Combustion Characteristics of Coal-Oil-Water Slurry in Furnaces

The ever increasing demands for energy which is coupled with stringent environmental regulations have made research in this field a top priority worldwide. This situation have enforced scientists and researchers to introduce, develop alternative renewable energy as well as to implement the reuse of low grade fossil fuel (mainly coal; plentiful reserves) in parallel with the depleted oil and gas reserves while maintaining the conceptual policies of cost-effective clean energy. The present thesis undertakes the simultaneous use of coal/oil/water mixture as an alternative fuel for use in boilers and industrial furnaces. The aim is -in one part- to develop a burner that ensures (i) stable burning of this mixture at varying operating condition, (ii) maximize the radiation flame properties of oil fames by the introduction of a proper percentage of pulverized , (iii) ease the supply of coal, oil to the combustion chamber by making a coal-oil-water slurries, (iv) overcoming the difficulties associated with startup, stabilization and efficient burning of standalone burning of pulverized coal and (v) comply with environmental regulations. For that purpose, the conventional swirl stabilized coaxial oil burner is modified via the replacement of the central oil atomizing nozzle by a carefully designed low-pressure air assisted atomizer that permits simultaneous admission and atomization of the well mixed coal-oil-water slurry without causing nozzle clogging. Subsequently, the burner is coaxially fitted to a horizontal, cylindrical, water-cooled, laboratory-scale combustor having an inner diameter of 0.4m and 2 m length. The pulverized coal From El-Maghara coal mine (Sinai, Egypt) of particle's size ≤ 30µm, diesel oil No. 2 and pure water represent the constituents of the well-mixed fuel slurry. Experiments are conducted on selected flames having constant input heat throughput and different air/ fuel ratios for three different blends (on mass basis) of oil/coal/water as follows: (Case1: pure oil; reference case), (Case2: 80%, 10%, 10%) and (Case3: 70%, 15%, 15%). The results are compared with the reference case when burning pure oil. The combustion characteristics are defined in terms of the cumulative rate of the heat transfer to cooling water jacket, heat flux to combustor walls and radial and axial profiles of mean gas temperature together with the dry volumetric gas analysis of (CO2, CO, NOx, SOx and O2) within the flame zone and at the combustor exit. The combustion efficiency is deduced from the measured results. The results indicate a pronounced increase of both the heat transfer to the cooling jacket and the combustion efficiency for case 2 (10% coal, 10% water), which is coupled with a decline of NOx emissions. Further increase in the percentage of coal and water in the fuel mixture (case 3) causes a pronounced deterioration of the overall combustion characteristics; indicating an upper limit of the loading ratios of coal and water to only 10% for each. The Egyptian coal is considered a significant alternative source of energy.