AFRL Develops Transportable Waste-to-Energy System

  • Published
  • By Heyward Burnette
  • Materials and Manufacturing Directorate
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  AFRL researchers are developing a transportable waste-to-energy system (TWES) to produce electricity from renewable energy at forward military operating locations. The Department of Energy's Federal Energy Management program is supporting the effort. 

By reducing the amount of fossil fuels required at military installations, the lab-developed TWES will reduce both the cost and the environmental impact associated with generating electricity. Further, the system's consumption of combustible waste will minimize reliance on outside contractors for waste disposal, as well as assist Air Force compliance with important environmental goals and standards.

AFRL researchers have completed construction of the system's first stage, the transportable furnace system (TFS), and installed it on a 48-foot-long, flatbed semitrailer. Before the furnace can burn solid waste, it must be preheated with a Beckett fuel burner, using either diesel or JP-8 fuel at a rate of around 5 gallons per hour. This type of burner is commonly used for heating buildings and performing industrial processes.

The TWES functions as follows. Bulky solid-waste items, such as wood, pallets, paper, plastics, and yard clippings, are dropped into a material holding compartment (i.e., a hopper) on the shredder to await processing. Next, the shredder reduces this material to scraps of less than 1/2 inch in all three dimensions. The shredded waste material then falls into a box from which it is subsequently vacuumed through a large, flexible hose and into the system's second hopper. From this holding location, the material drops through a rotary feeder into a pipe with air blowing through it. The rotary feeder helps measure the amount and speed at which the shredded waste is pneumatically conveyed into the furnace. The shredded waste flows steadily from the pipe into the preheated furnace, where it essentially becomes fuel, heating quickly and bursting into flame.

The energy generated from the burning fuel maintains the furnace temperature, sustaining the combustion process for additional shredded waste that continues to enter. The burning waste swirls through the furnace, and the resulting exhaust rises through the exhaust stack. During testing, the TFS burned wood at a rate of 150 lbs per hour. Stack emissions were clear with no visible smoke, and an inspection inside the furnace confirmed no residual soot.

AFRL researchers recently began the second stage of this project, designing the system's energy recovery component. Using a series of heat exchangers, this component will generate steam using the heat released from the burning waste. Potential uses of this steam energy include heating, absorption air conditioning, and electricity generation for forward operating bases and/or rural domestic bases. The prototype system will generate electricity with the functional capacity of a small power plant. When completed, the TWES will burn up to 500 lbs of waste per hour.