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Metal Casting Technologies : March 2005
3. Decrease in carbon pickup of the molten iron; 4. Decrease in the tensile, transverse & impact strengths of the iron; 5. Increase in chill depth; 6. Increase in the tendency of the iron to shrink & crack; 7. Reduction in the anneal ability of the iron which responds more readily to heat treatment; 8. Decrease in casting yield; 9. Excessive heat loss as a result of getting the moisture heated up to an elevated temperature; On evaluating the above-mentioned impact of moisture content in combustion air to cupola, it becomes urgent to optimize its presence. In this present era of hard energy conservation, the introduction of vapor absorption refrigerating system to reduce the moisture content in the air blast on utilizing the post recuperative waste heat, as depicted in the present paper, seems to have no other alternative. To enhance productivity on ensuring better quality of product with efficient utilization of input energy, the present model is peerless. 5.2 Oxygen enrichment: A faster combustion reaction is brought about by the concentration of oxygen in the blast and a corresponding decrease in nitrogen volume. Nitrogen not only does not contribute to combustion, but also it absorbs considerable amount of heat resulting in higher flue loss. Experiments reveal that the desired oxygen enrichment is from 1 to 6% with 4% considered optimum. The use of continuous oxygen enrichment results in: 5.2.1 Increase in productivity 5.2.2 Flexibility of material selection allowing lowest cost charge 5.2.3 Increased metal temperature 5.2.4 Increased metal temperature 5.2.5 Increased carbon pickup 5.2.6 Reduction in blast air, which has resulted in reduced air velocity within the cupola, thereby reducing stack emissions and refractory erosion 5.2.7 Considerable saving in fuel consumption. 6. CONCLUSION In conclusion, following points need to be mentioned hereunder in seriatim: 1. High content of moisture in combustion air leads to deteriorate the metallurgical properties of the product adversely within cupola. 2. On the basis of energy analysis, it appears that wastage of fuel is obvious for the above said presence of moisture. Additional fuel energy of the value 60.4 KW is wasted to feed 10,000 cfm of combustion air (Appendix -- 1). 3. Since some beneficial effects are also associated with the some presence of moisture, it needs to optimize the moisture content of combustion air. 4. Vapor absorption refrigeration system is the best option to alleviate the moisture content to optimize the same, since it utilizes the post recuperator waste heat to run the cycle. 5. In the present era of hard energy crisis and quality conscious market, dehumidification of combustion air by vapor absorption system utilizing waste heat and online generation of oxygen enriched blast through PSA system seems to be the unique solution for the efficient operation of cupola. 6. This model will bring an encouraging bright future in foundry cluster like Foundry Park. References 1. AFS cupola handbook 2. Ibid Appendix -- 1 CALCULATION TO FIND OUT THE WASTAGE OF ENERGY FOR MOISTURE CONTENT OF CUPOLA BLAST: yuBased on the data of AFS CUPOLA HANDBOOK, it appears that a reciprocating compressor operating at 2°C evaporator temperature will require about 0.9 bhp ton of refrigeration. Let us consider a cupola where 10,000 cfm (17,000m3/hr) of combustion air is fed. It is desired to reduce the moisture content of this air from 20.6 gm/m3 (9 grains/cft) to 6.9 gm/m3 (3 grains/cft). So in an 8 hr. operating day, approximately 1860 kg. of water is blown in the cupola in the form of excess moisture in the blast air, which needs to be eliminated. To do this with a refrigerated coil, it would require to cool the air to approximately 6°C from the ambient temperatures (32°C) for which it needs the refrigerant tem- perature as to be 2°C so the refrigerating machine would be to the order of 90 tons, thereby requiring 81 hp (60.4 kw) approximately. Of this 81 hp expended, only 53% is the useful work to condense the moisture. The remaining 47% is being used for unnecessary air-cooling. So 0.47 x 2,73,262=1,28,433 kcal/hr. heat must be put back into air to heat it to the original ambient air temperature of 32° C. This addition to the unuseful work of cooling makes a total unproductive energy consumption of (1,28,433 x 2)= 2,56,866 kcal/hr. Since only 53% of the cooling load is employed for useful work to remove moisture from air actually. So useful work= 1,44,830 kcal/hr. Actual energy input= 1,44,830 +1,56,866= 4,01,696 kcal/hr. So the efficiency of the cooling system appears to be 36% only. Navojit Basu is an Assistant Manager (Mechanical) at the Greater Calcutta Gas Supply Corporation in Kolkata India. Bimal Chaudhuri is the Professor of the Metallurgical Engineering Department at Jadavpur University in Kokata India. PK Roy is a General Manager at the Great Eastern Energy Corporation, Asansol, India. 30 METAL Casting Technologies March 2005