ÐÓ°ÉÔ­´´

Even sulphurous clouds have silver linings. Britain’s deserved reputation
for dragging its feet over European environmental regulations could ironically
be the saviour of its coal industry. If in the 1980s Britain had followed
Germany’s lead and installed expensive scrubbers and catalysts in its power
stations to reduce emissions of sulphur dioxide and oxides of nitrogen,
its coal would have been priced out of the domestic electricity market years
ago.

It is because Britain has barely begun cleaning up fumes that the power
generators can take advantage of new technologies that were not available
to the Germans but which dramatically reduce the price of pollution control.
On their own they might not be enough to make coal-fired power competitive
with gas-fired power, but go a long way towards that goal.

Before the privatisation of the electricity industry, the British government
estimated that to meet emissions standards laid down by the European Commission
it would have to spend £1 billion on its coal-fired power stations.
This would have enabled it to reduce emissions of sulphur dioxide (S0₂)
and nitrogen oxides (N0_x) to well below the 1980 levels by 2003. Powergen
and National Power, the power generation companies due to be privatised,
immediately saw that it would be less expensive, given the coal-fired plants’
remaining useful life, to close them and build gas-fired power stations
instead. Their reluctance to commit themselves to greater purchases of coal
led inevitably to the pit-closure proposal and subsequently to Michael Heseltine’s
review of energy policy.

But the £1 billion estimate was based on conventional technologies
– flue-gas desulphurisation (FGD) for sulphur dioxide, and selective catalytic
reduction (SCR) and low-NO_x burners for NO_x. All three are expensive. FGD
requires the installation of a piece of equipment about 20 metres high
between the boiler and the stack. Inside it wet calcium salts react with
the sulphur dioxide to make calcium sulphate, which can be precipitated
out of the smoke and removed (to be dumped somewhere). Low-NO_x burners
involve replacing the entire bed of the furnace with a design that allows
the flame to burn at a lower temperature through controlled ventilation
of the fuel, so that less nitrogen in the air is oxidised. SCR entails setting
up equipment between the boiler and chimney stack incorporating catalysts
based on platinum group metals to help break down NOx into nitrogen and
oxygen.

On average, FGD alone increases the cost of generating electricity from
coal by about 10 to 15 per cent. The other technologies are only marginally
cheaper: SCR costs about £1000 per tonne of NO_x removed. Although
low-NO_x burners can cost as little as £150 per tonne removed on fairly
new plants, they can only achieve a 20 to 50 per cent reduction in emissions,
and can cost much more – up to £1000 per tonne – on plants with only
a few years’ useful life left.

A far cheaper technology is now available for the first time. In the
1970s, Exxon experimented with injecting ammonia into a furnace flame and
found that it reduced the nitrogen oxide in the flame to nitrogen. It never
developed the idea much further, but scientists at the Electric Power Research
Institute (EPRI), a research arm of the electricity generating industry
in the US, picked up on the idea and tried injecting other chemicals. They
discovered that urea worked even better than ammonia. It was also a safer
chemical and more practical: it could be dissolved in water and injected
as a liquid. The reaction was:

2C0(NH₂)₂ + 4N0 + 0₂ –> 4N₂ + 2C0₂ + 4H₂0

A SHOT IN THE BOILER

The idea of injecting a solution of urea – in effect, concentrated urine
– into coal-fired boilers became a sort of joke in the industry. But one
company took it seriously. In 1986 a small firm called Fuel Tech, funded
largely by British investors, noticed the EPRI idea, bought the right to
manage the patents and began a series of experiments to improve the efficiency
of the chemical reaction. There were two problems. First, if the urea solution
touches the steam-carrying heating tubes in the boiler, they burst, and
the whole plant has to be shut down. Secondly, if the chemical meets the
flame at the wrong temperature, the results are counterproductive. Above
1100 °C, more NO_x is formed. Below 900 °C, ammonia – another pollutant
– is created.

But by 1989 Fuel Tech, with offices in London and Connecticut, had perfected
a way of spraying liquid into the furnace so that a fine chemical mist met
the rising flame at the right temperature and for just the right length
of time before evaporating. In small-scale trials, NO_x emissions were cut
by up to 80 per cent. The company then proved its case by installing the
system, dubbed Noxout, in 25 industrial boilers throughout Europe and the
US. But the research and development had cost $60 million, and Fuel Tech
needed a partner with access to the market. So it formed a joint venture
with a large American chemicals company called Nalco, based in Naperville,
Illinois.

