Usually, the users of compressors always choose compressors according to the maximum volume flow required by the device or system. However, the actual working conditions of the compressor vary with the needs of the process flow or gas-consuming equipment. When the gas consumption is less than the exhaust volume of the compressor, it is necessary to adjust the gas volume of the compressor so that the exhaust volume of the compressor can meet the requirements of the gas consumption and keep the pressure in the pipeline network stable.
The following are the commonly used gas volume adjustment methods for reciprocating compressors:
Speed regulation
Speed regulation is to adjust the exhaust volume by changing the speed of the compressor. The advantages of this regulation are continuous gas volume, small specific power consumption, constant pressure ratio of each level of the compressor, and no need to set up a special adjustment mechanism on the compressor; but it is only widely used in compressors whose driving machine is an internal combustion engine and a steam turbine. If the driving machine is an electric motor, a frequency converter needs to be configured. Since high-power and high-voltage frequency converters are expensive and require a lot of maintenance and repair work, this method is rarely used on reciprocating compressors driven by electric motors. In addition, variable speed regulation may have adverse effects on the operation of the compressor, such as valve flutter, large component wear, increased vibration, insufficient lubrication, etc., which also limits the wide application of this method.
Clearance cavity regulation
On the cylinder of the compressor, in addition to the fixed clearance volume, there is no other certain cavity. When adjusting, the cylinder working cavity is connected to increase the clearance volume, reduce the volume coefficient, and reduce the exhaust volume. This is the working principle of clearance cavity regulation. According to the different ways of accessing the auxiliary volume, it is divided into continuous, graded and intermittent adjustment, which is mostly used for large process compressors. The main disadvantages of this adjustment method are: usually manual adjustment, slow response speed, and generally need to be used in conjunction with other adjustment methods. Although the method of connecting the variable auxiliary clearance volume can achieve adjustment within the range of 0% 100% in principle, the system reliability is poor, there are many vulnerable parts, and it is difficult to maintain.
Bypass regulation
The exhaust pipe is connected to the intake pipe through the bypass pipeline and the bypass valve. When adjusting, as long as the bypass valve is opened, part of the exhaust gas will return to the intake pipe. This adjustment method is more flexible and simple, and the adjustment accuracy is also relatively high when equipped with an automatic control system. However, because all the compression work of the excess gas is lost, the economy is poor. Therefore, this method is suitable for occasional adjustment or small adjustment range.
Adjustment by pressing the intake valve
According to the length of the process of the intake valve being pressed, this method is classified into two methods: full-stroke pressing the intake valve and partial-stroke pressing the intake valve. For full-stroke pressing the intake valve adjustment, during the suction process, the gas is sucked into the cylinder. During the compression process, because the intake valve is fully open, the inhaled gas is pushed out of the cylinder. Assuming that a compressor has a one-stage double-acting cylinder, if only the intake valve on one side of the piston is pushed, the gas volume is reduced by 50%. If both sides are pushed open at the same time, the exhaust volume is zero. Therefore, the machine can achieve three-level adjustment of gas volume: 0, 50% and 100%. It can be seen that the adjustment range of the full-stroke pressing the intake valve is large, which is suitable for rough adjustment. The principle of partial-stroke pressure-open intake valve regulation is similar to that of full-stroke pressure-open intake valve, but it controls the amount of return gas by controlling the closing moment of the intake valve during the compression process, thereby realizing continuous regulation of gas volume. Since the compression work decreases almost in direct proportion to the exhaust volume, it also has high operating economy.