Wood Char Research Articles

Whisky decarbonisation potential using bio-waste

The objective was to investigate the potential of the Scottish Whisky industry to employ the circular economy to decarbonise and reduce costs, using its own bio-waste as a source of energy to power distilleries. The analysis uses a literature review of the fossil fuel energy for heat used in modern distilleries in terms of MJ/Lalcohol. It then determines the energy content of the whisky distillery bio-wastes: draff, pot ale, spent lees and wash (SLW). Outside the distillery there are bio-wastes in the barley straw on farms and from the malt-house, barley husks, rootlets and dark grains and the maturation barrel preparation area with a wood char waste. The energy in the wastes is also expressed as MJ/Lalcohol which then enables the determination of the proportion of the energy to operate the distillery that can be provided from the bio-waste. The distillery wastes all have a high water content, the amount of which is reviewed. The energy to evaporate this water is determined to give the net energy from the bio-wastes. The findings are that in the distillery, including the energy to evaporate water, requires 60 MJ/Lalcohol, with half of this used to evaporate water. Most of the energy in wet wastes is used to evaporate the water and there is only 8.7 MJ/Lalcohol to contribute to the distillery energy requirements. For dry draff and PAS the energy is sufficient to operate the distillery, but the energy to dry the draff has to be provided at some stage in the process. However, there is enough energy in barley straw and malthouse wastes to provide the rest of the heat required in a distillery and to completely decarbonise the whisky industry. This is the first time that all the bio-wastes have been assessed in whisky manufacture, from the farm to the maturation barrel stores. It is proposed that the best way to use these diverse bio-wastes is gasification of the solid wet waste to produce a biomass gasification gas (BGG) with direct burning of the BGG to generate the heat to burn the PA and SLW and evaporate the water.

Activated Carbons for Removing Ammonia from Piggery Vent Air: A Promising Tool for Mitigating the Environmental Impact of Large-Scale Pig Breeding

Unsustainable pig breeding is a great threat to the environment. Ammonia is one of the main pollutants emitted in piggery vent air. This work is a comparative survey that presents the findings on the effectiveness of ammonia adsorption from air using various activated carbons (ACs). Detailed consideration is given to the effects of (i) type of raw material (wood char, wood pellet, and commercial lignite-based char), (ii) preparation method (CO2, steam, and KOH activation), and (iii) activation conditions (temperature and KOH/char ratio), on the porous structure of ACs and their ammonia sorption capacity and reversibility. Response surface methodology and genetic algorithm were used to find optimum KOH activation conditions. Economic analyses of AC production were performed using process modeling in Aspen software. It was found that ACs obtained from wood char in KOH activation show a maximum ammonia capacity of 397 g/kg, which is at least 2.5-fold higher than that reached on ACs from physical activation. A lower activation temperature (<750 °C) and a higher KOH/char ratio (>3) were preferred for effective adsorption, regardless of the type of feedstock. High sorption reversibility was achieved (87–96%). This makes the obtained sorbents promising sorbents for ammonia removal from piggery vent air with potential subsequent application as nitrogen-enriched biochar for crop fertilization. Thus, it facilitates sustainable pig breeding.

Charring of and Chemical Changes in Historical Wood under Thermal Loading

Research in historical timber assessment is hindered by the limited availability of samples, yet understanding the fire resistance of historic wood is crucial for preservation efforts. There is an opinion that historic wood behaves similarly to contemporary wood in terms of fire resistance. The aim of this paper is to observe the rate of charring of historical pine wood during the experiment, the color changes in the sample that occurred due to thermal loading, and the changes in the chemical composition of pine wood. Test samples made from historic pine wood were loaded with a 50 kW∙m−2 radiation panel for 60 min. The charring process was faster at the beginning of the charred layer formation. The charring rate at the beginning of the test at a depth of 10 mm from the exposed side reached values from 1.28 mm∙min−1 to 3.16 mm∙min−1. At a depth of 30 mm from the exposed side, the individual charring rates approached a value of 1 mm∙min−1 (0.99 mm∙min−1 to 1.08 mm∙min−1). Observations during medium-scale testing revealed distinct layers forming on the exposed side: a charred layer, charring base, pyrolysis layer, and intact wood. The chemical composition of the wood changed under the influence of the thermal load. The relative contents of extractives and holocellulose decreased with the increasing temperature while the lignin content increased. The highest value of combustion heat was measured in the charred layer of the sample. Correlation analysis demonstrated a negative relationship between the combustion heat and holocellulose, while a positive correlation was found with the lignin content. Chemical changes were also monitored using the FTIR method. These findings provide valuable insights into the behavior of historic pine wood under thermal loading, which is essential for understanding and preserving historical structures.

