This paper will investigate how computer aided simulation tools may be used to evaluate the existing acid gas handling systems as well as potential modifications in these units. In particular, the benefits of changing amines, debottlenecking sulfur plants, oxygen enrichment, tail gas treatment options and general rules for optimizing these units will be reviewed. As a rule, it is always wise to determine the operational efficiency for each unit before any major modifications are initiated. This will hopefully prevent a new design from failing due to previously undetected internal or other problems.

Increasingly stringent sulphur emissions regulations often require renovation of older sulphur recovery units (SRUs) to improve overall recovery. Optimization or modification of an existing Claus SRU or the design of a new unit can be simplified by use of a process simulator. In this paper, Karl W. Mattsson-Bozé and Lili G. Lyddon of Bryan Research & Engineering present examples to show how TSWEET® can be used to model a Claus SRU and then to simulate modifications to aid in evaluating the best design.

Recovery of elemental sulphur from acid gas was first performed via the Claus process over 100 years ago. This article examines some Claus modifications which can alleviate operational difficulties and improve overall sulphur recovery.

Emphasis on environment concerns has pushed sulfur emissions to the fore-front. Present three stage Claus plants cannot reach the sulfur recovery requirement for small gas processing plants, therefore some form of special tail gas cleanup unit is required. Several processes yield higher recoveries than the three stage Claus unit but this paper is directed to an integrated system with a primary amine unit, a Claus unit, and a tail gas clean up unit. The overall sulfur recovery is in excess of 99.8%.

Integrated gas sweetening, sulfur and tail gas cleanup units (TGCU) were analyzed by a process simulation program, called TSWEET, to determine the sensitivity of the operating conditions and parameters on the performance of the system. The parameters investigated included the H2S/CO2 ratio in the acid gas from the main absorber, the hydrocarbon content of the acid gas, the reaction model for H2 and CO in the furnace, the formation and reaction of COS as well as CS2 and the CO2 slippage in the TGCU absorber. For the assortment of cases considered, the results showed that while some parts of the system were not overly sensitive to many of the operating conditions others were quite sensitive. Due to the complexity of the integrated system, a parameteric analysis is necessary to fully optimize the system.