Gasification Step Research Articles

Nuclear hydrogen production through carbonaceous-matter gasification. A physicochemical optimization

To reach the worldwide decarbonisation and the corresponding climate change mitigation, low-carbon energy sources must be used in the near-term and the role of the nuclear energy in pathways to produce net zero emissions is outstanding. This is not only because nuclear energy produces carbon-free energy, but also because it can supply high-temperature process heat to industrial applications such as the hydrogen production. Hydrogen is presently considered as the energy vector of the future to attain these environmental goals.In this paper, the possible use of a nuclear-assisted steam coal gasification process for hydrogen production is investigated in deep. As a modern High Temperature Gas Cooled Reactor (HTGR) is able to produce a gas outlet temperature of 950 °C, the nuclear heat can be transferred to a steam coal gasification plant via an intermediate helium circuit for providing the high-temperature process heat required by the endothermic gasification reactions between the steam and the carbonaceous matter.The nuclear-assisted gasification technology is considered to be attractive for the processing of an Argentine orthoasphaltite that is extracted from a minefield located in Neuquén province. The present research comprises both theoretical and experimental studies, which were addressed to get the necessary information about the optimal conditions for the hydrogen production though the steam gasification process using the Argentine orthoasphaltite as feedstock.A conceptual design of an energy complex for nuclear hydrogen, electricity and liquid fuels production is also proposed. In this conceptual design, the steam coal gasification reactor consists of two concentric vessels specially designed to separate the pyrolysis step occurring at low temperature and the char gasification step that takes place at higher temperatures. In this way, it is possible to give a full use to the volatile compounds that are present in the feedstock and are identified and characterized in this work.

ReaxFF-MD simulation investigation of the degradation pathway of phenol for hydrogen production by supercritical water gasification

Wastewater from the thermochemical conversion of coal and biomass contains a significant amount of phenolic structures compounds. The degradation of these phenolic compounds to hydrogen-rich gasses can prevent environmental pollution and save energy. Supercritical water (SCW) gasification of phenol is experimentally studied and a reactive force field molecular dynamics (ReaxFF-MD) simulation is conducted to investigate the catalytic mechanism of Ni/Al2O3 in the phenol degradation. The experimental results indicate that Ni/Al2O3 facilitates the conversion of phenol to 1-ethoxy butane via ring opening, which is a crucial step for complete gasification. The ReaxFF-MD simulation demonstrated that Ni facilitates the formation of H3O free radicals and Ni-phenol intermediates. H3O free radicals can be decomposed into H2 and OH free radicals. Both the generated OH free radical and Ni-phenol intermediate promote the ring-opening reaction of phenol. Ni promotes the direct decomposition of phenol into C1, C2, and C3 fragments, which is beneficial for further complete gasification.

Experimental study on the effect of temperature and oxygen on pyrolysis-gasification decoupling characteristics of Yili coal

Pyrolysis, as the initial process of coal clean utilization, is essential to ensure the operation of pyrolysis-gasification decoupling technology. This paper aims to investigate the effects of temperature and oxygen content on coal pyrolysis product distribution and the char structure and reactive properties. Results demonstrate that in the range of 800–1100 °C, the increase in temperature is conducive to the release of volatiles and tar cracking, to enhance the gas phase yield and syngas concentration. However, as Raman spectroscopy analysis shows, higher temperature (>900 ℃) will intensify the graphitization of char, which is not conducive to the next gasification step. In addition, oxygen introduction at 900 ℃ can accelerate the release of volatiles and intensify the occurrence of depolymerization reaction, which increased the gas yields of CO and CO2 in the gaseous product. Besides, the presence of trace oxygen in the pyrolysis process reduces the degree of coal char graphitization and improves the gasification reactivity. However, at high oxygen content (8 %) conditions, combustion occurs on the surface of the char as SEM results show, which destroys the structure and reduces the gasification activity of the char. Hence, the pyrolysis product distribution and post-pyrolysis char gasification activity can be adjusted by introducing trace oxygen in pyrolysis-gasification decoupling technology.

