Javad Abbasian

Regenerable mixed metal oxide sorbents for coal gas desulfurization at moderate temperatures

Abstract This paper reports on research conducted at the Institute of Gas Technology (IGT) for the development of durable metal oxide-based sorbents for fluidized-bed desulfurization of coal-derived fuel gases in the moderate temperature range of 350–550°C, which is currently of industrial interest. This study has systematically considered copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) oxides as bases for developing regenerable sorbents. The sorbent formulations prepared, their sulfidation performance and regenerability, and the physical and chemical properties of a select group of sorbents are presented and discussed. The results from multi-cycle evaluation tests of a few sorbents in a packed-bed reactor are also presented. The results of attrition resistance tests carried out according to the ASTM D 5757-95 method are also presented and their implications discussed in detail. Sorbents based on copper oxide were found to possess the best combination of high attrition resistance and sulfidation reactivity, sulfur removal efficiency, and pre-breakthrough conversion in the moderate temperature range of 350–550°C. Encouraging results were also obtained with sorbents based on manganese oxide; however, their regeneration necessitates very high temperatures that cannot be accommodated by current desulfurization systems requiring regeneration ignition temperatures of approximately 550°C. No sorbent based on iron oxide was found to have sufficient reactivity in the moderate temperature range.

Catalytic decomposition of ammonia in a fuel gas at high temperature and pressure

In connection with the purification of fuel gas for gas turbines in the IGCC process to meet NOx standards and maintain the thermal efficiency of the process, tests were carried out with a 7.5 cm pressurized reactor to decompose ammonia at high temperature (700–900°C) and pressure (2 MPa) using Ni-based catalysts. The effects of temperature, pressure, ammonia concentration and gas residence time were determined. The simulated coal gas composition was varied to allow assessment of the effect of contaminants (sulfur compounds and tars) on the ammonia decomposition efficiency of five catalysts under otherwise identical operating conditions. The results show that two of the catalysts tested are capable of efficiency reducing the concentration of ammonia in the gas.

Utilization of metal oxide-containing waste materials for hot coal gas desulfurization

Four metal oxide waste materials from metal processing operations and one coal bottom ash sample were procured and their reactivities toward hydrogen sulfide (H2S) were evaluated in the temperature range of 400°C to 600°C. A low-cost sorbent pelletization/granulation technique was applied to produce preliminary sorbent formulations in the form of attrition-resistant granules that were also evaluated. The results indicate that sorbents based on an iron oxide waste material, in the as-received as well as processed form, were the most reactive and exhibited the highest effective capacities for sulfur. The regeneration of these sorbents could be carried out over a relatively moderate temperature range, suggesting that the iron oxide waste material might be a viable candidate for the development of low-cost regenerable sorbents for H2S removal from hot coal gases under conditions of current practical interest.

Catalytic decomposition of ammonia in fuel gas produced in pilot-scale pressurized fluidized-bed gasifier

Abstract Integrated Gasification Combined Cycle (IGCC) process, incorporating pressurized gasification of solid fuels (coal, peat, biomass) and hot gas cleanup, is being developed worldwide to generate power with high efficiency and in an environmentally acceptable manner. The gasifier product gas contains, among others, ammonia and to a lesser extent hydrogen cyanide (HCN) which are converted to oxides of nitrogen (NO x ) when the gas is combusted in the gas turbine. Several nickel-based catalysts were developed and evaluated for decomposition of ammonia present in the gasifier product gas, at Enviropowers 15 MW th pilot plant in coal- and biomass-gasification tests. Up to 75% of ammonia in the product gas was decomposed at 800–900°C temperature range and 12–22 bar pressure.

ZnO-based regenerable sulfur sorbents for fluid-bed/transport reactor applications

Introduction High-temperature desulfurization of coal-derived fuel gases is an essential process in emerging power generation technologies, such as the Integrated Gasification Combined Cycle (IGCC), aiming to improve both the efficiency and environmental performance of power generation from coal. Hot gas desulfurization may be accomplished by using solid sorbents such as oxides of those metals that form stable sulfides. The effectiveness of a desulfurizing sorbent in treating such gases is related to the predicted equilibrium partial pressure of hydrogen sulfide (H2S), which will be present in a combination of the reduced form of the sulfide and oxide phases.

