The effect of the blend ratio and reactor temperature on the gasification characteristics of pyrolysis oil (PO) and black liquor (BL) blends with up to 20 wt% PO was studied in a pilot-scale entrained-flow gasifier. In addition to unblended BL, three blends with PO/BL ratios of 10/90, 15/85, and 20/80 wt% were gasified at a constant load of 2.75 MW_th. The 15/85 PO/BL blend was used to investigate the effect of temperature in the range 1000–1100 °C. The decrease in fuel inorganic content with increasing PO fraction resulted in more dilute green liquor (GL), and a greater portion of the feedstock carbon ended up in syngas as CO. As a consequence, the cold gas efficiency increased by about 5%-units. Carbon conversion was in the range 98.8–99.5% and did not vary systematically with either fuel composition or temperature. Although the measured reactor temperatures increased slightly with increasing PO fraction, both unblended BL and the 15% PO blend exhibited largely similar behavior in response to temperature variations. The results from this study show that blending BL with the more energy-rich PO can increase the cold gas efficiency and improve the process carbon distribution without adversely affecting either carbon conversion or the general process performance.

The integration between K₂CO₃ catalytic hydrothermal liquefaction (HTL) and gasification is explored to improve the gasification process. In this study, the CO₂ gasification characteristics and the activation energies of the chars derived from four kinds of HTL products, black liquor (BL), and virgin pine sawdust (PS) are investigated non-isothermally using a thermogravimetric analyzer. The complete conversion of BL char and HTL product chars was achieved at lower temperatures (1150 K) than that of PS char (1300 K). BL char showed the highest derivative thermogravimetric (DTG) peak, an indicator of high reactivity, followed by HTL product chars and PS char. HTL liquid product chars exhibited the lowest DTG peak temperature (1023–1058 K), which is advantageous for the low-temperature gasification. The activation energies were calculated isoconversionally using the Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Starink approximations. On the basis of the KAS method, the range of the activation energy for the HTL aqueous product char sample was 127–259 kJ/mol, which was wider than that for BL char (171–190 kJ/mol). The HTL process can improve the gasification feedstock reactivity, and the use of the HTL liquid product allows for the gasification at a low temperature.

The catalytic activity of alkali compounds in black liquor (BL) enables gasification at low temperatures with high carbon conversion and low tar and soot formation. The efficiency and flexibility of the BL gasification process may be improved by mixing BL with fuels with higher energy content such as pyrolysis oil (PO). The fate of alkali elements in blends of BL and PO was investigated, paying special attention to the amount of alkali remaining in the particles after experiments at high temperatures. Experiments were conducted in a drop tube furnace under different environments (5% and 0% vol. CO₂ balanced with N₂), varying temperature (800–1400 °C), particle size (90–200 µm, 500–630 µm) and blending ratio (0%, 20% and 40% of pyrolysis oil in black liquor). Thermodynamic analysis of the experimental cases was also performed.

The thermodynamic results qualitatively agreed with experimental measurements but in absolute values equilibrium under predicted alkali release. Alkali release to the gas phase was more severe under inert conditions than in the presence of CO₂, but also in 5% CO₂ most of the alkali was found in the gas phase at T = 1200 °C and above. However, the concentration of alkali in the gasification residue remained above 30% wt. and was insensitive to temperature variations and the amount of PO in the blend. Thermodynamic analysis and experimental mass balances indicated that elemental alkali strongly interacted with the reactor’s walls (Al₂O₃) by forming alkali aluminates. The experience indicated that adding PO into BL does not lead to alkali depletion during high temperature gasification.

The efficiency and flexibility of the BL gasification process may improve by mixing BL with more energy-rich fuels such as pyrolysis oil (PO). To improve understanding of the fuel conversion process, blends of BL and PO were studied in an atmospheric drop tube furnace. Experiments were performed in varying atmosphere (5% and 0% CO₂, balanced by N₂), temperature (800–1400 °C), particle size (90–200 μm and 500–630 μm) and blending ratio (0%, 20% and 40% of PO in BL on weight basis). Additionally, pine wood was used as a reference fuel containing little alkali. The addition of PO to BL significantly increased the combined yield of CO and H₂ and that of CH₄. BL/based fuels showed much lower concentration of tar in syngas than pine wood. Remarkably, the addition of PO in BL further promoted tar reforming in presence of CO₂. Unconverted carbon in the gasification residue decreased with increasing fractions of PO. Small fuel particles showed complete conversion at 1000 °C but larger particles did not reach complete conversion even at T = 1400 °C.

This study assesses the feasibility of black liquor/glycerol blends as potential gasification feedstock. The char gasification reactivity and kinetics were studied at T = 750 °C, 800 °C, 850 °C and 900 °C for 20% and 40% blends of glycerol with black liquor. Three qualities of glycerol were used including two industrial grade crude glycerols. Gasification rates were similar for all blends, indicating sufficient alkali metal catalysis also for the char blends (Alkali/C atomic ratio between 0.45 and 0.55). The blends with the most impure glycerol (containing K) were found to have the lowest activation energies (~120 kJ/mol) and reaction times for char gasification indicating fuel properties suitable for gasification. Char particles from different blends showed similar surface morphology as black liquor chars with even surface distribution of alkali elements. A loss of alkali (mainly, K) from the fuel blends during pyrolysis indicated the necessity to perform gas-phase studies of alkali release. Overall, these results encourage the use of glycerol as a potential gasification feedstock for catalytic gasification based bio-refineries.  

