Finding resilient refractory materials for slagging gasification systems have the potential to reduce costs and improve the overall plant availability by extending the service life. In this study, different refractory materials were evaluated under slagging gasification conditions. Refractory probes were continuously exposed for up to 27 h in an atmospheric, oxygen blown, entrained flow gasifier fired with a mixture of bark and peat powder. Slag infiltration depth and microstructure were studied using SEM EDS. Crystalline phases were identified with powder XRD. Increased levels of Al, originating from refractory materials, were seen in all slags. The fused cast materials were least affected, even though dissolution and slag penetration could still be observed. Thermodynamic equilibrium calculations were done for mixtures of refractory and slag, from which phase assemblages were predicted and viscosities for the liquid parts were estimated. © 2017 Elsevier Ltd

Black liquor gasification is a new process for recovery of energy and chemicals in black liquor from the Kraft pulping process. The process can be combined with catalytic conversion of syngas into motor fuels. The potential for motor fuel production from black liquor in Sweden is to replace about 25% of the current consumption ofgasoline and diesel. For Finland the figure is even higher while for Canada it is about 14% and for the USA about 2%. © 2009 American Institute of Chemical Engineers Environ Prog, 28: 316-323, 2009.

In this work two types of lignocellulosic biomass particles, European spruce and American hardwood (particle sizes from 100 μm to 500 μm) were pyrolysed with a continuous wave 2 W Nd:YAG laser. Simultaneously a high-speed camera was used to capture the behavior of the biomass particle as it was heated for about 0.1 s. Cover glasses were used as a sample holder which allowed for light microscope studies after the heating. Since the cover glasses are not initially heated by the laser, vapors from the biomass particle are quenched on the glass within about 1 particle diameter from the initial particle. Image processing was used to track the contour of the biomass particle and the enclosed area of the contour was calculated for each frame.

The main observations are: There is a significant difference between how much surface energy is needed to pyrolyses the spruce (about 75% more) compared to the hardwood. The oil-like substance which appeared on the glass during the experiment is solid at room temperature and shows different levels of transparency. A fraction of this substance is water soluble. A brownish coat is seen on the unreacted biomass. The biomass showed insignificant swelling as it was heated. The biomass particle appears to melt and boil at the front that is formed between the laser beam and the biomass particle. The part of the particle that is not subjected to the laser beam seems to be unaffected.

Stem wood powders were fired in a mullite-lined pilot-scale oxygen-blown pressurized entrained-flow gasifier. During repeated campaigns involving increases in fuel load and process temperature, slag formations that eventuated in the blockage of the gasifier outlet were observed. These slags were retrieved for visual and chemical characterization. It was found that the slags had very high contents of Al and, in particular, high Al/Si ratios that suggest likely dissolution of the mullite-based refractory of the gasifier lining due to interactions with the fuel ash. Possible causes for the slag formation and behavior are proposed, and practical implications for the design of future stem wood entrained-flow gasifiers are also discussed.

In this work, predictions from a reacting Computational Fluid Dynamics (CFD) model of a gasification reactor are compared to experimentally obtained data from an industrial pressurized black liquor gasification plant. The data consists of gas samples taken from the hot part of the gasification reactor using a water cooled sampling probe. During the considered experimental campaign, the oxygen-to-black liquor equivalence ratio (λ was varied in three increments, which resulted in a change in reactor temperature and gas composition. The presented numerical study consists of CFD and thermodynamic equilibrium calculations in the considered λ-range using boundary conditions obtained from the experimental campaign. Specifically, the influence of methane concentration on the gas composition is evaluated using both CFD and thermodynamic equilibrium. The results show that the main gas components (H 2, CO, CO2) can be predicted within a relative error of 5% using CFD if the modeled release of H2S and CH4 are specified a priori. In addition, the calculations also show that the methane concentration has large influence on the reactor outlet temperature and final carbon conversion.

This paper reports the first Computational Fluid Dynamics (CFD) model developed for biomass pyrolysis oil spray combustion using Finite-Rate Chemistry (FRC) approach. To make the CFD calculations feasible, a reduced mechanism for modeling the combustion of biomass Fast Pyrolysis Oil (FPO) based on the POLIMI 1412 mechanism and a model for eugenol oxidation was developed. The reduced mechanism consisted of 200 reactions and 71 species. This level of complexity was found to be a good tradeoff between predictive power and computational cost such that the reduced model could be used in CFD modeling. The predictive power of the reduced mechanism was demonstrated via 0D (adiabatic, premixed, constant pressure reactor), 1D (laminar counterflow flame) and 3D (CFD of a methane-air flat-flame piloted FPO spray flame) calculations. Results from CFD were compared against experimental data from non-intrusive optical diagnostics. The reduced model was successfully used in CFD calculations—the computational cost was approximately 2 orders of magnitude higher than that of a simplified model. Using the reduced mechanism, the concentration of pollutants, minor combustion products, and flame radicals could be predicted—this is added capability compared to already existing models. The CFD model using the reduced mechanism showed quantitative predictive power for major combustion products, flame temperature, some pollutants and temperature, and qualitative predictive power for flame radicals and soot. © 2021 The Authors

Industrial thermal plasma torches can heat a gas up to 5000–20,000 K, i.e., well above the temperature needed to replace the heat generated from the combustion of traditional fossil fuels (e.g., coal, oil, and natural gas) in large-scale process industry furnaces producing construction materials (e.g., iron, steel, lime, and cement). However, there is a risk for significant NOx emissions when air or N2 are used as plasma-forming gas since the temperature somewhere in the furnace always will be higher compared to the threshold NOx formation temperature of ∼1800 K. Torch NOx forms inside the high temperature region of the plasma torch (>5000 K) when air is used as gas. Process NOx forms instead when the hot gas (when air or nitrogen is used as plasma forming gas) from the plasma torch mixes with process air downstream the torch. By analysing the complex chemistry of both the torch- and process NOx formation with thermodynamic equilibrium and one-dimensional chemical kinetic calculations it was shown that adding H2 to the plasma-forming N2 gas significantly reduces the NOx emissions with more than 90 %. Verifying experiments with air, pure N2, and mixtures of H2 and N2 as plasma-forming gas were performed in a laboratory scale insulated laboratory furnace with different pre-heating temperatures of process air (293, 673, and 1073 K) which the plasma gas mixes with downstream the torch. Depending on the pre-heating temperature the NOx emissions were between 12,000–14,000 mg NO2/MJfuel when air was used as plasma forming gas. Substantial NOx emission reduction occurs both when N2 replaces air, where the NOx emissions was in the span of 8000–11,500 mg NO2/MJfuel and furthermore when H2 was mixed into the N2 gas stream. For the highest degree of H2 mixing (28.6 vol-%), the NOx emissions were between 450–1700 mg NO2/MJfuel depending on the pre-heat temperature of the process air, i.e., a reduction of 88–96 % and 85–94 %, respectively when air or N2 was used as plasma forming gas. The measured NOx emissions are then of the same order of magnitude as would be expected from the combustion of traditional fuels (coal, oil, biomass and pure H2). Finally, by analysing the aerodynamics in an axisymmetric furnace with an experimentally validated computational fluid dynamics (CFD) model using reduced chemistry for the NOx formation (19 species and 70 reactions), further guidelines into the process of NOx reduction from thermal plasma torches are given. 

