Biomedical Engineering Reference
In-Depth Information
13.1.2.3 Moisture
Moisture content (M) is determined by the test protocol given in
ASTM standards D-871-82 for wood, D-1348-94 for cellulose, D-1762-84
for wood charcoal, and E-949-88 for RDF (total moisture). For equilibrium
moisture in coal one could use D-1412-07. In these protocols, a weighed
sample of the fuel is heated in an air oven at 103 C and weighed after cool-
ing. To ensure complete drying of the sample, the process is repeated until
its weight remains unchanged. The difference in weight between a dry and a
fresh sample gives the moisture content in the fuel.
Standard E-871-82, for example, specifies that a 50 g wood sample be
dried at 103 C for 30 min. It is left in the oven at that temperature for 16 h
before it is removed and weighed. The weight loss gives the moisture (M) of
the proximate analysis.
Standard E-1358-97 provides an alternative means of measurement of
moisture using microwave. However, this alternative represents only the
physically bound moisture; moisture released through chemical reactions
during pyrolysis constitutes volatile matter.
Klass (1998) proposed an alternative means of measuring the proximate
composition of a fuel using thermogravimetry (TG). In these techniques, a small
sample of the fuel is heated in a specified atmosphere at the desired rate in an
electronic microbalance. This gives a continuous record of the weight change of
the fuel sample in a TG apparatus. The differential thermogravimetry apparatus
gives the rate of change in the weight of the fuel sample continuously. Thus,
from the measured weight loss-versus-time graphs, we can determine the fuel's
moisture, volatile matter, and ash content. The fixed carbon can be found from
Eq. (3.23). This method, though not an industry standard, can quickly provide
information regarding the thermochemical conversion of a fuel.
TG analysis provides additional information on reaction mechanisms,
kinetic parameters, thermal stability, and heat of reaction. A detailed data-
base of thermal analysis is given in Gaur and Reed (1995).
13.1.3 Analysis of Polymeric Components of Biomass
Thermochemical conversion of biomass (torrefaction in particular) greatly
depends on the polymeric composition of biomass. As explained in
Chapter 3, a typical biomass primarily include:
Ash
Extractives
Cellulose
Hemicellulose
Lignin.
Several techniques are available for the determination of the above
components of biomass. Determination of some of the components is
Search WWH ::




Custom Search