Circulating Fluidized Bed Gasifier Research Articles

Techno-economic evaluation of biomass-to-methanol production via circulating fluidized bed gasifier and solid oxide electrolysis cells: A comparative study

Methanol is considered a promising solution for decarbonizing the transportation and chemical industry sectors, being a worldwide traded commodity that can be synthesized from biomass, renewable electricity, CO2 and other carbon-rich gases. This study investigates the potential of Solid Oxide Electrolysis Cells (SOEC) in enhancing the performance of bio-methanol production from biomass gasification. The research explores three distinct biomass-to-methanol plant configurations, incorporating an oxygen-blown Circulating Fluidized Bed Gasifier (CFBG) and different SOEC systems, namely: (i) steam electrolysis for hydrogen generation, (ii) co-electrolysis of steam and CO2 separated from syngas and (iii) direct supply of purified bio-syngas to the SOEC. The study reveals that, although the choice of SOEC type and system configuration could impact energy conversion efficiency and carbon efficiency, all plants show similar performance. In terms of Levelized Cost of Fuel (LCOF) and total efficiency, the syngas-electrolysis configuration exhibits the lowest LCOF, 21.56 €/GJ, and comparable total efficiency of around 80 % to the steam-electrolysis configuration. On the other hand, the CO2-H2O-electrolysis configuration showed the highest LCOF due to higher electricity consumption and capital investment.

Experimental study and theoretical analysis on fluidized activation of coal gasification fly ash from an industrial CFB gasifier

The gasification fly ash (GFA), a bulk industrial solid waste from coal gasification process, urgently needs to be effectively disposed. In order to use the GFA as porous carbon materials, fluidized activation experiments of the GFA from an industrial circulating fluidized bed (CFB) gasifier were conducted in a bench-scale CFB test rig, as well as steam activation experiments of GFA in a vertical tube furnace and theoretical analysis on the activation process. Due to the ultrafine particle size, the GFA faces a fluidization problem and auxiliary particles are needed to stabilize its fluidization. In the fluidized activation, the pore structure of GFA particles becomes developed in a seconds-level time (about 1.5 s). The specific surface area (SBET) of activated GFA increases with temperature, maximally increasing by 48.9 % and reaching 204 m2/g. Steam activation experiments show that the GFA has an activation potential of 362 m2/g (SBET) and the pore structure evolution of GFA can be quantified by carbon conversion ratio. Based on this, the fluidized activation of GFA is found in the stage of pore development. By appropriately increasing the carbon conversion ratio (below 40 %), the fluidized activation effect of GFA is expected to be improved. Theoretical analysis indicates for the GFA the features of ultra-fine particle size and well-developed pore structure greatly enhance the diffusion rate of active component into the particles. Under the strong diffusion effect, increasing temperature is a critical means to realize the rapid and effective activation of GFA in a finite time.

Application of parametric trend life cycle assessment for investigating the carbon footprint of ammonia as marine fuel

PurposeThis study aimed to determine whether ammonia can genuinely help to reduce the carbon footprint of maritime activities. Given this, it was decided to investigate the life cycle of ammonia and its impact on the environment regarding the global warming potential.MethodsTo achieve this goal, the parametric trend life cycle assessment was applied to yield a general and reliable observation. The research was combined with a comprehensive dataset of over 2061 bulk carriers and eight different ammonia production methods: steam methane reforming, photovoltaics, electrolysis via wind, biomass downdraft gasifier, biomass circulating fluidized bed gasifier (CFBG) system, underground coal gasification (UCG) with carbon capture and storage (CCS), UCG without CCS, and 3-step Cu-Cl cycle. In addition, an existing ME-LGI (ME-liquid gas injection) engine was selected as the propulsion system.ResultsThe results from PT-LCA revealed that for estimating the carbon impact of ammonia as marine fuel from a well-to-wake (WTW) perspective, it is mandatory to focus on the well-to-tank (WTT) phase. The lowest carbon production pathway for the global warming potential (GWP) is the 3-step Cu-Cl cycle and eventually is the most potential route for using ammonia as fuel in the maritime industry. Finally, this study concludes with some formulas, based on regression analysis, which serves as rapid indications for comparing the overall carbon impact of thousands of bulk carriers equipped with the ME-LGI engine, carrying ammonia as fuel from different production methods.ConclusionsGiven these fuel production routes, the research has also demonstrated that ME-LGI engines can be a groundbreaking way to reduce the carbon footprint of ships. Additionally, the research findings showed that the environmental indicators proposed in this article have the potential to make a significant contribution to the industry. They are anticipated to assist stakeholders in overcoming the discrepancy problem generated by past studies that were so dissimilar from case to case that the scope, boundary of analysis, data, and assumptions they employed were far from current standards and rules. In addition, the GWP according to the ship power was compared and reviewed in terms of the well-to-wake (WTW). Thus, the proposed methodology for developing ammonia ship environmental indicators is to provide valuable insight into environmental policy and decision-making processes.