Particle properties such as size, shape and density play significant roles on particle flow and flame propagation in pulverized fuel combustion and gasification. A drop tube furnace allows for experiments at high heating rates similar to those found in large-scale appliances, and was used in this study to carry out experiments on pulverized biomass devolatilization, i.e. detailing the first stage of fuel conversion. The objective of this study was to develop a particle conversion model based on optical information on particle size and shape transformation. Pine stem wood and wheat straw were milled and sieved to three narrow size ranges, rapidly heated in a drop tube setup, and solid residues were characterized using optical methods. Different shape descriptors were evaluated and a shape descriptor based on particle perimeter was found to give significant information for accurate estimation of particle volume. The optical conversion model developed was proven useful and showed good agreement with conversion measured using a reference method based on chemical analysis of non-volatilized ash forming elements. The particle conversion model presented can be implemented as a non-intrusive method for in-situ monitoring of particle conversion, provided density data has been calibrated.

Biomass fast pyrolysis vapors contain a significant quantity of persistent aerosols, which can impact downstream processing by e.g. fouling of surfaces and deposition on downstream catalysts. In this study, aerosol concentrations and size distributions were measured by an impactor in two pyrolysis systems, a bench-scale fluidized-bed pyrolyzer and a pilot-scale cyclone pyrolyzer. In both units, the mass-based mode aerosol diameter was approximately 1 μm before aerosol collection devices in cooled vapors of 300–370 K but the number-based median was < 0.1 μm. Aerosols < 1 μm were formed and aerosols > 1 μm deposited during cooling of pyrolysis vapors from 620 to 370 K in the fluidized-bed pyrolysis system. The oil fraction collected from the aerosols constituted approximately 40 wt% of the total oils collected in both systems. Compared to the total collected oil, the oil fraction from the aerosols was enriched in lignin-derived components and anhydrosugars and had lower concentrations of low molecular weight cellulose derived oxygenates, such as hydroxyketones. 

The grate-kiln process for iron-ore pellet induration utilizes pulverized coal fired burners. In a developed infrastructure for H2, it might be desirable to heat the existing rotary kilns with renewably produced H2. Technical challenges of H2 heating of grate-kilns include high emissions of NOX and maintaining sufficient heat transfer to the pellet bed. This article examined cofiring (70% coal/30% H2) in 130 kW experiments using two different integrated burner concepts. Compared to pure coal combustion, cofiring creates a more intense, smaller flame with earlier ignition and less fluctuations. The process temperature and heat transfer are enhanced in the beginning of the kiln. The co-fired flames emit 32% and 78% less NOX emissions compared to pure coal and H2 combustion, respectively. We can affect the combustion behavior and NOX emissions by the burner design. H2/coal cofiring using integrated burners is probably an attractive solution for emission minimization in rotary kilns.

Pyrolysis oil is a complex mixture of different chemical compounds with a wide range of molecular weights and boiling points. Due to its complexity, an efficient fractionation of the oil may be a more promising approach of producing liquid fuels and chemicals than treating the whole oil. In this work a sampling system based on fractional condensation was attached to a cyclone pyrolysis pilot plant to enable separation of the produced pyrolysis vapors into five oil fractions. The sampling system was composed of cyclonic condensers and coalescing filters arranged in series. The objective was to characterize the oil fractions produced from three different Nordic feedstocks and suggest possible applications. The oil fractions were thoroughly characterized using several analytical techniques including water content; elemental composition; heating value, and chemical compound group analysis using solvent fractionation, quantitative 13C NMR and 1H NMR and GC x GC − TOFMS. The results show that the oil fractions significantly differ from each other both in chemical and physical properties. The first fractions and the fraction composed of aerosols were highly viscous and contained larger energy-rich compounds of mainly lignin-derived material. The middle fraction contained medium-size compounds with relatively high concentration of water, sugars, alcohols, hydrocarbonyls and acids and finally the last fraction contained smaller molecules such as water, aldehydes, ketones and acids. However, the properties of the respective fractions seem independent on the studied feedstock types, i.e. the respective fractions produced from different feedstock are rather similar. This promotes the possibility to vary the feedstock depending on availability while retaining the oil properties. Possible applications of the five fractions vary from oil for combustion and extraction of the pyrolytic lignin in the early fractions to extraction of sugars from the early and middle fractions, and extraction of acids and aldehydes in the later fractions.

