Combustion characteristics of Philippine coal blended with Indonesian Coal

Energy demand in the future will continue to rise with the growing economy and industrialization of developing countries. The Philippines, as one of the developing nations, is believed to increase its energy demand between now and 2030. For power generation, coal accounts for the 2nd largest market share as of 2010. However, when coal is used whether for energy generation or other activities, it is complemented by its environmental effects. Thus, modifications and adjustments were done and being done to use coal in an environmentally satisfactory and economically viable way. Clean Coal Technology (CCT) is used to describe technologies being developed that aims to reduce the environmental impact of energy derived from coal. Coal blending is one of the clean coal technologies that has been studied to address environmental issues associated with the use of coal. In the Philippines, reports show that there are huge available coal reserves and there is a great investment opportunities and support from the government that will increase the production of Philippine coal. Unfortunately, investigations on properties particularly combustion characteristics of Philippine coal and its blends are very few that opportunities to increase its fuel flexibility, improve its performance, and extend its acceptability to meet power plant specifications have been constraint. This study aims to determine the combustion characteristics of the Philippine coal and its blends with Indonesian coal using thermogravimetric analysis (TGA). The parent coals are crushed, pulverized, and sieved to attain the desired particle size between 106-150 µm. The coal blends are prepared as 20%, 40%, 60% and 80% of Philippine coal on a wt/wt basis. The TGA is operated using sample size of 5-10 mg, air flow rate of 30 ml/min, and a heating rate of 10oC/min from ambient temperature to 900oC. Philippine coal is classified as sub-bituminous A with high ash content while Indonesian coal is sub-bituminous B with low ash content. The proximate and ultimate analyses, as well as Gross Calorific Value, of coal blends were found to be additive properties that follows the linear additive rule, M = [1-x]Ma + xMb. In addition, the calorific value does not follow the linear additive expression but can be predicted and calculated from a derived correlation: {u1D444}=459.81({u1D436})+1439.74({u1D43B})+187.84({u1D446})+104.92({u1D434})12811.92 where Q is the gross heating value in kJ/kg and C , H, S, O, and A are the respective contents of carbon, hydrogen, sulfur, oxygen, and ash in weight percent. Combustion behavior like the ignition, peak and burnout temperatures of the coal blends exhibit additive properties as well. The ignition and peak temperatures are within the same range as that of the parent coal indicating high reactivity and ignites easily. The burnout temperature of the blends, however, increases with increasing content of the Philippine coal that is associated with the increasing amount of ash in the blend. For the ignition mechanism of coal blends, all blends follow the mechanism exhibited by the parent coal, that is, heterogeneous mechanism showing a one strong peak on the DTG curve and a sharp trend on weight loss on the TG curve as the coal starts to burn. The difference between the mechanism of the blends lies on the chemisorption of excess oxygen in the non-isothermal process that is linked to the ash content of the blends