The prospects for biomass co-firing have never been brighter. Opportunities are emerging for the development of biomass firing across the globe, from the US to Europe and Asia.

Biomass, in the energy production industry, refers to living and recently dead biological material that can be used as fuel. Biomass may also include biodegradable wastes. It is grown from a number of plants, including Miscanthus, switchgrass, hemp, wheat straw, corn, poplar, willow and sugarcane tops.

Industrial, municipal and commercial non-recyclable (low market value) waste includes paper, cardboard, packaging, industrial fibre and wood processing waste. When these carbon-based materials are co-fired with coal, CO2 emissions from coal fired power stations can be reduced in direct proportion to the quantity of biomass consumed.

E.ON’s new 44 MW Steven’s Croft biomass plant near Lockerbie in the UK is one of many recent European biomass initiatives.
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Biomass co-firing refers to the practice of introducing biomass as a partial substitute fuel in high-efficiency coal boilers. This is the nearest-term low-cost option for the efficient conversion of biomass into electricity. Co-firing has been tried, tested and evaluated for a variety of boiler technologies. After “tuning” the boiler’s combustion output, there is little or no loss in total efficiency, implying that biomass combustion efficiency is roughly 33-37 per cent.

Trials suggest that effective substitutions of biomass energy up to about 15 per cent of the total energy input can be made with little more than burner and feed intake system modifications to existing stations.

In addition to CO2 emission benefits, biomass in general has the advantage of containing significantly less sulphur than coal, so there is an SO2 benefit as well. Early test results also suggest that there is a NOx reduction potential of up to 30 per cent with woody biomass.

Co-firing has proven to be a low-capital investment option. Utilities are using existing coal fired plants to burn biomass and non-recyclables that are more environmentally friendly and produce lower emissions. Co-firing has been demonstrated successfully in more than 150 installations worldwide. With plant numbers increasing, the trend could soon become standard practice for reducing CO2 emissions in power facilities.

The economics of co-firing are highly site-specific, and depend on power plant type and the availability of low-cost biomass fuels. A typical co-firing installation includes modification to the fuel handling and storage system to accommodate biomass. Costs can increase significantly if facilities for wood drying, size reduction or a separate feed to the boiler are required. For pulverised coal boilers, retrofit costs range from $150-300 per kW of biomass generation. The lowest-cost opportunities are with cyclone boilers, for which the costs may be as low as $50 per kW.

The more important cost factor, however, is fuel supply. Costs for biomass fuels depend on factors such as climate, proximity to population centres, and the presence of industries that handle and dispose of wood. Usually the cost of biomass fuels must be equal to or less than the cost (per MBtu) of co-firing to be economically successful. Some utilities reduce fuel costs by co-firing with biomass. The Tennessee Valley Authority, for example, estimates that it will save $1.5 million per year in fuel costs by using co-firing at its Colbert plant.

US biomass growth

Biomass and non-recyclables compete with saltwater, hydroelectricity, wind and other forms of renewable energy. For example, one tonne of dry biomass will generate approximately 1 MW. Co-firing with coal means that the biomass reaches a higher temperature, and will thus be more efficient, generating about 1.4 MW per tonne of biomass.

“The cost per tonne of biomass and non-recyclables is still higher than coal, however,” said Tom Miles, president of TR Miles Technical Consultants, an engineering firm specializing in power plant co-firing. “The final kilowatt cost is the fuel, what is actually delivered to the boilers. Most biomass is in the order of $70 per tonne by the time it is delivered to the burner. That is seven cents per kWh fuel cost.

Biomass production routes.
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“Coal is at roughly five cents per kWh in the US, and cheaper energy than biomass. Coal prices have been steadily rising, however, gradually closing the gap, which is making co-firing with biomass and non-recyclables more attractive to plants.

“By comparison, natural gas is more expensive than coal generated power, about the same cost as biomass. Wind is now in the region of eight cents per kWh, because many of the ideal sites have now been used. All of a sudden, co-firing with switchgrass, corn stalks, wood or non-recyclable waste looks pretty interesting to the utilities from an economic point of view.

“Dedicated biomass and non-recyclable waste plants are not the most cost-efficient option,” Miles added. “If a utility wants to generate electricity from a renewable resource, it should look at co-burning that resource with coal, as opposed to building a new plant that generates power entirely from biomass.”

