M.S. Thesis: Environmental impacts of NOX reduction technologies in Waste to Energy facility in United States.
By Zhixuan Wu
Advisors: Dr. A.C. (Thanos) Bourtsalas and Prof. Nickolas J. Themelis
Department of Earth and Environmental Engineering
Fu Foundation School of Engineering & Applied Science
Columbia University
December 2018
WTE plants operate with primary and secondary measures for NOx destruction that takes place in the combustion occurring during the first pass in the boiler. Primary measures include air or fuel staging. Two techniques widely applied in WTE plants are the low NOx (LN) and the very low NOx (VLN) technologies. The main difference is the distribution of air, where in the VLN technique uses less air in the first pass of the boiler, and therefore less NOx is produced. In addition, VLN is typically used in new installations, while LN is mainly for retrofits.
The aim of this paper is to compare the environmental impact of the use of SNCR, LN/SNCR and SCR in WTE plants by using life cycle analysis. The aim of this paper is to compare the environmental and cost impacts of several SNCR techniques and SCR by using Life cycle analysis. The parameters considered, which is the novelty of the research paper, consists of the system pressure drop, ammonia slip, and its requirements to meet the ELV.
The key findings of this study were:
- LN/SNCR has shown the best environmental performance amongst the three technologies
- For SNCR and LN/SNCR, the reagent production and the flue gas emission to ambient air after the APC system are the two main categories that influence the environmental impact, while reheating of the flue gas is the major contribution to the environment for the SCR system.
- Fuel selection has a significant impact in the overall environmental performance of the SCR system. Natural gas would provide SCR with the best environmental performance followed by MSW incineration in second place.
- SCR with natural gas as reheating source has the best performance in mitigating the negative environmental impact compared to LN/SNCR and SNCR
- Adjusting the operating conditions in SCR, particularly reducing the operating temperature or recovering waste heat, would reduce the negative impact from resource depletion and global warming. However, the mitigated negative environmental impact is still higher than SNCR and LN/SNCR.