supply system. A water supply recirculation bypass is arranged in front of a water supply pump outlet check valve and connected to a deaerator water tank, the recirculation bypass is formed by connecting two branches in parallel, each branch is provided with a flow regulating valve, and third shut-off valves are arranged in front of and behind the flow regulating valves. Wherein one branch controls the corresponding flow regulating valve according to a flow signal of the water feeding pump so as to ensure the minimum flow required by the safe operation of the water feeding pump when the water feeding pump is started and the load is low. And the other branch is used as a standby flow adjusting means in a low-load working area where surge easily occurs in the pump set. The two sets of recirculation bypasses can meet the operation requirements of the water supply system under the condition from the minimum load to the maximum load of the unit, so that the unit can safely and stably operate under all load working conditions. And the method is suitable for being popularized in areas with unstable electrical loads or power plant units for peak regulation.

Description

Technical Field

[0001] The utility model belongs to the technical field of auxiliary machine operation systems of power plants, and specifically discloses a boiler water supply system of a power plant. Background Art

[0002] In recent years, the scale of new energy power generation in the form of photovoltaics, wind power, etc. installed and put into operation in my country has been increasing year by year, and the growth rate has far exceeded that of traditional thermal power generation. The proportion of new energy power generation in total installed capacity has continued to rise. New energy power generation has great intermittency and volatility, and its unstable output will have a huge impact on the power system. In addition, the cost of energy storage is relatively high at this stage, and the scale and efficiency of energy storage are not ideal, which makes it difficult to meet the goal of peak shaving and valley filling at the power grid end. In order to reduce the waste and loss of electricity, thermal power plants are increasingly used for peak regulation, and it is necessary to adjust the power generation in a relatively short period of time to adapt to unstable market demand.

[0003] The feedwater system is an important steam-water system in a thermal power plant. The stability of its operation directly affects the safety and economy of the boiler and the entire unit, and is related to the safety and stability of the entire power plant. When a thermal power plant participates in deep peak regulation, in some cases, the output power of the power plant needs to be reduced to below 50% THA or even 20% THA in a short period of time, and the output flow of the feedwater system fluctuates significantly. If the adjustment plan is improper and the flow of the feedwater pump is too small, the temperature of the water flow at the pump outlet will rise sharply, which may cause cavitation and endanger the safe and stable operation of the feedwater pump and the entire unit. Therefore, it is necessary to propose a response plan for the flow fluctuation of the feedwater pump under partial load conditions, so as to improve the stability of the operation of the feedwater pump and the feedwater system under the demand of flow fluctuation. Utility Model Content

[0004] In order to solve the technical problems listed in the background technology, the utility model provides a boiler water supply system for a power plant. The specific technical solution is as follows:

[0005] A boiler water supply system for a power plant comprises a water supply main line and a recirculation bypass connected in parallel with the water supply main line, wherein the water supply main line comprises a low-pressure water supply system, a medium-pressure water supply system and a high-pressure water supply system which are sequentially connected in the direction of water flow, and two ends of the recirculation bypass are respectively connected with the low-pressure water supply system and the high-pressure water supply system; the low-pressure water supply system comprises a deaerator water tank and a low-pressure water supply pipeline which are sequentially connected in the direction of water flow; the medium-pressure water supply system comprises a pre-pump and a medium-pressure water supply pipeline which are sequentially connected in the direction of water flow; the high-pressure water supply system comprises a water supply pump and a high-pressure water supply pipeline which are sequentially connected in the direction of water flow, and the end of the high-pressure water supply pipeline is connected to the inlet of a boiler economizer header; the output shaft of a feed pump turbine is connected to one end of a rotating shaft of a feed pump via a coupling, and the other end of the rotating shaft of the feed pump is connected to the rotating shaft of a pre-pump via a gear box.

[0006] The function of the pre-pump is to increase the pressure at the inlet of the feed pump to meet the necessary cavitation margin of the feed pump. This design allows the pre-pump to be coaxially driven by the feed pump turbine of the feed pump through the reducer, so that the operating change trends of the feed pump and the pre-pump are consistent, which is easier to control.

[0007] Preferably, the water supply system also includes a controller, a flow meter, a measuring nozzle and a flow regulating valve. The measuring nozzle is installed on the pipe wall of the medium-pressure water supply pipeline and is connected to the flow meter. The flow regulating valve is installed on the recirculation bypass. The controller is electrically connected to the flow meter and the flow regulating valve respectively.

