During on-site operation under wet gas compression, the volumetric efficiency of a twin-screw pump decreases sharply, the temperature in the pump rises significantly, severe vibration and even jamming can occur. To solve the problems caused by wet gas compression structurally, a method for optimizing the design of a decompression screw is proposed in this paper based on the characteristics of a twin-screw pump and screw compressor. A fluid-solid multi-field thermal-coupling scheme is used to calculate the pressure, temperature, deformation, outflow, and volumetric efficiency of a screw pump before and after optimization. The average deviation between the calculated outflow and the experimental results was no more than 5%, demonstrating the accuracy of the calculation. After optimization, the return flow between the pump stages was significantly reduced and the outflow had increased. When the pressure difference between the inlet and outlet was 1 MPa, the maximum increase was about 18%. With an increase of the gas volume fraction from 95% to 99%, the average increase of the volumetric efficiency was about 14%. The temperature rise in the chambers at all levels and the temperature difference between the inlet and outlet of the decompression screw pump were lower than those of a traditional screw pump. The deformations at the three clearances were also less than those of a traditional screw pump, which helps to avoid jamming caused by thermal expansion.
Keywords: Optimal design; Screw pump; multi-field coupling; wet gas compression.