Nigel Jefferson, sales director for commercial and renewable products at Viessmann, responds to Department for Environment, Food and Rural Affairs (DEFRA) update on RHI biomass emissions levels.

"In an update on the Renewable Heat Incentive (RHI) and Clean Air Act issued on Thursday June 7th, DEFRA confirmed that plans published in a paper in August 2011 by DEFRA, DECC and Ofgem are being taken forward.

The paper proposed that support under the RHI is restricted to boilers capable of complying with limits of 30g/GJ particulate matter and 150g/GJ nitrogen oxides.

Viessmann supports this anticipated amendment and is in favour of even stricter proposed EU emissions levels.

Installers and end-users should adopt clean technologies such as cyclonic combustion and Lambda controls which are already available and exceeding the new targets.

The biomass industry has a great future, helped by the introduction of the RHI. Particularly with regard to public sector policy, many new build and refurbishment projects must now consider the use of wood-burning heating.

However, the industry should take heed of concern, backed up by various studies, into the projected environmental impact of biomass boilers and the effects on human mortality in built-up areas.

It must respond by providing the cleanest, most advanced technology, if it is to avoid harming the long-term reputation of biomass as a suitable renewable heating option.

Many forward-thinking boiler manufacturers are already producing boilers that meet the tighter, emerging UK emissions regulations and which even comply with tougher upcoming EU regulations, expected to be 20 mg/MJ for dust.

A core technology that produces the lowest emissions of particulates and dust, and which will help end-users meet the new RHI requirements is cyclonic combustion.

For example, together with Lambda control, a digital modulating output control and KÖB filters, the method is allowing Viessmann’s Pyrot boiler to lead the market with 10 mg/MJ dust emissions (similar to those of an advanced gas combustion system, subject to fuel type) and efficiency levels of up to 92%.

The latest research conducted by Verenum Research, presented to Viessmann, in Switzerland looked at the type of particles emitted from a range of combustion furnaces and found that the emissions were more harmful from poorly controlled furnaces.

The study found that separating gasification and combustion into two distinct zones reduced the pollution levels.

Where a simple wood stove can produce around 2,000 mg/Nm3of CO a two-stage combustor will produce around 50 mg/Nm3but two-stage automatic combustion control only produces around 5 mg/Nm3.

CO is easy to monitor and is an excellent guide to the emissions of PAH, tar, and other toxic emissions.

If the toxicity of the emissions from a diesel car without particle filter is one on a scale then a poorly controlled stove could be as high as ten. In comparison, a modern automatically controlled two-stage furnace with Lambda control would be less than 0.2.

Yet there are many log and some larger pellet boilers on the market that are of a fairly crude design, without Lambda control, that claim to offer adequate combustion by maintaining flue gas temperature control only.

Installers and end-users are advised to search for these product features when specifying biomass boilers, not only to meet the latest policy changes if they are to take advantage of the RHI, but also the tightening of emissions levels in the future."