Upgrading CO2 from simulated power plant flue gas via integrated CO2 capture and dry reforming of methane using Ni-CaO

Integrated CO2 capture and utilisation via dry reforming of methane (ICCU-DRM) represents a promising and profitable route for directly capturing and converting CO2 from various CO2 sources. However, the influence of realistic flue gas conditions on ICCU-DRM remains unknown and challenging. Herein, we investigated the influence of the presence of H2O and O2 in power plant flue gas on integrated CO2 capture and DRM using Ni10-CaO dual functional material (DFM). It is found that H2O promoted the kinetics of CO2 capture, while the O2 oxidised Ni into NiO and prohibited the performance of utilisation of the captured CO2 during DRM. Specifically, the delay of pre-reduction of NiO and the coverage of catalytic sites by the formed CaCO3 decreased the process performance and efficiency. The reduction of NiO would instantly generate CO2 and hinder the contact between CH4 and Ni, resulting in a lower initial catalytic performance during the CO2 utilisation (DRM) of ICCU. Due to the occurrence of CH4 decomposition in DRM, the following CO2 capture step would produce CO in the flue gas, which could be problematic, owing to the carbon gasification reactions. An extra step of carbon steam gasification (CSG) after DRM could effectively remove most of the deposited carbon and by-produce syngas. Subsequently, the small amount of carbon residue after the CSG step could be preferentially combusted by O2 into CO2 in flue gas, and then be captured by CaO instead of generating CO. This study demonstrates the feasibility and challenges of ICCU-DRM under simulated power plant flue gas conditions and provides potential insights for future investigation and deployment of this integrated process.

High Temperature Winkler gasification of Rhenish lignite in an optimized 500 kWth pilot plant

Gasification processes are an important part of a broad variety of value chains from low grade feedstocks to energy. The process considered in this work consists of a 0.5 MWth fluidized bed gasifier, a gas cleaning unit and a catalyst test rig. This paper presents experimental results from the stand-alone operation of the gasifier in order to investigate the behavior of the gasification of two feedstocks, a dried lignite steam coal and a commercially available low sulfur, low ash lignite. Furthermore, the results of the gasification of the gasifier start-up material hearth furnace coke are given. The reactor with a height of 11 m and an inner diameter of 400 mm was operated at up to 870 °C. Carbon dioxide, steam and oxygen can be introduced into the reactor through different nozzle levels.Four test campaigns were conducted and seven balance points with different feedstock and loads were investigated. The results show carbon conversions of almost 96 % and cold gas efficiencies up to 65 % with coal from fluidized bed drying showing the highest cold gas efficiencies and carbon conversions. Several trace gases were measured by Fourier-Transform Infrared Spectroscopy and a positive correlation between benzene and methane concentration is detected.The experience gained serves as a basis for the gasification step in the polygeneration process and for gasification of other feedstock, especially biogenic and anthropogenic residues.

Recycling of polystyrene-based external thermal insulation composite systems – Application of combined mechanical and chemical recycling

The material recycling of complex waste streams such as external thermal insulation composite systems (ETICS) is challenging, which is why their recycling in the sense of a circular economy is currently hardly established. Therefore, the combined mechanical and thermochemical recycling of ETICS based on expanded polystyrene (EPS) is investigated experimentally and by simulating full process chains in order to evaluate circular economy opportunities. Model ETICS as example for building and construction waste is pretreated mechanically, followed by either pyrolysis and / or gasification steps, and full mass and energy balances are derived. By the combined recycling, inorganic compounds can be separated to a large extent allowing a pre-concentrate generation. The plastic-rich pre-concentrate is converted into either pyrolysis oil with a high styrene monomer content of 51 wt% or to synthesis gas in the subsequent thermochemical conversions. The holistic approach enables a high carbon recycling rate between 53 and 68 wt%. In addition, the investigation reveals technology limitations and opportunities to be further developed and optimized.

