Multi-stage screw compressor
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Solution Overview
Problem
Multi-stage screw compressors face efficiency deterioration due to gas leaks through outer diameter clearances between screw rotor lobe tips and the casing, particularly in high-pressure stages where increased operation differential pressures enhance leak rates, leading to wasted compression power and reduced efficiency.
Innovation Solution
The design incorporates screw rotors with increasing lead from the suction side to the discharge side in stages beyond the first stage, resulting in thicker lobe tips and shorter seal lines, which reduces gas leaks by increasing the lobe tip thickness and decreasing the seal line lengths, thereby minimizing efficiency loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the operation differential pressure of the high-pressure-stage compressor is increased to achieve higher discharge pressure, then the compression efficiency deteriorates due to increased gas leaks through outer diameter clearances
Solution Approach 1:
The patent applies local quality by varying the lobe thickness of the female rotor along its axial length. Specifically, the lobe thickness is increased on the discharge-side portion compared to the suction-side portion. This local variation in geometry creates different clearance characteristics at different axial positions, effectively reducing gas leakage through the outer diameter clearance in the high-pressure discharge region while maintaining compression performance.
Solution Approach 2:
The patent changes the geometric parameters of the screw rotors, specifically the lobe thickness distribution along the axial direction. By increasing the lobe thickness on the discharge-side portion of the female rotor, the patent modifies the clearance parameters to reduce gas leakage. This parameter change directly addresses the efficiency deterioration caused by high differential pressure without requiring a complete redesign of the compressor system.
2Loss of energy
If the lobe thickness of the female rotor is increased on the discharge-port side to suppress gas leaks, then the width of the boundary between adjacent working chambers increases, but this may affect the compression ratio and working chamber volume
Solution Approach 1:
The patent applies local quality by selectively increasing the lobe thickness only on the discharge-side portion of the female rotor, while maintaining or optimizing the lobe thickness on the suction-side portion. This localized modification suppresses gas leakage through outer diameter clearances in the high-pressure region without significantly affecting the overall working chamber volume and compression ratio, as the change is confined to a specific axial region rather than the entire rotor length.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively suppresses gas leaks between working chambers, enhancing the overall efficiency of the multi-stage screw compressor by reducing the impact of increased differential pressures on compression efficiency.
Implementation Method 1
a screw compressor includes a pair of male and female screw rotors that revolve while meshing with each other, and a casing that houses both the screw rotors. Both the screw rotors have helical lobes (grooves). This compressor sucks in and compresses a gas through an increase and decrease, along with revolutions of both the screw rotors, in the volumes of a plurality of working chambers formed by the grooves of both the screw rotors and the inner wall face of the casing surrounding both the screw rotors.
Data Source
AI summary
A multi-stage screw compressor includes a plurality of stages of compressor bodies that compress a gas in sequence. Each of the stages of compressor bodies has both male and female rotors that are housed revolvably in a casing in a mutually meshing state. The male and female rotors each include a rotor lobe section having a suction-side end face and a discharge-side end face on one end and the other end thereof in the axial direction and having a twisted lobe extending from the suction-side end face to the discharge-side end face. The male and female rotors in a downstream-stage compressor body of at least one certain stage, excluding an upstream-stage compressor body as the first stage, among the plurality of stages of compressor bodies are each configured such that their lead increases from the suction side in the axial direction of the rotor lobe section toward the discharge side.