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Coal is nasty stuff. Extracting it from the ground involves tearing
up landscapes with opencast mines, or risking human health and lives in
deep mines. The traditional way to unleash coal’s energy is by setting fire
to it, a reaction that produces sulphur dioxide, nitrogen dioxide, carbon
monoxide, a brew of aromatic hydrocarbons laced with toxic metals, to say
nothing of carbon dioxide, the most notorious greenhouse gas. On top of
all that, conventional power stations waste about two-thirds of the coal’s
energy.

Why bother? Because coal is the only fossil fuel available in quantities
that for practical purposes are inexhaustible. It is the only fuel capable
of providing the electricity needed for the economic development of central
and south Asia – unless Japan and Korea succeed in persuading the region
to go nuclear. Despite its drawbacks – and barring remarkable and unexpected
breakthroughs in research on fusion – coal will be driving the world’s power
stations well into the next century. But the power stations needed to achieve
these goals, and to replace those inefficiently belching out pollutants
in the Americas, Europe and Asia, will look very different in the future.

Coal is a very versatile fuel. It can be burned as a solid, a liquid,
or a gas. The hot gases that combustion releases drive steam generators
in today’s power stations, and they will probably power gas turbines in
the next generation of station. Further into the future, the gases may produce
electricity directly when they stream through a magnetic field, while hydrogen
from coal could be generating electricity in battery-like fuel cells. Many
of these technologies are far less polluting and capture coal’s energy more
efficiently than conventional power plants. But few are commercial yet.

EARLY PROGRESS

Despite the energy glut in the developed world since the mid-1980s,
researchers around the world have made much progress on coal over the past
decade, and are now beginning to demonstrate that their efforts are commercially
viable. In the US, which has coal reserves second only to China, the government
set up the Clean Coal Program five years ago with $2.75 billion for research
on new coal technologies. These subsidies are supposed to promote a revolution
in the way coal generates electricity. And although American power companies,
like their counterparts around the world, are notoriously reluctant to adopt
what they see as risky new technology, tougher environmental laws may force
them to change their ways.

Next month, the US Department of Energy will announce the fifth set
of clean coal grants, amounting to $568 million. This latest round of federal
funding is supposed to support the most advanced technologies available.
Earlier grants helped build prototype power stations using well-established
technology that industry has so far refused to adopt, for example, plants
burning gas derived from coal, or which burn solid coal in a ‘fluidised
bed’, a cauldron of crushed coal and limestone. Other projects demonstrated
ways to cut emissions of sulphur, the main cause of acid rain.

Last month, the department received 24 proposals for clean coal grants
from industry, requesting a total of $2.3 billion in federal funds. One
of the most ambitious proposals came from a group of eight companies who
want $221 million to build a plant based on a process called magnetohydrodynamics,
or MHD. The companies, including TRW, Textron, Westinghouse, Babcock and
Wilcox, and Montana Power, would contribute another $300 million to the
project. They spent about $1.5 million just preparing their proposal.

The idea behind an MHD plant goes back to 1831 when Michael Faraday
discovered that moving an electrical conductor through a magnetic field
creates an electric current. Conventional generators use this principle,
too, spinning a coil of copper wiring in a magnetic field. In an MHD plant,
however, hot, ionised exhaust gases from burning coal or gas act as the
conductor. Superconducting magnets create a powerful magnetic field surrounding
the exhaust channel (ordinary magnets would consume too much power, thereby
reducing the efficiency), and the stream of gases generates an electrical
current as it passes electrodes in the walls of the channel.

HIGHER EFFICIENCIES

The MHD process bypasses many steps in conventional coal-fired plants.
Conventional plants take heat from burning coal to turn water into steam,
which is used to spin turbines that in turn power a generator. Each step
involves a loss of efficiency. Such plants convert only about 32 to 35 per
cent of the heat from burning coal into electricity. A plant that includes
an MHD generator can achieve an efficiency of 50 per cent, and perhaps up
to 60 per cent, according to the DOE’s calculations. To reach this level,
however, an MHD system would need to work as part of an advanced form of
combined-cycle plant. In this setup, a second cycle of power generation
comprising traditional steam and turbine systems would extract energy from
the hot exhaust gases that emerge from the MHD generator.

MHD plants offer environmental benefits, too. The more efficient a plant,
the less carbon dioxide it emits per watt of electricity generated. The
MHD process also removes sulphur from coal: by a happy coincidence, the
most convenient agent to ionise combustion gases, potassium carbonate, reacts
with sulphur from the coal to form potassium sulphate, which can easily
be collected and recycled. On the other hand, because of its high operating
temperatures, an MHD plant produces high levels of polluting nitrogen oxides,
or NOx. These can be reduced, however, by carefully managing how the coal
is burned.

