Assessing the impact of thermal insulation on gaseous emissions in traditional brick kilns

Abstract

Globally, brick production relies heavily on traditional kiln technologies that depend on biomass and coal as primary fuels. These fuels, mainly composed of cellulose and other carbon compounds, release significant greenhouse gases during combustion. Under sufficient oxygen supply, complete combustion produces carbon dioxide (CO₂) as the primary by-product, but at the expense of increased fuel consumption. Conversely, inadequate oxygen supply reduces CO₂ emissions but increases carbon monoxide (CO) and nitrogen oxides (NOₓ), this trade-off has made thermal insulation an important strategy for moderating oxygen infiltration, improving heat retention, and influencing emission patterns in traditional kilns. This study investigated the impact of thermal insulation on gaseous emissions, focusing on CO₂, CO, NOₓ, nitric oxides, and flue gas temperature. A Quantitative research design was employed with three objectives: (i) to characterize thermal insulation used in traditional brick kilns, (ii) to determine emissions from thermally insulated kilns, (iii) to assess the effect of insulation on emission concentrations and flue gas temperature. From a sample of 73 kilns, 62 kilns with varying insulation thicknesses (10–235 mm) of mud and brick mortared insulation were selected. Emissions were measured using calibrated gas analyzers supported by a one-square-meter flux chamber, while supplementary data were collected through interviews and observations. Statistical analyses were applied to examine relationships between insulation thickness, emission concentrations, and flue gas temperature. The results of this study show a statistically significant negative relationship between insulation thickness and CO₂ emissions, with optimal reduction (86.36%) observed at 150 mm thickness using brick mortared insulation. However, this point also corresponded with increased CO and NOₓ emissions, suggesting incomplete combustion at lower internal temperatures due to cracks and falloffs in the insulating layer. Insulation thickness further showed a significant effect on flue gas temperature, confirming its role in modifying combustion dynamics. The study concludes that thermal insulation, while effective in reducing CO₂ emissions in traditional brick kilns, may inadvertently elevate other pollutant gases. These findings highlight the need for integrated kiln design approaches that balance thermal retention with combustion control. By addressing this trade-off, artisanal brick production can become both more energy-efficient and environmentally sustainable.