Final Report: Removal of Sulfur From Gasified Coal at or Above 800°CEPA Contract Number: EPD07027
Title: Removal of Sulfur From Gasified Coal at or Above 800°C
Investigators: Mackay, Richard
Small Business: Eltron Research & Development Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2007 through August 31, 2007
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2007) RFA Text | Recipients Lists
Research Category: SBIR - Air Pollution , Small Business Innovation Research (SBIR)
In this Small Business Innovation Research Phase I project, Eltron Research, Inc. (Eltron) developed a novel, proprietary approach for removing sulfur from gasified coal products at gasification temperatures of 800°C to 900°C. Coal contains substantial amounts of sulfur that, if not captured when burned, can significantly impact human health. Sulfur dioxide (SO2) and sulfur oxide (SOx) emissions are highly regulated. The method for sulfur removal is based on using sulfide ion conducting metal sulfides. At high temperatures, and under a sulfur partial pressure gradient, the sulfur contained in the gasified coal stream is selectively removed. Using a sulfide ion conducting separation membrane enables true hot gas cleanup of sulfur from gasified coal.
Ion conductivity is a thermally activated process, ideally suiting these materials to high temperature applications. Although there are several metal oxides that exhibit oxygen ion conductivity, such as yttria-stabilized zirconia or doped ceria, there are very few materials that exhibit sulfide ion conductivity. However, there is a class of novel mixed metal sulfides that does exhibit sulfide ion conductivity. Like stabilized zirconia and doped ceria, this class of metal sulfides is characterized as solid electrolytes, which means that they are pure ion conductors, with little, if any, electronic conductivity. An electronic pathway can be built into the membrane by mixing the solid electrolyte with an electronically conducting phase, which forms a two-phase composite. This strategy has been used for oxygen separation with oxygen ion conductors, and has now been successfully demonstrated for sulfur separation.
This method for sulfur removal differs dramatically from known methods based on sorbents. Calculations show reduced capital costs for installing a membrane-based separation unit compared to current technology. The absence of moving parts and continuous long-term operation of membrane-based separation will reduce operating and replacement costs. The direct removal of sulfur in the elemental state will further reduce the costs of sulfur recovery plants based on the Claus process.
The work plan was separated into four distinct tasks: (1) fabricating the novel ceramic composite separation membranes; (2) testing these membranes in reactors for sulfur removal from a hydrogen sulfide (H2S) feed; (3) testing for sulfur removal from simulated coal gas streams; and (4) performing an economic analysis of this technology at its current level of development.
In the course of this project, two distinct and single-phase sulfur conducting materials were prepared and characterized. Each were combined with two different, electronically conducting phases and sintered to high density. These four distinct composite compositions were tested in separation reactors. Sulfur separation rates of 0.063 ml/min·cm2 were obtained from a 1 percent H2S feed. Sulfur also was removed from a 0.25 percent COS feed. Significant improvements in processing these materials and in analyzing the sulfur flux were made.
The scope of this project was limited to hot gas cleanup of coal gasification products. The technology is readily adapted to sulfur cleanup of other gases, such as natural gas. Because coal is the fuel source for more than 50 percent of the electricity generated in the United States, this technology is applicable to a large commercial market. Other possible applications involve replacement of Claus plants, in petroleum refining for example.
The current method of desulfurizing gasified coal products is to cool the gas and pass it through chemical or physical solvents. The sulfur subsequently can be recovered from the solvent. The clean gas stream then must be reheated as it is fed to the gas turbine and combusted for power generation. The cooling and heating steps required result in efficiency losses. A 1 percent efficiency loss represents well over $100,000 per year in lost power sales per plant. If the sulfur can be removed successfully at high temperature, the efficiencies can be improved from the current level of 40 percent to 44 percent.
In 2004, coal-fired power plants generated 50 percent of the electricity in the United States; it is projected that the amount of energy generated in coal fired plants will increase to 57 percent by the year 2030. During that time, electricity sales will increase 50 percent to 5,341 billion kWh. Of the 347 gigawatts (GW) additional capacity to come online during that time, 50 percent will be from coal-fired power plants. In addition, regulatory mandates will require upgrading existing capacity, such as adding selective catalytic reduction equipment to 118 GW of coal-fired capacity. Flue gas desulfurization equipment must be added to 141 GW and supplemental fabric filters to 126 GW before 2030. Fifty-five percent of the new coal capacity is expected to be generated by integrated gasification combined cycle (IGCC) plants. International markets show even larger growth potentials. Clearly, in new plants, and in upgrades to existing plants, the energy market is huge, and the increased efficiency of hot gas cleanup has the potential to produce billions of dollars in profit.
Eltron has extensive experience in the area of ion selective ceramic membranes, in mixed ion and electron conducting materials, and in gas separation technologies; Eltron also has a state-of-the-art ceramics processing facility.
Eltron has proved the feasibility of using sulfide ion conducting membranes for hot gas desulfurization. During Phase II research, Eltron will begin making contacts with potential business partners who also are committed to commercializing this breakthrough energy production technology. By the completion of Phase II, Eltron will be ready to move the technology out of the lab and construct a demonstration scale unit that can be tied to an existing coal gasifier to demonstrate performance in an industrial setting at an appropriate scale.