If the DOE decides to back the MHD proposal, the eight-strong consortium
will build the world’s largest MHD plant by 1999 near Billings, Montana.
The plant would have a capacity of about 80 megawatts (about one-tenth the
capacity of a large thermal power station) and about a third of its electricity
would come from the MHD generator. Traditional gas and steam turbines would
provide the rest.

Because of its size, the Billings plant will be no more efficient than
a conventional power plant. Between 30 and 35 per cent of the heat will
be turned into electricity, says Gerry Funk, manager of the technical development
and engineering division at MSE, another of the industrial partners in the
project. But he says it would show that the technology is reliable, preparing
the way for larger, more efficient plants.

The Soviet Union, China, India, and Japan have also dabbled with MHD
technology. During the late 1980s, the Soviet Union planned to build a large
MHD plant powered by natural gas, rated at 580 megawatts. But the magnets
turned out to be too difficult and costly to produce and the MHD part of
the plant was never built. ‘Their programme ground to a halt about three
or four years ago,’ says Funk. The only fully integrated MHD plant is in
China, just outside Shanghai, rated at just 5 megawatts of power.

America’s largest MHD plant so far, in Butte, Montana, began tests in
February last year. The generator has a capacity of 1.5 megawatts of electricity;
its purpose is to test the system’s reliability through years of bombardment
with a blast of corrosive gases heated to 2700 °C.

MHD is an attractive idea, but government-funded projects to develop
it have more to do with political expediency than technological objectivity.
The trouble with MHD is that, while the idea works well in theory and in
small pilot plants, developing such power plants commercially will take
a lot of money – and may not be worthwhile. Much of the research so far,
in the US and the former Soviet Union, was driven by military interest in
the behaviour of high-temperature plasmas in rockets rather than a serious
effort to develop power sources.

Many countries that showed an early interest in the technology, such
as Britain and Australia, have now dropped it. An MHD power station would
pose serious technical difficulties, says Ian Smith, research manager of
the coal utilisation programme at CSIRO, Australia’s national research organisation.
The difficulties include burning coal at well over 2000 °C, and passing
the products through a duct at supersonic speeds. Not least of the problems
are the engineering difficulty of passing very hot gases just a few centimetres
from superconducting magnets operating at only a few degrees above absolute
zero. This adds up to a process that looks exciting on paper, but tricky
to turn into reality, says Smith. ‘It’s one of those technologies that people
sniff at because of its potential attractiveness and then back away from
because of the practical difficulties.’

Much better, he says, is to concentrate on developing plants in which
gasified coal drives turbines connected directly to generators, with a
secondary steam system running off the waste heat. Such combined cycle gas
turbines are as efficient as MHD plants are ever likely to be – and are
based on better established technologies. Several tried and tested processes
are available for turning coal into gas, by making it react with oxygen,
steam, carbon dioxide or hydrogen. The product consists of hydrogen, carbon
monoxide, carbon dioxide, hydrogen sulphide, methane and other hydrocarbons,
in proportions that vary according to the technology used. The problem comes
in removing the substances in coal that create ash when the fuel is burnt;
flying ash damages turbine blades and is one of the reasons behind the British
power industry’s ‘dash for gas’. So far, efforts to clean the gases from
coal combustion before they hit turbines have not been successful.

At the DOE in Washington, the MHD proposal must compete for funding
with many other ideas for generating electricity from coal. Most involve
more familiar technologies. Several groups propose to build small power
plants that convert coal into gas, which can be burned to generate power
more cleanly. Similar DOE-funded plants are already under construction.
Other companies want DOE funding for advanced methods of removing sulphur
dioxide and nitrogen oxides from flue gases at existing power plants, or
to remove sulphur from coal before it is burnt.

Ways of cleaning up coal are attracting particular interest in Australia,
which has large reserves of black coal. These bituminous coals produce more
heat per tonne than brown coals but contain more potential pollutants (see
‘Where the power lies’, this issue). A team at CSIRO has discovered that
agitating bituminous coals in a hot aqueous solution of caustic soda softens
potential pollutants in the coal. A dilute acid wash removes them. The process
leaches out many of the substances that form ash. The Australian Coal Industry
Research Laboratories are testing the process at a pilot plant at Maitland,
New South Wales. ACIRL will decide within the next year whether to go ahead
with a demonstration plant to assess the technique’s economic viability.

Cleaned-up coal has several attractions. Mixed with water as a slurry
it could substitute for heavy fuel oil, an idea that Australia, the world’s
largest coal exporter, is investigating with a view to exporting fuel in
this form to Japan. Coal-water mixtures could also fuel gas turbines in
advanced power generation, run diesel engines, or provide clean carbon for
aluminium and steel smelters. Meanwhile, the State Electricity Commission
of Victoria hopes to obtain enough clean coal from the Maitland pilot plant
to test the feasibility of using coal gas to drive a turbine directly.
The commission will use a turbine simulator to gather information about
how the technique performs. The main purpose of the simulator is not to
test black coal, however, but to help develop a way of using brown coal
in coal-fired turbines.

