Boiler water recirculation system and method for preventing overheating of furnace water-cooled wall under low load

Abstract

The present invention discloses a boiler water recirculation system and method for preventing overheating of the furnace water wall under low load. The system includes a boiler water circulation pump, a steam-water separator, a main water storage tank, a water wall intermediate mixing header, a water wall lower header, and a economizer. The economizer, the water wall lower header, the water wall intermediate mixing header, and the steam-water separator are connected in sequence through pipelines. The economizer inlet pipeline of the economizer is connected to the feed water pipe, and the gas outlet of the steam-water separator is connected to the superheater; the liquid outlet of the steam-water separator, the main water storage tank, and the boiler water circulation pump are connected in sequence and connected to the economizer inlet pipeline; the water wall intermediate mixing header is connected to a bypass water storage tank through a bypass water delivery branch pipe, and the water outlet of the bypass water storage tank is connected to the inlet of the boiler water circulation pump. This system can avoid overheating of the water wall and large fluctuations in wall temperature caused by low working medium flow under low load, and alleviate problems such as transverse cracks.

Description

Technical Field

[0001] The present invention belongs to the technical field of equipment safety in coal-fired thermal power plants, and particularly relates to a boiler water recirculation system and method for preventing overheating of the furnace water wall under low load. Background Art

[0002] With the continuous increase in the proportion of new energy, coal-fired units participate in deep peak shaving, frequently raise and lower loads, the fluctuation frequency and amplitude of the working medium parameters in the water wall change greatly, the wall temperature deviation of the water wall in the same screen is large, generating large thermal stress. During the operation of multiple ultra (ultra)-critical once-through boilers, transverse cracks on the fire side of the water wall are caused by fatigue stress, and even leakage shutdown occurs, seriously threatening the safety and stability of the unit.

[0003] Under the low load condition of the boiler, the furnace flame fullness is poor, the working medium flow rate is low, the hydrodynamic characteristics become poor, and it is easy to occur overheating of the water wall and large wall temperature fluctuations. Especially when the once-through boiler changes from the wet state to the dry state, the overheating of the water wall and large wall temperature fluctuations are more prominent.

[0004] At present, the technology mainly reduces the superheat degree and modifies the throttling orifice ring at the water wall inlet. Affected by the combustion characteristics and load characteristics in the furnace, the high-temperature area is easily transferred to the unmodified area, and the problem of overheating and large fluctuations in the wall temperature cannot be effectively solved. Summary of the Invention

[0005] Aiming at the problems of overheating and large fluctuations in the wall temperature of the existing technology, the purpose of the present invention is to provide a boiler water recirculation system and method for preventing overheating of the furnace water wall under low load. This system can avoid overheating of the water wall and large fluctuations in the wall temperature caused by low working medium flow rate under low load, and alleviate problems such as transverse cracks in the water wall.

[0006] In order to achieve the above purpose, the technical solution adopted by the device of the present invention is as follows:

[0007] A boiler water recirculation system for preventing overheating of the furnace water wall under low load, comprising: a boiler water circulation pump, an economizer, a lower header of the water wall, an intermediate mixing header of the water wall, a steam-water separator, a bypass water delivery branch pipe, a bypass water storage tank, an economizer inlet pipe, and a main water storage tank;

[0008] The economizer, the lower header of the water wall, the intermediate mixing header of the water wall, and the steam-water separator are sequentially connected by pipelines. The economizer inlet pipe of the boiler water circulation pump is connected to the feed water pipe, and the gas outlet of the steam-water separator is connected to the superheater;

[0009] The liquid outlet of the steam-water separator is sequentially connected to the main water storage tank and the boiler water circulation pump; the water outlet of the boiler water circulation pump is connected to the economizer inlet pipe;

[0010] The intermediate mixing header of the water wall is connected with a bypass water supply branch pipe, the bypass water supply branch pipe is connected with a bypass water storage tank, and the outlet of the bypass water storage tank is connected with the inlet of the furnace circulating pump.

