What is a Biomass System?
Biomass is a form of stored solar energy and although burning biomass releases carbon dioxide into the atmosphere, this is offset by the carbon dioxide absorbed in the original growth of the biomass, or captured by the growth of new replacement biomass. It is therefore seen as a very low carbon energy source, especially when compared to traditional forms of heating such as gas, oil or electricity.
A Biomass system is a boiler that is designed to burn solid fuels classed as biomass and normally the most popular biomass fuels are wood chip and wood pellets. Biomass heating systems can be used for space heating of buildings, hot water production and steam production. In terms of scale they can range from small domestic systems of say 10kWth through to medium systems of 50kWth to several MWth and to industrial or district heating systems of up to hundreds of MWth.
One of the key aspects of a Biomass boiler is that they operate most efficiently and are most reliable when operating continuously. For these reasons biomass boilers are very well suited to meeting the continuous heat loads of buildings such as hotels, nursing homes, swimming pools, and schools. They are also applicable to industrial operations that have constant heat demand.
Overall Biomass can play a significant role in helping the country meet a range of renewable energy and greenhouse gas emission reduction targets.
Benefits of a Biomass System
Biomass fuel costs are typically lower than the fossil fuel being replaced. The scale of savings depends on the price of the fossil fuel being replaced and the cost of the biomass fuel used. When replacing oil, LPG or electric heating systems the capital repayment can be quick and the savings significant.
Research indicates that using biomass for heating can typically give reductions in carbon emissions of around 90% relative to using fossil fuel heating systems.
Fuel Price Stability
When compared to fossil fuels biomass fuel prices are more stable and less affected by worldwide events. Although there will be some changes these are likely to be less extreme and more manageable than fossil fuel price changes.
Components of a Biomass System
The main components of a Biomass boiler system are:
- Biomass plant - the boiler
- Fuel and fuel store
- Method for getting the fuel from the store into the boiler
- Ancillary equipment - e.g. Buffer vessel/accumulator - required for the majority of installations
Biomass Boiler Plant
Biomass plant can range from small manually fed systems with few controls to fully automatic systems with sophisticated controls and monitoring facilities. Currently there is a wide range of biomass boilers to choose from, with the majority being from Europe. Several boilers can burn both wood chips and wood pellets, although generally those that are designed for pellets cannot be used for wood chips. Some of the key features of boiler plant are as follows:
- Automatic ash removal
- Sensors to constantly monitor flue gasses and enable automatic adjustments to combustion controls in the event of changes in the fuel
- An automatic fire flap or similar feature in the fuel feed to eliminate burn back
- An overheating cut out
- A robust fuel feed system
- A comprehensive set of controls to maintain optimum performance
- Plant that has been designed for minimal maintenance
Biomass Fuel and Fuel Store
The main types of biomass fuel are wood chips and wood pellets. The main characteristics of these are the moisture content, which determines the energy content (i.e. the calorific value) and the particle size/grade.
The cost of the biomass fuel is determined by the following:
- Type of fuel
- Market availability
- Quality of the fuel
- The form the fuel is delivered in
- Proximity of fuel source to the point of use
In terms of fuel store these can be in several types:
- Dedicated fuel store - above or below ground
- Integrated facilities within the building
- Removable external storage containers
For large systems the fuel (e.g. wood pellets) is normally delivered by a dedicated fuel supplier, typically in a 20 ton wagon, directly into the fuel store. The pellets are 'blown' into the fuel store and transferred into the combustion grate of the boiler via a mechanical handling system (e.g. screw auger).
Biomass boilers are best being operated more or less continuously (ideally between 30 and 100% of the rated output). The consequence of this is that a heat store (buffer vessel/accumulator) is often required to manage peak demands. Ultimately the exact design is determined by the site heat load and reaction times required.
Other ancillary equipment associated with a Biomass boiler includes connecting pipe work, ash extraction, fire dousing system, control and monitoring systems.
The type and size of flue required is determined by the type and size of boiler, the local authority requirements and the types of building surrounding the site.