The fly ash formation during suspension combustion of five different biomass powders (stem wood, bark, forest residue, willow, and reed canary grass) and the corresponding products from fast pyrolysis (bio-oil and biochar) of the powders was investigated. The fifteen fuels were burned in a drop tube furnace under normal (20 vol-% O2) and oxygen-enriched combustion conditions (40 vol-% and 60 vol-% O2). The trends in the data were used to discuss differences in combustion behavior and devise recommendations for the use of the fuels. There was a general difference in fly ash formation mechanism between the solid fuels (biomass and biochar) and the bio-oil fuels, which was attributed to parts of the ash-forming elements in bio-oil being dissolved in the oil. Oxygen-enrichment did not affect the release of inorganic elements to the gas phase for bio-oil combustion. Since the bio-oils generate lower fly ash during combustion, ~100 times compared to the original biomasses, they should be reserved for combustion technologies demanding fuels with very low ash content, whereas the biochar should be used in large scale combustion facilities with advanced gas cleaning technology operated by teams with experience of handling ash related operational problems. © 2021 The Author(s)

Fast pyrolysis is a promising thermochemical technology for converting biomass to energy, chemicals, and fuels. At RISE ETC, an industrially relevant pyrolysis pilot plant has been designed, constructed, and operated since 2011. The pilot plant is based on an externally heated cyclone reactor where both the pyrolysis reaction and the separation of products take place. The reactor design has shown to be beneficial since it produces oil with relatively low concentrations of inorganics. Pyrolysis of different Nordic biomasses, both forestry and agricultural, have been studied using the pilot plant and the results indicate that it is especially suitable for low grade fuels. The oil is collected in two separate steps, and the received two oil fractions have different chemical and physical properties, which opens up the possibility to use selected fractions in targeted applications. Oil fractionation has also been studied further in a separate fractional condensation system and the results show that it is possible to separate larger energy-rich lignin-derived material; medium-sized; and light water soluble compounds already in the oil collection step. The pilot plant has worked as a platform for pyrolysis research and for building up competence in the pyrolysis area. 

Pyrolysis is a promising thermochemical technology for converting biomass to energy, chemicals and/or fuels. The objective of the present paper was to characterize fast pyrolysis products and to study pyrolysis oil fractionation. The products were obtained from different Nordic forest and agricultural feedstocks in a pilot scale cyclone pyrolysis plant at three different reactor temperatures. The results show that the main elements (C, H and O) and chemical compositions of the products produced from stem wood, willow, forest residue and reed canary grass are in general terms rather similar, while the products obtained from bark differ to some extent. The oil produced from bark had a higher H/Ceff ratio and heating value which can be correlated to a higher amount of pyrolytic lignin and extractives when compared with oils produced from the other feedstocks. Regardless of the original feedstock, the composition of the different pyrolysis oil fractions (condensed and aerosol) differs significantly from each other. However this opens up the possibility to use specifically selected fractions in targeted applications. An increased reactor temperature generally results in a higher amount of water and water insoluble material, primarily as small lignin derived oligomers, in the produced oil.

Slag formation in the grate-kiln process is a major problem for iron-ore pellet producers. It is therefore important to understand the slag formation mechanism in the grate-kiln production plant. This study initiated the investigation by in situ sampling and identifying particles in the flue gas from a full-scale 40 MW grate-kiln production plant for iron-ore pelletizing. Particles were sampled from two cases of combustion with pulverized coal and heavy fuel oil. The sampling location was at the transfer chute that was situated between the traveling grate and the rotary kiln. The particle-sampling system was set up with a water-cooled particle probe equipped with nitrogen gas dilution, cyclone, and low-pressure impactor. Sub-micrometer and fine particles were size-segregated in the impactor, while coarse particles (>6 μm) were separated with a cyclone before the impactor. Characterization of these particles was carried out with environmental scanning electron microscopy (ESEM), and the morphology of sub-micrometer particles was studied with transmission electron microscopy (TEM). The results showed that particles in the flue gas consisted principally of fragments from iron-ore pellets and secondarily of ashes from pulverized coal and heavy fuel oil combustions. Three categories of particle modes were identified: (1) sub-micrometer mode, (2) first fragmentation mode, and (3) second fragmentation mode. The sub-micrometer mode consisted of vaporized and condensed species; relatively high concentrations of Na and K were observed for both combustion cases, with higher concentrations of Cl and S from heavy fuel oil combustion but higher concentrations of Si and Fe and minor P, Ca, and Al from coal combustion. The first fragmentation mode consisted of both iron-ore pellet fines and fly ash particles; a significant increment of Fe (>65 wt %) was observed, with higher concentrations of Ca and Si during heavy fuel oil combustion but higher concentrations of Si and Al during coal combustion. The second fragmentation mode consisted almost entirely of coarse iron-ore pellet fines, predominantly of Fe (∼90 wt %). The particles in the flue gas were dominantly iron-ore fines because the second fragmentation mode contributed >96 wt % of the total mass of collected particles.

Fast pyrolysis oil can be used as a feedstock for syngas production. This approach can have certain advantages over direct biomass gasification. Pilot scale tests were performed to investigate the route from biomass via fast pyrolysis and entrained flow gasification to syngas. Wheat straw and clean pine wood were used as feedstocks; both were converted into homogeneous pyrolysis oils with very similar properties using in-situ water removal. These pyrolysis oils were subsequently gasified in a pressurized, oxygen blown entrained flow gasifier using a thermal load of 0.4 MW. At a pressure of 0.4 MPa and a lambda value of 0.4, temperatures around 1250 °C were obtained. Syngas volume fractions of 46% CO, 30% H2 and 23% CO2 were obtained for both pyrolysis oils. 2% of CH4 remained in the product gas, along with 0.1% of both C2H2 and C2H4. Minor quantities of H2S (3 vs. 23) cm3 m−3, COS (22 vs. 94) cm3 m−3 and benzene (310 vs. 532) cm3 m−3 were measured for wood- and straw derived pyrolysis oils respectively. A continuous 2-day gasification run with wood derived pyrolysis oil demonstrated full steady state operation. The experimental results show that pyrolysis oils from different biomass feedstocks can be processed in the same gasifier, and issues with ash composition and melting behaviour of the feedstocks are avoided by applying fast pyrolysis pre-treatment.

