What is biomass?

BIOMASS OVERVIEW

Biomass is a renewable energy source that is obtained from living or once living material including wood, grass, wheat or suitable waste materials. Biomass is mostly used in the production of heat and the generation of electricity. When burnt, biomass sources release CO2, equivalent to the amount that a plant would release when it dies and decomposes. Hence, the carbon released has a limited effect on the environment as it is a part of the natural carbon cycle. This is unlike fossil fuels which continually increase the carbon levels in the environment when burnt.

The history of biomass heating is mainly based on basic biomass log stoves which were very high maintenance and not very energy efficient for the amount of warmth that they generated. Technological advancements have seen major improvements to these biomass devices which are now capable of operating at efficiency levels of over 95% which is comparable to modern oil-fired and gas-fired boilers.

If oil is currently used to fire a central heating boiler, biomass is the closest alternative renewable technology as the appliances operate in a very similar way but with lower CO2 emissions and residues.

Biomass for heating can take many forms but the main ones are likely to be wood chip or wood pellet. People have been producing energy from biomass for centuries, and in many parts of the world it is still the principle source of heat. However modern technologies are far more efficient and cleaner than the traditional open fire and there are an increasing number of fuels are being used namely logs, wood chips, wood pellets and wood briquettes.

Energy from biomass refers to energy produced from organic matter of recent origin. This excludes fossil fuels which have taken millions of years to evolve. 

Biomass is also referred to as ‘Bioenergy’ or ‘bio fuels’ (in terms of renewable energy). 

‘The Definition of Biomass’

 “Any solid, liquid or gaseous fuels produced from organic materials either directly from plants or indirectly from industrial, commercial, domestic or agricultural wastes”

However, we are only concerned with woody biomass. Producing energy from wood brings environmental and economic advantages both nationally and locally and has considerable potential within the UK. Biomass heating systems, unlike other renewable energy sources, do emit carbon dioxide. However, it is the carbon dioxide (CO2) taken from the atmosphere by trees for photosynthesis that is released during burning. This closed CO2 cycle means that biomass heating is considered a renewable energy source, and therefore eligible for the Renewable Heat Incentive (RHI).

For sustainably managed woodland, or energy crops, the process is similar. 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 absorbed by new tree growth.

Biomass heating systems in reality create small net emissions of CO2 to the atmosphere

through operations including harvesting, transport, processing and the construction and

commissioning of the boiler. Wood fuel emits 25 grams of CO2 per kilowatt-hour (g/kWh); Wind Energy emits 8g/kWh; gas emits 194g/kWh; oil emits 265g/kWh and coal emits 291g/kWh.

BIOMASS BOILERS

Biomass boilers generate hot water in the same way as conventional fossil fuel boilers and may therefore be used in much the same way with respect to boiler temperatures and pressures. Because they have a live fire within the combustion chamber, which cannot be turned on and off like a gas-fired boiler, they require a heat sink in which to dissipate excess heat when the demand is no longer there. It is therefore usual to combine biomass boilers with an accumulator, or buffer tank, which absorbs the energy from the biomass boiler and firing of the biomass boiler, is controlled by the rate at which energy is taken from the buffer tank.

The use of a buffer tank also allows the biomass boiler to be sized according to the maximum heating load which might be expected for, say 90% of the heating season, with the remainder of the heat load during peak demand times being met from the buffer tank. 

Other fuels are possible, such as miscanthus or oil seed rape cakes, and boilers are available which are capable of being adapted to different fuels, but care should be taken in considering such flexibility as it adds to the cost of the plant and conversion from one fuel to another will normally require recommissioning.

Biomass boilers require a conventional chimney flue, which can either be a simple stainlesssteel flue taken through the roof, or connected into an existing brick chimney, as long as it complies with statutory requirements.

Bioenergy is expected to play a key role in our ability to meet the 2020 renewables target as well as longer term carbon reduction targets to 2030 and 2050. Our analysis suggests that Bioenergy could account for up to half of the renewable energy required to meet the 2020 renewables target.

HOW DO MODERN BIOMASS BOILERS WORK?

In the case of wood chip and wood pellet boilers, the fuel is fed automatically into the boiler from the fuel store using an auger screw system. The fuel then burns in the combustion chamber, where a regulated flow of oxygen ensures a clean and efficient combustion process. The resulting hot gases then heat water in a heat exchanger which feeds the hot water storage tank, or for smaller stoves a back boiler, and ultimately the heating circuit (radiators in most cases).

Biomass boilers are as controllable as modern gas condensing systems; heating controls allow the user to adjust all personal parameters for the central heating and domestic hot water. 

Some controls even allow the user to switch on the boiler remotely via text messaging.

For more information about biomass boielrs for your business please contact Philip Smith-Lawrence psl@constantenergy.co.uk 0161-848-0027.