Method for controlling start and stop of cooling fan of air-cooled screw air compressor

Abstract

The invention discloses a method for controlling start and stop of a cooling fan of an air-cooled screw air compressor, which can ensure the stop temperature of the cooling fan, and can control the start and stop of the cooling fan according to the environment temperature and relative humidity of a client use site and the use pressure of the client rear end by using various data detected by a sensor. By utilizing the Antoine equation, the equation of the air water vapor partial pressure under the relative humidity working condition and the conversion formula of the Antoine equation, the pressure dew point value of the compressed air under the current exhaust pressure state can be calculated in real time, and the start-stop temperature of the cooling fan can be controlled in real time according to the real-time pressure dew point value, so that the cooling effect is improved. Therefore, the lubricating oil is in an optimal working temperature interval, the service life of the lubricating oil is prolonged, and more reliable operation of the screw air compressor is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of air-cooled screw air compressors, and in particular to a control method for starting and stopping a cooling fan of an air-cooled screw air compressor. Background Art

[0002] At present, air-cooled screw air compressors are usually started and stopped to control the exhaust temperature of the screw air compressor and avoid excessive cooling to reach the pressure dew point of the compressed air, which causes liquid water in the compressed air to precipitate into the lubricant and cause emulsification of the lubricant oil. That is, when the temperature sensor detects that the exhaust temperature exceeds a certain set value, the cooling fan is started to allow the cooling air to flow through the outer fin channel of the heat exchanger to exchange heat with the lubricant oil of the compressor, thereby reducing the exhaust temperature of the screw air compressor and avoiding the service life being affected by excessively high lubricant oil temperature; when the exhaust temperature detected by the temperature sensor is lower than a certain set value, the cooling fan is stopped, and no cooling air flows through the outer fin channel of the heat exchanger to exchange heat with the lubricant oil of the compressor, thereby increasing the exhaust temperature of the screw air compressor and avoiding the temperature being lower than the pressure dew point of the compressed air, causing liquid water in the compressed air to precipitate into the lubricant oil, causing emulsification of the lubricant oil and causing lubrication failure.

[0003] The current start-stop control method for the cooling fan of an air-cooled screw air compressor only presets the start-stop temperature value of the fan. The actual start-stop temperature value of the fan is fixed at 75°C for stop and 85°C for start. The start-stop temperature difference of the fan is 10°C to avoid the fan starting and stopping too frequently, thereby damaging the cooling fan. The temperature setting value recommended by the manufacturer is a fixed value, which does not take into account the impact of real-time changes in ambient temperature, relative air humidity and the use pressure of the customer's back end on this temperature. The environment in which the screw air compressor is used varies greatly. When used in some high-humidity and high-temperature environments, under the same working pressure state, the dew point temperature of the compressed air is higher, and the exhaust temperature will be lower than the pressure dew point temperature, causing liquid water to precipitate from the compressed air, resulting in emulsification of the lubricating oil. When used in some low-temperature and dry environments, under the same working pressure state, the dew point temperature of the compressed air is lower, and the exhaust temperature is still running at a relatively high state. Long-term high temperature is bound to affect the service life of the lubricating oil.

[0004] The difficulty of solving the above problems and defects is: the exhaust temperature of the screw air compressor must meet a temperature higher than the air pressure dew point value to avoid liquid water precipitation into the lubricating oil and cause the lubricating oil emulsification, and to avoid long-term high temperature, which is easy to cause the lubricating oil to carbonize and coke, affecting the service life of the lubricating oil. The air pressure dew point value is not a fixed temperature. It will change with the changes in the ambient temperature, the relative humidity of the ambient air and the exhaust pressure of the screw air compressor. In the high humidity and high heat summer, the air pressure dew point value is high, and in the dry and low temperature winter, the air pressure dew point value is low. The start and stop temperature of the cooling fan of the air-cooled screw air compressor is currently a fixed value, which can only cover a part of the working conditions that are consistent with the set temperature value. When it exceeds the working conditions, it is easy to cause the above-mentioned problems and affect the normal use of the screw air compressor.

[0005] Therefore, it is necessary to develop a control method for starting and stopping the cooling fan of an air-cooled screw air compressor to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to design a control method for starting and stopping the cooling fan of an air-cooled screw air compressor in order to solve the above-mentioned problem.

