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17 pages, 5667 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermodynamic and Experimental Investigation of Solar-Driven Biomass Pyro-Gasification Using H₂O, CO₂, or ZnO Oxidants for Clean Syngas and Metallurgical Zn Production

by Srirat Chuayboon and Stéphane Abanades

Processes 2021, 9(4), 687; https://doi.org/10.3390/pr9040687 - 14 Apr 2021

Cited by 11 | Viewed by 2690

Abstract

The solar gasification of biomass represents a promising avenue in which both renewable solar and biomass energy can be utilized in a single process to produce synthesis gas. The type of oxidant plays a key role in solar-driven biomass gasification performance. In this [...] Read more.

The solar gasification of biomass represents a promising avenue in which both renewable solar and biomass energy can be utilized in a single process to produce synthesis gas. The type of oxidant plays a key role in solar-driven biomass gasification performance. In this study, solar gasification of beech wood biomass with different oxidants was thermodynamically and experimentally investigated in a 1.5 kW_th continuously-fed consuming bed solar reactor at 1200 °C under atmospheric pressure. Gaseous (H₂O and CO₂) as well as solid (ZnO) oxidants in pellet and particle shapes were utilized for gasifying beech wood, and the results were compared with pyrolysis (no oxidant). As a result, thermodynamic predictions provided insights into chemical gasification reactions against oxidants, which can support experimental results. Compared to pyrolysis, using oxidants significantly promoted syngas yield and energy upgrade factor. The highest total syngas yield (63.8 mmol/g_biomass) was obtained from biomass gasification with H₂O, followed by CO₂, ZnO/biomass mixture (pellets and particles), and pyrolysis. An energy upgrade factor (U) exceeding one was achieved whatever the oxidants, with the maximum U value of 1.09 from biomass gasification with ZnO, thus highlighting successful solar energy storage into chemical products. ZnO/biomass pellets exhibited greater gas yield, particularly CO, thanks to enhanced solid–solid reaction. Solid product characterization revealed that ZnO can be reduced to high-purity Zn through solar gasification, indicating that solar-driven biomass gasification with ZnO is a promising innovative process for CO₂-free sustainable co-production of metallic Zn and high-quality syngas. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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23 pages, 4639 KiB

Open AccessArticle

Evaluation of Techno-Economic Studies on the bioliq^® Process for Synthetic Fuels Production from Biomass

by Nicolaus Dahmen and Jörg Sauer

Processes 2021, 9(4), 684; https://doi.org/10.3390/pr9040684 - 13 Apr 2021

Cited by 10 | Viewed by 3283

Abstract

Techno-economic studies by various research institutions on the costs for the production of biomass to liquid (BtL) fuels using the bioliq^® process were analyzed and evaluated. The bioliq^® process consists of decentralized pretreatment by fast pyrolysis plants for biomass energy densification, [...] Read more.

Techno-economic studies by various research institutions on the costs for the production of biomass to liquid (BtL) fuels using the bioliq^® process were analyzed and evaluated. The bioliq^® process consists of decentralized pretreatment by fast pyrolysis plants for biomass energy densification, and of a central gasification and synthesis step for synthesis of gas and synthetic fuel production. For comparison, specific material and energy flows were worked out for both process steps, and conversion efficiencies were calculated for the conversion of straw to diesel fuel via the Fischer-Tropsch synthesis. A significant variation of the overall process efficiency in the range of 33–46% was mainly a result of the different assumptions made for electricity generation at the central location. After breaking down the individual cost items to either fixed or variable costs, it turned out that the largest cost items in the production of BtL fuels were attributable to feedstock and capital costs. Comparison of the specific investments showed that, in addition to economies of scale, other factors had a significant influence leading to values between 1000 and 5000 EUR/kW. This, particularly, included the origin of the equipment purchase costs and the factors applied to them. Fuel production costs were found to range between 0.8 and 2.6 EUR/L. Possible cost reduction by learning potential was investigated, leading to an improvement by a few percent of production costs. A sensitivity analysis of the individual cost items by up to 30%, for “investments” and “biomass and transport” cost increases, led to higher manufacturing costs of up to 17% in both cases. By harmonizing the depreciation period and the chosen interest rate, the production costs changed from −16% to +17%. Similarly, effects could be shown by adjusting the costs for maintenance and servicing, and the plant operation time. A superposition of these effects in a best-case scenario led to cost reductions of 21%. The most expensive variant in the opposing worst-case scenario raised costs by up to 27%. This uncertainty contributed already fifty percent to a preliminary cost estimate based on a conceptual design. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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12 pages, 4558 KiB

