During the operation in the coal based sponge iron plant, a tremendous amount of heat is generated and significant part of this heat, associated with the waste gas, remains unutilized. It appears worth interesting to modify the process that facilitates the integration of heat available with the waste gas. In the present paper, for the utilization of heat of waste gas, two modifications, namely, case-1 and case-2, are proposed based on preheating of inlet streams. In case-1, preheating of feed material is considered, whereas in case-2, preheating of feed material as well as air is accounted. These cases are then compared with the existing waste heat recovery system of the plant based on coal consumption, operating and capital costs, profit, and payback period. It is found that both cases are better than the existing heat recovery system of the plant. However, case-2 is selected as the best heat recovery option. In comparison to the existing system, case-2 reduces coal and water consumption by 30.5% and 72.6%, respectively. Further, case-2 releases minimum waste gas to the atmosphere that makes the process environment friendly.
a b s t r a c tA survey is made on a typical coal based Indian sponge iron plant of capacity 500 t/d in order to identify the largest energy losses and find ways to increase the efficiency. The required data are obtained by measurements or taken from production industries. The process efficiency is about 51.31%. The energy balances of the process show that the gap between theoretical and actual energy consumption is 45.2% and the exhausts make up the largest loss of 43.5%. A huge amount of waste gas is generated during operation and substantial part of it associated with the waste gas, remains unutilized. The energy content in the exhaust gases which is found at useful temperature can be used in three different ways: by internal use; by external energy supply; or by power generation. The four possible potential areas are identified where energy is being lost and untapped. The largest improvements would be made by design modifications adopting a novel energy conservation scenario by process integration and thereby decreasing the coal and water consumption and by decreasing the cold fresh air.
This paper presents an approach to find the best modification in the coal-based sponge iron process with an aim to integrate energy in it. For this purpose, a few energy conservation cases are formulated by integrating unutilized energy present in possible areas of process flow sheet. When unutilized energy of the process is properly integrated, energy demand from outside sources can be reduced. It decreases coal consumption as coal is the only source of energy in this plant. For energy integration in sponge iron process pinch technology is applied on the actual data of plant. Based on this data, seven energy conservation cases are identified. Among these, two are selected for detailed analysis based on utility requirement. For these two cases capital investment required for energy integration, coal consumption, water requirement, energy consumption, profit, and payback period are compared. Based on these factors the best case is selected. The integrated design for the best case includes air preheating and cooling of kiln outlet using waste gas. Further, a modified case is discussed with preheating of feed to rotary kiln and air using waste gas. This case consumes 12.3% and 93.7% less energy and water, respectively, and gives 8.6% more profit in comparison to the previous case. Thus, the modified design is selected as the best option for energy integration. This design also satisfies the practical constraints of the process.
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