The above factors illustrate that biomass feed preparation is very important and forms an integral part of the briquetting process. The unit operations of the piston press and the screw press are similar except where the latest development in screw press technology has been adopted, i. e., where a preheating system has been incorporated to preheat the raw material for briquetting to give better performance commercially and economically to suit local conditions. In the present piston press operating briquetting plants, the biomass is briquetted after pre-processing the raw material but no preheating is carried out. Depending upon the type of biomass, three processes are generally required involving the following steps:

A. Sieving—Drying—Preheating—Densification—Cooling—Packing

B. Sieving—Crushing—Preheating—Densification—Cooling—Packing

C. Drying—Crushing—Preheating—Densification—Cooling—Packing

When sawdust is used, process A is adopted. Process B is for agro- and mill — residues which are normally dry. These materials are coffee husk, rice husk, groundnut shells, etc. Process C is for materials like bagasse, coir pith (which needs sieving), mustard and other cereal stalks.