Examination of boiler operation energy-ecological indicators during fuel burning with controlled residual chemical underburn

The issue of better fuel burning in boilers has usually been considered separately in terms of efficiency or fuel consumption ecological aspect. The authors have developed an efficiently ascertainable method of boiler fuel combustion according to the energy-ecological criterion, which provides for solution of both issues at the same time. In case of heating and industrial boilers, where the mentioned method has been applied, the controlled residual chemical underburn during fuel burning was considered as the simplest, cheapest and, at the same time, highly efficient way of such optimization. The authors have determined, using a physical & mathematical model developed by them, that among the factors having impact on the energy-ecological criterion value there are: boiler power, excess air ratio, heating surface soiling degree and air suction via furnace leaks. Impact of the above fuel combustion characteristics on CO and NOx emission was examined during the experimental research work. The type of burner, which could have impact on the boiler operation indicators, was also significant. DKVR 20-13 steam boilers equipped with various injection burners were examined. Figures 1 and 2 show the relationship between CO and NOx concentrations and excess air ratio as well as furnace loading for GMGB-5,6 burners. The research work performed has shown that along with the boiler loading and excess air factor increase, CO content in flue gas decreases, whereas NOx emission decreases with excess air factor and boiler loading decrease. Figures 3 and 4 demonstrate analogous test results for boilers with GMG-5M burners. Figures 5 and 6 show the relationship between CO as well as NOx concentrations and the excess air and loading increase of boiler with GMG-7 burners. With increase of the excess air ratio and boiler loading, CO concentration in flue gas decreases. On the other hand, decrease of nitrogen oxides concentration occurs in the same way as for the previously tested burner types due to decrease of the excess air ratio and boiler loading value. Figure 7 demonstrates, on the other hand, a relationship between nitrogen oxides concentration and the excess air ratio, boiler loading, burner type and air suction volume. Air suction into the furnace at proper loading, with closed and opened peep-holes, amounts respectively to 0.01–.0.04 for GMGB burners and 0.032–0.09 for GMG-m burners; nitrogen oxides concentration increase rate for GMGB burners (curves 1 and 2) is slightly higher compared with GMG-m burners. Figure 8 illustrates the dependence of the fuel burning quality indicators (i.e. carbon oxide and nitrogen oxides concentration) and flue gas temperature on air suction and the degree of screen surfaces soiling. Increased air suction at constant boiler loading is accompanied by certain decrease of CO concentration with simultaneous increase of the excess air ratio. On the other hand, temperature of flue gas behind the furnace depends on the degree of screen surfaces soiling. Due to decrease of the average screens efficiency, flue gas temperature behind the furnace increases, on average, by 20–21°C whereas nitrogen oxide concentration decreases with reduction of the excess air ratio. Based on the above results, the authors have established and implemented the best possible modes of industrial and heating boiler operation in terms of the energy-ecological criterion