Development of durable and reactive regenerable sorbents for high temperature flue gas desulphurisation

One of the emerging technologies for combined SO2 and NOx removal from flue gases is the copper oxide process, which is based on the use of a regenerable sorbent. Sorbent properties such as SO2 sorption capacity, reactivity, crush strength, and long-term durability have significant impact on the overall process cost. In this study, a number of sorbents were prepared by using various modifications of the sol-gel technique. Compared to the commercially available sorbent used for evaluation of the process, sorbents prepared by wet impregnation of sol-gel alumina exhibited comparable sulphur capacity and about seven times higher crush strength, while those prepared by incorporation of copper in the sol resulted in three times higher sulphur capacity and 55% higher crush strength. Significant improvement in long-term durability was also achieved with these sorbents. Preliminary economic evaluation indicates that these new sorbents have the potential to reduce the projected levelised process cost down to 3.17 mil/kWh, which is lower than the cost of current SO2 emission allowance.

ADVANCED SORBENT DEVELOPMENT PROGRAM DEVELOPMENT OF SORBENTS FOR MOVING-BED AND FLUIDIZED-BED APPLICATIONS

The integrated gasification combined cycle (IGCC) power system using high-temperature coal gas cleanup is one of the most promising advanced technologies for the production of electric power from coal in an environmentally acceptable manner. Unlike conventional low-temperature cleanup systems that require costly heat exchangers, high-temperature coal gas cleanup systems can be operated near 482-538 C (900-1000 F) or higher, conditions that are a closer match with the gasifier and turbine components in the IGCC system, thus resulting is a more efficient overall system. GE is developing a moving-bed, high-temperature desulfurization system for the IGCC power cycle in which zinc-based regenerable sorbents are currently being used as desulfurization sorbents. Zinc titanate and other proprietary zinc-based oxides are being considered as sorbents for use in the Clean Coal Technology Demonstration Program at Tampa Electric Co.s (TECo) Polk Power Station. Under cold startup conditions at TECo, desulfurization and regeneration may be carried out at temperatures as low as 343 C (650 F), hence a versatile sorbent is desirable to perform over this wide temperature range. A key to success in the development of high-temperature desulfurization systems is the matching of sorbent properties for the selected process operating conditions, namely, sustainable desulfurization kinetics, high sulfur capacity, and mechanical durability over multiple cycles. Additionally, the sulfur species produced during regeneration of the sorbent must be in a form compatible with sulfur recovery systems, such as sulfuric acid or elemental sulfur processes. The overall objective of this program is to develop regenerable sorbents for hydrogen sulfide removal from coal-derived fuel gases in the temperature range 343-538 C (650-1000 F). Two categories of reactor configurations are being considered: moving-bed reactors and fluidized-bed (bubbling and circulating) reactors. In addition, a cost assessment and a market plan for large-scale fabrication of sorbents were developed. As an optional task, long-term bench-scale tests of the best moving-bed sorbents were conducted. Starting from thermodynamic calculations, several metal oxides were identified for potential use as hot gas cleanup sorbents using constructed phase stability diagrams and laboratory screening of various mixed-metal oxide formulations. Modified zinc titanates and other proprietary metal oxide formulations were evaluated at the bench scale and many of them found to be acceptable for operation in the target desulfurization temperature range of 370 C (700 F) to 538 C (1000 F) and regeneration temperatures up to 760 C (1400 F). Further work is still needed to reduce the batch-to-batch repeatability in the fabrication of modified zinc titanates for larger scale applications. The information presented in this Volume 1 report contains the results of moving-bed sorbent development at General Electrics Corporate Research and Development (GE-CRD). A separate Volume 2 report contains the results of the subcontract on fluidized-bed sorbent development at the Institute of Gas Technology (IGT).

Stabilization and Regeneration of Spent Sorbents

The sulfur compounds present in coal are converted to hydrogen sulfide when coal is gasified. To comply with environmental regulations, a high fraction of the sulfur must be removed from the product gas stream. Calcium-based sorbents are the prime candidates for in-bed capture of sulfur.