A New Cryogenic Air Separation Process with Flash Separator

A new cryogenic air separation process with flash separator is developed. A flash separator is added to the conventional double-column cryogenic air separation process. The flash separator is used to replace the turbine required to recover a portion of the energy in the double-column air separation process. The flash separator served dual purposes of throttling and separation. Both the conventional and the new processes are simulated using Aspen Plus version 11.1 the model air flow rate and compositions are taken as 50000？Nm3/h of air at standard conditions of 1？atm and 25°C and feed composition of 79.1% N2 and 20.9% O2. The new process decreases the energy consumption and increases the productivity. 1. Introduction There are mainly three methods of air separation, cryogenic distillation, pressure swing absorption, and membrane separation. Although the latter two methods have become more competitive, cryogenic distillation remained the dominant choice for mass production of high-purity O2. The first cryogenic distillation unit with single-column was built in 1902 and shortly followed by double-column process. The double column consists of compressors, low- and high-pressure columns, and two sets of heat exchangers. The low- and high-pressure columns are thermally interconnected [1]. Although the double-column process is widely used, its high energy consumption remains challenging. Therefore in the recent past, the double column has been subjected to many energy-efficient modifications such as changing the operation condition of the low-pressure column from low to moderate pressure [2]. This modification resulted in smaller size of the column and 10% energy savings. The modification has also the advantage of argon recovery (up to 5% greater argon recovery over the conventional). Another modification is the addition of a heat pump to a side rectifier which is thermally linked to the two columns. The heat pump enhances the separation by providing a supplementary crude argon condensing duty [3]. Reference [4] did an exergy analysis of the double-column air separation process. It found that more than half of the exergy loss takes place in the liquefaction unit and almost one-third in the air compression unit, and minor exergy losses are taking place in the distillation unit and the main heat exchangers. Reference [5] has changed the design of the double column to single column using self-heat recuperation technology (i.e., heat from the top vapor stream is recuperated and exchanged with heat in the bottom liquid and feed streams). The author’s modifications