OCR Text |
Show exhibited an optimum reduction (minimum NO emissions) at a reburn stoichiometric ratio of 0.9. )( At this stoichiometry, the overall NO)( reductions ranged from 41 to 62 percent, with some coals displaying performance equivalent to that achieved with natural gas. The varied perfonnance achieved with the different coals demonstrates the impact that coal properties can have on the process performance. Figures 3 and 4 illustrate the impacts of coal nitrogen content and coal volatile matter on reburning effectiveness. In general, it appears that coal nitrogen content and coal volatile matter impact the perfonnance of bituminous coals, but do not appear to influence the reburning perfonnance of the low range coals, over the range of conditions investigated. In fact, the overall performance for the low rank coals were quite similar over the range of nitrogen and volatile matter content investigated. A critical consideration in the actual application of coal reburn technology to utility boilers is carbon loss. Figure 5 shows the loss on ignition results obtained for the ten coals tested. As expected, bituminous coals had the highest carbon loss, while low rank coals had the lowest carbon loss. The burnout achieved with the bituminous coals appeared to be sensitive to the coal volatile content. That achieved with the low rank coals was not sensitive to coal volatile content over the range of this parameter evaluated in this study. Conclusions The key objective of this project is to determine the potential for applying the coal reburning process to Canadian utility boilers. The results of parametric tests conducted with ten coals selected from a data base of Canadian coals indicate that NOll reductions between 41 to 62 percent are attainable with coal reburning at utility boiler conditions. In evaluating the impact of parameters such as nitrogen content and volatile matter content on the effectiveness of the coals, it was found that bituminous coal performance (in tenns of NO x reduction) improved with decreasing nitrogen content and increasing volatile content. Carbon burnout for bituminous coals also improved with increasing coal volatile content. However, these parameters were not able to correlate the NO x reduction or carbon burnout performance of the low rank coals evaluated. 5 |