Raghubir P. Gupta

Hot-gas cleanup—sulfur recovery technical, environmental, and economic issues

Abstract Advanced high-efficiency integrated gasification combined cycle (IGCC) power systems employing hot-gas cleanup are being developed to produce electric power from coal. Hot-gas cleanup consists of hot particulate removal and hot-gas desulfurization (HGD) technologies that match or nearly match the temperature and pressure of the gasifier and turbine generator. HGD is carried out using solid regenerable metal oxide sorbents that can remove the sulfur down to low parts per million and can be regenerated with air for multicycle operation. Economic studies have shown that HGD results in lower capital and operating costs than conventional cold gas desulfurization. Development of efficient sorbent desulfurization-regeneration reactor and tailgas treatment subsystems properly integrated with the overall IGCC systems is a key requirement for successful commercialization of HGD.

Design and operation of a pilot-scale catalytic biomass pyrolysis unit

RTI International is developing an advanced biofuels technology that integrates a catalytic biomass pyrolysis step and a hydroprocessing step to produce infrastructure-compatible biofuels. At the current stage of development, the catalytic biomass pyrolysis process is being scaled-up in a 1 tonne per day (1 TPD) pilot plant based on a single-loop transport reactor design with continuous catalyst circulation and regeneration. The chemistry of biomass pyrolysis is manipulated by the catalyst and by controlling the pyrolysis temperature, vapor residence time, and biomass-to-catalyst ratio. The pilot unit has been successfully operated with a novel catalyst that produces a bio-crude intermediate with 24 wt% oxygen. Product yields and composition in the pilot plant are consistent with results obtained in a laboratory-scale 2.54 cm diameter bubbling fluidized bed reactor. The overall mass balance was 93%, while the carbon closure was 83%.

Catalytic Ammonia Decomposition for Coal-Derived Fuel Gases

The objective of this study is to develop and demonstrate catalytic approaches for decomposing a significant percentage (up to 90 percent) of the NH{sub 3} present in fuel gas to N{sub 2} and H{sub 2} at elevated temperatures (550 to 900{degrees}C). The NH{sub 3} concentration considered in this study was {similar_to}1,800 to 2,000 ppmv, which is typical of oxygen-blown, entrained-flow gasifiers such as the Texaco coal gasifier being employed at the TECO Clean Coal Technology Demonstration plant. Catalysts containing Ni, Co, Mo, and W were candidates for the study. Before undertaking any experiments, a detailed thermodynamic evaluation was conducted to determine the concentration of NH{sub 3} in equilibrium with the Texaco gasifier coal gas. Thermodynamic evaluations were also performed to evaluate the stability of the catalytic phases (for the various catalysts under consideration) under NH3 decomposition conditions to be used in this study. Two catalytic approaches for decomposing NH{sub 3} have been experimentally evaluated. The first approach evaluated during the early phases of this project involved the screening of catalysts that could be combined with the hot-gas desulfurization sorbents (e.g., zinc titanate) for simultaneous NH{sub 3} and H{sub 2}S removal. In a commercial system, this approach would reduce capital costs by eliminating a process step. The second approach evaluated was high-temperature catalytic decomposition at 800 to 900{degrees} C. In a commercial hot-gas cleanup system this could be carried out after radiative cooling of the gas to 800 to 900{degrees}C but up stream of the convective cooler, the hot particulate filter, and the hot-gas desulfurization reactor. Both approaches were tested in the presence of up to 7,500 ppmv H{sub 2}S in simulated fuel gas or actual fuel gas from a coal gasifier.

Advanced Sulfur Control Processing

The primary objective of this project is to determine the feasibility of an alternate concept for the regeneration of high temperature desulfurization sorbents in which elemental sulfur, instead of SO{sub 2}, is produced. If successful, this concept will eliminate or alleviate problems caused by the highly exothermic nature of the regeneration reaction, the tendency for metal sulfate formation, and the need to treat the regeneration off-gas to prevent atmospheric SO{sub 2}, emissions. Iron and cerium-based sorbents were chosen on the basis of thermodynamic analysis to determine the feasibility of elemental sulfur production. The ability of both to remove H{sub 2}S during the sulfidation phase is less than that of zinc-based sorbents, and a two-stage desulfurization process will likely be required. Preliminary experimental work used electrobalance reactors to compare the relative rates of reaction of O{sub 2} and H{sub 2}O with FeS. More detailed studies of the regeneration of FeS as well as the sulfidation of CeO{sub 2} and regeneration of Ce{sub 2}O{sub 2}S are being carried out in a laboratory-scale fixed-bed reactor equipped with a unique analytical system which permits semi-continuous analysis of the distribution of elemental sulfur, H{sub 2}S, and SO{sub 2} in the reaction product gas.

Development of a Dry Sorbent-based Post-Combustion CO2 Capture Technology for Retrofit in Existing Power Plants

The objective of this research and development (R&D) project was to further the development of a solid sorbent-based CO2 capture process based on sodium carbonate (i.e. the Dry Carbonate Process) that is capable of capturing>90% of the CO2 as a nearly pure stream from coal-fired power plant flue gas with <35% increase in the cost of electrictiy (ICOE).