Reduction of PM Emissions from Biomass Combustion Appliances: Evaluation of Efficiency of Electrostatic Precipitators

Abstract

Particulate Matter (PM) emissions from small scale appliances burning wood fuels used for domestic heating is one of the major environmental issues in many European areas. Biomass combustion leads to the presence of high concentrations of PM10 measured in ambient air, especially during the winter season and in those areas where wood stoves and fireplaces are the main heating systems. In this study the efficiency of PM abatement of small scale electrostatic precipitator (ESP) are measured and compared for different appliances. In particular two different commercial systems specifically developed for domestic stoves have been tested in connection with different kinds of appliances; the two devices differ from their electrode length. Particle emissions were measured upstream and downstream of the ESPs to evaluate the efficiency of the devices. Both the devices have been used in connection with an 8 kW pellet stove and a 25 kW pellet boiler; the ESP with shorter electrode has been tested also with an advanced wood stove. Beech wood logs and a low quality pellet have been used in the tests. The gas composition of the fumes have been determined at the exit of the appliances in order to estimate the combustion performances of the stoves and boiler, in particular the amount of oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), nonmethanic gas phase hydrocarbon (VOC-NMet) have been measured. ESPs are specifically devoted to reduce particulate matter concentration in gas streams and their efficiency is dependant on particle resistivity and then it may change with the composition of the particle emitted. Another factor that can affect the efficiency of ESP is the level of fouling of the active surfaces and hence the aging of the precipitator may strongly reduce the abatement. These effects have been studied in the present work by measuring the mass concentration of total particulate matter and the total number concentration (TNC) of nanoparticles (with an aerodynamic diameter between 5.6 and 560 nm) in the different appliances with different fuels and under different operating conditions; in particular aging tests have been carried out to simulate the typical usage in a domestic installation. The test results show a good rate of abatement both on PM and nanoparticles for both the ESPs and in all conditions when the filters are clean, while a progressive reduction in the efficiency is observed after a long term use mainly in the smaller device where the active surfaces are lower.