The aim of this work was to investigate whether the use of individual tree components (i.e., stem wood, bark, branches, and needles of spruces) as feedstocks during oxygen blow gasification is more efficient than using mixtures of these components. Experiments were performed at three oxygen levels in an 18-kW oxygen blown fixed bed gasifier with both single and mixed component feedstocks. The composition of the resulting syngas and the cold gas efficiency based on CO and H2 (CGEfuel) were used as response variables to evaluate the influence of different feedstocks on gasification performance. Based on the experimental results and data on the composition of ∼26000 trees drawn from a national Swedish spruce database, multivariate models were developed to simulate gasifier performance under different operating conditions and with different feedstock compositions. The experimental results revealed that the optimal CGEfuel with respect to the oxygen supply differed markedly between the different spruce tree components. Additionally, the models showed that co-gasification of mixed components yielded a lower CGEfuel than separate gasification of pure components. Optimizing the oxygen supply for the average tree composition reduced the GCEfuel by 1.3–6.2% when compared to optimal gasification of single component feedstocks. Therefore, if single-component feedstocks are available, it may be preferable to gasify them separately because doing so provides a higher gasification efficiency than co-gasification of mixed components. © 2022 The Authors

Pyrolysis transforms bulky and heterogeneous lignocellulosic biomass into more easily-handled oils that can be upgraded into bio-based transportation fuels. Existing systems for monitoring pyrolysis processes and characterizing their products rely on slow and time-consuming wet chemical analyses. On-line near-infrared (NIR) spectroscopy could potentially replace such analyses, providing real-time data and reducing costs. To test the usefulness of NIR methods in characterizing pyrolysis oils and processes, biomass from conifers, Salix, and reed canary grass was milled and pyrolyzed at 675, 750, and 775 °C. Two separate pyrolytic fractions (aerosol and condensed) were produced in each experiment, and NIR spectra were collected for each fraction. Multivariate modelling of the resulting data clearly showed that the samples’ NIR spectra could be used to accurately predict important properties of the pyrolysis oils such as their energy values, main organic element (C, H and O) contents, and water content. The spectra also contained predictive information on the samples’ origins, fraction, and temperature treatment, demonstrating the potential of on-line NIR techniques for monitoring pyrolytic production processes and characterizing important properties of pyrolytic oils from lignocellulosic biomass.

Over the decades, computational methods have been used to model and describe the flow and ionization dynamics in plasma torches. However, the impact of the operational parameters such as gas flow rate, swirl number and input current density on flow is still inexplicit. In this study, the flow in a non-transferred plasma torch is modelled using COMSOL Multiphysics, and the influence of these parameters is studied. The analysis is carried out on an axisymmetric geometry with the conical-shaped cathode, nozzle-shaped anode, and Argon is used as the plasma gas. A thermal plasma (equilibrium discharges) is considered, i.e., the plasma is under partial to complete local thermodynamic equilibrium in which the magnetohydrodynamic (MHD) equations are solved. This is treated in the Equilibrium Discharge Interface in COMSOL’s plasma module that has been used in the present study. The laminar flow analysis is performed for low-velocity cases and turbulent flow analysis for higher velocities. It was found that the velocity increase across the plasma arc due to ionization and gas expansion, could be observed only for sufficiently high plasma inflow velocities. The position of the plasma arc is determined for different operating conditions. It was further found that the velocity has a negligible effect on the length of the plasma arc, whereas the dependency of the arc length and attachment point on the anode wall, to the input current density and cathode tip temperature is well explained. The paper concludes by presenting the variations in temperature and velocity of plasma arc due to swirling inflow

Adding high-value products, such as carbon-based electrode materials for electrochemical energy storage, to the value chain of biorefinery may increase the profits of the whole concept. In this work, carbon-based supercapacitor electrode materials were produced by chemical activation (using KOH) of two fractions of bio-oil (aerosol and condensed) as well as bio-char precursors, all of them originally made from fast pyrolysis of stem wood from pine and spruce. The produced materials show a hierarchical porous structure, a high surface area (1300–1500 m2 g−1) and, almost double the specific capacitance (149–152 F g−1 @ 50 mA g−1) compared to commercially available activated carbon (79 F g−1 @ 50 mA g−1). The benefit of using bio-oils compared to biochar is having an electrode material almost free from metal impurities alongside marginally higher energy storage performance. Together with the material yield in the production chain (fast pyrolysis and activation), a normalized energy storage value was presented for each material that may be used in the future to select the best techno-economic route for the whole concept. © 2022 The Authors

The development of a model of carbon oxidation has engaged researchers for decades. Yet many outstanding questions remain due to the inability to experimentally study the details of the oxidation. Today, novel techniques such as environmental transmission electron microscopy (ETEM), allowing for in-situ nanoscale observations of the oxidation process, can help illuminate some of these questions. In this study of few layer graphene (FLG), multi-walled carbon nanotubes (MWCNTs), buckminsterfullerene (C60), and nanodiamonds (NDs) oxidizing in temperatures up to 1100 °C and we analyze the importance of nanostructure for the thermal stability of nanocarbons. The study was complemented with thermogravimetric analysis (TGA) and the experiments were in good agreement with oxidation rates increasing sharply with temperature and the thermal stability of the materials MWCNTs, FLG, C60 and NDs in descending order. Based on the direct nanoscale visualization obtained in the ETEM the materials can be divided into two overall categories: materials with low strain sp2-bonds (FLG and MWCNT); and materials with high strain sp2-bonds (C60) or sp3-bonds (NDs). For materials in the first category, it is possible to identify several different phenomena as their oxidation rate increases as a function of temperatures whereas materials in the second category appear to be more influenced by extrinsic factors such as the electron beam and by structural transformation upon heating. This study clearly shows the value of adding ETEM results to traditional TGA investigations since it gives both a complementary and more detailed information about the dynamic oxidation process.

Particles filtered out of pyrolysis oil produced through fast pyrolysis of stem wood, willow, reed canary grass, bark, and forest residue were characterized using scanning electron microscopy and energy-dispersive spectroscopy with the aim of identifying particle categories and discussing transport mechanisms of particles and inorganics into the oil. Particles filtered out of both the condensed and the aerosol fractions of the oil displayed three types of morphology: (i) char-like structures (1-15 μm), (ii) spheres (100 nm to 1 μm), and (iii) irregularly shaped residue (50-500 nm). The char-like structures were identified as char. The spheres and irregularly shaped residue shared morphology and composition with tar balls and organic particles with inorganic inclusions. These particles could have formed either during the fast pyrolysis stage or through precipitation from the oil during storage. All particles consisted mainly of C and O but also small amounts of inorganics. The particles from the aerosol fraction of the oil had higher inorganics content than the particles from the condensed fraction. The results were discussed, and suggested transport mechanisms of inorganics into particles were presented.

