Fundamental Research On Waste Heat Utilization Of Steel Ladle By Thermoelectric Conversion

China's iron and steel industry has made great progress in energy saving and emission reduction,with the application of many waste-heat recovery technologies.However,the waste heat lost from the surfaces of metallurgical containers is not yet to be utilized.In this paper,thermoelectric generation technology is adopted to the waste heat recovery from the surfaces of steel ladles.Firstly,heat transfer behavior of a steel ladle filled with molten steel is comprehensively analyzed by numerical method.The temperature distribution and the path of heat loss are determined for subsequent design of the matched thermoelectric device.Then,a thermoelectric system is proposed that generates electricity by absorbing the radiant heat from the surfaces of ladles in the steel plant.The thermoelectric behavior of modules in thermoelectric system is analyzed via our custom-written C program.The effects of external resistance and modules' structure on thermoelectric performance are also discussed in the temperature range of wall surface of steel ladle.The results showed that:(1)The effect of non-uniform temperature and natural convection of molten steel is significant on heat transfer of ladle wall but less on temperature variation and heat dissipation of the surfaces.The temperatures of ladle wall and slag layer along thickness direction gradually decrease with time,but this variation mainly occurs in the range of working lining and inner half thickness of slag layer.The temperature variation of surfaces is so small that it can be neglected.So steel ladle can be regarded as steady heat source,which is advantageous for providing continuous and stable heat.(2)The surface of sidewall is the main path of heat loss of ladle.The waste heat loss from sidewall's surface accounts for more than half of the total.Moreover,radiant heat flux takes up roughly 70%of the total and is the main way of heat exchange with the environment.(3)The temperature of the radiation surface has a significant influence on thermoelectric behavior of the modules.Therefore,the uniformity and stability of wall surface need to be considered in order for the module to operate stably.The surface temperature distribution in the vertical direction of the sidewall has a large difference.However,the area of sidewall's surface under slag line is with a high and relatively uniform temperature,which is conducive to the stability of thermoelectric conversion and can be used as a heat source for waste heat recovery.(4)When the thermoelectric modules are irradiated by heated sidewall of the ladle,the optimum ratio of external resistance to internal resistance is in the range of 1.6 to 2.0.Further,the optimal configuration of the external resistance is necessary for a specific thermoelectric system by analyzing its thermal status.(5)For the thermoelectric system proposed in this paper,increasing the length of the thermoelectric legs and adopting the double-layer structure can significantly improve the conversion efficiency and the output power of the thermoelectric system.When the double-layer module with leg length of 15 mm is adopted,the output power can reach 83-304 W/m2 and the conversion efficiency is in the range of 3%to 6%.When this thermoelectric generation device is applied to the 250 ton ladle,the thermoelectric system can generate 120-400 kW·h of electricity per day.This system shows great energy saving potential.