Biocoal is carbon neutral and cost efficient, it offers a similar power output to coal, and can be burned in existing boilers with little or no modification. Robert Stokes explores its potential as a cogneration fuel.

Under construction: An artist’s impression of Thermogen’s future biocoal plant Credit: Thermogen Industries

A slow revolution in the use of biomass for firing or co-firing power generation is picking up pace this year as a number of competing technologies for the production of ‘biocoal’ move more convincingly towards full commercialisation.

Biocoal produced through torrefaction – in which dry biomass such as wood, paper, food waste and even sewage waste is slow-heated anoxically (to avoid combustion) at 200oC to 300oC to reduce moisture and drive off low-energy volatile chemicals – offers slightly degraded fuel with lower emissions and carbon footprints (it is carbon neutral) than traditional biomass, and certainly lower than coal.

According to the European Commission’s Strategic Energy Technologies Information Systems (SETIS), natural gas is the dominant fuel (about 40%) for European cogeneration, while solid fossil fuels account for 35%, and renewable fuels – chiefly biomass but also waste – are increasing in importance, and now account for 12% of the market.

Biomass and coal are mainly, although not necessarily, restricted to steam turbine cogeneration units, according to SETIS. Whether these are non-condensing or extraction steam turbines, they are based around boilers that can be fired by coal, wood, solid waste, gas or nuclear energy. Some use co-firing (such as coal and biomass), while others run only on biomass.

So how does biocoal play into the cogeneration and on-site power production story? Figuring it out requires a little patience, as the torrefaction tale is currently being told from the perspective of what it could do for large coal-fired power plants.

Investors in torrefaction are dazzled by the prospect of shiny ‘black pellets’ of biocoal that will sell globally in high volume as a commodity that attracts speculative investment from the markets, hedge funds and others. Most business plans for commercial-scale torrefaction plants hinge on selling black pellets to large power stations with a view to extending their operational life – by using biocoal for co-fuelling to reduce the carbon footprint and emissions to below the statutory thresholds, and prevent closure of the plants.

Using biocoal in co-firing reduces CO2, NOx and SOx emmissions, as well as carbon payments due under emissions trading schemes or similar low-carbon policies.

Biocoal can comprise up to 40% of the energy source for co-firing stations, with little or no modification of the burners needed. This is double the 20% ceiling that limits the use of ‘white pellets’, a wood biomass that, unlike biocoal, is not completely dried; indeed, 5% to 10% is the normal range for white pellets where the power plant has not been fitted to store, handle and mill them.

Some large power plants are already using biomass. The German utility RWE’s Tilbury B station in the UK runs entirely on white pellets from renewable sources of wood. The Swedish utility Vattenfall’s Danish plants run partly on biomass. Biocoal is likely to find a similar role.

Easy handling/storage

While prolonging the existence of large, coal-fired power stations may jar with apostles of cogeneration and on-site power production, there is no reason why biocoal cannot offer similar benefits to these forms of generation, its supporters say.

‘Biocoal is a new commodity that is a lot easier to handle and store, has higher energy density than traditional biomass, is low CO2 and low sulphur,’ says Michael Wild, principal partner at the Vienna-based project managers and consultants Wild & Partner.

IBTC chairman Michael Wild predicts big things for torrefies biomass Credit: Wild & Partner

The firm lists several good reasons for torrefying biomass: it broadens the feedstock base available: it significantly reduces transport and handling costs, and it shows practically zero biodegradation when stored – this is because it is hydrophobic (water repellent), so does not need the 24/7 temperature control and watertight storage that white pellets require. Torrefying also reduces the investment that co-firing with biomass needs, as it can often simply be mixed with coal and left with it in the open air.

In addition, it reduces the derating of generators that goes with non-standard operating conditions; it can be adapted for clients’ requirements; it burns better and more cleanly than traditional biomass; it has a large variety of applications, and it can help develop the biomass market towards commoditisation.

‘While biomass tends to be wet and in the wrong place, biocoal can go anywhere,” adds Wild. “It maximises the ability to concentrate valuable biomass resources into higher-energy black pellets, then move them wherever they are needed for cogeneration and on-site power production, large-scale power generation, as a feedstock for chemicals or gasification – or even in domestic stoves that currently burn wood pellets.’

