Physical and combustion characteristics of leached cane trash briquettes

Abstract

Sugarcane trash briquettes as a fuel allows nature conservation to be combined with energy production. Sugar cane trash is high in potassium (0.50% to 0.42%) and chlorine (0.02%). Raw biomass is not suited for thermal conversion due to its’ low energy density, high ash content and operational problems. Some inorganic elements are water- soluble and can be removed by leaching. The main objective of the study was to determine the effect of leaching to the physical and combustion characteristics of leached cane trash briquettes. The specific objectives were to determine the leaching characteristics of inorganic and organic matter from cane trash; fabricate the leached cane trash briquettes; evaluate the physical and combustion properties of the leached cane trash briquettes and analyze the combustion emissions. Sugarcane trash was collected from agricultural fields at Sony Sugar Company and reduced into sizes of 1 mm,5 mm and 10 mm following ISO 17827. The reduced sizes were subjected to leaching tests of varying temperature and time. Temperatures were 25 o C, 50 o C, 100 o C and time was 5, 30 and 60 minutes respectively. Leached briquettes were produced at a constant compaction pressure of 18 Mpa using starch as a binder. Briquettes from fine comminution of (1mm) leached for 60 minutes at 100 o C resulted in a fuel with substantial reduction in ash 33% (4.14 to 2.77), chlorine 100%(0.02 to 0), sulfur100% (0.06 to 0.02), potassium 75.24%(19.18 to 7.08), silicon 4.2%(16.64 to 15.93) and magnesium 44% (0.54 to 0.30). Briquettes were characterized in terms of Bulk Density ASTM-E871 (304.24±3.72) Kg/m 3 %, Mechanical Durability ASTMD440 (96.52±2.01)%, Ash ASTM-E1755 (3.12±0.41) wt.%, Moisture ASTM- E871(0.537±0.41)%, Volatiles ASTM-E872 (76.75±2.64) wt.% and Calorific Value ASTM-E711(17.81±0.41) MJ/kg. The calorific value was higher for the most severe treatment of Hot Soak, Long Duration, Pulverized Sugar Cane Trash (H-L-P) at 21.23 MJ/kg and lowest for the least severe treatment of Cold Soak, Short Duration, Chopped Sugar Cane Trash (C-S-C) at 14.51Mj/kg, the Mechanical Durability was 99.2 for H- L-P and 91.16 for C-S-C treatments; bulk density was 312 kg/m3 for H-L-P and 297 kg/m3 for C-S-C treatments. Ash content reduced with treatment severity with H-L- P having 2.66% and C-S-C attaining 3.95%. Improvements include increased Mechanical Durability (89.5 to 96.52) %, Bulk Density (274 to 304.24) Kg/m 3 and reduced Ash Content (4.14 to 2.77) wt.%. Leaching had effect of reducing emissions. Effects include increasing Higher Heating Value (16.85 to 17.99) MJ/kg and reducing CO (1484ppm to 698ppm). Other reductions were NO (199.80ppm to 147.0ppm), SO2(0.8ppm to 0.62ppm), NOx (205.9ppm to 175.8ppm) and Total Suspended Particles (62.20 mg/Nm3 to 35.38 mg/Nm3). In conclusion, leaching process has effects of increasing carbon and volatile matter and decreasing ash, chlorine, sulfur, and nitrogen compounds. Leaching improved the fuel properties of the feedstock, which is possibly due to the lower chlorine activity in terminating free radical chain reactions. Leaching as a pre-treatment method that improves the ignition and burning features of cane trash briquettes is highly recommended.