Thermal upgrading of hydrochar from anaerobic digestion of municipal solid waste organic fraction

Solid fraction obtained from anaerobic digestion of municipal solid waste organic fraction is a waste produced in noticeable amounts, which according to circular economy concept can be upgraded to produce new, value-added products like: hydrogen rich process gas and carbon rich solid material. In this study, thermal upgrading of hydrochar by steam gasification was analysed. Raw material was obtained through hydrothermal carbonization (HTC) of digestate from anaerobic digestion of wet fraction of municipal solid waste at 200 and 230 °C, and residence time of 60 and 120 min. The further gasification step was carried out at 800 °C and the residence time was 10 min under nitrogen with a steam atmosphere. The main objective of hydrochar upgrading through steam gasification was production of carbon-rich material with developed active surface area. The study presented promising results regarding proper management of mixed wastes, which have not yet been analysed in the literature. It was noted that low temperature and residence time are favouring active surface area development. Analysis of the main gaseous products of the gasification process showed that syngas is composed mainly of H2, CH4, CO2, O2, and CO. The hydrogen concentration was the highest noted for hydrochar obtained at highest temperature and residence time. Analysis of the concentration of each syngas component reveals that combined treatment of digestate from anaerobic digestion through the HTC and gasification process results in H2-rich syngas products and a high H2/CO ratio with parallel fair quality activated carbon.

Insight into biomass pyrolysis mechanism based on cellulose, hemicellulose, and lignin: Evolution of volatiles and kinetics, elucidation of reaction pathways, and characterization of gas, biochar and bio‐oil

Pyrolysis is the first step of gasification and combustion. The pyrolysis process of biomass is complicated, which is generally considered to consist of the pyrolysis of the three major components (i.e., cellulose, hemicellulose, and lignin). Understanding the pyrolysis behavior and product of each component holds a key to understanding the biomass pyrolysis mechanism. In this work, the pyrolysis behavior, pyrolysis kinetics, volatile evolution, and product characterization of the three major components are investigated. Results showed that pyrolysis characteristics and thermal stability of the three components were closely related to their unique chemical structures. During pyrolysis, the main pyrolytic volatiles of hemicellulose appeared first, followed by cellulose and then lignin volatiles in the 3D FTIR spectra. In term of pyrolysis products, gases were generated by the cracking of specific functional groups. Hemicellulose had the highest CO2 yield, whereas lignin had the highest CH4 yield due to the aromatic rings and methoxy groups in lignin structure. Whereas cellulose demonstrated the highest CO yield at high temperatures (above 550 °C). With increasing temperature, the carbon structures of carboxylic-C and O-alkyl-C in biochar decreased, while aryl-C was enhanced. This was due to the deoxygenation reactions such as dehydroxylation, decarboxylation, decarbonylation, and demethoxylation, resulting in a reduction in the number of oxygen-containing functional groups (such as –OH, –C=O, –COOH, and –OCH3), as well as the polycondensation reactions that formed more polycyclic aromatic hydrocarbon units during pyrolysis. The major components of cellulose bio-oil included anhydrosugars and furans. Whereas the bio-oils derived from hemicellulose and lignin showed the highest relative content of acids and phenols, respectively. Based on this analysis, the thermal decomposition pathways of cellulose, hemicellulose, and lignin were proposed.

CO2 Gasification Reactivity and Syngas Production of Greek Lignite Coal and Ex-Situ Produced Chars under Non-Isothermal and Isothermal Conditions: Structure-Performance Relationships

