A novel cryogenic vapor-recompression air separation unit integrated to oxyfuel combined-cycle gas-to-wire plant with carbon dioxide enhanced oil recovery: Energy and economic assessments

摘要

Oxyfuel carbon capture is both power and capital intensive due to oxygen demand. Consequently, oxyfuel requires the development of more efficient air separation units. This work proposes an alternative cryogenic distillation process for large-scale gaseous oxygen supply. Instead of using different pressure columns, the new air separation unit couples top vapor recompression to a single atmospheric cryogenic air distillation double-reboiler column, whose nitrogen-rich top vapor is compressed to heat the intermediate column reboiler, while the bottom reboiler is heated with compressed saturated air. Several processes for low-pressure oxygen gas supply were simulated and optimized. The power requirement of the new air separation unit producing atmospheric oxygen at 95%mol attained the best value of 139.0 kWh/t (oxygen basis). A sensitivity analysis for oxygen purity was performed showing that, even for higher purities, the new developed process achieves the lowest specific power for low-pressure gaseous oxygen production. The economic leverage of the new air separation unit is proven via successful supply of low-pressure oxygen to oxyfuel natural gas combined-cycle Gas To -Wire plant. Assuming carbon dioxide destination to enhanced oil recovery, even with an investment about 100% higher than the counterpart of a conventional air-fed combined-cycle Gas-To-Wire plant and despite net efficiency penalty of 6.88%, the oxyfuel combined-cycle Gas-To-Wire solution coupled to the new air separation unit was capable of achieving comparatively superior profitability under carbon taxation above 13.5 USD/t.