On the relationship between the compression ratio and molecular weight of rich gas compressors
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Our compressor is designed with an outlet pressure of 1.6 MPa at the second stage; currently, the outlet pressure at the second stage is 1.185 MPa. The compression ratio has increased significantly, while the inlet pressure at the second stage is normal. The compression ratios at the inlet and outlet of the first stage are close to the design values. What could be causing the low outlet pressure at the second stage, given that the temperatures are normal? Is it related to the properties of the medium gas?
What is the inlet pressure of your compressors now compared to before? Your current outlet pressure is 1.185, and the compression ratio has also increased; does that mean the inlet pressure is lower? What is the current flow rate compared to before?
Based on the meaning of your title, you should be referring to the relationship between the average molecular weight of a gas and the compression ratio; the higher the average molecular weight of the gas, the easier it is to compress it, which means the outlet pressure will be higher.
With a high molecular weight and high density, it shouldn’t be easy to compress, right?
The inlet diameter is set at 0.025; it’s larger now than before. The outlet pressure is lower than what was designed, while the flow rate remains unchanged. I think it’s because the medium, being gas, has become heavier and thus more difficult to compress
An increase in the inlet volumetric flow rate, an increase in inlet temperature, a decrease in the average molecular weight of the gas, an increase in the pressure drop between sections, and the opening degree of the anti-surge valve can all cause the outlet pressure to decrease.
As the inlet pressure increases and the outlet pressure decreases, the compression ratio must have decreased; the molecular weight of the gas increases, and the mass flow rate rises, which leads to a decrease in the compression ratio. As long as surge is avoided, there’s no problem.
Low backpressure results in low outlet pressure
The pressure at present should be system pressure, required by the process.