Anti-freezing control system and method for direct air-cooling unit

Abstract

The present application relates to a direct air cooling unit anti-freezing control system and method, and belongs to the field of air cooling units. The direct air cooling unit anti-freezing control system comprises a steam exhaust device, an air cooling island steam inlet butterfly valve, a distribution pipe, a vacuum extraction valve, a vacuum pump, a connecting pipeline, an air cooling island, a condensate water collection tank, condensate water temperature, steam exhaust temperature, steam exhaust pressure and condensate water collection tank temperature. The present application can accurately control the condensate water collection tank temperature of the condensate water collection tank, and achieve the purpose of air cooling island anti-freezing.

Description

Technical Field

[0001] This invention relates to a system and method, and more particularly to an anti-freezing control system and method for direct air-cooled units, which belongs to the field of air-cooled units. Background Technology

[0002] Exhaust steam pressure, as an important parameter of the cold end of thermal power generating units, plays a significant role in the safe and economical operation of the units. In northern my country, exhaust steam pressure control mainly adopts direct air-cooling systems, indirect air-cooling systems, and mechanical ventilation tower systems as the main technical means. During winter operation, due to the influence of environmental factors and unit load, the heat exchange tube bundles and water collection tanks are prone to freezing during exhaust steam pressure control. Severe freezing can lead to equipment damage and affect the safe and economical operation of the units.

[0003] Currently, in order to prevent equipment freezing, a series of antifreeze technologies are used, such as air-cooled island ACC control, warm-up heating, antifreeze protection, frost protection, and emergency water drainage. These technologies are all based on the abnormal steam and water temperature derived from exhaust pressure control, which leads to a series of technical measures, resulting in a large consumption of resources and increased antifreeze costs. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings in the prior art and to provide a direct air-cooled unit antifreeze control system and method with reasonable structural design, safety and reliability, and control method that meets the requirements, so as to achieve rapid and accurate control of condensate collection water temperature and achieve the purpose of antifreeze for direct air-cooled units.

[0005] The technical solution adopted by this invention to solve the above problems is as follows: A method for the anti-freezing control system of a direct air-cooled unit includes a direct air-cooling system. The direct air-cooling system includes an exhaust device, an air-cooled island inlet butterfly valve, a distribution pipe, a vacuum valve, a vacuum pump, connecting pipes, an air-cooled island, a condensate collection tank, a condensate temperature, an exhaust temperature, an exhaust pressure, and a condensate collection water temperature. A condensate temperature sensor is arranged inside the exhaust device. A distribution pipe is installed at the top of the air-cooled island, and a condensate collection tank is installed at the bottom of the air-cooled island. A condensate collection water temperature sensor is arranged inside the condensate collection tank. The condensate collection tank is connected to the exhaust device via a connecting pipe and extends into the exhaust device. The distribution pipe is connected to the air-cooled island via the connecting pipe. The island's inlet butterfly valve is connected to the exhaust device. The connecting pipes near the exhaust device are arranged to measure exhaust temperature and pressure. The counter-current tube bundle in the air-cooled island is first connected to a vacuum valve via connecting pipes, and then to a vacuum pump. The key feature is the following specific steps: A condensate temperature measuring point is set in the exhaust device to collect the condensate temperature in real time. The condensate temperature is used as a control point to control the condensate temperature in the exhaust device. Based on the relationship between condensate temperature and exhaust pressure, indirect control of the exhaust pressure is achieved. Direct control of the condensate temperature is achieved by changing the fan speed of the air-cooled island, and indirect control of the condensate collection water temperature is achieved.

[0006] Preferably, the exhaust pressure of the present invention is obtained by converting the condensate temperature into pressure using the "Water and Steam Properties Table" and is used instead of the exhaust pressure. P1 = exhaust pressure after condensate temperature conversion and P0 = exhaust pressure, i.e., P1 = P0.

