Solar Powered Biomass Gasification

Biomass gasification is currently the most promising bioenergy approach, in terms of both small scale and medium/large scale power and fuel production. Bio-syngas can be used to fuel steam turbine power generators, can be converted into liquid fuels such as diesel/gasoline/jet fuel, or it can be used as a heat source (as in CHP).

In order to make the process of biomass gasification more efficient, scientists at the University of Colorado, Colorado State University, and the National Renewable Energy Lab have collaborated to devise ways of using solar energy to achieve bio-gasification.

The large, 32-square meter (38-square yard) heliostat reflects sunlight onto the primary concentrator, which focuses the sun to a single point. “It’s basically similar to using a magnifying glass to concentrate sunlight to a point, although we use mirrors instead of lenses,” explains Carl Bingham, staff engineer at NREL. This concentrated sunlight, which has been reduced to a beam measuring 10 centimeters (4 inches) in diameter, is reflected a second time at a target area inside the test building where researchers run their experiments.

“The original intent was to see what we could do with highly concentrated solar radiation,” Bingham says. By tightening the focus of the sunlight or increasing its concentration, temperatures pushing greater than 2,000 degrees Celsius (3,632 degrees Fahrenheit) can be reached. “The idea is that heating things with concentrated sunlight gets things very hot, very quickly,” he says. In addition to scorching temperatures, the furnace allows for the selective heating of the sample surfaces.

...“What we discovered was that at temperatures of about 1,200 degrees C (2,192 degrees F) the short, rapid pyrolysis or gasification in the presence of steam of the biomass, produced syngas with usage in excess of 90 percent of the biomass,” he says. This is significant, Weimer explains, because conventional gasification processes require a partial oxidation of the feedstock, which leads to yield loss. In addition, the very rapid heating for a very short time prevented the formation of tars. This eliminates the need for cleaning the syngas before it’s reformulated to fuel, which is a pricey capital cost for a biomass plant, Weimer says.

...As biomass flows through the tube, either by itself or with some inert gas or steam, the feedstock is heated to high temperatures for only a few seconds. The kinetics of this reaction are closely monitored for various feedstocks and used to develop mathematical models that predict how the solar reactors at NREL should behave. These models are then used to design the reactors that will be used for on-sun demonstrations.

This includes a secondary concentrator, which is a cone-shaped device that essentially wraps the sunlight around the reaction tube. The biomass is gasified as the tube absorbs the heat. “Our students build these reactors here in the shop in our department. They mount them on skids. They put the skids in the back of a pickup truck and drive up to NREL where they locate the reactors in the corner of the test building,” Weimer explains.

“With the biomass we’re really in the sweet spot,” Weimer explains. “The materials issues associated with the water splitting go away.” But there are other challenges. The biggest of these is finding biomass feedstocks independent of the food chain. “At the conditions that we operate, however, we can handle huge variability in feedstocks,” he says. Weimer’s team has gasified grasses, sorghum and even lignin. “Our feedstock could be lignin, sawdust, forestry waste, spent grains from a brewery, switchgrass, corn stover, sorghum,” he says. “It could also be municipal solid waste or paper. It could even be glycerin.” __Source

As the technologies for bioenergy conversions improve, the chorus of naysayers are looking more and more cut off from reality. Maize ethanol has provided some early benefits, but is only the beginning. Energy from grain is a first generation, nearly obsolete method for producing energy. Profit margins for corn ethanol are being constantly trimmed as commodities prices rise. Cellulosic biomass forms of energy production will come online slowly, beginning this year.

The various bioenergy production methods will experience a constant shakeout for the next decade or two as each new method tries to displace the currently reigning method.