Degree Type

Thesis

Date of Award

2010

Degree Name

Master of Science

Department

Mechanical Engineering

First Advisor

Song C. Kong

Abstract

This study is focused on the effects of nitrogen content in biomass feedstock on the producer gas composition and the flue gas NOx emissions from a pilot-scale gasification and combustion system. Biomass gasification has the potential to produce carbon negative

energy by using renewable resources. The greenhouse gases emitted by burning fossil fuels have to be reduced, and biomass gasification is one of the means to achieving this. When the biomass-derived gas is burned, NOx emissions are a critical factor that can limit the use of the system. The government regulations limit the amount of NOx that can be emitted into the atmosphere. These emission regulations are becoming more stringent every year.

Hence it is imperative to design combustion systems that can produce low NOx emissions without compromising the intended purpose for heat and power generation. This work is aimed at helping with the design of a low NOx burner by conducting experimental investigations on an existing burner. In this study, tests were conducted in a pilot-scale fluidized bed gasifier using biomass

feedstock with different nitrogen contents. The producer gas from the gasifier undergoes a gas cleaning phase before its combustion in a burner. Fuel NOx and thermal NOx contributed to the total NOx formation in the burner. The main precursor to fuel NOx is ammonia in the producer gas. Ammonia and tars were collected from the producer gas using IEA (International Energy Agency) tar protocol and analyzed using spectrophotometer and GC-FID (Gas chromatograph-flame ionization detector), respectively. The producer gas and the exhaust flue gas were analyzed using a micro gas chromatograph (Micro-GC). The NOx variation was investigated for different equivalence ratios and different flow rates of the producer gas. Results show that there is a direct and proportional relationship between nitrogen in biomass, ammonia in producer gas, and NOx in the flue gas. Additionally, NOx emissions do not vary noticeably with the overall equivalence ratio in the present burner but vary significantly with increased heat rate. It was also found that thermal NOx is less significant than fuel NOx, which constitutes a majority of the total NOx emissions when biomass derived producer gas is used. The flame length in a diffusion flame along with the residence

time seems to have a major influence on the NOx emissions from the burner.

These results form an essential part in understanding the fuel NOx behavior and functions as an important tool in the development of a low NOx burner, which was the overall objective of this project. This thesis work is mainly focused on the experimental investigation of the fuel NOx behavior and the effect of fuel nitrogen on the NOx formation in the burner. These experimental results along with detailed chemical analysis of ammonia oxidation mechanisms under different conditions will give a better understanding of the

fuel NOx formation and will aid in the design of low NOx burners.

DOI

https://doi.org/10.31274/etd-180810-418

Copyright Owner

Sharan Sethuraman

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

102 pages

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