New or revised pages:
(latest at top)
20 December 2009
Site history
|
|
One of the most economical renewable resources is to
generate electricity or heat from household garbage and other waste.
Many countries have ignored this free and constant supply of fuel. Many
others exploit it. This map, from the Confederation of European
Waste-to-Energy Plants website, shows that there were about 425 such
installations in 2006 in W.Europe. In the USA, there are about 90 such
installations and about 100 in Japan. In the developing world, China has
about 20 plants either in service or about to be put into service.
According to various sources, Denmark holds the crown
by using about 54% of its household garbage (26% of total waste) to generate electricity and
heat, followed closely by Switzerland. The USA disposes of about 16% by
this means.
Historically, the full scale implementation of the notion started in
France in the early 1920s, although the seeds were laid in Denmark some
20 years earlier. The Nettoiement de Paris built an incinerator to take
care of the mountains of garbage that they didn't know what to do with
and they used the heat from it to generate electricity. Stated like
this, the idea sounds simple but it had enormous problems. The
combustion of the waste was inefficient and there were complaints of
nauseous smells and dirt from the plant and this gave the process a bad
name. The solid waste from it was still organically active because of
the poor combustion. Of course, modern plant is not like that; it is
virtually non-polluting and certainly not smelling. A couple of years
ago, I visited a plant in Lausanne, Switzerland and was impressed at
just how odourless and clean it was. You can read all about this visit
and how the plant works in this page. Waste
wood from forestry, house demolition, carpentry etc., if unsuitable for paper
or chipboard production, may be used for this purpose, either alone or
added to other waste. Some plants also accept tyres and other
high-pollution wastes.
In recent times, the city of Naples had enormous problems with waste, to
the extent that Prime Minister Silvio Berlusconi made an electoral
pledge to have the city cleaned up. True to his word, a number of
waste-to-energy plants are being constructed despite local opposition,
partly from organised crime factions which controlled some of the
garbage collection and were responsible for the debacle, in the first
place. The first of these plants opened in the first quarter of 2009.
Denmark
claims to have the most efficient waste-to-energy system in Europe. Two
organisations, RenoSam and Ramboll have published a brochure,
Waste-to-Energy
in Denmark, and I reproduce the Summary from it, with
acknowledgement of the source:
Although incinerating waste to generate electricity and heat is the most
efficient method of dealing with it, other methods may also be used. In
cases where there is a large quantity of a specific type of waste, it
may be more efficient to consider other methods. For example, in the
case of large poultry processing plants, large quantities of feathers
and wet body parts are not efficiently incinerated. In this case, it may
be better to place the waste in a pyrolytic reactor which produces a number of
gases most of which may be burnt to produce electricity and heat. That
having been said, pilot plants in a number of countries have not been
greatly successful and neighbours have complained of nauseous smells.
This does not mean that the process cannot be perfected and made
odour-free. Another example, and probably the least efficient, is to cap
landfill sites, collect gases that emanate from them, extract the
methane and use that as the fuel to generate electricity and heat or
simply inject it into a standard natural gas mains. Of course, this
process does not reduce the size of landfills, which is one of the
principal advantages of incinerating household garbage and other waste.
On the other hand, if the methane is added to a natural gas mains, this
method has a relatively low capital cost although this has to be
amortised over a shorter number of years because the gas will not been
produced indefinitely.
Slightly different, another waste-to-energy process is used in cement
manufacture. The cement is made by adding the raw materials to a rotary
kiln which is usually heated by a fuel oil burner, which calcines them.
This is obviously a very energy-intensive process. By adding oil-soluble
waste(sump oil, used solvents etc.) to the fuel oil, this can reduce
costs without affecting the quality of the cement. The downside is that
a higher quality flue gas treatment is required to avoid the emission of
pollutants.
The amount of energy which is available from household garbage has been
cited as equivalent to about one quarter of that of fossil fuels, weight
for weight. This means that, on an average, 4 tonnes of garbage produces
the same energy as about 1 tonne of fossil fuel. After incineration,
volume for volume, the quantity of solid waste is higher than when
burning natural gas or oil and comparable with that of steam coal. This
is about 1/10 of the volume of the initial garbage. This has to be
landfilled correctly but it is a much less onerous task than landfilling
raw garbage because it is largely biologically inert as well as much smaller in
volume. There is also almost no risk of the landfill allowing pests to
proliferate.
In correctly designed waste to energy power plants, ferrous, non-ferrous
and precious metals, including toxic heavy metals (mercury, lead,
cadmium etc.) are extracted from the
waste streams and provide additional valuable income for the plant as
they are all recyclable. Much concern has been made of toxic gases being
emitted including "dioxins", presumably meaning chlorodioxin compounds.
For the anecdote, the dioxin and furan emissions from domestic wood
burning and garden refuse burning exceeds that from modern
waste-to-energy combined heat and power plants by a factor of more than
30!
Again, proper plant design will eliminate all risk of exceeding permitted
levels of toxic gases; with the exception of nitrous oxide, many plants
succeed in keeping the level of toxic gases down to about 1/10 of the
allowable emissions, according to the most stringent regulations. Nitrous oxide is perhaps slightly more difficult to
control but nevertheless do not generally exceed between one half and
one third of the permitted levels.
As thermal plants do not emanate
odours, they are frequently placed close to inhabited zones
or actually within industrial zones, sometimes even in city centres! This allows excellent exploitation
of the heat in combined heat and power plants.
|