Investigation of steam and CO2 gasification for biochar using a circulating fluidized bed gasifier model in Aspen HYSYS

Researchers are focusing their efforts on renewable energy sources to avoid future global energy and environmental crises. One of the renewable energy sources, biomass, can be processed using a variety of techniques and thermodynamic cycles. Biomass gasification, for example, has several environmental and technical benefits. Biochar, on the other hand, is produced by the use of a thermal pretreatment technique to biomass, and it can be used to overcome the drawbacks of biomass in gasification operations. Despite the fact that biochar improves the quality and volume of syngas, there is a few research on this topic in the literature.Although researchers have used a variety of process simulators, the number of gasification systems developed in the Aspen HYSYS simulator is very limited, and no circulating fluidized bed (CFB) gasification model for biochar gasification has ever been reported to our knowledge. Based on the non-stoichiometric equilibrium technique, a unique CFB gasifier model was developed in this work. The impacts of various operating parameters on the syngas were evaluated. In addition, the gasification performance of 10 biochar samples with varying physicochemical features was compared to the physicochemical qualities of solid fuels in a steam and CO2 mixture. As a result, biochar samples with a high carbon content formed an H2-rich syngas with a high calorific value during steam gasification. According to parametric studies, the optimum gasification temperature is about 700 °C, the optimum gasification pressure is 1 bar, and the optimum ratios of steam/biochar and CO2/biochar are between 0.2–0.3 and 0.5–1.0, respectively.

Dimethyl ether production from rice straw: process modelling and simulation

Climate change has been a worldwide concern for recently centuries, and exploitation as well as use of fossil fuels dominantly contribute towards the environmental degradation. Several types of alternative energy resources have been taken into account and evaluated in order to find out viable options for the future, and dimethyl ether (DME) is one of those that are worth serious consideration. In this research, a continuous DME production process was developed and simulated using Aspen HYSYSTM. Rice straw, the most popular type of biomass in Vietnam, was chosen to be feedstock for the fuel production. The proposed process consists of five major sections: rice straw pretreatment and gasification for synthesis gas (syngas) generation using a circulating fluidized bed gasifier (CFBG); water-gas shift reaction (WGSR) for H2/CO ratio adjustment in syngas; gas cleaning stage where H2O, H2S and CO2 are removed; DME synthesis via direct production pathway; and DME purification for separation of main product and recycling of methanol. The simulation results indicated a production capacity of approximately 2,307 kg of DME per hour and chemical energy conversion efficiency (ηDME) from biomass into DME of 75%. In addition to that finding, an investigation into the gasifier's operating parameters was conducted for the purpose of maximizing amount of DME generated. From investigation data obtained, the operating temperature of CFBG, steam to biomass (S/B) ratio, and equivalence ratio (ER) that fulfilled such an aim were concluded to be 900oC, 0.27, and 0.32, respectively. This work offers a novel option for utilization of massive availablity of agricultural residues in Vietnam by turning it into a type of promising fuel, and therefore lessen environmental burden as well as may develop Vietnam's energy market.

High-fidelity investigation of thermochemical conversion of biomass material in a full-loop circulating fluidized bed gasifier

Olive oil production urges the energy companies to exploit the potential of the residues as biomass fuels for clean energy production. Circulating fluidized bed (CFB) gasifier gains global interest within these several years due to its promising solution for converting biomass material to renewable energy. However, the multi-physics processes and multiscale structures inside the gasifier impede the experimental measurements. As an alternative, a reactive multiphase particle-in-cell approach is developed in this work to simulate the gasification process of olive oil waste in a pilot-scale full-loop CFB gasifier. After the model validation, the heat transfer properties of solid phase and the effect of size-induced segregation on solid thermochemical properties are explored. The results show that the low-temperature biomass particles injected highly influence the spatial distribution of solid temperature and solid heat transfer coefficient (HTC). A larger particle size gives rise to a higher HTC. Moreover, the temperature and HTC of biomass are larger than that of sand. A wide and narrow residence time distribution of sand in the riser and cyclone can be observed. The scale of biomass dispersion is respectively larger and the same as that of sand in horizontal and vertical directions. Particles in the dense region have a smaller HTC, Reynolds number, and temperature. Superficial gas velocity improves the uniformity of solid distribution. Elevating the gas velocity and initial bed temperature enhances solid dispersion intensity.

