Engro 40 Years' Experience Of Total Recycle Urea Plant

摘要

This paper shares the learning's of Engro 40 years' experience, revamping of urea plant to improve efficiency & capacity, many catastrophic incidents & operational emergencies of total recycle urea plant. Engro's urea-1 plant voyage started from 515MTD urea plant with local ammonia venting without vent stack systems to the EPA and OSHA practiced 780MTD capacity plant with two vent stack systems which is the part of this paper. Under the energy improvement drive engro approached casale trays for their latest design and high efficiency trays for the urea reactor. Rapid and complete depressurization of ammonia reservoir (13met) in the atmosphere without vent stack systems is one the major catastrophic incident in the history of engro which lead to in level-2 emergency, as a result of such incidents engro had gone through a wide-ranging project named large ammonia release (LARA) to handle such incidents in future by making the plant inherently safe. Plant major hardware modifications to make it inherently safe are also part of this paper. Urea plant reactor bulged due to weep-hole leakage which causes plant shut down for 40 days, major learning of this incidents are also part of the paper. Bursting of pressure safety devices during startup & shut down was frequent at urea plant in last 30year's. Reactor pressure during aqua ammonia circulation was reduced to max 1500psig from 3000psig and high pressure loop pressure was also maintained at lower side to avoid pressure safety device (PSD) rupturing and hammering. This paper also covers change in urea plant startup & shut down sop which gives rise to 90% decrease in PSD rupture. A pressure safety device is the last line of defense in case of pressurization of any vessel. This paper also covers many incidents, of rupturing of PSD of high pressure decomposer; gas condenser; low pressure decomposer and high pressure absorber cooler, due to abnormal urea plant operations. High pressure decomposer sight glass leakage and emergency plant shut down is also covered in this paper. Some of the incidents eventually came in front in the form of level-1 emergencies. Carbon dioxide carried over about six times in the history of Engro total recycle urea plant operation due to different abnormal plant operations so far. This paper also shares the learning's of C02 carryover emergencies in 40 years' Engro total recycle urea plant.