Effects of binder on the quality and thermal decomposition characteristics of pellets from herbal medicine waste

With the extensive application of herbal medicine worldwide, a large amount of herbal medicine waste (HMW) is generated each year. In this study, pellets are produced using HMW feedstocks with modified starch, sodium silicate, and carboxymethyl cellulose as the binders. The quality and thermal decomposition characteristics of the pellets are studied. The results show that the binder can improve the quality of the pellets, which facilitates storage and handling. The effects of organic binders are stronger than those of inorganic binders. The relaxation density, compressive strength, and durability characteristics of the pellets are linearly correlated with the amount of binder added. At a content of 2 wt.%, all the pellets meet the commercial standard quality. The maximum weight losses for pellets pyrolysis occur at 338 ~ 346 °C with the mass loss rates of 4.92 ~ 5.28%/min, while that for combustion is at 298 ~ 305 °C and 17.49 ~ 28.55%/min. The binder slows the volatilization process and reduces the pyrolysis activation energy of pellets from 209.71 kJ/mol to 134.53 ~ 175.39 kJ/mol. The activation energies for pellet combustion with and without binder are in the ranges of 17.43 ~ 63.70 kJ/mol and 22.79 ~ 67.52 kJ/mol, respectively. The comprehensive combustibility index (S) of the pellets with binder ranges from 5.29 to 8.17 × 10⁷%²/(min²·°C³). The results of this study indicate that pelletization is a feasible option for the treatment of solid HMW and the resultant pellets can be used as a sustainable solid fuel.