The presented work explores the structural properties, gasification reactivity, and syngas production of Greek lignite fuel (LG) and ex-situ produced chars during CO2 gasification. Three different slow pyrolysis protocols were employed for char production involving torrefaction at 300 °C (LG300), mild-carbonization at 500 °C (LG500), and carbonization at 800 °C (LG800). Physicochemical characterization studies, including proximate and ultimate analysis, X-ray Diffraction (XRD), and Raman spectroscopy, revealed that the thermal treatment under inert atmospheres leads to chars with increased fixed carbon content and less ordered surface structures. The CO2 gasification reactivity of pristine LG and as-produced chars was examined by thermogravimetric (TG) analysis and in batch mode gasification tests under both isothermal and non-isothermal conditions. The key parameters affecting the devolatilization and gasification steps in the overall process toward CO-rich gas mixtures were thoroughly explored. The gasification performance of the examined fuels in terms of carbon conversion, instant CO production rate, and syngas generation revealed an opposite reactivity order during each stage. TG analysis demonstrated that raw lignite (LG) was more reactive during the thermal devolatilization phase at low and intermediate temperatures (da/dtmax,devol. = 0.022 min−1). By contrast, LG800 exhibited superior gasification reactivity at high temperatures (da/dtmax,gas. = 0.1 min−1). The latter is additionally corroborated by the enhanced CO formation of LG800 samples under both non-isothermal (5.2 mmol) and isothermal (28 mmol) conditions, compared to 4.1 mmol and 13.8 mmol over the LG sample, respectively. The pronounced CO2 gasification performance of LG800 was attributed to its higher fixed carbon content and disordered surface structure compared to LG, LG300, and LG500 samples.

The effect of alkali and alkaline earth metals oxides addition on oxygen uncoupling rate of copper-based oxygen carrier: A kinetic and experimental investigations

• Oxygen uncouples ability of CuO at low temperatures tested by adding AAEMs oxides. • 5% wt of Na 2 O, K 2 O, MgO, and CaO added to CuO. • An isothermal test was done; MgO, CaO enhanced the process and Na 2 O, K 2 O declined. • Kinetic analysis has been conducted for a more in-depth investigation. • Kinetic results was matched with the experimental, in both MgO was the best. Oxygen uncoupling is one of the most valued properties of oxygen carriers in chemical looping field. It allows to combust the fuel without gasification step and significantly enhances reactivity in all chemical looping fuel oxidation technologies (combustion, gasification, and reforming). Furthermore, it progressed recently to produce pure oxygen (Chemical looping air separation). However, few materials have this merit, among which CuO has the highest reactivity and oxygen transport (uncoupling) capacity. However, it needs a high temperature (about 950 °C) for a high effective reaction rate; in contrast, it suffers high attrition rate and sintering about this temperature. This work aimed to test the ability to enhance the uncoupling at lower temperatures by adding a small amount of common alkali and alkaline earth metals (AAEMs) oxides. CuO was prepared with 5%wt of Na 2 O, K 2 O, MgO, and CaO. An isothermal test was conducted in TGA at (850, 890, and 930 °C) to investigate the effect of additions. For deeper investigation, kinetic analysis has been conducted based on isothermal results. The model of reaction inferred was A 2 α of Avrami-Erofeev ( g α = - l n 1 - α 1 / 2 ) for pure CuO and with all additions, and then the activation energies and pre-exponential factors were calculated. Accordingly, CaO addition showed little increase in the reaction rates while the effect of MgO was significant. In contrast, Na 2 O and K 2 O addition declined the uncoupling rate.

Study on pyrolysis characteristics of lump coal in the context of underground coal gasification

Coal reaction in dry distillation zone, as an essential step in underground coal gasification (UCG), is of great significance to be studied about its characteristics in a comprehensive way. This study simulated the pyrolysis process of lump coal in UCG tunnel in a laboratory. Lump coal samples were heated in nitrogen environment at 200–600 °C. The functional groups, pore structure, and microcrystalline structure of coal samples were analyzed by Fourier transform infrared spectrometer, scanning electron microscope, and X-ray diffractometer. The results showed that, as final pyrolysis temperature increased, the contents of hydroxyl, aliphatic, and aromatic groups all showed decreasing trends. The escalation of CHar/CC and CH2/CH3 implied that the condensation degree of aromatic structure and the branching degree of fatty chain increased. With the temperature increasing, volatile substances such as CO2 and CH4 were released. Coal samples had higher porosity and gradually turned hollowed. The d002 (Interlinear Spacing of Microcrystalline) of the coal sample decreased, Lc (final stacking height) increased and Lc/d002 (stacking layer numbers) decreased, indicating that the crystal structure of coal samples tended to be more disordered.

