Opinion

Quality control

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The domestic RHI sets out minimum fuel quality standards, without which householders are unable to claim their RHI payments, explains Robert Burke, HETAS

HETAS has been working with Gemserv and Woodsure to launch a biomass suppliers list, so that householders will be able to find a local supplier and meet the RHI criteria.

For domestic users, automatic pellet and chip fired stoves and boilers and modern batch fed appliances mean it’s now possible to provide lower output heating for the smaller home. Using a biomass stove or boiler offers an ideal way for developers to meet their target carbon emissions, and the domestic RHI makes biomass extremely attractive and cost effective especially in rural areas compared to other fuels like oil.

To ensure safe and efficient operation of wood and biomass appliances, it’s essential that a good quality fuel is used. Moisture content has the biggest effect on heat output as any water in the fuel has to evaporate away before the wood or biomass will burn, using up energy and reducing the amount of useful heat as opposed to steam up the chimney.

To help end users identify good quality, sustainable fuel, HETAS certifies the Woodsure accreditation scheme for woodfuel. The scheme has four categories covering logs, chips, briquettes and pellets. HETAS has also been approved as the UK certification body for ENplus by the European Pellet Council (EPC). ENplus is the only Europe wide assurance scheme for pellets which meet the new European standard (EN14961-2) for solid biofuels. As the dedicated certification body for the UKsolid biomass industry HETAS is able to certify both producers and traders under the ENplus scheme.

ENplus certification sets out minimum standards for ash content, ash melting temperature, wood pellet size, dust, moisture content and heat output. Pellets with low ash content will burn more efficiently, whereas high ash levels could point to impurities in the pellets such as bark. A low ash melting temperature below 1200°C could lead to clinker, potentially damaging the appliance.

Having a consistent pellet size is important; domestic appliances usually take 6mm pellets whereas commercial boilers take 8mm pellets. Each individual appliance will have been installed and commissioned for a specific pellet diameter, and if the wrong size is used it will affect combustion conditions meaning the boiler becomes less efficient. Wood pellet dust will also affect the appliance by blocking the feed system, and to comply with ENplus wood pellets should contain less than 1 percent dust. ENplus certified pellets should have a moisture content of 10 percent or less and should emit 4800 kW/h of heat per tonne of fuel burnt. Both requirements are important for the safe and efficient combustion of pellet burning appliances.

The scheme also covers distribution as pellets need to be handled correctly in transit, otherwise they can start to break down causing a high percentage of dust in the boiler hopper feed which can clog up the a biomass boiler. All of these issues are addressed by the certification process.

For boiler and chimney manufacturers, fuel quality is also of paramount importance. Burning biomass with high moisture content will reduce efficiency combustion and in some cases affect the figures that manufacturers claim. Installers will get frequent call backs to equipment that isn’t working properly, or is expensive to run. The end result is general dissatisfaction with the boiler or heating system – simply because the end user was not using guaranteed quality fuel.

A full list of approved fuel suppliers is available on the HETAS website at www.hetas.co.uk.