Advanced Sulfur Control Concepts in Hot-gas Desulfurization Technology. Quarterly Report, April 1--June 30, 1997 PDF Download
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Languages : en
Pages : 43
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Three areas of research were pursued during the past quarter. Experimental CeO2 sulfidation and regeneration tests examined the effect of SO2 concentration and gas flow rate on the production of elemental sulfur during regeneration. The maximum number of cycles using a single sorbent charge was increased to 13, and initial tests using a second source of CeO2 (from Molycorp, Inc.) were carried out. In the process analysis effort, a third case study based on single-stage desulfurization using CeO2 sorbent was added. Capital and operating costs for this option were estimated under base case conditions. The sensitivity of the annual levelized cost of all three cases to variations in sorbent durability, sorbent unit cost, O2 and N2 unit cost, and capital cost was examined. As the sorbent cost was reduced, based on smaller sorbent replacement rate and/or smaller sorbent unit cost, the annual levelized cost of all three processes decreased, and the cerium process became more attractive. For example, at a sorbent replacement rate of 0.1% of the sorbent circulation rate, both cerium processes should be less costly than the single-stage zinc sorbent process. As the sorbent replacement rate approaches zero (infinite sorbent lifetime), income from the sulfur by-product and export steam produced by the cerium processes exceeds the other process costs and a profit of $2 to 2.5 million appears possible. In contrast, the annual levelized cost of the zinc-based process at zero sorbent replacement rate is about $5 million.
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Pages : 43
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Three areas of research were pursued during the past quarter. Experimental CeO2 sulfidation and regeneration tests examined the effect of SO2 concentration and gas flow rate on the production of elemental sulfur during regeneration. The maximum number of cycles using a single sorbent charge was increased to 13, and initial tests using a second source of CeO2 (from Molycorp, Inc.) were carried out. In the process analysis effort, a third case study based on single-stage desulfurization using CeO2 sorbent was added. Capital and operating costs for this option were estimated under base case conditions. The sensitivity of the annual levelized cost of all three cases to variations in sorbent durability, sorbent unit cost, O2 and N2 unit cost, and capital cost was examined. As the sorbent cost was reduced, based on smaller sorbent replacement rate and/or smaller sorbent unit cost, the annual levelized cost of all three processes decreased, and the cerium process became more attractive. For example, at a sorbent replacement rate of 0.1% of the sorbent circulation rate, both cerium processes should be less costly than the single-stage zinc sorbent process. As the sorbent replacement rate approaches zero (infinite sorbent lifetime), income from the sulfur by-product and export steam produced by the cerium processes exceeds the other process costs and a profit of $2 to 2.5 million appears possible. In contrast, the annual levelized cost of the zinc-based process at zero sorbent replacement rate is about $5 million.
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Languages : en
Pages : 28
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Twenty-five reduction/sulfidation tests plus one sulfidation/regeneration test were completed during the quarter. The reduction/sulfidation tests examined the behavior of six cerium oxide sorbents from different sources with reaction variables of temperature, pressure, gas composition and flow rate. Most significantly, steam was added to the sulfidation feed gas for the first time. Tests using pre-reduced sorbents and tests in which reduction and sulfidation occurred simultaneously were performed. Prebreakthrough H2S concentrations less than 10 ppmv were obtained over a range of reaction conditions with prebreakthrough concentrations as low as 1 ppmv achieved at the most favorable conditions. The general response to reaction variables was as expected except when feed rate was varied. In some of these cases the FPD breakthrough time did not correspond to expectation. The single regeneration run was conducted at 600 C and 2 atm using 12% SO2 in N2 at a feet rate of 400 sccm. This was the first regeneration test at other than 1 atm pressure; favorable results were obtained. The only experimental objective remaining is additional high pressure regeneration testing.
