Biomass Boilers,CHP, Steam
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Guide to burning waste wood



What is Waste Wood?


Virgin timbers are not waste wood and not subject to special regulatory controls (i.e. subject to normal biomass emissions controls) when burned as fuel in appliance.


However where virgin timber is mixed with waste timber, or any other waste, the mixed load is classed as waste wood.


Non virgin timber such as off cuts, shavings, chippings and sawdust from the processing of non-virgin timbers (whether un-treated or treated) are waste wood.


Un-treated non-virgin waste wood, despite not having been treated with any chemicals, is waste wood.


Treated non-virgin timber is any timber that has been treated (e.g. to enhance the performance of the original wood) or made into panel board of any sort is waste wood.


The Categories of waste wood


The wood recycling industry grade waste wood into four grades A, B, C and D as follows:



Material Description

Typical source

Typical Materials


Non treated, Non Virgin

Distribution, Retailing and Packaging.

Secondary manufacture e.g. joinery.

Pallet reclamation


Visibly ‘clean’ recycled waste wood mainly from packaging waste, scrap pallets, packing cases and cable drums, and process off-cuts from the manufacture of untreated products.


Treated, Non Virgin

As Grade A plus construction and demolition operations, transfer stations

May contain Grade A wood together with other waste wood sourced from construction and demolition activities, transfer stations, civic amenity sites and the manufacture of furniture from solid wood


Treated, Non Virgin

All the above plus municipal collections, recycling centres, transfer stations and civic amenity recycling sites.

May contain the above grades of waste wood and from similar sources, but will predominantly consist of panel products such as chipboard, MDF, plywood, OSB and fibreboard.


Treated, Non Virgin and


All the above plus fencing, track work and transmission pole contractors.

Is hazardous waste consisting of wood which has had copper, chrome, arsenic (CCA) preservation treatments and creosote. It can only be disposed of by incineration or hazardous waste landfill.


Permitting requirements for burning waste wood in England & Wales


The relevant legislation is The Environmental Permitting (England and Wales) Regulations 2010). This replaces the former Pollution Prevention and Control (PPC) and Waste Management Licensing Regulations (WML).


The Environmental Permitting Regulations (EPR) enact the EUs “The Waste Framework Directive” and the “The Industrial Emissions Directive” (IED). The IED is a recast of “The Waste Incineration Directive” (WID), “The IPPC Directive” (IPPC) and “The Large Combustion Plant Directive” (LCPD).


There are still many industry references to WID, PPC, LA-PPC etc. but these are now all encompassed by the EPA. The table below shows the new legislation and the previous equivalent regulations.



New Legislation

Former Regulation



EPR Part A

IPPC Part A1


IPPC Part A2

EPR Part B


EPR Schedule 13







Permit Exemption


Permit Exemption is available for small appliances burning lass than 50kg/hr (0.4MW) where less than 5 tonnes of fuel are stored on site and where the operator is burning its own waste. EPR Schedule 3, Part 1, Chapter 2, Section 2 Burning of waste as a fuel in a small appliance (U4)


Part A Permit


A Part A permit is obtained from the Environment Agency (EA) and applies to Combustion Activities in categories from 20 to 50 MWth and above 50MWth (Large Combustion Plant) and will require Continuous Emissions Monitoring (CEMs).


Part B Permit


A permit for activities listed in Schedule 1 Part B of the EPA can be obtained from the Local Authority (LA)


The table below provides a summary of the Permitting requirements.



Plant size

Pollution Control Regime


Biomass fuel arising

From natural sources

< 20 MWth

20-50 MWth

> 50 MWth

Clean Air Act

Sch.1 P2,Sect.1.1 Part B

Sch.1 P2,Sect.1.1 Part A(1)




Waste or waste derived

Biomass exempt from WID (IED) (untreated wood)

<0.4 MWth (50kg/h)

0.4-3 MWth (50-1000kg/h)

>3 MWth (>1000kg/h)

>50 MWth

Clean Air Act

EPR (Part B)

EPR (Part A)

Sch.1 P2,Sect.1.1 Part A(1)





Residues for which WID (IED) applies (treated wood)

< 3MWth


SWIP Schd.13A, IED Ch. IV

EPR (Part A) IED Ch. IV





What type of boiler is required?


