The International Energy Agency (IEA) has published a Insights on the effects of domestic heating with biomass on air quality. Among its conclusions, the analysis highlights that modern biomass boilers and stoves meet strict emission limits when used appropriately, although it predicts an increasingly stringent adjustment of them at legislative level in the EU.
Ensure low emissions
The combustion of solid biomass can emit several pollutants in the air, which has caused that the heating with biomass in the residential sector has been seen with suspicion at times.
The emission levels of residential heating vary significantly according to the team, how it is operated and the characteristics of the biofuel used.
For example, open fireplaces and traditional wood stoves generate high emissions of air pollutants and their use should be discouraged in urban areas for air quality reasons, according to the IEA analysis.
In contrast, modern biomass boilers and stoves meet strict emission limits when used appropriately.
What air pollutants does the combustion of solid biomass emit?
The combustion of solid biomass can release volatile organic compounds (VOC) and particles (carbon from biomass, soot and tar). Incomplete combustion also emits carbon monoxide (CO).
In addition, the combustion of solid biomass produces gaseous pollutants such as NOx and SOx and, if the wood is contaminated with heavy metals and organic chlorine compounds, they can emit even more pollutants.
In large biomass installations, flue gas cleaning equipment can reduce emissions to acceptable levels when properly designed.
In small-scale heating, uncontaminated woody biomass is commonly used. In the header image, the typical organic carbon (OC) and particulate (PM) fractions are shown according to different biomass heating technologies.
Better biomass than fossil fuels
Fossil fuels for heating, especially coal, produce high emissions of air pollutants.
For example, coal combustion for residential heating can cause PM emissions from 20 to 430 g / GJ (Butcher and Ellenbecker, 2012), and higher emissions of sulfur dioxide (SO2) than biomass fuels.
The analysis also notes that the particulate emissions of natural gas are lower than those of solid biofuels.
How to improve the efficiency of household equipment
The complete combustion of the biomass minimizes the release of pollutants into the air.
Ensuring complete combustion requires ideal mixing of combustible gases and combustion air, adequate air-fuel ratio and residence time in the combustion chamber and sufficient flame temperature.
To solve the consequences of incomplete combustion there are secondary measures, such as catalytic converters and electrostatic precipitators, which reduce emissions.
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Manual and automated equipment
The way in which the heating equipment works greatly influences the emissions, especially in boilers and stoves operated manually.
In manual systems, the ignition, the amount of biofuel introduced in the combustion chamber and the level of combustion air supplied must be administered with great care, in accordance with best practices, to minimize emissions.
The manual management of these conditions to ensure almost complete combustion is complicated, so that actual emissions can significantly exceed those defined under test conditions.
This highlights the importance of considering real-world operating conditions when developing emission standards.
The automated devices more sophisticated can maintain the necessary conditions for achieve a almost complete biomass combustion and, therefore, generate very low emissions when they are operated properly.
The relevance of biofuel quality
Using appropriate biofuels is also key. To keep emissions at low levels, the moisture content, size and ash content of the biofuel must be appropriate.
The application of quality standards for biofuels, such as ENplus® for wood pellets, and for combustion and emission measurement systems, they can further minimize the impact of residential heating with biomass on air quality.
The legislation that comes: more restrictions
In 2017, the European Commission announced the imposition of infractions against 16 member states for excessive levels of PM10 (solid particles with diameter less than 10 μm).
Consequently, it is likely that regulations, monitoring and the obligatory nature of meet emission levels become stricter for residential heating systems with solid biomass.
Italy, which has the largest market for domestic pellet heating equipment in Europe, has recently approved new legislation to classify biomass stoves according to the level of polluting emissions.
Heating with solid biomass offers a renewable alternative and with fewer carbon emissions than systems based on fossil fuels, but It is possible that European policies will increasingly require a progressive limitation of emissions.
Objective: further reduce emissions
Minimize emissions through use of sophisticated technologies, having a proper selection of biofuel and implementing the better practices will be key to the future of the residential biomass heating market.
This is already evident in countries such as Germany, the Netherlands or France where eligibility for subsidies to install biomass boilers is related to minimum emission criteria.
More information www.iea.org