Coal-fired power generation wet cooling unit cooling tower winter anti-freezing method and control strategy

Abstract

The application discloses a winter anti-freezing method and control strategy for a cooling tower of a coal-fired wet cooling unit, which is characterized by technical transformation of the original cooling tower in a cooling system, so that the cooling system of the wet cooling unit can adjust the heat exchange amount between circulating water and external air, and the purpose of winter anti-freezing of the cooling tower is achieved. The application mainly transforms the cooling tower and the connecting pipeline in the cold end system, divides the filler into two layers, and arranges a tubular water distribution system at the top of the two layers of fillers. The water distribution system can respectively distribute the circulating cooling water of the upper and lower layers of fillers. According to the environmental temperature, the distribution proportion of the circulating cooling water in the upper and lower layers of fillers is adjusted, so that the heat exchange amount between the circulating cooling water and the external air is adjusted. By using the system, the anti-freezing problem can be solved, and when the environmental temperature is relatively low, the distribution proportion of the circulating water in the lower water distribution system can be increased, the output of the circulating water pump can be reduced, and the economy of the unit is improved.

Description

Technical Field

[0001] This invention belongs to the field of energy conservation and consumption reduction technology for coal-fired power units, specifically relating to a method and control strategy for winter antifreeze of cooling towers in coal-fired wet-cooled power units. Background Technology

[0002] In cold northern regions, wet-cooled chilled units commonly face freezing problems in winter, especially those units that also provide winter heating and operate with zero output from the low-pressure cylinder. Currently, the main anti-freezing measures include installing wind curtains, baffles, or adding anti-freezing pipes. However, in severely cold regions like Northeast China, these methods are still insufficient to completely solve the freezing problem for wet-cooled units. Furthermore, because these anti-freezing measures neither effectively reduce the circulating water volume nor the head of the circulating water pumps, the energy consumption of the circulating water pumps remains high in winter. Using anti-freezing pipes alone results in insufficient water flow, making it difficult to adequately heat the cold air, leading to severe icing at the air inlet of the natural draft cooling tower in winter. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the above-mentioned traditional antifreeze technology and provide a new method and control strategy for winter antifreeze of cooling towers in coal-fired wet cooling units, so as to solve the problems of severe icing in natural ventilation cooling towers and excessive energy consumption of circulating water pumps in winter in the prior art.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method and control strategy for winter antifreeze of cooling tower of coal-fired wet cooling unit includes a cooling water inlet pipe, a main valve and a circulating water pump at the outlet of the inlet pipe, and the pipeline at the rear end of the circulating water pump is divided into two branches, namely the lower packing branch and the upper packing branch.

[0006] A first valve is installed on the lower packing branch, and the end of the lower packing branch is connected to the lower pipe-type water distribution system; a second valve is installed on the upper packing branch, and the end of the upper packing branch is connected to the upper pipe-type water distribution system.

[0007] The natural ventilation cooling tower is provided with upper and lower filling zones, and an unfilled zone is provided around the upper and lower filling zones.

[0008] A further improvement of the present invention is that:

[0009] Preferably, a main valve is provided at the outlet end of the cooling water inlet pipe.

[0010] Preferably, the circulating water pump is connected to a circulating water pump frequency converter.

[0011] Preferably, the upper and lower unfilled areas are irregularly shaped annular rings with irregular edges.

[0012] Preferably, whether the upper and lower unfilled areas are filled with filler can be determined based on the ambient temperature.

[0013] A method and control strategy for winter freeze protection of cooling towers in coal-fired wet-cooled power units includes the following four modes:

[0014] Mode 1: When the ambient temperature is below -25℃ or the low-pressure cylinder of the unit is running at zero output, the second valve is closed. The circulating water only passes through the lower packing branch to the lower pipe water distribution system for spraying. The circulating water only passes through the lower packing area for cooling. The area without packing is not filled with packing.

