Engineering Properties of Biomass - Engineering and Science of Biomass Feedstock Production and Provision - page 17

compositions. For example, a wood log consists of stem wood (white wood) and
bark. Stem wood has a lower ash content compared to the bark by tenfold. As a
result, bark may not be an excellent fuel source for combustion to produce heat and
power. Therefore, biomass has to be fractionated and engineered by biomass pro-
cessing in order to extract the appropriate parts for particular end-user application.
Engineering properties of biomass are those that control the way biomass is pre-
pared for either its handling or its conversion to other forms. These properties can
be divided into structural, compositional, thermal, and electromagnetic properties.
Structural properties may manifest themselves in the form of mechanical and physi-
cal properties. Compositional properties are chemical constituents of the biomass.
Thermal properties relate to heating and cooling rates and heat transfer between the
material and its environment as well as the calorific value of biomass. Electromagnetic
properties relate to the response of the material when exposed to waves from elec-
tromagnetic spectra. These four properties are highly interrelated, i.e., the change in
one influences a change in the others. These material properties can be studied sepa-
rately, keeping in mind that their unavoidable interactions are important.
Considerable research has been conducted on agricultural and forest material
properties over the last 50 years. Much of these properties can be extended and
applied to biomass. Professor Mohsenin of Penn State University was first to collect
and publish the state of the art in definitions and measurements of thermal [ 1 ], elec-
tromagnetic [ 2 ], and physical properties [ 3 ] of agricultural material. Since then,
numerous topics and articles have been published on the properties of foods [ 4 , 5 ]
and woody products [ 6 ]. More recently, methods of evaluating the compositional
properties of biomass were presented [ 7 ]. The ASABE Book of Standards main-
tains updated properties for agricultural and forest materials. Similarly, International
Organization for Standardization (ISO) is in the process of establishing procedures
for biomass properties characterization.
Energy providers are including bioenergy in their portfolio as the demands for
energy are increasing and the known petroleum resources are dwindling.
Environmental concerns with burning coal are shifting attention to biomass as an
alternate solid fuel [ 8 ]. Conversion processes, whether they are simply converting
biomass to heat and power or involve more complex biomass to gaseous or liquid
fuels conversions, require high-quality and cost-competitive feedstock [ 9 ]. Simple
combustion may utilize feedstock with a wide range of moisture contents, mixtures
of species bark and stem wood, and a wide range of sizes and ash content. The more
complex processes such as chemical or enzymatic hydrolysis require feedstocks
with close tolerances in particle size and density [ 10 ]. Meeting tight specifications
can be challenging as forest feedstocks are highly variable in many of the relevant
physical and chemical compositions. The source of the feedstock will have direct
impact on the available quantities of biomass and the cost of harvesting and logis-
tics. Understanding these characteristics is an important element in ensuring that
new investments in bio-industry match the available feedstock supplies.
The engineering properties of biomass highly affect the quality of feedstock
for densification and eventually their use in either biorefinery or in a combustion
application. These properties include density, particle size, flowability, moisture