Municipal solid waste (MSW) has the potential to be processed into a fuel, commonly referred to as refuse-derived fuel (RDF). The development of RDF goes back to the 1970s when front-end processing for waste reduction was first applied to new landfilling practices as an alternative to open dumping (e.g. in Pompano Beach, Fla. and Madison, Wis.). From this initial process for shredding and ferrous metals recovery, additional advances led to more materials recovery and processing for a higher quality organic fraction. But the history of mixed waste processing is one with mixed successes, and it is only recently that today’s mixed waste processing systems are showing their value.
One early success story was Ames, Iowa. Since 1975, RDF has been co-fired with coal in boilers at the City of Ames Municipal Electric Utility, which utilizes pulverized coal as its primary fuel along with 35,000 tons per year of RDF. It is used as a supplemental fuel for 10 percent, by mass, of the fuel feedstock. However, Ames’ long-standing success has not been enjoyed by others who retrofitted coal-fired utility boilers to co-fire RDF with coal. Projects in Baltimore, Chicago, Milwaukee, Rochester, N.Y., and St. Louis were among those where large RDF production facilities were built to supply large electric utility boilers but have not sustained operations.
Problems with storage, feeding and slagging in these boilers were among the issues that caused these projects, implemented in the late 1970s and operated into the early 1980s, to cease. Particular issues related to RDF production techniques were partially responsible for their failure to provide a long-term solution. At these facilities, shredding was followed by ferrous removal, and air classification was the common next step. This approach fractured glass and other friable materials in the waste stream and, upon going through air classification, combined them with the combustible fraction. These fine, non-combustible particles caused wear and slagging inside the combustion chamber.
Unfortunately, the processing lessons learned at a facility in New Orleans, were not applied to these co-firing projects. The National Center for Resource Recovery Inc. (NCRR), working as a consultant for the City of New Orleans selected Waste Management Inc. to build, own and operate a facility called Recovery 1, which started operating in 1976 and ceased in 1987. Recovery 1 processed 750 tons per day of waste, applying a trommel before shredding to isolate glass and other recyclables as well as using other new techniques for materials recovery. In the process, it prepared a shredded product that today we might call very clean RDF. In Louisiana, where natural gas was and still is the primary fuel of choice, no solid fuel boilers existed to use that RDF and so this material was landfilled. Nonetheless, the process proved to be useful for both demonstrating that ferrous and nonferrous metals and glass could be recovered from processing waste and that the organic byproduct was a useful substitute to consider for coal replacement or as a fuel directly in its own boiler.
While some co-firing projects were struggling, other RDF facilities have been operating successfully in the U.S. In LaCrosse, Wis., Excel Energy owns and operates two fluidized bed power production units that have been co-firing RDF and hog fuel on a 50/50 heat rate basis since 1987.
Other facilities in Detroit; Hartford, Conn.; Honolulu; Palm Beach, Fla.; and Rochester, Mass., have successfully been using a simple RDF 100 percent of the time in dedicated boilers to produce power since the late 1970s or early 1980s.
Part II of Gershman’s column, “...This is Now,” will be available in the Winter 2012 issue of Renewable Energy from Waste.
Harvey Gershman, email@example.com, is president of Gershman, Brickner & Bratton, Inc., Solid Waste Management Consultants.