Different concentrations (0.1 and 1 M K⁺/Na⁺) of salt solutions (K₂CO₃, Na₂CO₃, NaOH and NaCl) were used to impregnate alkali in sawdust. After devolatilization, char samples were gasified at different temperatures (750–900 °C) under CO₂ in a macro-thermogravimetric analyzer for gasification kinetics. Morphologically, three classes of chars could be identified. Chars experiencing the highest catalytic influence were in Class-2 (0.5 M K₂CO₃ and 1 M NaOH) with a swollen and molten surface. In contrast, Class-1 (wood char like) and Class-3 (with salt deposits) chars showed moderate and low catalytic effect on gasification reactivity respectively. It is believed to be related to char surface swelling and alkali salt used. At 850 °C or below, the reactivity increased linearly (Class-1 and Class-3 Char) with initial alkali content up to 2200 mmol alkali/kg of char (except for NaCl). The same reaction rate was maintained until 3600 mmol/kg of char of alkali loading (Class-2) and then decreased. However, no trend was observed at 900 °C due to drastic change in reactivity of the samples, probably due to alkali transformation. Among the salts, K₂CO₃ (0.5 M) was found to be the most suitable for catalytic gasification due to its high catalytic activity in combination with relatively low carbon leaching.

This paper describes the development of a multiscale equivalent reactor network model for pressurized entrained flow biomass gasification to quantify the effect of operational parameters on the gasification process, including carbon conversion, cold gas efficiency, and syngas methane content. The model, implemented in the commercial software Aspen Plus, includes chemical kinetics as well as heat and mass transfer. Characteristic aspects of the model are the multiscale effect caused by the combination of transport phenomena at particle scale during heating, pyrolysis, and char burnout, as well as the effect of macroscopic gas flow, including gas recirculation. A validation using experimental data from a pilot-scale process shows that the model can provide accurate estimations of carbon conversion, concentrations of main syngas components, and cold gas efficiency over a wide range of oxygen-to-biomass ratios and reactor loads. The syngas methane content was most difficult to estimate accurately owing to the unavailability of accurate kinetic parameters for steam methane reforming.

Tar and soot in product gas have been a major technical challenge toward the large-scale industrial installation of biomass gasification. This study aims at demonstrating that the formation of tar and soot can be reduced simultaneously using the catalytic activity of alkali metal species. Pine sawdust was impregnated with aqueous K2CO3 solution by wet impregnation methods prior to the gasification experiments. Raw and alkali-impregnated sawdust were gasified in a laminar drop-tube furnace at 900–1400 °C in a N2–CO2 mixture, because that creates conditions representative for an entrained-flow gasification process. At 900–1100 °C, char, soot and tar decreased with the temperature rise for both raw and alkali-impregnated sawdust. The change in tar and soot yields indicated that potassium inhibited the growth of polycyclic aromatic hydrocarbons and promoted the decomposition of light tar (with 1–2 aromatic rings). The results also indicated that the catalytic activity of potassium on tar decomposition exists in both solid and gas phases. Because alkali salts can be recovered from product gas as an aqueous solution, alkali-catalyzed gasification of woody biomass can be a promising process to produce clean product gas from the entrained-flow gasification process at a relatively low temperature.

This study evaluated the techno-economic performance and potential benefits of methanol production through catalytic gasification of forest residues and lignin. The results showed that while catalytic gasification enables increased cold gas efficiencies and methanol yields compared to non-catalytic gasification, the additional pre-treatment energy and loss of electricity production result in small or no system efficiency improvements. The resulting required methanol selling prices (90-130 €/MWh) are comparable with production costs for other biofuels. It is concluded that catalytic gasification of forest residues can be an attractive option as it provides operational advantages at production costs comparable to non-catalytic gasification. The addition of lignin would require lignin costs below 25 €/MWh to be economically beneficial.

Based on char gasification experiments in an isothermal thermogravimetric analyzer, a suitable concentration of alkali salt (K2CO3) was chosen for impregnation due to almost five-fold increase in gasification reactivity and relatively low amount of carbon leaching during impregnation. Furthermore, an optimum method for wet alkali impregnation was proposed based on the several tests performed by varying temperature and time. To study the catalytic effect on tar and soot yield, untreated and impregnated woody biomass were gasified under entrained flow condition between 900 oC and 1200 oC. Impregnation leads to 70% lower tar yield from gasification around 1000 oC and 1100 oC. The lowest amount of soot was detected for the same temperature range whereas the soot yield was one order of magnitude higher for untreated biomass. For tar, this influence became insignificant at a higher temperature (1200 oC). This defines the suitable temperature range for alkali catalyzed gasification without the loss of catalytic activity.