Improving specific power consumption of cryogenic air separation plants using waste heat of carbon capture power plants.

A cryogenic air separation unit (ASU) with double column configuration produces pressurized oxygen (PGOX) at purity of 99.6% and above. A single column configuration is sufficient to produce at a purity of 95%, which is required for carbon capture power plants (CCPP). It requires less capital and consumes lower power than a double column configuration. It further makes an economic sense if the unutilized bone-dry low purity (waste) nitrogen, also called pressurised impure gaseous nitrogen (PiGAN), may be heated by the waste heat available in CCPP. It is expanded in a gas-based reheat cycle to produce electricity. This may partially offset the power consumed in the ASU. Using exergy analysis, pressure of PiGAN is determined in such a way that the net power consumed by ASU (power consumed minus power generation in power cycle) is minimized. At this pressure of PiGAN, single column ASU consumes 12.5% less power than double column ASU.采用双塔配置的深冷空气分离装置（cryogenic air separation unit, ASU）可生产纯度达99.6%及以上的加压氧气（pressurized oxygen, PGOX）。单塔配置即可满足碳捕获发电厂（carbon capture power plants, CCPP）所需的95%纯度产品的生产需求，且其基建投资更低、能耗也低于双塔配置。若未被利用的无水低纯（尾气）氮气——又称加压不纯气态氮（pressurised impure gaseous nitrogen, PiGAN）——可利用碳捕获发电厂的余热进行加热，则单塔配置将具备更优的经济性。该加压不纯气态氮可通过燃气再热循环膨胀发电，从而部分抵消深冷空气分离装置的运行能耗。通过㶲分析（exergy analysis），可确定加压不纯气态氮的最优压力，使得深冷空气分离装置的净能耗（实际能耗减去循环发电收益）降至最低。在此最优压力下，单塔深冷空气分离装置的能耗较双塔配置低12.5%。