Date of Award
Master of Science
Energy security and global climate change are two of the greatest challenges that face the next century and it will be up to this generation to figure out a solution to these monumental challenges. Nearly everything ranging from commerce to travel to education relies on abundant and cheap energy to function and progress. For the last 150 years, this energy has come through the combustion of fossil fuels which are limited by their very nature. As these fuels are combusted to produce heat and power, various harmful gasses are emitted into the atmosphere and can lead to "acid rain," smog, depletion of the ozone layer, and even a heating of the earth's surface. Gasification of biomass provides one possible solution to both of these problems by utilizing a renewable energy source that is abundant and has the potential to be carbon negative. NOx emissions are regulated by the government and could potentially be the limiting factor on the potential of biomass gasification to have a major impact in overcoming the two greatest challenges of today. It is believed one of the primary causes of NOx emissions is due to nitrogen found in the feedstock that is gasified. This work is aimed at both developing the tools necessary to understand the detailed systems involved in biomass gasification, as well as to characterize the NOx emissions that result from the combustion of the biomass-derived producer gas.
In the current work, a two-fold approach is taken to address this issue. First, a process model is created utilizing the software Aspen Plus to simulate data taken from a pilot-scale gasification system utilizing maple and oak wood as the feedstock and air as the gasification medium. This model uses a mass balance approach to simulate the gasification process. A system of cyclones filter out the particulate matter in the producer gas before the gas is burned. Second, the effects of fuel-NOx are studied experimentally utilizing a newly developed lab-scale, low-swirl combustion apparatus. This combustion apparatus is first tested using natural gas that contains low concentrations of ammonia for four swirlers with varying effective areas. A single swirler is chosen to conduct tests to analyze the effect of ammonia concentration on NOx emissions from the producer gas.
Results of the current work can be summarized as follows. (1) A biomass gasification model was created to model the gasification of wood feedstock. This model shows very good agreement with experimental results for all components except hydrogen in the producer gas. (2) For the swirlers studied, NOx emissions are reduced as the swirl strength increases. (3) For a natural gas flame, both the equivalence ratio and effect of thermal NOx are important considerations when trying to achieve low NOx emissions. (4) For the combustion of producer gas, higher equivalence ratios reduce the overall NOx emissions. The above results show the need for a greater understanding of producer gas combustion in low-swirl burners for a wide variety of compositions in order to better control overall emissions in the future.
Jordan A. Tiarks
Tiarks, Jordan A., "Investigation of biomass gasification and effects of ammonia on producer gas combustion" (2012). Graduate Theses and Dissertations. 12486.