A Study On The Capacity Expansion And Innovation Of The High-pressure Circle Of The 750t/d Urea Plant In LTH

The application of isobaric double recycle(IDR) technique in urea production in the Company of Natural Gas & Chemistry in Luzhou(LTH) is analysed particularly in this paper, and the defects in 5 aspects of the IDR technology process have also been found out based on the analyses of the layout of the installation, conditions of the technical operation, design of the project, etc. A new urea process-self-stripping with ammonia is presented to revamp the high-pressure circle of the current IDR method by an analyses and comparing the stripping with CO2 to that with ammonia, and the balance of material and energy is calculated on the revamped main equipments, and the applicable measures on the revampment are also presented.The production capacity of the same plant with present IDR technique can be enhanced from 750t/d to 1000t/d if this new technique is applied. In the revamped technology process, as the ammonia stripping tower has been canceled, the IDR high pressure loop process will be predigested and the problems of unreasonable heating utilization ratio resulted from the loop of E1-R1 -E1 in the IDR urea will be resolved, and the problem of operation difficulty caused by small differentialpressure between El and R1. In order to utilize heat energy with reason, the self-thermal balance is employed in the synthesis tower with the result that steam consumption in the stripping tower has decreased and the total steam consumption in the system is also cut down. For the gas phase pipeline of the synthesis tower has been canceled and the top of the synthesis tower has been enclosed at the meantime, the utility ratio of the synthesis can be improved. The technology process of passive air can be predigested with passive air enters directly into the synthesis tower with CO2 gas, and the oil content in the system can decrease as the air compressor has been stopped. A self-stripping tower is used instead of CO2 stripping tower with results that the operation pressure of the stripping tower E2 is cut down and the efficiency of stripping is improved and circle material in the system is reduced. About 85 percent of the feeding CO2 is circling in the high pressure loop, and only 15 percent of that returns in form of methyl ammonium so that concentration of callback liquid falls and the pipeline is not choked easily any more.