Open AccessFeature PaperArticle

Hybrid Models for Efficient Control, Optimization, and Monitoring of Thermo-Chemical Processes and Plants

by Thomas Freudenmann, Hans-Joachim Gehrmann, Krasimir Aleksandrov, Mohanad El-Haji and Dieter Stapf

Processes 2021, 9(3), 515; https://doi.org/10.3390/pr9030515 - 12 Mar 2021

Cited by 2 | Viewed by 2373

Abstract

This paper describes a procedure and an IT product that combine numerical models, expert knowledge, and data-based models through artificial intelligence (AI)-based hybrid models to enable the integrated control, optimization, and monitoring of processes and plants. The working principle of the hybrid model [...] Read more.

This paper describes a procedure and an IT product that combine numerical models, expert knowledge, and data-based models through artificial intelligence (AI)-based hybrid models to enable the integrated control, optimization, and monitoring of processes and plants. The working principle of the hybrid model is demonstrated by NO_x reduction through guided oscillating combustion at the pulverized fuel boiler pilot incineration plant at the Institute for Technical Chemistry, Karlsruhe Institute of Technology. The presented example refers to coal firing, but the approach can be easily applied to any other type of nitrogen-containing solid fuel. The need for a reduction in operation and maintenance costs for biomass-fired plants is huge, especially in the frame of emission reductions and, in the case of Germany, the potential loss of funding as a result of the Renewable Energy Law (Erneuerbare-Energien-Gesetz) for plants older than 20 years. Other social aspects, such as the departure of experienced personnel may be another reason for the increasing demand for data mining and the use of artificial intelligence (AI). Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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19 pages, 1909 KiB

Open AccessFeature PaperArticle

Sequential Hydrothermal Processing of Sewage Sludge to Produce Low Nitrogen Biocrude

by Joscha Zimmermann, Klaus Raffelt and Nicolaus Dahmen

Processes 2021, 9(3), 491; https://doi.org/10.3390/pr9030491 - 9 Mar 2021

Cited by 22 | Viewed by 3866

Abstract

A hydrothermal pre-treatment has been developed to improve sewage sludge quality or to produce low nitrogen biocrude via hydrothermal liquefaction (HTL) in a subsequent step. The mild hydrothermal pre-treatment (150 °C) step was performed with deionized water, sulfuric acid (0.5 M), or citric [...] Read more.

A hydrothermal pre-treatment has been developed to improve sewage sludge quality or to produce low nitrogen biocrude via hydrothermal liquefaction (HTL) in a subsequent step. The mild hydrothermal pre-treatment (150 °C) step was performed with deionized water, sulfuric acid (0.5 M), or citric acid (0.5 M) to solubilize nitrogen containing compounds in the aqueous supernatant. Downstream, the residual solid material was liquefied with the addition of sodium carbonate via hydrothermal liquefaction (350 °C). The pre-treatment with citric acid transferred up to 66.7 wt. % of nitrogen into the aqueous supernatant, while 62.0 wt. % of carbon was recovered in the solid. Due to the pre-treatment lipids retained in the sewage sludge solid, which increased the favored biocrude yield up to 42.9 wt. % and the quality evaluating value H/C_eff ratio significantly to 1.48. Multi-method characterization of the resulted biocrude samples showed a lower concentration of N-heterocycles, while long-chain aliphatics and free fatty acid are increased. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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15 pages, 8451 KiB

Open AccessArticle

Co-Production of Aromatics in Biomass and Waste Gasification

by Carlos Mourao Vilela, Evert Boymans and Berend Vreugdenhil

Processes 2021, 9(3), 463; https://doi.org/10.3390/pr9030463 - 4 Mar 2021

Cited by 4 | Viewed by 2825

Abstract

Climate changes will have a huge impact on society, one that cannot be truly predicted. However, what is known is that our dependence on fossil feedstock for energy, fuel and chemical production will need to shift towards more biobased and circular feedstock. This [...] Read more.

