Fuel Pelletization with a Binder: Part I — Identification of a Suitable Binder for Spent Mushroom Compost−Coal Tailing Pellets

Spent mushroom compost and coal tailings are wastes that could be used as energy sources, through combustion in a fluidized-bed. Our previous pelletization studies produced a denser, yet friable fuel, which produced dust on transport, handling, and feeding. Thus, a suitable binder for these materials was required to enhance pellet properties. Inorganic (caustic soda) and organic (starch) binders were selected for a range of tests. Pelletization at elevated temperatures was also assessed to evaluate the softening of any lignin present in the straw component of the mushroom compost. Small amounts (up to 1 wt %) of both binders increased pellet tensile strength, where starch had more pronounced impacts, doubling the tensile strength to 411 kPa. Pelletization at elevated temperatures (45−75 °C), however, improved overall pellet quality more significantly, increasing the tensile strength to over 600 kPa, although additional temperature increases (up to 125 °C) did not result in further improvements. Whether a binder or elevated temperature is used at the pelletization stage is strongly dependent on the comparative costs of these options, relative to improvements in product quality. The effect of these binders on combustion will also be a crucial factor to consider, which is assessed in the second part of this paper.