Process analysis and improvement of a Claus unit of an existing gas plant

摘要

This research is a part of Master degree research programme at Cranfield Universityto study Claus process and perform process analysis on an existing Sulphur recoveryunit in a gas plant.The Mellitah Plant, in Western Libya, is a gas plant designed to treat raw gas andcondensate from offshore gas fields in several processing units where the sour gas(H2S, CO2, COS, SC2) is removed to meet the international emission standard, in orderto control the emission and pollution from the flue gas. The acid gases are treated inClaus unit where H2S is converted to sulphur in multi-reaction steps. These reactionsstart in a combustion reaction zone, thermal reactor, to produce a suitable mixture ofH2S to SO2. The mixture reacts in Claus catalytic reactors to produce sulphur vapour.The sulphur vapour is condensed in multi-condensing steps after each catalyticreactor.The ultimate aim of this research is to carry out the process analysis for Claus unit inorder to recover the waste energy to increase the plant productivity, minimise the useof the plant utilities, and decrease the environmental pollution. A process model of theplant was developed and validated in Aspen HYSYS. The process was then analysed,the analysis has resulted in a significant increase in Claus unit overall conversion ratiowhich has increased from 61% to 97.63% H2S base. Consequently, Claus unitproductivity has increased by approximately 1.72 times. In addition, a higher amountof energy is recovered in a form of heat by heating the boiler feed water to produceboth high pressure steam in the waste heat boiler and low pressure steam in 1st and2nd sulphur condensers. Both high pressure and low pressure steam total productionare increased by 1.5 times. All this has been achieved at high conversion ratio numberof 2 in tail gas which represents optimum O2/H2S ratio in the thermal reactor feed andthe high conversion number can be kept in between 1.5 to 3 during plant normaloperation.