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Catalytic tar conversion and the prospective use of iron-based catalyst in the future development of biomass gasification: a review

Authors:
Ramadhani Bakari at Dodoma University
Ramadhani Bakari
Thomas Kivevele at The Nelson Mandela African Institute of Science and Technology
Thomas Kivevele
Joseph H Kihedu at University of Dar es Salaam
Joseph H Kihedu
Yusufu Abeid Chande Jande at The Nelson Mandela African Institute of Science and Technology
Yusufu Abeid Chande Jande
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Biomass is a promising renewable energy source which is available globally, mostly in developing countries where access to clean and affordable energy is a critical problem. Biomass gasification is an interesting technology that can convert biomasses to a more versatile fuel known as syngas, the energy which can substitute conventional fossil fuels in the future. Syngas can amenably be combusted to produce power and heat as well as a feedstock for synthesis of chemicals and other fuels. The biomass gasification is facing severe operational challenges, one of the problems being tar formation and its removal techniques. Tar condenses at reduced temperature, thus causing blockage in the downstream equipment such as compressors and engines. Many studies have considered syngas cleaning by physical removal and thermal cracking unsuitable as they need downstream processing of scrub liquor and utilizes a part of the produced gas in maintaining the thermal cracking temperature, respectively. The utilization of catalysts has been an interesting focus; however, it has not yet been fruitful as many of the developed catalysts deactivate rapidly, and they are expensive or toxic. The motives of the current study are to review tar formation characteristics and trends on catalytic conversion. In addition, the study elucidates the fascinating behaviour of metallic and oxides of the iron-based catalyst under different syngas composition (oxidizing and reducing environments). The behaviours of the iron-based catalyst indicate its fundamental role in developing a catalyst for tar cracking with respect to less toxic, inexpensive, abundant, and regenerable alternatives. Graphical abstract
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REVIEW ARTICLE
Catalytic tar conversion and the prospective use of iron-based
catalyst in the future development of biomass gasification: a review
Bakari Ramadhani
1,2,3
&Thomas Kivevele
1,2
&Joseph H. Kihedu
4
&Yusufu A. C. Jande
1,2
Received: 15 January 2020 / Revised: 4 June 2020 / Accepted: 10 June 2020
#Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
Biomass is a promising renewable energy source which is available globally, mostly in developing countries where access to
clean and affordable energy is a critical problem.Biomass gasification is an interesting technology that can convert biomasses to
a more versatile fuel known as syngas, the energy which can substitute conventional fossil fuels in the future. Syngas can
amenably be combusted to produce power and heat as well as a feedstock for synthesis of chemicals and other fuels. The biomass
gasification is facing severe operational challenges, one of the problems being tar formation and its removal techniques. Tar
condenses at reduced temperature, thus causing blockage in the downstream equipment such as compressors and engines. Many
studies have considered syngas cleaning by physical removal and thermal cracking unsuitable as they need downstream pro-
cessing of scrub liquor and utilizes a part of the produced gas in maintaining the thermal cracking temperature, respectively. The
utilization of catalysts has been an interesting focus; however, it has not yet been fruitful as many of the developed catalysts
deactivate rapidly, and they are expensive or toxic. The motives of the current study are to review tar formation characteristicsand
trends on catalytic conversion. In addition, the study elucidates the fascinating behaviour of metallic and oxides of the iron-based
catalyst under different syngas composition (oxidizing and reducing environments). The behaviours of the iron-based catalyst
indicate its fundamental role in developing a catalyst for tar cracking with respect to less toxic, inexpensive, abundant, and
regenerable alternatives.
Keywords Biomass gasification .Syngas .Tar removal .Catalyst .Iron-based catalyst .Biomass conversion
1 Introduction
The growing concerns over fossil fuel price, increased energy
demand due to rapid industrialisation and increased popula-
tion, and foreseen damage of climate change through global
warming is a contemporary threat to the quality of life of
populations, plants, and animals [1–6]. At present, the global
energy matrix is 80–85% dependent on fossil fuel as the pri-
mary energy source; however, depending on the country, the
dependency varies from 32.1 to 100% [7,8]. The combustion
of fossil fuelcontributes about 70% of total global GHG emis-
sions in the form of CO
2
[9].