Biomass in Europe

Biomass is one of the fastest growing electricity sources in Europe. Its share of the 27-nation European Union’s (EU’s) primary energy production reached 10 per cent in 2006, showing a steady growth of 5-9 per cent per annum. At the same time, other energy sources, such as coal, oil and gas have seen their market share decrease from 2001 to 2006. The biomass sector is well positioned to continue expanding its share in primary energy and electricity production.

Its main advantage over other renewable energy sources is a stable power supply that is suitable for baseload service. Life cycle net carbon emissions per unit of bioelectricity are below 10 per cent of the emissions from fossil fuel-based electricity. This leads many to accept biomass as a “carbon-neutral” source.

Definitions of biomass vary to include the following feedstocks:

  • wood and wood wastes from forestry and industry
  • agricultural residues from harvesting or processing
  • energy crops grown specifically for energy applications
  • food waste from food and drink manufacture
  • industrial waste and co-products from manufacturing and industrial processes.

Wood and wood wastes are a prime biomass source at present, accounting for 70 per cent of the overall biomass used in the EU. Transportation can add significantly to the costs and total process carbon footprint, so the biomass industry originally flourished in countries with large domestic wood and paper industries such as Finland and Sweden.

However, as urban and industrial waste disposal increases in scale, and becomes more expensive and difficult – due to increased landfill taxes and bans on certain waste streams in landfill sites – many waste management companies and investors are looking to profit from landfill.

Biomass technologies

Six primary technologies are used to process biomass into heat and power or biofuels:

  • combustion
  • gasification
  • pyrolysis
  • extraction
  • fermentation
  • anaerobic digestion.

Biomass is mostly used for heat and power generation. At present, biomass co-firing is the most cost-effective use of biomass for power generation. The efficiency can reach 45 per cent, or 85-90 per cent with CHP plants.

Biomass integrated gasification is close to full commercialisation, integrated gasification combined cycles are already in use and anaerobic digestion is expanding. Bio-refineries may eventually produce competitive biofuels.

Co-firing could remain a dominant technology for several more years. However, gasification and other methods of biomass utilisation could expand significantly in the medium to long term.

Market support is vital

The EU Biomass Action Plan is a pan-European framework for biomass sector development. Finland, as the most mature and largest market in Europe, can provide a good example of what may be achieved.

The Finnish National Climate and Energy Strategy specifically stresses and promotes the use of forest chips, agrobiomass fuels and biogas as well as the small-scale use of wood, through the increased consumption of wood pellets.

The Finnish government has developed and employed a number of financial and market support measures, such as funding of R&D projects, energy taxation, tax relief, production subsidies for electricity and forest chips, and investment subsidies. At the start of 2008, a quota was introduced requiring biofuels to account for a fixed percentage of the transport fuel markets.

Taxation is a major tool for implementing environmental policy. In Finland, an environment tax for fossil fuels has been imposed since 1990. The tax on fossil fuels is based on the carbon content of the fuel. Solid biofuels used for heat generation are exempt from the tax. Fuels used for electricity generation are not taxed, but an electricity tax is imposed on the consumption of electricity.

The biomass industry in Finland is also supported by subsidies for renewable electricity. Subsidies for forest chips remain among the highest.

Biomass in SouthEast Asia

In Southeast Asia, biomass from crop residues, municipal solid waste and forest residues is abundant, while its contribution to total power generation has increased over the last five years.

Biomass represents about 40 per cent of the total energy consumption in Southeast Asia. In countries such as Nepal the biomass share is as high as 92 per cent, while in countries such as Malaysia biomass only contributes 7 per cent to the total energy consumption. However, this is still much higher than the 3 per cent average in the US and Western Europe.

The main source of biomass in Southeast Asia is wood. In Indonesia, wood accounts for 80 per cent of the country’s biomass used for energy generation. In Southeast Asian countries, 10-50 per cent of woodfuel is sourced from natural forests. Agricultural residues, such as rice husks, straw, and coconut husks are the other main source of biomass fuels.

An Asian Institute of Technology study estimated sustainable biomass production for energy in Malaysia, the Philippines and Thailand at 0.4-1.7, 3.7-20.4 and 11.6-106.6 Mt/yr, respectively. The maximum annual electricity generation potential from this sustainable biomass production is estimated to be about 4.5 per cent, 79 per cent and 195 per cent of the total electricity generation in 2000 in Malaysia, the Philippines and Thailand, respectively.

