February 24, 2006
Household garbage finds new life as fuel
Useful products from unlikely things
As technology marches on, useful products keep appearing derived from unlikely sources.
Who would have dreamed a couple of decades ago that used frying fat from your neighbourhood greasy spoon restaurant could be turned into economical diesel fuel called biodiesel? Or that a series of space satellites would yield the means for controlling the operation of roadbuilding equipment?
Or that ordinary household garbage could yield not only fuel for generating electricity, but material that can be used as roadbuilding aggregate?
The technology that does that is called plasma gasification, and a pilot plant is to be built in Ottawa to process 75 tonnes of municipal garbage daily. The planned result is the generation of a synthetic gas to fuel engines to drive turbines to generate enough electricity to serve about 3,600 homes, with about eight to 12 tonnes of glass-like slag left — slag that can be crushed and used as aggregate.
Plasma gasification is a concept that can be difficult for a layman to understand. Because it involves intense heat (1000<0x00B0> C) some environmentalists have opposed the idea, believing it is simply another name for incineration. Its proponents, however, including the Plasco Energy Group, insist that it is definitely not incineration.
Instead, they say, it is “a non-incineration thermal process that uses the intense and controllable heat from plasma arc generators in an oxygen-starved environment to decompose” the material being treated into simple molecules. There are no emissions of any sort.
The pilot plant planned for Ottawa will be built by Plasco without cost to the city, and will operate for a year from its proposed start-up in October, 2007. Randy Bennett, a Plasco vice-president, said in a recent interview that the firm expects to be able to go on-site this April to begin construction.
“Then, late in the fall, we expect to be testing waste, doing end-to-end integration of the equipment. That will go on for some months. And we expect, even in the worst case, to be in full demonstration mode in October, 2007.
“We’ve never build (a plant) of this size before, so we’re giving ourselves time to make sure everything works.”
Bennett said the slag left behind in the gasification process has some commercial value.
The most obvious use for it is to crush it and use it as roadbuilding aggregate. But, he said, it can also be powdered and used to replace part of the Portland cement in some concrete mixes.
“We’ve done some very minor testing doing that,” Bennett said. “We haven’t done any long-term tests. It’s just not where we’re concentrating our efforts. But it’s definitely been done. Our Spanish partners are looking at using it in tiles and a whole bunch of other things because they think it has a very strong commercial use.”
The Spanish partners he referred to is a firm called Hera S.L., which is Spain’s second largest waste management company.
It’s a firm, Bennett said “that is always on the lookout for new technologies” because it knows that thinking about the medium term “is not going to be the solution any more.”
After the two firms formed a partnership in 2003, Plasco shipped its five-tonne-per-day demonstration plant to Spain where, said Bennett, it has proven the effectiveness of the technology.
A city the size of Ottawa generates about 800 tonnes of garbage daily, Bennett said. “A lot of it goes to the city’s landfill in the west end. Some of it is recycled, but a couple of hundred tonnes goes to a waste management dump.”
It is that few hundred tonnes that are of interest to Plasco, because the city “wants us to take tonnage that ordinarily goes into the landfill because it will help extend the life of the landfill.”
As Bennett described the process, “a garbage truck will enter the city’s . . . landfill and be weighed. Some trucks will be diverted down the road to us. It will be dumped and the waste will go through a one-pass shred. We’ll take out things like barbeques because there’s no need for us to process big chunks of metal, and the waste will be fed through our system.
“We get a gas that will be cleaned and go into a gas storage tank, and it will go from the tank into a gas engine, at which point we would have emissions to the atmosphere for the first time.”
That engine will drive turbines generating electricity, which will be sold to the local power grid.
As for the slag that’s left, the amount will depend on the waste stream going into it “so it could be anywhere from eight to 12 tonnes.
“And it’s very safe. It doesn’t leach.”
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