Ethanol from wood – can it pay?
Recently there has been a push by the federal and state governments to increase the production of fuels from biomass as a substitute for fossil fuels such as oil, coal and natural gas. However, a recent headline announced that more fossil fuel energy is used to produce ethanol from corn and wood than the energy provided by the ethanol produced. This is a disturbing thought, given that each year over a billion bushels of corn are converted to ethanol! It would also mean that efforts to make ethanol from wood in Tennessee should be stopped. But is it true?
The controversial headline comes from a recent study by David Pimentel at Cornell University and Tad Patzek at the University of California/Berkley. This study reported that ethanol production from corn required 29% more fossil fuel energy inputs than the energy contained in the ethanol produced. The numbers for other feedstocks were even worse: 50% more for switchgrass and 57% more for wood.
Dr. Pimentel has produced other reports critical of ethanol production from corn in the past. However, there have been a number of other researchers that have pointed out possible errors and shortcomings in his methods, and have contradicted his conclusions. In general, other researchers have concluded that ethanol produced from corn provides a net energy surplus of about 30%.
But what about wood as a source of ethanol? One of the advantages of wood products is that wood requires relatively little energy to grow and process. Thus it is surprising that wood could be a less efficient energy source than other feedstocks. A closer look at Pimentel and Patzek's recent study reveals a number of problems with their analysis of using wood for ethanol production. For example, they assume that large amounts of nitrogen fertilizer (made using natural gas) will be required to replenish the forest soils. However, because wood is very low in nitrogen content, fertilization of forest soils is not necessary. Pimentel and Patzek also assume that the steam used in the ethanol production process would be generated by burning fossil fuels. However, steam for current wood processing steps – e.g. for kiln drying lumber and for pulp and paper making – is usually generated by burning wood waste. Steam for ethanol production from wood is likely to come from wood waste also.
A final, fundamental shortcoming of Pimentel and Patzek's ethanol-from-wood analysis is that they assume that ethanol would be the only product from the trees. This means that all of the energy “costs” are carried by the ethanol produced in their analysis. But this is very unlikely. Currently, harvesting of a forest stand produces a number of different products: veneer, grade lumber, railway ties, pulp chips, hog fuel and mulch. If ethanol production from wood becomes a reality, it will probably be just one more product in the mix – not the only product. This makes the ‘energy efficiency' of ethanol production much higher.
The forests of Tennessee cover more than ½ of the state and represent an enormous natural and renewable resource. Efforts are underway to try to convert some of this resource into liquid fuels. Whether the final product is ethanol or bio-oil or something else, wood from Tennessee may become an important substitute for fossil fuels.