The countries of Southeast Asia have adequate government policy-level support for the development of biomass-based power generation projects. In addition developers are given investment incentives, guaranteed minimum prices, power purchase agreements with the utility grid, exemptions pertaining to the import of equipment and certain tax credits. Existing guidelines pertaining to renewable energy grid-based projects are a major driver for biomass-based power generation in Southeast Asia.

New opportunities in biomass

China and India have massive potential markets for co-firing biomass. In both countries, there is a massive use of coal as a fuel source, but there is a large agricultural sector producing a lot of usable biomass waste. However, there is little use of that biomass waste in co-firing as yet. This is largely because the horizontal integration between farmers and power station managers is not yet in place, and the transport infrastructure necessary to get the biomass from many small farms to large central power plants is not yet fully developed.

Nordic countries have pioneered the biomass industry and turned into leading equipment and service providers for the biomass power generation market, but other countries are joining in. Since 2004, Germany, the UK, Hungary, Poland, the Netherlands, Spain, Austria, Belgium and Italy have been steadily increasing the number of biomass co-fired plants.

Governments are designing specific policies to support the biomass sector. The UK published its biomass strategy in 2007. Although this doesn’t define specific targets for biomass energy, it does provide a strategic overview of the biomass industry contribution to achieving the country’s commitments on CO2 emission reduction and renewable energy share in the power mix.

Italy has passed a financial law on new Green Certificates for biomass in 2008. Poland’s energy policy, adopted in 2005, stipulates that 1000 MW in biomass co-firing plants should be installed between 2005 and 2010.

As a result, the biomass industry is firmly taking root in many European countries. With new biomass utilisation technologies nearing full commercial deployment, growing concern over waste disposal being backed by legislation, and the interest of project developers and investors in new projects increasing, the biomass industry is well placed to continue expanding its share of the European energy mix.

NETBIOCOF project (2005-07) research, co-financed by the European Commission, has reported on co-firing experiences in Europe in great depth. There have been around 100 co-firing units in Europe. Experience has been positive with woody biomass, whereas herbaceous biomass has caused problems, due to its higher inorganic matter content and higher risk of slagging and fouling.

Depending on the technology, even the high-inorganic content or high-moisture biomass can be used. Many plants are in trials or demonstrations, for example in the UK and US. On the other hand, co-firing plants in the Netherlands, Denmark, Finland and Sweden mostly operate on a commercial basis.

biomass material availability

The principal biomass materials available as fuels for energy conversion plants in sufficient quantities to be relevant to co-firing in coal-fired power plants are:

  • surplus cereal straws and other baleable, dry agricultural residues
  • forestry and sawmill residues
  • specific industrial, agricultural and other waste materials of plant or animal origin
  • energy crops grown specifically for use as fuels
  • dried and pelletised wood fuels, produced in large quantities in North America, Scandinavia, Russia and Northern European countries
  • olive processing wastes available in large quantities, in dry granular or pelletised form, from countries with large olive oil production industries, such as Spain, Italy, Greece, Turkey, Tunisia and Portugal
  • dry solid residues from the palm oil production industry in Far Eastern countries such as Malaysia and Thailand.

Thessaloniki, situated 500 km north of Athens, is a major centre of the Greek oil industry. It is home to a Hellenic Petroleum refinery and a number of petrochemical plants. In late 2005, a 390 MW combined-cycle power plant, which represents the country’s first independent power station (IPP), came online to supply electricity to the Hellenic Petroleum site.

The IPP is owned by Thessaloniki Power, a company created by Hellenic Petroleum. The plant also includes a 400 kV substation, from which the output is sent to HTSO, a power transmission company that is the high-voltage grid business of the former Public Power Corporation.

Demand peaks

The maximum demand of the power system on mainland Greece in 2006 was approximately 10 000 MW, generated mainly by steam plants, fuelled with locally mined lignite and hydro stations. The Thessaloniki plant is one of five combined cycles built in recent years and was the first IPP to be licensed in September 2001. From the outset the IPP was designed as a merchant plant to supply HTSO 24 hours in advance on the basis of availability and energy demand.