Sept/Oct 2007

The new face of coal

By G. White

Boundary Dam mine and dozer

Worldwide coal consumption is expected to increase by 74 per cent from 2004 to 2030.1 It is very difficult to envision how rapidly developing economies such as India and China will be able to reduce their dependence on coal and coal-based technologies. All indications are that the 74 per cent is a good number.

By its very nature, coal is abundant, available, and affordable. It is widely distributed around the globe and it is particularly abundant in western Canada. As a solid material found relatively close to the surface, the locations of coal deposits are well known. Coal has been in place for millions of years and it is increasingly being exploited by countries throughout the world to drive economic growth.

And yet, this consumption of coal is at odds with the worldwide demand to reduce greenhouse gas emissions. Each tonne of coal consumed for combustion has the potential to produce between 1.8 and 3.2 tonnes of CO2, depending on the quality of the coal. At today’s global consumption of approximately 5 billion tonnes per year,2 this amounts to at least 10 billion tonnes of CO2 emissions per year from coal alone. Almost none of this CO2 is captured and it ultimately ends up in the earth’s atmosphere where many of the world’s experts believe that it is contributing to global warming. And much of the world’s coal is used directly for electricity production. Electricity supply and demand are growing on all fronts and along with them the CO2 emissions from fossil fuels.

So here we have the issue: how can we reduce the CO2 footprint of coal while at the same time expanding consumption at a rate of 74 per cent over 25 years? Some solutions exist and they may be more plausible than we might think.

Some History

In Canada, many remember the pollution issues in the Great Lakes that resulted from effluent releases by neighbouring large industries and municipalities. We can also remember the excessive sulphur dioxide and nitrogen oxide emissions into the atmosphere leading to acid rain and smog. Later, there was the depletion of the ozone layer, a global issue. To a great extent, these issues have been repaired or, at least, been made acceptable, by the implementation of good policy, regulations, and technology. If the pollution and SO2 and NOx issues were prevalent in the 1970s, and they are now under control, we know that it takes 30 years or so to implement effective change. Now, 17 years after the initial attempts of the United Nations to deal with the economic benefits of growth in carbon utilization versus the consequential damages associated with CO2 emissions, we are becoming aware of how challenging it is to find a solution for coal-produced CO2.

Furthermore, our past successes at cleaning the environment do not offer much assistance with regards to the CO2 predicament for a number of reasons:

  • Effluent, SOx and NOx (ES&N) issues were local in nature, as was the solution. CO2 is a global issue.
  • ES&N volumes were measured in thousands of tonnes of emissions. CO2 output is measured in billions of tonnes.
  • There is an immediate local impact of effluent (visible pollution), SOx (acid rain), and NOx (smog) that provides instant feedback on cleanup progress. No so with CO2, whose impact is still disputed by some and has a secondary nature (reduction in ice caps as a result of warming for example).
  • Finally, the opportunities to resolve the issues associated with ES&N were readily available as add-ons to existing processes. The fact is, we have no technology that will rid us of CO2 emissions once the CO2 is formed. If we are going to utilize carbon-based fuels for energy production, the best we can do is reduce our consumption and capture the CO2 that is produced.

All of this supports a conclusion that it will take more than the 30 years to effect a real change in this complex issue. This conclusion is entirely consistent with the progress made in the first 17 years.

Long-term CO2 reduction scenarios for coal-fired power capacity

Leaving the policy and regulatory decisions to others, and solely dealing with thermal electricity production from coal, how are the technology leaders responding to the concurrent demand for more coal consumption and the reduction of greenhouse gas emissions? This question—from a coal perspective - has to be answered in two parts. Firstly, how are we going to reduce the emissions from the existing fleet of coal-fired power plants in Canada and, secondly, what are we going to do to reduce or eliminate the carbon footprint of new coal plants planned to satisfy growth.

The existing fleet

Conventional coal combustion, the type used in almost every coal-fired power plant in the world, is becoming more efficient. This allows less fuel to be burned to make the same amount of energy, resulting in fewer CO2 emissions. The impact of this is significant. Worldwide, we find that the newest plants can be as much as 90 per cent more efficient than the oldest.

Older plants are usually smaller than the newest plants, largely because advanced materials of construction were not available years ago. As a consequence, operating temperatures and pressures were lower and, in the world of power generation, this means that the older plants are less efficient. Smaller plants were prevalent years ago because demand growth for power was much less than now and the market could not support large plants.

Smaller plants are less efficient because they lack economies of scale.

Efficiency has a notable impact on emissions. A modern 600 MW ultra-supercritical power plant will produce about 500 tonnes of CO2 per hour at full load, while somewhere in the world, four, smaller, older 150 MW (say circa 1970) plants, producing the same amount of power, create as much as 850 tonnes of CO2 per hour. When each of these older plants is retired there is a significant opportunity to reduce CO2 emissions, even if the retired unit is replaced by another coal plant.

Some would argue that no new coal plants should be built. However, this position belies the economic benefits of coal and ignores the fact that the massive replacement of the world’s oldest plants would result in significant GHG reductions without the risk of implementing different technology.

