Harnessing thermoelectric power from transient heat sources: Waste heat recovery from silicon production

Thermoelectric generators (TEGs) are compact and robust devices for converting heat into electrical power. In this work, we investigate the response of a bismuth-telluride based TEG to the transient environment of a silicon production plant, where there is a periodic change in the average temperature of the heat source. We establish a dynamic mathematical model that reproduces results from industrial, on site experiments, both at steady-state and under transient conditions. By simultaneously changing the design and location of the TEG, a peak power density of 1971 Wm-2 can be obtained without exceeding material constraints of the TEG, with an average power density of 146 Wm-2. In the transient case, the average power density generated during one silicon casting cycle is in all investigated cases found to be only 7-10% of the peak power density as the peak value of the power is only maintained for a couple of minutes. The fractional area is defined as the ratio of the total area of thermoelectric modules to the total system cross-sectional area of the TEG. We find that the power generated can be increased by reducing the fractional area, provided that the TEG is at a fixed position. If the TEG can be placed as close as possible to the heat source without exceeding the material constraints, the peak power density and the average power density reach maximum values as functions of the fractional area, beyond which the power begins to decline. The optimal fractional area that gives maximum power depends strongly on the cooling capacity. We find that with a higher cooling capacity, it is beneficial to design the TEG with a higher fractional area and place it as close as possible to the silicon melt. Possible venues to improve the performance of TEGs that operate under transient conditions are suggested.