[0008] In this way, the water supply flow in the system can be measured in real time and the data can be transmitted to the controller, which then controls the flow control valve to achieve water supply flow regulation by controlling the flow of the recirculation bypass.

[0009] Preferably, the low-pressure water supply pipeline is built with two sets of coarse filters arranged in parallel, and a first shut-off valve is provided on the pipeline before and after each set of coarse filters; a fine filter is provided at the inlet of the water supply pump.

[0010] The first shut-off valve can be controlled electrically, either individually or by connecting to a controller for centralized control of opening and closing. Two sets of coarse filter and first shut-off valve are provided, one for operation and one for backup, which is more reliable.

[0011] Preferably, a check valve and a second shut-off valve are arranged on the high-pressure water supply pipeline in sequence according to the water flow direction, one end of the recycling bypass is connected to the high-pressure water supply pipeline at the inlet of the check valve, and the other end is connected to the water inlet of the deaerator water tank.

[0012] Preferably, the recirculation bypass includes two sets of flow regulating valves connected in parallel through pipelines, and a third shut-off valve is provided on the pipelines before and after the flow regulating valves.

[0013] In the above technical solution, the exhaust steam of the high-pressure cylinder of the main steam turbine is used as the steam source for the normal operation of the feedwater pump steam turbine, and the auxiliary steam is used as the backup steam source during commissioning, startup and low load. The high and low pressure steam sources of the feedwater pump steam turbine can be switched automatically. When the load of the main steam turbine is as low as 30% or below, and the pressure and flow of the low-temperature reheat steam are insufficient to drive the feedwater pump, the auxiliary steam is automatically put into use to supplement the insufficient steam source energy.

[0014] In the above technical solution, the two sets of valve groups involved in the recirculation bypass are independent of each other. One set of flow control valves receives flow data from the flow measurement nozzle of the medium-pressure water supply pipeline. When the output flow of the water supply pump is lower than 30% of the rated flow, the flow control valve automatically opens to divert the output flow of the water supply pump to the deaerator water tank. The recirculation bypass flow is adjusted according to the main pipeline to increase the actual flow of water supply and prevent cavitation of the water supply pump. The other set of flow control valves arranged in parallel is used as a backup flow control means and is started in the working section where surge is prone to occur, such as low load of the water supply pump group.

[0015] Among them, the flow regulating valve can be pneumatically operated, and the third shut-off valve can be electric, which can effectively avoid the situation where the recirculation cannot proceed smoothly.

[0016] In the above technical solution, since the feed water may be vaporized after passing through the flow regulating valve and gas-liquid two-phase flow may occur, the flow regulating valve should be arranged close to the deaerator water tank.

[0017] Compared with the prior art, the utility model has the following advantages:

[0018] The utility model provides a water recirculation bypass connected to the deaerator water tank in front of the non-return valve at the outlet of the water feed pump. The recirculation bypass is formed by two branches connected in parallel. A flow regulating valve is installed on each branch. A third shut-off valve is provided before and after the flow regulating valve. One of the branches controls the corresponding flow regulating valve according to the flow signal of the water feed pump to ensure the minimum flow required for the safe operation of the water feed pump when it is started and at low load. The other branch serves as a backup flow regulating means in the working area where the pump unit is prone to surge at low load. In this way, the operating requirements of the water feed system under the conditions of minimum load to maximum load of the unit can be met, so that the unit can operate safely and stably under all load conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of a boiler water supply system for a power plant in an embodiment of the utility model;

[0020] Among them, 10-low-pressure water supply system, 11-low-pressure water supply pipeline, 12-coarse filter, 13-first shut-off valve;

[0021] 20-medium pressure water supply system, 21-medium pressure water supply pipeline, 22-flow measurement nozzle, 23-fine filter;

[0022] 30-high-pressure water supply system, 31-high-pressure water supply pipeline, 32-check valve, 33-second shut-off valve;

[0023] 40 - recirculation bypass, 41 - recirculation pipeline, 42 - flow control valve, 43 - third shut-off valve. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model is described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on this embodiment, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0025] Referring to the attached drawings, it can be seen that a specific implementation of a boiler water feed system of a power plant includes a low-pressure water feed system 10 , a medium-pressure water feed system 20 , a high-pressure water feed system 30 and a recirculation bypass 40 .

[0026] The low-pressure water supply system 10 includes a deaerator water tank, a low-pressure water supply pipeline 11, a coarse filter 12 and a first shut-off valve 13; there are two sets of coarse filter 12, one for operation and one for backup, and the first shut-off valve 13 is provided before and after the coarse filter 12.

