War on Coal?
Coal is used to produce more electricity worldwide than any other energy source, and is hence sometimes referred to as King Coal. However, coal is also one of the largest anthropogenic sources of carbon dioxide globally and coal-fired power plants are a major source of mercury emissions, non-mercury metallic toxics, acid gases, and organic air toxics including dioxin. A 2010 study by the Clean Air Task Force in the US  estimated that air pollution from coal-fired power plants accounts for more than 13,000 premature deaths, 20,000 heart attacks, and 1.6 million lost workdays in the U.S. each year. The total monetary cost of these health impacts is over $100 billion annually.
China, USA and India are ranked as the top three coal-consuming nations, with China presently consuming close to 50% of global demand. Growing recognition that coal is one of the prime contributors to local air pollution and climate change has led many governments to look for alternatives. Some NGOs and environmental groups even labelled these efforts a “war on coal”. In an effort to reduce the dependence on coal, China has embarked on a so-called “anything but coal” diversification strategy for the domestic power sector, which entails aggressive and ambitious build-out of hydropower and modern renewables, but also LPG and nuclear power. However, despite this strategy, according to the IEA  , China has still added a staggering 600GW of coal fired power plant capacity since 2005 and the number of proposed new plants ranks in the hundreds. The main reason for this has been the fast growing demand for electricity and the relatively low cost of coal, most notably in absence of a price on carbon. Several emerging economies are expanding their fleet of coal-fired power plants for similar reasons.
In the US, however, the rapid rise of shale gas has led to a shift away from coal, which in return led to a spike in coal consumption in the European Union a few years ago, caused by low-cost US coal and the availability of cheap CO2 certificates. However, the rapid rise of renewable energy and the absence of demand growth have recently reduced the EU consumption of coal again. In North America and Europe, two-thirds of power plant projects planned since 2010 were either postponed or completely withdrawn .
According to the IEA, there are over 2,300 coal-fired power stations worldwide (7,000 individual units). Approximately 620 of these power stations are in China. President Obama’s recently announced new regulations on power-plant carbon emissions, the Clean Power Plan, calls for a 32% emissions cut by 2030, as compared with 2005 levels. According to an assessment by the Institute for Energy Research , this will take more than 70GW of electricity generation, mostly coal, offline.
The term clean coal is used primarily in reference to carbon capture and storage, which pumps and stores CO2 emissions underground, and plants using integrated gasification combined cycle (IGCC). Both technologies add substantially to the cost of coal power and CCS is not technically feasible at all locations. IGCC plants can cost up to 6,000$/kW and rank among the most expensive types of power plants, whilst still emitting more CO2 per kWh than gas fired power plants.
Critics of so-called clean coal point to the environmental impacts of coal extraction, high costs to sequester carbon, and uncertainty of how to manage end result pollutants and radionuclides.
Coal Investments under Pressure
As one of the main contributors to climate change, coal power is a main topic in the upcoming climate summit, UNFCCC’s COP 21 in Paris in December 2015. Obama’s Clean Power Plan, China’s “anything but coal” strategy and the European Union’s stricter emission legislation are efforts towards lowering the emissions of CO2, the main goal of the summit. Whether the international community will agree on binding emission reduction targets by e.g. including carbon-pricing mechanisms remains to be seen. Previous summits have failed to do so. However, all these policy initiatives and the global debate put increasing pressure on existing and planned coal power plants, adding substantial risk premiums to their investment profile. An increasing number of financial institutions among which are university and church investment funds, but also the Bank of America have publicly stated not to invest in such projects any longer. The World Bank in its recent strategic directive  says only to invest in coal in exceptional cases, e.g. when there are no cleaner alternatives.
Co-firing of Biomass
To reduce emissions of CO2 and to achieve renewable energy targets many countries, most notably in Europe, have supported co-firing of biomass in coal-fired power plants. Generally white pellets are used, the use of which is limited to 10% in the case of co-milling and 10% to 30% if a separate mill is installed. These white pellets can be made from sustainably managed forests or using the many waste streams that are presently unused, such as bark, branches and tops, sawdust etc. However, apart from additional investment costs the lower specific calorific value of white pellets also derates the power plant, causing effective loss of capacity and basically stranding a part of the investment.
