EFFECT OF CONTROL SYSTEM DESIGN ON THE FUEL EFFICIENCY OF A FLUIDIZED BED HEAT TREATING FURNACE

摘要

Fluidized bed annealing furnaces used for annealing low- and medium-carbon wire products have been used for a number of decades as an environmentally friendly alternative to more traditional heat treating systems based on molten lead. Recent investigations into heat transfer rates to wires immersed in a fluidized bed have shown that the heat transfer rate is relatively constant over a wide range of fluidizing rates, contrary to earlier thinking. As a result, it is possible to modulate air/gas flow rates in these systems without affecting product quality due to variable heat transfer rates. Typically, systems have operated at constant fluidizing air flow rates with either on/off gas control, or modulating gas only, resulting in high effective excess air operation and resulting low thermal efficiency. This work investigates the result of operating a fluidized bed with modulating air/fuel flow rates at fixed air/fuel ratios, resulting in improved thermal efficiency. Results indicate that significant fuel savings can be achieved, particularly at lower load levels.