Biomass particles (75-1000μm) were fed at 9.0-66.5mgmin-1 (2.9-21.7W) using a particle feeder that dispensed particles by gravity through an injection tube. Feed rate was controlled by altering the velocity of a pusher block. Particles were agitated using a vibration motor and fed onto a balance and mass readings were continuously logged. Factors impacting reproducibility and feed rate stability were investigated as well as the effects of particle size and of pusher block velocity. Statistical analysis was applied to investigate patterns in particle feed rate data. Particle aggregation was identified as a factor which influenced feed rate stability and thereby also influencing reproducibility. Feed rate correlated well with pusher block velocity (R2=0.99). Statistical analysis showed strong indications (P values <0.01) of two patterns (clustering and trends) in the feed rate data which were attributed to changes in particle bed appearance with time. With all else being equal, particle size affected feed rate but not feed rate stability. A higher vibration amplitude was needed to agitate smaller particles. It was concluded that particle agitation control is a key to stable feeding of small biomass particles at low rates.

Fast pyrolysis of biomass results in a renewable product usually denoted pyrolysis oil or bio-oil, which has been suggested to be used as a direct substitute for fuel oil or as a feedstock for production of transportation fuels and/or chemicals. In the present work, fast pyrolysis of stem wood (originated from pine and spruce), willow, reed canary grass, brown forest residue and bark has been performed in a pilot scale cyclone reactor. The experiments were based on a biomass feeding rate of 20 kg/h at three different reactor temperatures. At the reference condition, pyrolysis of stem wood, willow, reed canary grass, and forest residue resulted in organic liquid yields in the range of 41 to 45% w/w, while pyrolysis of bark resulted in lower organic liquid yields. Two fractions of pyrolysis oil were obtained, denoted as the condensed and the aerosol fraction. Most of the water soluble molecules were collected in the condensed fraction, whereas the yield of water insoluble, heavy lignin molecules was higher in the aerosol fraction. Based on the results of the present work, willow, reed canary grass and forest residue are considered as promising raw materials for production of pyrolysis oil in a cyclone reactor.

Woody biomass is being considered a potential co-firing fuel to reduce coal consumption in iron-ore pelletizing rotary kilns. An important consideration is the slagging inside the kiln caused by ash deposition that can lead to process disturbances or shutdowns. In terms of ash chemistry, co-firing woody biomass implies the addition of mainly Ca and K to the Si- and Al-dominated coal-ash (characteristic of high-rank coals) and Fe from the iron-ore that are both inherent to the process. An alkali-laden gaseous atmosphere is also present due to the accumulation of alkali via the recirculation of flue gas in the system. The slagging propensity of blending woody biomass with coal in the grate-kiln process was studied based on the viscosity of the molten phases predicted by global thermochemical equilibrium modeling. This was carried out for variations in temperature, gaseous KOH atmosphere, and fuel blending levels. Results were evaluated and compared using a qualitative slagging indicator previously proposed by the authors where an inverse relationship between deposition tendency and the viscosity of the molten fraction of the ash was established. The results were also compared with a set of co-firing experiments performed in a pilot-scale (0.4 MW) experimental combustion furnace. In general, the co-firing of woody biomass would likely increase the slagging tendency via the increased formation of low-viscosity melts. The fluxing behavior of biomass-ash potentially reduces the viscosity of the Fe-rich aluminosilicate melt and intensifies deposition. However, the results also revealed that there are certain conditions where deposition tendency may decrease via the formation of high-melting-point alkali-containing solid phases (e.g., leucite). 

Iron-ore pelletizing plants use high-rank coals to supply the heat necessary to process ores. Ash material from coal, in combination with iron-ore dust originating from the disintegration of the pellets, can cause deposition/slagging which often leads to severe production losses and damage. Deposition/slagging is most prominent in the hot areas of the grate-kiln setup and is more severe at the inlet of the rotary-kiln, i.e., the transfer-chute. Following on from our previous work, high-rank bituminous coals with potential for use in the pelletizing process were combusted in a pilot-scale (0.4 MW) pulverized-coal fired experimental combustion furnace (ECF). The fly-ash particles and short-term deposits were characterized to shed light on the observed difference in slagging/deposition tendencies of the coals. Global thermodynamic equilibrium modeling, in combination with viscosity estimates, was used to interpret the experimental findings and investigate the effect of the coal-ash composition upon deposition/slagging. This approach was carried out with and without the presence of Fe2O3-rich pellet-dust under oxidizing conditions within the temperature range at the transfer-chute of iron-ore pelletizing rotary-kilns. Based on the findings, a Qualitative Slagging Indicator (QSI) was proposed that can help pre-screen new solid fuels for potential slagging issues. The proposed QSI highlights the following: (1) an inverse relationship between viscosity and slagging/deposition tendency of the coals was observed (2) as viscosity decreases (either with increasing temperature or due to the change in the coal-ash composition), stronger deposits will form that will complicate the mechanical removal of the deposited layer. It was therefore inferred that low viscosity molten phases facilitate deposition/slagging, which is exacerbated by the presence of fluxing agents (e.g., CaO, MgO, K2O, Na2O, and Fe2O3) in the deposits. The low viscosity coal-ash-induced molten phases are also more likely to interact with the Fe2O3-rich pellet-dust that results in further decreases in viscosity, thereby intensifying depositions. The results from this work complement the on-going research by our group to elucidate and alleviate ash-related problems in industrial grate kilns.

Combustion-generated fly ash particles in combination with the particles arising from the disintegration of iron-ore pellets, could give rise to the build-up of deposits on the refractory linings of the induration facility. Due to climate change and other environmental issues, there is a desire to cut down on use of fossil fuels. Therefore, it is of interest to investigate the feasibility of replacing coal with less carbon-intensive alternatives such as upgraded biomass, e.g., biochar and pyrolysis bio-oil. While the combustion of biomass can be carbon-neutral, the effects of biomass ash upon slagging during the iron-ore pelletizing process in a grate-kiln setup is unknown. In the present study, the effect of the interaction between the pellet dust and biomass-ash upon melt formation and the viscosity of the resulting melt, which can collectively affect melt-induced slagging, was theoretically assessed. The slagging potential of 15 different biomass fuels, suitable for the pelletizing process, was quantified and compared with one another and a reference high-rank coal using a thermodynamically derived slagging index. The replacement of coal with biomass in the pelletizing process is a cumbersome and challenging task which requires extensive and costly field measurements. Therefore, given the wide-ranging nature of the biomasses investigated in this study, a prescreening theoretical approach, such as the one employed in the present work, could narrow down the list, facilitate the choice of fuel/s, and help reduce the costs of the subsequent experimental investigations. © 2020 by the authors.