[0015] Mode 2: When the ambient temperature is below -10℃ and the unit is providing heating, the first valve is opened, and after a high-temperature water film forms in the packing, the second valve is opened. Part of the circulating water flows through the upper packing branch to the upper pipe-type water distribution system for spraying. After leaving the upper packing area, part of the circulating cooling water first contacts the lower pipe-type water distribution system for heat exchange, then drips into the lower packing area, merging with the already formed water film. As the ambient temperature changes, the valve opening is adjusted to raise the temperature of the upper circulating cooling water and lower circulating cooling water, regulating the heat exchange of the natural draft cooling tower, preventing freezing in the packing area, and leaving the unfilled areas unfilled.

[0016] Mode 3: When the ambient temperature is higher than 15℃, the first valve is closed, and the circulating water only passes through the upper packing branch to the upper pipe water distribution system for spraying. The circulating water passes through the upper packing area and the lower packing area in sequence for cooling, and the areas without packing are not filled with packing.

[0017] Mode 4: When the ambient temperature is higher than 30℃, the first valve is closed, and the circulating water only passes through the upper packing branch to the upper pipe water distribution system for spraying. The circulating water passes through the upper packing area and the lower packing area in sequence for cooling, and the areas without packing are filled with packing.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention discloses a method and control strategy for winter freeze protection of cooling towers in coal-fired wet-cooled power units. The method improves the structure of the natural draft cooling tower in the cooling system by dividing the packing layer into upper and lower layers, allowing the wet-cooled power unit's cooling system to offer multiple modes of operation and increasing the flexibility of heat exchange control. The invention primarily improves the natural draft cooling tower and its connecting pipes. Heat exchange can be controlled by altering the circulating water flow rate or by adjusting the ratio of circulating cooling water in the upper and lower packing layers. In winter, when there is a risk of freeze due to low temperatures, the ratio of circulating water in the lower packing layer can be increased to reduce heat exchange, while simultaneously reducing the head of the circulating water pump and lowering pump energy consumption. In summer, when temperatures are high, packing can be added to the unpacked area to increase heat exchange, and the ratio of circulating water in the upper packing layer can be increased until all circulating water is distributed in the upper packing layer to meet the unit's cooling requirements. This method not only solves the freeze protection problem but also provides more flexible heat exchange control during moderate to high ambient temperatures in spring and autumn, improving the unit's economy. In high-temperature summer environments, the increased volume of the packing area enhances the overall cooling capacity of the cooling system, improving overall cooling efficiency and effectively alleviating the problem of high back pressure in summer. The modification of the original unit mainly focuses on the cooling tower and its related piping, making the modification relatively simple and easy to implement.

[0020] Furthermore, a valve is installed before the circulating water pump to facilitate the start-up and shutdown of the pump.

[0021] Furthermore, the circulating water pump is connected to a circulating water pump frequency converter, which can control the changes in the circulating water pump flow rate.

[0022] Furthermore, the filled area is surrounded by an unfilled area, creating a ring-shaped structure inside the natural draft cooling tower due to the influence of the unfilled area. After removing the filler around the circumference of the cooling tower, the remaining water distribution system generates a large-area water curtain. This also heats the cold air entering the interior, reducing the risk of the natural draft cooling tower freezing in winter.

[0023] The present invention also discloses a winter antifreeze control strategy for cooling towers of coal-fired wet cooling units. This strategy determines the operating mode of the cooling unit under different operating conditions by analyzing the ambient temperature and the unit's operating mode, thereby improving the unit's economy and solving the problem of cooling tower antifreeze. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the system structure of the present invention.

[0025] Wherein: 1-Cooling water inlet pipe; 2-Main valve; 3-Circulating water pump; 4-Circulating water pump frequency converter; 5-Lower packing branch; 6-Upper packing branch; 7-First valve; 8-Second valve; 9-Upper unpacked area; 10-Upper pipe water distribution system; 11-Lower pipe water distribution system; 12-Lower unpacked area; 13-Upper packing area; 14-Lower packing area; 15-Natural draft cooling tower. Detailed Implementation

[0026] See Figure 1 This invention discloses a method and control strategy for winter antifreeze of cooling towers in coal-fired wet-cooled units, which is an invention that realizes flexible antifreeze of coal-fired wet-cooled units and regulation of cooling tower heat exchange.

