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 59

time of 60 min for both mesquite and juniper samples. The model results compare
well with the experimental results except at the upper temperature limit. At tem-
perature of 300

C, TCM overpredicts the mass loss from the woody biomass. The
kinetic constants of cellulose used to model the torrefaction process resulted in
increased losses of cellulose at higher temperatures in the TCM. The variation in
mass loss with increase in residence time for an initial heating rate of 20

°

C/min is
plotted in Fig. 8 . Following residence times were studied: 30, 45, 60, and 120 min.
Effect of higher residence time on mass loss was negligible at lower torrefaction
temperatures, while an increase in temperature resulted in increased mass loss due
to higher time and energy available for the volatilization of cellulose and lignin
present in the biomass. Higher percentages of cellulose are released from the
sample resulting in higher mass loss.
As the heating rate increased, the results showed an increased retention of mass
at higher torrefaction temperatures when compared to the lower heating rates.
Higher heating rates do not allow suf

°

cient time for the volatiles to escape out from
the biomass which causes lower mass loss during the initial heat up period. Hence,
higher heating rates can be employed to reduce the loss of combustible volatile
matter from the biomass at higher temperatures.

Energy Conversion Ratio (ECR) and Heating Value of the Torrefied Sample

The heating value and the chemical composition of the three components were used
to monitor the change in heating value of the torre ed biomass with reference to the

raw samples. Energy conversion ratio (ECR) which is de ned as the ratio of the

energy content of the torre ed sample to the energy content of the raw biomass and

the ratio of the heating value of the torre ed biomass to raw biomass was also

Fig. 8 Variation in mass loss
with increase in torrefaction
temperature and residence
times. M Mesquite; J Juniper

90

80

70

60

M-30 min
M-45 min
M-60 min
M-120 min
J-30 min
J-45 min
J-60 min
J-120 min

50

40

30

200 220 240 260 280 300

Temperature ( o C)