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 55

3.2.4 Laboratory Oven Tests

After determining the optimal torrefaction temperature, large samples of each

biomass were torre ed in a laboratory oven using nitrogen, argon, and carbon

dioxide as the purge gas. Torre ed samples were then sent to commercial testing

labs for analysis. Figure 5 shows the properties of the raw and torre ed samples. As

expected, torrefaction of the raw biomass resulted in reduced moisture content in
the biomass. Torrefaction of raw biomass also resulted in an increased ash and

xed
carbon content for all biomass tested. The increase in ash and FC is mostly due to
the decrease in moisture content and liberation of light weight volatiles during
torrefaction. Biomass torre ed in an argon or nitrogen environment exhibits little

difference in fuel properties. However, the fuel properties of biomass torre ed in

carbon dioxide are slightly different.
Previous research (Lawrence et al. 2009 ) has shown that coal biomass blends

with a ratio of coal to biomass greater than 80:20 result in several combustion issues
due to the fuel properties of the raw biomass. With the fuel properties of torre

-

ed
biomass being much better than raw biomass, it is entirely feasible that blended
fuels with a ratio of coal to torre

ed fuel greater than 80:20 could be used in co-

firing applications.
Knowing the actual HHV of the torre ed biomass (HHV TB ), the actual amount

of energy retained can be calculated (Sect. 3.2.3 ). Due to inherent mass loss from
torrefaction, the energy retained provides the percentage of the raw biomass
retained within the torre ed biomass. The resulting calculated values of energy

retained for both biomasses in each purge gas environment can be seen in Table 2 .

Ash Moisture Fixed carbon Volatile matter

77.99

66.09 69.51

70.45 71.14

74.60

74.52

73.19

80

70

60

50

40

23.26

23.56 30

16.71

22.22

20

15.53

18.63

14.25 20.19

10

19.43

4.84

3.56 0

4.3

1.67 5.85

2.39

5.69

2.43

4.14

2.34

6.25

1.91

1.08

Raw

1.15

Nitrogen

1.13

Argon

CO2

Raw

Nitrogen

Mesquite

Argon

CO2

Juniper

Fig. 5 Proximate analysis of raw and biomass torrefied using different mediums (Eseltine 2011 )