Advanced Sulfur Control Concepts in Hot-gas Desulfurization Technology. Quarterly Report, April 1--June 30, 1998 PDF Download
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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 : 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 : 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 : 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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Pages : 28
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The last six cycles of a 25-cycle sorbent durability test were completed, final installation of the flame photometric detector was accomplished, and fifteen tests whose aim was to determine the minimum prebreakthrough H2S concentration over reduced CeO2 were performed. There was little, if any, evidence of sorbent deterioration in the durability test. During the durability test the author confirmed that, when using pre-reduced sorbent and a clean system, the prebreakthrough H2S concentration was less than 100 ppmv, the detection limit of the thermal conductivity detector (TCD). Consequently, a more sensitive flame photometric detector (FPD) which permitted measurements of H2S concentrations of 1 ppmv or less was installed. The FPD and TCD were connected in parallel so that, when desired, the entire H2S breakthrough curve could be measured. Most of the quarter was devoted to conducting reduction-sulfidation tests to determine the minimum prebreakthrough H2S concentrations which could be achieved using prereduced CeO2. Fifteen runs involving variations in reduction-sulfidation temperature, H2S concentration in the feed gas, and feed gas volumetric flow rate were completed. In all tests the prebreakthrough H2S concentration was less than 10 ppmv, and in many of the tests the H2S concentration was equal to or less than 1 ppmv for an extended time period.
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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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Pages : 22
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