[0027] The medium-pressure water supply system 20 includes a pre-pump, a medium-pressure water supply pipeline 21 , a flow measurement nozzle 22 (including a flow meter and a measurement nozzle) and a fine filter 23 .

[0028] The flow measurement nozzle 22 measures the water flow in real time and transmits the data to the regulating valve.

[0029] The high-pressure water supply system 30 includes a water supply pump, a high-pressure water supply pipeline 31 , a check valve 32 and a second shut-off valve 33 .

[0030] The recirculation bypass 40 includes a recirculation pipeline 41, a flow regulating valve 42 and a third shut-off valve 43, which are connected from the outlet of the water pump to the check valve 32 and to the water inlet of the deaerator water tank; the recirculation pipeline 41 is formed by two branches connected in parallel. A flow regulating valve 42 is provided on each branch, and a third shut-off valve 43 is provided before and after the flow regulating valve 42. The flow regulating valve 42 receives the flow signal from the flow measuring nozzle 22, controls the flow of the recirculation pipeline 41, and ensures the safe operation of the water supply system.

[0031] Example 1

[0032] like Figure 1 As shown, when the unit is operating normally or the load is higher than 30% THA, the feed water pump flow rate is always higher than the minimum allowable flow rate (30% THA). The recirculation line 41 is closed, the feed water flows out from the deaerator water tank, enters the pre-pump after being filtered by the coarse filter 12, enters the feed water pump after being filtered by the fine filter 23, and flows into the boiler economizer through the high-pressure feed water pipeline 31. The flow measurement nozzle 22 after the pre-pump measures the feed water flow rate in real time.

[0033] Example 2

[0034] like Figure 1As shown, during the start-up phase of the water feed pump or when the unit participates in deep peak regulation or a unit failure occurs, the flow of the water feed pump fluctuates greatly, and the water feed flow is lower than the allowable minimum flow (30% THA) for a short period of time. The flow regulating valve 42 receives a signal from the flow measuring nozzle 22, automatically opens the recirculation pipeline 41, and increases the water feed flow to ensure that the actual water feed flow is not lower than the minimum flow required for the safe operation of the water feed pump. The recirculation pipeline flow is adjusted according to the main pipeline, so that the water supply system and the entire unit can operate safely and stably.

[0035] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A power plant boiler water supply system, characterized in that: It includes a water supply main line and a recirculation bypass connected in parallel with the water supply main line, the water supply main line includes a low-pressure water supply system, a medium-pressure water supply system and a high-pressure water supply system which are connected in sequence according to the water flow direction, and both ends of the recirculation bypass are connected to the low-pressure water supply system and the high-pressure water supply system respectively; the low-pressure water supply system includes a deaerator water tank and a low-pressure water supply pipeline which are connected in sequence according to the water flow direction; the medium-pressure water supply system includes a pre-pump and a medium-pressure water supply pipeline which are connected in sequence according to the water flow direction; the high-pressure water supply system includes a water supply pump and a high-pressure water supply pipeline which are connected in sequence according to the water flow direction, and the end of the high-pressure water supply pipeline is connected to the inlet of the boiler economizer header; the output shaft of the feed pump turbine is connected to one end of the feed pump rotating shaft through a coupling, and the other end of the feed pump rotating shaft is connected to the pre-pump rotating shaft through a gear box.

2. A power plant boiler water supply system according to claim 1, characterized in that: It also includes a controller, a flow meter, a measuring nozzle and a flow regulating valve. The measuring nozzle is installed on the wall of the medium-pressure water supply pipeline and is connected to the flow meter. The flow regulating valve is installed on the recirculation bypass. The controller is electrically connected to the flow meter and the flow regulating valve respectively.

3. A power plant boiler water supply system according to claim 2, characterized in that: The low-pressure water supply pipeline is equipped with two sets of coarse filters arranged in parallel, and a first shut-off valve is provided on the pipeline before and after each set of coarse filters; a fine filter is provided at the inlet of the water supply pump.

4. A power plant boiler water supply system according to claim 3, characterized in that: A check valve and a second shut-off valve are arranged on the high-pressure water supply pipeline in sequence according to the water flow direction. One end of the recirculation bypass is connected to the high-pressure water supply pipeline at the inlet of the check valve, and the other end is connected to the water inlet of the deaerator water tank.

5. A power plant boiler water supply system according to claim 4, characterized in that: The recirculation bypass includes two sets of flow regulating valves connected in parallel through pipelines, and a third shut-off valve is arranged on the pipelines before and after the flow regulating valves.

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