Computing Simulation Of The Cryogenic Purification Process

Traditionally,medium-scale or small-scale ammonia plants tend to adopt feed-gas purifying process like the cuprammonium washing,the combined methanol system or the methanation process which have peculiarities of low precisions and high feed-gas and energy consumptions.Those processes make the medium-scale and small-scale ammonia plants costly.Recently,successful applications and promotions of the sieve-sorption system and the bi-methyl energy-saving refining process improve the producing capacities,expand producing lines,lower the producing costs,and also enhance the stability of the whole system.However, high content of inert gases in recycle gas and high content of purge gas still puzzle the medium-scale and small-scale ammonia plants and make them running at the high-cost level (sometimes,the methane content of some feed-gas is as high as 2-3%).Getting rid of inert gases and improving the refining level have been among the most active demands in ammonia-producing area,and also been listed as one of the important missions in the chemical industry in the "11^th five-year plan ".Accordingly,the inorganic chemical industry lab in Dalian University of Technology integrates cryogenic purification process in C.F.Braun ammonia plant with past designing experiences of purifying processes in large-scale ammonia plants to simulate and develop feed-gas purification process for medium-scale and small-scale ammonia plants.Braun ammonia process which was born in 20^th century 60's offers a new though for feed-gas purification process.After put in operation,a series of optimizations and improvements have been done for the process which make it very competitively among many ammonia processes.Feed-gas is not limited to nature-gas,and coal or heavy oil can also put into considerations.The cryogenic purification process is located right after the the methanation process.In the methanation process,CO and CO₂ are turned into CH₄.Then the crude syn-gas pass through the ammonia chiller and the sieve dryer to get rid of CO₂ and H₂O.After all these steps,syn-gas comes into the cold-box where the cryogenic process is taking.The cold-box has a very important purpose:lower the content of Ar and CH₄ in the syn-gas,and get prepare for the afterward compressing and synthesizing processes.In this thesis,the system of the cold-box has been simulated and calculated,and accordingly,four types of physical property methods are taken into account.After meticulous comparisons,physical property of PR-BM is proposed for real purpose.