To ensure sustainable development of the society, the only
possibility is to emphasize on clean and green energy through
searching for the ideal renewable energy resources [10,11].
Amongst the available resources, it ought to note thatbiomass
is considered a prominent form of energy which can deliver
steady energy as fossil fuels [12,13].
Biomass contributes about 10–14% of the global energy
requirement, while in rural and remote areas of developing
countries, its contributions are more than 90% [2,14,15].
Biomass gasification is one of the effective thermochemi-
cal conversion processes that convert the energy values of
biomass to permanent gases (H
2
, CO, and CH
4
)calledsyngas,
the hydrogen-rich gas with stable energy content like fossil
fuels [1,16]. The syngas from biomass is more useful than its
*Yusufu A. C. Jande
yusufu.jande@nm-aist.ac.tz
1
Department of Materials, Energy Sciences and Engineering, The
Nelson Mandela African Institution of Science and Technology, P.
O. Box 447, Arusha, Tanzania
2
Water Infrastructure and Sustainable Energy Futures
(WISE-Futures), African Centreof Excellence, The Nelson Mandela
African Institution of Science and Technology, P. O. Box 9124,
Arusha, Tanzania
3
Department of Petroleum and Energy Engineering, The University of
Dodoma, P. O. Box 11090, Dodoma, Tanzania
4
Department of Mechanical and Industrial Engineering, University of
Dar es Salaam, P. O. Box 35131, Dar es Salaam, Tanzania
https://doi.org/10.1007/s13399-020-00814-x
/ Published online: 27 June 2020
Biomass Conversion and Biorefinery (2022) 12:1369–1392
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Among the primary methods to remove tar inside a biomass gasifier, the use of a bed of catalyst particles has been recalled above. 49,50 The literature 5 reports catalysts based on Al, Ca, Ce, Fe, La, Mg, Ni, Ti, Zn and Zr for gasification of biomasses such as rice hull, corncob, animal manure, wood sawdust, corn stalk, maize stalk and almond shells. The resistance of catalysts to sintering/attrition in FB systems represents a key issue for improving the efficiency of the tar abatement process. ...
... The resistance of catalysts to sintering/attrition in FB systems represents a key issue for improving the efficiency of the tar abatement process. While details of the role of catalysts are available elsewhere, 5,[49][50][51] it is here recalled that, when using almond shells as biomass for FB gasification, the presence of catalysts such as calcined dolomite, olivine and a MgO-NiO mixture allowed the production of a syn-gas with H 2 content of around 52-56%. 46 FB gasification has been the focus of extensive modelling activity. ...
... Hoang et al. 36 reported outcomes from steam gasification: most data agree with a content of H 2 in the producer gas of between 45% and 54% (white oak, wood, straw and sawdust were used as raw fuel), even better than the typical ranges reported by Thomson et al. 58 for syn-gas from FB steam gasification (35-40% for H 2 ; for other compounds, they listed 25-30% for CO, 20-25% for CO 2 and 9-11% for CH 4 ). Ramadhani et al. 50 confirmed the great variability of the syn-gas composition when, upon FB steam gasification, the operating conditions (temperature, flow rate of the gasifying agent versus flow rate of biomass, biomass nature and composition) are changed. Referring to rice husk, sugarcane bagasse, wood pellets/chips, pinewood and almond shells as biomass, the H 2 content in producer gas can range from 38% to 60%, and the CH 4 content can be from negligible up to 8%. ...
Fluidised bed gasification of biomasses and wastes to produce hydrogen‐rich syn‐gas – a review
Article
Full-text available
The sustainable fulfilment of world energy demand should be based on the diversification of the energetic portfolio and, at the same time, on the decrease of the use of fossil fuels in favour of renewable energy sources. This perspective review article focuses its attention on a particular source of renewable energy, i.e. biomass. As non‐fossil materials of natural origin, biomasses are formed by storing, in the noble and stable form of chemical bonds, solar energy. Gasification has been here chosen as biomass thermoconversion route: general concepts and history, chemical reactions and uses of syn‐gas, and the role of tar, are addressed. Fluidised beds are discussed as reactors to carry out biomass gasification, also considering that a new approach based on dual interconnected fluidised bed schemes can realise the concept of sorption‐enhanced gasification (to increase H2 productivity). Syn‐gas and tar characteristics are presented and, finally, an original case study concerning the fluidised bed gasification of civil and industrial sludges is presented. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).
