Boiler efficiency analysis using direct and indirect method

Abstract

Boiler efficiency could be analyzed using two different methods, direct and indirect. The direct method provides the overall efficiency based on input and output while indirect method shows the losses in each process which is more valuable in identify the inefficient process. Therefore, in this study, the effect of different boiler load on the efficiency of the boiler is analyzed using both methods. In addition, the analysis using indirect method also shows the effect of boiler load on the losses in dry flue gas and moisture in air. Data of the temperature, pressure and flow rate of the steam, flue gas, air and fuel are measured onsite. The flue gas analysis was performed to obtain the percentage of flue gas components. Direct efficiency and indirect efficiency based on heat losses at different points were calculated. From the study, it is found that, the efficiency of the boiler increased with the increment of boiler load and reach the maximum efficiency of 83.3% for direct method and 89.8% for indirect method at 55% load. Operating above 55% load will results in the decrement of boiler efficiency for both direct and indirect method. As the load increase, the amount of excess air is increasing which increase the combustion efficiency. However, as the excess air quantity increased further, the heat loss due to the excess air is higher than the heat input by the combustion therefore decreased the efficiency of the boiler. This result could give a clue to the boiler operator to tune the excess air rate when operating the boiler more than 55% load.