• Energy Research

Abstract Direct reduction of iron ore pellets (DRI) with and without biomass was studied using hydrogen as the reducing agent. The influences of temperature and time on the reduction rate of pellets were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET (Bet specific surface area) tests were adopted to interpret the mechanism of Fe 2 O 3 reduction with H 2 , as well as explore the role of biomass in pellets during the reduction process. Results show that the biomass not only improve the reduction extent of the pellets, but also increase the reduction velocity index (RVI) of the pellets by 1.12%/min. The BET test indicates that the existence of biomass can create porosity in pellets by dehydration and combustion/pyrolysis, which increases the contact area between iron oxide and reducing gas during reduction process, and decreases the apparent activation energy of pellets from 122 kJ mol −1 (without biomass) to 111 kJ mol −1 (with biomass). For the DRI process, the crucial reduction step FeO → Fe is controlled by the intrinsic interfacial chemical reaction.

Abstract Kinetic study and syngas production from pyrolysis of forestry waste (pine sawdust (PS)) were investigated using a thermogravimetric analyzer (TGA) and a fixed-bed reactor, respectively. In TGA, it was found that the pyrolysis of PS could be divided into three stages and stage II was the major mass reduction stage with mass loss of 73–74%. The discrete distributed activation energy model (DAEM) with discrete 200 first-order reactions was introduced to study the pyrolysis kinetic. The results indicated that the DAEM with 200 first-order reactions could approximate the pyrolysis process with an excellent fit between experimental and calculated data. The apparent activation energies of PS ranged from 147.86 kJ·mol −1 to 395.76 kJ·mol −1 , with corresponding pre-exponential factors of 8.30 × 10 13 s −1 to 3.11 × 10 25 s −1 . In the fixed-bed reactor, char supported iron catalyst was prepared for tar cracking. Compared with no catalyst which the gas yield and tar yield were 0.58 N m 3 /kg biomass and 201.23 g/kg biomass, the gas yield was markedly increased to 1.02 N m 3 /kg biomass and the tar yield was decreased to only 26.37 g/kg biomass in the presence of char supported iron catalyst. These results indicated that char supported iron catalyst could potentially be used to catalytically decompose tar molecules in syngas generated via biomass pyrolysis.

Abstract The evaluation of chemical looping combustion (CLC) for CO2 capture was conducted via a thermogravimetric analyzer (TGA) and a laboratory-scale fluidized bed using pine sawdust (PS) as fuel and metal ferrites, MFe2O4 (M = Cu, Ni and Co), as oxygen carriers. Metal ferrites were prepared by sol-gel method. The fresh, reduced and after five redox cycles oxygen carriers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and accelerated surface area porosimetry. Thermodynamic simulation was performed using software HSC Chemistry 6.0. The TGA results indicated that CuFe2O4 shows a lower initial reaction temperature, and CoFe2O4 has a faster oxygen uptake rate. Both carbon conversion (xc) and carbon capture efficiency (ηCO2) increased with temperature. The maximum values of xc and ηCO2 were 96.86% and 95.48%, 95.45% and 94.25%, and 95.17% and 94.04% for CuFe2O4, CoFe2O4, and NiFe2O4 at 900 °C, respectively. The CuFe2O4 shows higher reaction reactivity, while NiFe2O4 has a higher catalytic activity for decomposition of tar in fluidized bed tests. The XRD results show CoFe2O4 is more readily reduced to FeO, which agreed with the results of thermodynamic simulation, and three metal ferrites can be regenerated completely after five cycles. The values of xc and ηCO2 remained high for both CuFe2O4 and CoFe2O4, while a significant decrease in xc and ηCO2 for NiFe2O4 was observed after five cycles due to significant sintering. Both CuFe2O4 and CoFe2O4 are more applicable as oxygen carriers in biomass CLC compared with NiFe2O4.

Abstract Pyrolysis kinetics of pine wood, rice husk and bamboo ( Bambusa chungii ) were studied via thermo-gravimetric analysis technique under low heating rates. The result of model-free procedure showed that the lignocellulosic pyrolysis according to one-step reaction model is dominated by the diffusion effects. However, the complex features of variations are caused by the mechanism changes, which are hard to be determined. The distributed activation energy model (DAEM) kinetic results indicated that the activation energy distribution for pseudo components follows the orders of: E 0 (lignin) > E 0 (cellulose) > E 0 (hemicelluloses), σ (lignin) > σ (hemicelluloses) > σ (cellulose). The Fraser–Suzuki deconvolution fits better with the experimental data than DAEM. The pyrolysis mechanism of pseudo components after deconvolutions follows the theoretical models: third order model f ( α ) = (1 − α ) 3 for hemicelluloses and lignin, random scission model f ( α ) = 2( α 1/2 − α ) for cellulose. The apparent activation energy for pseudo hemicelluloses is 162.84 ± 26.45 kJ/mol for pine wood, 168.63 ± 28.47 kJ/mol for rice husk and 154.55 ± 26.49 kJ/mol for bamboo, respectively. The E α value increases with the conversion with little deviation to its mean value. Similar E α vs. α dependencies also are observed for pseudo celluloses, which has E α of 188.14 ± 24.42 kJ/mol for pine wood, 206.71 ± 24.88 kJ/mol for rice husk and 190.45 ± 23.79 kJ/mol for bamboo, respectively.

