Advanced Pollution Control for Gasification of Varied Opportunity Fuels

Abstract

Advances in gasification technology have opened up a number of commercial opportunities to generate energy from a wide range of non-traditional feed stocks. Gasification technology platforms from a number of providers are in development with the goal of creating modular solutions for supplying the energy needs of local communities, often in solutions as small as 10 to 20 MW increments. Such technologies offer potential project developers the ability to explore local opportunities for fuel supply from a number of sources. These opportunity fuels cover a wide range of potential energy sources as far reaching as recovered plastic, recovered tires, poultry litter, and a wide variety of woody biomass. The syn-gas produced from the gasification of such varied opportunity fuels contains a number of undesired trace components. These components will need to either be removed via gas conditioning, or alternatively be combusted with the syn-gas in an oxidation step which will produce a flue gas requiring air pollution control. Gas conditioning requirements vary depending on the desired end use of the syn-gas whether as a utility quality fuel or as an intermediate to a further chemical pathway. Flue gas target levels are defined by current environmental legislation. The potential pollutants produced in the flue gas pathway include Particulate Matter, Hydrogen Chloride, Sulfur Dioxide, Sulfuric Acid Mist, and Oxides of Nitrogen. To ensure operational compliance of the system stack emissions both now and in the future, proper pollution control technology is paramount. This presentation will address an emerging air pollution control technology that embodies all of these removal steps in a single device specifically designed to meet current and expected future environmental needs. EISENMANN’s recently patented multi-pollutant control system, the Wet Electrostatic Precipitator Dual Field or WESP-2F, includes the use of a pre-scrubbing chamber for large PM, SO2, and water soluble NO2 removal. Following the quench and pre-scrubbing region, a specially tuned downflow wet ESP field is responsible for finer PM and Sulfuric Acid aerosol removal, as well as an important Ozone producing stage that oxidizes non-water soluble forms of NOx. As the gas continues to travel through the system, a secondary scrubbing chamber is used to further reduce NOx by scrubbing the newly formed NO2 that has been formed from the oxidation of other forms of NOx through the use of Ozone produced by the electrostatic precipitator. The final polishing stage of the system includes an upflow wet electrostatic precipitator field for the removal of newly oxidized material as well as any heavy metals present. Research and testing on the aforementioned system took place using a pilot sized unit operating a slipstream off a 20 MW commercial sized gasifier testing a number of opportunity fuels. Expected performance was validated proving high removal efficiencies for pollutants specifically addressed earlier. Results from a wide variety of opportunity fuels will be discussed. Current implementation of the technology in gasification projects following the flue gas pathway is underway and is currently viewed as an acceptable solution to the environmental regulations associated with the plant requirements.