Saving power by modifying a double column air separation plant to produce high and low purity pressurized gaseous oxygen simultaneously

摘要

Large Steel plants require oxygen at purities of 90% and 99.5%. These purities are required in blast furnace for iron-making and in basic oxygen furnace for steel-making respectively. Though air separation plants in steel plant consume very high power, they are generally not designed to produce oxygen with dual purities and blast furnace continues to consume high-purity oxygen that is thermodynamically a big wastage of power. This work proposes modification of a conventional double column configuration to produce oxygen at purities of 99.5% and 90% simultaneously at pressures of 40 bar and 10 bar respectively with different flow rates. Impure liquid oxygen is drawn a few plates above pure liquid oxygen sump at the bottom of the low pressure column. Recovery of oxygen increased from 91.7% to 99.9% and specific power consumption reduced by 16.7%. Flexibility in product mix requires operational adjustments of rotary equipment. With outlet pressure of booster air compressor fixed, two turbines have to be placed in parallel instead of one. The same flexibility is achieved with one turbine if outlet pressure of booster compressors can be suitably varied. It is made feasible by using separate motors for compressor stages that further reduced power consumption by 5.4%.