Green Design: Operation Optimization Of A Pulsed-sieve-plate Column

In the process for recovering caprolactam from wastewater using a pulsed-sieve-plate column, benzene, which is used as the extracting solvent, may seriously impact the environment due to its emission during the normal operation of the process. The quantity of benzene is optimized by green design methodology to obtain an optimum trade-off between environmental protection and economic profit, and an environmental impact cost is introduced to quantify the impact of benzene emissions on the environment. The environmental impact cost of benzene was estimated as 35000 RMB/ton in China after consultations with some senior chemical engineers in industry and some environmental experts. The optimum Rv is 5.7 using green design with total annual profit 1700000RMB, while the optimum Rv is 8.5 using traditional design with total annual profit 3400000RMB. The difference between the two profits is chiefly due to the impact of benzene emission on the environment. In this case, the emission of benzene to the environment has a great impact on selecting the optimum Rv. So the optimum Rv is finally chosen as 5.7 in this process, correspondingly, the concentration of caprolactam in the wastewater decreases from 6.4% to 1.1%, and the COD decreases from about 87000mg/L to 44000mg/L. This realizes the optimum combination between environmental protection and economic profit. Now, the improved recovering process using the above green design result is operated-normally in Juhua Group.A scale-up rule for the pulsed-sieve-plate column is proposed, which is helpful for the design of the pulsed-sieve-plate column. The scale-up rule is:In addition, inherently safer chemical processes design is introduced, and a software of green design for chemical process is finished.