Abstract
Cryogenic air separation units (ASU) are the predominant method for delivering high-purity pressurized O2 at large capacities to relevant industrial processes. This study presents an exergoeconomic assessment of the integration of two-phase expanders (TPE) in two ASU configurations with (1) intermediate liquid oxygen pumping followed by gaseous O2 compression and (2) total liquid oxygen pumping to the delivery pressure. A comprehensive exergy analysis showed that TPE integration in the latter resulted in exergy efficiency increase of 1.1%-points and specific power consumption (SPC) reduction 15.5 kWh/ton (-4.4%), while for the former, the exergy efficiency increase amounted to 1.8%-points with 17.9 kWh/ton (-5.2%) lower SPC. A complete thermodynamic mapping for the different cases was presented. From an economic perspective, total liquid pumping reached levelized cost of oxygen reductions of 1.68 euro/ton (-4.7%), while in the configuration with gas compressors it was limited to only 0.45 euro/ton (-1.2%), relative to analogous ASU configurations with JouleThomson valve expansion. The total liquid pumping scheme with TPE presented a cost reduction of 4.3 euro/ton (-11.2%) relative to the gaseous O2 compression counterpart. N2 by-product monetization can further improve the plant economic performance. Based on this assessment, integration of reliable TPE technology for incremental efficiency gains of pressurized O2 production in ASUs presents a promising opportunity to profitably contribute to energy efficiency and decarbonization goals.
NSTL
Elsevier