[0011] As a further improvement of the present invention, the intermediate mixing header of the water wall includes a front wall water wall intermediate mixing header, a left wall water wall intermediate mixing header, a rear wall water wall intermediate mixing header, and a right wall water wall intermediate mixing header. The inlets of the four bypass water supply branch pipes are respectively connected with the front wall water wall intermediate mixing header, the left wall water wall intermediate mixing header, the rear wall water wall intermediate mixing header, and the right wall water wall intermediate mixing header, and the outlets of the four bypass water supply branch pipes are connected with the bypass water storage tank.

[0012] As a further improvement of the present invention, flow meters and flow regulating valves are arranged on the four bypass water supply branch pipes.

[0013] As a further improvement of the present invention, the flow meter and one flow regulating valve are connected with a remote controller.

[0014] As a further improvement of the present invention, the bypass water storage tank is connected with the inlet of the furnace circulating pump through a bypass water supply pipeline.

[0015] As a further improvement of the present invention, a bypass stop valve is arranged on the bypass water supply pipeline.

[0016] As a further improvement of the present invention, a stop valve is arranged on the original pipeline between the steam-water separator and the furnace circulating pump.

[0017] As a further improvement of the present invention, a first stop valve is arranged on the outlet pipe of the furnace circulating pump.

[0018] A control method for a furnace water recirculation system for preventing overheating of the furnace water wall under low load includes the following steps:

[0019] The feed water enters the economizer, the lower header of the water wall, the intermediate mixing header of the water wall, and the steam-water separator in sequence through the economizer inlet pipeline; and enters the superheated steam heating system after passing through the steam-water separator;

[0020] The intermediate mixing header of the water wall also collects wet water through the bypass water supply branch pipe and enters the bypass water storage tank;

[0021] The wet water in the bypass water storage tank is pumped into the economizer inlet pipeline by the furnace circulating pump, the water temperature rises after being mixed with the feed water, and the heated mixed water enters the economizer and then enters the lower furnace water wall again after being heated by the economizer.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] A boiler water recirculation system for preventing overheating of the furnace water wall under low load according to the present invention is connected in sequence by a economizer, a lower header of the water wall, an intermediate mixing header of the water wall and a steam-water separator through pipelines. The economizer inlet pipeline of the economizer is connected to a feed water pipe, and the gas outlet of the steam-water separator is connected to a superheater; the liquid outlet of the steam-water separator, a main water storage tank and a boiler water circulation pump are connected in sequence and then connected to the economizer inlet pipeline; the intermediate mixing header of the water wall is connected to a bypass water storage tank through a bypass water conveying branch pipe, and the water outlet of the bypass water storage tank is connected to the inlet of the boiler water circulation pump. A water conveying pipeline is added between the intermediate mixing header of the water wall and the boiler water circulation pump to convey part of the wet state water in the intermediate header to the economizer inlet pipeline, mix it with the feed water and then enter the economizer, and after being heated by the economizer, enter the lower furnace water wall again, increasing the working medium flow rate of the lower furnace water wall, avoiding overheating of the water wall and large fluctuations in wall temperature caused by low working medium flow rate under low load, and alleviating problems such as transverse cracks. This system can avoid overheating of the water wall and large fluctuations in wall temperature caused by low working medium flow rate under low load, and alleviate problems such as transverse cracks. This system has a simple structure, can effectively increase the working medium flow rate of the lower furnace water wall, reduce the fluctuation range of the water wall wall temperature of a (ultra) supercritical once-through boiler under low load, and improve the safety and stability of the unit.

[0024] Furthermore, the present invention can increase the water temperature at the economizer inlet, reduce the extraction steam volume of the high-pressure heater, and improve the economy of the unit.

[0025] Furthermore, the present invention can increase the flue gas temperature at the economizer outlet, alleviate problems such as reduced activity of the denitration catalyst, low denitration efficiency and high ammonia escape caused by too low flue gas temperature under low load. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 FIG. is a schematic structural diagram of a boiler water recirculation system for preventing overheating of the lower furnace water wall under low load according to the present invention.