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... [33,66,[80][81][82] The presence of CaO, MgO and CaCO 3 (basic nature) in Dol catalyst allows a progressive rupture of the aromatic and phenolic rings from the biomass, promoting cellulose, hemicellulose and lignin cracking. [62,66,81,[83][84][85] Corella et al. [62] propose a mechanism for removing tar with CaO that explains how the rings are progressively, one-by-one, being opened by the catalyst and H 2 O. ...
... [33,66,80,81,82] In addition, Fe species (Lewis acid) improves the catalytic reforming reactions of the tar generated from the gasification stage. [33,66,[81][82][83][84] Lewis acidity predominates in NiMo/Al, it is related to the electronic availability due to the bimetallic character as a result of its free electron d orbitals. In NiMo/Al the Lewis acid sites allow a better interaction between the tar and the gaseous compounds by electronic effects. ...
Catalytic Gasification and Reforming of Residual Biomass in a Bench Scale System with Low Cost Catalysts
Article
Full-text available
  • Nov 2023
This paper demonstrates the effectiveness of using of different catalysts for reforming tars contained in the syngas of biomass gasifiers. The conversion of the tar content allows to obtain high quality syngas and to maximize the gas fraction. A bench scale equipment consisting of an autothermal fluidized bed gasifier and a downstream packed bed reformer was used. Pine sawdust was selected as the feedstock for gasification. TGA analysis showed that the temperature must be above 350 °C to ensure the ignition of the biomass and maintain the process in an autothermal steady‐state. Dolomite and pyrolysis char were used to test of the fluidized bed catalysts. In the reformer, dolomite, pyrolysis char, iron doped activated carbon and spent HDS catalyst were used. All catalysts decreased the CO2 concentration in the product gas and increased H2, CH4 and CO. When iron doped activated carbon is used, tar contents below 60 g/Nm³ in the product gas could be obtained, reaching less than 1 g/Nm³. The best value of LHV (lower heating value) was obtained with pyrolysis char as a catalyst (4.8 MJ/Nm³). The results demonstrate that catalytic biomass gasification with downstream tar reforming with low‐cost catalysts is a promising solution for energy applications.
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... Samadi et al. developed a stoichiometric equilibrium model for predicting energy production from gasification and evaluated the effects of operating conditions on performance, highlighting the challenges in optimizing gasification processes [28]. Ramadhani et al. reviewed challenges in tar formation and its removal, emphasizing the need for less toxic, inexpensive, and regenerative catalyst alternatives [29]. This review carried out by Situmorang et al. discussed challenges in the development and application of small-scale biomass gasification systems, such as the need for lowering investment costs and supportive policies [30]. ...
Retrofitting Biomass Combined Heat and Power Plant for Biofuel Production—A Detailed Techno-Economic Analysis
Article
Full-text available
  • Jan 2024
Existing combined heat and power plants usually operate on part-load conditions during low heating demand seasons. Similarly, there are boilers designated for winter use that remain inactive for much of the year. This brings a concern about the inefficiency of resource utilization. Retrofitting existing CHP plants (especially for those with spare boilers) for biofuel production could increase revenue and enhance resource efficiency. This study introduces a novel approach that combines biomass gasification and pyrolysis in a polygeneration process that is based on utilizing existing CHP facilities to produce biomethane, bio-oil, and hydrogen. In this work, a detailed analysis was undertaken of retrofitting an existing biomass combined heat and power plant for biofuel production. The biofuel production plant is designed to explore the polygeneration of hydrogen, biomethane, and bio-oil via the integration of gasification, pyrolysis, and renewable-powered electrolysis. An Aspen Plus model of the proposed biofuel production plant is established followed by a performance investigation of the biofuel production plant under various design conditions. An economic analysis is carried out to examine the profitability of the proposed polygeneration system. Results show that the proposed polygeneration system can achieve 40% carbon efficiency with a payback period of 9 years and an internal rate of return of 17.5%, without the integration of renewable hydrogen. When integrated with renewable-power electrolysis, the carbon efficiency could be significantly improved to approximately 90%; however, the high investment cost associated with the electrolyzer system makes this integration economically unfavorable.
