Special Issue "Thermochemical Conversion Processes for Solid Fuels and Renewable Energies: Volume II"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 10722

Special Issue Editors

Priv.-Doz. Dr.-Ing. habil. Falah Alobaid
E-Mail Website
Guest Editor
Institute of Energy Systems and Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
Interests: thermal power generation; flexibility; energy storage systems; dynamic process simulation; 3D CFD numerical methods; conversion of low‐rank solid fuels; carbon capture, utilization, and storage
Special Issues, Collections and Topics in MDPI journals
Dr.-Ing. Jochen Ströhle
E-Mail Website
Guest Editor
Energy Systems and Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
Interests: carbon utilization and storage; conversion of low‐rank solid fuels through combustion or gasification; 3D CFD numerical methods
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This new Special Issue is a continuation of the previous Special Issue “Thermochemical Conversion Processes for Solid Fuels and Renewable Energies”, which was closed in October 2020 including 10 valuable peer-reviewed papers.

The new Special Issue welcomes basic scientific studies on the latest research progress in terms of the development and optimization of conversion processes, especially for intermittent renewable energy sources, with the thermodynamic analysis, CFD, and process simulation of these systems. The topics of interest to this Special Issue include but are not limited to:

  • Gasification and combustion of alternative fuels (e.g., biomass, refuse-derived fuel, solid recovered fuel, and low-rank coal);
  • Technological combinations of conversion processes based on renewable sources (power-to-fuel);
  • Carbon capture and storage/utilization CCS/U technologies (carbon capture-to-fuel);
  • Renewable energy for heating and cooling purposes to reduce peak demand, including energy storage systems to mitigate grid imbalances;
  • Thermodynamic study, CFD, and process simulation of the above-mentioned topics.

Priv.-Doz. Dr.-Ing. habil. Falah Alobaid
Dr.-Ing. Jochen Ströhle
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2300 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (27 papers)

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Editorial

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Editorial
Special Issue “Thermochemical Conversion Processes for Solid Fuels and Renewable Energies: Volume II”
Appl. Sci. 2022, 12(15), 7478; https://doi.org/10.3390/app12157478 - 26 Jul 2022
Viewed by 210
Abstract
The increasing share of renewable energy sources draws attention to a critical challenge [...] Full article
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Editorial
Special Issue “Thermochemical Conversion Processes for Solid Fuels and Renewable Energies”
Appl. Sci. 2021, 11(4), 1907; https://doi.org/10.3390/app11041907 - 22 Feb 2021
Cited by 3 | Viewed by 686
Abstract
The world society ratifies international measures to reach a flexible and low-carbon energy economy, attenuating climate change and its devastating environmental consequences. The main contribution of this Special Issue is related to thermochemical conversion technologies of solid fuels (e.g., biomass, refuse-derived fuel, and [...] Read more.
The world society ratifies international measures to reach a flexible and low-carbon energy economy, attenuating climate change and its devastating environmental consequences. The main contribution of this Special Issue is related to thermochemical conversion technologies of solid fuels (e.g., biomass, refuse-derived fuel, and sewage sludge), in particular via combustion and gasification. Here, the recent activities on operational flexibility of co-combustion of biomass and lignite, carbon capture methods, solar-driven air-conditioning systems, integrated solar combined cycle power plants, and advanced gasification systems, such as the sorption-enhanced gasification and the chemical looping gasification, are shown. Full article
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Research

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Article
Thermal Performance Evaluation of a Tubular Heat Exchanger Fitted with Combined Basket–Twisted Tape Inserts
Appl. Sci. 2022, 12(10), 4807; https://doi.org/10.3390/app12104807 - 10 May 2022
Cited by 3 | Viewed by 285
Abstract
Features of the tubular type of heat exchanger were examined experimentally in the current study. A rig is fitted with a novel insert as a negative heat transfer increase technique. The core fluid used is air under steady heat flux and a turbulent [...] Read more.
Features of the tubular type of heat exchanger were examined experimentally in the current study. A rig is fitted with a novel insert as a negative heat transfer increase technique. The core fluid used is air under steady heat flux and a turbulent discharge state (6000 ≤ Re ≤ 19,500) conditions. Two heat transfer augmentation inserts are employed; one is the basket turbulators utilized as a turbulator and placed inside the heat exchanger with a constant pitch ratio (PR = 150 mm), and the other is the basket turbulators together with twisted tape that are installed at the core of the basket turbulators. The measurements illustrated that the Nusselt number (Nu) was found to be higher by about 131.8%, 169.5%, 187.7%, and 206.5% in comparison with the plain heat exchanger for basket turbulators and the combined basket–twisted tape inserts with y/w = 6, 3, and 2, respectively. The highest thermal efficiency factor of the increased tubular heat exchanger is 1.63 times more elevated than that of the simple heat exchanger on average, due to a binary basket-quirky strip for a twisting percentage y/w equal to 2 under steady pumping energy. Further, practical correlations for the Nusselt number, as well as friction characteristics, were established and presented. Full article
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Article
Microstructural Analysis and Mechanical Properties of a Hybrid Al/Fe2O3/Ag Nano-Composite
Appl. Sci. 2022, 12(9), 4730; https://doi.org/10.3390/app12094730 - 08 May 2022
Cited by 2 | Viewed by 378
Abstract
This work aims to define the microstructure and to study the mechanical properties of an Al matrix incorporated with various amounts of Fe2O3 (3, 6, 9, 12 and 15 wt.%) with a constant amount of Ag at 1 wt.%. Al/Fe [...] Read more.