Nalco-Fuel Tech (NFT) still had to persuade the power industry to buy
its technology. Paradoxically, cheaper pollution control can be bad news
for generating companies. Emissions controls are always politically imposed;
if meeting them is expensive, the generating companies can argue that they
will have to increase electricity costs, so hurting economic growth, jobs,
and political popularity. But cheap systems that meet the standards mean
inconvenience, rather than expense, to the generators and so are harder
to argue against.

Moreover, power companies are understandably wary of radical inventions,
especially those which entail shutting down their power stations at huge
cost, and particularly those which add equipment that could fracture those
precious heating tubes.

This conservatism discourages innovation through a catch-22. New ideas
for reducing pollutants simply do not get tested on full-scale plants; but
the industry distrusts anybody whose technology has not had full-scale tests.

NFT eventually got around this problem by developing a computer program
to predict the temperature at any point in a furnace. The program models
the flow of air and flame from the burning coal up through the boiler over
the so-called bull nose inside the furnace and past the heating tubes. Given
the specifications and blueprint of any boiler, NFT’s complex model can
identify exactly where the temperature drops to the critical level at which
the urea reaction will take place at any load of power production. Per Christiansen,
NFT’s president, boasts that the company will guarantee exactly how much
NO_x reduction, by-product formation and chemical use can be achieved in
a given boiler on the basis of the computer predictions alone.

Eventually in 1992 one power generator, WEPCO in Wisconsin, agreed to
test Noxout in its Valley power plant in Milwaukee, with four 70-megawatt
coal-fired boilers. The results of the two-week test enabled NFT to show
the process’s realistic costs: it can remove 70 per cent of NO_x from the
flame for a cost of about £250 per tonne of NO_x removed. That makes
it four times cheaper than SCR and more effective (for a comparable price)
than a low-NO_x burner, which would anyway only be economic in a new plant.

FLEXIBLE FRIEND

Furnace injection also has other advantages. The equipment required
is small and can easily be fitted into a crowded old power plant: it consists
of some storage tanks (about the size of a petrol tanker lorry), pumps,
control valves and computers to adjust the volume of liquid spraying through
the nozzle. It is also flexible – it can be adjusted as the plant’s power
output varies. Compared to FGD, SCR or a low-NO_x burner, most of Noxout’s
cost is for the chemicals, so it is a running rather than a capital cost
– like the difference between changing to unleaded petrol and replacing
the car engine.

NFT is the only company working that has reached the stage of full-scale
tests. It now has over 50 systems installed and 60 commercial orders from
Germany, Sweden, Switzerland, the former Czechoslovakia, Taiwan and the
US. Noxout’s only significant drawback is that it creates a little nitrous
oxide (N₂O), a greenhouse gas. But NFT says that a new version
of Noxout solves this problem by converting the urea into a chemical that
overcomes this, but it is keeping details confidential.

What about sulphur dioxide? EPRI’s scientists have been experimenting
with injecting dry lime for some time, but the results are disappointing.
Acurex, an American company based in Mountain View, California, invented
a device for injecting an emulsion of wet lime into the furnace of a coal-fired
boiler, instead of into the exhaust stream. Then a Canadian power generator,
Ontario Hydro, patented the use of a combination of calcium carbonate and
urea. Meanwhile NFT has adapted Noxout to use a slurry of urea and calcium
hydroxide, and claims that the hydroxide works better than carbonate because
it reacts with the urea to improve the efficiency of both.

NFT’s process has recently been tested for the first time on a solid-waste
incinerator in Pennsylvania. It looks impressive in trials. The company
claims it can remove up to 80 per cent of the sulphur dioxide for a lower
capital cost than FGD, which removes 90 per cent.

Germany and Japan, the first countries to install pollution control
equipment on power stations in the early 1980s insisted on the proven technologies
of FGD for sulphur dioxide removal and SCR to catch NO_x. Nobody would order
SCR now. And if furnace injection lives up to its promise, FGD may soon
be a thing of the past too. Britain is therefore well placed to get the
work done cheaper – a strange reward for its procrastination over pollution.

Matt Ridley is a freelance journalist specialising in environmental
and biological issues.