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... As mentioned in the previous section, the catalyst can be loaded in the gasifier to reduce tar production and enhance the quality of the produced syngas, and the catalyst can also work outside the gasifier to reduce the operating temperature for the thermal cracking of tar. Based on the composition of the catalyst, the applied heterogeneous catalysts can be mainly classified as transition metal (Ni-, Pt-, and Fe-based) catalysts [7,[48][49][50], alkaline (K-based) catalysts [51], alkaline earth (Ca-based) catalysts [52,53], and natural mineral (dolomite, bauxite, and olivine based) catalysts [47,48,54]. ...
Recent progress of the transition metal-based catalysts in the catalytic biomass gasification: A mini-review
Article
  • Jul 2023
  • FUEL
Biomass is regarded as an important renewable resource, which plays a critical role in the development of sustainable energy systems. Biomass can be converted into energy or valuable chemicals by combustion, liquefaction, pyrolysis, and gasification. Among these processes, thermal gasification cracks biomass into light species at high temperatures, which can be applied to biomass with the greatest variety. As the target product of biomass gasification, syngas or H2-rich gas are very important intermediates in the petrochemical industry. However, the troublesome tar produced during gasification could bring a series of problems. Catalytic biomass gasification is a promising strategy to greatly alleviate these issues. The transition metal-based catalysts for catalytic biomass gasification have been studied in the last decades. Various transition metal catalysts for biomass gasification are reviewed in this article, including monometallic and bimetallic Ni-based catalysts, and other Fe-, Co-, and Pt-based catalysts. The performance of these catalysts is evaluated based on applied reaction parameters, the quality of produced syngas, and the performance of tar reduction. The applications of DFT calculation and AI for mechanism studies of biomass gasification have been summarized, and the cause of catalyst deactivation and regeneration of spent catalysts are also discussed. Therefore, the target of this article is to elucidate conventional biomass conversion pathways and review the recent progress on catalyst development in the biomass gasification process.
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... Yet, although Ni-and Fe-based materials show high activity toward hydrogen-rich gas production [36], Fe and Ni metals rust and corrode easily [25]. But nickel toxicity poses more environmental and safety challenges than iron [37]. Iron is less toxic, cheaper, and more readily available but is also more prone to rapid deactivation [38]. ...
Catalytic pyrolysis of waste cooking oil for hydrogen-rich syngas production over bimetallic Fe-Ru/ZSM-5 catalyst
Article
  • Aug 2023
  • FUEL PROCESS TECHNOL
Waste cooking oil (WCO) energy development offers an effective method for producing renewable fuels, enabling simultaneous resource recovery and pollution reduction. This study aims to develop a novel bimetallic Fe(Ni)-Ru/ZSM-5 catalyst toward H2-rich syngas production from WCO. The results show that Fe-Ru/ZSM-5 produced a higher maximum H2 yield (84.05 μmol·gcat.−1·s−1) than did Ni-Ru/ZSM-5 (41.76 μmol·gcat.−1·s−1) when fed at a 50 L/min rate at an optimal temperature of 700 °C. Fe-Ru/ZSM-5 presented a more prolific microporous distribution, whose structure contributes to the diffusion of the short-chain hydrocarbon intermediate reactants to enhance hydrogen production. Fe(III) can help to improve the conversion ratio of benzene and the anti‑carbon deposition capability of the catalyst. The dealumination and oxidation decreases the stability of the catalyst and may lead to inactivation. Furthermore, this study discusses the mechanism of bimetallic-loaded catalysts combining noble metals with transition metals in WCO pyrolysis. The results point to effective new approaches to increase H2 production through the catalytic pyrolysis of WCO.
