AM-01-35 NEW SELECTIVE H2S REMOVAL PROCESS FOR THE REFINING INDUSTRY

Description:

In the future the concentration of H2S in off-gases from refinery desulphurization processes is expected to increase as a result of reduced contents of sulphur in road transportation fuels due to stricter specifications. Higher capacity for recovering H2S from the process off-gas and subsequent conversion of the removed H2S to elemental sulphur in a Claus plant is then required to retain gaseous sulphur emissions. As part of the evaluation of alternative processing concepts for more efficient and selective removal of H2S from the off-gas process streams, Statoil’s Mongstad Refinery has facilitated testing of a new co-current gas-solvent contactor, named FramoPure 200, developed by Framo Purification. In principle the complete gas absorption unit comprises three serially configured contactor/separator units. As the off-gas flow is routed through the three contactor stages, the gas is exposed to solvent having sequentially lower sour gas loading. With this configuration the solvent obtains a higher H2S loading capacity than is typical for a one-stage counter-current contactor, for instance an absorption tower. At the same time, a superior absorption rate of H2S to other gas constituents can be achieved. Due to the short gas-liquid contact time, the absorption of other gases, as for instance CO2, is very low, and this will potentially free up Claus plant capacity. In order to test the performance of this concept, a skid mounted test unit has been installed to work in parallel to the existing counter-current DIPA plant at the Mongstad Refinery. Typical gas feed for this plant contains 2.5 % H2S and 1.5 % CO2. The gas absorption kinetics of H2S and CO2 have been modelled as a function of solvent loading, loading capacity, partial pressure of the gases and reaction rate constants. The model, verified experimentally, has been applied to simulate the total process. Thus far it has been demonstrated that the off-gas can be purified to an acceptable level of H2S (25 ppmv), with minimum co-absorption of CO2 . In the FramoPure unit only 10 % of the CO2 is co-absorbed compared to 60 % in a counter-current contactor. In addition, the extent of H2S removal is achieved with the FramoPure contactor volume being 40 times smaller than the volume in the counter-current contactor. Clearly, this performance demonstrates that significant processing capacity can be made available for the downstream Claus plant by applying the contactor developed by Framo Purification.