Biomass as the future of green heating
Stephen Laws looks at the future for biomass boilers and the issues surrounding their specification for heating and hot water in domestic, commercial and public-sector applications.
Government initiatives for sustainable-energy systems such as biomass boilers are providing a real incentive for all sectors of the market to take a greener approach — from private developers and businesses to schools and hospitals. With the advent of Part L 2006 of The Building Regulations, renewable-energy technologies have become an integral part of every new building.
Biomass is considered to be ‘carbon neutral’; its combustion does not add to the existing carbon cycle, unlike burning fossil fuels which re-introduces carbon that has been stored for millions of years. Biomass is one of the oldest sources of fuel for mankind and still one of the most abundantly used worldwide. ‘Biomass’ is usually applied to a huge range of solid organic fuels, ranging from specifically-grown energy crops (such as straw, willow rotation coppice and wood) to organic by-products (including wood pellets and wood chips). Wood pellets are the most refined biomass fuel, being made exclusively from compressed sawdust and wood shavings.
An important factor in the selection of an appropriate biomass fuel is the calorific value, which ranges from as much as 17 MJ/kg for wood pellets to as little as 8 MJ/kg for green softwood. A key factor in the difference is the moisture content of the fuel.
Wood products are composed of long-chain hydrocarbons that have to undergo pyrolytic decomposition into short chain compounds to produce heat. Before this can happen, all moisture has to be driven off, which takes some of the internal energy of the fuel. The greater the moisture content of the fuel, the more energy will be used for this instead of creating usable heat.
Wood pellets have a carefully controlled moisture content, typically around 10% by volume, whereas wood that has been air-dried for at least a year will contain at least 20% moisture.
Evident advantages for wood pellets over other wood-based fuels are significantly lower storage, transportation and handling costs and a consistent and reliable heat output. Before the recent fuel hike, UK suppliers of wood pellets tended to pitch the price a little below that of 35 second heating oil (for a comparable calorific value). In some European countries, wood-pellet burning is an established technology, and prices are much lower than oil and gas.
Biomass is a developing market in the UK and, as with any new technology, potential users tend to look to suppliers for a complete solution. This is reflected in Clyde’s approach to developing its biomass boiler package, which includes advice on specification, commissioning, installation and maintenance. We will tailor a complete package to your specific requirements that includes boiler, storage silo and automated pellet delivery system. We also recognise that although there is growing interest in renewable energy, some users may not want to feel ‘locked in’ to this type of system. So unlike dedicated bio-fuel boilers on the market, Our Trio biomass boiler is of a design that allows simple conversion from wood pellet to natural gas or oil firing if required at any point in the future. Therefore, a secure heat supply can be ensured without the need for an additional, fossil fuel boiler. As an added benefit, this standard configuration also ensures a highly competitive price.
Advanced control of heat output and safety considerations are of paramount importance today. Although biomass may be an age-old fuel, our expectations of combustion technology should be no less than for gas or oil. The biggest danger for a biomass boiler is back-burning, particularly when it has an automated fuel-feed system providing an uninterrupted conduit all the way back to the storage silo. Incoming European legislation will stipulate at least two levels of protection against back-burning for pellet burners. Pre-empting this, Clyde already has three levels of protection for the burner— safety shut-off valves on the fuel feed, an internal water sprinkler system and physical disconnection of the pellet supply.
The cost of a domestic biomass boiler depends on the type and size of system. As an example, the Energy Savings Trust (EST) estimates that you need a 20 kW wood pellet boiler to supply heating and hot water for a three-bedroom semi-detached house. The installed cost of such a system is currently around £5000, which is more than a corresponding condensing gas boiler. However, the biomass boiler could deliver annual savings of up to £350 in energy bills and save between six and seven tonnes of CO2 per year.
Environmental targets and rising fuel bills are also prompting interest in biomass from schools and colleges. While some are also considering solar power and wind turbines, a wood-pellet boiler has the advantage of providing energy on demand regardless of the weather conditions. According to the EST, a typical small primary school is expected to have an annual heat usage of 50 MWh, so switching to biomass boilers could save thousands of tonnes of carbon dioxide emissions every year in this sector alone.
There is little doubt that demand for environmentally sensitive approaches to domestic and commercial heating and hot water is set to grow in our bid to delay the damaging effects of climate change. As developers of a range of sustainable-energy products, we are finding that biomass boilers are proving one of the most popular options.
However, it is important that the industry does not see this market simply as a huge sales opportunity. For renewable energy to be truly successful in the UK it is essential that companies offering these products take the time to look at the overall requirements of each application and consider the practicalities of the system before securing a sale.
Stephen Laws is technical director with Clyde Energy Solutions