Fly ash particles from the combustion of solid-fuels together with disintegrated particles arising from iron-ore pellets result in accumulation of deposits on the refractory linings of the grate-kiln induration machine during the iron-ore pelletizing process. The deposits amass in the high-temperature regions of the induration furnace thus disturbing the flow of gas and pellets. Therefore, to tackle the above-mentioned issues, an understanding of deposit formation mechanism is of crucial importance. This study was conducted with the objective of addressing the effect of disintegrated iron-ore pellet dust on deposit formation and the mechanisms behind deposition (slagging) in the grate-kiln process. A comprehensive set of experiments was conducted in a 0.4 MW pilot-scale pulverized-coal- fired furnace where three different scenarios were considered as follows; Case 1 (reference case): Coal was combusted without the presence of pellet dust. Case 2: Natural gas was combusted together with simultaneous addition of pellet dust to the gas stream. Case 3: Coal was combusted together with the addition of pellet dust simulating the situation in the large-scale setup. Fly ash particles and short-term deposits were characterized and deposition was addressed in Part I of this study. In light of the experimental observations (Part I) and the thermochemical equilibrium calculations (Part II), a scheme of ash transformation during the iron-ore pelletizing process was proposed. The dissolution of hematite particles into the Ca-rich-aluminosilicate melt (from the coal-ash constituents) decreased the viscosity and resulted in the formation of stronger (heavily sintered) deposits. Overall, this pilot-scale work forms part of a wider study which aims at deepening the understanding of ash transformation phenomena during the large-scale pelletizing process.

To initiate the elucidation of deposit formation during the iron-ore pelletization process, a comprehensive set of experiments was conducted in a 0.4 MW pilot-scale pulverized-coal-fired furnace where three different scenarios were considered as follows; Case 1 (reference case): Coal was combusted without the presence of pellet dust. Case 2: Natural gas was combusted together with simultaneous addition of pellet dust to the gas stream. Case 3: Coal was combusted together with the addition of pellet dust simulating the situation in the large-scale grate-kiln setup. Particles and deposits were sampled from 3 positions of different temperature via a water-cooled sampling probe. Three distinct fragmentation modes were identified based on the aerodynamic particle diameter (Dp). The fine mode: Particles with 0.03 &lt; Dp &lt; 0.06 μm. The first fragmentation mode: Particles with 1 &lt; Dp &lt; 10 μm. The second fragmentation mode: Coarse particles (cyclone particles, Dp &gt; 10 μm). A transition from a bimodal PSD (particle size distribution) to a trimodal PSD was observed when pellet dust was added (Case 3) and consequently the elemental bulk composition of the abovementioned modes was changed. The most extensive interaction between pellet dust and coal-ash particles was observed in the coarse mode where a significant number of coal ash globules were found attached to the surface of the hematite particles. The morphology of the sharp-edged hematite particles was changed to smooth-edged round particles which proved that hematite particles must have interacted with the surrounding aluminosilicate glassy phase originating from the coal ash. The short-term deposits collected during coal combustion (Case 1) were highly porous in contrast to the high degree of sintering observed in the experiments with pellet dust addition (Case 3) which is attributed to the dissolution of hematite particles in the aluminosilicate glassy phase. The results suggest that pellet dust itself (Case 2) has low slagging tendency, independent of temperature. However, when coal-ash is present (Case 3), auxiliary phases are added such that tenacious particles are formed and slagging occurs.

A fast sensor for simultaneous high temperature (above 800 K) diagnostics of nitrogen oxide (NO) concentration and gas temperature (T) based on the spectral fitting of low-resolution NO UV absorption near 226 nm was applied in pilot-scale LKAB’s Experimental Combustion Furnace (ECF). The experiments were performed in plasma and/or fuel preheated air at temperatures up to 1550 K, which is about 200 K higher than the maximal temperature used for the validation of the developed UV NO sensor previously. The UV absorption NO and T measurements are compared with NO probe and temperature measurements via suction pyrometry and tuneable diode laser absorption (TDL) using H2O transitions at 1398 nm, respectively. The agreement between the NO UV and NO probe measurements was better than 15%. There is also a good agreement between the temperatures obtained using laser-based, optical, and suction pyrometer measurements. Comparison of the TDL H2O measurements with the calculated H2O concentrations demonstrated an excellent agreement and confirms the accuracy of TDL H2O measurements (better than 10%). The ability of the optical and laser techniques to resolve various variations in the process parameters is demonstrated.

A new fast sensor for simultaneous high temperature diagnostics (above 800 K) of nitrogen oxide (NO) concentration and gas temperature (T) was developed based on the spectral fitting of low-resolution NO UV absorption near 226 nm. The sensor was intended for process control in future low-carbon footprint heavy process industries using renewable powered electro fuels (e.g. H2, NH3) or plasma torches as heat source. Due to excitation of molecular vibration, the shape of the selected NO feature, including (0, 0), (1, 1), and (2, 2) vibrational transitions of the A2Σ+ − X2Π2 electronic system had a strong temperature sensitivity at temperatures above 800 K. The fitting was made using the well-known NO molecular constants of the A2Σ+ − X2Π2 electronic system. To reduce the computational time, a library of the molecular spectra calculated at different temperatures was created. The fitting of an experimental spectrum representing the convolution of the instrument line function of the spectrometer with the molecular spectra was performed using the pre-calculated library spectra. Based on comparison with conventional measurement methods, the accuracy of the developed sensor was within 15% for NO and about 40 K for T, clearly showing the potential for fast in situ diagnostics in hot process gases. © 2020, The Author(s).

This work describes the morphological and material changes in the iron powder during four regeneration-combustion cycles. The regeneration in H2 and combustion in air experiments were made in a fluidized bed (FB) and an entrained flow reactor (EFR), respectively. The average size of the iron oxide particles more than doubled between the first and fourth combustion cycles, and many of the particles were hollow. The regeneration step did not change the size of the particles but increased their porosity. A mechanism is proposed that describes the formation of large-diameter hollow particles which increases as a function of the regeneration-combustion cycles. The observed increase in particle size and the change in particle morphology complicates the iron fuel concept, as it leads to a degradation of the structural stability of the particle with time.

