Compressed air is widely used in industrial production. In the factory, several air compressors are installed in one place to form an air compressor station. Sichuan Jiuhe Chemical Industry Co., Ltd. has an air compressor station equipped with three 110kW reciprocating piston air compressors to compress hydrogen.
Due to the uneven use of hydrogen in production, the gas consumption is changing dynamically. Sometimes several hydrogen compressors need to be operated at the same time for gas supply, and sometimes even the gas produced by one hydrogen compressor can not be used up, but the hydrogen compressor is still running at full speed. The hydrogen compressor is equipped with exhaust pressure regulating device when leaving the factory. When the hydrogen pressure in the air storage tank exceeds the set pressure, the butterfly valve on the inlet pipe of the compressor will automatically close and the compressor will enter the idle unloading state. When the hydrogen in the air storage tank is lower than the set pressure, the butterfly valve on the inlet pipe of the compressor will open automatically, and the compressor will enter the full load working state again. The set value has a hysteresis loop. For example, set the hydrogen pressure in the air storage tank to 0.815MPa and the hysteresis loop to 0.045MPa. In this regulation mode, the variation range of air supply pressure is 0.045MPa. At full load, the working current of the air compressor is close to the rated current of the motor; During idling unloading, the working current of the air compressor is about 50% of the rated current of the motor. This part of current does not useful work, but the idling loss of machinery at rated speed. Although the regulating device can also regulate the pressure, the regulation accuracy of the pressure is low and the pressure fluctuation is large; The compressor always works at the rated speed, with large mechanical wear and high power consumption.
According to the air compression theory, the shaft power PZ(kw), exhaust volume QD (m3 / min) and shaft speed n (R / min) of the compressor comply with the following formula:
In the formula: Mr - average torque input by the compressor, N / m, K - coefficient related to cylinder volume, pressure, temperature and leakage
N2- adjusted compressor speed, r/ min, V - cylinder volume, m3
According to the above theoretical analysis, under the condition that the cylinder volume of the compressor cannot be changed, only adjusting the speed of the compressor can change the exhaust volume; The compressor is a constant torque load, and the shaft power of the compressor changes in direct proportion to the speed; When the total exhaust volume of the compressor is greater than the air supply volume, adjusting the air supply pressure by reducing the compressor speed is an effective method to achieve the economic operation of the compressor.
Reducing the compressor speed and adjusting the air supply pressure is an effective method to achieve the economic operation of the compressor, and the frequency conversion speed regulation method is an efficient speed regulation method. Consider installing a pressure transmitter on the air storage tank to feed back the pressure signal to the terminal of the frequency converter to form a constant pressure air supply system with an air supply pressure of 0.8MPa. In this example, a KE300A-132kW frequency converter is selected, and Sennas DG13W=bz-a, 1.6Mpa is selected for pressure transformer air supply.
The frequency converter controls the first compressor. Given the operation keyboard on the frequency converter for regulation, the multi-functional outputs T1 and T2 of the frequency converter are respectively connected to the start / stop circuit of the self coupling decompression starter of the second and third compressors, so that the output of the frequency converter can control the operation or shutdown of the other two compressors.
During manual operation, the first compressor is controlled by the frequency converter, and the second and third compressors can be manually started / stopped by the self coupling decompression starter. During automatic operation, the first compressor operates with frequency conversion first. When the output frequency of the frequency converter has reached 50.00Hz and the air supply is still insufficient, the output nodes T1 and T2 of the frequency converter act to start the second and third compressors; If the air supply is greater than the given value, the system will automatically stop the second and third compressors, and the constant pressure air supply can be realized through closed-loop adjustment.
Hydrogen is a combustible gas, and the working site of the compressor is in danger of explosion. The protection grade of ke300a series frequency converter is IP20. Obviously, it can not be installed in places with explosion risk. The frequency converter shall be installed in the power distribution room without explosion risk, and the remote control box shall be used to operate next to the compressor. The remote control box should also be selected as intrinsically safe.
After three months of operation, the compressor has achieved the expected purpose. No matter how the production gas is changed, the pressure of constant pressure gas supply is maintained at about 0.8MPa, and the gas supply quality is greatly improved. The measured power saving rate is 26%, and great economic benefits are obtained.