Turning Waste to Energy in Downtown Seattle

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Seattle Steam Co., a major supplier of heat to downtown Seattle buildings, is going to begin turning waste into a source of energy. The company began construction yesterday on a hybrid heating plant, with a boiler that is able to burn waste wood as well as Seattle Steam's current primary energy source, natural gas. According to this article by Seattle Times reporter Will Mari, Seattle Steam plans that about 60 percent of the new boiler's energy will come from waste wood collected from urban construction sites, sawmills, factory crates and pallets, and other products.

Combusting waste wood closes the "carbon loop," said Patrick Mazza, research director for Climate Solutions, a Seattle-based research and advocacy group.

"You're contrasting a fuel source that has been notably volatile in terms of price with a local, renewable fuel source," he said. "It's one of those things that we know to do well, but that we've kind of forgot during the age of cheap energy."

But what of the greenhouse gases released by burning wood? Coverage by Bill Virgin at the P-I addressed this issue in a question to Seattle Steam President Stan Gent:

Burning wood actually will release more of those gases than burning natural gas, Gent says. But advocates of such a switch argue that over the full life cycle of the tree, the net release is zero, since the tree is absorbing and storing carbon dioxide while growing.

The ash produced from burning the wood will be collected and sold to concrete companies, which can use the waste as an industrial nutrient.

As Mike Mann of the Office of Sustainability and the Environment told the Times, the $25 million plant will prevent 50,000 metric tons of carbon from being released each year, by replacing the use of a fossil fuel with the use of waste wood. The facility is expected to open in July 2009.

You can read previous waste-to-energy articles in the Worldchanging archives, including our piece on Denmark's iconic Kalundborg industrial park, or Alex's posts on the neobiological industry and Svend Auken's energy plan.

Image courtesy of Seattle Steam Co.


I have to admit I'm scratching my head over this. Yeah, I get the life-cycle analysis. But, this is wood that would have been landfilled, and instead we're releasing its CO2 into the atmosphere. Doesn't seem like something to cheer about. And you don't even mention the particulate pollution issues. In the old days, we called this a "waste incinerator" and fought like hell against it.

Posted by: Phil Mitchell on October 9, 2008 7:46 AM

If the wood is landfilled, it will release CO2 slowly as it decomposes (and we don't get to harvest the remaining energy in it). If the wood is landfilled and gets wet in an anaerobic environment (no oxygen) it will release methane, which is a much worse greenhouse gas than CO2. Burning it just releases all the carbon into the atmosphere in one quick burst. I don't think that's a problem, since every btu from the wood displaces who knows how many btus of fossil energy (1 btu of natural gas plus all the btus needed to get it there in that form, ready to burn, including military energy expenditures).

Having said that, the highest use of construction "waste" is to reuse it, which requires some kind of recycling center like Bring Recycling in Eugene, Oregon.

Hopefully, the engineers working on this project understand that doing everything in their power to ensure complete combustion will reduce the particulates and other emissions down to miniscule levels.

My understanding is that often times, the phrase "Waste Incinerator" refers to a facility that burns all kinds of things--not just biological resources. That means electronics, plastic bottles, you name it. Cleaning up emissions from that kind of facility is anywhere from laughably expensive to impossible.

Even though they're doing a great job using district energy and bringing biomass into the mix, I think they're missing out on a significant opportunity by not going with pyrolysis. If they chose to burn the biomass in the absence of oxygen, they could use some of the resulting combustible syngas (containing 50% of the original carbon) to run the process and use the rest for steam production. The biochar that remained would sequester the other half of the carbon and can be used as an impressive soil amendment (I've heard reports of 300-800% yield increases). The process is carbon negative if the biomass is locally sourced and the biochar is locally used.

Of course, to make this economically viable, Seattle Steam would have to get into the wholesale biochar business and I'm not sure if they're into that degree of diversification.

Posted by: greensolutions on October 10, 2008 10:33 AM

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