DEVELOPMENT AND PERFORMANCE EVALUATION OF ALTERNATIVE FUELS FOR FIRING CUPOLA FURNACE IN THE FOUNDRY INDUSTRIES

Abstract

An experimental research work was conducted to characterise Erythrophleum suaveolens (ES) charcoal and Okaba coal (OK). The tests were conducted for proximate analysis and ultimate analysis of ES charcoal and Okaba coal. The determined values of moisture, ash, volatile matter and fixed carbon were 0.94%, 6.13%, 6.77% and 86.16% for ES charcoal, while for OK coal the values were 9.4%, 11.6%, 35.3% and 43.7% respectively. The determined values of carbon, hydrogen, oxygen, nitrogen, sulphur and calorific value were 77.5%, 9%, 5.48%, 1.89%, 0.003% and 30,066.54 kJ/kg for ES charcoal while for OK coal the values were 71%, 5.9%, 21.2%, 1.9%, 0.6% and 26009.78 kJ/kg, respectively. The ES wood chemistry was also determined (C: 47.520%; H: 6.246%; O: 40.90%; N: 0.252%; Ash: 1.00%; S: 0.001%; calorific value: 20829.33 kJ/kg). The ES charcoal satisfies the cupola furnace requirements for moisture (< 1%), ash (< 13.45%), sulphur (0.9%) and volatile matter (< 30.3%). The high volatile matter (35.3%) and sulphur (0.6%) values of OK coal depicts that it cannot be a good reducing fuel for production of iron. Hence the blend of OK coal and ES charcoal was experimented. An ES charcoal and Okaba coal-fired cupola furnace was designed and constructed for the experimentation purpose. Scraps of cast iron were melted and the melt ratios for ES charcoal-fired cupola furnace with oxygen enrichment (Eso), ES charcoal without oxygen enrichment (Esw), coke and the blend of Okaba coal and ES charcoal (OK/ES) were 9.2:1, 7:1, 6.94:1 and 5.6:1, respectively. The results showed that with oxygen enrichment there was 24 % increase in melt rate when compared with Esw and 39 % increase when compared with OK/ES fuel based. When the cupola furnace was fired with ES charcoal, it recorded 20% increase in melt over when it was fired with the blend of OK coal and ES charcoal and marginally higher than when coke was used (0.86%). The ultimate strength, yield stress, hardness and percentage elongation of the cast iron samples produced from ES charcoal and Okaba coal-fired cupola furnace were 439.0 N/mm2, 309.64 N/mm2, 219.5 Bs and 15% respectively while the values for the blend of OK/ES fuel based were 447.87 N/mm2, 314.81 N/mm2, 223.9 Bs and 15.4%, respectively. The impact energy was found to be 21 J and 24 J for ES and OK/ES iron samples respectively. The ES and OK/ES iron samples when compared with cast iron of coke based sample have higher percentage elongation which implies a relatively longer range of plasticity. The results of the chemical compositions of the samples showed that carbon equivalence (CE) of 3.91 and 4.12 for ES and OK/ES iron samples implies that the samples may be classified as hypoeutectic grey cast iron. Multiple linear regression models were formulated for the effects of air pressure, melting time and fuel consumed on melting rate in iron melting cupola furnace. An average value of R2 of 99.7% confirms the validity of the models and established the existence of statistically significant relationships between the melting rate and the control variables. The developed computer program (CAPPMEC, 2016) based on the generated empirical models predicted the melting rate of the furnace and were validated with experimental values with an error less than 5%.