Biomass Heating and Boilers

Emissions & CAA

emmisionsThe Clean Air Acts
Because of their efficiency, the range of HDG boilers produce just a fraction of the emissions limit imposed by the Clean Air Act, and most of the commercial range are listed as "exempt appliances".

The Clean Air Acts of 1956 and 1968 were introduced to combat increasing smog pollution in cities and large towns. The Act gives local authorities powers to control emissions from industrial premises and to create "smoke control areas" where smoke emissions from flues are prohibited. They are in place in many towns and cities in the UK and have lead to a major reduction in smoke and sulphur dioxide emissions over time.

An offence can be to emit smoke from a chimney of a building, furnace or boiler, or to acquire an "unauthorised fuel" unless it is used in an "exempt" appliance.

The local authority Environmental Health Officer is responsible for enforcing the legislation in a smoke control area. However the Officer can approve the installation of a biomass boiler if satisfied that the appliance will not emit smoke and indeed, this is almost always the case.

This is because the measured output of a commercial sized boiler with 400 kW output (Endress VR-W burning wood chip) shows a full load emission of 13.7g/hr, which is approximately 2% of the 700g/hr limit for a boiler of this size.

In addition, all HDG commercial biomass boilers are "exempt appliances" as defined by the Clean Air Act and suitable for installation inside Smoke Control Zones.
NOx Emissions
Due to the high temperatures at which combustion takes place in a biomass boiler, nitrogen oxides (NOx) are emitted. Nitrogen oxides contribute to global warming in the upper atmosphere and to acid rain, which can damage trees and even entire forest ecosystems. However, the relative output of NOx per kWh of biomass is lower than that produced by other fuels including natural gas and oil, and if we include emissions in production, electric heating.

The aim of BREEAM (Building Research Establishment Environmental Assessment Method) is to reduce the emission of nitrogen oxides into the atmosphere. In general buildings can be assessed for their harm to the environment and standards are set to improve new buildings by reducing the level year by year.

In fact biomass NOx emissions are considered low enough per kWh of heat produced to not only be a neutral influence on the overall BREEAM rating, but get close to providing a credit in the assessment against other environmentally negative influences.

This may not continue as standards increase, but biomass is clearly a positive way to restrict the NOx production overall.

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