[0007] The present invention achieves the above-mentioned purpose through the following technical solutions: A method for controlling the start and stop of a cooling fan of an air-cooled screw air compressor comprises the following steps: Step 1: Detect the suction temperature T1 and relative humidity RH of the air-cooled screw air compressor suction port; detect the exhaust temperature T2 of the air-cooled screw air compressor exhaust port; detect the air supply pressure P1 of the air supply port of the air-cooled screw air compressor; Step 2: Through the PLC controller, according to the suction temperature T1, use the Antoine equation P=10^((AB) / (T+C)) / 101325*760 / 100000, where A, B, and C are corresponding constants, and substitute the suction temperature T1 to calculate the saturated water vapor pressure value P of the air at the suction port of the screw compressor; Step 3: Through the PLC controller, using the formula Ps=P*RH, according to the detected relative humidity RH, calculate the water vapor partial pressure value Ps of the air at the corresponding humidity; Step 4: Through the PLC controller, using the transformation form of the Antoine equation, T=B / (A-lg((P1+1)*Ps*100000*760 / 101325))-C, calculate the pressure dew point value T3 of the air under the exhaust pressure state of the air-cooled screw air compressor based on the air supply pressure P1 and the water vapor partial pressure Ps of the air under relative humidity; Step 5: According to the calculated pressure dew point value T3, set the stop temperature of the cooling fan to T4, T4=T3+5℃, and the start temperature of the cooling fan to T5=T4+10℃; Step 6: Use the exhaust temperature T2 to compare with T4 and T5 respectively. If T2≤T4, the cooling fan is controlled to stop running; if T2≥T5, the cooling fan is controlled to start.

[0008] The beneficial effects of the present invention are: The control method of the present application can ensure the stop temperature of the cooling fan. According to the ambient temperature and relative humidity at the customer's site and the operating pressure at the customer's back end, various data detected by sensors, the Antoine equation, the equation for the air water vapor pressure under relative humidity conditions and the conversion formula of the Antoine equation can be used to calculate the pressure dew point value of the compressed air under the current exhaust pressure state in real time. Based on this real-time pressure dew point value, the start and stop temperatures of the cooling fan can be controlled in real time, thereby ensuring that the lubricating oil is in the optimal operating temperature range, increasing the service life of the lubricating oil, and ensuring more reliable operation of the screw air compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a flow chart of the present invention; Figure 2 Schematic diagram of the installation location of each sensor.

[0010] Explanation of the reference numerals: 1-air filter assembly; 2-intake valve; 3-compressor; 4-motor; 5-inverter; 6-oil-gas separation tank; 7-oil separator core; 8-aftercooler; 9-oil cooler; 10-oil filter; 11-PLC controller; 12-first temperature sensor; 13-humidity sensor; 14-second temperature sensor; 15-pressure sensor. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0012] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0014] In the description of the present invention, it should be understood that the terms "upper", "lower", "inside", "outside", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the product of the invention is usually placed when in use, or are directions or positional relationships commonly understood by those skilled in the art. These directions or positional relationships are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0015] Furthermore, the terms “first”, “second”, etc. are merely used for distinguishing descriptions and should not be understood as indicating or implying relative importance.

[0016] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms such as "setting" and "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0017] To solve the technical problem, it is necessary to set the start and stop temperature of the cooling fan to a variable value, and to make real-time calculations and judgments based on the ambient temperature, relative humidity and pressure conditions used, so that the start and stop temperature of the cooling fan can automatically change according to the actual ambient temperature, relative humidity and pressure conditions of the air compressor to control the start and stop of the cooling fan. Based on this, we propose the following embodiments.

[0018] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings.

[0019] like Figure 1 and 2 As shown, a method for controlling the start and stop of a cooling fan of an air-cooled screw air compressor comprises the following steps: The first step: a first temperature sensor 12 and a humidity sensor 13 are arranged at the air intake of the air-cooled screw air compressor to detect the air intake temperature T1 and the relative humidity RH of the air intake of the air-cooled screw air compressor; a second temperature sensor 14 is arranged at the air exhaust of the air-cooled screw air compressor to detect the air exhaust temperature T2 of the air exhaust of the air-cooled screw air compressor; a pressure sensor 15 is arranged at the air supply of the air-cooled screw air compressor to detect the air supply pressure P1 of the air supply of the air-cooled screw air compressor; Step 2: Through the PLC controller, according to the suction temperature T1, use the Antoine equation P=10^((AB) / (T+C)) / 101325*760 / 100000, where A, B, and C are corresponding constants, and substitute the suction temperature T1 to calculate the saturated water vapor pressure value P of the air at the suction port of the screw compressor; Step 3: Through the PLC controller, using the formula Ps=P*RH, according to the detected relative humidity RH, calculate the water vapor partial pressure value Ps of the air at the corresponding humidity; Step 4: Through the PLC controller, using the transformation form of the Antoine equation, T=B / (A-lg((P1+1)*Ps*100000*760 / 101325))-C, calculate the pressure dew point value T3 of the air under the exhaust pressure state of the air-cooled screw air compressor based on the air supply pressure P1 and the water vapor partial pressure Ps of the air under relative humidity; Step 5: According to the calculated pressure dew point value T3, set the stop temperature of the cooling fan to T4, T4=T3+5℃, and the start temperature of the cooling fan to T5=T4+10℃; Step 6: Use the exhaust temperature T2 to compare with T4 and T5 respectively. If T2≤T4, the cooling fan is controlled to stop running; if T2≥T5, the cooling fan is controlled to start.

