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Biomass/Wood Boilers

biomass2-round-250x250Introduction

Biomass-Vitolig-BoilerBiomass is recently produced organic matter which can be burnt as a fuel and falls into two main categories; woody biomass including forest products, untreated wood products and short rotation coppice, and non-woody biomass including animal waste, food processing waste and high energy crops. For small scale applications woody biomass is generally used, taking the form of wood pellets, chips and logs. Burning biomass can be considered carbon neutral, since the amount of CO2 released is equal to the amount that was absorbed by the plant during its growth.

Technology

Biomass_How It worksThe two main biomass heating systems are stand-alone stoves which may also have a back boiler to provide hot water, and boilers providing central heating and hot water. There are three main types of fuel supply, logs which must usually be loaded by hand, wood chips and wood pellets which can both be automatically loaded from a storage hopper. The automation of loading these burners means less hassle and mess. Wood pellets are a denser form of energy than wood chips and can therefore be stored in a smaller hopper.

Modern wood burning boilers have an efficiency of around 90%, a far cry from traditional open fires which have an efficiency of around 20%.

Considerations

Biomass_Pellet PicStorage space is required to hold the fuel, which tends to become more economical as the quantity delivered increases. This makes it sensible to have the largest store that is practical. Often these stores can be built entirely or partially underground. Access to the store for delivery and transport of the fuel to the boiler/stove must also be considered.

The supply of the fuel is also important. All wood fuel will have some moisture content, but the lower this is the more efficiently it will burn and the more cost effective transportation will be. The carbon footprint involved in delivery should also be considered, the less distance that the fuel has to travel, the lower this will be.

The Clean Air Act provides regulations regarding the burning of wood. If the proposed system falls within a Smoke Control Area then the appliance installed should be chosen from the exempt list.

The flue must be compatible with the system installed, chimneys can be fitted with a lined flue. If the building is listed or in an Area of Oustanding Natural Beauty then planning may be required before fitting a flue.

A well designed system using wood chips can provide heat at approximately 0.8p/kWh which is significantly cheaper than oil, LPG and mains gas, giving a very reasonable payback period.

Okofen 20kW Pellet Boiler