Page 31 - Mines and Minerals Reporter eMagazine - Volume October 2021

TECHNOLOGY

Results and discussion The reducing gaseous products (CO, CH4, H2) released from the
three major components of straw-type biomass were investi-
Thermodynamic basis of biomass gated using a gas composition analyzer to reveal the gaseous
pyrolysis and suspension magnetization roasting regulations of the mixture in the biomass fast pyrolysis pro-
cess [43,44]. Fig. 2a presents the gas flow of gaseous products
0
Cellulose, hemicelluloses, and lignin used to generate reduc- at a temperature of 800 C and a biomass dose of 20 wt% using
ing gases such as H2 and CO are three main components of a mixture of hematite and straw-type biomass. The trends of
the straw-type biomass used in the SMR process. However, gas flow in CO and H2 were similar and they both increased
in addition to the general formula of cellulose, a lack of regu- intensely and dropped drastically.
larity between the repeating units in the structures of hemi-
celluloses and lignin makes it difficult to describe by a specific It was obvious that the gas flow rate of CO peaked at 124 s and
general formula. The molecular formulas of the three compo- rapidly decreased from 1.03 to 0.003 mL/s when the roasting
nents can only be determined by elemental analysis (Table 1), time was prolonged to 800 s. Similarly, the maximum gas flow
giving: C3.55H5.60O2.59 for straw-type biomass. Therefore, value rate of H2 was 0.85 mL/s at a roasting time of 184 s. By
the pyrolysis reactions of strawtype biomass under an N2 at- Comparing the curve trend of CO to that of H2, the early peak
mosphere described by Eqs. (2)–(5) are shown in Table 3. appearance of CO could be discovered. A suitable explanation
of the results is that the generation of H2 was caused by the
The gaseous products (H2, CO, CH4) generated from straw- rearrangement of lignin, aromatic bonds, condensation and
type biomass are utilized in the SMR experiments as reducing dehydrogenation reactions at a high temperature range (160–
0
agents. The top oxide of iron is Fe2O3, and the main experi- 900 C) in the fast pyrolysis process of straw-type biomass. The
mental reduction process is Fe2O3-Fe3O4. However, the trans-
formation of Fe3O4-FeO-Fe is possible in the SMR process. The
gradual deoxidizing mechanisms described by Eqs. (6)–(12)
are shown in Table 3. The relationships between temperature
and Gibbs free energy (DG) are displayed in Table 3. Under the
experimental conditions, the DG of Eqs. (7) and (10) is always
negative, which reveals that the transformation from hema-
tite to magnetite occurs spontaneously. Higher temperatures
are beneficial for the overreduction shown in Eq. (5). Simi-
larly, it is obvious that overreduction occurs easily at higher
temperatures according to Eq. (8). However, the action trends
have only been evaluated by theoretical thermodynamic anal-
ysis, and thus, further experiments are needed [42].
Fig. 2.b. Effects of roasting time on gaseous products. (Cumulative Gases
Reducing gaseous products analysis Emission)

Table 3 Reduction reaction of iron ore and biomass in the SMR process.

Equation number Reactions ΔG-T (kJ/mol)
(2) C H O pyr!olysis → CO2(g)+ CO(g) + H2O(g)+ H2(g) –
3:55
5:6
2:59
(3) C +CO2(g) → 2CO(g) ΔG =29.67-4.23 x 10 T
- 2
(4) C + H2O(g) →CO(g) + H2(g) ΔG =22.83-3.39 x 10 T
- 2
(5) CH4 + H2O(g)→CO(g) + 3H2(g) ΔG =35.98-5.84 x 10 T
- 2
(6) 12FeO3 + CH → 8Fe3O +CO (g) + 2H2O(g) ΔG =3.27-51.38 x 10 T
- 1
4
4
2
(7) 3Fe2O + CO(g) →2Fe3O4 +CO2(g) ΔG =13.31-1.36 x 10 T
- 2
3
(8) Fe3O4 + CO(g)→3FeO+ CO2(g) ΔG =3.78-6.03 x 10 T
- 3
(9) FeO + CO(g) → Fe + CO2(g) ΔG =2.95-5.13 x 10 T
- 3
(10) 3Fe2O3 + H2(g) → 2Fe3O4 + H2O(g) ΔG =6.47-2.20 x 10 T
- 2
(11) Fe3O4 + H2(g)→3FeO+ H2O(g) ΔG =10.62-1.44 x 10 T
- 2
(12) FeO + H2(g) → Fe + H2O(g) ΔG =3.89-3.25 x 10 T
- 3
OCTOBER 2021 / MINES & MINERALS REPORTER 29