Various physical treatment of biomass prior to its conversion into liquid, solid or gaseous products are available. The main purpose of the selected treatment depends

on the requirement of the conversion process, that is, to have the biomass at appropri­ate size for easiness or strength and durability in handling and processing. Specifically biomass conversion can be enhanced via increased digestibility [18] from increased specific surface area and reduced degree of polymerization and cellulose crystallinity [19].

Generally, different biomass may have different density and resistance that may hinder in handling, transportation, and storage. These limitations, however, can be overcome via densification of the biomass to improve its properties such as bulk density, that is, from 40-200 to 600-800 kg/m3 [20], abrasion resistance, im­pact resistance, compressive strength, water resistance, and long-term performance [21, 22].

Process for biomass densification includes agglomeration that increases the parti­cle size. This can be performed using pressure [23] in such techniques like extrusion, pelletizing, roll briquetting [24-26], and compaction [20, 22]. Another technique is tumble agglomeration that uses binding agents [23] that chemically or physically adhere to solid surfaces and form a bridge between the biomass particles.

On the other hand, appropriate sizing of biomass can also improve its physical properties for enhanced combustion efficiency via higher burning rates [27]. Full automatic operation and complete combustion in furnaces can also be achieved when the biomass is homogenously densified [28].

Grinder and sieve shaker are used to provide homogeneous particle size for the biomass feedstock. This eases the feeding process of biomass into the gasifica­tion system. For more efficient feed preparation, biomass is dried and subsequently ground and sieved to a range of 250-500 ^m to enable smooth feeding and minimum fluidization velocity [2, 29].

Moreover, biomass ash may have high inorganic trace elements that can cause slagging, fouling, and corrosion in combustion equipment. However, the quantity of these trace elements such as potassium, sodium, and chlorine content can be reduced via leaching, that is, washing [30].

As for hydrolysis of biomass into fuels, different mechanical size reduction tech­niques can be applied mainly to reduce cellulose crystallinity. The techniques and its uses are listed in Table 17.1.