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Languages : en
Pages : 47
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Experimental effort during the past quarter was restricted to the fixed-bed reactor. Effort during April was devoted to the sulfidation and regeneration of cerium oxide. Sulfidation tests were plagued by over-sulfidation, i.e., the quantity of H2S removed from the gas phase exceeded the stoichiometric amount associated with the conversion of CeO2 to Ce2O2S. This was initially attributed to the formation of Ce2S3 which was found to be thermodynamically possible in the highly reducing feed gas. However, the addition of steam to the feed gas to prevent Ce2S3 formation did not eliminate the over-sulfidation problem. Later tests indicated that the apparent over-sulfidation was due to reaction between H2S and the walls of the reaction vessel. Apparently the alonizing treatment to passivate the reactor walls was either ineffective at the reaction conditions or had deteriorated with use to the point that protection was no longer viable. Limited Ce2O2S regeneration results, although very qualitative, were quite favorable. In one regeneration test in an O2-N2 atmosphere, no SO2 or H2S were detected by the chromatograph in the regeneration product. Significant amounts of total sulfur were detected, and the test had to be terminated prematurely when elemental sulfur caused the product line leading to the chromatograph to plug. Experimental tests during May and June examined the regeneration of FeS as a function of temperature, gas feed composition, and gas flow rate. Complete regeneration was achieved with as much as 75% of the sulfur liberated in elemental form. Low regeneration temperature and large ratios of H2O to O2 in the feed gas promote the formation of elemental sulfur. A number of changes in the reactor system were made during the quarter, including improvements to the sulfur condenser and filters on the reactor product line leading to the gas chromatograph.
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Languages : en
Pages : 22
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Pages : 27
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The primary objective of this research project is the direct production of elemental sulfur during the regeneration of known high temperature desulfurization sorbents. The contract was awarded to LSU on April 12, 1994, and this quarterly report covers accomplishments during the first 2 1/2 months of the project. Effort during the initial 2 1/2 month period has been limited to Tasks 1 and 2, and involves a search of the literature to identify concepts for producing elemental sulfur during regeneration of known metal oxide sorbents and a thermodynamic evaluation of these concepts. While searching and evaluating the literature is a continuing process, concentrated effort on that phase is now complete and a detailed summary is included in this report. Three possible concepts for the direct production of elemental sulfur were identified in the LSU proposal, and the literature search has not uncovered any additional concepts. Thus, the three concepts being investigated involve: (1) regeneration with SO2, (2) regeneration with mixtures Of 02 and H2O, and (3) regeneration with H2O. While concept (3) directly produces H2S instead of elemental sulfur, the concept is included because the possibility exists for converting H2S to elemental sulfur using the Claus process. Each of the concepts will ultimately be compared to the Direct Sulfur Recovery Process (DSRP) under development by RTI. DSRP involves initial sorbent regeneration to SO2, and the inclusion of additional processing steps to reduce the SO2 to elemental sulfur.
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Languages : en
Pages : 44
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Favorable results were achieved in the sulfidation of CeO2 by H2S and the regeneration of Ce2O2S by SO2. Successful removal of approximately 99% of the H2S from the sulfidation gas to levels of about 100 ppmv (or lower), and the production of approximately 12% elemental sulfur (as S2) in the regeneration product gas were highlights. Final effort in the preliminary phase included a ten-cycle test at standard sulfidation and regeneration conditions with little or no sorbent deterioration. In the initial test of the detailed experimental phase of the program, the authors investigated the effect of temperature on the regeneration reaction. Results of preliminary tests showed that the Ce2O2S-SO2 reaction did not occur at 350 C, and all subsequent regeneration tests were at 600 C where the reaction was rapid. Significant progress has been made on the process analysis effort during the quarter. Detailed process flow diagrams along with material and energy balance calculations for six design case studies were completed in the previous quarter. Two of the cases involved two-stage desulfurization with steam regeneration, three used two-stage desulfurization with SO2 regeneration, and the sixth was based on single-stage desulfurization with elemental sulfur recovery using the DSRP concept. In the present quarter, major process equipment was sized for each of the six cases. Preliminary annual operating and levelized total cost estimates were then completed for two design cases--one involving two-stage desulfurization with SO2 regeneration and the second based on single-stage desulfurization with DSRP.
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