实际气体对CO_2离心压缩机CFD模拟的影响

CFD Simulation Including Real Gas Effects of CO_2 Centrifugal Compressor

气体的可压缩性对大型尿素装置及天然气开采中的高压二氧化碳压缩机的设计具有非常重要的影响。本文应用基于SW的CO_2实际气体状态方程,研究压缩性系数对压缩机级阻塞域以及流动损失的影响。研究结果表明:在近临界点处,阻塞域会随着压缩性系数的减小而减小。随着流量增大,实际气体算例率先在回流器进口处出现阻塞,导致能量损失过大。在相同的进口流量系数下,理想气体介质与实际气体介质在叶轮流道内流动基本相似,不同位置处,速度分布各不相同;相同质量流量下,由于密度不同使得体积流量互不相同,这对准确预测流动损失造成了很大的影响。对比0.5倍叶高处叶片两侧静压分布,发现沿着气流方向,实际气体模型静压分布更均匀,与设计工况相符。在离心压缩机选型设计过程中,前一级回流器出口参数对后一级叶轮选型会产生较大的影响。本文通过提取设计条件下两种不同介质算例回流器出口处体积流量,对比发现理想气体工况较实际气体偏高,这对后一级通流部件选型造成很大影响。

The compressibility of the gas has an important influence in the design of high pressure gas CO2 compressors for large scale urea plant and gas exploitation. In this paper the CO2 real gas equation of state based on Span and Wanger is applied to analyze the influence of the compressibility coefficient on the choke margin of the compressor stage and the flow loss. The results show that close to the critical point, the choke margin decreases with a decreasing coefficient of compressibility. As the mass flow increases, choking appears first at the inlet of the return channel for the real gas case, which leads to a large energy loss. For the same inlet condition, the flow for the ideal gas and the real gas case is basically similar for the impeller flow channel, although at various locations, the velocity distribution is different. Due to the different density, the volume flow rate differs. This phenomenon has a larger impact on the prediction of the flow loss. Comparing the static pressure distribution on both sides of the blade at 0.5 times blade height, the static pressure distribution of the real gas model is more uniform and conforms to the design condition in the flow direction. In the type selection of the design process of the centrifugal compressor, the outlet parameters of the stage have a great impact on the next stage. According to compare outlet volume flow of ideal gas and real gas in the return channel, found the ideal gas volume flow is much higher, this result have a large impact on type selection for flow component in next stage.