I am just back from a stimulating and thought-provoking IEACCC workshop on cofiring biomass with coal – the ninth in the series. Concern about the Coronavirus meant that several presentations were pre-recorded and then slotted into the programme. Although we missed the chance to question the speakers, the presentations were of a very high standard and ran smoothly.
The workshop began with two site visits. The first was to Nippon Steel Engineering which has a bench scale plant developing a new fuel from woody biomass and brown coal. The process improves the quality of both fuels and produces a standardised product. NSE have a patent on a lignite-biomass mix torrefied briquette and the project is supported by NEDO. Then we were back on the coach for a quick tour of the Shin Onoda power station, run by Chugoku Electric Power Company. This 1000 MW power plant was commissioned in 1986 and runs pretty much constantly. At Shin Onoda they currently burn 2.6 Mt/y of imported coal and cofire about 20,000 t/y of wood chips. They aim to increase the rate of cofiring to up to 300,000 t/y using wood pellets from North America and Australia. A feed-in tariff (FIT) will help them cofire at a ratio up to 10.4%. The two main modifications are to adapt one mill exclusively for pellets and to alter the boiler burner. Shin Onoda is on a compact site of only 290,000 m2 and uses well-maintained state-of-the-art technology. Emissions are kept to 60 ppm NOx and 68 ppm SOx. There is also an ESP to capture fly ash.
The workshop proper opened the following day with welcome addresses from Dr Andrew Minchener (IEACCC), Makoto Nunokawa (NEDO) and Nobuhiro Abe (Kitakyushu Convention and Visitors Association). By 2030 Japan aims to have 26% of its power sourced from coal plant and renewables will be supported. The electricity companies in Japan currently cofire around 3% biomass. Already 13 coal-fired power plants in Japan have tried cofiring biomass. The use of imported wood is increasing rapidly and is expected to reach 5 Mt/y by 2025. However, there are growing concerns about the sustainability of the biomass for cofiring. In April 2019 biomass for cofiring lost its eligibility for the FIT so the low carbon price means that it cannot compete with coal.
Wenping Hu’s (EPPEI) recorded presentation was particularly interesting. China has huge potential for cofiring, but only a few projects are in operation – most are in the planning stage. In June 2018 the NEA of China announced 89 cofiring projects at a previous IEACCC Cofiring workshop. However, very few are active; of 56 projects announced that would cofire agricultural and forestry wastes, only 2 are in operation; the other 56 have been suspended, largely due to a lack of supportive polices such as a fixed price. On the other hand, much research continues in China on the effective co-gasification of biomass and coal. China produces more than one billion tonnes of biomass a year and less than half of it is used as fertiliser, fuel, feed or bedding. CFB gasification is being researched in China, although the large scale projects previously announced are currently stalled. There is massive potential in China to cofire agricultural residues, but the policies need to be in place.
The advantages of torrefaction were outlined by Michael Wild (International Biomass Torrefaction Council). Torrefied biomass is a more homogeneous material than wood chips and is more similar to coal – it ships, stores, mills and combusts in a similar way. Gordon Murray (Wood Pellet Association of Canada) discussed the sustainability of biomass and described the various schemes in operation. There are national standards in the UK, Netherlands, Belgium and Denmark and the EU Renewable Energy Directive (RED II) recently introduced sustainability criteria. There are various third party certifiers including the Forest Stewardship Council (FSC), Programme for the Endorsement of Forest Certification (PEFC) and the Sustainable Biomass Programme (SBP). The SBP is designed for the utility industry. Canada has 9% of the global forest and all Canadian pellet exporters are SBP certified.
CFD modelling is a popular tool for examining and fine-tuning various aspects of cofiring. For example, it has been used to balance fuel and air to improve combustion and to optimise boiler efficiency.
Presentations from Ramboll and Loesche examined the transport and milling of wood pellets in more detail. Presenters from Firefly AB and the University of Greenwich described the attendant risks of handling biomass – mainly fires, explosions and the health hazards of inhaling biomass dust.
Oxyfuel combustion of biomass with coal and carbon capture and storage (CCS) was explored as a way to reduce emissions to a minimal level. This topic is gathering support as it has potential as a method to help countries achieve their Paris Agreement goals.
Although SCR for NOx control is not a major part of cofiring biomass, it is important for coal-fired power plants. The catalysts in SCR can be poisoned by Na, P and K which are present in higher concentrations in biomass than coal, so a high biomass content tends to deactivate the catalysts. But this impact is usually minor if biomass is cofired at a rate of 10-20%.
The Cofiring 9 workshop had an applied and industrial focus which reflects the status of the technologies. There was much discussion about the conversion of biomass and its combustion. The use of agricultural residues clearly has potential, but there are challenges in turning it into reality, partly due to the issues with slagging, fouling and corrosion. Wood pellets are well established and work continues on torrefaction. The sustainability debate rumbles on, but seems to be more of a media concern than a scientific one.
The safety issues when handling biomass are critical – plenty of pictures of unwanted fires and explosions were shown. But cofiring biomass clearly has a role in reducing emissions of CO2 from coal-fired power plant and, when combined with CCS has the potential to result in negative emissions, so it is definitely a topic that merits further research, discussion and collaboration.
COFIRING 9 – our workshop on cofiring biomass with coal took place 25 – 27 February 2020 in Kokura, Japan.
