Researchers test biomass gasification pretreatment

By Ryan C. Christiansen
Web exclusive posted Nov. 14, 2008 at 10:07 a.m. CST

Researchers at the University of Nevada, Reno are developing a biomass pretreatment method to help optimize the gasification of biomass, such as wood, corn stover, rice straw, and switchgrass. Using a hot pressurized water hydrothermal process followed by a hot nitrogen torrefaction process, the researchers are converting biomass into a carbon-neutral black, crumbly char, similar in shape and size to coal.

"[Through torrefaction], you increase the energy density of the biomass by exposing the material to a certain temperature level in the absence of oxygen, and so you can use nitrogen, for instance, so that oxidation processes do not occur," said Victor Vasquez, an associate professor in the chemical engineering department at the university and one of the researchers. "You dry out a lot of the water and you dry out some of the volatile compounds and in the end, you end up with a product that has a higher energy density and a reduced amount of water. The material becomes quite hydrophobic."

One of the main barriers to biomass-based energy production is biomass feeding systems must be engineered to accommodate different forms of biomass and some biomass is difficult to handle or prepare for use, Vasquez said. Through pretreatment, the biomass product becomes molecularly uniform and dense, which helps to optimize gasification. A byproduct of the process is a sugary water solution that could be converted to ethanol or other fuels.

"At this point, we are trying to quantify [the byproduct]," Vasquez said. "The aqueous solution contains a certain amount of sugars. Right now, we're trying to chemically quantify what is the amount of sugars in the solution. A sugar-based solution is more valuable, because you could use it for fermentation or other purposes."

The pretreatment study is part of a larger $4.6 million study by the Gas Technology Institute. Another partnering organization is the Renewable Energy Institute International which will conduct a techno-economic analysis of different biomass-to-energy options in Nevada. Vasquez said he hopes to have small, mobile, pilot-scale systems available for demonstration by the end of 2009.