This technology, known as hydrothermal drying (HTD), aims to increase
the energy efficiency of brown coals by reducing their moisture by as
much as 50 per cent. This is done by heating the coal under pressure in
an HTD plant to reduce its capacity to hold moisture – by weight, brown
coal can contain more than two-thirds water. The turbine simulator, which
operates at pressures of 10 atmospheres and temperatures of 1350 °C,
can then be used to determine the combustion behaviour of the resulting
coal-water slurries, and to evaluate corrosion, erosion and deposition of
contaminants on the turbine blades.

Working with a West German company, Lurgi, the commission is also investigating
another technique for reducing the moisture content of brown coals, known
as steam-fluidised bed drying. Lurgi has set up a steam-drying plant in
Victoria’s Latrobe Valley where finely crushed coal is dried in a fluidised
bed using superheated steam at about 110 °C as the fluidising medium.
The technique was invented 10 years ago by Owen Potter, a chemical engineer
at Monash University in Melbourne. When he failed to interest Australian
companies in the technology, he sold the licence to develop it to Lurgi.
While Lurgi wants to pulverise the dry coal and use it in conventional generating
technology, the commission is keen to see how suitable the dry coal is for
turning into a gas for driving turbines.

There is another developing technology that offers a way to convert
the energy in coal directly to electricity without wasteful mechanical processes
and without the formidable engineering of MHD. This is the fuel cell, essentially
a battery running on a continuous flow of chemicals, usually gases. Fuel
cells consume hydrogen as fuel, oxidising it to create a flow of electrons
from cathode to anode, producing electricity and heat while giving off water
and carbon dioxide. The hydrogen fuel usually comes from natural gas but
it could come from gasified coal.

Fuel cells emerged from the need for compact, silent and efficient sources
of power for special jobs, for example, inside spacecraft or military gadgets.
The different types are named according to their electrolyte, the material
at the cell’s core. NASA’s spacecraft, most famously the Apollo missions,
have carried phosphoric acid cells since the 1960s. More powerful ‘molten
carbonate’ cells, with an electrolyte of lithium and potassium carbonates,
were developed during the 1980s. These operate at higher temperatures of
about 650 °C. The third generation of cells, solid-oxide fuel cells
with zirconia as an electrolyte, operate at even higher temperatures, around
1000 °C.

This technology, combined with coal gasification, seems to offer an
efficient way of producing electricity from coal with virtually none of
the environmental damage that thermal power stations cause. Fuel cells do
produce carbon dioxide, but at less than half the rate of thermal power
stations.

CELL POWER

Researchers from the University of Wollongong in New South Wales described
the concept of such a plant to the Fifth Australian Coal Science Conference,
organised by the Australian Institute of Energy in Melbourne last month.
The raw coal enters a conventional gasifying plant, which produces a fuel
gas at between 650 °C and 1000 °C. This gas passes through a cleanup
process, removing extraneous particles, sulphur, nitrous oxide and other
substances. The cleaned-up gas then passes to the anodes of a stack of fuel
cells, which also consume air, to produce DC electricity. Hot exhaust gas,
mainly carbon dioxide and water, from the fuel cells’ cathodes creates steam
to drive a turbine, producing more electricity. The overall efficiency could
be more than 45 per cent.

There are snags. Although engineers have accumulated a lot of experience
with small fuel cells, no one has yet built a commercial-sized plant. Tokyo
Electric Power Company operates the world’s largest fuel-cell power station
on the shores of Tokyo Bay, but it is a first-generation phosphoric acid
plant, producing just 11 megawatts. The long-term reliability of fuel cells
is also still in question.

According to Ron Wolk, director of the advanced fossil power systems
department at the Electric Power Research Institute (EPRI) in Palo Alto,
California, such technical problems will be solved with ‘grunt-work engineering’.
He says a more important hurdle on the way to commercial success is making
them cheaper. At the moment, two American companies build molten carbonate
fuel cells in small prototype manufacturing facilities, at a maximum rate
of about 2 megawatts of capacity per year. Without the benefit of mass production,
their fuel cells are far too expensive for the commercial market. ‘It’s
a classic case of how you establish a market,’ he says.

