Planning and air quality

Planning and air quality  /  Biomass boilers  /  Air quality assessment

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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 Camden. 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.

The air pollution emissions of concern from biomass boilers are particulate matter (PM10/PM2.5) and nitrogen oxides (NOx). Other relevant emissions include poly-aromatic hydrocarbons(PAH) and where treated wood is used as a fuel heavy metals, dioxins and furans can be released.

The whole of the Borough of Camden has been declared an Air Quality Management Area for breaching the air quality standards for PM10 and NO2. The installation of biomass boilers introduces new pollution sources into Camden. Controlling emissions from these heating appliances is imperative to prevent the further degradation of air quality. We require an air quality assessment to be included in planning applications including biomass boilers.

The London Borough of Camden has been designated a Smoke Control Area under the Clean Air Act 1993. In accordance with this legislation no heating appliance, regardless of fuel, may emit smoke in areas designated as Smoke Control Areas without undergoing strict testing and certification to a British Standard protocol.

Installing a biomass boiler in a smoke control area without the relevant testing having been undertaken, and the necessary exemptions having been granted, means the operator runs the risk of prosecution under the Act. Subsequently all biomass boilers operated in Camden must be certified as ‘exempt’ appliances.

We have powers under the Clean Air Act to request the measurement of dust emissions from the biomass boiler exhaust stack and require arrestment plant to be installed to control dust emissions. The Clean Air Act is primarily aimed at controlling smoke, grit and dust, this 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.

The biomass boiler information form below should be completed and included with your planning application.

The information contained in this form will also provide the information we require for approving the boiler in accordance with Clear Air Act 1993.

Guidance on best practise measures to control emission are outlined in the biomass boiler emission control note below.

• download: biomass boiler information request form (PDF 44KB)
• download: biomass boiler air pollution emission control (PDF 48KB)
• help with PDFs

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 Table 1 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 Part B Installations under the LAPPC regime. Larger boilers are regulated by the Environment Agency as A1 installations. The 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.

Table 1: Summary of pollution control legislation applicable to the operation of biomass boilers

Fuel	Plant Size	Pollution Control Regime	Regulator
Biomass fuel arising from natural sources	< 20 MWth	Clean Air Act	Local Authority
	20-50 MWth	LA-PPC	Local Authority
	>50 MWth	IPPC	Environment Agency
Waste or waste derived biomass exempt from WID,	<0.4-3 MWth and < 50 kg/hr	Clean Air Act	Local Authority
	0.4 - 3 MWth and 50 - 1000 kg/hr	LA-PPC	Local Authority
	> 3 MWth and >1000 kg/hr	IPPC	Environment Agency
	> 50 MWth	IPPC	Environment Agency
Waste or waste derived biomass to which WID applied	< 3 MWth	WID, LA-IPPC	Local Authority
	> 3 MWth	WID, IPPC	Environment Agency

Best practice for controlling pollution emissions from biomass boilers

National guidance will be published in 2009 that will outline the best available techniques for controlling emissions from biomass boilers. Until this guidance is produced the London Borough of Camden has identified a number of best practise 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 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 eg straw, woodchips, wood pellets, briquetts.

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 practise for controlling emissions to air:

1. combustion chamber design and provision of secondary air supply
2. combustion air control technology - lamdar 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 a  multi-cyclones or ceramic filter

Boiler operation

The biomass boiler, abatement technology and stack should be associated with 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.

Boiler stack height

The height of biomass boilers exhaust stack must be calculated to ensure effective dispersion of pollution emissions. Stack height approval is a requirement of the Clean Air Act 1993. We require dispersion modelling to be used to determine stack height and demonstrate the impact of emissions on local air quality. This shall be presented as an air quality assessment with your planning application.

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 deliver 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.

More information

For further information please contact the Air Quality Officer

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Page last updated Oct 24, 2008 3:25 PM