Pelletised fuel production from coal tailings and spent mushroom compost — Part I: Identification of pelletisation parameters

Abstract

This study investigates the technology of manufacturing pellet blends for energy production from two discarded materials in industry. Coal tailings material is the fine discard produced as a result of coal cleaning. Although it still has a significantly high calorific value, over a million tonnes of coal tailings are deposited in lagoons every year in the UK alone. Spent mushroom compost (SMC) consists of fibrous compost substrate and a wet casing layer used during mushroom production. In the form of pellets, these materials become more homogeneous, easily stored and transported, and suitable for use in power plants or gasifiers. The characterisation of the fuel properties shows that the two materials have a complimentary status for pelletisation and energy production in terms of particle types, carbon source, calorific value and volatile matter content. Pelletisation tests were carried out using a small compression rig for various pressures, moisture contents and mixture compositions. The quality of the pellets was assessed using density, swelling, tensile strength and durability. It was necessary to keep the moisture contents for coal tailings at about 10% and for SMC at 20% before pelletisation in order to maximise the bonding strength of the originally wet materials. Pressures above 6000 psi did not produce noticeably denser or stronger pellets. The pellets from coal tailings and SMC blends had a tensile strength proportional to the SMC fraction. The SMC pellets were more durable than the coal tailing pellets due to the intertwined compost fibres. It was also noted that the SMC addition to the coal tailings did not increase the durability of the pellets due to the limited binding effect between the two materials.