Climate changes will have a huge impact on society, one that cannot be truly predicted. However, what is known is that our dependence on fossil feedstock for energy, fuel and chemical production will need to shift towards more biobased and circular feedstock. This paper describes part of an important technology development that uses biogenic and plastic-containing waste streams for the co-production of aromatics with fuels and/or chemicals. This paper captures the first decade of this technology development from idea towards a large Process Demonstration Unit operated and validated within a large gasification R&D infrastructure. The scale-up was successful, with supporting tools to optimize and identify the limits of the technology. Benzene and toluene are directly removed from the product gas with 97% and 99% efficiency, respectively. The next steps will be to include this development in larger piloting and demonstrations for the co-production of aromatics from biomass gasification (biobased chemicals) or aromatics from plastic-containing waste gasification (circular chemicals). Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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17 pages, 1273 KiB

Open AccessFeature PaperArticle

Gasification of Biomass in Supercritical Water, Challenges for the Process Design—Lessons Learned from the Operation Experience of the First Dedicated Pilot Plant

by Nikolaos Boukis and I. Katharina Stoll

Processes 2021, 9(3), 455; https://doi.org/10.3390/pr9030455 - 3 Mar 2021

Cited by 32 | Viewed by 5852

Abstract

Gasification of organic matter under the conditions of supercritical water (T > 374 °C, p > 221 bar) is an allothermal, continuous flow process suitable to convert materials with high moisture content (<20 wt.% dry matter) into a combustible gas. The gasification of [...] Read more.

Gasification of organic matter under the conditions of supercritical water (T > 374 °C, p > 221 bar) is an allothermal, continuous flow process suitable to convert materials with high moisture content (<20 wt.% dry matter) into a combustible gas. The gasification of organic matter with water as a solvent offers several benefits, particularly the omission of an energy-intensive drying process. The reactions are fast, and mean residence times inside the reactor are consequently low (less than 5 min). However, there are still various challenges to be met. The combination of high temperature and pressure and the low concentration of organic matter require a robust process design. Additionally, the low value of the feed and the product predestinate the process for decentralized applications, which is a challenge for the economics of an application. The present contribution summarizes the experience gained during more than 10 years of operation of the first dedicated pilot plant for supercritical water gasification of biomass. The emphasis lies on highlighting the challenges in process design. In addition to some fundamental results gained from comparable laboratory plants, selected experimental results of the pilot plant “VERENA” (acronym for the German expression “experimental facility for the energetic exploitation of agricultural matter”) are presented. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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20 pages, 5202 KiB

Open AccessArticle

Creating Values from Biomass Pyrolysis in Sweden: Co-Production of H₂, Biocarbon and Bio-Oil

by Ilman Nuran Zaini, Nanta Sophonrat, Kurt Sjöblom and Weihong Yang

Processes 2021, 9(3), 415; https://doi.org/10.3390/pr9030415 - 25 Feb 2021

Cited by 17 | Viewed by 4413

Abstract

Hydrogen and biocarbon are important materials for the future fossil-free metallurgical industries in Sweden; thus, it is interesting to investigate the process that can simultaneously produce both. Process simulations of biomass pyrolysis coupled with steam reforming and water-gas-shift to produce H₂, [...] Read more.

Hydrogen and biocarbon are important materials for the future fossil-free metallurgical industries in Sweden; thus, it is interesting to investigate the process that can simultaneously produce both. Process simulations of biomass pyrolysis coupled with steam reforming and water-gas-shift to produce H₂, biocarbon, and bio-oil are investigated in this work. The process simulation is performed based on a biomass pyrolysis plant currently operating in Sweden. Two co-production schemes are proposed: (1) production of biocarbon and H₂, and (2) production of biocarbon, H₂, and bio-oil. Sensitivity analysis is also performed to investigate the performance of the production schemes under different operating parameters. The results indicated that there are no notable differences in terms of the thermal efficiency for both cases. Varying the bio-oil condenser temperature only slightly changes the system’s thermal efficiency by less than 2%. On the other hand, an increase in biomass moisture content from 7 to 14 wt.% can decrease the system’s efficiency from 79.0% to 72.6%. Operating expenses are evaluated to elucidate the economics of 3 different cases: (1) no bio-oil production, (2) bio-oil production with the condenser at 50 °C, and (3) bio-oil production with the condenser at 130 °C. Based on operation expenses (OPEX) and revenue alone, it is found that producing more bio-oil helps improving the economics of the process. However, capital costs and the cost for post-processing of bio-oil should also be considered in the future. The estimated minimum selling price for biocarbon based on OPEX alone is approx. 10 SEK, which is within the range of the current commercial price of charcoal and coke. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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15 pages, 3775 KiB