Improving Hydrothermal Carbonization (htc) Processes by Hydrochar Gasification

Hydrochar is produced by means of hydrothermal carbonization at relatively low temperatures (180-260°C) in sub-critical water. While, in many respects similar to biochar, its physical and chemical properties differ significantly (Basu, 2018). Of particular interest for this work are the higher energy density and lower ash content, that make hydrochar a possible feedstock for gasification plants with energy generation purposes. A gasification step is used instead of direct combustion to convert solid fuels in energy to achieve cleaner combustion and higher efficiency (Wang and Stiegel, 2016). In this work a 400 kg/h hydrochar gasification plant was modelled to identify optimal conditions and energetic yield of hydrochar obtained from municipal sewage. The fixed bed, updraft, gasification reactor was modeled in detail using a multi-scale, multiphase methodology already widely tested on biomass (Corbetta et al., 2015; Ranzi et al., 2014). The gas solid kinetic model was coupled with a detailed gas-phase kinetic scheme with over 200 species, including reaction intermediates, and 2000 reactions for reliable product yield prediction. Using Visual Basic Application as an interface, the predictions from the detailed simulation package were delivered to a commercial simulation package to model the energy generation section of the plant. Aspen HYSYS V10 was used for this purpose for the simplicity of integration and its widespread use in similar industrial plants. The gasification was carried out with air, air enriched in oxygen to 28%, air enriched in oxygen to 35% and pure oxygen with different amounts of steam to control the temperature in the chamber and at different values of equivalence ratio. The gasification performance was evaluated in terms of lower heating value of the generated fuel gas while the H2S formation was accounted for only in a superficial manner using rules of thumb derived from previous experimental experience.

Thermochemical conversion of sewage sludge-derived hydrochars: Volatiles release and char gasification kinetics

Hydrothermal carbonization (HTC) combined with subsequent thermochemical conversion is an effective approach for sewage sludge (SS) to energy. In this work, HTC pretreatment of SS was performed. Then the properties of released volatiles and the remaining char-CO2 gasification after pyrolysis were evaluated via the multiple kinetic model and combined instrumental analyses. The gasification behavior of these samples exhibited slightly different due to high ash content and limited fixed carbon, although the aromatic structure in the hydrochars developed as HTC proceeded. Kinetic analysis indicated that volume reaction model (VRM) with chemical reaction order of 1.5 showed high correlation coefficients (R2>0.99) for all carbonized samples. There was an obvious kinetic compensation effect in the char gasification step, and activation energy (E) and pre-exponential factor (A) of these samples followed a positive correlation relationship as lnA = 0.1037 × E + 0.3579. The formation of fixed carbon in the hydrochar samples was conserved during pyrolysis, which lowered the average gasification reactivity of char. Py-GC/MS demonstrated that the chemical composition of pyrolytic volatiles was found to be mainly determinant by HTC conditions. The share of aromatics in the volatiles was in a positive correlation with the evolution of carbon functionality in the hydrochar samples. Above in all, HTC temperature exerted a more significant effect on the fuel properties of hydrochar samples than HTC duration did, which also indicated by their subsequent thermochemical conversion. These findings can provide essential knowledge on the thermochemical conversion of hydrochar samples and favor the designing, optimization, and scaling up of the process.

Devolatilization of Residual Biomasses for Chemical Looping Gasification in Fluidized Beds Made Up of Oxygen-Carriers

