Thermal energy utilization of high temperature ash: Current situation and prospects

Abstract

Not only is the use of waste heat an important way for companies to reduce fuel costs but it is also an important step in achieving the goal of decreasing peak carbon dioxide emissions. Solid fuels still make up a large proportion of China’s energy consumption structures, and the amount of ash generated and the remaining thermal resources are enormous. When considering coal alone, the theoretical recoverable amount of waste heat associated with the ash can be as much as 15.87 Mt of standard coal per year. An analysis of thermal energy utilization of high temperature ash (TEUHA) was conducted. It was found that the existing direct utilization method had a thermal efficiency in the range of 12% to 92%. However, the process is complicated, and the heat carrier is susceptible to contamination. Indirect utilization could avoid pollution issues, but heat loss was severe and maximum thermal efficiency was calculated as only 59%. Combined with the waste heat characteristics of the ash and the heat demand, a “Point-Point” model of TEUHA using phase-change materials as the heat carrier is proposed. This approach not only avoids ash pollution to the thermal environment, but it also increases the energy harvesting efficiency and realizes a high-quality utilization of thermal energy.