[0020] This application is based on the ambient temperature, relative humidity and the operating pressure of the customer's backend at the customer's site, using various data detected by sensors, using the Antoine equation, the equation for the water vapor pressure of air under relative humidity conditions and the conversion formula of the Antoine equation, and can calculate the pressure dew point value of the compressed air under the current exhaust pressure state in real time. Based on this real-time pressure dew point value, the start and stop temperature of the cooling fan can be controlled in real time, thereby ensuring that the lubricating oil is in the optimal operating temperature range, increasing the service life of the lubricating oil, and ensuring more reliable operation of the screw air compressor.

[0021] like Figure 2As shown, the air-cooled screw air compressor used in the present application includes an air filter assembly 1, an air intake valve 2, a compressor 3, a motor 4, a frequency converter 5, an oil-gas separation tank 6, an oil separation core 7, an aftercooler 8, an oil cooler 9, an oil filter 10, a PLC controller 11, a first temperature sensor 12, a humidity sensor 13, a second temperature sensor 14, and a pressure sensor 15. The frequency converter 5 is connected to the motor 4, and the motor 4 is connected to the compressor 3. The compressor 3 is also connected to the air filter assembly 1, the oil-gas separation tank 6, and the oil cooler 9, respectively. An oil filter 10 is arranged between the compressor 3 and the oil cooler 9, an air intake valve 2 is arranged between the air filter assembly 1 and the compressor 3, and the oil separation core 7 is installed in the oil-gas separation tank 6. The oil-gas separation tank 6 is also connected to the oil cooler 9, the oil separation core 7 is connected to the aftercooler 8, and the PLC controller 11 is respectively connected to the inverter 5 and the cooling fan motor of the oil cooler 9. The air-cooled screw air compressor is a prior art, and the connection relationship and working principle of the structure are not further explained here. The present application sets a first temperature sensor 12 and a humidity sensor 13 at the air intake port of the air filter assembly 1, sets a second temperature sensor 14 at the exhaust port of the compressor 3, and sets a pressure sensor 15 on the pipeline between the oil separation core 7 and the aftercooler 8. The data of the first temperature sensor 12, the humidity sensor 13, the second temperature sensor 14, and the pressure sensor 15 are all transmitted to the PLC controller 11.

[0022] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for controlling the start and stop of a cooling fan of an air-cooled screw compressor, characterized in that: The following steps are involved: Step 1: Detect the suction temperature T1 and relative humidity RH of the air-cooled screw air compressor suction port; detect the exhaust temperature T2 of the air-cooled screw air compressor exhaust port; detect the air supply pressure P1 of the air supply port of the air-cooled screw air compressor; Step 2: Through the PLC controller, according to the suction temperature T1, use the Antoine equation P=10^((AB) / (T+C)) / 101325*760 / 100000, where A, B, and C are corresponding constants, and substitute the suction temperature T1 to calculate the saturated water vapor pressure value P of the air at the suction port of the screw compressor; Step 3: Through the PLC controller, using the formula Ps=P*RH, according to the detected relative humidity RH, calculate the water vapor partial pressure value Ps of the air at the corresponding humidity; Step 4: Through the PLC controller, using the transformation form of the Antoine equation, T=B / (A-lg((P1+1)*Ps*100000*760 / 101325))-C, calculate the pressure dew point value T3 of the air under the exhaust pressure state of the air-cooled screw air compressor based on the air supply pressure P1 and the water vapor partial pressure Ps of the air under relative humidity; Step 5: According to the calculated pressure dew point value T3, set the stop temperature of the cooling fan to T4, T4=T3+5℃, and the start temperature of the cooling fan to T5=T4+10℃; Step 6: Use the exhaust temperature T2 to compare with T4 and T5 respectively. If T2≤T4, the cooling fan is controlled to stop running; if T2≥T5, the cooling fan is controlled to start.

2. A control method and regulation method for starting and stopping a cooling fan of an air-cooled screw compressor according to claim 1, characterized in that: A first temperature sensor and a humidity sensor are arranged at the air intake of the air-cooled screw air compressor, a second temperature sensor is arranged at the air exhaust of the air-cooled screw air compressor, and a pressure sensor is arranged at the air supply of the air-cooled screw air compressor.

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