What a gas!

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There used to be just CNG, LPG and the odd whiff of biogas from some of the more committed organic ­vegetarian-whole earth-green types.

Now there is a new member of the gas club: LFG (landfill gas), emanat­ing from that august body, the ARC (Auckland Re­gional Council). In fact, I exaggerate. LFG has been around longer than the ARC, and has been signifi­cant mostly for its malodor­ous persistence.

But of late, parsimonious times have driven two bodies corporate, the ARC and the AEPB (Auckland Electric Power Board) to contemplate harvesting the stuff for a useful purpose.

In the good old days, rubbish tips were informal affairs—cheap, uncompacted, expansive, messy, and a paradise for scavengers, both human and animal. Obnoxious chemicals used often to escape and pollute, while a putrid stench seared the nostrils.

In larger centres tips have now moved upmarket to become ‘landfills’, under the watchful eye of public authorities. They are now carefully constructed with waterproof clay completely enclosing compacted rubbish—gigantic pies of refuse sealed in a crust of clay! Not only does the clay restrain leaching chemicals, but it is a barrier to gas exchange as well.

Where oxygen has ready access to rubbish, decom­position mainly produces the greenhouse gas carbon dioxide, with a little hydrogen. In the new sealed landfills, oxygen cannot penetrate readily, and once what is present is consumed, decomposition becomes anaerobic, with combustible methane as a major product.

Methane is that less than sweet-smelling effluvium that cows (and others) belch out, and happens to be an even less desirable greenhouse gas than carbon dioxide. To get rid of the methane, wells have been drilled into the landfill and gas piped to central flaring-off points at both of the ARC’s Rosedale and Greenmount refuse sites.

But if it burns, couldn’t it be useful? The vigilant ARC has been ruminating on possible uses for LFG since 1987.

They have determined that quality and quantity are sufficient to be com­mercially valuable. Propos­als for use of the gas were sought early in 1990 and two alternatives emerged: upgrading the gas to natural gas quality for use in city gas mains or burning it in engines to generate electricity.

Since electricity genera­tion proved more eco­nomic, the ARC/AEPB joint venture was devel­oped. Gas collection and quality will be the preserve of the ARC, while the AEPB will generate the electricity.

Useful amounts of gas are expected to be pro­duced for 10-20 years. Waste heat from the generation of electricity could conceivably be sold to industrial users as well. Within a few years you will not only be paying to get rid of your refuse, but you’ll be buying some of it back again to run the vacuum cleaner!

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