(81c) UCSRP: A Flexible Sulfur Removal Process for Sweetening Natural Gas

Arun Basu, Howard Meyer, Dennis Leppin, Jim Zhou and Ajay Makkuni

Gas Technology Institute

Abstract:

With the recent activities in the area of unconventional natural gas (such as, Shale Gas) in the U.S., the need for a low-cost sulfur removal technology for processing relatively small as well as large CO₂-rich gas streams has increased significantly.  In a conventional amine-based NG processing plant, the H₂S-rich stream from the stripper unit is treated in a Claus process for the production of elemental sulfur (the gas-phase reaction is 2H₂S + SO₂  = 3S + 2H₂O).  The Claus process has specific inherent limitations including (i) the need for a tail-gas clean-up unit (e.g., Shell Claus Off-gas Treatment: SCOT) due to equilibrium-limited reaction, (ii) inability to handle low sulfur production capacities (typically, for less than 20 tons/day sulfur), and (iii) the need for an additional CO₂-separation step prior to the Claus step if the gas stream from the Amine unit contains relatively high CO₂ (typically, if the CO₂ /H₂S ratio is greater than 2.3).

Gas Technology Institute (GTI) has been working with the University of California, Berkeley, for further development of their UCSRP (University of California Sulfur Recovery Process) technology.  In this process, the Claus reaction is conducted in liquid phase at about 250-300 ^oF (and at any pressure) to produce liquid sulfur in the presence of an organic solvent and a homogeneous catalyst.  A gas mixture consisting of a part of the H₂S-rich feed gas plus the unreacted H₂S stream from the UCSRP reactor is combusted with air in a furnace to form SO₂ (plus a small amount of sulfur) which is recovered in an absorber/stripper unit for recycle to the UCSRP reactor.  As the overall sulfur recovery is 99.9+%, there is no need for a tail-gas clean-up unit.  The UCSRP process can be scaled down to sulfur capacities significantly lower than 20 LT/day.  For CO₂-rich feed streams from an amine plant, the gas can be processed directly in a UCSRP unit without a separate CO₂ removal unit.  For direct processing of natural gas with relatively low CO₂ levels that already meet pipeline specifications, the UCSRP process will replace Amine/Claus-SCOT units; for higher CO₂ levels in feed natural gas, the exit gas from the UCSRP reactor will be treated to remove CO₂.without the complexity inherent when H₂S is also present in the stream.

For the processing of a H₂S-rich gas stream from an amine plant stripper with sulfur production at about 76 LT/day, Kellogg, Brown and Root Inc. had estimated the capital cost for an UCSRP plant to be about 60% and the operating costs to be about 68% of those for a three-stage Claus/SCOT plant.