Last week the IEA Clean Coal Centre gathered around 100 people from government offices, utilities, engineering companies, research organisations and universities to Sotacarbo Research Centre, Sardinia, Italy, for its 6th International Workshop on Cofiring Biomass with Coal.
The workshop began with a visit to a Coal Mine Museum onsite to the Sotacarbo Research Centre before the Welcome reception. The workshop was formally opened on 14 September by Professor Alessandro Lanza, the president of Sotacarbo Research Centre. He gave the delegates a warm welcome and a comprehensive introduction to his research centre, especially their efforts on CCS.
As the first key note speaker, Mr Han Shui, the Chief Engineer of China National Energy Administration (NEA), lifted the delegates’ sprits by announcing for the first time in public that China NEA is going to issue a ‘Guidance on Promoting Cofiring Biomass with Coal’ before the end of this year. NEA plans to build several cofiring demonstration projects in the 13th Five-Year Plan period that will burn coal with biomass or sludge. This announcement excited many delegates who would like to share with China their expertise and experience.
Paul James from Ramboll Energy compared some fuel substitution options to reduce CO2 emissions at existing coal plants. Although switching to 100% wood pellets reduced emissions by 90%, the problems lie with the supply, storage and handling requirements for the wood pellets. Partial substitution of coal with wood chips has the advantages of flexible operation and reduced CO2 emissions.
Dr Gregory Dunnu gave a comprehensive presentation on the utilisation of biomass in coal fired power plants. Based on GE’s experiences, he concluded that full conversion of fossil fuel plants to biomass is feasible. However, there will be impacts on performance and unit operation. Biomass retrofit of existing plants offers a reliable power solution to meet renewable energy targets.
Various international perspectives were delivered by the IEA Paris, US DOE/NETL, Electric Power Planning and Engineering Institute (EPPEI) of China, Centre for Research and Technology Hellas (CERTH) / Chemical Process and Energy Resources Institute (CPERI) Greece, and TECSOL Ltd Colombia. Raimund Malischek gave the IEA’s view on the role cofiring biomass with coal could play in carbon reduction. Biomass cofiring and CCS are crucial in reducing the carbon intensity of the coal fleet. In an IEA scenario, almost 1.1 Gt of CO2 captured in 2050 is linked to biomass with CCS, corresponding to 16% of total CO2 captured globally, and around 0.7 Gt is captured from coal plants with cofiring. Jeffrey Hoffmann from US DOE/NETL assessed the technical feasibility of adding cofiring with biomass to CCS to achieve net-negative CO2 emissions. Coupled with advanced CCS technologies, he concluded that cofiring coal and biomass can offer a pathway for deep CO2 emission reductions. Dr Xiang Li outlined the Chinese technological routes and engineering applications to cofiring straw and sludge. Funded by the 7th EU Framework Programme, (agro-)biomass co-firing in lignite-fired power plants in South East Europe was studied by CERTH and reported by Mr Karampinis. In Colombia, the rainy seasons are from April to June and October to November. During these time, hydropower supplies 80% of national power generation. For the rest of the year, more than 50% of the country’s energy demands are met by thermal power generation. Mr Rincon thought that cofiring bagasse from sugarcane with coal has a large potential in Colombia.
While Europe and Canada are rich with cofiring experience, economic emerging countries have just begun to realise its advantages. Knowledge sharing can be invaluable. Therefore, this year’s workshop tried to focus on practical activities and industry experience. Doosan Babcock UK has extensive experience in biomass conversions and cofiring over a 30 year period including Tilbury, Ironbridge, Atikokan and Drax plants. Graham Welford shared Doosan Babcock’s experiences using their most recent project at the Lynemouth coal-fired power plant. Canadian company OPG converted a coal-fired unit at Thunder Bay power plant to 100% advanced wood pellet firing. Although it is not cofiring, the experience of the conversion process, such as cooperation between suppliers, researchers and utilities, is relevant for cofiring conversion of power plants. There are a number of options available for the direct co-firing of solid biomass materials in large pulverised coal fired boilers, including: pre-mixing the biomass with the coal, added dedicated biomass mills, 100% conversion of one existing mill, parallel boilers, and gasification. Collins Ndibe brought German IFK’s experience on co-milling and co-firing of torrefied biomass at Hanasaari Power Plant B, Helsinki. Results from China Guodian’s biomass gasification project was shared by Peihong He. Amer Power station is the pioneer and leader in the Netherlands on biomass co-firing since 2000. However, the biomass explosion on the 10 September 2014 shocked the whole industry. RWE Generation told the workshop the lessons they have learned on fuel storage and transport.