This work aims to define the microstructure and to study the mechanical properties of an Al matrix incorporated with various amounts of Fe2O3 (3, 6, 9, 12 and 15 wt.%) with a constant amount of Ag at 1 wt.%. Al/Fe2O3 + Ag hybrid nano-composite samples are manufactured using powder metallurgy. An aluminum matrix is considered an important alloy, owing to its properties such as being lightweight, strong and corrosion and wear resistant, which enable it to be used in many applications, such as electronics, aerospace and automotive purposes. Various examinations have been performed for the samples of this work, such as Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD) analysis to estimate the microstructure and phases of manufactured nano-composites. Mechanical testing is also carried out, such as micro-hardness testing, compressive testing and wear testing, to estimate the mechanical properties of the hybrid nano-composites. The results of FESEM and XRD demonstrate that Fe2O3 and Ag nanoparticles are uniformly distributed and dispersed into the Al matrix, whereas the mechanical tests show that enhancement t micro-hardness, compressive strength of 12 wt.% Fe2O3 + 1Ag and wear rate decrease to a minimum value of 12 wt.% of Fe2O3 + 1Ag. Full article
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Article
Microstructural Analysis and Mechanical Characterization of Shape Memory Alloy Ni-Ti-Ag Synthesized by Casting Route
Appl. Sci. 2022, 12(9), 4639; https://doi.org/10.3390/app12094639 - 05 May 2022
Cited by 1 | Viewed by 329
Abstract
The purpose of the current research is to study the microstructure and mechanical properties of Ni-Ti-Ag shape memory alloys prepared by the casting route. Ag (grain size at 1 mm) was incorporated into Ni-Ti alloys at varying percentages of weight (0, 1.5, 3 [...] Read more.
The purpose of the current research is to study the microstructure and mechanical properties of Ni-Ti-Ag shape memory alloys prepared by the casting route. Ag (grain size at 1 mm) was incorporated into Ni-Ti alloys at varying percentages of weight (0, 1.5, 3 and 4.5 wt.% Ag) to produce shape memory alloys using a Vacuum Arc Re-melting (VAR) furnace. Microstructural analysis was defined by FESEM microscopy and XRD examinations, while the transformation temperatures of the Ni-Ti-Ag shape memory alloy were determined by DSC examination. On the other hand, determination of mechanical properties was carried out using micro-hardness and compressive tests. The results of this work show that Ag was dispersed homogeneously into the Ni-Ti alloy. Moreover, two primary phases (austenite phase and martensite phase) emerged with few impurities. The results of the XRD examination show that the number of Ag peaks increased with the increase in weight percentage of Ag. The transformation temperature of the austenitic phase was defined as −1.6 °C by DSC. The mechanical characterizations increased with the increase in weight percentages of Ag (1.5, 3 and 4.5 wt.%), and significantly affected the mechanical properties of the Ni-Ti alloy. An improvement in compressive strength (42.478%) was found for the alloy with 3 wt.% Ag, while the micro-hardness results show a slight decrease in micro-hardness (8.858%) for the alloy with 4.5 wt.% Ag. Full article
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Article
A High Thermal Conductivity of MgO-H2O Nanofluid Prepared by Two-Step Technique
Appl. Sci. 2022, 12(5), 2655; https://doi.org/10.3390/app12052655 - 04 Mar 2022
Cited by 1 | Viewed by 453
Abstract
In this paper, the main goal is to study the impact of nanopowder volume concentration and ultrasonication treatment time on the stability and thermophysical properties of MgO-DW nanofluid at room temperature. The co-precipitation method was utilized to prepare pure MgO nanoparticles with an [...] Read more.
In this paper, the main goal is to study the impact of nanopowder volume concentration and ultrasonication treatment time on the stability and thermophysical properties of MgO-DW nanofluid at room temperature. The co-precipitation method was utilized to prepare pure MgO nanoparticles with an average particle size of 33 nm. The prepared MgO nanopowder was characterized by using XRD, SEM, and EDX analyses. Then, MgO-DW nanofluid was obtained with different volume concentrations (i.e., 0.05, 0.1, 0.15, 0.2, and 0.25 vol.%) and different ultrasonication time periods (i.e., 45, 90, 135, and 180 min) by using a novel two-step technique. With volume concentration and ultrasonication time of 0.15 vol.% and 180 min, respectively, good stability was achieved, according to the zeta potential analysis. With increasing volume concentration and ultrasonication time period of the nanofluid samples, the thermal conductivity measurements showed significant increases. As a result, the maximum enhancement was found to be 25.08% at a concentration ratio of 0.25 vol.% and agitation time of 180 min. Dynamic viscosity measurements revealed two contrasting trends with volume concentration and ultrasonication time. The lowest value of relative viscosity was gained by 0.05 vol.% MgO-DW nanofluid. The chemical and physical interactions between MgO nanoparticles and DW molecules play an important function in determining the thermal conductivity and dynamic viscosity of MgO-DW nanofluid. These findings exhibit that MgO-DW nanofluid has the potential to be used as an advanced heat transfer fluid in cooling systems and heat exchangers. Full article
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Article
Dynamic Process Simulation of a Molten-Salt Energy Storage System
Appl. Sci. 2021, 11(23), 11308; https://doi.org/10.3390/app112311308 - 29 Nov 2021
Cited by 4 | Viewed by 498
Abstract
The main objective of this work was the construction of a numerical model using Advanced Process Simulation Software to represent the dynamic behaviour of a thermal storage system (TSS). The storage model was validated by comparing the results with the measured data of [...] Read more.
