Characterization of Emissions from Small Scale Biomass Gasifier

Abstract

Gasification of biomass has the potential to address many issues related to both the world's energy future and greenhouse gas emissions. Gasification can be carried out in a variety of ways depending on the end-use application of the synthesis gas (syngas) or producer gas. Gasification can also use a variety of feedstocks. Gasifying agricultural waste to generate electricity or provide heating and cooling solutions has the potential to utilize waste products while providing necessary energy. Unfortunately, there are environmental and human health concerns related to the conversion of biomass to energy and the combustion of the bio-derived fuel, as well as efficiency concerns related to the technology. In this study, The Power Pallet, a commercially available integrated gasification reactor, engine and generator was used to quantify the contaminants in the unfiltered producer gas, the filtered producer gas, and the engine exhaust and determine the engine's ability to reduce contaminants through filtration and combustion. The system was also tested to determine the effect of generator loading on operating conditions, emissions, and overall efficiency. The study used a fixed-bed downdraft modified Imbert reactor with a Kubota spark-ignited natural gas engine with a Mecc Alte 10kW generator. Organic solvent, gaseous and particulate matter emissions were characterized at three locations in the gasification system to determine the packed bed filter and engine's ability to reduce concentrations of contaminants. Contaminants, such as benzene, toluene, ethylbenzene, and xylenes (BTEX) and PM, in the gasifier system were cleaned up through the packed bed filter and through combustion in the engine. PM concentrations were approximately 70 mg/Nm3 in the pre-filtered producer gas but concentrations were reduced 98-99% through the packed bed filter. PM concentrations did not change significantly during the combustion in the engine yet specific concentrations of PM were below federally mandated emissions limits for Tier 4 diesel engines. Combustible compound were 99% consumed in the engine and specific concentrations of carbon monoxide were below federally mandated levels from the engine's exhaust. Concentrations of BTEX compounds were reduced to a small degree in the packed bed filter and significantly reduced in the engine. Although concentrations of benzene in engine exhaust were greater than 10 ppm, operating the gasification system in a well-ventilated environment would ensure that the ambient air concentrations of BTEX compounds are below federal limits and protect human health and the environment from the hazards. The efficiency of the reactor increased significantly with increasing electrical load because the reactor operates at constant temperature and the higher flow rates of biomass meant that the heat loss was a smaller portion of the work from the engine. The overall system efficiency increased with increasing electrical load and the efficiency of the engine was fairly steady over the small range of generator loads tested.