Towards higher industrial efficiency in future waste-to-energy plants with high temperature latent heat storage-based thermal buffering technology

Abstract

Modern Waste-to-Energy plants have the increasing potential to solve the urban waste accumulation issue faced around the world. However, their plant efficiencies are constrained by the temperature fluctuation of the steam and the high temperature corrosion on the ferrous surfaces. With the purpose of solving both issues, this PhD thesis proposes a latent heat based thermal buffering technology to replace the traditional refractory bricks on the waterwall. Using Aluminium Alloy based phase change materials as buffering media, this technology aims at reducing the temperature fluctuation of the steam, avoiding the corrosion in traditional superheater, and as well superheating the steam directly on the waterwall. In order to achieve this design outcome, this thesis adopts a comprehensive design procedure, including the material selection by a novel assessment methodology, compatibility study of the encapsulation and core materials, numerical investigation with computational fluid dynamic and Modelica tools, experimental study with a laboratory scale setup, and techno-economic study to quantify the energy savings and potential paybacks. At the end of the study, a laboratory scale brick prototype is developed. The results of experimental studies show that this prototype is able to buffer the thermal fluctuation from the furnace side and reduce the steam fluctuation from 10-20 °C to 2-4 °C, and at the mean time upgrade the steam output to an extra 20 °C. The numerical model, validated by the experimental results with a relative standard deviation less than 2%, showcases the technology integration scheme of this technology into the modern Waste-to-Energy plants, and concludes that a high steam output temperature of 600 °C could be achieved with multiple stages of buffering refractory bricks installed. With the technology specifications, the new plant would generate an extra power output of 10.1 MW and requires a payback time of 7.5-8,5 years if the bricks could serve 5 years and more without major replenishment. While being highly prospective, this thermal buffering technology requires further research on the manufacturing method and flue gas corrosion issues, to increase its technology availability and market potential in the future.