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Tar conversion of biomass syngas in a downstream char bed
Article
Full-text available
  • Mar 2020
  • FUEL PROCESS TECHNOL
The catalytic conversion of biomass-derived tars over char during long tests (over 6 h) is studied. The syngas is generated in a steam-blown fluidized-bed gasifier employing wood pellets and conducted to a second tubular reactor where non-activated char particles are fluidized. The gasifier operated at 750 °C whereas the temperature of the secondary reactor was varied between 750 °C and 875 °C. The evolution of the tar conversion, gas composition and internal structure of the used catalysts were studied. At 750 °C, the initial catalytic activity of the char was low and deactivation occurs rapidly. However, as the reactor temperature increased, the catalytic activity of the char improved significantly. At 875 °C, the initial conversion of tar was above 70% and over 64% after 5 h of operation. Moreover, the conversion of the heaviest tars was above 80% during the entire test. At this temperature, the decrease in tar conversion is attributed to the consumption of the char by steam gasification since its catalytic activity increased during of the test. In these conditions the char bed with an initial weight of 32 g converted approximately 12 g of tars (benzene not included) after 5 h of operation.
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Hydrogen and syngas production from steam gasification of biomass using cement as catalyst
Article
Full-text available
  • Mar 2020
Biomass gasification is a promising technology to achieve high-quality syngas in the presence of one or more gasification agents. Nevertheless, operational problems associated with tar formation caused a major obstacle for further progress in biomass gasification. Tar can be minimized in producer gas by catalytic cracking. The purpose of this work was to study the air-steam gasification of pine sawdust with calcined cement as catalyst. The reactivity of calcined cement toward hydrogen production and tar elimination was evaluated. Results showed that catalytic gasification of biomass increased hydrogen concentration and also tar cracking. With cement as an additive in gasification bed, the highest hydrogen concentration (50.3 vol%) and lowest tar yield (0.49 g/Nm³) were achieved. With additional cement loading from 0 to 9 wt%, H2 content increased from 38.1 vol% to 50.3 vol%, while tar yield decreased from 6.92 g/Nm³ to 0.49 g/Nm³.
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Ni-based catalysts for steam reforming of tar model derived from biomass gasification
Article
Full-text available
  • Jan 2019
Tar formation during biomass gasification is a major barrier to utilise the produced syngas, which clogs processing equipment. In the present study, steam reforming of gasification-derived tar (phenol, toluene, naphthalene, and pyrene) was catalysed by Ni/dolomite, Ni/dolomite/Al2O3, Ni/dolomite/La2O3, Ni/dolomite/CeO2, and Ni/dolomite/ZrO2 for hydrogen production. The steam reforming experiment was conducted in a fixed bed reactor at 700 °C and the steam-to-carbon molar ratio of 1 under atmospheric pressure. After the catalytic test, the spent catalysts were characterised by thermogravimetric analysis and variable-pressure scanning electron microscope. The aim of this study is to investigate the catalytic activity of Ni-based catalysts in terms of tar conversion and their deactivation characteristic. The current results revealed that all the catalysts showed almost full conversion of tar (98.8%-99.9%) and considerably low amount of coke deposited in the form of amorphous and filamentous carbon (15.9-178.5 mg g cat⁻¹ ). Among the catalysts studied, Ni/dolomite/La2O3 gave the highest catalytic activity for steam reforming of gasified biomass tar and lowest coke formation.
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Analytical assessment of tar generated during gasification of municipal solid waste: Distribution of GC–MS detectable tar compounds, undetectable tar residues and inorganic impurities
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  • May 2020
  • FUEL
Tar, one of the most challenging impurities in the syngas generated from the gasification of municipal solid waste (MSW), can severely restrict its applicability in advanced utilization systems such as solid oxide fuel cells, gas engines and combined cycle gas turbines. Due to the complexity in sampling and analysis of tar, very limited studies have explored the development of comprehensive analytical procedure to provide insights into the distribution of GC–MS detectable tar compounds, GC–MS undetectable tar residues and inorganic impurities in the syngas from MSW gasification. In this study, Syngas generated from a downdraft fixed-bed gasifier (under different operating conditions) was sampled and analysed to understand the changes in the distributions of tar compounds and to verify the applicability of a sequential analytical procedure for syngas with different contents and distributions of tar and inorganic impurities. The procedure was developed to analyse and quantify the tar compounds and inorganic impurities in tar sampling solutions. The GC–MS analysis of three types of tar containing solutions (collected tar, gravimetric tar solution and evaporated condensate), gravimetric tar procedure (rotary evaporation and weighing), three separation/isolation methods (adsorption, dilution and decomposition) and quantification of inorganic compounds (cations and anions) were studied. With this sequential analytical procedure, enhanced detection and quantification (EDQ) of GC–MS detectable tar compounds at low concentration and correction on the GC–MS undetectable tar contents based on quantification of inorganic impurities were achieved. Distribution of tar and inorganic impurities was determined which revealed the impacts of operating conditions on syngas from MSW gasification.
