Combustion of distillery sludge mixed with coal in a drop tube furnace and emission characteristics

Abstract

Co-combustion of coal with distillery sludge waste (DSW) was investigated in a laboratory-scale Drop Tube Furnace (DTF) plant. This study examined the feasibility of combustion of sludge with coal using preliminary testing methods, such as thermogravimetric, ultimate and proximate analysis followed by combustion experiments. These methods helped to identify burnout efficiency, emitted pollutants, and metal constituents in the bottom/fly ash. The ratios of coal to DSW in the feed was 90:10%, 95:5%, 98:2% and 100:0% by dry weight basis. The vibrator feeder and airflow rate were set at the rate of 1.5 kg/h and 150 L/min with slightly negative pressure. The concentration of gases (i.e. nitrogen oxides (NOx), sulphur dioxide (SO2), carbon mono-oxide (CO), hydrocarbon (HC)) and particulate matter (PM) on DSW combustion was measured and compared with the combustion of coal. The pattern of gaseous emission and combustion efficiency showed high degree linear combinations through Pearson’s correlation coefficient. The decrease in the concentration of PM (76.67 ± 10.41 mg/m3 to 91.33 ± 17.62 mg/m3) and SO2 (444 ± 20.63 mg/m3 to 156.60 ± 12.26 mg/m3), increase in the concentration of NOx (136 ± 15.41 mg/m3 to 387 ± 15.2 mg/m3) and CO (26.15 ± 5.36 mg/m3 to 824.32 ± 43.70 mg/m3), unburnt carbon percentage in the fly ash, and clinker formation were taken into account to optimum the sludge proportion in the DTF under a given set of combustion conditions. Most importantly, an increase in sludge quantity (i.e. 2%, 5%, and 10%) showed a decrease in the burnout efficiency (98.41%, 95.91%, and 92.6%, respectively).