Recovery status and prospect of low-grade waste energy in China

Energy shortage has seriously hindered the economic development in many countries. The energy conservation and waste heat recovery are paid more attention recently, especially in developing countries, where the energy utilization efficiency is often neglected for accelerating development before energy price is rapidly rising up. In China, the metallurgy industry, cement industry, ceramic industry, glass industry produces a lot of low-grade waste energy which is specially defined as waste gas of low temperature, molten slag of high temperature and the fuel of low LHV (low heating value) in this paper. The recovery rate of this low-grade waste energy is very low in the past. Since the energy is getting exhausted and its price is rapidly growing up, this low-grade energy is going to be recovered more and more by different methods for maintaining sustainable development. This paper tries to give a preliminary overview of the status of low-grade waste energy recovery in China. The low-grade waste energy includes the sensible heat of low-temperature gas from cement kiln, sintering machine, glass smelting furnace, or ceramic kiln, etc. and the chemical heat of low LHV gas from blast furnace and converter. The power generation technology of low-temperature waste recovery has been increasingly applied in cement industry and sintering industry. Although it contains a lot of sensible heat, the hot molten slag, another type of low-grade waste energy, is difficult to extract the applicable energy because of granulation technology limit. In order to study the key problem in low-grade waste energy recovery, Tsinghua University and KunMing SunWise Corp. co-instituted the Tsinghua-Sunwise Joint R&D center for industrial energy-saving and emission reducing technology, which is concentrating on cement kiln waste heat recovery, sintering waste heat recovery, molten slag waste heat recovery, blast furnace and converter gas waste heat recovery. The recovered waste heat can generate electricity for saving energy and reducing pollutant and CO
₂
emission. In order to improve the waste energy recovery rate and energy utilization efficiency, it is suggested that heat transfer analysis, thermal system analysis and advanced combustion technology should be adopted for optimizing the waste heat exploitation. The rich experience of developed countries in waste heat recovery is valuable for researcher to reference.