Waste Heat Recovery from an Electric Melting Furnace
Mäkelä, Roni (2018)
2018
Konetekniikka
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2018-12-05
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201811212646
https://urn.fi/URN:NBN:fi:tty-201811212646
Tiivistelmä
The use of an electric melting furnace is one of the methods for producing rock melt for the manufacturing of mineral wool. Due to the high electrical power and temperature involved in the melting, the electric melting furnace emits a considerable amount of waste heat in various forms. The purpose of this thesis was to find out how the waste heat from the electric melting furnace could be utilized in the best possible way. The main objective was to find economically feasible ways to improve the energy efficiency through more effective utilization of the waste heat.
The recoverable waste heat streams of the electric melting furnace consist of heat bound to the off-gas as well as to the furnace’s oil and water cooling. Different options for utilizing these waste heat streams were evaluated. However, truly potential possibilities for waste heat recovery were noted to be scarce. For the off-gas, improving on the current system was proposed. By mixing the gas with less air and optimizing its operating times, a greater share of the heat could be utilized. The waste heat from oil and water cooling could, in turn, be utilized by a suitable technical solution for facility heating. This would significantly reduce the dependence on expensive gas fired heaters.
However, the temperatures currently used by the furnace’s water cooling do not support waste heat recovery. Thus, the possibility to increase temperature in the water cooling system was studied as a part of the thesis. The study investigated the limiting factors of the temperature increase and their suitability for the examined electric melting furnace. It was found that the design criteria for the cooling of pyrometallurgical furnaces are not valid in all respects for the electric melting furnace. Clear obstacles for the temperature increase were not observed.
Process data related deficiencies were a recurring theme in the thesis. The observed deficiencies not only made the investigation difficult, but also negatively affected the accuracy of the obtained results. If similar studies are to be carried out in the future, more attention needs to be paid to the availability and quality of process data. Some suggestions for improvement on the subject were given in the thesis.
The recoverable waste heat streams of the electric melting furnace consist of heat bound to the off-gas as well as to the furnace’s oil and water cooling. Different options for utilizing these waste heat streams were evaluated. However, truly potential possibilities for waste heat recovery were noted to be scarce. For the off-gas, improving on the current system was proposed. By mixing the gas with less air and optimizing its operating times, a greater share of the heat could be utilized. The waste heat from oil and water cooling could, in turn, be utilized by a suitable technical solution for facility heating. This would significantly reduce the dependence on expensive gas fired heaters.
However, the temperatures currently used by the furnace’s water cooling do not support waste heat recovery. Thus, the possibility to increase temperature in the water cooling system was studied as a part of the thesis. The study investigated the limiting factors of the temperature increase and their suitability for the examined electric melting furnace. It was found that the design criteria for the cooling of pyrometallurgical furnaces are not valid in all respects for the electric melting furnace. Clear obstacles for the temperature increase were not observed.
Process data related deficiencies were a recurring theme in the thesis. The observed deficiencies not only made the investigation difficult, but also negatively affected the accuracy of the obtained results. If similar studies are to be carried out in the future, more attention needs to be paid to the availability and quality of process data. Some suggestions for improvement on the subject were given in the thesis.