Trash Into Gas, Efficiently? An Army Test May Tell

THERE is an indisputable elegance to the idea of transforming garbage into fuel, of turning icky, smelly detritus into something valuable.

But big drawbacks have prevented the wholesale adoption of trash-to-gas technology in the United States: incineration is polluting, and the capital costs of new plants are enormous. Gasification systems can expend a tremendous amount of energy to produce a tiny amount of electricity. Up to this point, it hasn’t seemed worth the trouble.

Mike Hart thinks that he has solved those problems. In a former Air Force hangar outside Sacramento, his company, Sierra Energy, has spent the last several years testing a waste-to-energy system called the FastOx Pathfinder. The centerpiece, a waste gasifier that’s about the size of a shower stall, is essentially a modified blast furnace. A chemical reaction inside the gasifier heats any kind of trash — whether banana peels, used syringes, old iPods, even raw sewage — to extreme temperatures without combustion. The output includes hydrogen and synthetic natural gas that can be burned to generate electricity or made into ethanol or diesel fuel. The FastOx is now being prepared for delivery to Sierra Energy’s first customer: the United States Army.

Ethanol has long been promoted as an alternative fuel that increases energy independence, and federal law requires the use of greater amounts of it. But most ethanol in this country is produced from corn or soybeans, and many people worry that the mandate is pushing up food prices. Ethanol produced from trash — or agricultural waste, as others are trying — would allay such concerns.

Ineos Bio, a Florida company, announced last month that it had produced ethanol from gasified wood waste, using a method that it expects to be commercially viable, and KiOR Inc. will make one million to two million gallons of diesel...

How It Works

Waste is fed into the top of the gasifier while oxygen and steam are injected into the bottom. The injection of oxygen and steam is one of Sierra Energy’s patented innovations.

The waste descends, by gravity, inside the gasifier passing through four reaction zones:

Drying occurs when the hot syngas produced at the bottom of the gasifier rises and passes through the waste in the top zone of the unit, drying the waste as it passes.

Devolatization is where the majority of the organic matter is driven off into syngas.

Partial oxidation occurs when carbon-containing materials in the waste react with the injectors. This reaction creates high temperatures in the range of 4,000°F allowing for the thorough conversion of remaining carbon into syngas.

Melting of inorganic compounds results from the high temperatures occuring in the partial oxidation zone. These compounds collect at the bottom of the unit and are continuously removed as inert stone (slag) and recycled metals.

The simple design of our FastOx gasifier enables all of these steps to occur in a single unit, giving us an advantage over other conversion technologies that require complex systems and units to accomplish each of these steps.

http://www.sierraenergycorp.com/innovation/technology-overview/

The general point of these systems is to liberate more energy stored in the organic compounds in the waste material than the liberation process takes. So you invest some energy (as heat, in this case) to extract the potential energy from the organic material in a ready-to-use format.

All well and good. The problem historically has been scaling such things up to a commercially-viable level without undesired side effects (c.f. “Changing World Technologies” and the odor issues with their commercial plant).

Thanks for posting that.

Partial oxidation occurs when carbon-containing materials in the waste react with the injectors.

The injectors are consumed? If so, I wonder what they are composed of and how do they monitor the rate at which they are used?

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