The ability to utilise domestic waste, agricultural residues, and aquatic biomass can bring cofiring biomass to a new socially meaningful level. The Energy Research Centre of the Netherland (ECN) have made it possible to cofire some difficult feedstocks. Michiel Carbo introduced ECN’s patented technology, TORWASH (Torrefaction + Washing), which can upgrade low grade feedstock into a commodity fuel. Mitsubishi Hitachi Power Systems Europe GmbH, on the other hand, can convert the large coal-fired power plants into 25% biomass cofiring, full biomass firing, or plant that can switch between biomass and/or coal. NOx control and ash management technologies have been developed by Johnson Matthey Catalysts GmbH Germany, and Magaldi Group, Italy.
Biomass torrefaction, pyrolysis, and combustion are widely studied academic topics. Javier Gil, from National Renewable Energy Centre where biomass torrefaction biomass has been studied since 2006, reported the impact of raw material on production costs and the methodology for evaluating feedstocks. Is torrefaction the most efficient way to upgrade woody biomass for cofiring? Birte Everts compared seven scenarios for pellets, wood chips or torrefied wood. She concluded that pre-treatment integration allows the energy input to be used more efficiently for power generation and fuel upgrading. Woody biomass with integrated multi-stage steam heated torrefaction can be cofired most efficiently. Direct cofiring of wood chips is least efficient. The influence of the torrefaction process temperature on pyrolysis product and its composition were evaluated by Mr Moeller from RWTH Aachen University, Germany. Characteristics of tars formed during co-pyrolysis of coal and biomass were studied by Professor Pisupati at Pennsylvania State University, USA. Co-pyrolysis and co-gasification of coal with micro-algae were studied by Dr Sanna at Heriot-Watt University, UK. Combustion of Turkish lignite with pine chips and under oxyfuel combustion conditions were reported by Professor Atimtay from Middle East Technical University, Turkey, while cofiring combustion characteristics of Bambusa balcooa was reported by Dr Bada from the South African University of Witwatersrand. Ignition behaviour of biomass particles in a down-fire reactor for optimisation of cofiring was analysed by Dr Li from University of Strathclyde, UK and the influence of KCl and SO2 during combustion was analysed by Thomas Ekvall. Release of inorganic trace elements and gas phase potassium during combustion of biomass were studied by Dr Blasing at IEF-2, Germany and Dr Mason at University of Leeds, UK.
The workshop presentation sessions were closed by Dr Andrew Michener OBE with an exciting message that the IEA Clean Coal Centre, together with China EPPEI, is going to bring Cofiring 7 to China in 2017. This is the first time for the Cofiring workshop to go to Asia. Apart from continuing the technical topics (fuel supply and preparation, environmental impact, operational options), the next workshop will emphasise the drivers for large scale commercial deployment (policies/regulation, investment incentives) and how best to achieve cooperation between China and international technology companies.
The workshop concluded with a visit to the CFB cofiring unit at Enel Sulcis Power Plant in Portoscuso. The CFB boiler was the largest in the world when completed in 2005. The fuel flexibility of fluidised bed combustion allows the unit to fire up to 15% biomass (by calorific value) and a proportion of the high sulphur local coal, whilst meeting emissions requirements without downstream deSOx or deNOx.
Overall we can see a trend in the development of biomass cofiring. A decade or so ago people considered cofiring a few percent biomass in coal-fired plant. Then it increased and now there is full conversion of some units in some western countries. However, China wants to promote only cofiring biomass with coal in order to reduce the risks of problems with the supply of biomass fuel. The fuel of choice in the West is wood pellets, while economic emerging countries such as China, South Africa, Greece, and Columbia, are interested in cofiring agricultural residues. China is also interested in cofiring sludge not only to reduce the use of coal and CO2 emissions but also to reduce air pollution from the scattered burning of these agricultural and sludge wastes.