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Towards synthetic fuels production from biomass gasification: Tar content at low temperatures
Article
  • Jun 2020
  • BIOMASS BIOENERG
Biomass conversion into biofuels and biogas is a promising way for power and heat generation. Lately, research has focused on the production of biomethane based on biomass gasification followed by methanation as an alternative to fossil natural gas. The challenge of this process remains in the intensive gas cleaning and required tar removal. In order to study tar removal from the producer gas downstream biomass gasification, solid–vapor and liquid–vapor equilibrium must be known for different tar concentrations, ranging between 0.001 and 100 g.Nm⁻³. To assess tar removal by condensation at low temperatures, psychrometric charts are developed. Since the composition of tar is complex, toluene, phenol, indene, naphthalene and fluoranthene are selected as tar representatives. Each component is studied separately in four different producer gas compositions formed mainly of hydrogen, carbon monoxide, carbon dioxide and methane in addition to water and nitrogen. Methods for calculating saturation, isenthalpic and constant relative concentration lines are presented. Psychrometric charts of the different tar components are finally plotted at atmospheric pressure. Results show that temperature of 196.15 K is required to reduce the tar content to 0.001 g.Nm⁻³.
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Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification: a review
Article
  • Mar 2020
Presently, the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas (GHG) emissions. Among alternatives, hydrogen (H2) produced from biomass gasification is considered a green energy sector, due to its environmentally friendly, sustainable, and renewable characteristics. However, tar formation along with syngas is a severe impediment to biomass conversion efficiency, which results in process-related problems. Typically, tar consists of various hydrocarbons (HCs), which are also sources for syngas. Hence, catalytic steam reforming is an effective technique to address tar formation and improve H2 production from biomass gasification. Of the various classes in existence, supported metal catalysts are considered the most promising. This paper focuses on the current researching status, prospects, and challenges of steam reforming of gasified biomass tar. Besides, it includes recent developments in tar compositional analysis, supported metal catalysts, along with the reactions and process conditions for catalytic steam reforming. Moreover, it discusses alternatives such as dry and autothermal reforming of tar.
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Tar elimination from biomass gasification syngas with bauxite residue derived catalysts and gasification char
Article
  • Nov 2019
  • APPL ENERG
Efficient elimination of tar is a challenge to the development of biomass gasification as a viable clean energy technology. Catalytic reforming is effective in reducing biomass-derived tars. However, commercial metal-based catalysts are expensive and prone to deactivation. Developing economically viable and environmentally benign catalysts from renewable materials is therefore very attractive. This study focuses on the development of an effective tar elimination process utilizing alternative catalysts derived from bauxite residue, a solid waste material from the alumina production. In this work, the catalytic performance of reduced and activated bauxite residue in facilitating naphthalene (a model biomass tar compound) decomposition was studied in a fixed-bed reactor under cracking and reforming environments. Bauxite residue catalyst in reduced form was found to be active for naphthalene reforming, mainly due to its high metallic iron content. However, under wet syngas environments, bauxite residue catalyst was easily deactivated by steam. To address the steam deactivation of bauxite residue catalyst, biochar as a reducing agent, as well as a co-catalyst and adsorptive-support, was proposed to mix with bauxite residue. In this study, biochar from biomass gasification has been successfully employed as a reducing agent to reduce iron oxides in bauxite residue to metallic iron in an inert environment. Results from catalyst activity testing showed that the bauxite residue-biochar mixed catalyst led to highly effective and sustained naphthalene conversion in a reforming environment, since the iron content in bauxite residue was maintained in its reduced form in the presence of biochar.
