| OCR Text |
Show rather than solely for warmup or standby duty. CNG through East Ohio Gas evaluated cofire at Kent State and Painesville, a chain grate and spreader stoker, respectively, equipped with a single Coen DAZ burner (1). GRI evaluated cofiring at a Vanderbilt University spreader stoker equipped with dual Coen DAZ burners (2). These evaluations showed cofiring improved operational flexibility, increased efficiency, and reduced NOx emissions and opacity. The quantified benefits based on these evaluations were extrapolated to the operating economics of other stoker units by CNG and GRI. On that basis, it was concluded that the benefits of cofiring from 5 to 20 percent gas would justify the incremental fuel cost differential in many cases. It was also clear, however, that the system was not optimized. The initial three evaluations also showed that work was needed on the burner concept for the sustained cofire application and on the applications engineering to the boiler performance. Specifically, the Coen DAZ register burner used in most installations to date has a relatively large throat diameter and requires a large watertube penetration. Construction costs rise sharply with extent of pressure part modification. Because of the large wall penetration required, the burner positioning was usually dictated by access rather than by performance enhancement considerations. Additionally, the gas burner was effectively limited to load turndown of about 2:1. For larger turndowns, the flame tended to have insufficient momentum to penetrate the combustion gases over the bed. The intended benefits of cofiring were therefore not achieved for high turndown. In summary, the early cofiring evaluations showed that extending the cofire concept to a true sustained gas use with coal held considerable promise of a sizable new gas market. The results also showed, however, that additional work was needed in both market development and burner jboiler engineering if cofire was to deliver the full potential of operational, efficiency and environmental benefits. To further develop the potential of this initial cofiring experience, GRI initiated a project in September 1994 with the team of Acurex Environmental, The Coen Company, 3 |
