Method to Produce Durable Pellets at Lower Energy Consumption Using High Moisture Corn Stover and a Corn Starch Binder in a Flat Die Pellet Mill

Abstract

A major challenge in the production of pellets is the high cost associated with drying biomass from 30 to 10% (w.b.) moisture content. At Idaho National Laboratory, a high-moisture pelleting process was developed to reduce the drying cost. In this process the biomass pellets are produced at higher feedstock moisture contents than conventional methods, and the high moisture pellets produced are further dried in energy efficient dryers. This process helps to reduce the feedstock moisture content by about 5-10% during pelleting, which is mainly due to frictional heat developed in the die. The objective of this research was to explore how binder addition influences the pellet quality and energy consumption of the high-moisture pelleting process in a flat die pellet mill. In the present study, raw corn stover was pelleted at moistures of 33, 36, and 39% (w.b.) by addition of 0, 2, and 4% pure corn starch. The partially dried pellets produced were further dried in a laboratory oven at 70 °C for 3-4 hr to lower the pellet moisture to less than 9% (w.b.). The high moisture and dried pellets were evaluated for their physical properties, such as bulk density and durability. The results indicated that increasing the binder percentage to 4% improved pellet durability and reduced the specific energy consumption by 20-40% compared to pellets with no binder. At higher binder addition (4%), the reduction in feedstock moisture during pelleting was <4%, whereas the reduction was about 7-8% without the binder. With 4% binder and 33% (w.b.) feedstock moisture content, the bulk density and durability values observed of the dried pellets were >510 kg/m 3 and >98%, respectively, and the percent fine particles generated was reduced to <3%.

Changes in the Crystallinity Degree of Starch Having Different Types of Crystal Structure after Mechanical Pretreatment

“…formation. Mechanical pretreatment of starch samples led to defect accumulation in the crystal structure, thus causing the disruption of double helices of amylopectin and single helices of amylase due to the rupture of hydrogen or glycosidic bonds, as well as the release of interspersed amylose molecules into the amorphous phase ( Figure 6) [10,26,[35][36][37]. It was shown that longer duration of mechanical activation leads to gradual amorphization of the crystalline structure of A-, B-, and C-type starches, so their crystallinity degree decreases.…”

“…In particular, mechanical pretreatment of cellulose in a planetary ball mill gives rise to a reactive product that is characterized by disordered ultrastructure, increased specific surface area, and reduced crystallinity degree [23,24]. For starch, mechanical pretreatment also reduces the grain size and increases the content of the amorphous phase, making it possible to alter the hydrating and paste-forming properties of modified starch [25,26].…”

Pelleting of Pine and Switchgrass Blends: Effect of Process Variables and Blend Ratio on the Pellet Quality and Energy Consumption

“…Idaho National Laboratory (INL) has developed a high-moisture pelleting process that can help to reduce pellet-production costs significantly. Tumuluru [21][22][23], Tumuluru et al [40], Bonner et al [41], and Hoover et al [42] have all successfully tested this process on both woody and herbaceous biomass, as well as chemically pretreated biomass, in both pilot and commercial-scale pelleting systems. In this process, the biomass is pelleted at a higher moisture content of > 15% (w.b.…”

Pelletization of pristine Pteris vittata L. pinnae powder and its application as a biosorbent of Cd(II) and Cr(VI)

“…Upon cooling, solid bridges are formed between components that strengthen the pellet [14]. By the combined interaction between the moisture content and the biomass components (proteins, starch and/ or lignin) at high temperature and pressure, the proteins present in the biomass undergo plasticization/denaturation and the starch added as binders undergoes gelatinization that promotes better binding of the particles [14,15]. Also, the waxes and lignins present in the biomass could have undergone a glass transition at 40-50 °C and 65-75 °C, respectively, as reported by Stelte et al [11].…”