Open AccessFeature PaperArticle

Machine Learning-Based Prediction of Selected Parameters of Commercial Biomass Pellets Using Line Scan Near Infrared-Hyperspectral Image

by Lakkana Pitak, Kittipong Laloon, Seree Wongpichet, Panmanas Sirisomboon and Jetsada Posom

Processes 2021, 9(2), 316; https://doi.org/10.3390/pr9020316 - 8 Feb 2021

Cited by 18 | Viewed by 3059

Abstract

Biomass pellets are required as a source of energy because of their abundant and high energy. The rapid measurement of pellets is used to control the biomass quality during the production process. The objective of this work was to use near infrared (NIR) [...] Read more.

Biomass pellets are required as a source of energy because of their abundant and high energy. The rapid measurement of pellets is used to control the biomass quality during the production process. The objective of this work was to use near infrared (NIR) hyperspectral images for predicting the properties, i.e., fuel ratio (FR), volatile matter (VM), fixed carbon (FC), and ash content (A), of commercial biomass pellets. Models were developed using either full spectra or different spatial wavelengths, i.e., interval successive projections algorithm (iSPA) and interval genetic algorithm (iGA), wavelengths and different spectral preprocessing techniques. Their performances were then compared. The optimal model for predicting FR could be created with second derivative (D2) spectra with iSPA-100 wavelengths, while VM, FC, and A could be predicted using standard normal variate (SNV) spectra with iSPA-100 wavelengths. The models for predicting FR, VM, FC, and A provided R² values of 0.75, 0.81, 0.82, and 0.87, respectively. Finally, the prediction of the biomass pellets’ properties under color distribution mapping was able to track pellet quality to control and monitor quality during the operation of the thermal conversion process and can be intuitively used for applications with screening. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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18 pages, 5802 KiB

Open AccessFeature PaperArticle

Design, Modelling, and Experimental Validation of a Scalable Continuous-Flow Hydrothermal Liquefaction Pilot Plant

by Ib Johannsen, Björn Kilsgaard, Viktor Milkevych and Dale Moore

Processes 2021, 9(2), 234; https://doi.org/10.3390/pr9020234 - 27 Jan 2021

Cited by 21 | Viewed by 3920

Abstract

In this study, the design and practical implementation of a novel, scalable plug-flow pilot plant for hydrothermal liquefaction of organic feedstock is presented. The overall discussion comprises the system’s design, process modelling, and simulation, as well as results for an experimental validation of [...] Read more.

In this study, the design and practical implementation of a novel, scalable plug-flow pilot plant for hydrothermal liquefaction of organic feedstock is presented. The overall discussion comprises the system’s design, process modelling, and simulation, as well as results for an experimental validation of the proposed design with a focus on fluid dynamics and heat transfer. The design criteria take into account the scalability of the plug-flow processing system, optimized non-isothermal flow conditions of highly viscous liquids in a tubular system at harsh process conditions, specifically high pressure and medium temperatures, and overall maintenance suitability. A novel forced flow oscillation system as well as unique heat exchange design to reduce the energy consumption during system operation, maximize local flow mixing, and minimize plugging are proposed and experimentally tested. To achieve a better understanding and optimization of Hydrothermal Liquefaction (HTL) (and other) processing systems, a mathematical model of heat transfer coupled with non-isothermal fluid flow was also developed and implemented. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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19 pages, 4060 KiB

Open AccessFeature PaperArticle

Oxygen-Blown Gasification of Pulp Mill Bark Residues for Synthetic Fuel Production

by Fredrik Weiland, Sandra Lundström and Yngve Ögren

Processes 2021, 9(1), 163; https://doi.org/10.3390/pr9010163 - 15 Jan 2021

Cited by 6 | Viewed by 3310

Abstract

Synthetic fuel production via gasification of residual biomass streams from the pulp and paper industry can be an opportunity for the mills to enable improved resource utilization and at the same time reduce the production of excess heat. This paper summarizes initial oxygen-blown [...] Read more.

