Biomass energy describes heat and power produced from wood, forest and agricultural residues and wastes, and a wide range of organic wastes such as animal slurry and kitchen waste.
What is Biomass Heating?
Modern technology converts biomass to heat, power and liquid fuels efficiently and conveniently. Modern automatic wood heating is very common across Europe, particularly in Austria, Denmark, Sweden and Finland.
Wood and other biomass is a significant resource which, as long as re-growth or replanting takes place, emits no net carbon into the atmosphere as growing biomass absorbs carbon.
An integrated wood fuel and energy production system provides a sustainable and clean approach that has the added advantage of stimulating local woodland management and local economic benefits including jobs.
Why Wood Fuel?
Wood was the first fuel mankind learned to use. The first fires of primitive peoples burned wood for warmth and cooking. It is a natural resource which can be regenerated unlike fossil fuels, which will eventually run out.
Until 200 years ago, wood was the main fuel for heating in the UK, and this influenced much of woodland management. The advent of coal, oil and gas, the use of wood as a serious heating fuel in the UK diminished tremendously.
The last two decades have seen a major industry develop in mainland Europe with hundreds of thousands of high-efficiency, automatic heating systems in service.
The UK and the UK have been exceptionally slow to take up this technology, but, over the last few years, it has become established in the UK and the UK and is now being actively supported by the governments. These systems are rapidly becoming commonplace with examples of installations across the British Isles, from small domestic to large industrial applications.
Is Wood-Burning Carbon Neutral?
Carbon dioxide (CO2) is taken from the atmosphere and used by trees to grow. When these trees die and decay or are burned, this CO2 is released back into the atmosphere.
In a mature, unmanaged forest the amount of carbon being absorbed by growing trees is the same as the amount being given off by decaying dead trees, and by the animals, microbes etc. that live off the trees as they live and die.
For sustainably managed woodland, or energy crops, the process is similar. On balance, wood is never removed faster than it is added by new growth. Therefore the CO2 released when the wood fuel is burned is never more than the CO2 being taken up by new growth. It is therefore termed ‘carbon neutral’.
Do Biomass Boilers Damage Woodlands?
No, a demand for wood-fuel creates a market for timber and wood residues which would otherwise have no market or go to landfill. It can provide financial support to woodland management activity, and have a positive impact on flora and fauna if managed appropriately.
Trees grow every summer using the energy of the sun to fix carbon from the atmosphere. Every woodland has a sustainable yield of timber, which can be harvested indefinitely without depleting the resource in any way. Wood is carbon neutral and does not contribute to greenhouse gases.
Burning wood in a biomass boiler gives off carbon dioxide just like fossil fuels, but this is balanced by the carbon absorbed by the growing trees. Un-harvested wood will give off the same amount of carbon dioxide when it eventually decomposes as it would have done if burnt in a boiler. Burning wood replaces the burning of fossil fuels, for more information see the Carbon Cycle.
Is Wood-Fuel Clean?
Wood chips and pellets present no risk if accidentally released into the environment, unlike oil which is a serious pollutant and gas which can explode. There are no harmful by-products. The flue gas is smoke-free and the ash content of between 0.5% and 3% by volume (depending on material), is minimal.
Unlike coal ash, clean wood ash is an excellent fertiliser and can be used in the garden or returned to the forest. Modern appliances burn very cleanly with minimal smoke.
How Much Maintenance do Biomass Boilers Need?
Biomass boilers need a lubrication service every 800 hours of operating time and a major service after 2400 hours of operation. In most applications, boilers are not firing all of the time: a school may only clock-up 2400 hours in a year.
Even boilers providing base-load heat will still have 98.5% availability, taking service requirements into account.
How Much Ash is Produced?
Binder boilers are highly efficient, converting the energy contained within the wood fuel into heat, leaving very little ash containing no combustible material. Around 5kg of ash should be expected for every 1000kg wood-fuel consumed. Binder boilers convey the ash to removable trays or bins.
Do Biomass Boilers Smoke?
Traditionally wood was used in open fires or primitive wood stoves, which burned very inefficiently. This not only made it expensive – with up to 85% of the useful heat going up the chimney – but also polluting with smoky fires.
This is still a persistent, if outmoded view of wood burning: modern wood heating is clean, efficient, convenient and cost effective. Modern boilers control the airflow, use thick boiler insulation and re-burn flue gases giving colourless flue gas. Unlike many biomass boilers, most Binder boilers are approved under the Clean Air Act for Smoke Control Areas.
How Safe are Biomass Boilers?
Modern, sophisticated and fully automatic Binder boilers are very safe to operate offering a three-stage protection system:
- A rotary valve forms part of the final fuel dosing system from the fuel transport to the boiler stoker auger. The design is a 5 blade steel rotor with high-density rubber tips. This provides an effective airtight seal, which prevents airflow within the stoker auger and thus inhibits burn back.
- A capillary bulb thermostat monitoring the surface temperature of the stoker auger when activated operates through the boiler PLC such that if the thermostat senses a temperature above its preset setpoint (typically 45°C) the system automatically stops the upstream fuel transport auger and pulse activates the stoker auger to move the burn into the hearth.
- A capillary bulb direct acting thermostatic water valve monitoring the surface temperature of the stoker auger coupled to a static douse tank will if the valve senses a temperature above its preset setpoint (typically 55°C) flood the stoker auger to extinguish the burn back.
Read more about biomass fuel here.