Progressive inhibition of [formula omitted] reaction in wood char packed bed by in-situ evolving [formula omitted]: Experimental insights and theoretical analysis

Previous research on Char reactions with gas phase compounds under micro-thermogravimetry systems shows that hydrogen inhibits heterogeneous char reactions. However, its impact on larger gasification systems with evolving hydrogen profiles remains largely unexplored. This study examines a macro-scale wood char bed to understand the influence of in situ evolving hydrogen on char reactions. When subjected to a specific steam flux, carbon conversion and pore morphology changes are mainly confined to the bed’s upstream, with the downstream char retaining its original characteristics. Numerical investigations reveal over 75 % of species production and consumption occurs within the initial 20 % of bed height. Fourier-transform infrared spectroscopy confirms hydrogen-induced inhibition in downstream segments, showing a shift from C–OH to C–H bonds. Particle-scale analysis indicates significantly higher rates of hydrogen diffusion and adsorption compared to H2O, impeding downstream C+H2O reactions. Increased temperature, higher reactant concentrations, or reduced residence time can overcome this inhibition, enhancing conversion rates. These findings are critical for optimizing steam-to-biomass ratios in oxy-steam gasification systems for generating hydrogen-rich syngas.

Changes in Physical and Water Sorption Characteristics of Three Solid Woods after One-Sided Surface Charring.

One-sided surface charring of wood is a modification process used to lower moisture absorption and improve the resistance to biological degradation for durable surface exterior claddings. Cupressus lusitanica, Gmelina arborea, and Tectona grandis wood samples from fast-growth plantation were charred with a hot plate using three temperatures (300, 350, and 400 °C ± 3 °C) for 10 min. Wood density, surface quality (color and presence of splits), and sorption characteristics (wetting rate and water uptake) were evaluated. Results show that samples charred at 300 °C presented a lower loss of density and thickness than samples charred at 400 °C. Changes in the chemical structure of the wood as a result of the high temperatures caused a decrease of all color parameters (L*, a*, and b*). These values decreased in the samples charred at 400 °C for the three species. Also, the presence of cracks and splits on the surface, or in some cases the presence of detachments from the charring surface, was mostly observed in the samples charred at 350 and 400 °C. One-sided surface charring reduced the liquid water sorption of wood samples in comparison with that of reference samples, especially for C. lusitanica and T. grandis. G. arborea, due to the composition of its anatomical structure and its initial density, chars faster than the other species, causing a greater loss of density, wetting rate values like those of the reference wood, and higher values of water uptake.

CO2 conversion to CO by fluidized bed biomass gasification: Measuring CO2 utilization via stable carbon isotope ratios

Thermochemical conversion of CO2 in biomass gasification is a promising technology for utilizing CO2 as a feedstock to produce a CO-rich gas. Simultaneous decomposition reactions of biomass and various gas-solid and gas-gas reactions form the product gas in this process. The overlap in sub-processes makes it challenging to assess the conversion of feedstock CO2 with common methods like mass balancing. This work introduces stable carbon isotope ratio analysis (δ13C) to identify the sourcing of carbonaceous product gas components and determine the conversion of CO2. This methodology is applied to evaluate experiments conducted for one hour of continuous operation in a lab-scale fluidized bed gasifier. Softwood pellets and wood char are used as fuel, with Olivine as a bed material, a target heating temperature of 1000 °C and atmospheric pressure. Product gas with more than 80 vol% CO was generated when wood char was used as fuel. Stable carbon isotope measurements show that CO2 is converted at 48–93% in this process, underpinning the position of biomass CO2 gasification as carbon capture and utilization technology. These results were up to 25% higher than suggested by mass balancing, with higher discrepancies at lower CO2 conversions when using softwood as fuel. Therefore, stable carbon isotope ratio measurement can be a valuable tool for improving the process understanding of biomass CO2 gasification. The results can be used for carbon accounting and the technical development of gasifiers with high CO2 utilization efficiency.