Synthetic fuel production via gasification of residual biomass streams from the pulp and paper industry can be an opportunity for the mills to enable improved resource utilization and at the same time reduce the production of excess heat. This paper summarizes initial oxygen-blown gasification experiments with two bark residues from a European pulp and paper mill, i.e., a softwood bark and a hardwood bark. The gasification process was characterized by measuring syngas yields and process efficiency to find optimum operating conditions. In addition, impurities in the syngas and ash behavior were characterized. Maximum yields of CO and H₂ were obtained from softwood bark and amounted to approximately 29 and 15 mol/kg fuel, respectively. Optimum cold gas efficiency was achieved at an oxygen stoichiometric ratio of λ = 0.40 and was approximately 76% and 70% for softwood bark and hardwood bark, respectively. Increased λ had a reducing effect on pollutants in the syngas, e.g., higher hydrocarbons, NH₃, HCl, and soot. The situation for sulfur species was more complex. Evaluation of the bark ashes indicated that slag formation could start already from 800 °C. Furthermore, a non-intrusive laser diagnostics technique gave rapid feedback on the millisecond scale. Measured syngas temperature and water content were in good agreement with the applied reference methods. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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14 pages, 2125 KiB

Open AccessFeature PaperArticle

Study of a Method to Effectively Remove Char Byproduct Generated from Fast Pyrolysis of Lignocellulosic Biomass in a Bubbling Fluidized Bed Reactor

by Jong Hyeon Ha and In-Gu Lee

Processes 2020, 8(11), 1407; https://doi.org/10.3390/pr8111407 - 4 Nov 2020

Cited by 13 | Viewed by 3406

Abstract

A critical issue in the design of bubbling fluidized bed reactors for biomass fast pyrolysis is to maintain the bed at a constant level to ensure stable operation. In this work, a bubbling fluidized bed reactor was investigated to deal with this issue. [...] Read more.

A critical issue in the design of bubbling fluidized bed reactors for biomass fast pyrolysis is to maintain the bed at a constant level to ensure stable operation. In this work, a bubbling fluidized bed reactor was investigated to deal with this issue. The reactor consists of inner and outer tubes and enables in situ control of the fluidized-bed level in the inner-tube reactor with a mechanical method during biomass fast pyrolysis. The significant fraction of biochar produced from the fast pyrolysis in the inner-tube reactor was automatically removed through the annulus between the inner and outer tubes. The effect of pyrolysis temperature (426–528 °C) and feeding rate (0.8–1.8 kg/h) on the yield and characteristics of bio-oil, biochar, and gaseous products were examined at a 15 L/min nitrogen carrier gas flow rate for wood sawdust with a 0.5–1.0 mm particle size range as a feed. The bio-oil reached a maximum yield of 62.4 wt% on a dry basis at 440 °C, and then slowly decreased with increasing temperature. At least 79 wt% of bio-char byproduct was removed through the annulus and was found in the reactor bottom collector. The GC-MS analysis found phenolics to be more than 40% of the bio-oil products. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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15 pages, 9139 KiB

Open AccessArticle

Thermo-Acoustic Catalytic Effect on Oxidizing Woody Torrefaction

by Edgar A. Silveira, Luiz Gustavo Oliveira Galvão, Lucélia Alves de Macedo, Isabella A. Sá, Bruno S. Chaves, Marcus Vinícius Girão de Morais, Patrick Rousset and Armando Caldeira-Pires

Processes 2020, 8(11), 1361; https://doi.org/10.3390/pr8111361 - 28 Oct 2020

Cited by 21 | Viewed by 2611

Abstract

The torrefaction (mild pyrolysis) process modifies biomass chemical and physical properties and is applied as a thermochemical route to upgrade solid fuel. In this work, the catalytic effect of thermo-acoustic on oxidizing woody torrefaction is assessed. The combined effect of two acoustic frequencies [...] Read more.