[0007] The specific formula is as follows: P1 = F(x + a);

[0008] P1 = P0;

[0009] Where: P1 = condensate temperature conversion steam pressure;

[0010] x = condensate temperature;

[0011] a = constant, design value for condensate subcooling;

[0012] F is converted from temperature to pressure using the "Table of Properties of Water and Water Vapor";

[0013] P0 = Exhaust pressure.

[0014] Preferably, the condensate temperature and the condensate collection water temperature of the present invention are respectively set in the exhaust steam device and the condensate collection water tank, and are also located upstream and downstream of the connecting pipe between the exhaust steam device and the condensate collection water tank, respectively. The change trend of the condensate temperature is the same as the change trend of the condensate collection water temperature.

[0015] The condensate collection water temperature is obtained by calculation from the condensate temperature and is used to replace the condensate collection water temperature. Let t1 = condensate temperature obtained by calculation and t0 = condensate collection water temperature, that is, t1 = t0.

[0016] The specific formula is as follows: t1 = x + b;

[0017] Limf(t1) = t0;

[0018] t1 = t0;

[0019] Where: t1 = condensate collection water temperature after condensate temperature conversion;

[0020] x = condensate temperature;

[0021] b = constant, the design temperature drop value for the connecting pipe;

[0022] t0 = Temperature of condensate collection water.

[0023] Preferably, the present invention indirectly controls the exhaust steam pressure by directly controlling the condensate temperature.

[0024] Preferably, the present invention indirectly controls the temperature of the condensate collection water by directly controlling the temperature of the condensate.

[0025] Compared with the prior art, the present invention has the following advantages and effects: (1) The structure of the present application is reasonable, safe and reliable, and reduces the time cycle of condensate collection water temperature change based on the previous exhaust pressure control. By controlling the condensate temperature, the condensate collection water temperature control is realized, which directly shortens the collection and control cycle, making the condensate collection water temperature control more timely, accurate and stable. At the same time, it also reduces the trigger probability of various antifreeze protections of the direct air-cooled island, thereby achieving the purpose of antifreeze of the direct air-cooled unit; (2) Without considering equipment failure, the existing control mode can achieve the condensate subcooling to the design value. If the subcooling is abnormal, it can be analyzed directly from the perspective of equipment failure, narrowing the scope of fault analysis when the condensate subcooling is abnormal; (3) By setting different condensate temperature target values, more direct and accurate data support is provided for the optimal operation mode of the unit under different condensate temperature control modes. Attached Figure Description

[0026] Fig. 1 This is a schematic diagram of the direct air-cooled unit system structure according to an embodiment of the present invention.

[0027] Fig. 2 This is a curve showing the relationship between condensate temperature and exhaust steam pressure in an embodiment of the present invention.

[0028] In the diagram: Direct air-cooled system: exhaust device 1, air-cooled island inlet butterfly valve 2, distribution pipe 3, vacuum valve 4, vacuum pump 5, connecting pipe 6, air-cooled island 7, condensate collection tank 8, condensate temperature 9, exhaust temperature 10, exhaust pressure 11 and condensate collection temperature 12. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0030] Example

[0031] See Figs. 1-2 The anti-freeze control system for this direct air-cooled unit includes an exhaust device 1, an air-cooled island inlet butterfly valve 2, a distribution pipe 3, a vacuum valve 4, a vacuum pump 5, a connecting pipe 6, an air-cooled island 7, a condensate collection tank 8, a condensate temperature 9, an exhaust steam temperature 10, an exhaust steam pressure 11, and a condensate collection water temperature 12. The exhaust device 1 contains the condensate temperature 9. The air-cooled island 7 has a distribution pipe 3 at its top and a condensate collection tank 8 at its bottom. A condensate collection water temperature 12 is provided; the condensate collection water tank 8 is connected to the exhaust steam device 1 via a connecting pipe 6 and extends into the exhaust steam device 1; the distribution pipe 3 is first connected to the air-cooled island inlet butterfly valve 2 via a connecting pipe 6, and then connected to the exhaust steam device 1, with the exhaust steam temperature 10 and exhaust steam pressure 11 arranged on the side near the exhaust steam device 1; the counterflow tube bundle of the air-cooled island 7 is first connected to the vacuum valve 4 via a connecting pipe 6, and then connected to the vacuum pump 5.