Augmenting bamboo strength and thermal stability for sustainable construction

In modern timber structures, the prevalent use of metal fasteners for structural connections introduces concerns related to their high thermal conductivity, which can induce excessive charring of adjacent wood and compromise joints fire resistance. To address this, the exploration of high-strength bio-materials presents a promising alternative. In this study, an eco-friendly methodology was employed to augment the densification of bamboo, resulting in the creation of composite-modified bamboo without the use of organic thermosetting resin. Comprehensive investigations were conducted to evaluate its mechanical properties and high-temperature performance. Microscopic alterations were unveiled through Fourier Transform Infrared spectroscopy (FT-IR) and scanning electron microscopy, complementing each other in revealing substantial changes. The results of chemical constituents and FT-IR analyses corroborated the observed alterations. A noteworthy observation is that the modification of composite materials significantly increased modulus of elasticity, bending, and tensile strengths of bamboo, with a slight improvement in compressive strength. Additionally, it concurrently enhanced ductility. The thermal stability of composite-modified bamboo exhibited an initial increase followed by a subsequent decline over duration. The increased density induced by hot pressing facilitated the formation of a denser charring layer, effectively serving as a protective shield against external heat and oxygen. Consequently, this limited the degradation of bamboo constituents under high-temperature conditions. The optimal alkaline treatment duration for 9 mm thick bamboo was determined as 7 h based on the methodology established in this investigation.

Pilot-scale pyrolysis and activation of typical biomass chips in an interconnected dual fluidized bed: Comparison and analysis of products

A 150 kg/h novel pilot dual fluidized bed (DFB) was designed, constructed, and commissioned. In this study, six types of biomass chips were investigated and compared in interconnected pyrolysis and activation/gasification systems using dolomite as bed material, and employing steam and flue gas as activation agents. The maximum iodine and methylene blue adsorption capacities were 436.79 mg/g (pear wood char) and 203.65 mg/g (walnut wood char), respectively, indicating high adsorption capacity of char. The carbon fixation ratios were 34.70–53.75 wt%, and the maximum lower heating value of 9.34 MJ/Nm3 was achieved for pyrolysis gas with the highest CO and H2 contents of 44.30 vol% and 16.18 vol%, respectively. The maximum phenolic compounds reached 73.46% for mesquite wood chips oil. Oils collected from the riser contained fewer organic species compared to oil from pyrolyzer. Furthermore, energy efficiencies were found to range from 66.70% to 84.91%, and the total energy yields were 67.12–87.08%. The internal rate of return and payback period of the process were 33.25–44.29% and 3.0–2.2 years, respectively. Co-production of activated biochar, combustible gas, and oils from the interconnected DFB system exemplifies noteworthy environmental and economic advantages for sustainable energy practices.

Effects of plasma treatment on biodegradation of natural and synthetic fibers

This study investigates the application of plasma treatment as a means to enhance biodegradation and modify the structural characteristics of fibrous composites. The methodological component of the study includes the selection of the research object; production of composites; low-temperature plasma treatment, and treatment of biodegradability and mechanical strength of samples. The strengthening of fibers with cellulose leads to a significant improvement in mechanical strength. Such an indicator as mechanical strength increases from 18 to 21 MPa. Treatment of natural fibers with low-temperature plasma led to an increase in mechanical strength from 18 to 25 MPa. Treating reinforced fibers with low-temperature plasma currently results in an even greater enhancement in mechanical strength, increasing from 18 to 29 MPa.The electron microscopy of samples reveals some differences in cell wall microfibrils between plasma-treated and non-treated samples. The non-treated fibres are found to have chips and voids. Meantime, the plasma-treated fibres show structural changes in certain regions which resemble wood charring. Through a comprehensive analysis, this research underscores the substantial impact of plasma treatment on the degradation kinetics and morphological features of cellulose-based composites. The results reveal distinct alterations in the composition and behavior of plasma-treated fibres, signifying a shift towards enhanced biodegradability. The natural fibres examined in this study contained 28–30% lignin, whereas the composites exhibited a lower lignin content of 21–23%. These findings corroborate the inference that plasma treatment induces significant changes in fibre structure, accelerating the biodegradation process by 7 days.

