Pilot-scale grinding and briquetting studies on variable moisture content municipal solid waste bales - Impact on physical properties, chemical composition, and calorific value

Low bulk density, variable moisture content, and particle size of municipal solid waste (MSW) create feeding, handling, storage, and transportation challenges. In this study, MSW bales were size-reduced in stage-1 and stage-2 hammer mill grinders fitted with 50.8-mm and 6.35-, 12.7-, and 19.05-mm screens. Ground MSW was densified further in a pilot-scale briquette press by varying moisture content in the range of 10-25% wet basis (w.b.). At 40% (w.b.) MSW moisture content, the stage-1 grinder fitted with a 50.4-mm screen took about 136kWh/ton, while the stage-2 grinder fitted with a 19.05-mm screen took about 151kWh/ton. The bulk density of MSW after stage-1 and stage-2 grinding was about 25-50 kg/m³. Unit bulk and tapped density were in the range of 680-850 kg/m³, 478-315 kg/m³, and 346-540 kg/m³ post briquetting, and 591-830 kg/m³, 295-458 kg/m³, and 319-519 kg/m³ post five days of storage at 20 °C. The durability was about 93.40-98.54% post briquetting, and after five days of storage. Increasing the moisture content and screen size decreased density and improved durability. Briquetting energy increased to 120 kWh/ton at a higher moisture content and larger grind size. MSW flow characteristics improved after briquetting. Higher lignin content (≈30%) and calorific value (19-21 MJ/kg) suggest MSW is suitable for thermochemical conversion. Ash content in the MSW was in the 11.9-14.8% range. CT-scan images of the briquettes showed a network of interconnected pores formed due to compression of various MSW fractions.