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Update on a Mobile Indirect Biomass Liquefaction System

Minnesota’s forestry operations produce 300,000 tons a year of wood waste that is not used in any existing or proposed facility. Through the process of indirect liquefaction, this waste can be converted into liquid fuels that could be transported to remote off-grid sites and reformed to hydrogen to power fuel cells to produce electricity. Using distributed power generation to off-grid sites eliminates the need to build transmission lines at remote sites, which ultimately saves utility ratepayers money. In addition, the wood-to-fuel technology provides a non-fossil energy-based, nearly carbon dioxide neutral method to fuel backup generators. Even in areas that are served by the grid, this saves utility ratepayers the cost of maintaining large backup power production systems. Ratepayers may also be able to take advantage of future carbon credits or avoid carbon taxes applied to fossil energy-based power production.

The Energy & Environmental Research Center (EERC) has developed and tested at small scales much of the technology necessary for distributed indirect liquefaction systems. With funding provided by customers of Xcel Energy through a grant from the Renewable Development Fund and the U.S. Department of Energy through the EERC Centers for Renewable Energy and Biomass Utilization, the EERC designed and built a mobile, demonstration-sized indirect wood waste liquefaction system and operated it in order to determine best construction and operating practices, overall system productivity, and necessary design changes to make the concept more commercially viable. The system was originally described in this column in the April 2011 issue.

The system uses a unique gasifier to convert the wood waste into synthesis gas, which is cleaned and compressed and flows to a gas-to-liquids (GTL) reactor to convert the gas to a liquid. In this program, we focused on the production of methanol, the simplest alcohol, because it can be easily reformed into hydrogen which can be used to power fuel cells to efficiently make electricity at sites separate from the biomass resource. The gasifier was specially designed by the EERC to handle wet wood waste with up to 40% moisture, thereby saving the need to separately dry the wood before gasification, as most commercial gasification units require.

Project funding provided by customers of Xcel Energy through a grant from the Renewable Development Fund, and the U.S. Department of Energy.By John P. Hurley, Senior Research Advisor, Energy & Environmental Research Center (EERC)