The main objective of this work was the construction of a numerical model using Advanced Process Simulation Software to represent the dynamic behaviour of a thermal storage system (TSS). The storage model was validated by comparing the results with the measured data of the storage process of the Andasol 2 solar power plant. Subsequently, a system analysis and system optimisation were carried out, and the stand-alone concept of the thermal storage system is presented. Stand-alone refers to an isolated use of the storage system without a solar power plant. During power peaks, this storage medium is heated with excess electrical power and later returned to the electrical grid through a steam cycle. Then, the system was optimised by modelling four models based on the type of storage medium and the temperature difference of the storage system. The four models, Andasol 2, SSalt max, Hitec, and Carbonate, were evaluated and compared in terms of the improvement in capacity and efficiency that can be achieved. The comparison shows that the preferred storage medium is carbonate salt due to the increases in both efficiency and capacity. The greatest increase in efficiency in terms of power generation can also be achieved with the Carbonate model (18.2%), whereas the amount of increase was 9.5% and 7.4% for each of SSalt max and Hitec, respectively. The goal of this analysis and system optimisation of a thermal salt storage system is to stabilise and relieve the local power grid. Full article
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Article
Experimental Study of the Influence of Gas Flow Rate on Hydrodynamic Characteristics of Sieve Trays and Their Effect on CO2 Absorption
Appl. Sci. 2021, 11(22), 10708; https://doi.org/10.3390/app112210708 - 12 Nov 2021
Cited by 1 | Viewed by 378
Abstract
An experimental study was conducted in the sieve tray column to investigate the influence of gas flow rate on the hydrodynamic characteristics of the sieve tray, such as total tray pressure drop, wet tray pressure drop, dry tray pressure drop, clear liquid height, [...] Read more.
An experimental study was conducted in the sieve tray column to investigate the influence of gas flow rate on the hydrodynamic characteristics of the sieve tray, such as total tray pressure drop, wet tray pressure drop, dry tray pressure drop, clear liquid height, liquid holdup, and froth height. The hydrodynamic characteristics of the sieve tray were investigated for the gas/water system at different gas flow rates from 12 to 24 Nm3/h and at different pressures of 0.22, 0.24, and 0.26 MPa. In this study, a simulated waste gas was used that consisted of 30% CO2 and 70% air. The inlet volumetric flow rate of the water was 0.148 m3/h. The temperature of the inlet water was 19.5 °C. The results showed that the gas flow rate has a significant effect on the hydrodynamic characteristics of the tray. The authors investigated the effect of changing these hydrodynamic characteristics on the performance of a tray column used for CO2 capture. Full article
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Article
A Comparison Study on the Improved Operation Strategy for a Parabolic trough Solar Power Plant in Spain
Appl. Sci. 2021, 11(20), 9576; https://doi.org/10.3390/app11209576 - 14 Oct 2021
Cited by 6 | Viewed by 383
Abstract
The present work focuses on the development of a detailed dynamic model of an existing parabolic trough solar power plant (PTSPP) in Spain. This work is the first attempt to analyse the dynamic interaction of all parts, including solar field (SF), thermal storage [...] Read more.
The present work focuses on the development of a detailed dynamic model of an existing parabolic trough solar power plant (PTSPP) in Spain. This work is the first attempt to analyse the dynamic interaction of all parts, including solar field (SF), thermal storage system (TSS) and power block (PB), and describes the heat transfer fluid (HTF) and steam/water paths in detail. Advanced control circuits, including drum level, economiser water bypass, attemperator and steam bypass controllers, are also included. The parabolic trough power plant is modelled using Advanced Process Simulation Software (APROS). An accurate description of control structures and operation strategy is necessary in order to achieve a reasonable dynamic response. This model would help to identify the best operation strategy due to DNI (direct normal irradiation) variations during the daytime. The operation strategy used in this model has also been shown to be effective compared to decisions made by operators on cloudy periods by improving power plant performance and increasing operating hours. Full article
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Article
Influences of the Pretreatments of Residual Biomass on Gasification Processes: Experimental Devolatilizations Study in a Fluidized Bed
Appl. Sci. 2021, 11(12), 5722; https://doi.org/10.3390/app11125722 - 20 Jun 2021
Cited by 4 | Viewed by 673
Abstract
The European research project CLARA (chemical looping gasification for sustainable production of biofuels, G.A. 817841) investigated chemical looping gasification of wheat straw pellets. This work focuses on pretreatments for this residual biomass, i.e., torrefaction and torrefaction-washing. Devolatilizations of individual pellets were performed in [...] Read more.
