Developments In Thermal Treatment Technologies
May 2008
By Professor Nickolas J. Themelis
A 2007 WTERT survey showed that the global waste-to-energy capacity (WTE) increased in the period 2001-2007 by about 4 million metric tons per annum. By far, the principal technology used globally for energy recovery from municipal solid wastes is combustion of “as received” MSW on moving grates (“mass burn” or stocker technology). The three dominant grate technologies, by Martin, Von Roll, and Keppel-Seghers, represent about 75% of the total growth in capacity. In the same period, Japan and China built several plants that were based either on the direct smelting or on fluid bed combustion of solid wastes. In China, there have been some mass-burn new plants and also over forty circulating fluid bed WTEs, using technologies developed by the Institute of Thermal Power Engineering of Zhejiang University and by the Institute of Engineering Thermophysics of the Chinese Academy of Sciences. WTE technologies in China are actively supported by the national and local governments and many more plants are projected as sprawling cities are running out of landfill space. Japan is the largest user of thermal treatment of MSW in the world (40 million tonnes) and some of the newest plants use stoker technology, such as the Hiroshima WTE designed by the famous architect Taniguchi and the Sendai WTE that uses advanced oxygen enrichment technology. However, there are also over 100 thermal treatment plants based on relatively novel processes. The Direct Smelting and the Ebara fluid bed technologies developed in Japan require pre-processing of the MSW, combust the resulting syngas to generate steam, and produce a vitrified residue. The Thermoselect Gasification and Melting technology, originally developed in Europe, has been adopted successfully in seven Japanese facilities by JFE, a company with extensive experience both in high temperature metal processing and with various MSW thermal treatment technologies, including mass burn. This paper also includes a brief report on the results of a study by WTERT on ways to increase beneficial uses of WTE ash in the U.S.