Size Distribution of Ultrafine Particles Generated from Residential Fixed-bed Coal Combustion in a Typical Brazier

Daniel M Masekameni,Mary Gulumian,Tafadzwa Makonese,Derk Brouwer,Isaac T Rampedi

doi:10.4209/aaqr.2018.03.0105

Abstract

Ultrafine particles (with a small mean diameter) released from domestic coal combustion are an important parameter to consider in air pollution, as they affect air quality and human health. It has been suggested that poor combustion conditions release particles of different sizes enriched with health-damaging chemicals, such as polycyclic aromatic hydrocarbons. Furthermore, both smouldering and highly efficient combustion conditions release particles, which are often carcinogenic. Information on the particle size distribution (PSD) of char or soot emitted from fixed-bed domestic coal combustion is limited, with many studies reporting on wood combustion. This study investigated the influence of coal combustion phases (ignition, flaming, and coking) on the particle number concentration and size distribution of ultrafine particles. D-grade bituminous coal was crushed to a particle diameter (O) of 40–60 mm and combusted in a laboratory designed coal brazier (Imbaula) during experimental investigations of the particle size distribution normalised to the particle number concentration against the particle diameter. Experiments were carried out using the reduced smoke top-lit updraft method, colloquially known as the Basa njengo Magogo (BnM) method. The tests were carried out in a laboratory-controlled environment. Particulate matter was monitored using a NanoScan Scanning Mobility Particle Sizer (SMPS). Particles from the top-lit updraft (TLUD) showed an ultrafine geometric mean diameter centred at approximately 109 ± 18.4 nm for the ignition phase, 54.9 ± 5.9 nm for the pyrolysis/flaming phase, and 31.1 ± 5.1 nm for the coking phase. The particle mode diameter rapidly increased during the ignition phase (145 nm) and gradually decreased during the flaming phase (35 nm) and the coking phase (31 nm). This study shows that during smouldering combustion conditions (ignition), the particle diameter increases, whereas it decreases as the temperature increases. This information is essential for estimating particle deposition in the lungs and the associated health risks.

Highlights

Over half of the global population continue to depend on solid-fuels for domestic cooking and heating, with the majority found in developing countries (Bonjour et al, 2013; International Energy Agency, 2015)
D-grade bituminous coal was crushed to a particle diameter (Ø) of 40–60 mm and combusted in a laboratory designed coal brazier (Imbaula) during experimental investigations of the particle size distribution normalised to the particle number concentration against the particle diameter
The present study focused on the submicron particles (11 nm–365 nm) and aimed to assess the number size distribution of particles emitted from fixed-bed coal combustion in typical braziers using the top-lit updraft (TLUD) method

Summary

Introduction

Over half of the global population continue to depend on solid-fuels for domestic cooking and heating, with the majority found in developing countries (Bonjour et al, 2013; International Energy Agency, 2015). Efforts to separate largescale combustion particles from residential solid-fuel burning suggested that particles from the industrial operation are more than 100 nm in diameter but can grow during the accumulation mode to 1000 nm (Kumar et al, 2011). Particulate matter (PM) emissions from residential coal burning are estimated to be at a size range of lower than 100 nm. The particle diameter can grow to 300 nm during accumulation mode (Morawska et al, 2008). This differentiation based on size fraction can be used in source apportionment exercises (Naeher et al, 2007)

Methods

Results

Conclusion