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 67

4 Summary and Conclusion

The use of nitrogen and argon as a purge gas during the torrefaction of the two
biomass tested produced the same results. Torrefaction of mesquite and juniper
using carbon dioxide as the purge gas resulted in a higher weight loss. The higher
amount of weight loss when using CO 2 can be attributed to the reaction of the CO 2
purge gas with fixed carbon contained within the biomass.

Overall, the use of carbon dioxide as a torrefaction medium results in a biomass
with a smaller HHV than the same biomass torre

ed in nitrogen or argon. There-
fore, given the higher amount of weight loss with CO 2 and the smaller HHV, the
amount of energy retained in the torre ed biomass is lowest when torrefying in a

CO 2 environment. However, grindability studies show that biomass that is torre ed

in a CO 2 environment is easier to grind than biomass torre ed in N 2 . That is

biomass torre ed in a CO 2 environment will require less energy to pulverize.

Considering all of these factors, it is suggested that carbon dioxide is a better
torrefaction medium than nitrogen and argon. Although, higher weight losses and
more moisture absorption were observed when using CO 2 , the increased grinda-
bility and possibility that less energy would be required to produce high-quality fuel
make CO 2 the better torrefaction medium.
A simple TCM based on independent parallel reactions has been developed to
model the torrefaction of woody and fibrous biomass in order to predict mass loss,

heating value of biomass at any stage of torrefaction versus temperature (or time).
Mass loss predicted by the TCM was compared with the experimental data obtained
from TGA. It is shown that heat value of the torre

ed biomass increased with
increase in pretreatment temperatures, while the energy retention ratio decreased at
high temperatures due to loss of higher amounts of combustible volatile matter at
higher temperatures.
Chemical composition of the fuels and correlations developed to estimate the
heating values can be used effectively to study the variation in heating values with
respect to the fuel properties. The RQ term defined as the amount of CO 2 mol
produced per unit mole O 2 consumed used extensively in the biological literature
has been applied to combustion applications. RQ factor has been used to estimate
the amount of CO 2 which is a measure of GWP. Lower the RQ, lower the amount
of CO 2 produced for every mole of oxygen consumed for combustion process and
lower the CO 2 in tons per GJ which is shown to be approximately equal to

0.1 times RQ.
Further, a term called RQ process,biomass is introduced to determine the effect of
using a renewable fuel along with fossil fuels. RQ process,biomass for both mesquite
and juniper (which does not use water or electricity for cultivation) was estimated to
be 0.03 based on woody biomass lifecycle analysis. Method for estimating the
RQ blend for the blend of coal and biomass was presented, and the RQ blend for 90:10
blends of coal and torre ed biomass was 0.82 (where RQ for biomass is zero)

which is lower than the RQ factor of raw coal which is 0.92.