Advanced Gasification By-Product Utilization

Abstract

With the passing of legislation designed to permanently cap and reduce mercury emissions from coal-fired utilities, it is more important than ever to develop and improve upon methods of controlling mercury emissions. One promising technique is carbon sorbent injection into the flue gas of the coal-fired power plant. Currently, this technology is very expensive as costly commercially activated carbons are used as sorbents. There is also a significant lack of understanding of the interaction between mercury vapor and the carbon sorbent, which adds to the difficulty of predicting the amount of sorbent needed for specific plant configurations. Due to its inherent porosity and adsorption properties as well as on-site availability, carbons derived from gasifiers are potential mercury sorbent candidates. Furthermore, because of the increasing restricted use of landfilling, the coal industry is very interested in finding uses for these materials as an alternative to the current disposal practice. The results of laboratory investigations and supporting technical assessments conducted under DOE Subcontract No. DE-FG26-03NT41795 are reported. This contract was with the University of Kentucky Research Foundation, which supports work with the University of Kentucky Center for Applied Energy Research and The Pennsylvania State University Energy Institute. The worked described was part of a project entitled ''Advanced Gasification By-Product Utilization''. This work involved the development of technologies for the separation and characterization of coal gasification slags from operating gasification units, activation of these materials to increase mercury and nitrogen oxide capture efficiency, assessment of these materials as sorbents for mercury and nitrogen oxides, assessment of the potential for leaching of Hg captured by the carbons, analysis of the slags for cement applications, and characterization of these materials for use as polymer fillers. The objectives of this collaborative effort between the University of Kentucky Center for Applied Energy Research (CAER), The Pennsylvania State University Energy Institute, and industry collaborators supplying gasifier char samples were to investigate the potential use of gasifier slag carbons as a source of low cost sorbent for Hg and NOX capture from combustion flue gas, concrete applications, polymer fillers and as a source of activated carbons. Primary objectives were to determine the relationship of surface area, pore size, pore size distribution, and mineral content on Hg storage of gasifier carbons and to define the site of Hg capture. The ability of gasifier slag carbon to capture NOX and the effect of NOX on Hg adsorption were goals. Secondary goals were the determination of the potential for use of the slags for cement and filler applications. Since gasifier chars have already gone through a devolatilization process in a reducing atmosphere in the gasifier, they only required to be activated to be used as activated carbons. Therefore, the principal objective of the work at PSU was to characterize and utilize gasification slag carbons for the production of activated carbons and other carbon fillers. Tests for the Hg and NOX adsorption potential of these activated gasifier carbons were performed at the CAER. During the course of this project, gasifier slag samples chemically and physically characterized at UK were supplied to PSU who also characterized the samples for sorption characteristics and independently tested for Hg-capture. At the CAER as-received slags were tested for Hg and NOX adsorption. The most promising of these were activated chemically. The PSU group applied thermal and steam activation to a representative group of the gasifier slag samples separated by particle sizes. The activated samples were tested at UK for Hg-sorption and NOX capture and the most promising Hg adsorbers were tested for Hg capture in a simulated flue gas. Both UK and PSU tested the use of the gasifier slag samples as fillers. The CAER analyzed the slags for possible use in cement applications. The division of tasks reduced overall (Abstract truncated)