The chemical looping gasification of residual biomasses—operated in fluidized beds composed of oxygen-carriers—may allow the production of biofuels from syngas. This biomass-to-fuel chain can contribute to mitigate climate change, avoiding the accumulation of greenhouse gases in our atmosphere. The ongoing European research project Horizon2020 CLARA (G.A. 817841) investigates wheat-straw-pellets (WSP) and raw-pine-forest-residue (RPR) pellets as feedstocks for chemical looping gasification. This work presents experimental results from devolatilizations of WSP and RPR, in bubbling beds made of three different oxygen-carriers or sand (inert reference), at 700, 800, 900 °C. Devolatilization is a key step of gasification, influencing syngas quality and quantity. Tests were performed at laboratory-scale, by a quartz reactor (fluidizing agent: N2). For each pellet, collected data allowed the quantification of released gases (H2, CO, CO2, CH4, hydrocarbons) and mass balances, to obtain gas yield (ηav), carbon conversion (χavC), H2/CO ratio (λav) and syngas composition. A simplified single-first order-reaction model was adopted to kinetically analyze experimental data. WSP performed as RPR; this is a good indication, considering that RPR is similar to commercial pellets. Temperature is the dominating parameter: at 900 °C, the highest quality and quantity of syngas was obtained (WSP: ηav = 0.035–0.042 molgas gbiomass−1, χavC = 73–83%, λav = 0.8–1.0); RPR: ηav = 0.036–0.041 molgas gbiomass−1, χavC = 67–71%, λav = 0.9–1.0), and oxygen-carries generally performed better than sand. The kinetic analysis suggested that the oxygen-carrier ilmenite ensured the fastest conversion of C and H atoms into gases, at tested conditions.

Analysis of the Carbothermic Reduction of Iron Ore-Coke Composite Mixtures by Microwave Heating

Abstract In recent decades, microwave energy has been successfully experimented for mining and metallurgy processes and is considered a promising new method for ironmaking. In this context, in the present work, self-reducing mixtures composed of fines of iron ore and coke were prepared, intending to evaluate the degree of reduction of iron ore using microwave energy, applying different contents of coke, levels of power, and reaction times. For this, the degree of reduction was assessed as a function of these variables. Additionally, the reduction kinetics was investigated using chemical and diffusional models, and the microstructure of the samples was evaluated using scanning electron microscopy (SEM). The highest degree of reduction obtained after the experiments was greater than 60% and a statistical investigation showed that the reaction time is the factor with the greatest influence on these results, followed by microwave power and coke content. The investigation of the reaction kinetics showed that the process is chemically controlled, depending on the gasification steps governed by the Boudouard reaction. The images obtained by SEM led to the conclusion that the temperature inside the sample reached 1200°C. Pig iron was found both in the form of whiskers and in the form of metallic droplets.

Coal direct chemical looping process: 250 kW pilot-scale testing for power generation and carbon capture

Chemical looping combustion (CLC) is an energy conversion technology that can produce concentrated CO2 stream without the need for a gas separation step, and thus, has the potential to drastically reduce the energy consumption and cost associated with CO2 capture in power generation. The coal-direct chemical looping (CDCL) process is a CLC technology that uses a moving bed reducer configuration that can directly consume coal as a feedstock without requiring an upstream gasification step. An integrated 250 kWth CDCL pilot unit using iron-based oxygen carriers was constructed and demonstrated for over 1000 h of testing. The principles for the CDCL pilot unit design and operation are summarized in this article. During the 288-hour continuous operation testing, the CDCL pilot unit achieved >96% coal conversion with a CO2 purity of >97%. Low carbon carryover into the combustor, i.e. <2%, was also confirmed during the test, which shows the capability of the moving bed reactor to retain and convert coal using the oxygen available on the iron-based oxygen carrier. The results from the pilot unit testing confirms the CDCL concept as a promising coal combustion technology for heat and power generation with CO2 capture.

Kinetic modeling of Indian lignites pyrolysis in the context of underground coal gasification (UCG)

Pyrolysis is an important step in combustion and gasification of any solid fuel. In this work, we have studied the kinetics of the pyrolysis of three Indian lignite samples via thermogravimetric experiments and mathematical modeling. Applicability of various kinetic models viz. the single global reaction model, the consecutive reaction model and the distributed activation energy model (DAEM) are evaluated. The kinetic parameters of the models were estimated based on the experimental data. Kinetics of the evolution of the volatile matter was studied independently by using a specially designed fixed-bed reactor and the relevant kinetic parameters were estimated.