The torrefaction (mild pyrolysis) process modifies biomass chemical and physical properties and is applied as a thermochemical route to upgrade solid fuel. In this work, the catalytic effect of thermo-acoustic on oxidizing woody torrefaction is assessed. The combined effect of two acoustic frequencies (1411, 2696 Hz) and three temperatures (230, 250, and 290 °C) was evaluated through weight loss and its deviation curves, calculated torrefaction severity index (TSI), as well as proximate, calorific, and compression strength analysis of Eucalyptus grandis. A new index to account for the catalytic effects on torrefaction (TCEI) was introduced, providing the quantitative analysis of acoustic frequencies influence. A two-step consecutive reaction numerical model allowed the thermo-acoustic experiment evaluation. For instance, the thermogravimetric profiles revealed that the acoustic field has a catalytic effect on wood torrefaction and enhances the biomass oxidation process for severe treatments. The kinetic simulation of the acoustic coupling resulted in faster conversion rates for the solid pseudo-components showing the boosting effect of acoustic frequencies in anticipating hemicellulose decomposition and enhancing second step oxidizing reaction. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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Review

Jump to: Research

26 pages, 1074 KiB

Open AccessFeature PaperReview

Integration of Gasification and Solid Oxide Fuel Cells (SOFCs) for Combined Heat and Power (CHP)

by Paula Costa, Filomena Pinto, Rui Neto André and Paula Marques

Processes 2021, 9(2), 254; https://doi.org/10.3390/pr9020254 - 29 Jan 2021

Cited by 31 | Viewed by 4346

Abstract

This paper reviews the most recent information about the main operations to produce energy from carbonaceous materials, namely biomass and wastes through the integration of gasification, syngas cleaning and solid oxide fuel cells (SOFCs), which have shown to be a good option for [...] Read more.

This paper reviews the most recent information about the main operations to produce energy from carbonaceous materials, namely biomass and wastes through the integration of gasification, syngas cleaning and solid oxide fuel cells (SOFCs), which have shown to be a good option for combined heat and power (CHP) production, due to high efficiency and low environmental impact. However, some challenges still need to be overcome, mainly when mixed feedstocks with high contents of hazardous contaminants are used, thus syngas cleaning and conditioning is of major importance. Another drawback is SOFC operation, hence new materials especially for the anode has been proposed and tested. An overall process to produce CHP by gasification integration with SOFC is proposed. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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24 pages, 2204 KiB

Open AccessFeature PaperReview

State-of-the-Art Char Production with a Focus on Bark Feedstocks: Processes, Design, and Applications

by Ali Umut Şen and Helena Pereira

Processes 2021, 9(1), 87; https://doi.org/10.3390/pr9010087 - 2 Jan 2021

Cited by 21 | Viewed by 3476

Abstract

In recent years, there has been a surge of interest in char production from lignocellulosic biomass due to the fact of char’s interesting technological properties. Global char production in 2019 reached 53.6 million tons. Barks are among the most important and understudied lignocellulosic [...] Read more.

In recent years, there has been a surge of interest in char production from lignocellulosic biomass due to the fact of char’s interesting technological properties. Global char production in 2019 reached 53.6 million tons. Barks are among the most important and understudied lignocellulosic feedstocks that have a large potential for exploitation, given bark global production which is estimated to be as high as 400 million cubic meters per year. Chars can be produced from barks; however, in order to obtain the desired char yields and for simulation of the pyrolysis process, it is important to understand the differences between barks and woods and other lignocellulosic materials in addition to selecting a proper thermochemical method for bark-based char production. In this state-of-the-art review, after analyzing the main char production methods, barks were characterized for their chemical composition and compared with other important lignocellulosic materials. Following these steps, previous bark-based char production studies were analyzed, and different barks and process types were evaluated for the first time to guide future char production process designs based on bark feedstock. The dry and wet pyrolysis and gasification results of barks revealed that application of different particle sizes, heating rates, and solid residence times resulted in highly variable char yields between the temperature range of 220 °C and 600 °C. Bark-based char production should be primarily performed via a slow pyrolysis route, considering the superior surface properties of slow pyrolysis chars. Full article

(This article belongs to the Special Issue Process Design of Biomass Thermochemical Conversion)

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