Research and development of a high-efficiency two-stage oil-injected screw air compressor
In order to enhance the energy efficiency of air compressors,a two-stage oil-injected screw air compressor with a rated power of 250 kW was developed.A novel rotor profile designed specially for this application was adopted in the low-and high-pressure stage compressors.A series of innovative design was adopted in the structure of the air compressor.The key operating parameters of the air compressor,such as interstage pressure and oil injection flowrate,were optimized,and then an experimental test was carried out on a well-instrumented test rig to evaluate the energy efficiency of the developed air compressor prototype.The experimental results show that the volumetric efficiency of the air compressor can reach 95.6%at the optimal speed of 1 330 r/min,while the adiabatic efficiency of the low-and high-pressure stage compressors can reach 93.3%and 88.6%,respectively.The energy efficiency of the developed air compressor prototype was evaluated according to GB 19153-2019 standard.The air compressor prototype all can reach the energy efficiency of the first stage of constant speed oil-injected rotary air compressor under 100%,70%and 40%load,respectively.Considering the overall performance of the compressor under rated load and part load,the specific power of its unit can reach 5.72 kW/(m3·min),which is 7.7%lower than the corresponding value of first-stage energy efficiency,which has reached"dual first-stage energy efficiency",and achieved energy efficiency upgrade of the like screw air compressor products.In addition,the effects of change in rotating speed on the p-V indicator diagram and efficiencies of low and high stage of the two-stage screw compressor were researched experimentally.It is found through research that the p-V indicator diagram in the low pressure stage compression process is lower than that of the adiabatic compression process,and the change in rotating speed exerts only a minor influence on it.However,the p-V indicator diagram in the high pressure stage compression process is affected considerably due to gas leakage.Increased rotating speed would cause the high pressure stage compression process curve gradually becoming gentle;Moreover,with the change of the rotating speed,the efficiencies of the low-and high-pressure stage compressors present different change trends,yet both the volumetric efficiency and adiabatic efficiency of the high pressure stage compressor are very sensitive to the rotating speed.The results may provide some references for the energy efficiency upgrade of screw air compressors.
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