[0032] In this embodiment, the exhaust pressure is obtained by converting the condensate temperature 9 to the pressure using the "Water and Steam Properties Table". This pressure is used to replace the exhaust pressure 11. P1 is set as the exhaust pressure after the condensate temperature 9 is converted, and P0 is set as the exhaust pressure 11, i.e., P1 = P0.

[0033] The specific formula is as follows: P1 = F(x + a)

[0034] P1 = P0

[0035] Where: P1 = condensate temperature; steam pressure after conversion.

[0036] x = condensate temperature;

[0037] a = constant, design value for condensate subcooling;

[0038] F is converted from temperature to pressure using the "Table of Properties of Water and Water Vapor";

[0039] P0 = Exhaust pressure 11.

[0040] In this embodiment, the condensate temperature 9 and the condensate collection temperature 12 are respectively located in the exhaust steam device 1 and the condensate collection tank 8. They are also located upstream and downstream of the connecting pipe 6 between the exhaust steam device 1 and the condensate collection tank 8, respectively. The variation trend of the condensate temperature 9 is the same as that of the condensate collection temperature 12. The condensate collection temperature is obtained by calculation from the condensate temperature 9 and replaces the condensate collection temperature 12. Let t1 = the temperature obtained by calculation from the condensate temperature 9 and t0 = the condensate collection temperature 12, that is, t1 = t0.

[0041] The specific formula is as follows: t1 = x + b;

[0042] Limf(t1) = t0;

[0043] t1 = t0;

[0044] Where: t1 = condensate temperature; condensate collection temperature after conversion;

[0045] x = condensate temperature;

[0046] b = constant, the design temperature drop value for connecting pipe 6;

[0047] t0 = condensate collection water temperature 12.

[0048] The process of the antifreeze control method for the direct air-cooled unit in this embodiment is as follows: A condensate temperature 9 measuring point is set in the exhaust device 1 to collect the condensate temperature in the exhaust device 1 in real time; the condensate temperature 9 is used as the control point to control the condensate temperature in the exhaust device 1, and the relationship between the condensate temperature 9 and the exhaust pressure 11 is converted to achieve indirect control of the exhaust pressure 11; by changing the fan speed of the air-cooled island 7, the condensate temperature 9 is directly controlled, and the condensate collection water temperature 12 is indirectly controlled.

[0049] In this embodiment, based on the relationship table between condensate temperature and exhaust pressure, the condensate temperature 9 is directly controlled within the range of 45-55℃, and the exhaust pressure 11 is indirectly controlled within the range of 9.6-15.7kPa, and the condensate collection water temperature 12 is indirectly controlled within the range of 45-55℃.

[0050] Comparison table of condensate temperature and exhaust pressure

[0051]

[0052] In this embodiment, the condensate temperature 9 is directly controlled at 50°C, which indirectly controls the exhaust steam pressure 11 at 12.3 kPa, and indirectly controls the condensate collection water temperature 12 at 50°C.

[0053] Control methods:

[0054] The antifreeze method for direct air-cooled units shall be carried out according to the following steps:

[0055] Step 1) control process: Before the program starts, the following conditions are judged: turbine operating status; air-cooled island inlet butterfly valve 2 open status; air-cooled island 7 operating status; vacuum valve 4 open status; vacuum pump 5 operating status; and the above conditions are judged to be met simultaneously.

[0056] Step 2) Control process: Program startup.

[0057] Step 3) control process: Data acquisition: Condensate temperature 9 is acquired; exhaust steam temperature 10 is acquired; exhaust steam pressure 11 is acquired; condensate collection water temperature is acquired; acquisition is continuous.

[0058] Step 4) control process: The operator sets the target temperature of condensate temperature 9 to 50℃.