In Canada, there are many coal-fired power plants with heat rate efficiencies in the order of 10,200 KJ/kWh, each producing 0.90 tonnes of CO2 per kWh. A new coal plant, recently commissioned in Japan, has a comparable efficiency of 8,187 KJ/kWh and makes 0.72 tonnes of CO2 per KWh. While the opportunities for GHG reduction are greater in developing nations (where plants are generally older, smaller, and less efficient), even in Canada a potential 20 per cent reduction in CO2 emissions will result if Canada’s oldest plants are replaced with best available new coal combustion technology.

The good news is that almost all of Canada’s coal-fired plants will require replacement on an economic basis within the next 30 years. This gives us at least a modicum of ability to meet some GHG reductions without additionally taxing our natural gas resources or resetting our electricity supply mix portfolio. This, in turn, translates into significant savings in transmission and distribution infrastructure. The age of Canada’s coal-fired fleet is skewed towards the 1970s (older, less efficient plants), so a replacement strategy applied to these plants would have better than average impact when efficiencies are considered.

This is a powerful scenario for all concerned. Replace existing coal-fired power plants with new efficient ones at the end of their economic life and save up to 20 per cent in GHG emissions over the next 30 years.

New supply

New power supply is another matter. Developed countries, especially Canada, have suffered from the CO2 issue on two fronts. We have always been big consumers of fossil fuels for power generation, but in addition to our high historical consumption, our real rate of growth in consumption is high. Canada’s size and climate assure this. In essence, we have always produced a lot of CO2 and our growth rate is adding to the problem year over year. Should we therefore reduce our dependence on coal for new supply?

If we do so, we will inevitably change our electricity supply mix, something akin to changing the investment mix in a stock portfolio. It can be done, but in doing so, the risk profile of the portfolio changes. Changing the supply mix by favouring one type of electricity generation process over another can have costly and long-term implications for the operability of an established power grid. Policy-makers in Ontario found this out when they discovered that closing centrally located coal plants would negatively impact power production from other sources in the existing interconnected power grid. Maintaining the supply mix means that the proportions of coal, natural gas, nuclear, hydro, etc. would stay pretty much the same in the long term. How can this be achieved while reducing the CO2 footprint of coal?

The proponents of cleaner natural gas are quick to point out that, on an equivalent power production basis, natural gas produces less than half of the CO2 that coal produces. The reason for this is that natural gas contains more energy than coal (each of the natural gas carbon atoms is surrounded by four hydrogen atoms and all are combustible) and the processes for making power from natural gas are more efficient than the coal-fired process. If coal’s share of the new power generation supply were to be turned over to natural gas, it would represent a significant and problem-solving solution to the GHG reduction commitment in Canada. The only issue with this scenario is that natural gas may not be with us for the duration, and even if it is, it has a tendency to be very expensive, just at the times that our economy can least afford it. Instead of thinking only about converting coal-fired electricity production to gas we must start to think about converting coal to gas. Coal can be converted to a form of gas called synthesis gas, and this synthesis gas, can be transported and, with a few plant modifications, easily be used in natural gas, fired power plants to make electricity.

The gasification process itself has been known for years, but until the emergence of the CO2 issue, there has never been an economic reason to develop it fully. This has changed in today’s carbon constrained world. Major players in the global energy market, including General Electric, Siemens of Germany, and Sasol in South Africa, have fully developed gasification processes now available, and the interest in these processes worldwide is growing.

The coal gasification process has a secondary major advantage. Along with the production of the synthesis gas, which is much cleaner than coal, the process also produces a pure stream of CO2, which can be captured as a by-product. When the by-product CO2 is sequestered in the earth and prevented from seeping back to the atmosphere, we then have a solution that exploits the availability, abundance, and affordability of coal without suffering the consequential damages of the carbon emissions. CO2 sequestration is a proven technology and is currently being done with large quantities of CO2 from an operating gasification plant in North Dakota. The CO2 is being piped from North Dakota to the Weyburn oil field in Saskatchewan, where it is not only being stored, but also used to enhance the recovery of oil from the depleted field.

The synthesis gas from coal behaves similarly to natural gas, and therefore the power production process is as efficient as the natural gas process. This further reduces the carbon footprint of the coal.

This new supply scenario would call for the construction of integrated gasification combined cycle (IGCC) power plants, fuelled by gasified coal, to serve coal’s share of future power generation growth in Canada. CO2 from the process would be stored in the ground instead of being released to the atmosphere. Acid gases and particulate matter from the gasification process are negligible, and even existing natural gas power plants can be converted to utilize synthesis gas from coal.

To meet immediate pent-up demand for new generation (and there is much of this), new natural gas plants could be built immediately adjacent to coal fields. The gas plants could be fired on natural gas in the early years when the gasification processes are nascent, but they would be converted to synthesis gas operation at the earliest opportunity.

The benefits

Over the next 30 years, Canada can become a leader in CO2 mitigation strategies. The coal strategy, if implemented as described above, would result in significant CO2 reductions where no current plan exists. This coal strategy does not have to stand on its own. When it is combined with other important efforts such as conservation, the use of renewables, development of new hydro, refurbishment and new-build of nuclear, along with judicious use of precious natural gas, Canada has a real opportunity to meet the challenge that is Kyoto while maintaining its economic prosperity.

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