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Bio-oil can substitute for fuel oil or diesel in many static applications including boilers, furnaces, engines and turbines for electricity generation which was been thoroughly reviewed in 2004 [1] and many aspects have not changed verymuch. The most significant changes since then are: An appreciation of the potential for fast pyrolysis to be a pre-treatment method i.e. for bio-oil to be an effective energy carrier Greater interest in bio-oil as a precursor for second-generation biofuels for transport Greater awareness of the potential for fast pyrolysis and biooil to offer more versatile processes routes to a wider range of products and contribute to biorefinery concept development. Considerably greater interest in upgrading bio-oil sufficiently for it to be used for heat, power and other applications with greater confidence by users Fig. 12 summarises the possibilities for applications for biooil and the main developments are expanded below. 5.1. Pretreatment method for energy carrier Biomass is a widely dispersed resource that has to be harvested, collected and transported to the conversion facility. The low bulk density of biomass, which can be as low as 150 kg/m3, means that transport costs are high and the number of vehicle movements for transportation to a large scale processing facility are also very high, with consequent substantial environmental impacts. Conversion of biomass to a liquid by fast pyrolysis at or near the biomass source will reduce transport costs and reduce environmental concerns as the liquid has a density of 1.2 kg/m3 e nearly 10 times higher than lowdensity crops and residues. This not only reduces the number of vehiclemovements and costs by up to 87%, it also reduces costs of handling and transportation by virtue of it being a liquid that can be pumped. This leads to the concept of small decentralised fast pyrolysis plants of 100,000e300,000 t/y for production of liquids to be transported to a central processing plant. It is also possible to consider mixing the byproduct char with the bio-oil to make a slurry to improve the energy content of the product as advocated by KIT and Dynamotive, but the pyrolysis process will then require that its process energy needs are met from another source. Adoption of decentralised fast pyrolysis with transportation of the resultant liquid to a central gasification and fuel synthesis plant has both technical and economic advantages and disadvantages as summarised in Table 9. The impact of inclusion of fast pyrolysis as a pre-treatment step on BTL cost and performance has been analysed [178]. 5.1.1. Co-firing Co-processing of biomass with conventional fuels is potentially a very attractive option that enables full economies of scale to be realised as well as reducing the problems of product quality and clean up. Most current co-firing applications are those where the biomass fuels are added to the coal feed and this is widely practised at up to 5% on the energy demand of the power station. A few applications involve conversion to a fuel gas via gasification followed by close coupled firing to the power station boiler. There are also some examples of co-firing fast pyrolysis liquids including a coal fired power station at Manitowac in the USA using the byproduct from liquid smoke production [191]. Large-scale tests have been carried out, where pyrolysis liquids from the Red Arrow operation were co-fired with coal for the commercial production of electricity [192]. The combustion of bio-oil was clean and efficient with no adverse changes on the boiler operation or on the emission levels. There is also some limited experience of successfully firing bio-oil in a natural gas fired power station in the Netherlands. |
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