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Researchers develop Transportable Waste-to-Energy System

  • Published
  • By Mindy Cooper
  • AFRL Materials and Manufacturing Directorate
TYNDALL AIR FORCE BASE, Fla. --  The Air Force Research Laboratory Materials and Manufacturing Directorate here is developing a Transportable Waste-to-Energy System to produce electricity at forward military operating locations. This program is supported by the Department of Energy's Federal Energy Management Program.

Executive Order (EO) 13423, signed in January 2007, requires that federal agencies increase their domestic use of renewable energy and produce it in an environ¬mentally and economically sound, sustainable manner. EO 13423 suggests implementation at facilities not within the United States. Researchers from the AFRL directorate's Airbase Technologies Division are developing a Transportable Waste-to-Energy System (TWES) to produce electricity from renewable energy.

"The system would reduce the amount of fossil fuel consumed at each forward military operating location where it would be installed. Forward operating bases currently use MEP-12 generators to supply electricity. The system could also be implemented at domestic military bases," explained Mr. Walt Waltz, the Robotic Group Lead.

According to Mr. Waltz, the system under development consists of two stages, a furnace and an energy recovery unit. The AFRL researchers have completed construction of the first stage, the Transportable Furnace System (TFS), and have installed it on a 48-foot-long, flat-bed semi-trailer. The TFS shreds and burns solid waste including wood, paper and plastic. The system is comprised of a furnace which is nine feet tall and 6 1/2 feet in diameter, a liquid fuel burner, an eight-foot-tall shredder, two hoppers to hold the shredded solid fuel, and two air blowers.

"Before the furnace can burn solid waste, it is preheated with a Beckett fuel burner, using either diesel or JP-8 fuel at a rate of around five gallons per hour. This type of burner is commonly used to heat buildings and for industrial processes," Mr. Waltz explained, "After 30 minutes of pre-heating, the burner is removed and its port is sealed. No more liquid fuel is required."

Bulky solid waste items like wood, pallets, paper, plastics, and yard clippings are dropped into a hopper on the shredder. Material is shredded down to less that 1/2 inch in all three dimensions. The shredded waste material falls from the shredder into a box, and from there the material is vacuumed through a large flexible hose and into the system's second hopper. From the second hopper 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 furnace and is now fuel. Because the furnace is pre-heated, this shredded fuel heats and bursts into flame.

Mr. Waltz explained that the energy from the burning fuel maintains the furnace temperature, sustaining the com¬bus¬tion process for the additional shredded waste that continues to enter. The burning waste swirls through the furnace, and the exhaust rises through the exhaust stack. During testing, the TFS burned wood at a rate of 150 pounds per hour. A total of 15 burn tests have been completed to date. During these tests, the system operated continuously for up to six hours. No additional liquid fuel or gas was used to burn the solids. After initial adjustments, the system performed steadily and burned well. 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 energy recovery component. With a series of heat exchangers, this com¬ponent will generate steam using the heat released from the burning waste. This steam energy can potentially be used for heating, absorption air conditioning, and/or electricity generation at the forward operating bases or rural domestic bases. The prototype system will generate electricity, functioning as a small power plant. When completed, the TWES will burn up to 500 pounds of waste per hour.

"The TWES will reduce costs and lessen the environmental impact associated with the generation of electricity by reducing the amount of fossil fuels required at mili¬tary installations," Mr. Waltz said, "By consuming combustible waste, it will also reduce the need for out¬side contractors to dispose of waste created at those locations and help the Air Force comply with important environmental goals and standards."