The ULTRA (Ultra Low Temperature Reaction Adsorption) process is an Amoco proprietary sulfur plant tail gas cleanup process for attaining sulfur recoveries of 99.7% or better. This process is an extension of the Amoco-licensed CBA design and was proven at a pilot unit operation completed in August 1982. This paper presents the process flow scheme, its relation to the CBA, an investment cost analysis, a comparison of the pilot plant results with laboratory findings, and a summary of the pilot plant operation.
The ULTRA process resembles the conventional CBA process in that the Claus reaction occurs at a sub-dewpoint temperature so that the elemental sulfur is largely retained on the catalyst as an absorbed phase, which is then regenerated periodically. It differs from the conventional CBA in that the CBA feed stream is pre-treated to remove water, reduce organic sulfur compounds to trace amounts, and establish the optimal ratio of reactants ahead of the CBA reactor.
The ULTRA (Ultra Low Temperature Reaction Adsorption) process is an Amoco proprietary sulfur plant tail gas cleanup process for attaining sulfur recoveries of 99.7% or better. This process is an extension of the Amoco-licensed CBA design1 with the ULTRA unit pre-treating the CBA feed stream to increase recovery from 99% to 99.7% or more.
In the CBA process, a final catalytic convertor is operated at a temperature below the sulfur dew point to increase conversion by the Claus reaction by shifting the reaction equilibrium. Sulfur formed is largely retained on the catalyst as an adsorbed phase instead of leaving the convertor in the effluent vapor, thus further increasing the equilibrium conversion. The catalyst is periodically regenerated by a hot slip stream from the Claus unit to remove the adsorbed sulfur and ensure continued activity.
The ULTRA-CBA resembles the conventional CBA1 in that the Claus reaction occurs at this low temperature. It differs from the conventional CBA in that water is removed, organic sulfur compounds are reduced to trace amounts, and the optimal ratio of reactants is established in the ULTRA unit ahead of the CBA reactor, all of which increases reaction efficiency. This paper discusses the results of the ULTRA pilot operation which was retrofitted to operate in combination with a 22 LTD two reactor Claus plant and CBA tail gas clean-up unit. The test was completed in August 1982.
The flow diagram of the ULTRA-CBA process is shown in Figure 1. The principal process steps are; (1) hydrogenation, (2) water removal, (3) oxidation, and (4) Cold Bed Adsorption (CBA) with the ULTRA unit acting as a pre-treatment for the CBA reactor. To retrofit ULTRA to a conventional CBA plant, only steps (1) to (3) would have to be added.
As shown in the more detailed flow diagram, figure 2, the Claus plant tail gas, heated to the hydrogenation temperature, goes to a hydrogenation catalytic reactor where all sulfur species (SO2, COS, CS2 and sulfur vapor) are converted to H2S. The effluent gas from the hydrogenation reactor is cooled and enters a direct-contact quench tower where 90% or more of the water is condensed.