It is possible to burn Grade A, or possibly Grade B, waste wood in a standard industrial biomass boiler (subject to any additional emissions controls to comply with permitting requirements) but Grade C (or possibly Grade B) may require what is known as a WID compliant boiler. Although the WID regulations have now been amalgamated into the IED a boiler that complies with the requirements of the IED (to hold the combustion gases at a temperature of 850°C for a minimum of 2 seconds) it is generally referred to as a WID compliant boiler. A WID compliant boiler is larger and more expensive than a standard industrial biomass boiler.



Type of boiler required for a process where a Part B permit is required


Industrial Biomass Boiler


Industrial Biomass Boiler WID (IED) Compliant may be required


Industrial Biomass Boiler WID (IED) Compliance will be required


Hazardous Waste Incinerator – Part A Permit required


Please note the above is a guide to the boiler type in respect of the combustion process and not the requirements with regard to emissions where additional equipment (e.g. mesh filter) and ongoing emissions monitoring (e.g. annual or Constant Emissions Monitoring (CEMs)) may be required subject to any requirements that satisfy the terms of the Part B emissions Permit.


The Permitting Process


The first step in the process is to establish which category the waste wood falls into and then make the necessary application. As a basic guide see the table below:


Regarding the process to obtain emissions permit, these are the basic steps:


  1. Undertake a regulatory review of the burning of waste biomass as the basis of any pre-application discussions with Local Environmental Health officials, about the requirements for permitting, and to discuss specific issues associated with the operation of the biomass boilers. This can be particularly important in some areas if there are Air Quality Management Area for Nitrogen Dioxide (NO2) or fine particles (PM10).  This could have implications for the height of the chimney and control of particulate emissions (multi-cell cyclone vs ceramic filter); 
  2. Review details of the proposed biomass boiler installation at the particular site. Information relating to the proposed installation, layout plans and elevations drawings, the type and quantity fuel to be burned, the locations of the boilers on-site, etc.
  3. Confirm the requirements for the height of the chimney using the D1 calculation procedure approved for use by Local Authorities, and undertake a DEFRA biomass screening air quality assessment to determine whether there is a need for detailed assessment using atmospheric dispersion modelling. The DEFRA biomass screening assessment would utilise current estimates of background air quality for the local area and the chimney dimensions determined by the D1 calculation.
  4. Complete the Part B permit application form for the biomass boiler and prepare a series of technical appendices based upon the questions in the Part B permit application.


Emissions Abatement and Monitoring

Increasing the chimney stack height can allow a greater dispersion of pollutants and therefore it may be possible to achieve compliance with Permit requirements by adjusting the stack height to achieve the required emission concentrations at ground level (see note 3 above regarding D1 calculation procedure). However where it is not possible to achieve emissions requirements with stack height additional abatement measures will be required.

Binder biomass boilers are equipped with Cyclones which ensure that they comply with emissions for RHI and Clean Air Act on standard biomass fuel (pellets and woodchip) but to comply with Part B Permit emissions on waste wood fuel it may be necessary to provide additional particulate abatement equipment such as:

  • Mesh Filter (also referred to as bag filters)
  • Ceramic Filter
  • Electrostatic Precipitator
  • Wet electrostatic precipitator

Where levels of nitrogen in the fuel can lead to high NOx emissions these can be effectively reduced with the use of Selective Non-Catalytic Reduction (SNCR) equipment which injects Urea or Ammonia into the flue gases.

In addition to the abatement equipment there may also be a requirement to provide emissions monitoring



Emission Limit

Monitoring requirements


< 1MW 250 mg/m³

> 1MW 150 mg/m³

Continuous with alarm

Disregard 30 mins from cold start


60 mg/m³


Continuous with alarm



400 mg/m³


Witness at commissioning

Organic compounds

20 mg/m³


Manual annual test

Chlorine (Hydrogen Chloride)

If burning paint or coated wood where WID does not apply

100 mg/m³


Manual annual test

Hydrogen Cyanide

If burning melamine faced wood

5 mg/m³


Manual annual test


If burning plywood, chipboard, fibreboard

5 mg/m³


Manual annual test


The above comments are for general guidance and the requirements for specific projects should be evaluated on a case by case basis. Please call our technical dept.