[0059] Step 5) control process: The air-cooled island 7 adjusts the speed of the air-cooled fan through PID control.

[0060] Step 6) control process: Determine the condensate temperature 9. If the condensate temperature 9 is equal to the target value of 50℃, then execute step 7; otherwise, execute step 5.

[0061] Step 7) control process: The program control process ends.

[0062] Based on the above description, those skilled in the art are already able to implement it.

[0063] Furthermore, it should be noted that the specific embodiments described in this specification may differ in the shape and name of their components, etc. The above description is merely illustrative of the structure of the present invention. All equivalent or simple variations made based on the structure, features, and principles described in this patent concept are included within the protection scope of this patent. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to substitute them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, all of which should fall within the protection scope of this invention.

Claims

1. A method for controlling the anti-freezing system of a direct air-cooled unit, comprising a direct air-cooling system, the direct air-cooling system including an exhaust device, an air-cooled island inlet butterfly valve, a distribution pipe, a vacuum valve, a vacuum pump, connecting pipes, an air-cooled island, a condensate collection tank, condensate temperature, exhaust temperature, exhaust pressure, and condensate collection temperature. The exhaust device contains a condensate temperature sensor. A distribution pipe is installed at the top of the air-cooled island, and a condensate collection tank is installed at the bottom of the air-cooled island. The condensate collection tank contains a condensate temperature sensor. The condensate collection tank is connected to the exhaust device via a connecting pipe and extends into the exhaust device. The distribution pipe is first connected to the air-cooled island inlet butterfly valve via a connecting pipe, and then connected to the exhaust device. The connecting pipe contains the exhaust temperature sensor and exhaust pressure sensor on the side near the exhaust device. The counter-current pipe bundle in the air-cooled island is first connected to the vacuum valve via a connecting pipe, and then connected to the vacuum pump. The method is characterized by: The specific steps are as follows: Set a measuring point for condensate temperature in the exhaust steam device, collect the condensate temperature in the exhaust steam device in real time, use the condensate temperature as a control point to control the condensate temperature in the exhaust steam device, and calculate the relationship between condensate temperature and exhaust steam pressure to indirectly control the exhaust steam pressure; by changing the speed of the air-cooled island fan, the condensate temperature can be directly controlled, and the temperature of the condensate collection water can be indirectly controlled.

2. The method for anti-freezing control system of direct air-cooled unit according to claim 1, characterized in that: The exhaust pressure is obtained by converting the condensate temperature into pressure using the "Water and Steam Properties Table". This pressure is used to replace the exhaust pressure. P1 = exhaust pressure after condensate temperature conversion, and P0 = exhaust pressure. The specific formula is as follows: P1 = F(x + a); P1=P0; Where: x = condensate temperature; a = constant, design value for condensate subcooling; F is converted from temperature to pressure using the "Table of Properties of Water and Water Vapor".

3. The method for the anti-freeze control system of a direct air-cooled unit according to claim 1, characterized in that: The condensate temperature and the condensate collection water temperature are respectively set in the exhaust steam device and the condensate collection water tank. They are also located upstream and downstream of the connecting pipe between the exhaust steam device and the condensate collection water tank, respectively. The variation trend of the condensate temperature is the same as that of the condensate collection water temperature. The condensate collection water temperature is obtained by calculation from the condensate temperature and is used instead of the condensate collection water temperature. The specific formula is as follows: t1 = x + b; Limf(t1) = t0; t1=t0; Where: t1 = condensate collection water temperature after condensate temperature conversion; x = condensate temperature; b = constant, the design temperature drop value for the connecting pipe; t0 = Condensate collection water temperature.

4. The method for the anti-freeze control system of a direct air-cooled unit according to claim 1, characterized in that: By directly controlling the condensate temperature, the exhaust steam pressure can be indirectly controlled.

5. The method for the anti-freeze control system of a direct air-cooled unit according to claim 1, characterized in that: By directly controlling the temperature of the condensate, the temperature of the condensate collection water can be indirectly controlled.

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