The higher-energy density of biocoal compared with traditional biomass means it can generate the same power output from less throughput, so plant size can be more compact.

‘You can also achieve higher temperatures,’ Wild confirmed to Cogeneration & On-Site Power Production. ‘So you can get into high-efficiency steam cycles. And if you were thinking about putting biocoal into a gasification unit, the gas fire could be physically smaller and the energy efficiency would be better than with traditional biomass, where a lot of the energy would be going into drying woodchip. With biocoal, you get more hydrogen, which could be used for transport, and you could create the syngas you get back into liquid fuels.’

Biocoal’s history

Research and development of biocoal stretches back beyond a decade. ‘But it is no longer a myth,’ says Wild, whose own company is part of the Austrian ACB consortium, that also includes technology company Andritz AG and the Austria-based biomass-combustion technology supplier Polytechnik Luft- und Feuerungstechnik GmbH.

And experience is growing in making and using this fuel. The best known biocoal production installations in continuous operation include: New Biomass Energy, (Mississippi, USA), which in January made its third bulk shipment (3,600 tonnes) of black pellets in a year, for co-firing tests by a major, but unidentified, European utility; and Andritz ACB (Austria) whose pilot pellet production plant in Frohnleiten started up last autumn.

Other torrefaction plants of note include Andritz/ECN (Denmark); Stramproy Green (Steenwijk, the Netherlands); Topell Energy (The Hague, the Netherlands), which has a commercial-scale torrefaction plant at Duiven and will sell and license its torrefaction to other plants worldwide; and Torr Coal (Sittard, the Netherlands), which has a production plant in Dilsen-Stokkem, Belgium.

Microwave technology

All biocoals are not equal though. Diverse technologies in demonstration projects to date have centred mainly on various forms of turbo-drying of materials, including wood chips and forestry waste, and municipal waste.

However, an innovative way to produce high-quality torrefied biomass, which uses microwave heating, is now progressing towards commercialisation after encouraging trials with a prototype in the UK.

The Targeted Intelligent Energy System (TIES) system developed by Rotawave – a subsidiary of the Aberdeen-based Energy Environmental Group, which owns the intellectual property for TIES – allows extraction of water, petroleum products and organic oils at very low cost from resources including biomass, oil drill cuttings and refinery, and food waste

TIES involves the combined use of microwave and a unique ceramic phase-separation drum in a process that maximises heat and mass transfer. According to Rotawave, this reduces plant size, material hold-ups and operating costs. The solid end-products vary from inert minerals to high-calorific-value chars that can be pelletised.

TIES, which Rotawave licenses out, is currently used to activate carbon regeneration, for sterilisation and rendering of food wastes, pyrolysis, soil decontamination, extraction of oils from biomass and conversion into renewable fuels.

‘Working with wood is quite difficult,’ Rotawave’s technical director Garth Way told Cogeneration and On-Site Power Production. ‘It is a good insulator, and usually comes in a range of moistures and in different particle sizes.

‘The technical magic we’ve brought to it is that while only 10% of the energy needed to convert the wood to biocoal is actually microwave, that little amount gives you the confidence that it is cooked right through – or, to use a chef’s analogy, is it cooked in the middle?’

The company says tests have shown that Rotawave TIES biocoal pellets have a moisture content of less than 5% by weight as received.

‘Fully cooked’ wood that is drier than white pellets, and in which carbonisation is limited, produces more batch consistency, making pelletisation easier and more stable.

‘Other biocoal technologies have really struggled with consistency,” says Way. ‘We’ve been technically assessed by Black & Veatch, by Leeds and other universities, and have had independent assessors in to check our numbers.’

Those numbers were aired in a conference presentation in London in April, when Way compared coal, green wood chips, wood pellets (white pellets) and Rotawave TIES biocoal pellets across a range of parameters. The numbers were:

Gross calorific value, as received (MJ/kg): coal: 25; biocoal pellets: 24; white pellets: 18; and wood chips: 10.

Bulk density (kg/m3): biocoal pellets: 750; coal: 700; white pellets: 650; and wood chips: 285.

Energy density (GJm3): biocoal pellets: 18; coal: 17.5; white pellets: and 11.05; wood chips: 2.85.

