Optimization on shaft seals for a twin-screw steam compressor based on a novel uniform property region (UPR) model on discharge end-face

•A model on leakage prediction from screw compressor discharge end to shaft seals.•Effects of several main parameters in shaft seals were analyzed.•Several suggestions were given on optimizing the shaft seals.•Pressure on screw compressor discharge end-face should be calculated by UPR model. Different from other types of compressor, pressure distribution on twin-screw compressor discharge end-face is related to both operating pressure and the lobe number, instead of being regarded as discharge pressure. In this paper, a mathematical model is developed based on a novel uniform property region (UPR) model to predict leakage through shaft seals, which was validated with experimental data. Simulation results show the leakage flow rate of shaft seals decreases dramatically and then reduces slightly with carbon rings number increases. The flow diameter of balance pipe determines the balance between internal and external leakage. Based on the analysis, several suggestions were given on optimizing shaft seals. For the discussed steam compressor, the number of carbon rings can be reduced from 4 to 1 and the flow diameter of balance pipe should be adjusted from 10 mm to 5 mm with a regulating throttling valve.