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 46

in tons per GJ of energy release. Biology literature de nes RQ as a ratio of moles of

CO 2 produced (or CO 2 eliminated) to stoichiometric oxygen (O 2 ) moles consumed
typically during oxidation reaction, e.g., oxidation of nutrients in the body which
results in release of energy for maintaining the normal warmth (37

C) of the body.
The RQ factor for fat, protein, and carbohydrates, the three basic nutrients of the
body, is 0.7, 0.8, and 1, respectively (Hall 1905 ; Richardson 1929 ; Morinaka et al.
2012 ; McClave et al. 2003 ). However, senior citizens have problem of excreting
CO 2, and hence, they are prescribed low RQ diet (e.g., fat with low RQ). Such a
concept has been recently introduced in thermal systems in order to select low RQ
fuel for power generation (Annamalai 2013 ). This method of RQ concept for esti-
mating the CO 2 emission from different fuels was elaborated here to estimate the
global warming potential (GWP) of fossil and as well as renewable fuels.
Current chapter presents the results obtained from TGA studies on CO 2 torre-
faction of woody biomass which dominates the rangelands and grasslands of
southwestern United States (mesquite and juniper), batch torrefaction of samples
using a laboratory oven, modeling the weight loss during torrefaction using a three-
component model and application of RQ concept to estimate GWP of different fuels.

°

2 Materials and Methods

2.1 Thermogravimetric Analyzer

All TGA tests were performed utilizing a TA Instruments Q600 thermal analyzer
located at the Coal and Biomass Energy Laboratory (CABEL) at Texas A&M
University. Ground biomass samples of size between 540 and 890 m were used for

the TGA tests. Around 10 mg sample was used for each TGA study. The instrument
is capable of highly reproducible measurements with

μ

± 1 % accuracy. The purge gas

fl flow was regulated to below 20 psi using a pressure regulating valve attached to the

purge gas tank. During experiments, the flow rate of the purge gas was controlled

via the TA Instrument Explorer software installed on the connected PC and regu-
lated via the internal mass

fl

flow controller in the Q600. Purge air was used after each
test run to cool the furnace back to an ambient temperature. The TA Instrument
Explorer software allows for direct control of several test parameters and can also
be utilized to create a step by step test procedure. Two separate test procedures were
used for the torrefaction and pyrolysis tests completed with the Q600. A constant
heating rate of 20

fl

C/min was used for the pyrolysis tests where the samples were
heated from room temperature till 900

°

C. For the torrefaction tests, the samples
were heated at a constant heat rate till the torrefaction temperature and then
maintained at the same temperature for a given time period. After the torrefaction
process, the samples were again heated at a constant heating rate till 900

°

° C. All the

tests were carried out in an inert environment by flowing nitrogen, argon, and

carbon dioxide depending upon the environment which has to be used for the
torrefaction and pyrolysis study.

fl