The European research project CLARA (chemical looping gasification for sustainable production of biofuels, G.A. 817841) investigated chemical looping gasification of wheat straw pellets. This work focuses on pretreatments for this residual biomass, i.e., torrefaction and torrefaction-washing. Devolatilizations of individual pellets were performed in a laboratory-scale fluidized bed made of sand, at 700, 800, and 900 °C, to quantify and analyze the syngas released from differently pretreated biomasses; experimental data were assessed by integral-average parameters: gas yield, H2/CO molar ratio, and carbon conversion. A new analysis of devolatilization data was performed, based on information from instantaneous peaks of released syngas, by simple regressions with straight lines. For all biomasses, the increase of devolatilization temperature between 700 and 900 °C enhanced the thermochemical conversion in terms of gas yield, carbon conversion, and H2/CO ratio in the syngas. Regarding pretreatments, the main evidence is the general improvement of syngas quality (i.e., composition) and quantity, compared to those of untreated pellets; only slighter differentiations were observed concerning different pretreatments, mainly thanks to peak quantities, which highlighted an improvement of the H2/CO molar ratio in correlation with increased torrefaction temperature from 250 to 270 °C. The proposed methods emerged as suitable straightforward tools to investigate the behavior of biomasses and the effects of process parameters and biomass nature. Full article
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Article
Process Simulation of Steam Gasification of Torrefied Woodchips in a Bubbling Fluidized Bed Reactor Using Aspen Plus
Appl. Sci. 2021, 11(6), 2877; https://doi.org/10.3390/app11062877 - 23 Mar 2021
Cited by 2 | Viewed by 1125
Abstract
A comprehensive process model is proposed to simulate the steam gasification of biomass in a bubbling fluidized bed reactor using the Aspen Plus simulator. The reactor models are implemented using external FORTRAN codes for hydrodynamic and reaction kinetic calculations. Governing hydrodynamic equations and [...] Read more.
A comprehensive process model is proposed to simulate the steam gasification of biomass in a bubbling fluidized bed reactor using the Aspen Plus simulator. The reactor models are implemented using external FORTRAN codes for hydrodynamic and reaction kinetic calculations. Governing hydrodynamic equations and kinetic reaction rates for char gasification and water-gas shift reactions are obtained from experimental investigations and the literature. Experimental results at different operating conditions from steam gasification of torrefied biomass in a pilot-scale gasifier are used to validate the process model. Gasification temperature and steam-to-biomass ratio promote hydrogen production and improve process efficiencies. The steam-to-biomass ratio is directly proportional to an increase in the content of hydrogen and carbon monoxide, while gas yield and carbon conversion efficiency enhance significantly with increasing temperature. The model predictions are in good agreement with experimental data. The mean error of CO2 shows the highest value of 0.329 for the steam-to-biomass ratio and the lowest deviation is at 0.033 of carbon conversion efficiency, respectively. The validated model is capable of simulating biomass gasification under various operating conditions. Full article
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Article
Thermo-Economic Comparisons of Environmentally Friendly Solar Assisted Absorption Air Conditioning Systems
Appl. Sci. 2021, 11(5), 2442; https://doi.org/10.3390/app11052442 - 09 Mar 2021
Cited by 2 | Viewed by 790
Abstract
Absorption refrigeration cycle is considered a vital option for thermal cooling processes. Designing new systems is needed to meet the increasing communities’ demands of space cooling. This should be given more attention especially with the increasing conventional fossil fuel energy costs and CO [...] Read more.
Absorption refrigeration cycle is considered a vital option for thermal cooling processes. Designing new systems is needed to meet the increasing communities’ demands of space cooling. This should be given more attention especially with the increasing conventional fossil fuel energy costs and CO2 emission. This work presents the thermo-economic analysis to compare between different solar absorption cooling system configurations. The proposed system combines a solar field, flashing tank and absorption chiller: two types of absorption cycle H2O-LiBr and NH3-H2O have been compared to each other by parabolic trough collectors and evacuated tube collectors under the same operating conditions. A case study of 200 TR total cooling load is also presented. Results reveal that parabolic trough collector combined with H2O-LiBr (PTC/H2O-LiBr) gives lower design aspects and minimum rates of hourly costs (5.2 $/h) followed by ETC/H2O-LiBr configuration (5.6 $/h). H2O-LiBr gives lower thermo-economic product cost (0.14 $/GJ) compared to the NH3-H2O (0.16 $/GJ). The absorption refrigeration cycle coefficient of performance ranged between 0.5 and 0.9. Full article
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Article
Evaluation of Waste Blends with Sewage Sludge as a Potential Material Input for Pyrolysis
Appl. Sci. 2021, 11(4), 1610; https://doi.org/10.3390/app11041610 - 10 Feb 2021
Cited by 4 | Viewed by 729
Abstract
In line with the requirements of the circular economy, the European Union’s waste management legislative changes also concern the treatment of sewage sludge. Although sewage sludge production cannot be prevented, its quantities may be reduced by the synergetic effect of energy recovery via [...] Read more.
