Using Gasification to Process Municipal Solid Waste By Joseph W. Schilli Volume 12, Number 4 • Winter 2004 A Publication of the Environmental and Resource Manageme nt Group of HDR T he United States leads the world in generating municipal solid waste (MSW) with a per capita average ofabout 4.6 pounds per day. Consequently, determining what to do with all of that garbage grows ever more important. The country is making strides first by setting the pace in recycling and also by being a leader in converting waste to energy through specialized combustion processes. Now, there is movement to adapt an industrial technology called gasification to serve as yet anotheroption in solid waste management. Put simply , MSW is the garbage pr oduced by residential households, commercial busin esses , industrial opera tions such as factories and institutional facilities like schools and hospi tals. With annual MS W production topping 229 million tons, gasification can ease the burden on landfills by processing solid waste and at the same time serve as a valuable fuel resource through the production of powerand other commercial materials. Gasification Explained The basic chemical processes behind gasification have been known for years. In fact, facilities that used gasification to produce oil from coal date back to the early 1900s. Gasification can be generally defined as a process for the production of gaseous or liquid fuels from organic material within the feedstock. Dependent on the feedstock, materials such as metals may also be recovered. There are two fundamental stages in the gasification process: • Organics in the feedstock are broken down into compounds consisting largely of carbon and hydrogen. • These compounds then undergo reactions to form a liquid or gas with a significant energy content. There have been significant research and development efforts related to processing solid waste with gasification and related technologies since the 1970s. For example, pyrolysis, a technology similar to gasification, attained commercial operation in a facility in Baltimore during the late 1970s and early 1980s. Unfortunately , the facility experienced persistent technical problems and eventually had to cease the pyrolysis operation. Today, close to 100 firms claim to have an operational gasification technology and/or a research and development effort related to gasification. Finding Alternatives for Solid Waste Management The processing of MS W in general has changed subst antially during the past two decades. Vast numbers of small, poorly controlled landfills are being replaced with fewer but larger and highly engineered facilities. But just as important as improving the efficiency of landfills is reducing the amount of materials going into them. It begins with source reduction – a strategy of modifying how products are made and used in a way that reduces the volume and toxicity of waste. Recycling also is a crucial component of solid waste management and has more than doubled since 1990. Today , the U.S. diverts about 30 percent of MSW away from landfill s with those raw materials being converted back into usable products. Another 15 percent of the country’ s MSW now goes through thermal processing before entering the landfill. But combustion facilities have met with stricter operating standards intended to lessen the impact on air quality and control disposal of ash byproduct. Some facilities were closed but others implemented Levels of carbon monoxide, nitrogen oxides, particulate matter , sulfur dioxide and dioxin present in airemissions from the Thermoselect process all fall well within U.S. standards.
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