Sandwich-structure inspired super-tough and fire-resistant plywood containing vinyl acetate-ethylene based adhesive reinforced by melamine amino trimethyl phosphate and sodium lignosulfonate

The flammability of wood composite materials inevitably limits its broadly applications, inspired by the sandwich structure, we propose an intumescent flame-retardant vinyl acetate-ethylene based adhesive reinforced by melamine amino trimethyl phosphate and sodium lignosulfonate compounds (IFRs), then being incorporated in adhesive layer to prepare fire-proofing plywood. The formaldehyde-free adhesive incorporated with 23 wt% IFRs in plywood (FR plywood) resulted in a significant reduction in the peak heat release rate (pHRR, −51 %) and a great delay in time to pHRR (219 s) compared with that of the sample neat plywood. Additionally, the shear strength and bending strength of sample FR plywood present significant increase of 150 % and 73 %, respectively, compared to that of the neat plywood. By incorporating the IFRs into the plywood adhesive layers, low-flammability gasses can be released under heat to dilute flammable volatile gasses together with the wood decomposition in the gaseous phase, simultaneously, generated polyphosphoric acids to facilitate the charring of wood under heat, leading to a cohesive and dense phospho-carbonaceous structure in the condensed phase. Thus, this work provides an efficient and simple strategy to prepare fire-proofing plywood with excellent mechanical performance, is worth commercializing in plywood industry.

Manganese- and Nitrogen-Doped Biomass-Based Carbons as Catalysts for the Oxygen Reduction Reaction

Manganese- and nitrogen-doped carbon materials were produced using NaOH-activated wood char and wood-processing residues such as wood chips and black liquor and evaluated as oxygen reduction catalysts for further application in fuel cells or metal–air batteries. The elemental and chemical composition, with special attention given to types of nitrogen bonds and the structure, morphology, and porosity of the obtained catalyst materials were studied. The catalytic activity was assessed in an alkaline medium using the rotating-disk electrode method. It has been shown that synthesized and doped N-Mn catalytic materials based on biomass precursors with different chemical structures are a promising alternative to modern oxygen reduction catalysts based on precious metals.

Temperature of Wood Char Particles Burning in a Fluidized Bed Reactor

In the present work it was studied the fluidized bed combustion of char particles made with wood of Mozambican origin to find out the evolution of the particles temperature during the combustion process. Samples of wood species Afzelia quanzensis and Pterocarpus angolensis were carbonized at 850 ºC in a nitrogen flow. Afterwards some of these char particles with sizes in the 9 to 13 mm range were burned in a bubbling fluidized bed, while at the same time their interior temperatures were measured. From the experiments, it was found that for these chars fragmentation was absent and that the measured temperatures with a thermocouple inserted into the particles was similar to the values that were obtained by means of an energy balance carried out at the surface of the particle.

Singlet Oxygen Quantum Yields of Pyrogenic Dissolved Organic Matter from Lab-Prepared and Wildfire Chars.

Wildfires or prescribed fires release pyrogenic dissolved organic matter (pyDOM) into the environment, which can photochemically produce singlet oxygen (1O2) in sun-lit surface waters. 1O2 quantum yields (ΦΔ) are well-studied for non-pyrogenic DOM, but little is understood about the 1O2 generation from pyDOM, especially the ΦΔ values from real wildfire samples and their wavelength dependence. In this study, time-resolved 1O2 phosphorescence was used to determine the wavelength-dependent ΦΔ values for pyDOM generated from wildfire char and a series of lab-prepared chars produced by combusting oak and pine wood. Wildfire and most lab-prepared pyDOM generally had similar ΦΔ values (2.1-2.7%) at 365 nm compared to the reference Suwannee River Natural Organic Matter (SRNOM) isolate (2.4%). Interestingly, pyDOM from the highest combustion temperature char was found to possess extremely low ΦΔ values compared to SRNOM and other pyDOM at all excitation wavelengths. In addition, it was revealed that the predicted steady-state concentration of 1O2 from pyDOM was similar to that from SRNOM, indicating that the addition of pyDOM from wood chars may not strongly impact surface water photochemistry.

Comparison between two-step and single-step kinetic models for non-isothermal CO2 gasification of biomass char generated by fast pyrolysis

Kinetic analysis plays a critical role in the gasification process. The kinetics of CO2 gasification for various wood chars, which were prepared in a single particle reactor (SPR), were studied using a non-isothermal method in a thermogravimetric analyzer. To statistically derive significant conclusions, the data obtained from the gasification of fast pyrolyzed chars are used to compare the performance of the volumetric model (VM), grain model (GM), random pore model (RPM), integrated core model (ICM), and two-step (first step: VM; second step: ICM) parallel model. The obtained results show that most |DDTG| curves show one local minimum, representing at least one reaction step. When combined with the TG curves, the gasification process exhibits a distinct devolatilization and char gasification component. ICM has a better performance compared to the other single-step models. The two-step model significantly improves over the single-step model due to the additional equation. The two-step model's average deviation DEV(X) is 0.95 %, which shows an 80 % improvement compared to ICM (DEV(X) = 4.64 %). The predicted activation energy (devolatilization: 54.8–76.2 kJ/mol; gasification: 185.7–247.5 kJ/mol) falls within a reasonable range, which is consistent with the findings reported in the literature.