In an attempt to get the fuel cell industry on its feet, the DOE is
contributing $16.5 million towards a 2-megawatt fuel cell plant in Santa
Clara, California, which is due to open by early 1995. The rest of the $47
million cost will come from the local electricity company, EPRI, and Energy
Research Corporation (ERC) in Danbury, Connecticut, which is building the
fuel cells. If the plant works well, ERC says it will offer similar plants
to other electricity companies. The cost to the first customers will still
be high, but as an incentive, ERC will offer them a share of the revenue
from all future sales. If enough customers sign up, ERC will build a large-scale
manufacturing base, bringing the price down from around $5000 per kilowatt
of capacity to about $1200, which is about the same as the cost of building
a coal-fired power station.

Meanwhile in Australia, a consortium of public and private enterprises,
brought together by the CSIRO and including BHP, the country’s largest company,
and the state power authorities of New South Wales and Victoria, has enough
faith in fuel cells to set up Ceramic Fuel Cells to develop third-generation
cells commercially. These cells, which could have efficiencies of up to
60 per cent, have electrolytes of solid ceramic made from zirconia and yttrium
oxide. One reason for Australia’s interest is that it supplies 70 per cent
of the world’s zircon.

Commercial success for fuel cells will not necessarily help the coal
industry immediately. All these fuel cell projects use natural gas, not
gas from coal. But if natural gas prices rise, as seems likely when exploitable
resources run short over the next few decades, fuel cells might switch over
to coal gas (see ‘A very dirty business’, this issue). Running fuel cells
on coal gas would mean more efficient use of coal, while eliminating most
of the emissions of sulphur dioxide and nitrogen oxides that now pour from
conventional power stations.

This month, in an effort to kick-start development of the technology,
the ERC and EPRI plan to hook up a 20-kilowatt stack of fuel cells to a
coal gasification plant in Louisiana. In the past, simulated coal gas has
tended to be used to test the performance of fuel cells. M-C Power, the
main competitor to ERC in the fuel cell business, has applied for government
funding to conduct a similar experiment in Indiana.

The increased efficiencies of combined-cycle gas turbines, fuel cells
and MHD will all reduce the amount of carbon dioxide that power stations
produce per unit of electricity generated. But no known technology will
eliminate it. The Japanese government has chosen the area as a target for
its Research Institute for Innovative Technology for the Earth, which is
due to begin work in earnest this year. One team of genetic engineers will
be trying to improve the photosynthetic properties of a new breed of microorganisms,
which could then be used to fix carbon dioxide in industrial exhaust gases.
Another team of researchers will look for new catalysts to help turn carbon
dioxide into useful chemicals. Another idea under investigation is to pump
carbon dioxide to the seabed where it would lie in store – the gas becomes
denser than sea water at 3000 metres below sea level. The cost, however,
would be colossal.

This type of research is worlds away from the realities of today’s electricity
industry. The most modern technology in place at a current coal plant might
be an assembly of thousands of huge bags to capture fine particles of fly
ash from exhaust emissions. Some plants still use electrostatic precipitators,
a technology developed early this century, to do the same thing.

In the US, most coal-fired plants built before the Clean Air Act of
1978 do not even have ‘scrubbers’ to remove sulphur dioxide. Technologies
that would minimise pollution by changing the combustion process itself,
such as fluidised-bed combustion, are still almost unknown among commercial
energy generators. Even coal gasification, which most scientists describe
as a proven technology, has yet to catch on commercially. Robert Lumpkin,
director of coal utilisation projects at Amoco Corporation, a member of
the National Coal Council, says most electricity companies ‘are scared of
gasification plants’ because the chemical processes are unfamiliar.

Wolk of EPRI says that American generating companies are a conservative
breed, unlikely to adopt unproven technologies such as MHD or fuel cells.
There is little reward for an electricity company that takes a risk because
regulations require it to pass any savings on to consumers, he says. Joseph
Goffman, a lawyer specialising in pollution control at the Environmental
Defense Fund, an environmental pressure group based in Washington DC, says
many environmentalists have come to share Wolk’s views. He says that a utility
and its shareholders should be allowed to profit financially for taking
risks that cut the environmental costs of generating energy.

The law that will force the US’s power companies to try some of these
technologies was passed by Congress in 1990, as an amendment to the 1978
Clean Air Act. It will require the country’s largest coal-burning companies
to halve their emissions of sulphur by 1995, and by half again by 2000.
Emissions of sulphur will then be capped at the level set for 2000. If an
electricity company wants to build a new plant to meet rising demand, it
will have to cut back sulphur emissions in its existing plants by an equal
amount, or buy the right to emit a certain amount of sulphur from other
power companies. These ’emissions credits’ are likely to become very expensive
as such companies fight for the right to pollute.

Although, even with these incentives, the era of truly clean coal, whether
driving MHD, fuel cells or super-efficient gas turbines, is at least one
generation of technology in the future, those countries developing the new
technologies now will be the ones that will benefit later.

Additional reporting by Ian Anderson in Melbourne and Michael Cross,
a freelance journalist based in London.