Burning natural gas to produce all that heat is the second largest expense at most ethanol plants -- trailing only the cost of the corn used for ethanol production. One estimate says Iowa's annual production of more than one billion gallons of ethanol accounts for about 16 percent of the state's demand for natural gas.
That has Iowa State University researchers working with an Ames company to develop a renewable and cost effective alternative to the natural gas burned by most ethanol plants.
The technology involves partial combustion of biomass -- that could include corn stalks, distillers grains, waste wood or other biorenewables -- to produce a mixture of hydrogen, carbon monoxide, methane and other flammable gases. The resulting mixture is known as producer gas and it can replace natural gas in an ethanol plant's heaters. The producer gas can also be upgraded to what's known as syngas, a mixture that can be converted into high-value transportation fuels, alcohols, hydrogen, ammonia and other chemicals.
Producer gas is made by injecting biomass into a fluidized bed gasifier, a thermal system that pumps air up through a bed of hot sand, creating bubbles and a sand-air pseudo fluid. A reaction between the biomass and the hot sand-air mixture produces flammable gases. The process also generates its own heat to sustain the reaction. It's a system that's reliable, produces few emissions and can be efficiently integrated into a plant's existing natural gas boilers and dryers.
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