In line with the requirements of the circular economy, the European Union’s waste management legislative changes also concern the treatment of sewage sludge. Although sewage sludge production cannot be prevented, its quantities may be reduced by the synergetic effect of energy recovery via choosing a proper technology. Sewage sludge is difficult to apply as fuel alone, because of its high moisture and ash content. However, its energy use will be increased by adding suitable waste materials (different types of plastics, waste tires and paper rejects). Most recently, the thermal utilization of sewage sludge via incineration or pyrolysis has grown in importance. This article describes the fuel parameters of particular waste materials and of their blends with sewage sludge in connection with laboratory-scale thermal decomposition in an inert atmosphere, for their potential use in a semi-pilot plant pyrolysis unit. For pyrolytic application, the results of thermogravimetric analysis are needed in order to know the maximal temperature of thermal decomposition in an inert atmosphere, maximal mass losses, and weight loss rates. The samples of different thermoplastics mixed with sewage sludge, and low-density polyethylene blends with sewage sludge, had the lowest residual masses (70–74%) and the highest weight loss rates (11–19%/min). On the other hand, the blend of polyester rejects from tire processing, paper rejects and sewage sludge had the second highest residual mass (60%) and the lowest weight loss rate (3%/min). Full article
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Article
Experimental Parameter Study on Synthesis Gas Production by Steam-Oxygen Fluidized Bed Gasification of Sewage Sludge
Appl. Sci. 2021, 11(2), 579; https://doi.org/10.3390/app11020579 - 08 Jan 2021
Cited by 6 | Viewed by 1007
Abstract
The conversion of biogenic residues to fuels and chemicals via gasification and synthesis processes is a promising pathway to replace fossil carbon. In this study, the focus is set on sewage sludge gasification for syngas production. Experiments were carried out in a 20 [...] Read more.
The conversion of biogenic residues to fuels and chemicals via gasification and synthesis processes is a promising pathway to replace fossil carbon. In this study, the focus is set on sewage sludge gasification for syngas production. Experiments were carried out in a 20 kW fuel input bubbling fluidized bed facility with steam and oxygen as gasification agent. In-situ produced sewage sludge ash was used as bed material. The sensitivity of the key operation parameters gasifier temperature, oxygen ratio, steam to carbon ratio, and the space velocity on the syngas composition (H2, CO, CO2, CH4, CxHy, H2S, COS, NH3, and tars) was determined. The results show that the produced syngas has high H2 and CO concentrations of up to 0.37 m3 m−3 and 0.18 m3 m−3, respectively, and is thus suitable for synthesis of fuels and chemicals. By adjusting the steam to carbon ratio, the syngas’ H2 to CO ratio can be purposely tailored by the water gas shift reaction for various synthesis products, e.g., synthetic natural gas (H2/CO = 3) or Fischer–Tropsch products (H2/CO = 2). Also, the composition and yields of fly ash and bed ash are presented. Through the gasification process, the cadmium and mercury contents of the bed ash were drastically reduced. The ash is suitable as secondary raw material for phosphorous or phosphate fertilizer production. Overall, a broad database was generated that can be used for process simulation and process design. Full article
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Article
A Detailed One-Dimensional Hydrodynamic and Kinetic Model for Sorption Enhanced Gasification
Appl. Sci. 2020, 10(17), 6136; https://doi.org/10.3390/app10176136 - 03 Sep 2020
Cited by 4 | Viewed by 943
Abstract
Increased installation of renewable electricity generators requires different technologies to compensate for the associated fast and high load gradients. In this work, sorption enhanced gasification (SEG) in a dual fluidized bed gasification system is considered as a promising and flexible technology for the [...] Read more.
Increased installation of renewable electricity generators requires different technologies to compensate for the associated fast and high load gradients. In this work, sorption enhanced gasification (SEG) in a dual fluidized bed gasification system is considered as a promising and flexible technology for the tailored syngas production for use in chemical manufacturing or electricity generation. To study different operational strategies, as defined by gasification temperature or fuel input, a simulation model is developed. This model considers the hydrodynamics in a bubbling fluidized bed gasifier and the kinetics of gasification reactions and CO2 capture. The CO2 capture rate is defined by the number of carbonation/calcination cycles and the make-up of fresh limestone. A parametric study of the make-up flow rate (0.2, 6.6, and 15 kg/h) reveals its strong influence on the syngas composition, especially at low gasification temperatures (600–650 °C). Our results show good agreement with the experimental data of a 200 kW pilot plant, as demonstrated by deviations of syngas composition (5–34%), lower heating value (LHV) (5–7%), and M module (23–32%). Studying the fuel feeding rate (22–40 kg/h), an operational range with a good mixing of solids in the fluidized bed is identified. The achieved results are summarized in a reactor performance diagram, which gives the syngas power depending on the gasification temperature and the fuel feeding rate. Full article
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Article
Operational Flexibility of a CFB Furnace during Fast Load Change—Experimental Measurements and Dynamic Model
Appl. Sci. 2020, 10(17), 5972; https://doi.org/10.3390/app10175972 - 28 Aug 2020
Cited by 7 | Viewed by 1045
Abstract
The share of power from fluctuating renewable energies such as wind and solar is increasing due to the ongoing climate change. It is therefore essential to use technologies that can compensate for these fluctuations. Experiments at 1 MWth scale were carried out [...] Read more.
