Heat recovery can only be practiced successfully with crucible furnaces to a limited extent, and
only with great effort, depending on the system configuration.
As a rule, the temperature range of the cooling water lies between 30 and 65 °C.
In practice, a temperature difference of about 27 K is common, independent of these range limits. Heating pumps work efficiently at
approx. 80 °C. Above 72 °C, the limescale precipitates out of the cooling water,
the water lines become clogged, and the water has to be treated accordingly.
Practical applications include:
Treatment of washing water and heating of rooms in winter. With a 5-t furnace with 3,000 kW, approx. 810 kW of heat energy is absorbed by the cooling water (empirical value; coil and crucible wall losses, excluding the converter[1]), which can only be used economically to a very small extent. There is a large number of engineering companies involved in the field of heat recovery. The furnace’s cooling water reaches 65 °C; the return temperature is limited to 72 °C because of limescale precipitation. Heat pumps only work economically at around 80 °C. A direct increase to a usable temperature is therefore not possible.
References
- Herbert H. Netzel: Induktionsofenhandbuch. 3rd edition, Eigenverlag IES, Witten 2003, p. 222. Empirical value, not a manufacturer specification. In the section on cooling water quantities (p. 118), the same handbook gives 810 kW or 1,050 kW for the same example furnace, with different scope stated. We standardise on 810 kW (coil and crucible wall).