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Taken with Chips

15 November 2009

G30 wood chips

Before deciding on biomass as a renewable and sustainable energy source, it is crucial to talk to all relevant parties - including the fuel supplier - from the very outset to ensure the installation is appropriate and sustainable

AMONG THE MOST POPULAR alternative energy sources in public and commercial premises are wood burning boilers. Biomass fuel absorbs as much CO2 when growing as it releases when it is converted to energy making it carbon-neutral. A wide range of biomass can be used for fuel from agricultural wastes such as straw, energy crops such as willow and oil seed rape and wastes from food production, to wood chips and wood pellets.
For most commercial applications it is wood chip and pellet boilers that appear to be the most attractive option. Carbon neutral and cheaper than oil, gas and electricity alternatives, wood as a biomass source is readily available in the UK, although large biomass power stations will mostly source volume supplies from overseas.
Early adopters of these biomass systems are already reaping the rewards. Stansted Airport's new £50m terminal extension has reduced gas consumption by nearly 40 percent since installing a new 2MW biomass boiler system last year. One of the largest boilers in commercial use for heating purposes in the UK, it uses 2,500 tonnes of woodchip fuel each year from Forestry Commission Certified sources.
Across the country biomass heat is being considered for installations of various sizes in schools, leisure centres, community halls, hospitals and offices. AHS Energy is based in Northiam, Sussex and delivers up to 150,000 tonnes a year of wood chips to its customers from its depots in 12 and 25 tonne loads. The size of delivery lorries and the number of deliveries is just one of the things potential users need to consider before ordering a biomass boiler system, suggests Edward Wilkinson of AHS Energy.
AHS Energy used to provide wood chips mainly for the landscaping market. It still does this but since it acquired a wood recycler at Padworth near Reading and converted it to a fuel depot, it now has the capacity to supply the landscaping market in the summer, and the biomass market for the winter. At the Padworth site, AHS Energy’s wood supplies are naturally dried, then chipped, screened and graded, ready for delivery.
Wood is a natural product and just as ‘on tap’ as gas, oil or electricity fuels that most people are used to. As Wilkinson explained, before deciding to install a biomass boiler, there are a number of related issues that need to be taken into account.
Key amongst these is the delivery of the fuel to the site. A typical hospital installation, for example, would need up to 25 tonnes per day in a single articulated lorry load to be delivered to the site. Access to the site through neighbouring streets, and the size of turning space on the site to deposit the wood chips into the storage hopper, should be considered at the start, since if smaller lorries are needed, there could be more deliveries possibly at a higher costs.
The wood chips come in several different grades: the most popular is G30 which has a maximum 30mm chip size; G50 and G100 are sized accordingly. A vital early consideration is the moisture content of the wood, in order to ensure that the boiler performs at its optimum. Often this will mean that the fuel supply has to come with a maximum moisture content of 30 percent, but this is tailored according to clients’ needs
An alternative is wood pellets made from the bi-products of sawmills and wood processing plants, compressed and reduced to a pulp before being shaped into cylinder shapes. The pellets are very dense and require less storage space but are about three times more expensive than wood chips.
Currently AHS Energy delivers about 100 25 tonne loads per week from various sites to its customers across the country. It plans to open further sites across the UK that will be no more than 100-150 miles from its customers. Wilkinson says that there is a current myth that fuel needs to be sourced from no more than 25 miles, and indeed AHS are in talks with government policymakers to have this clarified. As Wilkinson says, “Oil and gas don’t come from 25 miles away.” As the biomass markets develop, there will be a need to source the fuel on a regional and national basis to ensure supply. “To chip and store wood on a small scale is not economically viable and there is likely to be more risk of business failure and supply interruption,” explains Wilkinson.
AHS Energy operates customer contracts of between three and ten years in length and it can deliver within 24-48 hours from stock. It also has plans to develop a wood burning 4.5mW CHP power station in Northiam to generate enough electrical power for 6,000 homes. Costing some £15m to build, it aims for the plant to be operational by 2011 to demonstrate its own confidence in wood chips as a secure and effective fuel source.

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