Methane is one of the main gas species produced during biomass gasification and may be a desired or undesired product. Syngas CH4 concentrations are typically &gt;5 vol-% (when desired) and 1–3 vol-% even when efforts are made to minimize it, while thermochemical equilibrium calculations (TEC) predict complete CH4 decomposition. How CH4 is generated and sustained in the reactor core is not well understood. To investigate this, accurate quantification of the CH4 concentration during the process is a necessary first step. We present results from rapid in situ measurements of CH4, soot volume fraction, H2O and gas temperature in the reactor core of an atmospheric entrained-flow biomass gasifier, obtained using tunable diode laser absorption spectroscopy (TDLAS) in the near-infrared (1.4 µm) and mid-infrared (3.1 µm) region. An 80/20 wt% mixture of forest residues and wheat straw was converted using oxygen-enriched air (O2&gt;21 vol%) as oxidizer, while the global air-fuel equivalence ratio (AFR) was set to values between 0.3 and 0.7. Combustion at AFR 1.3 was performed as a reference. The results show that the CH4 concentration increased from 1 to 3 vol-% with decreasing AFR, and strongly correlated with soot production. In general, the TDLAS measurements are in good agreement with extractive diagnostics at the reactor outlet and TEC under fuel-lean conditions, but deviate significantly for lower AFR. Detailed 0D chemical reaction kinetics simulations suggest that the CH4 produced in the upper part of the reactor at temperatures &gt;1700 K was fully decomposed, while the CH4 in the final syngas originated from the pyrolysis of fuel particles at temperatures below 1400 K in the lower section of the reactor core. It is shown that the process efficiency was significantly reduced due to the C and H atoms bound in methane and soot. © 2021 The Authors

The efficiency of the gasification process and product quality largely depend on the degree of fuel conversion. We present the real-time in-situ tunable diode laser measurements of main carbon and oxygen-containing species in the hot reactor core of a pilot-scale entrained flow biomass gasifier (EFG). The concentrations of CO, CO2, CH4, C2H2, H2O, soot, and gas temperature were measured during the air and oxygen-enriched gasification of stem wood at varying equivalence ratios. The experiments were made at the upper and lower optical ports inside a 4 m long, ceramic-lined, atmospheric EFG, allowing to access the degree of the fuel conversion inside the reactor. The exhaust composition was measured by micro-GC, FTIR, and low-pressure impactor. There was a good agreement between the data measured inside the reactor and at the exhaust for oxygen-enriched gasification implying that the chemical reactions are practically frozen downstream the optical ports. For air, the data indicated that the gasification reactions are still active at the measurement locations. Significant concentrations of C2H2, up to 5000 ppm, were found inside the reactor. 

This paper reports on the development of the tunable diode laser absorption spectroscopy sensor near 4350 cm⁻¹ (2298 nm) for measurements of CO and H₂O mole fractions and soot volume fraction under gasification conditions. Due to careful selection of the molecular transitions [CO (υ″ = 0 → υ′ = 2) R34–R36 and H₂O at 4349.337 cm⁻¹], a very weak (negligible) sensitivity of the measured species mole fractions to the temperature distribution inside the high-temperature zone (1000 K < T < 1900 K) of the gasification process is achieved. The selected transitions are covered by the tuning range of single diode laser. The CO and H₂O concentrations measured in flat flames generally agree better than 10 % with the results of 1-D flame simulations. Calibration-free absorption measurements of studied species in the reactor core of atmospheric pilot-scale entrained-flow gasifier operated at 0.1 MW power are reported. Soot concentration is determined from the measured broadband transmittance. The estimated uncertainties in the reactor core CO and H₂O measurements are 15 and 20 %, respectively. The reactor core average path CO mole fractions are in quantitative agreement with the µGC CO concentrations sampled at the gasifier output.

Tunable diode laser absorption spectroscopy (TDLAS) was employed to measure several important process parameters at two different locations inside the reactor of an atmospheric air-blown 0.1 MW biomass gasifier. Direct TDLAS at 2298 nm was employed for CO and water calibration-free scanned wavelength modulation spectroscopy at 1398 nm for H2O and gas temperature and direct TDLAS at 770 nm for gaseous elemental potassium K(g) under optically thick conditions which correspond the first in situ measurements of K(g) and temperature in a reactor core and in biomass gasification respectively. Actual average temperatures in the reactor core were significantly higher than the uncorrected thermocouple measurements in the gas stream. The CO concentrations at the lower optical access port were comparable to those obtained by GC at the exhaust. In gasification mode similar H2O values were obtained by the two different TDLAS instruments. The reaction time was faster for peat than for stem wood.

Combustion facilities run on pulverized biomass often exhibit fluctuations in fuel feeding and, thus, equivalence ratio and would benefit from fast process control based on optical λ sensors installed in the reactor core. The conversion of softwood powder is investigated in an atmospheric entrained-flow reactor (EFR) operated close to stoichiometry using two different burners (swirl and jet) and three oxygen concentrations (21, 30, and 40%). Tunable diode laser absorption spectroscopy (TDLAS) is used to conduct time-resolved (0.1-1 s) in situ measurements of the gas temperature, carbon monoxide (CO), water vapor (H2O), gaseous atomic potassium [K(g)], and soot volume fraction in the lower part of the reactor core and in the exhaust of the EFR. At both locations, the measurement parameters show significant, correlating fluctuations. The local equivalence ratio is derived from a comparison of measured CO and H2O concentrations (for fuel-rich and fuel-lean conditions, respectively) to thermodynamic equilibrium calculations (TEC) and found to vary in a wide range (0.8-1.3). Soot production decreases with an increasing local equivalence ratio and oxygen enrichment and is lower for the swirl compared to the jet burner. The measured K(g) concentrations follow the general behavior predicted by TEC around stoichiometry. In the relevant temperature range (1100-1700 K), K(g) is 2-4 orders of magnitude higher under fuel-rich than fuel-lean conditions, with a sharp transition at stoichiometry. While K(g) concentrations are lower than TEC in the reactor core and under fuel-rich conditions, excellent agreement is found at the exhaust after complete fuel conversion. Precise, wide dynamic range detection of K(g) using TDLAS enables discrimination between fuel-rich and fuel-lean conditions and has the potential for lambda sensing close to the hot reaction zone of combustion plants.