[0027] Following the direction of the circulating water flow, the circulating water first passes through the main valve 2 and enters the circulating water pump 3, then flows along the main pipeline to two branch lines 5 and 6. The circulating water pump 3 is connected to a circulating water pump frequency converter 4. The lower packing branch line 5 is equipped with a first valve 7 and a lower pipe-type water distribution system 11, and the upper packing branch line 6 is equipped with a second valve 8 and an upper pipe-type water distribution system 10. The terminals of both branches are natural draft cooling towers 15. The natural draft cooling tower 15 is equipped with an upper packing area 13 and a lower packing area 14. The upper packing area 13 and the lower packing area 14 are filled with water-spraying packing throughout. Then, the outermost water-spraying packing is removed along the circumference of the tower, forming an annular unpacked area 9 and 12. This area can receive the annular water curtain formed by the upper water distribution systems 10 and 11. This water curtain has a high temperature, which can improve the antifreeze ability. The upper water curtain can fall into the lower packing layer 14 at a higher temperature, which improves the antifreeze ability of the lower packing layer 14 to a certain extent.

[0028] The working method and control strategy of this invention:

[0029] When the ambient temperature is below -25℃ or the unit's low-pressure cylinder is operating at zero output, the second valve is closed, and the circulating water only flows through the lower packing branch 5 to the lower pipe-type water distribution system 11 for spraying. The circulating water only passes through the lower packing area 14 for cooling, and the unpacked areas 9 and 12 are not filled with packing. Because the unpacked areas 9 and 12 are not filled with packing, and the circulating water only passes through the lower packing layer, the overall heat exchange of the circulating water is reduced, which can effectively prevent the packing layer from freezing.

[0030] When the ambient temperature is below -10℃ and the unit is supplying heat, the first valve 7 is opened, and after a high-temperature water film forms in the packing, the second valve 8 is opened. Part of the circulating water passes through the upper packing branch 6 and enters the upper pipe-type water distribution system 10 for spraying. After leaving the upper packing area 13, part of the circulating cooling water first contacts the lower pipe-type water distribution system 11 for heat exchange, and then drips into the lower packing area 14, merging with the formed water film. As the ambient temperature changes, the valve opening is adjusted to raise the temperature of the upper circulating cooling water and lower circulating cooling water, thus regulating the heat exchange of the natural draft cooling tower and preventing freezing in the packing area. The unpacked areas 9 and 12 are not filled with packing. This method increases the heat exchange of the cooling tower by increasing the circulating water distribution ratio in the upper packing branch 6. Simultaneously, when the circulating water drips into the lower packing layer 14, it contacts and exchanges heat with the lower circulating water, raising its temperature and preventing freezing due to the high heat exchange.

[0031] When the ambient temperature is above 25℃, the first valve 7 is closed. The circulating water then flows only through the upper packing branch 6 to the upper pipe-type water distribution system 10 for spraying. The circulating water is cooled sequentially through the upper packing area 13 and the lower packing area 14. Areas 9 and 12 without packing are left unfilled. Leaving packing at this time reduces construction work, avoids operational complexity, and lowers implementation costs. This operating mode is equivalent to that of a conventional wet-cooled chiller unit.

[0032] When the ambient temperature is above 30℃, the first valve 7 is closed, and the circulating water only flows through the upper packing branch 6 to the upper pipe-type water distribution system 10 for spraying. The circulating water passes sequentially through the upper packing area 13 and the lower packing area 14 for cooling, while the unpacked areas 9 and 12 are filled with packing. At this time, the ambient temperature is high, and the packing is used to increase the overall heat exchange of the cooling tower, reduce the back pressure of the unit, and improve the unit's economy.

