Advanced Sulfur Control Concepts for Hot Gas Desulfurization Technology. Quarterly Report, January 1--March 31, 1997 PDF Download
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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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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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Languages : en
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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Languages : en
Pages : 22
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Pages : 35
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The last experimental tests involving FeS regeneration in both the atmospheric pressure and high pressure electrobalance reactors were completed during the quarter. The effects of temperature, reactant composition, and flow rate were studied in the atmospheric pressure electrobalance in atmospheres of O2/N2, H2O/N2, and O2/H2O/N2. The same parameters plus pressure were studied in the high pressure electrobalance. Essentially all runs were carried out at volumetric flow rates sufficiently large to eliminate external mass transfer resistance. The initial regeneration rate was found to be a weak function of temperature and to be first-order in both O2 and H2O. In tests involving both O2 and H2O, the initial reaction rate was equal to the sum of the individual rates involving O2 only and H2O only. The effect of pressure on the initial reaction rates in high pressure tests was somewhat unexpected in that the initial rate increased with pressure between 1 and 5 atm, and subsequently decreased between 5 and 15 atm. Statistical analysis and correlation of the electrobalance data have been completed and results are presented in this report. Equations for the initial rate of regeneration of FeS in O2 and H2O as a function of temperature and reactive gas concentration have been developed. Slow progress has been made with the fixed-bed reactor. A number of reactor scoping tests involving FeS regeneration in O2 and H2O, and CeO2 sulfidation in H2S were completed during the quarter. Chromatographic product gas analysis is now working reliably. Final repairs on the PMT temperature controller for the Antek total sulfur analyzer were completed and the unit seems to be functioning as expected. The Antek and GC responses in FeS regeneration runs in which all sulfur should be liberated as SO2 tracked reasonably well.
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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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Pages : 59
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Good progress was made on both the experimental and process modelling fronts during the past quarter. All experimental tests used the fixed-bed laboratory reactor to study the sulfidation of CeO2 with H2S and the regeneration of Ce2O2S using SO2. A number of experimental problems were solved (or at least alleviated) during the quarter including malfunctioning mass flow controllers, excessive bed pressure drop, and elimination of the H2S plateau during early stages of sulfidation tests. Most CeO2 sulfidation tests were carried out a 800°C and 5 atm using a sulfidation gas containing 1% H2S, 10 % H2, balance N2. At these conditions sulfidation of CeO2 was rapid and complete. Sulfur material balance closure was satisfactory, and, except for the unexpected H2S plateau during the prebreakthrough period, the sulfidation results were as expected. Near the end of the quarter, the cause of the H2S plateau was tentatively identified as being due to reaction between H2 and elemental sulfur deposited downstream of the sorbent in the bottom of the reactor and in tubing leading to the gas chromatograph. The sulfur deposits occurred during regeneration tests, and chemically cleaning the lines between regeneration and sulfidation coupled with reducing the temperature of the transfer line during sulfidation greatly reduced the H2S plateau. A brief examination of the effect of sulfidation temperature between 700 and 850°C showed relatively little temperature effect, although the slope of the active portion of the breakthrough curve was somewhat smaller at 700°C, which is consistent with a smaller reaction rate at this temperature.
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