High-temperature Sulfur Removal Research Articles

Improving the efficiency of CaO-based sorbent by SrCO3 for high-temperature sulfur removal during coal combustion

AbstractWith the goal of adding the appropriate amount of SrCO

High-Temperature Sulfur Removal from Biomass-Derived Synthesis Gas over Bifunctional Molybdenum Catalysts

Removal protocol: Molybdenum-based catalysts are efficient for the removal of H2S and organic sulfur species from gasified biomass at high temperatures. Water, which is ubiquitous in biomass, impedes desulfurization. In situ X-ray absorption spectroscopy analysis shows that H2S is removed from the biomass-derived producer gas through the sulfidation of MoO3 to MoS2, whereas MoO2 is the active phase for the removal of thiophene.

Integrated Process Configuration for High-Temperature Sulfur Mitigation during Biomass Conversion via Indirect Gasification

Sulfur present in biomass often causes catalyst deactivation during downstream operations after gasification. Early removal of sulfur from the syngas stream post-gasification is possible via process rearrangements and can be beneficial for maintaining a low-sulfur environment for all downstream operations. High-temperature sulfur sorbents have superior performance and capacity under drier syngas conditions. The reconfigured process discussed in this paper is comprised of indirect biomass gasification using dry recycled gas from downstream operations, which produces a drier syngas stream and, consequently, more-efficient sulfur removal at high temperatures using regenerable sorbents. A combination of experimental results from NREL’s fluidizable Ni-based reforming catalyst, fluidizable Mn-based sulfur sorbent, and process modeling information show that using a coupled process of dry gasification with high-temperature sulfur removal can improve the performance of Ni-based reforming catalysts significantly.

Manganese and ceria sorbents for high temperature sulfur removal from biomass-derived syngas – The impact of steam on capacity and sorption mode

Syngas derived from biomass and coal gasification for fuel synthesis or electricity generation contains sulfur species that are detrimental to downstream catalysts or turbine operation. Sulfur removal in high temperature, high steam conditions has been known to be challenging, but experimental reports on methods to tackle the problem are not often reported. We have developed sorbents that can remove hydrogen sulfide from syngas at high temperature (700°C), both in dry and high steam conditions. The syngas composition chosen for our experiments is derived from statistical analysis of the gasification products of wood under a large variety of conditions. The two sorbents, Cu-ceria and manganese-based, were tested in a variety of conditions. In syngas containing steam, the capacity of the sorbents is much lower, and the impact of the sorbent in lowering H2S levels is only evident in low space velocities. Spectroscopic characterization and thermodynamic consideration of the experimental results suggest that in syngas containing 45% steam, the removal of H2S is primarily via surface chemisorptions. For the Cu-ceria sorbent, analysis of the amount of H2S retained by the sorbent in dry syngas suggests both copper and ceria play a role in H2S removal. For the manganese-based sorbent, in dry conditions, there is a solid state transformation of the sorbent, primarily into the sulfide form.

Regenerable Manganese-Based Sorbent for Cleanup of Simulated Biomass-Derived Syngas

During biomass gasification, sulfur contained in the feedstock is converted primarily to hydrogen sulfide. Conventional technologies for sulfur removal such as amine scrubbing and ZnO sorption operate at much lower temperatures than those of gasification and tar reforming and are thus thermally inefficient for cleanup of biomass-derived syngas. This work aims to develop options for high-temperature sulfur removal. In this research, we focus our investigation on the regeneration chemistry of a manganese-based sorbent for sulfur removal at the high temperature, high steam conditions (700 °C and up to 68% steam) used for biomass gasification and subsequent syngas conditioning. We found that regeneration conditions that have a small amount of air or steam in combination with air would allow for equal sulfidation and regeneration time. We also demonstrated the effectiveness of both fresh and regenerated sorbents in protecting downstream tar and methane reforming catalysts.

Investigation on Desulfurization Performance and Pore Structure of Sorbents Containing Zinc Ferrite

Regenerable and durable sorbents for high-temperature sulfur removal are desired to achieve advanced power generation using coal gas fuel. Different precipitation methods using ammonia and urea were studied in this work to prepare zinc ferrite-silica composite particles. Two sorbents containing those powders were extruded and were evaluated in desulfurization performance and durability during cycles of repeated desulfurization at pressurized simulated coal gas conditions. Both sorbents could reduced sulfur compounds to less than 1 ppm during consecutive desulfurization cycles operated at 723 K and 0.98 MPa. The sorbent prepared by ammonia precipitation exhibited higher performance at initial sulfidation but declined in sulfidation kinetics after 20 cycles of tests. The urea-precipitated sorbent maintained its performance during the same desulfurization cycles. Although the residual sulfur was gradually increased for both sorbents, the sorbents maintained over 75% of their initial sulfur capacity at the end of the test. Pore distribution obtained by mercury porosimetry showed significant loss of mesopores of the ammonia-precipitated sample during the cycles, while the urea-precipitated sorbent maintained its mesopore structure. The primary particles of zinc ferrite in the fresh and spent sorbents were observed using FE-TEM. Primary particles of zinc ferrite in the ammonia-precipitated powder were much smaller (10-20 nm) than those of the urea-precipitated powder (100 nm diameter). Rapid decline in the ammonia-precipitated sorbent was due to the sintering of the fine primary particles. The latter kept their size after cyclic desulfurization. The durability of the sorbent was strongly affected by the primary particle size as determined by the preparation method and sorbent preparation is an important factor to enhance durability of the sorbent.

95/06325 High-temperature sulfur removal under fluidized bed combustion conditions - a chemical interpretation

95/06325 High-temperature sulfur removal under fluidized bed combustion conditions - a chemical interpretation

The sulfidation and regeneration of half-calcined dolomite

High-temperature sulfur removal from fuel gas, such as in the Westinghouse fluidized bed coal gasification process, may be achieved using dolomite in the reaction ▪ Although the regeneration process reduced the sorbent requirement and solid waste handling, a major problem has been the difficulty in completing regeneration and the decrease in regenerability with sulfidation/regeneration cycles. Reactions were carried out in a pressurized TG system and structural information of the solid products was obtained employing scanning electron microscopy, energy dispersive analysis by X-ray, electron microprobe analysis, and X-ray diffraction. The morphological changes during half-calcination, sulfidation, regeneration and cyclic sulfidation/regeneration reactions were correlated with chemical kinetic measurements obtained from TGA. A reaction mechanism which postulates the migration and crystallite growth of MgO onto CaS crystals explains the deterioration in dolomite regenerability, and is supported by the kinetic TG measurements. Time at temperature, and desulfurization temperature are the significant variables which control the regenerability of the product calcium sulfide.

What's new in high temperature sulfur removal systems for fluidized-bed coal gasification

High temperature sulfur removal can be achieved with calcium-based sor-bents (e.g. dolomite) in fluidized-bed çoal gasification systems now being developed for power generation. The use of dolomite offers the opportunity to meet environmental emission standards, to minimize energy losses, and to reduce electrical energy costs. In addition to removing sulfur from the low-Btu gas, the complete sulfur removal system must be integrated with the total power plant and environment to assure compatibility. Critical requirements for achieving commercial system include establishing criteria for ‘acceptable’ sorbents, establishing integrated sulfur removal/gasification process design parameters, predicting trace element release, predicting sorbent attrition, developing an economic regeneration and/or once through process option, developing a spent sorbent processing system, and establishing safe and reliable disposition options for spent sorbent. Design and operating parameters are being developed and potential process limitations are identified.