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Evaluating tar production via the release of volatile matters for H2-rich syngas production
Article
  • Sep 2019
  • INT J HYDROGEN ENERG
Tar measurement and calculation is crucial for understanding the in-situ tar elimination and hydrogen-rich syngas production during the biomass gasification process. In this study, the method of evaluating tar production was proposed and studied on a two-stage fixed-bed reactor. Two different groups of oxidized and reduced oxygen carriers were investigated for comparison. The collected tar was tested on a gas chromatography–mass spectrometry (GC-MS) system. The types of the tar were all belonged to aromatic hydrocarbons. The H2 composition in the syngas was over 34% in three reduced-OC conditions. The carbon percentage identified by the GC-MS was at the range of 93.75–95.05 wt%. The average carbon from the char combustion period was 2.85 mmol. The tar yield in the three oxidized-OC conditions was 43 ± 22 mg/g, 53 ± 11 mg/g, and 62 ± 8 mg/g, respectively. The result indicated that the reduced OC had a catalytic effect for increasing the H2 composition in syngas. On the other hand, the oxidized OC influenced the reactions by providing with lattice oxygen. The evaluation of the produced tar was beneficial for a further understanding of the mechanism for producing the H2-rich syngas.
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Effect of fuel blend composition on hydrogen yield in co-gasification of coal and non-woody biomass
Article
  • Mar 2019
  • INT J HYDROGEN ENERG
In this study, torrefaction of sunflower seed cake and hydrogen production from torrefied sunflower seed cake via steam gasification were investigated. Torrefaction experiments were performed at 250, 300 and 350 °C for different times (10–30 min). Torrefaction at 300 °C for 30 min was selected to be optimum condition, considering the mass yield and energy densification ratio. Steam gasification of lignite, raw- and torrefied biomass, and their blends at different ratios were conducted at downdraft fixed bed reactor. For comparison, gasification experiments with pyrochar obtained at 500 °C were also performed. The maximum hydrogen yield of 100 mol/kg fuel was obtained steam gasification of pyrochar. The hydrogen yields of 84 and 75 mol/kg fuel were obtained from lignite and torrefied biomass, respectively. Remarkable synergic effect exhibited in co-gasification of lignite with raw biomass or torrefied biomass at a blending ratio of 1:1. In co-gasification, the highest hydrogen yield of 110 mol/kg fuel was obtained from torrefied biomass-lignite (1:1) blend, while a hydrogen yield from pyrochar-lignite (1:1) blend was 98 mol/kg. The overall results showed that in co-gasification of lignite with biomass, the yields of hydrogen depend on the volatiles content of raw biomass/torrefied biomass, besides alkaline earth metals (AAEMs) content.
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Reforming of tar from biomass gasification in a hybrid catalysis-plasma system: A review
Article
  • Mar 2019
The generation of tar in biomass gasification is highly undesirable since the condensation and agglomeration of tar causes clogging and contamination of downstream equipment, leading to low energy efficiency and high maintenance cost. Currently, the most widely used methods for tar reforming are catalytic reforming and plasma reforming. However, the main drawbacks for these two processes are: (i) the rapid catalyst deactivation caused by poisoning, sintering and coke deposition for catalytic reforming, and (ii) low energy efficiency, low selectivity of syngas and the formation of undesirable byproducts for plasma reforming. Recently, therefore, the hybrid plasma-catalysis system has attracted much attention for tar reforming, since it can overcome the above-mentioned drawbacks and generate a synergy effect. The addition of catalyst in plasma could change the discharge properties of plasma, and the plasma could also modify the catalyst property and change the status of reactants. At present, very few review articles have reported and compared the performances of tar reforming in the plasma-only, catalysis-only and hybrid plasma-catalysis system. Therefore, this review paper focus on: (i) the deactivation characteristics and modification methods of steam-reforming catalysts, as well as the mechanism of tar catalytic reforming; (ii) the performance of tar reforming in various plasma reactors and the reaction mechanism based on the analysis of byproducts and energetic plasma species; and (iii) the possible synergistic effect of plasma and heterogeneous catalyst in a hybrid plasma-catalysis system caused by the multiple interactions of plasma and catalysts.
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