Biomass boilers

The burning of wood in heating appliances results in the release of pollution emissions that can have an impact on air quality in Mid Devon.

The actual levels of emissions in the flue gases depend on the biomass boiler design, the fuel characteristics and how the boiler is operated. The impact of emissions on the environment, in particular local receptors, is related to the dispersion of emissions influenced by the height of the boiler exhaust stack.

We have powers under The Clean Air Act 1993 to request the measurement of dust emissions from biomass boiler exhaust stacks and can enforce the installation of arrestment plants to control dust emissions. The Clean Air Act 1993 is primarily aimed at controlling smoke, grit and dust. The legislation does not serve to mitigate fine particulate matter emissions.

The technical details of the biomass boiler, emission concentrations, fuel specification, fuel storage and delivery arrangements in addition to a determination of stack height must be submitted to us for approval. Our Biomass Boiler Information Form should be completed and included with your planning application, if planning permission is required. Please see our Planning webpages for more information on planning applications.

Pollution control legislation applicable to biomass boilers

The operation of a biomass boiler may require regulation under the Pollution Prevention and Control Regulations and the Waste Incineration Directive depending on the size of the boiler and type of biomass fuel, see the table below. For example, waste wood that has been treated with preservatives or coatings may potentially have high levels of heavy metals, halogenated compounds, generate dioxins and furans respectively. The combustion of this type of wood is regulated under the Waste Incineration Directive.

Biomass boilers using waste wood from timber merchants or forest residues require regulation as LAPPC Part B Installations under the Local Authority Pollution Prevention and Control (LAPPC) regime. Larger boilers are regulated by the Environment Agency as A1 installations. The Integrated Pollution Prevention and Control (IPPC) regime is a much broader level of pollution control covering air, land, water, noise as well as energy and waste reduction and accident prevention. A formal application for a permit must be made to us or the Environment Agency, in order to operate these types of biomass boilers, see IPPC – Guide for Applicants.

Summary of pollution control legislation applicable to the operation of biomass boilers

MW = megawatt, thermal.
LAPPC = Local Authority Pollution Prevention and Control.
IPPC = Integrated Pollution Prevention and Control (Environment Agency).
WID = Waste Incineration Directive (Local Authority and Environment Agency)

For more information on LAPPC and WID please see Regulated Installations .

If your boiler is regulated by the Environment Agency, visit their website for further information.

Best practice for controlling pollution emissions from biomass boilers

We have identified a number of best practice techniques for controlling emissions from biomass boilers related to fuel use, boiler design and operation. We require these measures to be adopted at new development sites that include biomass boilers as renewable energy sources.

Fuel use

The characteristics of the fuel used in biomass boilers have an important influence on pollution emissions. These include the origin of the fuel, chemical and physical properties. The use of quality wood fuel benefits reductions in pollution emissions from biomass boilers. This can be achieved through the use of wood that complies with biomass quality standards such as CEN/TC 335 and ONORM. The fuel specifications and classes for all solid biofuels are set out in CEN/TS 14961:2005, which defines certain chemical and physical parameters and property classes.

We require wood fuel used in biomass boilers to meet recognised fuel quality standards in particular CEN/TS 14961:2005.

Generally wood fuel of a consistent size and density is more favourable in terms of lower pollution emissions; wood pellets display these characteristics. Fuel quality control must be considered to guarantee that a constant supply of good quality wood is delivered and used throughout the operation of a biomass boiler.

Boiler design specifications

Matching fuel specification and biomass boiler design

There are various types of biomass boilers such as underfeed stoker boilers, moving or reciprocating grate boiler and plan grate boilers. It is important that the biomass boiler combustion system is applicable to specification of the wood that will be used in the boiler. Consideration should be given to moisture and ash content of the fuel, whether this is wet or dry and the type of fuel e.g. straw, wood chips, wood pellets or briquettes.

Biomass boiler standard

BS EN 303-5:1999 applies to heating boilers for solid fuels, hand and automatically fired, nominal heat output of up to 300kW. This standard covers properties such as performance, efficiency, emissions, thermal output, pressure testing, safety measures and testing. We require biomass boilers <300kw to meet the efficiency standards of EN303-5:1999. Boilers >300kw should have an efficiency rating above 85%.

Boiler design features

There are various biomass boiler design parameters that optimise combustion and ensure continuous performance. The technical design features below are considered best practice for controlling emissions to air:

1. combustion chamber design and provision of secondary air supply
2. combustion air control technology - Lambda sensor
3. flue gas recirculation
4. automatic de-ashing
5. heat-exchange cleaning
6. automatic fuel feed system
7. automatic ignition
8. variable load management and modulating ability, including the use of an accumulation tank
9. particulate matter arrestment plant such as multi-cyclones or a ceramic filter

Boiler operation

The biomass boiler, abatement technology and stack should be associated with a written maintenance schedule and in accordance with the manufacturer's instructions. This will ensure continued performance and control of emissions. The biomass boiler should be serviced at least once a year by a trained service engineer. Staff operating and maintained the boiler should receive appropriate training and instructions from the boiler manufacturer.

Fuel delivery, storage and handling

There should be sufficient space for storing fuel inside buildings and for most dry biomass stores, good ventilation. This will be necessary to prevent the build up of condensation, allow additional drying and to prevent the formation of moulds; the spores of which can present a serious health hazard if inhaled.

Consideration must be given to how the delivery of fuel into the store will take place. This typically requires both vehicular access and a convenient way to transfer the fuel from the delivery lorry into the store.

With some fuels such as wood pellets, it can be important to ensure that they are not handled too roughly as they can disintegrate into sawdust, which may cause difficulties for combustion. It is generally considered best practice to minimise the number of handling steps with wood pellets.