Comprehensive Review on Bio-Briquettes Developed from Processed Cashew Nut Shell Wastes

Cashew nut shells (CNS) are the primary waste produced during the processing of cashew nuts; and needs constant attention to handle or valorize these wastes effectively. As a result, these CNS wastes are processed into solid briquettes citing their significant calorific content, thus making them as a promising renewable biofuel for combustion based applications. In most cases, these wastes are pre-treated either through de-oiling or carbonizing prior to compaction, thus removing the harmful hydrocarbons present in them in form of CNS liquids. Presently, this chapter focus on summarising various data related to these CNS wastes and their briquettes in terms of their availability, chemical characteristics, pre-treatment and processing technique, fuel and combustion properties as reported in various literatures. Here, availability depicts the current trend in global consumption of these snack nuts and the proportionate amount of waste shells produced; while, chemical characteristics focused on discussing their anatomy, proximate, lignocellulosic and elemental compositions. Following this, pre-treatment and processing techniques list out the various practises followed to remove CNSL, process de-oiled CNS cakes into bio-char through carbonization, and briquetting of pre-treated CNS wastes along with their compacting techniques prescribed by various researchers. Lastly, fuel and combustion properties brief out about the fuel traits of developed CNS briquettes along with their burning characteristics; and include parameters like proximate and elemental compositions, density and compressive strength, and results related to their combustion and water boiling tests. Moreover, all the reported results and data in this study were in accordance with the international testing standards; and ranged in between their permissible range.