PREPROCESSING & DENSIFICATION

	Forest residue pellets generated using twin screw extruder Biomass pellets for heating, power, and biofuels generation Biomass granules for energy generation

Handling, transport and storage of crop residues (corn stover, cotton stalk, straws), processing wastes (cotton gin waste, peanut husk, sawdust) and forest biomass (residues, slashes, thinning wastes) to produce fuels, chemicals and bioproducts are challenging tasks due to wide spread distribution, uneven moisture content and low bulk density of these feedstock. Solution to this problem is to densify this feedstock in such a way that the feedstock can be converted into uniform size, shape, and moisture content and high bulk density for efficient and economic utilization. Densification is the process of converting high moisture (~50% wb) and low bulk materials (60 kg/m3) into low moisture (~8% wb) and high bulk density product (650 kg/m3).
The densification process involves with three main unit operations: drying, size reduction/chopping and pelletization/granulation. The product of densification is called pellets or granules, which are similar to the characteristics of cereal grains. A typical moisture content of the pellets varies from 6 to 8 % (wet basis). If biomass does not require any artificial drying, the total energy required to densify biomass is about 5% of the heating value of the dry biomass.

The cost and energy consumption of densified products can be further reduced significantly by biomass granulation or by binderless densification technology. Granulation is the method of making granules using liquid binders. In biomass granulation technique, the targeted liquid binder may be a starch based (corn or potato wastes) or lignin based binders (black liquor, bio-oil). Pretreatment of biomass by steaming and torrefaction (slow pyrolysis) before densification can further increase the heating value (10%) and bulk density (30%) of the product, but the high quality product may be compromised by the additional cost involved in pre-treating the biomass. Opportunities still exist to develop low cost densified products for versatile applications.

Current Projects and Future Directions:

1. Densification characteristics of cotton stalk residues
2. Pelleting and briquetting characteristics of forest residues, chestnut and hybrid sweetcum tree species
3. Role of lignin as a binder during densification of biomass
4. Feasibility of developing low cost granulation technique for microalgae based biomass and lignocellulosic biomass
5. Techno-economic evaluation of biomass Pelleting and Briquetting Technologies
6. Effect of pretreatment methods (AFEX, steam explosion, torrefaction) on the quality of biomass pellets

TORREFACTION

	Torrefied pine chip View presentation: Torrefaction Reaction Kinetics of Southern Pine Wood, presented in the 2009 Bioenergy Engineering Conference Bellevue, Washington >>
	Green pine chip
	View presentation: Biomass Torrefaction – A Promising Pretreatment Method for Thermo-Chemical Conversion Technologies presented at the IEA Bioenergy Conference, Vancouver, BC Canada Aug 23-26, 2009 >>

Torrefaction is a process of partial volatilization of biomass in the absence of oxygen to increase the energy density of biomass. Torrefaction of biomass results in low moisture content, high energy density and hydrophobic and the physical characteristics are similar to coal. Thermal pretreatment or torrefaction of biomass is a promising method to preprocess the low quality biomass into high energy density feedstock with consistent and uniform physical and chemical characteristics. It will be a promising future technology for long distance transport, long term storage and improving thermal conversion by reducing downstream cleaning and processing costs. During torrefaction of biomass, some of the highly reactive volatile compounds are removed from the biomass as vapors and results in clean, dark brown colored solid biomass with higher energy density.  The energy density of biomass could be increased closer to the energy density of coal (22-23 MJ/kg) used for heat and power generation. The treated biomass is brittle and hydrophobic in nature.
 Developing optimal process conditions for the production of high quality biomass in the batch reactors were limited due to poor heating rate, process longevity and low productivity. There is also a lack of understanding of thermo-chemical degradation of biomass during torrefaction process and the reaction kinetics of biomass torrefaction process. Investigating thermal degradation of biomass constituents such as cellulose, hemicellulose and lignin at moderate heating ranges (200-300oC) would further understand the theory behind torrefaction process. During torrefaction process, the final quality of biomass depends on a multitude of variables including feedstock moisture content, particle size, heating rate, temperature, and residence time. Little or no work has been report on the effect of various process variables on the quality of the final product. Development of a continuous biomass torrefaction reactor is also required to investigate the effect of various process parameters for scale up operations, to integrate the pre-treatment technology into the existing or future thermo-chemical based biorefinery.

Current Projects and Future Directions:

1. Torrefaction of forest biomass for co-firing application
2. Pilot scale production of torrefied biomass for power generation
3. Compaction characteristics of torrefied biomass
4. Effect of torrefaction pretreatment method on the quality of pyrolysis and gasification products.