[0033] The design concept of this invention:

[0034] This invention proposes a winter antifreeze method and control strategy. When the unit is operating at low load or with zero output from the low-pressure cylinder, and the demand for circulating water and heat exchange is low, the packing area of ​​the cooling tower is reduced, thereby reducing the heat exchange capacity of the cooling tower. This reduces the head of the circulating water pump while still meeting the unit's requirements, achieving an antifreeze effect. The design of a packing-free area is intended to create a high-temperature water curtain, improving the unit's antifreeze capability and versatility under extreme low-temperature conditions. This design allows for flexible control of the cooling tower's heat exchange capacity, significantly increasing the selection of operating modes and improving the unit's economic efficiency.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method and control strategy for winter antifreeze of cooling towers in coal-fired wet-cooled power generation units, characterized in that, It includes a cooling water inlet pipe (1), and the outlet end of the cooling water inlet pipe is equipped with a circulating water pump (3). The outlet end of the circulating water pump (3) is divided into two branches, namely the lower packing branch (5) and the upper packing branch (6). The lower packing branch (5) is equipped with a first valve (7), and the upper packing branch (6) is equipped with a second valve (8). The lower packing branch is connected to a lower pipe water distribution system (11), and the upper packing branch is connected to an upper pipe water distribution system (10). The natural ventilation cooling tower (15) has an upper filling area (13) and a non-filling area (9) around the upper filling area (13); the natural ventilation cooling tower (15) has a lower filling area (14) and a non-filling area (12) around the filling area (14).

2. The method for preventing freezing of a cooling tower in a coal-fired wet-cooled unit during winter, as described in claim 1, is characterized in that... A main valve (2) is provided at the rear end of the cooling water inlet pipe (1).

3. The method for preventing freezing of a cooling tower in a coal-fired wet-cooled unit during winter, as described in claim 1, is characterized in that... The circulating water pump (3) is connected to the circulating water pump frequency converter (4).

4. The method for winter antifreeze of a cooling tower in a coal-fired wet-cooled unit as described in claim 1, characterized in that, The unfilled regions (9) and (12) are irregularly shaped annular rings.

5. A method for winter freeze protection of a cooling tower in a coal-fired wet-cooled power unit as described in claim 1, characterized in that, The unfilled areas (9) and (12) can be filled with filler.

6. A method for preventing freezing of cooling towers in coal-fired wet-cooled power units during winter, characterized in that, Includes the following four modes: Mode 1: When the ambient temperature is below -25℃ or the low-pressure cylinder of the unit is running at zero output, the second valve (8) is closed. The circulating water only passes through the lower packing branch (5) and comes to the lower pipe water distribution system (11) for spraying. The circulating water only passes through the lower packing area (14) for cooling. The unfilled areas (9) and (12) are not filled with packing. Mode 2: When the ambient temperature is below -10℃ and the unit is providing heating, the first valve (7) is opened first, and the second valve (8) is opened after the packing forms a water film with a higher temperature. Some circulating water passes through the upper packing branch (6) and comes to the upper pipe water distribution system (10) for spraying. After leaving the upper packing area (13), some circulating cooling water first comes into contact with the lower pipe water distribution system (11) for heat exchange, and then drips into the lower packing area (14) to merge with the water film that has been formed. As the ambient temperature changes, the valve opening is adjusted to achieve the heating of the upper circulating cooling water and the cooling of the lower circulating cooling water, thereby regulating the heat exchange of the natural ventilation cooling tower and preventing freezing in the packing area. The unpacked areas (9) and (12) are not filled with packing. Mode 3: When the ambient temperature is higher than 15℃, the first valve (7) is closed, and the circulating water only passes through the upper packing branch (6) to the upper pipe water distribution system (10) for spraying. The circulating water passes through the upper packing area (13) and the lower packing area (14) in sequence for cooling. The unfilled areas (9) and (12) are not filled with packing. Mode 4: When the ambient temperature is higher than 30℃, the first valve (7) is closed, and the circulating water only passes through the upper packing branch (6) to the upper pipe water distribution system (10) for spraying. The circulating water passes through the upper packing area (13) and the lower packing area (14) in sequence for cooling, and the unfilled areas (9) and (12) are filled with packing.

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