To compare the volume of each fuel required for a specified amount of energy, energy densities expressed as m3 per 36 GJ: wood chips: 12.6; white pellets: 3.3; coal: 2.1; and biocoal pellets: 2. MWh per tonne: coal: 6.94; biocoal pellets: 6.67; white pellets: 4.72; and wood chips: 2.78.

Thus, the conclusion is, a container of Rotawave TIES biocoal will be almost as heavy as the same volume of coal but it packs more energy for the same volume of material and is not far behind coal in the power that can be generated from a tonne. Rotawave TIES biocoal beats white pellets out of sight on energy density.

No need for boiler modification

But what does it behave like in an unmodified boiler – will it foul the system or produce unwanted slag?

Rotawave announced in April that year-long technical trials part-funded by the UK government’s Technology Strategy Board, with the UK utility giant SSE and the University of Leeds, revealed that TIES gives a quicker, more efficient, lower carbon, lower capital cost option than direct biomass for co-firing coal-fired power plants.

The company concluded that biocoal produced in this way could be introduced into coal-fired generation as a way to reduce carbon emissions with minimal or no need for capital-intensive refurbishment to adapt plant to the new fuel.

Microwave is the key to Rotawave’s torrefaction process Credit: Rotawave

Way says there are no reasons why biocoal made like this could not also be used for cogeneration and on-site power production across a range of systems and generating capacities. He expresses an interest in cooperating with the industry.

‘If anyone is interested in exploring this, then come and talk to us,’ he says. ‘In general, biocoal is an alternative to white pellets biomass. If you are generating power, you know that carbon costs are going to hit you. If you want to get benefits from government incentives and regulations in many countries, you will be asking what is the best way of getting a carbon neutral fuel into existing infrastructure.’

The European Union (EU) incentivises the use of biomass that comes from a renewable bio-source – a provision that rules out waste. So would or should biocoal be considered as a renewable source?

‘Why wouldn’t it be?’ Way responds. ‘We’ve done a lot of work looking at the carbon footprint of our supply chain.’

One charge levelled at using microwave technology to make biocoal is that it must surely involve heavy electricity consumption. “This suggestion is a red herring,” counters Way. ‘The electricity cost in one TIES biocoal project moving towards commercialisation is only about 2% of the sales price of the product per tonne. So it is not a massive factor.’

What would it cost to convert existing plant? Rotawave has not worked through examples for typical cogeneration and on-site power production, but calculations for large power stations are worth rehearsing to reinforce some of the fundamentals involved.

The UK’s Department of Energy and Climate Change estimates the cost of converting a coal-fired power station to traditional biomass, (rather than biocoal), to be around US$700 per kW of generation capacity. For a typical 500 MW plant, that works out at an eye-watering $350 million.

Rotawave’s Garth Way invites discussion with cogeneration Credit: Rotawave

But it starts to get interesting when these costs are broken down. Materials storage and handling – which are both easier and far cheaper with biocoal – accounts for around 69% to 89% of cost, while combustion and emission control cover the rest – some 11% to 31%; the range under each heading reflects differences for various facets of the project – project management, engineering, procurement, construction and commissioning.

‘Using this example, our proposition is that you would save £180 million ($280 million) of the £225 cost by using biocoal instead of traditional biomass,’ says Way.

‘We can go even further. In the tests we’ve done, we did not modify the plant and we co-fired at about 20% biocoal. The plant was happy: flame stability was OK, the milling amps were OK (there would be no extra wear on milling machinery that grinds the pellets), and the reject rate on the milling was OK. There were no signs of incomplete combustion of biocoal, which was a good indicator, though the test was obviously not for thousands of hours.’

Way concedes that this applies to all well-made torrefied material within the right specification, although Rotawave claims significant benefits for biocoal produced by TIES. The door is open to the cogeneration industry to discuss how the technology might be tailored to its needs.

One high-profile convert to TIES biocoal is Cate Street Capital (Portland, New Hampshire), a US-based cleantech venture capital firm. In 2011, it agreed a deal valued at more than $20 million for its portfolio company Thermogen Industries to secure exclusive rights to use the Rotawave technology to make torrefied wood for sale in North America.

