Biomass Fuel Quality Enhancement and Respiratory Quotient (RQ) for Ranking Fossil and Biomass Fuels Based on CO2 Emissions - Novel Combustion Concepts for Sustainable Energy Development - page 51

3.2 Thermogravimetric Analysis

3.2.1 Mesquite

The thermograms for pyrolysis and torrefaction of mesquite using N 2 , Ar, and CO 2
as the purge are shown in Figs. 1 and 2 . The TGA thermograms for each purge gas
have the same relative shape and can be broken down into three different zones:
drying, active pyrolysis zone, and passive pyrolysis zone. For simplicity, the
thermograms for each torrefaction temperature were overlaid on the same plot. For
torrefaction, each thermogram follows the weight loss curve for pyrolysis until
reaching the torrefaction temperature. At this point, the thermogram follows a
vertical line resulting from weight loss due to the sample being held at a constant
temperature for the duration of torrefaction. Overlaying the thermograms of sam-
ples that were pyrolyzed and torri ed using different purge gasses gives more

insight as to the effect of the purge gas upon the breakdown of the biomass.
Overlays of both argon and carbon dioxide versus nitrogen (the reference gas) are
shown in Figs. 1 and 2 , respectively, (Eseltine 2011 ).
From initial inspection, it is clear that there is very little difference in the ther-
mograms from the pyrolysis and torrefaction in nitrogen and argon. Both nitrogen
and argon exhibit roughly the same amount of weight loss at a given torrefaction
temperature. Slight differences in weight loss between these two purge gases can be
attributed to differences in the biomass samples being tested. Comparison of the
thermograms using nitrogen and carbon dioxide as the purge gas shows a noticeable
difference between the two gases. For torrefaction temperatures above 240 ° C,

samples torre ed using CO 2 as the purge gas have a higher amount of weight loss

TGA Thermograms - Mesquite Nitrogen vs. Argon Comparison

100

Pyrolysis - Nitrogen
Pyrolysis - Argon
200°C - Nitrogen
200°C - Argon
220°C - Nitrogen
220°C - Argon
240°C - Nitrogen
240°C - Argon
260°C - Nitrogen
260°C - Argon
280°C - Nitrogen
280°C - Argon
300°C - Nitrogen
300°C - Argon

90

80

70

60

50

40

30

20

0

100 200 300 400 500 600 700 800

Temperature (°C)

Fig. 1 Comparison of thermograms from pyrolysis and torrefaction of mesquite wood using N 2
and Ar as the purge gases, adapted from Eseltine ( 2011 )