So we have a global installed base of 2,300 coal-fired power plants, a large part of which might become obsolete in the near future for the reasons explained above. At an average size of 700MW and an average cost of 3,000$/kW, this represents an overall investment of close to $5 trillion. All of these locations are permitted, hooked up to the electricity grid and have logistical facilities capable of handling large volumes of feedstock. Co-firing of white pellets is limited to 30% so cannot effectively replace coal. A solution to keep using these assets is to upgrade the biomass to a quality level comparable to coal. At present there is only one technology capable of turning biomass into a coal-like product in terms of physical properties and that is torrefaction.
Torrefaction is a kind of controlled roasting process, whereby e.g. wood chips are heated to a temperature level between 250 and 320 °C in an oxygen deprived atmosphere. Depending on the input material and process conditions chosen, about 30 % of the dry mass is converted into gases, which are burned in a separate combustion chamber to dry the incoming biomass and for heating the process. The resulting material is black, brittle, hydrophobic and has a heating value in the range of coal. After grinding, the material can be densified and pressed into black pellets to create bio-coal.
The following are the advantages of torrefaction:
• Torrefaction improves the durability of the biomass. The polar characteristics of the biomass fuel are destroyed and therefore the refined fuel is (almost) hydrophobic. Depending on the process performance and fuel quality the refined biomass may be stored outside on the existing coal yards. Additionally it is less susceptible for biodegradation.
• The disintegration of the ligno-cellulosic structures of the biomass fuel leads to better grindability of the material compared to unprocessed biomass. In most cases the existing coal mills can be used for co-milling the torrefied biomass without significant changes.
• The energy content of torrefied biomass is higher than unprocessed biomass and far exceeds the energy content of wood pellets due to the loss of hemicelluloses with low energy content. Therefore, the same amount of fuel energy is cheaper in logistics, requires less area for storage, less investment in handling equipment, less energy for milling, and less energy for transportation.
• Because of the coal-like properties of the torrefied biomass, the existing coal logistics, and downstream handling systems can be used. That leads to a high flexibility in feedstock and a fall back option in case torrefied fuels are temporarily unavailable at the market.
• The impact on flue gas cleaning and power plant by-products is expected to be similar to untreated biomass fuels.
Different reactor technologies, most of which were developed for other applications, are currently being used to perform torrefaction. These include fluidized bed reactors, screw reactors, multi hearth furnaces, rotating drum reactors, microwave reactors, belt dryers and others. Some torrefaction technologies are capable of processing feedstock with small particles such as sawdust and others are capable of processing large particles. Only a few, including rotating drum reactors, can handle a large spectrum of particle sizes.
Although the market for black pellets has not yet fully developed, a number of torrefaction companies have the ability to produce consistent quality product at scale and are developing a pipeline of projects globally. One of these companies is TorrCoal, based in the Netherlands, with a commercial scale demonstration factory in Dilsen-Stokkem, Belgium. TorrCoal is part of A.Hak Renewable Energy’s portfolio of renewable energy companies. Since 2010 TorrCoal has been producing black pellets at commercial scale for a number of different customers. TorrCoal uses the proven and robust indirectly heated rotating drum technology, enabling a wide variety of feedstock.
Scale of Opportunity
A typical black pellet production facility with two lines is capable of producing up to 100,000 tons of black pellets per year. Given the fact that a medium sized coal plant consumes up to 1.5 million tons of coal per annum, we would need 15 black pellet production facilities to feed the power plant. This creates enormous economic opportunities, which are much larger than the replaced coal mining business. According to a recent study , replacing coal with biomass in an existing pulverised coal power plant would only increase the cost of electricity by $0.01/kWh, but would increase the number of jobs by 37%. A typical 500MW plant in the US employs 2,538 people in the coal sector, which could be replaced by 3,481 jobs in the biomass value chain.
So instead of retiring older PC power plants we should consider converting them to run on bio-coal. This is cleaner, creates jobs and also keeps despatchable power in the mix, adding to the security of the overall energy system.
 Schneider, C., and Jonathan Banks. 2010. The Toll From Coal: An Updated Assessment of Death and Disease from America’s Dirtiest Energy Source. Clean Air Task Force, September 2010.