Pyrolysis is the heating of the biomass in the absence of air at temperatures of 300- 500°C. Under these conditions the products are gas, charcoal and an oil (bio-oil) which after treatment can be used in a diesel engine. The main treatment is to reduce the viscosity which is too high to be used in a diesel engine. The possible uses of pyrolysis products are given in Fig. 4.8. The crude bio-oil can be used in gas turbines and engines but for the standard diesel engine it requires upgrading. The bio-oil can also be used in boilers and co-fired in power stations and after gasification it can be

converted into transport fuels. It can be a source of chemicals. The charcoal can be used for industrial processes or as a source of heat. The pyrolysis liquid can have a number of names such as pyrolysis oil, bio-oil, bio-crude-oil and wood oil. Bio-oil is a dark brown acidic liquid consisting of a complex mixture of oxygenated hydrocar­bons and water which is not miscible with petroleum-based fuels. Some of the proper­ties of wood-derived bio-oil are given in Table 4.10.

Bio-oil can replace fuel oil in static operations such as boilers, furnaces, engines and turbines for the production of heat and electricity but to be used as a transport fuel the viscosity needs to be reduced.

Conclusions

Biomass is a solid biofuel which can be in all forms of wood — from trees, crop resi­dues, animal and municipal waste — in addition to crops specifically grown for energy.

Energy can be extracted from biomass by direct burning, co-firing with coal, gasifica­tion and pyrolysis. Gasification and pyrolysis can yield liquid fuels and can be used in electricity generation. The process for the generation of petrol and diesel in the Fischer-Tropsch (FT) process is discussed in Chapter 7. The main use of biomass has been in the generation of electricity and in combined heat and power systems.

The estimates of the energy available in biomass vary greatly from 93 to 1135 EJ against the global energy requirement of 425 EJ. It is clear at first glance that bio­mass can provide a significant amount of energy and Table 4.7 indicates that most regions do not use a high proportion of their potential. Biomass use is perhaps more efficient than biodiesel and bioethanol as the whole plant can be used rather than only a small proportion. However, other studies indicate that there may have been an overestimation of the biomass actually available. The surplus biomass may be much smaller after woodfuel has been taken into consideration. In addition, biomass is widely spread and seasonal and will require collection and transport if it is to be used and this will reduce the amount available. The other problem is that biomass can only be used once and there are insufficient amounts available for all uses espe­cially in the UK. It may be that the FT process for diesel and petrol production will be the most suitable for biomass. For biomass to be adopted as a sustainable source of energy, it requires government help in terms of tax concessions and provision of sites. The lack of government support is not the only impediment to the introduction of biofuels, as local opposition to renewable schemes such as wind farms has been strong in many cases. One example of local opposition triumphing over government initiative was the projected biomass electricity generation plant in Cricklade, Wiltshire, which was not granted planning permission (Upreti and van der Horst, 2004). A number of other similar schemes (27%) have been rejected for similar rea­sons. The plan was to build a 5.5 MW power station at Kingshill Farm, an estab­lished recycling site, to generate electricity under a Non-fossil Fuel Obligation (NFFO 3) contract capable of supplying electricity to more than 10,000 homes, at a time when Swindon was expanding rapidly. The site required 36,000 t of dry wood supplied from a 30-mile radius using forestry wastes and SRC. The rationale for the site was as follows:

1. Good access to forestry wastes.

2. The area was suitable for growing SRC.

3. Good road connections for fuel delivery.

4. Good access to electricity distribution.

5. It delivered electricity in a decentralized location.

6. Local employment, 15 permanent jobs and other jobs during construction.

7. Diversification in local agriculture.

However, despite these points individuals and organizations opposed the develop­ment and the main objections included:

• It would set a precedent for other local industrial developments.

• It would contradict local designations, the Area of Special Archaeological Significance and Rural Buffer Zone.

• It would lead to a large increase in the movement of heavy goods vehicles (HGVs).

• The six chimneys proposed were very tall and would affect the view.

• Approximately 117 million l of water would be lost into the atmosphere.

• The power station would produce smell, dust, noise and other emissions.

• Long-term general health impacts.

• Damage to Cricklade’s south-east meadows and water systems.

• Possible lack of compensation if anything should go wrong.

• There would be a negative effect on property prices.

These concerns were clearly very powerful and in September 2000 the application was rejected for the following reasons:

The Biomass Power Station is a major development proposal which would, if allowed, seriously undermine the openness of the rural landscape, resulting in a loss of coun­tryside creating an inappropriate form of major development in the Rural Buffer, contrary to the Wiltshire Plan Review and Policy DP 13 of the Wiltshire County Structure Plan 2011 Proposed Modifications.

(Upreti and van der Horst, 2004)

It was concluded that public relations strategies by developers, role of the media in amplifying risk, lack of proper information and lack of public understanding of bio­mass power plants were the main reasons for the lack of success. The UK government needs to generate a public awareness of the benefits and need for sustainable electric­ity generation or NIMBYism will prevail.