The April 2015 Calbuco eruption pyroclastic density currents: deposition, impacts on woody vegetation, and cooling on the northern flank of the cone

The 22-23 April 2015 eruption of the Calbuco volcano (Southern Andes, Chile) led to extensive pyroclastic density currents (PDCs) interactions with vegetation. We seek to describe the PDCs which affected both Tepu and Frío rivers, northern Calbuco, from their timing and deposition to cooling and erosion, as well as their impacts on forests. Our investigation is based on field stratigraphy, forest disturbance assessment, and geothermometry from degassing pipes and charcoal. These PDCs reached at least ~540-603 °C, as estimated from fumaroles, and consisted of both concentrated and dilute PDCs during the first pulse (22 April) at Tepu and mainly during the second pulse (23 April) at Frío. Effects of PDCs on forest vegetation recorded in Tepu consisted of heating, abrasion, burial, and impact force. On the valley floor, trees were buried with up to 4 m of deposits from the concentrated PDCs, and all trees in this deposition zone died with no subsequent sprouting. Conversely, in the margins of the valley, defoliated fallen trees and standing shrubs indicate scorching due to the passage of dilute PDCs, and some of them were later sprouting. Estimated impact forces required to produce toppling range from 1.5 to 3.7 kPa, and PDC velocities reached up to 36 m s-1. Charring of the buried wood involved an emplacement temperature of 400-550 °C within PDC deposits. The rapid watershed formation may have facilitated infiltration, decreasing the temperature in the basal part within the deposits at the Tepu river. Runoff during the subsequent months triggered lahars and caused the rivers to incise the deposits and transport sediment downstream. This set of observations provides valuable insights into how the interaction between volcanic phenomena and margine forest on the valley floors informs eruptive processes, dynamics, and impacts. Our study is also relevant to interpret the thermal history and potential hazards of PDCs.

What is the color when black is burned? Quantifying (re)burn severity using field and satellite remote sensing indices

BackgroundTrends of increasing area burned in many regions worldwide are leading to more locations experiencing short-interval reburns (i.e., fires occurring two or more times in the same place within 1–3 decades). Field and satellite indices of burn severity are well tested in forests experiencing a single recent fire, but the reliability of these indices in short-interval reburns is poorly understood. We tested how a commonly used field index (the Composite Burn Index, CBI) and satellite index (the Relative differenced Normalized Burn Ratio, RdNBR) compared to eight individual field measures of burn severity in short-interval reburns vs. areas burned in one recent fire, and whether results depended on whether the first fire was stand replacing (fire that is lethal to most dominant trees).ResultsCorrespondence between both CBI and RdNBR with individual burn severity measures differed in short-interval reburns compared to single fires for some metrics of burn severity. Divergence in the relationship between both CBI and RdNBR vs. field measures was greatest when short-interval reburns followed a prior stand-replacing fire, and measures were more comparable to single fires when the first fire was non-stand replacing (i.e., lower severity). When short-interval reburns followed prior stand-replacing fires, CBI and RdNBR underestimated burn severity in the second fire for tree-canopy metrics (e.g., canopy cover loss, tree mortality), as young forests in early developmental stages are more sensitive to a second fire. Conversely, when short-interval reburns followed prior less-than-stand-replacing fires, both CBI and RdNBR overestimated burn severity for forest-floor metrics, as past low severity fires leave behind live fire-resistant trees and can stimulate resprouting understory vegetation. Finally, neither CBI nor RdNBR accurately detected deep wood charring—an important phenomenon that occurs in short-interval reburns.ConclusionOur findings inform interpretability of commonly used indices of burn severity in short-interval reburns by identifying how individual burn severity metrics can be under- or over-estimated, depending on the severity of the fire preceding a reburn. Adjustments to burn severity measurements made in short-interval reburns are particularly critical as reburned areas increase.

