Hardening furnace gas savings by retro‐fitting regenerative burners at Metabrasive Ltd

Following an in‐depth study of gas usage at Metabrasive undertaken in 1981, it was decided to treat the reduction of hardening furnace gas consumption as a priority and a paper on hardening furnace gas savings was prepared. A detailed monitoring exercise of the “Wellman” conventionally designed furnace, with a 32 air/gas nozzle mix burner system and brick refractory lining, carried out by independent consultants, showed a net gas consumption of 485 kwh/tonne. The first furnace modification at Metabrasive consisted of the fitting of a recuperative burner system with 8 burners and 4 recuperators, a low density solid hearth and ceramic fibre lined walls and roof. Detailed monitoring by the same consultants showed that a combustion air pre‐heat to 350°C was possible yielding a saving of approximately 25% and a pay‐back period of 2 years. Good even heat distribution and shorter heat‐up and cool‐down times were achieved. The second modification was carried out in 1984, with only slight changes in detail. These were the use of fully proportional air/gas controllers instead of a 3‐step system and high density refractory pads in front of the lower burners to eliminate wear caused by high velocity gases. Problems have been experienced with both these units. The refractory inlet quarts to the recuperators were found to be particularly susceptible to oxide attack. They were made using a metallic fibre reinforced refractory which spalled due to growth of the fibres. Clean air is now ducted from outside the plant which has alleviated the problem. The air valve Honeywell control motors we found to be particularly affected by heat, in spite of being provided for this duty. Sheilding has solved this problem. It was planned to modify the third furnace in 1985 with the same, albeit improved, system. However, combustion technology had moved on rapidly and the regenerative burner systems had reached the proven stage. This method was, therefore, adopted for this furnace.