The share of power from fluctuating renewable energies such as wind and solar is increasing due to the ongoing climate change. It is therefore essential to use technologies that can compensate for these fluctuations. Experiments at 1 MWth scale were carried out to evaluate the operational flexibility of a circulating fluidized bed (CFB) combustor during transient operation from 60% to 100% load. A typical load following sequence for fluctuating electricity generation/demand was reproduced experimentally by performing 4 load changes. The hydrodynamic condition after a load change depends on if the load change was in positive or negative direction due to the heat stored in the refractory/bed material at high loads and released when the load decreases. A 1.5D-process simulation model was created in the software APROS (Advanced Process Simulation) with the target of showing the specific characteristics of a CFB furnace during load following operation. The model was tuned with experimental data of a steady-state test point and validated with the load cycling tests. The simulation results show the key characteristics of CFB combustion with reasonable accuracy. Detailed experimental data is presented and a core-annulus approach for the modeling of the CFB furnace is used. Full article
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Article
Energy and Exergy Analyses of an Existing Solar-Assisted Combined Cycle Power Plant
Appl. Sci. 2020, 10(14), 4980; https://doi.org/10.3390/app10144980 - 20 Jul 2020
Cited by 5 | Viewed by 1134
Abstract
Solar-assisted combined cycle power plants (CCPPs) feature the advantages of renewable clean energy with efficient CCPPs. These power plants integrate a solar field with a CCPP. This integration increases the efficiency of solar power plants while decreasing the CO2 emissions of the [...] Read more.
Solar-assisted combined cycle power plants (CCPPs) feature the advantages of renewable clean energy with efficient CCPPs. These power plants integrate a solar field with a CCPP. This integration increases the efficiency of solar power plants while decreasing the CO2 emissions of the CCPPs. In this paper, energy and exergy analyses were performed for an existing solar-assisted CCPP. The overall thermal efficiency and the exergetic efficiency of each component in the power plant were calculated for different solar field capacities. Also, a parametric study of the power plant was performed. The analysis indicated that the exergetic efficiency of the power plant components has its lowest value in the solar field while the condenser has the lowest exergetic efficiency in the combined cycle regime of operation. Further, a parametric study revealed that the thermal efficiency and the exergetic efficiency of the power plant as a whole decrease with increasing ambient temperature and have their highest values in the combined cycle regime of operation. Owing to these results, an investigation into the sources of exergy destruction in the solar field was conducted. Full article
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Article
Influence of Pressure on Gas/Liquid Interfacial Area in a Tray Column
Appl. Sci. 2020, 10(13), 4617; https://doi.org/10.3390/app10134617 - 03 Jul 2020
Cited by 2 | Viewed by 872
Abstract
The influence of pressure on the gas/liquid interfacial area is investigated in the pressure range of 0.2–0.3 MPa by using a tray column test rig. A simulated waste gas, which consisted of 30% CO2 and 70% air, was used in this study. [...] Read more.
The influence of pressure on the gas/liquid interfacial area is investigated in the pressure range of 0.2–0.3 MPa by using a tray column test rig. A simulated waste gas, which consisted of 30% CO2 and 70% air, was used in this study. Distilled water was employed as an absorbent. The temperature of the inlet water was 19 °C. The inlet volumetric flow rate of water was 0.17 m3/h. Two series of experiments were performed; the first series was performed at inlet gas flow rate 15 Nm3/h, whereas the second series was at 20 Nm3/h of inlet gas flow rate. The results showed that the gas/liquid interfacial area decreases when the total pressure is increased. The effect of pressure on the gas/liquid interfacial area at high inlet volumetric gas flow rates is more significant than at low inlet volumetric gas flow rates. The authors studied the effect of decreasing the interfacial area on the performance of a tray column for CO2 capture. Full article
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Article
Process Control Strategies in Chemical Looping Gasification—A Novel Process for the Production of Biofuels Allowing for Net Negative CO2 Emissions
Appl. Sci. 2020, 10(12), 4271; https://doi.org/10.3390/app10124271 - 22 Jun 2020
Cited by 14 | Viewed by 1458
Abstract
Chemical looping gasification (CLG) is a novel gasification technique, allowing for the production of a nitrogen-free high calorific synthesis gas from solid hydrocarbon feedstocks, without requiring a costly air separation unit. Initial advances to better understand the CLG technology were made during first [...] Read more.
Chemical looping gasification (CLG) is a novel gasification technique, allowing for the production of a nitrogen-free high calorific synthesis gas from solid hydrocarbon feedstocks, without requiring a costly air separation unit. Initial advances to better understand the CLG technology were made during first studies in lab and bench scale units and through basic process simulations. Yet, tailored process control strategies are required for larger CLG units, which are not equipped with auxiliary heating. Here, it becomes a demanding task to achieve autothermal CLG operation, for which stable reactor temperatures are obtained. This study presents two avenues to attain autothermal CLG behavior, established through equilibrium based process simulations. As a first approach, the dilution of active oxygen carrier materials with inert heat carriers to limit oxygen transport to the fuel reactor has been investigated. Secondly, the suitability of restricting the air flow to the air reactor in order to control the oxygen availability in the fuel reactor was examined. Process simulations show that both process control approaches facilitate controlled and de-coupled heat and oxygen transport between the two reactors of the chemical looping gasifier, thus allowing for efficient autothermal CLG operation. With the aim of inferring general guidelines on how CLG units have to be operated in order to achieve decent synthesis gas yields, different advantages and disadvantages associated to the two suggested process control strategies are discussed in detail and optimization avenues are presented. Full article
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Article
A New Design of an Integrated Solar Absorption Cooling System Driven by an Evacuated Tube Collector: A Case Study for Baghdad, Iraq
Appl. Sci. 2020, 10(10), 3622; https://doi.org/10.3390/app10103622 - 23 May 2020
Cited by 7 | Viewed by 1383
Abstract
The electrical power consumption of refrigeration equipment leads to a significant influence on the supply network, especially on the hottest days during the cooling season (and this is besides the conventional electricity problem in Iraq). The aim of this work is to investigate [...] Read more.
