Low Temperature Gasification of Corn Stover - UMM Encounters Problems

It was interesting for me to read about a unique gasifier that UMM (University of Minnesota, Morris) was experimenting with.

UMM’s goal was to create the first gasifier that incinerates the fuel temperatures of 1,000 degrees or lower, producing gas that can be used to create steam for UMM’s system while also preserving minerals in the ash so it can be used in soils. Now, most solid fuel gasifiers burn heavy density wood at a temperature of about 3,000 degrees, and the ash produced can only be used for limited purposes, such as wallboard.

I think the lower temperature gasification is interesting from many aspects. I am wondering if this is the same as pyrolysis (from all accounts it seems so), or whether this low-temp gasification has features that differentiate it from pyrolysis.

Either way, the following was the unique problem faced by the team at UMM:

But when the system was first fired up, operators learned that gasifying loose stover (which was used as the feedstock) posed substantial problems. The stover is moved into the burner, where air is blown through from the bottom of the burner for combustion. But the loose stover has a density of three pounds per cubic foot and the air moved it around in the burner and created a hole in which all the air would move through instead of maintaining a steady flow.

So, the folks decided that corn stover, the way it was used, would not be appropriate. They turned to a company to compact the stover into a form similar to compressed sawdust fireplace logs. The new stover “logs” have a much higher density of 50 pounds per cubic foot (compared to the 3 lb per cubic foot of loose stover). The density is expected to help the fuel remain in place in the burner and even out the heat and air distribution in the gasification process.

Of course, it costs to compact the stover. How the whole compacting process will affect the economics is not known presently. But this presents an interesting case study in waste biomass gasification

Source credit: Morris Sun Tribune