A Mobile Indirect Biomass Liquefaction System

By John P. Hurley | March 21, 2011

The biomass industry knows all too well that transportation costs often stymie a project. Distributed or even portable energy and fuels production may be one method for diminishing the economic impacts of transportation costs in biomass utilization.

To test this idea, the University of North Dakota Energy & Environmental Research Center is building a mobile system for converting cellulosic waste into liquid products. The work is being funded through the Xcel Energy Renewable Development Fund and the U.S. DOE through the EERC Centers for Renewable Energy and Biomass Utilization. The system is currently under construction. Parametric testing will be performed with the system during the summer and fall.

In the EERC program, the technology will be demonstrated by building and testing a 200 pound per hour fixed-bed downdraft biomass gasifier, air-blown and with specialized gas cleaning to produce the syngas. The system will be integrated with approximately 3-meter-long packed-bed catalytic reactors for producing the liquid fuels and highly automated to minimize labor requirements. A design review has already confirmed the fixed-bed biomass gasifier selection as the lowest capital cost system for indirectly producing methanol. The methanol produced will then be tested by IdaTech LLC of Bend, Ore., to determine if it is of sufficient purity to power a fuel cell used to produce heat and electric power.

A strong advantage of the EERC gasification system is that it can be used with green or wet wood. This reduces the need for drying the wood before gasification, resulting in substantial energy and processing savings. In fact, the high moisture content creates syngas with a significantly higher hydrogen content than if the moisture were not present. High hydrogen content is especially useful when making a liquid fuel from the gas stream since the hydrogen-to-carbon ratio in a liquid fuel is much greater than that of the wood itself. By increasing the hydrogen content in the gas stream, higher carbon conversion efficiencies can be reached.

By producing a liquid fuel for electricity generation elsewhere, overall biomass-to-electric power conversion efficiency is reduced relative to firing the syngas directly in a generator. However, by making a liquid fuel, the site at which the power is required can be decoupled from the site of the biomass resource. In this project, the biomass resource targeted is wet legacy piles of wood waste found at sawmills throughout Minnesota. These piles, often produced years ago, still contain a significant energy content but have degraded to the point at which they cannot easily be used as commercial products such as garden mulch. Rather than incinerating them, the EERC technology would turn the waste piles into a revenue stream through the production and sale of a carbon-neutral liquid fuel.

Although the gasification design is new and unique, the EERC will be using commercially available technologies for gas compression and conversion. Initial laboratory testing of some of the subsystems shows that it may be possible to significantly improve the productivity of the system by using more experimental methods such as gas separation membranes or by modifying commercially available equipment to make it more useful in remote settings. These modifications will be the subject of a future article.

Author: John P. Hurley
Senior Research Advisor, Energy & Environmental Research Center
(701) 777-5159