Thermogen had evaluated several different torrefaction technologies, including those using indirect heating and drying. “None of the processes were able to produce consistently torrefied material, capable of being successfully pelletised at commercial scale – with the exception of Rotawave’s TIES,” Thermogen CEO and president Richard M Cyr told Cogeneration & On-Site Power Production.

‘This game-changing technology could revolutionise the use of torrefied wood on a worldwide scale. It is smart technology that creates a new energy commodity in mass quantities that is efficient, environmentally sensitive and renewable,’ Cyr adds.

Thermogen’s Richard Cyr (left) foresees a positive future for biocoal sales in the US and abroad Credit: Thermogen Industries

Thermogen’s main production facility is now being built at Millinocket, Maine, and Cyr says the company expects to complete construction and begin production of its Aurora Black torrefied wood pellets in mid-2014. At full capacity, it is designed to 454,000 tonnes of Aurora Black annually.

In February, Thermogen also signed a letter of intent to build a torrefied wood pellet manufacturing facility on land adjacent to a terminal at Eastport, Maine. This will be capable of producing 181,000–272,000 tonnes of torrefied wood pellets annually, and Thermogen aims to start construction as early as possible in 2014.

Thermogen says its mission is to help preserve and extend the life of existing energy infrastructure by making it possible for coal-fired power plants and large institutions that burn coal to use more biomass efficiently as they strive to meet emerging environmental regulations and energy policies.

‘Aurora Black can supplement the use of coal in existing facilities or replace it altogether,’ says Cyr. “In either scenario, Aurora Black helps coal burners reduce harmful emissions, meet newer, more stringent clean air standards, and cost-effectively meet renewable energy goals.’

The production facilities in Millinocket and Eastport are strategically located to transport product efficiently and ship it overseas, or to transport it by rail and truck to domestic markets.

According to a 2007 study led by the University of Aberdeen, and a 2012 report by the London-based market analysts and consultants Hawkins Wright, the global market opportunity for torrefied wood is estimated to be many tens of millions of tonnes per year by the year 2020.

The study by Hawkins Wright into the supply chain economics of torrefied biomass stresses that its main advantage is in the way that its higher energy density reduces sensitivity to the cost of transport.

The study found that each shipment of torrefied fuel carries about 40% more energy by volume than conventional white pellet, and well over three times that of wood chip. ‘Importantly, this means that torrefied fuel can compete with white pellet when shipped in smaller vessels, creating flexibility for suppliers and traders,’ say the consultants.

Industry cooperation

‘The studies have identified a clear market for torrefied wood as a new form of clean, sustainable and energy-dense fuel,’ says Thermogen’s Cyr.

As suppliers gear up to exploit this, Way says: ‘I don’t think there is too much competition between torrefied biomass people. In fact, we need to be hitting the market with millions of tonnes pretty rapidly.’

Rotawave is a member of the International Biomass Torrefaction Council (IBTC), formed in December 2012 under the aegis of Aembio, the Brussels-based European Biomass Association. IBTC is significant as it provides a ‘shop front’ trade body to promote the technology for the first time.

‘We’ve all been discussing what we can share to help each other commercially and to shape public perception,” Way says. One issue exercising the industry is whether it can develop an international standard for black pellets so that customers can be certain about the quality and characteristics of what they are buying, whatever the source. “There’s a massive opportunity for this material to become a new form of energy transfer in a solid form,’ says Wild, who chairs the IBTC.

Secure and reliable supplies of biocoal at competitive prices are just what a range of industries including cogeneration and on-site power have been waiting for.

On costs, Rotawave’s Way says: ‘I would suggest that if you converted to 100% biocoal in 2013 in the UK, it would be cheaper than coal, and our modelling suggests that between now and 2030 the line on the graph showing price versus time will remain below £70 per MWh for 100% biocoal firing, while the equivalent cost for 100% coal, with carbon costs and renewables subsidies included where they apply to these fuels, would be above £170 per MWh.’

While such figures are based around a model of large power plants, Rotawave is convinced that cogeneration and on-site power production would benefit significantly too.

Projections will vary by location, depending on local taxes and subsidies. However, the biocoal industry is clearly confident of its long-term future as it believes that financial penalties on coal, combined with the commoditisation and incentivisation of renewables, will continue to widen the generating cost advantages of torrefied biomass.

Robert Stokes is a freelance journalist, who writes on the energy sector.

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