The electrical power consumption of refrigeration equipment leads to a significant influence on the supply network, especially on the hottest days during the cooling season (and this is besides the conventional electricity problem in Iraq). The aim of this work is to investigate the energy performance of a solar-driven air-conditioning system utilizing absorption technology under climate in Baghdad, Iraq. The solar fraction and the thermal performance of the solar air-conditioning system were analyzed for various months in the cooling season. It was found that the system operating in August shows the best monthly average solar fraction (of 59.4%) and coefficient of performance (COP) (of 0.52) due to the high solar potential in this month. Moreover, the seasonal integrated collector efficiency was 54%, providing a seasonal solar fraction of 58%, and the COP of the absorption chiller was 0.44, which was in limit, as reported in the literature for similar systems. A detailed parametric analysis was carried out to evaluate the thermal performance of the system and analyses, and the effect of design variables on the solar fraction of the system during the cooling season. Full article
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Article
Steam Gasification of Lignite in a Bench-Scale Fluidized-Bed Gasifier Using Olivine as Bed Material
Appl. Sci. 2020, 10(8), 2931; https://doi.org/10.3390/app10082931 - 23 Apr 2020
Cited by 7 | Viewed by 1099
Abstract
The gasification of lignite could be a promising sustainable alternative to combustion, because it causes reduced emissions and allows the production of syngas, which is a versatile gaseous fuel that can be used for cogeneration, Fischer-Tropsch synthesis, or the synthesis of other bio-fuels, [...] Read more.
The gasification of lignite could be a promising sustainable alternative to combustion, because it causes reduced emissions and allows the production of syngas, which is a versatile gaseous fuel that can be used for cogeneration, Fischer-Tropsch synthesis, or the synthesis of other bio-fuels, such as methanol. For the safe and smooth exploitation of syngas, it is fundamental to have a high quality gas, with a high content of H2 and CO and minimum content of pollutants, such as particulate and tars. In this work, experimental tests on lignite gasification are carried out in a bench-scale fluidized-bed reactor with olivine as bed material, chosen for its catalytic properties that can enhance tar reduction. Some operating parameters were changed throughout the tests, in order to study their influence on the quality of the syngas produced, and pressure fluctuation signals were acquired to evaluate the fluidization quality and diagnose correlated sintering or the agglomeration of bed particles. The effect of temperature and small air injections in the freeboard were investigated and evaluated in terms of the conversion efficiencies, gas composition, and tar produced. Full article
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Article
Comparison of Equilibrium-Stage and Rate-Based Models of a Packed Column for Tar Absorption Using Vegetable Oil
Appl. Sci. 2020, 10(7), 2362; https://doi.org/10.3390/app10072362 - 30 Mar 2020
Cited by 6 | Viewed by 1140
Abstract
In this study two mathematical models, rate-based and equilibrium-stage models in Aspen Plus process simulator, were used to simulate the tar absorption processes using soybean oil as a solvent in a research lab-scale experiment. The matching between simulation results and experimental data shows [...] Read more.
In this study two mathematical models, rate-based and equilibrium-stage models in Aspen Plus process simulator, were used to simulate the tar absorption processes using soybean oil as a solvent in a research lab-scale experiment. The matching between simulation results and experimental data shows a good agreement. The simulation results predicted by the rate-based model show a higher level of agreement than the equilibrium model compared with the experimental data. Analysis study of tar absorption process was carried out which revealed the effect of temperature and flow rate on the soybean oil, and height-packed bed on tar removal efficiency. The methodology of selecting the optimum (most economical) operation conditions has also been performed in this study. Full article
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Article
Determination of a Complete Conversion Model for Gasification of Lignite Char
Appl. Sci. 2020, 10(6), 1916; https://doi.org/10.3390/app10061916 - 11 Mar 2020
Cited by 2 | Viewed by 1297
Abstract
The conversion of solid fuels via gasification is a viable method to produce valuable fuels and chemicals or electricity while also offering the option of carbon capture. Fluidized bed gasifiers are most suitable for abundantly available low-rank coal. The design of these gasifiers [...] Read more.
The conversion of solid fuels via gasification is a viable method to produce valuable fuels and chemicals or electricity while also offering the option of carbon capture. Fluidized bed gasifiers are most suitable for abundantly available low-rank coal. The design of these gasifiers requires well-developed kinetic models of gasification. Numerous studies deal with single aspects of char gasification, like influence of gas compositions or pre-treatment. Nevertheless, no unified theory for the gasification mechanisms exists that is able to explain the reaction rate over the full range of possible temperatures, gas compositions, carbon conversion, etc. This study aims to demonstrate a rigorous methodology to provide a complete char gasification model for all conditions in a fluidized bed gasifier for one specific fuel. The non-isothermal thermogravimetric method was applied to steam and CO2 gasification from 500 °C to 1100 °C. The inhibiting effect of product gases H2 and CO was taken into account. All measurements were evaluated for their accuracy with the Allan variance. Two reaction models (i.e., Arrhenius and Langmuir–Hinshelwood) and four conversion models (i.e., volumetric model, grain model, random pore model and Johnson model) were fitted to the measurement results and assessed depending on their coefficient of determination. The results for the chosen char show that the Langmuir–Hinshelwood reaction model together with the Johnson conversion model is most suitable to describe the char conversion for both steam and CO2 gasification of the tested lignite. The coefficient of determination is 98% and 95%, respectively. Full article
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Article
Non-Energy Valorization of Residual Biomasses via HTC: CO2 Capture onto Activated Hydrochars
Appl. Sci. 2020, 10(5), 1879; https://doi.org/10.3390/app10051879 - 10 Mar 2020
Cited by 6 | Viewed by 1389
Abstract
This study aims to investigate the CO2 sorption capacity of hydrochar, obtained via hydrothermal carbonization (HTC). Silver fir sawdust was used as a model material. The batch runs went at 200 °C and up to 120 min. The hydrochar was activated with [...] Read more.
