Biomass fuels have numerous characteristics that can affect the performance of a boiler system. The three that influence the performance the most (and which also affect costs) are calorific value, moisture content and particle size.
Wood pellet fuel is very dry, with 6-10 percent moisture content. It therefore has a higher calorific value compared to wood chips, which have a moisture content of 25-50 percent. As they are made from compressed sawdust, pellets are more homogeneous and therefore exhibit more consistent combustion characteristics.
The European Committee for Standardisation (CEN) is developing a standard (CEN/TC 335) that will specify typical standardised characteristics for a number of biofuels within the European Union. The quality of some fuel products, for example woody pellets, are already specified according to DIN 51731 or ONORM M7135.
A crucial consideration is the size of the fuel store and the volume of deliveries. This depends on the size of the system. Fuel for a wood-chip boiler system should be stored for one to two weeks. This allows flexibility in the supply chain.
The costs of running a biomass heating system can be significantly lower than that of a fossil-fuel based system. Arguably, this depends solely on the type of fossil fuel.
Wood-chip fuel is currently available at £75 - £90 per metric tonne, depending on the quality of the fuel. Generally, based on a 35 percent moisture content and an 85 percent boiler efficiency, this translates into 2 - 4 pence per kWh.
The critical reader will be concerned about the complex and environmentally-negative effects of wood-fuel fired systems - and not without reason. Most of the environmental issues of using wood as a fuel relate to the emissions resulting from their transportation and the air pollution that results from combustion.
Basically, due to its nature, biomass fuel is zero-rated for the EU Emissions Trading Scheme and the UK Climate Change Agreement. This means that the installation of a biomass system will contribute to a company's CO2 targets and environmental compliance.
In addition to this, local planning authorities should be informed about a potential biomass boiler project at the earliest possible stage. The planning authority will be able to advise on the requirements of the Building Regulations and planning permissions. This is particularly important for all non-domestic installations or installations above 45 kW, and environmental issues such as smoke control zones or air quality management areas.
The use of electrostatic filters is the best way of cleaning flue gases, with the highest separation of fine particulates below 30 mg/Nm3. Unfortunately, these filters are also one of the biggest items in terms of capital cost and physical size.