Advanced Sulfur Control Concepts for Hot Gas Desulfurization Technology. Quarterly Report, January 1995-March 1995 PDF Download
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Languages : en
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Author:
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Author:
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Category :
Languages : en
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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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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 : 31
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In the area of gas analysis, most of the attention during the past quarter was devoted to gaining an understanding of the operation of the Antek total sulfur analyzer, and making appropriate modifications in the unit. The primary problem is that the resistance of the capillary flow restrictor is not large enough, and the amount of sulfur which reaches the UV-analyzer results in the analyzer becoming saturated. We have added a N2 diluent flow downstream of the pyrotube tube which, we believe, will permit the unit to be operated at pressures to about 50 psig. Use of larger diluent flow rates to permit higher pressure operation is not feasible since larger diluent rates increase the back pressure on the quartz pyrotube (which operates at 1050°C) to unsafe levels. In the meantime, Antek is studying the redesign of the capillary flow restrictor to provide larger flow resistance. Studies on the regeneration of FeS in the atmospheric pressure reactor were almost completed during the quarter. Only a series of multicycle sulfidation-regeneration tests remains. The effects of reactive gas mol fraction and temperature have been examined using both O2/N2 and H2O/N2 atmospheres. The initial rate of regeneration was found to be a weak function of temperature and first-order in both O2 and H2O concentration. In a test series in which the reactive gas contained both O2 and H2O, the experimental initial rate was effectively equal to the sum of the individual initial rates, suggesting that the two reactions proceed independently of one another. Detailed correlation and statistical analysis of the data is currently being done. Principal effort during the quarter using the high pressure electrobalance was devoted to studying the regeneration of FeS in a H2O/N2 atmosphere.
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Pages : 36
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Both the Antek total sulfur analyzer and the modifications to the Shimadzu GC-14A gas chromatograph to be used for analysis for SO2 and H2S were delivered during the quarter. Problems were faced during the installation and calibration phases of both instruments. By the end of the quarter we believe that the GC problems have been solved, but problems remain with the Antek analyzer. It appears that too much sulfur (as SO2) reaches the UV detector and causes it to become saturated. This shows up as a maximum in the instrument calibration curve. At 200 psia, the capillary flow restrictor allows a total flow rate of about 180 sccm, and the maximum occurs at about 1 % H2S in the calibration gas. Reducing the pressure so that the total flow is reduced to about 25 sccm shifts the calibration curve maximum to about 5.7% H2S. It appears that we must reduce the total flow rate to the detector or provide additional dilution. This may be accomplished by increasing the resistance of the capillary restrictor, by diverting a portion of the flow leaving the pyrotube to vent, or adding an inert such as N2 to the gases exiting the pyrotube. We are in contact with Antek representatives about the problem. Both the atmospheric pressure and high pressure electrobalances were used during the quarter to study the regeneration of FeS in atmospheres of O2/N2 or H2O/N2. In the atmospheric pressure unit the effects of temperature (600 - 800°C), flow rate (130 - 500 sccm), and reactive gas mol fraction (0.005 to 0.03 O2 and 0.1 to 0.5 H2O) are being studied. Regeneration tests completed to date in the high pressure unit have utilized only O2/N. and the parameters studied include temperature (600 - 800°C), flow rate (500 - 1000 sccm), pressure (1 - 15 atm) ad O2 mol fraction (0.005 - 0.03).
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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 : 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.
