Effect of Biomass Torrefaction on the Syngas Quality Produced by Chemical Looping Gasification at 20 kWth Scale.

The innovative Biomass Chemical Looping Gasification (BCLG) process uses two reactors (fuel and air reactors) to generate nitrogen-free syngas with low tar content under autothermal conditions. A solid oxygen carrier supplies the oxygen for partial oxidation of the fuel. This study investigated the BCLG process, conducted over 25 h of continuous operation at 20 kWth scale, using ilmenite as the oxygen carrier and wheat straw pellets as fuel (WSP). The effect of using torrefied wheat straw pellets (T-WSP) on the syngas quality was assessed. In addition, the impact of several operational variables on the overall process performance and syngas yield was analyzed. The primary factors influencing the syngas yield were the char conversion through gasification and the oxygen-to-fuel ratio. Higher temperatures, extended residence times of solids in the fuel reactor, and using a secondary gasifier led to increased char conversion, enhancing H2 and CO production. Optimizing the air reactor design could enhance the CO2 capture potential by inhibiting the combustion of bypassed char. While char conversion and syngas yield with T-WSP were lower than those with WSP at temperatures below 900 °C, T-WSP achieved a higher syngas yield under conditions favoring high char conversion. The presence of CH4 and light hydrocarbons showed minimal sensitivity to operating conditions variation, limiting the theoretical syngas yield. Overall, the CLG unit operated smoothly without any agglomeration issues.

Influence of an Oxygen Carrier on the CH4 Reforming Reaction Linked to the Biomass Chemical Looping Gasification Process.

A major challenge in biomass chemical looping gasification (BCLG) is the conversion of CH4 and light hydrocarbons to syngas (CO + H2) when the goal is the use for bioliquid fuel production. In this work, tests were performed in a batch fluidized bed reactor to determine the catalytic effect on the CH4 reforming reaction of oxygen carriers used in the BCLG process. Three ores (ilmenite, MnGB, and Tierga), one waste (LD slag), and five synthetic materials (Fe10Al, Fe20Al, Fe25Al, Cu14Al, and Ni18Al) were analyzed. These results were compared to those obtained during ∼300 h of continuous biomass gasification operation in a 1.5 kWth BCLG unit. The low-cost materials (ores and waste) did not show any catalytic effect in the CH4 reforming reaction, and as a consequence, the CH4 concentration values measured in the syngas produced in the continuous prototype were high. The synthetic oxygen carriers showed a catalytic effect in the CH4 reforming reaction, increasing this effect with increasing temperature. With the exception of the Ni-based oxygen carrier (used as a reference), the Cu-based oxygen carrier, working at 940 °C, showed the best catalytic properties, in good agreement with the low CH4 concentration values measured in the syngas generated in the continuous unit. The tests performed in a batch fluidized bed reactor were demonstrated to be very useful in determining the catalytic capacity of oxygen carriers in the CH4 reforming reaction. This fact is highly relevant when a syngas with a low CH4 content is desired as a final product.

Upgrading of pine tannin biochars as electrochemical capacitor electrodes.

Biochar derived from the pyrolysis of pine tannin is a green and available by-product of oil manufacturing that presents interesting features after having been activated by KOH at 650 °C. Different weight ratios of KOH to biochar were used and the resulting activated carbons (ACs) presented highly developed specific surface areas of up to 2190 m2 g-1, well-connected porosity and high oxygen content, leading to enhanced electrochemical performance when used as electrochemical capacitor electrodes in a 1 M H2SO4 aqueous electrolyte. Galvanostatic charge/discharge experiments evidenced that the best material achieved a maximum electrode capacitance of up to 232 F g-1 (at 0.5 A g-1) with a capacitance retention of 70% at 10 A g-1 using commercial mass loadings (i.e., approx. 10 mg cm-2). In addition, long cycling stability with a residual capacitance of 92 to 94% after 10,000 cycles at 5 A g-1 was achieved. These results prove that ACs derived from pine tannin biochars have great potential for their commercial use as electrochemical energy storage devices.

Biomass Chemical Looping Gasification of pine wood using a synthetic Fe2O3/Al2O3 oxygen carrier in a continuous unit.

Biomass Chemical Looping Gasification is a novel technology allowing high quality syngas production at autothermal conditions without CO2 emissions to the atmosphere and low tar generation. This work compiles gasification results corresponding to 38 h of continuous operation in a 1.5 kWth unit using pine wood as fuel and a synthetic Fe-based oxygen carrier, Fe20Al. The main operating conditions such as temperature (T = 820-940 °C), steam-to-biomass ratio (S/B = 0.05-0.65), and oxygen-to-biomass ratio (λ = 0.2-0.6) were analyzed at steady state conditions using a novel method for controlling oxygen in the process. A syngas composed by 37% H2, 21% CO, 34% CO2 and 7% CH4, and tars below 2 g/Nm3 could be obtained at autothermal conditions, leading to a syngas yield of 0.8 Nm3/kg dry biomass and a cold gas efficiency of 68%. The material maintained a high reactivity although some Fe lost was observed.