The precise control of bio-based combustion is challenging due to the varying composition and moisture content of the fuels, difficulties in achieving stable fuel feeding, and complex underlying thermochemical processes. We present simultaneous online diagnostics of two combustion parameters, the equivalence ratio and fuel moisture content, in a pilot-scale environment. The parameters were evaluated by analysing the H2O and CO2 concentrations. These were measured using a Fourier transform infrared (FTIR) spectrometer (exhaust) and tuneable diode laser (TDL) absorption spectroscopy (combustion chamber) in pilot-scale diesel and pulverized biomass combustion. Liquid H2O was added into the combustion chamber to represent fuel moisture. The equivalence ratio of diesel and wood combustion was varied by adjusting the flows of combustion air in a staged manner or by using rapid periodic variations (on the order of seconds). The moisture fuel levels calculated using the measured fuel and water flow rates (flow method) and the FTIR and TDL H2O and CO2 concentrations agree within 3% (absolute) for both fuels. The TDL and FTIR equivalence ratios agreed quantitatively for both diesel and biomass combustion. However, close to stoichiometry, the TDL values for biomass are up to 15% lower than the FTIR values, indicating ongoing combustion at the location of the TDL measurements. © 2022 The Authors

The work demonstrates the performance of the optical extinction technique for real-time diagnostics of the fluctuations in biomass particle flows. The online measurements of fluctuations of density were used to determine the biomass particle mass flow fluctuations. Biomass flows were produced using laboratory biomass particle feeder (mass flux up to 10 g/min) and the hopper-screw feeding system of the pilot-scale entrained flow rector, mass flux up to 500 g/min, located at SP ETC in Piteå. The experiments showed that the time-averaged extinction appeared to be linearly related to the real particle mass flow. The relatively fast variations in biomass feeding rates measured using the extinction technique were confirmed by fast balance measurements (in laboratory feeder experiments) and by real-time tunable diode laser CO and H2O concentrations measured in the reactor core of the entrained flow gasifier.

In order to successfully integrate biomass pyrolysis oils as starting materials for conventional oil refineries, upgrading of the pyrolysis oils is needed to achieve desired properties, something which can be performed either as part of the pyrolysis process and/or by separate catalytic treatment of the pyrolysis intermediate oil products. In this study, the quality of stem wood-derived pyrolysis oil was improved via ex situ catalytic hydropyrolysis in a bench-scale pyrolyzer (stage 1), followed by catalytic hydro-coprocessing with fossil co-feed in a laboratory-scale high pressure autoclave (stage 2). The effect of pyrolysis upgrading conditions was investigated based on the quality of intermediate products and their suitability for hydro-coprocessing. HZSM-5 and Pt/TiO2 catalysts (400 °C, atmospheric pressure) were employed for ex situ pyrolysis, and the NiMoS/Al2O3 catalyst (330 °C, 100 bar H2 initial pressure) was used for hydro-coprocessing of the pyrolysis oil. The application of HZSM-5 in the pyrolysis of stem wood under a N2 atmosphere decreased the formation of acids, ketones, aldehydes, and furans and increased the production of aromatic hydrocarbons and phenolics (guaiacols and phenols). Replacing HZSM-5 with Pt/TiO2 and N2 with H2 resulted in complete conversion of guaiacols and significant production of phenols, with further indications of increased stability and reduced coking tendencies.

A non-transferred plasma torch is a device used to generate a steady thermal plasma jet. Plasma torches have the potential to replace fossil fuel burners used as heat sources in the process industry. Today, however, the available plasma torches are of small scale compared to the power used in the burners in the process industry. In order to understand the effects of large scales on the plasma flow dynamics, it is essential to understand the operation of the plasma torch under different operating conditions and for different geometries. In this study, the analysis of a non-transferred plasma torch has been carried out using both computational and experimental methods. Computationally, the magnetohydrodynamic (MHD) equations are solved using a single-fluid model on a 2D axisymmetric torch geometry. The experiments are performed using emission spectroscopy to measure the plasma jet temperature at the outlet. This paper explains the changes in the arc formation, temperature, and velocity for different working gases and power inputs. Furthermore, the possibilities and disadvantages of the MHD approach, considering a local thermal equilibrium, are discussed. It was found that in general, the computational temperature obtained is supported by the experimental and equilibrium data. The computational temperatures agree by within 10% with the experimental ones at the center of the plasma torch. The paper concludes by explaining the significant impact of input properties like working gas and power input on the output properties like velocity and temperature of plasma jet. © 2023 Author(s).

Soot concentration measurements were performed using diode-laser extinction in an atmospheric air-blown entrained flow gasifier at two vertical levels. The gasifier was operated at different air-fuel equivalence ratios and with variations in fuel and burner configurations. Two fuels were investigated: wood powder and peat powder. These were burned using two burner configurations, one giving a rotating flow inside the gasifier (swirl), and one where the fuel and air were injected parallel with the gasifier axis (jet). The diode-laser measurements were performed at the wavelength 808 nm from which the soot concentrations were estimated, and additionally at 450 nm in order to gain insight into the spectral dependence of the extinction to estimate measurement quality. Additional diagnostic techniques were used, such as an electrical low-pressure impactor (ELPI) for soot size distributions and gas chromatography for species concentration measurements. The results show that wood powder produces higher soot concentrations than peat powder, especially at lower air-fuel equivalence ratios. Furthermore, the burner configuration had in general much less impact than the choice of fuel on the soot concentration.

Buildup of deposit material in chunks on refractory linings caused by combustion of various fuels is a well-known problem. This study characterizes the short-term deposits on refractory material in a grate-kiln process, carried out through in situ measurements using a water-cooled probe with a part of a refractory brick mounted in its end. Sampling was carried out during combustion of both oil and coal. A significant difference in deposition rates was observed; deposition during oil firing was negligible compared to coal firing. The deposits are mainly hematite particles embedded in bonding phase, mainly comprising Si, Al, Fe, Ca, and O. Moreover, it was found that the prevailing flue-gas direction determines the formation of the deposits on the probe and that inertial impaction controls the deposition rate. However, this rate can also be affected by the amount of air-borne particles present in the kiln.