PG1/12(04) - Wood Combustion

  
  PG1/12 sets emission limits for wood burning boilers between 0.4 and 3 MW -  roughly equivalent to feed rates of 90 to 600 kg/hour. Plant which is smaller than this limit is subject to much lesser controls - principally through the Clean Air Act (e.g. avoiding dark smoke) and the Environmental Protection Act (avoidance of nuisance odour or soot). Hence the large number of plant specified at 0.35 MW in the UK.

Boiler plant which falls inside the thresholds of PG1/12 is expected to comply with the guidance note requirements. Relevant requirements will be summarised in the site specific authorisation (soon to be called a permit) which is issued by the local authority (England and Wales) or Scottish Environmental Protection Agency.

The main requirement of PG1/12 revolves around the control of certain emissions. The 1995 note sets the following limits:

Total particulate matter

200 mg/m3

Organic compounds

20 mg/m3

Carbon monoxide for existing processes

              ... for new appliances <1MWth

              ... for new appliances >1MWth

*

250 mg/m3

150 mg/m3

Formaldehyde

5 mg/m3

Hydrogen chloride

100 mg/m3

Hydrogen cyanide

5 mg/m3
*Emission limits for carbon monoxide for existing plant were suspended in 1995 and are currently agreed on a site specific basis.

Carbon monoxide

The limit for CO has changed a number of times. It was initially set at 400mg/m3 but this limit was removed in a 1995 revision due to the concerns of the cost to industry of meeting such standards. Consequently, for plant installed before the 1995 revision was published (known as "existing" plant), CO limits are agreed on a site specific basis according to the level which can be achieved.

Plant installed since 1995 has a CO limit of 150 mg/m3. There are few problems meeting this limit with modern boiler plant designed to achieve such levels. The second limit of 250 mg/m3 is largely irrelevant as the diseconomies of scale associated with continuous monitoring costs mean that plants are typically either specified at 0.35 MW (to fall outside the regime) or at 1.3 MW.

The working drafts of the 2004 consultation draft proposed a tightening of CO emissions for existing plants to 150mg/m3 for plants rated >1MW. Work by BFM Ltd showed that 75 to 90% of such existing plant could not meet such levels. Therefore, operators of such plants would be faced with a stark choice:

  • Rely on the co-operation of the local regulator to use their discretionary power to allow a higher level of CO emission in the authorisation

  • Replace the boiler plant

  • Close the boiler plant, burn fossil fuel and send waste wood to landfill.

The first option is far from reliable and, with the current state of the sector, few furniture sites have sufficient funds to afford £300k to £500k for a new boiler plant. Therefore, the main impacts of the proposed tighter CO limits are likely to be the reduced competitiveness of the UK furniture sector and an increased environmental impact. The move would also provide further encouragement for the shift of more production overseas to unregulated economies.

The revised 2004 note retained the existing CO limits, though it is noted in section 2.3 that "a review by industry of existing combustors and their emissions is underway. The emission limits .... may be revised in the light of that review. Publication of any revised limits is expected before the end of 2004. In particular the carbon monoxide limit for pre1995 plant is being examined." The review by industry referred to in this paragraph is the Benchmarking wood combustion study by BFM Ltd.

Board material burning

Limits on formaldehyde, hydrogen chloride and hydrogen cyanide are also applicable to wood burning. These will only be relevant to sites burning treated timber based products, e.g.:

¨           Formaldehyde from chipboard, plywood, fibreboard and similar material

¨           Hydrogen chloride where painted or PVC coated wood is burned

¨           Hydrogen cyanide from melamine faced wood

Few if any sites have problems with these three limits. However, it is worth stressing the importance of avoiding the production of hydrogen chloride. This gas is produced through the burning of PVC such as edge-band trimmings. HCl rots the internal workings of boiler plant. Furthermore, plant which burns PVC will be subject to the EU Waste Incineration Directive and conventional boiler plant could not meet the associated emission limits.