An improved autoclave technology has made MSW an economically, environmentally and socially viable feedstock for production of renewable energy and bio-based chemicals. Major oil exporters may profit rather than lose, in a carbon-constrained world
Source: Energy Policy, Department of Physical Resource Theory, Chalmers University of Technology, Göteborg, Sweden
Advantages of using municipal solid waste (MSW) as a feedstock for production of renewable energy (both liquid fuels and electricity) are well established. These advantages include a consistent supply that is related to the geographical distribution of population, one which is not dependent on weather and climate as are agricultural feedstocks, a collection and delivery infrastructure that is mature and already in place, substantial reduction of waste being disposed of in landfills, many of which are approaching full capacity in large metropolitan areas, and tipping fees that can offset some of the cost of separating MSW into ‘biogenic’ material of organic origin (such as food waste, paper and cardboard which are essentially primary and secondary biomass), plastics and metal. In addition, when the biogenic fraction is used to replace fossil feedstocks including oil and coal, there will be an associated beneficial decrease in the release of greenhouse gases.
Then why is the biogenic portion of MSW not being used more widely to produce renewable energy? Unfortunately, the challenges often outweigh the advantages. The cost of traditional separating and pre-processing MSW are often not adequately offset by tipping fees, and there is often concern about possible unknown contaminants and associated environmental implications. In most cases where MSW is currently being separated for recycling or further use, this inefficient process is being done manually in facilities known as materials recovery facilities, or MRFs, where poorly paid laborers are constantly
exposed to an unpleasant work environment, including many potentially dangerous pathogens. Indeed, it is surprising that in the 21st century, society and industry has failed to come up with more advanced, hygienic and economically viable process to accomplish this task, but now it appears that a revolutionary technology may be poised for commercialization.
Autoclave Technology
An autoclave is a vessel used to treat and sterilize items or materials with heat, steam and pressure. Small autoclaves are often used to treat and sterilize glassware, medical instruments, etc. in laboratories, and for numerous other uses. Industrial autoclaves have been used to process MSW, thus eliminating the need for hand separation by means of manual labor, while continuing to provide jobs needed to run the equipment. However, high capital and operating costs, and inefficient separation of mixed waste streams due to melting of plastics at high temperature, have typically resulted in this approach not being economically and practically viable.
CleanTech Biofuels Inc. (www.cleantechbiofuels.net), a company in St. Louis, Missouri, is the exclusive licensee of an improved autoclave technology that uses lower temperature and pressure in a unique biomass recovery process for MSW. These improvements are incorporated in a patented process that is owned by a British company and licensed to CleanTech Biofuels for use in North America. These recently patented improvements result in lower capital and operating costs, and a more efficient mechanical separation of the renewable biogenic material consisting mostly of plant-based materials, plastics and metals, into separate clean and sanitized streams. The resultant biogenic material is a remarkably uniform cellulosic or biogenic feedstock that is well suited to conversion to renewable energy, as well as for a wide range of other commercial applications that may include bio-based chemical production.
CleanTech Process
The process first involves delivery of unsorted household MSW on to a tipping floor where oversized bulky items such as appliances and furniture are removed by hand. The remaining material is conveyed into a sealed and pressurized vessel where low-pressure steam is introduced. The contents are batch-processed in vessel for 45 minutes. Following this sterilization, the contents of the autoclave are emptied onto a mechanical screening system or trommel that separates the biogenic material from the plastic and metal fractions. Eddy currents and magnets are utilized to separate the ferrous and non-ferrous metals, and mixed plastics are hand sorted from the remaining stream in the absence of optical sorting equipment.
The biogenic material can be used as a feedstock for production of renewable liquid biofuels, electricity, and bio-products. Plastics and metals are sold into recycling markets. Typically 50 to 55% of the processed MSW is organic biomass. Further processing of the biomass can ensure ash content for the biogenic material of approximately 10% and a moisture content to match requirements of the end user. The material can also be sized as needed, from a compost-like consistency, into pellets, cubes or briquettes.
Commercialization
The first commercial facility to utilize the improved autoclave biomass recovery process was built in Coff’s Harbour, Australia. The Coffs Harbour plant has been operating successfully for over two years. The plant takes residuals from a material recycling facility and, via the biomass recovery process, recovers the remaining organic material that has made it through the MRF.
CleanTech Biofuels, Inc. intends to build a commercial-scale demonstration plant in the United States. This facility will be used to demonstrate economic viability of the process at a commercial scale while providing commercial scale samples of biomass feedstock for potential end users for evaluation in their own pilot and small commercial conversion facilities. CleanTech Biofuels has been contacted by over 25 technology companies that have requested commercial size quantities of their biomass for testing and evaluation.
The CleanTech feedstock is highly competitive from an economic standpoint compared to many other alternatives. In the United States, current delivered costs of woody biomass and agricultural energy crops such as switchgrass are approximately US$75 and US$100/dry ton, respectively, while the CleanTech biomass is less than $US55/dry ton. Additionally, the potential exists for CleanTech to blend its biomass with other forestry or agricultural feedstocks, thus utilizing their material to offset their higher prices of these other feedstocks while providing a reliable supply chain solution for the bio-based energy and chemical industries.
Conversion efficiency of the CleanTech cellulosic biomass is typically better than other feedstocks utilized for biochemical conversion processes. This is a result of lignin being removed from wood during the pulping process prior to use as pulp to produce paper and cardboard. These materials constitute a large proportion (65-75%) of the CleanTech biomass. CleanTech biomass is also well suited for thermochemical conversion to renewable liquid biofuels, electricity and other bio-products. However, since thermochemical conversion technologies are typically less sensitive to feedstock composition, the price advantage of CleanTech biomass would presumably be the preferred economic driver in these instances.
Co-locating at Transfer Stations
Waste transfer stations are facilities where municipal solid waste is unloaded from collection vehicles and briefly held while it is reloaded onto larger long-distance transport vehicles for shipment to landfills or other treatment or disposal facilities. By combining the loads of several individual waste collection trucks into a single shipment, communities can save money on the labor and operating costs of transporting the waste to a distant disposal site. They can also reduce the total number of vehicular trips traveling to and from the disposal site. Co-locating the biomass installations at the waste transfer stations will reduce the impacts and costs of trucks traveling to and from the main disposal site, and when properly sited, designed and operated they can eliminate problems for residents living near them.
Projected Benefits
The United States generates approximately 225 million tonnes of MSW per year, and approximately 50% of this is biogenic material. If only half of this material were recovered and converted to liquid biofuels at an efficiency of approximately 300 litres/dry tonne of feedstock (an efficiency that numerous emerging biofuel companies are projecting), this would lead to production of 33.75 billion litres of fuel annually. In addition, the CleanTech biomass recovery process results in over an 80% reduction in material being delivered to landfills, thus providing the opportunity to substantially extend their useful life, delay the need to expand or create new landfills, while reducing the negative environmental impacts associated with such facilities. These examples demonstrate the enormous economic, environmental, social and energy security benefits offered by the Biomass Worldwide/CleanTech Biofuels improved autoclave technology.

