Research On Power Generation Of Waste Heat Recovery From Aluminum Reduction Cell’s Sidewalls Based On Thermoelectric Conversion

Abstract:The aluminum reduction industry is a large energy consumer. In2008, the total consumption of electrolytic aluminum is about5%of the all country current consumption, and about half of the energy dissipites from the cell to the surroundings and becomes waste heat. As a result, the effective utilization of the aluminum electrolysis waste heat is an important measure to energy saving in the aluminum metallurgical industry. Thermoelectric generation is a technology for directly converting thermal energy into electric energy by thermoelectric effect, it has no moving parts, and it is compact, quiet, highly reliable and environment friendly. In the field of industrial waste heat recovery, low temperature waste heat can not be recycled effectively by conventional methods, while thermoelectric generation can convert the low temperature waste heat into electric energy directly.In this paper, thermoelectric generation technology was applied to the waste heat recovery from aluminum reduction cell’s sidewalls. According to the structural characteristics of aluminum reduction cell’s shell, thermoelectric generators were designed and manufactured. The purpose of energy saving was achieved through the recovery of low-grade waste heat. The main contributions of this dissertation are summarized as follows:(1) Based on the actual physical structure and application, a numerical model of signal thermoelectric generator was established. The influence of contact effects was considered, and approximate expressions of output power, current and matched load were deduced by the model. The results indicate that the existence of contact electric resistance is just like the increase of the thermoelectric module’s internal resistance, which leads to the deceases of output power. The thermal contact resistance reduces the output power by reducing the temperature difference between the two sides of the thermocouples. The matched load of thermoelectric generator is not equal to the internal resistance unlike most circuit.(2) The performances of parallel thermoelectric generator and series thermoelectric generator were studied by theoretical analysis and experimental test. The analytical model of parallel thermoelectric generators and series thermoelectric generators were developed by theoretical analysis and calculation, and the two analytical models were verified by experimental test. The results indicate that only when all of the thermoelectric modules in the series or parallel thermoelectric generators have the same inherent parameters, and the influence of contact thermal resistance is ignored, the series or parallel properties of the thermoelectric generators are the same as that of common DC power.(3) The influence of the magnetic field on the output performance of thermoelectric generator was studied. It was theoretically explained that the influence of magnetic field on the output performance of thermoelectric generator is very little. To the thermoelectric generator made of bismuth telluride, it is proved by experiment test that the influence of magnetoelectric effect and thermomagnetic effects on the open circuit performance and output power of the thermoelectric generator is negligible.(4) An experimental platform was built, which can be used to test the performance of thermoelectric module in various complex cases. A thermoelectric module was selected, which is very suitable for working in the cooling holes of aluminum reduction cell.(5) The thermoelectric generators were designed and manufactured. A waste heat generating system was built, and the system was tested on the spot of aluminum reduction cell. The result shows that the temperature difference of thermoelectric generator can reach100℃, output power of the waste heat generating system made up of18thermoelectric generators is290W.The research of this dissertation provides a new idea and method of energy saving in aluminum electrolysis, the method can also be extended to the application of other industrial waste heat recovery, and it is of good significance both in theory and practice.