Performance characterization of a pilot-scale oxygen enriched-air and steam blown gasification and combustion system

Abstract

The use of air as biomass gasifying agent yields low heating value product gas and is only suitable for heat and power applications. Steam and oxygen gasification on the other hand can increase gas heating value as well as main gas constituents suitable for production of liquid fuels through synthesis processes. Experiments were carried out to investigate the influence of using oxygen enriched-air and steam mixture as gasifying agents on syngas composition, heating value, fuel-N conversion to ammonia, and NOX emissions during gasification and combustion. The oxygen content in the enriched air was varied from 21% (v/v, atmospheric air) to 45% and 80% on dry basis. On wet basis, the oxygen percentages are equivalent to 30% and 40%. All tests were maintained at fixed bed temperature of 800 °C and steam to biomass ratio (S/B) approximately 0.17. In addition tests were also conducted using three different biomass feedstocks with nitrogen content varying from 0.05 to 1.4 wt%. The NOX emissions from syngas combustion were characterized from different burner operating conditions such as varying heat rates and equivalence ratio. It was shown that oxygen-enriched air and steam gasification favors the increase of combustible gas components such as H2, CO, CH4 and lighter hydrocarbons and improves the lower heating value of syngas up to 28% and 43% for seed corn and wood, respectively. For all tested biomass feedstocks, results showed that ammonia and NOX concentrations increase as the oxygen percentage in air increase. This, in turn, resulted in higher NOX emissions during combustion. Chapter 1 – Introduction 1.1 – The Needs for Green and Renewable Energy. Energy has always been the foundation for growth in population, economics and technologies. Worldwide, fast growing population couple with evermore energy dependent technologies in the modern age indicates that energy consumption demands are expected to rise dramatically. Fossils fuels—natural gas, petroleum, and coal—has made up the majority contribution to the world energy supply system, however, fossil fuel reserves are finite and fast depleting. Moreover, the usage of fossil fuels has led to the increasing emissions that are harmful to both human health and the environment. Therefore to avoid the energy crisis and reduction of the use of fossil fuels, considerable efforts and proactive decisions need to be made with respect to extracting and utilizing renewable energy resources. In order to achieve the two goals, the feasible solutions are: 1) to improve the efficiency of existing fossil fuel conversion processes; 2) the use of renewable resources such as hydropower, geothermal, wind, solar, and biomass. Of the two options, the second option has additional advantages besides solving GHG emissions and petroleum fuels shortage. For example, the development and usage of renewable energy can help the government to develop national energy supply and become less dependence on foreign resources. Furthermore, renewable energy enhances economic development of rural areas.