[0028] In the figure: 1 - furnace water circulation pump, 2 - front wall water wall intermediate mixing header, 3 - left wall water wall intermediate mixing header, 4 - rear wall water wall intermediate mixing header, 5 - right wall water wall intermediate mixing header, 6 - bypass water delivery branch pipe, 7 - flow meter, 8 - flow regulating valve, 9 - bypass water storage tank, 10 - bypass water delivery pipeline, 11 - bypass stop valve, 12 - economizer 18 inlet pipeline, 13 - first stop valve, 14 - second stop valve, 15 - main water storage tank, 16 - steam-water separator, 17 - water wall lower header, 18 - economizer. Detailed implementation manners

[0029] In order to make the objectives and technical solutions of the present invention clearer and easier to understand, the following further describes the present invention in detail with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more. In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0031] The following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments:

[0032] As Figure 1As shown in the figure, the present invention provides a boiler water recirculation system for preventing overheating of the furnace water wall under low load, which includes a boiler water circulation pump 1, a front wall water wall intermediate mixing header 2, a left wall water wall intermediate mixing header 3, a rear wall water wall intermediate mixing header 4, a right wall water wall intermediate mixing header 5, a bypass water delivery branch pipe 6, a flow meter 7, a flow regulating valve 8, a bypass water storage tank 9, a bypass water delivery pipeline 10, a bypass stop valve 11, a economizer inlet pipeline 12, a first stop valve 13, a second stop valve 14, and a main water storage tank 15.

[0033] The inlet of the boiler water circulation pump 1 is connected to the water wall intermediate mixing headers 2 / 3 / 4 / 5, and the outlet of the boiler water circulation pump is connected to the economizer inlet pipeline 12.

[0034] The connecting pipeline between the boiler water circulation pump 1 and the water wall intermediate mixing header is divided into four bypass water delivery branch pipes 6 and one bypass water delivery pipeline. The inlets of the four bypass water delivery branch pipes are respectively connected to the front wall water wall intermediate mixing header 2, the left wall water wall intermediate mixing header 3, the rear wall water wall intermediate mixing header 4, and the right wall water wall intermediate mixing header 5, and the outlets of the branch pipes are connected to the bypass water storage tank 9. The inlet of the bypass water delivery pipeline 10 is connected to the water storage tank 9, and the outlet of the bypass water delivery pipeline 10 is connected to the inlet of the boiler water circulation pump 1.

[0035] In the present invention, by adding a water delivery pipeline between the water wall intermediate mixing header and the boiler water circulation pump, part of the wet state water in the intermediate header is transported to the inlet pipeline of the economizer 18, mixed with the feed water and then enters the economizer 18, and after being heated by the economizer 18, it enters the lower furnace water wall again, increasing the working medium flow rate of the lower furnace water wall.

[0036] As a preferred embodiment, a flow meter 7 and a flow regulating valve 8 are installed on each of the four bypass water delivery branch pipes 6 to regulate the water flow rate from the water wall intermediate mixing headers of the four walls to the water storage tank, and a bypass stop valve 11 is installed on the main pipeline between the water storage tank and the boiler water circulation pump.

[0037] The present invention can also achieve remote automatic control. For example, the flow meter 7 and a flow regulating valve 8 can be connected to a remote controller to achieve remote monitoring and control.

[0038] A stop valve 14 is installed on the original pipeline between the steam-water separator 16 and the boiler water circulation pump to prevent the working medium in the separator from entering the boiler water circulation pump when the low load system is put into operation.

[0039] The outlet of the boiler water circulation pump 1 is connected to the economizer inlet pipeline 12 through a water delivery pipeline, introducing the wet state water in the water wall intermediate header into the economizer inlet pipeline 12. It can increase the water temperature at the inlet of the economizer, reduce the extraction steam volume of the high-pressure heater, and improve the economy of the unit. Further, it can increase the flue gas temperature at the outlet of the economizer, alleviating the problems of reduced activity of the denitration catalyst, low denitration efficiency, and high ammonia escape caused by too low flue gas temperature under low load.