This study aims to investigate the CO2 sorption capacity of hydrochar, obtained via hydrothermal carbonization (HTC). Silver fir sawdust was used as a model material. The batch runs went at 200 °C and up to 120 min. The hydrochar was activated with potassium hydroxide impregnation and subsequent thermal treatment (600 °C, 1 h). CO2 capture was assayed using a pressure swing adsorption (PSA) process. The morphology and porosity of hydrochar, characterized through Brunauer-Emmett-Teller, Barrett-Joyner-Halenda (BET-BJH) and scanning electron microscopy (SEM) analyses, were reported and the sorbent capacity was compared with traditional sorbents. The hydrochar recovered immediately after the warm-up of the HTC reactor had better performances. The Langmuir equilibrium isotherm fits the experimental data satisfactorily. Selectivity tests performed with a model biogas mixture indicated a possible use of hydrochar for sustainable upgrading of biogas to bio-methane. It is conceivably a new, feasible, and promising option for CO2 capture with low cost, environmentally friendly materials. Full article
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Review

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Review
Application of Nanofluids in CO2 Absorption: A Review
Appl. Sci. 2022, 12(6), 3200; https://doi.org/10.3390/app12063200 - 21 Mar 2022
Cited by 6 | Viewed by 597
Abstract
The continuous release of CO2 into the atmosphere as a major cause of increasing global warming has become a growing concern for the environment. Accordingly, CO2 absorption through an approach with maximum absorption efficiency and minimum energy consumption is of paramount [...] Read more.
The continuous release of CO2 into the atmosphere as a major cause of increasing global warming has become a growing concern for the environment. Accordingly, CO2 absorption through an approach with maximum absorption efficiency and minimum energy consumption is of paramount importance. Thanks to the emergence of nanotechnology and its unique advantages in various fields, a new approach was introduced using suspended particles in a base liquid (suspension) to increase CO2 absorption. This review article addresses the performance of nanofluids, preparation methods, and their stability, which is one of the essential factors preventing sedimentation of nanofluids. This article aims to comprehensibly study the factors contributing to CO2 absorption through nanofluids, which mainly addresses the role of the base liquids and the reason behind their selection. Full article
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Review
Biomass-Based Chemical Looping Gasification: Overview and Recent Developments
Appl. Sci. 2021, 11(15), 7069; https://doi.org/10.3390/app11157069 - 30 Jul 2021
Cited by 11 | Viewed by 1223
Abstract
Biomass has emerged as one of the most promising renewable energy sources that can replace fossil fuels. Many researchers have carried out intensive research work on biomass gasification to evaluate its performance and feasibility to produce high-quality syngas. However, the process remains the [...] Read more.
Biomass has emerged as one of the most promising renewable energy sources that can replace fossil fuels. Many researchers have carried out intensive research work on biomass gasification to evaluate its performance and feasibility to produce high-quality syngas. However, the process remains the problem of tar formation and low efficiency. Recently, novel approaches were developed for biomass utilization. Chemical looping gasification is considered a suitable pathway to produce valuable products from biomass among biomass conversion processes. This review paper provides a significant body of knowledge on the recent developments of the biomass-based chemical looping gasification process. The effects of process parameters have been discussed to provide important insights into the development of novel technology based on chemical looping. The state-of-the-art experimental and simulation/modeling studies and their fundamental assumptions are described in detail. In conclusion, the review paper highlights current research trends, identifying research gaps and opportunities for future applications of biomass-based chemical looping gasification process. The study aims to assist in understanding biomass-based chemical looping gasification and its development through recent research. Full article
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Review
Design and Implementation of the Solar Field and Thermal Storage System Controllers for a Parabolic Trough Solar Power Plant
Appl. Sci. 2021, 11(13), 6155; https://doi.org/10.3390/app11136155 - 02 Jul 2021
Cited by 9 | Viewed by 856
Abstract
Dynamic simulation provides an efficient approach for improving the efficiency of parabolic trough power plants and control circuits. In the dynamic simulation, the possibilities and operating conditions of the plant are evaluated regarding materials, processes, emissions, or economics. Several studies related to the [...] Read more.
Dynamic simulation provides an efficient approach for improving the efficiency of parabolic trough power plants and control circuits. In the dynamic simulation, the possibilities and operating conditions of the plant are evaluated regarding materials, processes, emissions, or economics. Several studies related to the dynamic simulation of the parabolic trough technology are summarised and discussed in this work. This study is the first research that presents a thorough description of the advanced control circuits used in the solar field and thermal storage system of a parabolic trough power plant. This power plant was implemented using advanced process simulation software (APROS). The dynamic model was built based on the real specifications of the power plant. Full article
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