Catalytic pyrolysis of rain tree biomass (RTB), a typical horticultural waste, was investigated with nano-NiO as catalyst produced from hazardous nickel plating slag (NPS). It appeared from the analyses by FTIR, TGA, XRD, BET, and FESEM/EDX that nano-NiO produced had a SBET and mean particle size of 53.4 m2/g and 112.3 nm. The catalytic pyrolysis kinetics of RTB with and without catalyst were studied by Friedman method. It was found that the activation energy (Ea) was in the range of 177 to 360 kJ/mol at a conversion rate of 0.1 - 0.75. The results further revealed that the H2 increase ratio in pyrolysis above 500 °C was more than 40% in the presence of catalyst. Consequently, this study showed the great potential of nano-NiO as a high-efficiency catalyst in recovering energy from biomass.

The pyrolysis process of two microalgae, Chlorella pyrenoidosa (CP) and bloom-forming cyanobacteria (CB) was examined by thermo-gravimetry to investigate their thermal decomposition behavior under non-isothermal conditions. It has found that the pyrolysis of both microalgae consists of three stages and stage II is the major mass reduction stage with mass loss of 70.69% for CP and 64.43% for CB, respectively. The pyrolysis kinetics of both microalgae was further studied using single-step global model (SSGM) and distributed activation energy model (DAEM). The mean apparent activation energy of CP and CB in SSGM was calculated as 143.71 and 173.46 kJ/mol, respectively. However, SSGM was not suitable for modeling pyrolysis kinetic of both microalgae due to the mechanism change during conversion. The DAEM with 200 first-order reactions showed an excellent fit between simulated data and experimental results.

Ex situ catalytic pyrolysis of biomass using char-supported nanoparticles metals (Fe and Ni) catalyst for syngas production and tar decomposition was investigated. The characterizations of fresh Fe-Ni/char catalysts were determined by TGA, SEM–EDS, Brunauer–Emmett–Teller (BET), and XPS. The results indicated that nanoparticles metal substances (Fe and Ni) successfully impregnated into the char support and increased the thermal stability of Fe-Ni/char. Fe-Ni/char catalyst exhibited relatively superior catalytic performance, where the syngas yield and the molar ratio of H2/CO were 0.91 Nm3/kg biomass and 1.64, respectively. Moreover, the lowest tar yield (43.21 g/kg biomass) and the highest tar catalytic conversion efficiency (84.97 wt.%) were also obtained under the condition of Ni/char. Ultimate analysis and GC–MS were employed to analyze the characterization of tar, and the results indicated that the percentage of aromatic hydrocarbons appreciably increased with the significantly decrease in oxygenated compounds and nitrogenous compounds, especially in Fe-Ni/char catalyst, when compared with no catalyst pyrolysis. After catalytic pyrolysis, XPS was employed to investigate the surface valence states of the characteristic elements in the catalysts. The results indicated that the metallic oxides (MexOy) were reduced to metallic Me0 as active sites for tar catalytic pyrolysis. The main reactions pathway involved during ex situ catalytic pyrolysis of biomass based on char-supported catalyst was proposed. These findings indicate that char has the potential to be used as an efficient and low-cost catalyst toward biomass pyrolysis for syngas production and tar decomposition.

Abstract Thermogravimetric kinetics and pyrolytic tri-state products analyses towards insights into understanding the pyrolysis mechanism of Spirulina platensis with calcium oxide were investigated using a thermogravimetric analyzer and a fixed bed reactor, respectively. The pyrolysis kinetics were studied by Friedman method and results indicated that the f(α)=(1-α)4 with A0 = 1.99E+10s−1 and f ( α ) = − 1 / l n ( 1 − α ) with A0 = 8.33E+11s−1 were suitable for Spirulina platensis and Spirulina platensis + CaO (stage II) pyrolysis, respectively. According to pyrolysis behaviors and kinetics analyzed, the potential reaction behaviors of CaO during the pyrolysis of Spirulina platensis were explored. Spirulina platensis pyrolytic tri-state products analyzed indicated that, when CaO as additive, the gas yield markedly increased with more H2, CO content and less CO2 content and the bio-oil yield significantly decreased. Moreover, the contents of aromatic compounds, aliphatic compounds, phenols and ketons obviously increased in bio-oil with the appreciably decreased in the contents of esters, N-containing compounds, O-containing compounds and acids. Based on the evolutionary mechanism of CaO and pyrolytic tri-state products, the pyrolysis mechanism of Spirulina platensis with calcium oxide was proposed.