[0040] The principle of the present invention is as follows: a water conveyance pipeline is added between the intermediate mixing header of the water-cooled wall and the furnace water circulation pump to convey part of the wet state water in the intermediate header to the inlet pipeline of the economizer 18, mix it with the feed water and then enter the economizer 18. After being heated by the economizer 18, it enters the lower furnace water-cooled wall again, increasing the working medium flow rate of the lower furnace water-cooled wall, avoiding overheating of the water-cooled wall and large fluctuations in wall temperature caused by low working medium flow rate at low load, and alleviating problems such as transverse cracks.

[0041] The present invention also provides a control method for a furnace water recirculation system to prevent overheating of the lower furnace water-cooled wall at low load, including the following steps:

[0042] The feed water sequentially enters the economizer 18, the lower header of the water-cooled wall 17, the intermediate mixing header of the water-cooled wall and the steam-water separator 16 through the economizer inlet pipeline 12; after passing through the steam-water separator 16, it enters the superheated steam heating system;

[0043] The intermediate mixing header of the water-cooled wall also collects wet state water through the bypass water conveyance branch pipe 6 and enters the bypass water storage tank 9;

[0044] The wet state water in the bypass water storage tank 9 is pumped into the economizer inlet pipeline 12 by the furnace water circulation pump 1, the water temperature rises after mixing with the feed water, and the heated mixed water enters the economizer 18 and then enters the lower furnace water-cooled wall again after being heated by the economizer 18.

[0045] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A boiler water recirculation system for preventing overheating of the furnace water wall under low load, characterized in that, Comprising: A furnace circulating pump, an economizer, a lower header of a water wall, an intermediate mixing header of a water wall, a steam-water separator, a bypass water conveyance branch pipe, a bypass water storage tank, an economizer inlet pipe, and a main water storage tank; The economizer, the lower header of the water wall, the intermediate mixing header of the water wall, and the steam-water separator are sequentially connected by pipelines. The economizer inlet pipe of the furnace circulating pump is connected to a feed water pipe, and the gas outlet of the steam-water separator is connected to a superheater; The liquid outlet of the steam-water separator is sequentially connected to the main water storage tank and the furnace circulating pump; the water outlet of the furnace circulating pump is connected to the economizer inlet pipe; The intermediate mixing header of the water wall is connected with a bypass water conveyance branch pipe. The bypass water conveyance branch pipe is connected with the bypass water storage tank, and the outlet of the bypass water storage tank is connected with the inlet of the furnace circulating pump; The intermediate mixing header of the water wall includes a front wall intermediate mixing header of the water wall, a left wall intermediate mixing header of the water wall, a rear wall intermediate mixing header of the water wall, and a right wall intermediate mixing header of the water wall. The inlets of the four bypass water conveyance branch pipes are respectively connected to the front wall intermediate mixing header of the water wall, the left wall intermediate mixing header of the water wall, the rear wall intermediate mixing header of the water wall, and the right wall intermediate mixing header of the water wall. The outlets of the four bypass water conveyance branch pipes are connected to the bypass water storage tank; Flow meters and flow regulating valves are arranged on the four bypass water conveyance branch pipes; The flow meter and one flow regulating valve are connected to a remote controller; The bypass water storage tank is connected to the inlet of the furnace circulating pump through a bypass water conveyance pipe; A bypass stop valve is arranged on the bypass water conveyance pipe; A stop valve is arranged on the original pipeline between the steam-water separator and the furnace circulating pump; A first stop valve is arranged on the outlet pipe of the furnace circulating pump.

2. The control method of a boiler water recirculation system for preventing overheating of the furnace water wall under low load according to claim 1, characterized in that, Including the following steps: The feed water enters the economizer, the lower header of the water wall, the intermediate mixing header of the water wall, and the steam-water separator in sequence through the economizer inlet pipe; and enters the superheated steam heating system after passing through the steam-water separator; The intermediate mixing header of the water wall also collects wet water through the bypass water conveyance branch pipe and enters the bypass water storage tank; The wet water in the bypass water storage tank is pumped into the economizer inlet pipe by the furnace circulating pump, the water temperature rises after being mixed with the feed water, and the heated mixed water enters the economizer and then enters the lower furnace water wall again after being heated by the economizer.

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