Towards understanding the role of K during biomass steam gasification

Steam gasification is known to be catalyzed by K. However, the exact mechanisms are not identified to this day. In the present study, the catalytic influence of K on biomass steam gasification and its interaction with Si was investigated. The study was conducted through thermogravimetric analysis (TGA) on rice husks as a Si-rich biomass and K2CO3 as a model K-compound. Experiments were conducted in three different configurations: biomass or inorganic compound alone; mixtures of biomass and inorganic powders; biomass and inorganic compound without contact in a two-compartment crucible. It was shown that K has a catalytic effect on both the pyrolysis and the gasification steps. These effects occur even when the K-compound is not in direct contact with the biomass. Therefore, it demonstrates that the mechanisms involve the gas phase through the volatilization of a K-compound, most likely KOH(g). However, the observed catalytic effect on rice husks was weaker than the effect obtained in the case of beech wood, a Si-poor and more generally ash-poor biomass, under the same conditions. It shows that there is a competition between i) the influence of K on the biomass pyrolysis and char gasification kinetics and ii) the interaction of K with SiO2 inherent to the biomass.

Biomass torrefaction as an emerging technology to aid in energy production.

Biomass torrefaction has gained widespread attention due to its benefits as a standalone process to improve biomass properties to be at par or similar to those for coal in electricity generation or as a pretreatment step before pyrolysis and gasification processes. It has also found application in other processes like steel production where it is aiming to replace coal or work alongside coal by co-firing the coal with biomass at certain proportions. There have been a lot of papers on biomass torrefaction review, but this paper tried to look at a different angle to show other aspects of torrefaction and how it links to other technologies as well as the chemistry behind it. Overall, the process has seen a big shift in the technology it utilizes, and the hope is that it will make the process more viable and applicable in future.The focus starts from the raw biomass, how it is analysed and the different analysis that are performed to determine relevant information about biomass properties. There are different reactors that are used but to date there is not a preferred one as they have their pros and cons. However, the focus mostly is the process not which reactor to use as they have all not shown any significant differences. The main product of the process, torrefied biomass determines the efficiency and how it can be applied to other technologies. To date, biomass torrefaction is for co-firing with coal for energy generation and as a pretreatment step for pyrolysis and gasification. Due to varying types of biomass in different countries, the technology has not yet reached its full potential, but the hope is it will with calls for use of renewable sources of energy.Other areas like modelling torrefaction of biomass have not been looked at in this review. However, the paper sets the foundations for such detailed reviews.

Biomass chemical-looping gasification coupled with water/CO2-splitting using NiFe2O4 as an oxygen carrier

Bio-syngas generation with flexible H2 to CO ratios via biomass chemical-looping gasification (CLG) coupled with water/CO2-splitting using NiFe2O4 as an oxygen carrier (OC) was proposed in the present work. The presence of NiFe2O4 OC promotes biomass conversion, especially bio-char conversion at elevated temperature stage. Addition steam and/or CO2 into the carrying gas increased the weight loss rates of biomass. Up to 5.88 wt%/min and 4.97 wt%/min of the maximum weight loss rates were achieved during biomass conversion with NiFe2O4 OC in CO2 and steam flows in a TGA reactor, respectively. With NiFe2O4 as an oxygen carrier, an optimal lattice oxygen/biomass mass ratio is 0.51 giving the highest syngas yield of 0.77 m3/kgbiomass in the absence of steam or CO2 at 850 °C. Steam/biomass mass ratio of 2.25 gave the maximum carbon conversion of 92.53% and syngas yield of 1.38 m3/kgbiomass suggesting that steam addition significantly improves the biomass conversion and the syngas yield. Introducing a fraction of CO2 into steam could reduce the steam consumption as well as enhance the carbon conversion in biomass gasification step. NiFe2O4 OC serves as an effective catalyst for tars cracking in biomass-CLG. The tars content in the syngas generated in biomass-CLG with NiFe2O4 is 2.83 g/m3, which is much lower than that (14.25 g/m3) in biomass gasification with inert ZrO2. The productivities of H2 and CO are 211 ml/gOC and 101 ml/gOC in water- and CO2-splitting steps. The proposed approach can potentially be applied for providing bio-syngas with flexible H2 to CO ratios from 1:1 to 2.2:1 for purpose of various synthesis processes such as Fischer-Tropsch, acetic acid, and oxo-synthesis.