November - December 2008

From: Distributed, Renewable Bioenergy

At the Scrubbing Edge

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To burn, renewable biogas must first have its moisture, carbon dioxide, siloxanes, hydrogen sulfide, and other contaminants removed; each requires a dedicated system.  Afterward, engines get (hopefully) high-quality fuel, and the resulting emissions can pass tough emissions standards.

So far, the combinations of scrubbing systems—developed under conditions that often differ significantly and do not necessarily carry over to new applications—have proven to be expensive and not always reliable. Consequently, power projects at landfills and digesters may be put at higher risk. Negative results range from increased engine wear and higher maintenance labor to outright project failure.

The quest for technology to deliver higher performance, at lower cost, is never-ending.

One of several newly emerging systems is this, for removal of what is often a significant contaminate, hydrogen sulfide. For combating this, an iron redox reaction process, stemming from research and development undertaken at the University of Toronto, has now been licensed to an Ontario firm, Eco-Tec, which markets industrial gas treatment processes. Eco-Tec’s VP for business development Carmine Fontana gives a quick overview:

The hydrogen sulfide is simply absorbed in a high-efficiency, gas-liquid contact process, with proprietary chemistry mixtures within a chamber. Afterward, the solution flows to another vessel for regeneration by air. Extracted sulfur is then filtered and caked for disposal.

The results, he says, are “excellent,” and come at less than half the cost of previous-generation hydrogen sulfide scrubbers, thanks to smaller equipment that can mount on a small skid. A pilot was fielded in mid–2008 at a food processing plant in the UK, where onsite biogas is now being captured to power two Jennbacher reciprocating engines.

A previous-generation version is offered in the United States as the “Lo Cat” and “Mini-Cat” system from Merichem Gas Technology Products of Schaumberg, IL, which has recently fielded a pilot version at the Eastern Creek MSW plant near Sydney, Australia.

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