Abstract:

Whenever a high-pressure fluid stream, or simply stream HP, is depressurized, a potential for mechanical energy recovery exists. On the other hand, pressurizing a low-pressure fluid stream, or simply stream LP, always requires mechanical energy. In principle, a work exchanger (WE)may be applied to any high-pressure processing systems where it is also desirable to recover mechanical energy to offset the energy requirement for pressurization of low pressure streams. Because the gas streams in the chemical process often appear with big flux and high pressure, there are great potential to recover work in the process industry. But, it is difficult to forecast and appraise the work recovery result between two gas streams because gas is compressible. For the two kinds of structure of gas-gas WE, the reciprocating machine and the centrifugal machine, their thermodynamic processes were analyzed and the equations of work recovery efficiencies were proposed. The in-depth simplified work recovery efficiency equations of the work transfer process in two WE structures were presented through reasonable assumption and were compared finally. The work recovery efficiency equation of centrifugal machine was also extra influenced by initial volume flow ratio than the reciprocating machine. In order to see what pure influence of the stream phase state on the work recovery efficiency, the influence of initial volume flow ratio was expected to be neglected. So the reciprocating machine was chosen to take as example and its performance of work exchange between two streams with different phase states were compared. Two WE structures corresponded to different work recovery efficiency equations. The simplified work recovery efficiency equation of reciprocating machine followed a power function of compression ratio. Its work recovery efficiency decreased with increasing compression ratio, while for centrifugal structure, the work recovery efficiency was relevant to not only pressure ratio but also initial volume flow ratio. Furthermore, because the centrifugal structure did not involve minimal pressure differential, a centrifugal machine could achieve higher LP compression than a reciprocating machine. The present work compared the work recovery efficiency between the streams with different phase states. The result showed that with the same compression ratio and initial volume flow ratio, liquid-liquid reciprocating work exchanger had the highest work recovery efficiency value. Its ideal value was 100%. The work recovery efficiency values of gas-liquid WE and liquid-gas WE decreased successively, while the value of gas-gas WE was the lowest. The work recovery efficiency equation of centrifugal machine had also extra influence by initial volume flow ratio than the reciprocating machine.

摘要：

化工过程中气体流股经常具有流量大、压力高的特点，因而有功量回收应用潜力，而气体可压缩的特点给功量回收效率分析带来困难。针对功量交换器往复式和离心式两种机械结构，分别对气体-气体（气气）功量交换推导了功量回收效率表达式，并通过合理假设进行简化，对比分析了两种结构下功量回收效率理论值。并对两种结构形式下不同物流相态匹配的功量回收效率计算式进行了表述，针对往复式结构能够突出物流相态对气体功量回收效率的特殊影响，对往复式结构下不同物流相态匹配下的功量回收效率进行了比较和分析。研究表明，功量交换结构对气体功量回收效率有重要影响，往复式结构功量回收效率为随压比增大而减小的幂函数关系，而离心式结构功量回收效率还与高低压流股初始体积流量比有关。离心式结构能够实现比往复式结构大的功量回收效率和高于高压流股初始压力的目标压力。在同样压比下，往复式结构中液液功量交换具有最高的功量回收效率（理想值为100%），气液功量交换和液气功量交换值依次减小，而气气功量回收效率最低，而离心式结构同样还与高低压初始体积流量比有关。