Article: Making the best of garbage gas

[Guest guest]

As " Energy ministers and officials from 74 countries were in Paris for

the two-day meeting on the future of nuclear energy, as concerns about

global warming and fossil fuel supplies renew governments' interest in

atomic power. " I think we need to seriously explore a variety of options

....

 

*Smile*

Chris (list mom)

 

 

http://www.alittleolfactory.com

 

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http://www.newscientist.com/article.ns?id=dn7048

 

 

Making the best of garbage gas

 

10:41 01 March 2005

Duncan Graham-Rowe

<http://www.newscientist.com/data/images/ns/9999/99997048F1.JPG>

Energy from waste dumps

 

Methane generated by rotting rubbish in landfill dumps could make a far

greater contribution to the world's energy supply. A new way of

harvesting the gas should mean that many landfill dumps that till now

were thought to be too small to produce usable amounts of the gas will

be able to provide a viable supply.

 

In Europe alone, landfill has the potential to generate as much as 94

billion cubic metres of methane each year. Yet according to the European

Commission's energy directorate only about 1% of this is being tapped.

The rest of it goes to waste, as landfill operators burn it off to

prevent a build-up of dangerous quantities of the flammable gas.

 

As well as wasting energy, flaring off methane pumps pollutants into the

environment. These are caused by impurities in the methane and the low

temperature of the flare, says Greg Miller, who set up a firm called

SusBus in 1998 in Durham, UK, to look for ways to use methane from

landfill gas as fuel for buses.

 

Methane forms in landfill when organic waste decomposes in the absence

of oxygen. At some landfills the gas is collected and used to power

vehicles or to heat nearby buildings. Till now this has been practical

only for landfills that produce large volumes of methane. But Viktor

Popov at the Wessex Institute of Technology, in Southampton, UK, says

simple modifications to existing landfills will make it possible to

extract methane from any site.

 

 

No oxygen required

 

 

Methane is usually extracted by sinking pipes or wells into the landfill

and sucking the gas out. But if the surroundings are not airtight,

sucking out methane also sucks in air. This is not only difficult to

separate from the methane; it also means methane production slows down.

" You don't want oxygen in there because that would prevent anaerobic

digestion, " says Popov. As a result the only landfill sites suitable for

methane extraction are those that are large and deep enough to restrict

the entry of air.

 

Popov's solution is to cover landfills with a membrane that prevents air

contaminating the methane. The membrane consists of three layers: a

middle permeable layer sandwiched between two relatively impermeable

layers, which would probably be made of clay.

 

The plan is to pump carbon dioxide, which can itself be extracted from

the landfill gas, into the permeable layer so the CO2 is slightly above

atmospheric pressure. This creates a barrier that prevents air being

drawn into the landfill. As the methane is sucked out of the ground CO2

is in turn sucked into the landfill from the membrane.

 

" It's an ingenious solution, " says Miller. " The biggest stumbling block

in getting this methane is to remove the nitrogen, " he says. The

greatest potential for this new system is in North America, where

landfills are still a common way of disposing of rubbish. In Europe the

long-term plan is for landfills to be phased out, though this is not

likely to happen for some time.

 

But even when rubbish is no longer being buried in landfills, old dumps

will continue to be sources of energy. " After closure a landfill will

continue to produce methane for 15 to 20 years, " says Popov.

 

Journal reference: Renewable Energy (vol 30, p 1021)

 

 

 

 

 

 

 

[Guest guest]

My husband worked on a landfill gas retrieval project at Puente Hills, the

largest landfill operating in the U.S. It is the biggest landfill gas power

plant in CA, called the Puente Hills Energy Recovery Facility. He really enjoyed

designing the testing procedures and equipment while he was contracted there.

 

BTW, the completed portion of the landfill has been turned into a nature

preserve. It's quite a wilderness right in the middle of the cities and

freeways, all trees and greenery and wildlife. Amazing. If I'm not mistaken,

Puente Hills is one of the better-run trash heaps we've got going. My husband

said that delegates come from all over to tour the facility.

 

jaime