Kinetics of the CO2 gasification of woods, torrefied woods, and wood chars. Least squares evaluations by empirical models

The gasification kinetics of chars forming from biomass materials was studied by kinetic equations of type dX/dt = Af(X) exp(− E/(RT)) where X is the conversion of the sample, A is the pre-exponential factor, E is the activation energy and f(X) is a suitable model function. The theoretically deduced f(X) models in the literature are rarely applicable for chars of biomass origin because of chemical and physical inhomogeneities and irregularities. Hence, empirical f(X) functions were determined by a method proposed four years ago (Várhegyi in Energy Fuels 33:2348–2358, 2019). The parameters of the models were obtained by the method of least squares. Thermogravimetric experiments from an earlier work were reevaluated to explore the possibilities of the approaches employed. The experiments belonged to untreated birch and spruce woods; torrefied woods; chars prepared at a higher temperature; and chars formed at high heating rates (ca. 1400 °C min−1). Common kinetic features were found for the CO2 gasification of the chars studied. The reliability of the results was carefully tested by evaluating smaller and larger groups of the experiments and comparing the results. The method proved to be suitable for the determination of realistic f(X), E, and A from single modulated experiments, too. The models described well the gasification of chars forming from different woods through a wide range of temperature programs and thermal pretreatments.

Oxidative Conversion of Chars Generated from the Fixed-Bed Pyrolysis of Wood Torrefied at Different Temperatures and Holding Times

Fixed-bed pyrolysis of torrefied spruce wood, for a heating temperature of 800 K, results in char yields between about 27–57 wt% (versus 23 wt% for untreated wood), depending on both pre-treatment temperatures (533–583 K) and holding times (8–25 min). In this study char oxidation behavior and kinetics are investigated by means of thermogravimetric analysis. The differential thermogravimetric curves always showed a low-temperature zone of slow rates (oxidative devolatilization), followed by a high-rate zone with a well-defined peak (oxidation). As the torrefaction severity increases, the temperature range of the oxidative devolatilization enlarges. Moreover, the oxidation rates become slower (both burning and burnout temperatures tend to increase). As already found for untreated wood chars, the two stages are well described by a linear and a power-law rate reaction, respectively. Volatiles released from the devolatilizations are approximately around 20 wt%, but torrefaction causes lower activation energies (66–92 kJ/mol versus 117 kJ/mol). The oxidation activation energies also decreas (170–168 kJ/mol versus 193 kJ/mol), accompanied by small variations in the reaction order.

A phenomenological description of biomass powder combustion in internal combustion engines

An alternative strategy to implement the use of biofuels in internal combustion engines is to use minimally refined biofuels and redirect savings to engine modifications. While the idea of using coal dust in engines has been studied extensively, the combustion of micronized biomass powder has not been given due consideration. To understand and describe the phenomena, several exploratory tests were conducted in a single-cylinder diesel engine. The engine was operated with micronized powders of cellulose, wood char, wheat straw, chestnut wood, rice husk and pine bark with an average particle size of 20 μm. Cellulose combustion was found to be difficult to initiate, mostly because of endothermic depolymerization reactions. Despite its lower volatile content, wood char showed improved performance over cellulose. Both combustible powders presented premixed-like heat release profiles. Carbon monoxide, released during partial combustion of submicronic particles in the early stages of the compression stroke was found to be the main combustion driver. Nitrogen testing with wheat straw highlighted the occurrence of a torrefaction process leading to the formation of water with small amounts of pyrolysis products. A numerical study using adimensional numbers indicates that the transition from kinetically-limited to convection-limited CO production process is restricted to particles smaller than 50 μm as in-cylinder temperatures increase.

Online monitoring of alkali release during co-pyrolysis/gasification of forest and agricultural waste: Element migration and synergistic effects

Fuel blends may be used to meet several operational needs in thermal conversion of biomass waste, including optimization of ash properties and fuel conversion efficiency. In this study, online alkali measurements using surface ionization are employed to study synergistic effects produced by inorganic elements during co-pyrolysis/gasification of wood and straw waste. Synergistic effects on the fuel conversion behavior are not observed during co-pyrolysis, while alkali migration from straw to wood is clearly observed above 600 °C by online alkali monitoring. In contrast, synergistic effects on char conversion and alkali release are substantial during co-gasification. Positive effects on char reactivity during most of the gasification process are attributed to alkali migration from the straw to the wood char, and the most pronounced effect occurs at a gasification temperature of 900 °C and a straw content of 25%. Negative effects on char reactivity are observed at the final gasification stage, which is associated with a significantly reduced alkali release from fuel blends compared to pure wood char. The effect is attributed to the migration of silicon, phosphorus, and aluminum to the wood char, as revealed by scanning electron microscopy with energy dispersive spectroscopy, where the elements react with alkali to form catalytically inactive compounds. The mixing of biofuels is concluded to result in substantial effects on the fuel conversion efficiency, which should be taken into consideration in thermochemical conversion of biomass.