Numerical study of biomass gasification in a 0.3 MWth full-loop circulating fluidized bed gasifier

Biomass gasification process in a three-dimensional pilot-scale circulating fluidized bed (CFB) gasifier is numerically simulated via the multiphase particle-in-cell approach. The physical and thermochemical properties of gas and solid phases (i.e., temperature, density, and viscosity, pressure, and species) in the gasifier under high temperature are comprehensively explored. The results show that the size- and density-induced segregation causes the accumulation of biomass particles in the standpipe. Elutriation of biomass particles leads to the presence of low-temperature endothermic zones and high-temperature exothermic regions in the riser. The large contents of combustible gas species exist in the left part of the riser. Continuous decrease of O2 is due to gas species oxidation, while the reduction of N2 results from the release of gas species. The dense region has a large content of N2 but a small content of combustible gas species. Large turbulent gas viscosity appears in the riser. Enlarging the gas velocity decreases the solid concentration but increases the gas temperature. Gasification temperature has an insignificant influence on the solid concentration and the contents of combustible gas species. Based on the relationship between the solid transportation and gas–solid thermochemical properties, the current work provides a guideline for the optimization of CFB gasifiers, for example, the loop seal is advised to be optimized to enhance the gasification performance of this kind of apparatus.

Process Modelling and Simulation of Waste Gasification-Based Flexible Polygeneration Facilities for Power, Heat and Biofuels Production

There is increasing interest in the harnessing of energy from waste owing to the increase in global waste generation and inadequate currently implemented waste disposal practices, such as composting, landfilling or dumping. The purpose of this study is to provide a modelling and simulation framework to analyze the technical potential of treating municipal solid waste (MSW) and refuse-derived fuel (RDF) for the polygeneration of biofuels along with district heating (DH) and power. A flexible waste gasification polygeneration facility is proposed in this study. Two types of waste—MSW and RDF—are used as feedstock for the polygeneration process. Three different gasifiers—the entrained flow gasifier (EFG), circulating fluidized bed gasifier (CFBG) and dual fluidized bed gasifier (DFBG)—are compared. The polygeneration process is designed to produce DH, power and biofuels (methane, methanol/dimethyl ether, gasoline or diesel and ammonia). Aspen Plus is used for the modelling and simulation of the polygeneration processes. Four cases with different combinations of DH, power and biofuels are assessed. The EFG shows higher energy efficiency when the polygeneration process provides DH alongside power and biofuels, whereas the DFBG and CFBG show higher efficiency when only power and biofuels are produced. RDF waste shows higher efficiency as feedstock than MSW in polygeneration process.

A deep learning approach for prediction of syngas lower heating value from CFB gasifier in Aspen plus®

Aspen Plus® is one of the practicable software for investigation of the biomass gasification characteristics. Also, artificial neural networks (ANN) as a deep learning approach are often used in the prediction of parameters such as syngas composition, lower heating value (LHV), exergy, etc. However, to our best knowledge, a universal deep learning model based on the thermodynamic equilibrium approach to predict LHV of syngas in circulating fluidized bed (CFB) gasifier is not available in literature yet. In this paper, a unique CFB gasifier model was developed in Aspen Plus® as a tool to create a total of over 1 million datasets for the training of a deep learning model that predicts the LHV of the syngas. The CFB gasifier model was found to be in agreement with the results when compared with the experimental data in the literature. 56 biomass with various elemental and proximate properties were gasified in a newly developed CFB gasifier model under different operating conditions by using sensitivity analysis in Aspen Plus®. A novel artificial neural network model, which is regularized with Levenberg-Marquardt algorithm was used as a deep learning model with a 6-12-1 tangent sigmoid architecture to predict LHV of syngas in circulating fluidized bed (CFB) gasifier, requiring minimal specificity as compared to commercial simulators require significant modelling effort and test runs. Results showed that the estimated LHV of the syngas in an agreement with the calculated values. The coefficient of determination score was calculated as R2 > 0.99 for all datasets.

Effect of process parameters on circulating fluidized bed coal gasification using 3D full‐loop CFD simulation

AbstractThis article presents a 3D full‐loop computational fluid dynamics (CFD) simulation of a circulating fluidized bed gasifier (CFBG). The simulation results are validated against the experimental data and found to be in good agreement. Thereupon, the effect of the process parameters, ie, temperature, pressure, air/coal (A/C) ratio, and steam/coal (S/C) ratio, on the performance of the gasifier is analyzed. The effect of temperature on the hydrodynamics was found to be small. The CO and H2 increase, whereas the CO2 and H2O decrease with an increase in temperature. While the effect of pressure on the outlet species mole fraction is negligible, the gas and solid axial velocity decrease with an increase in pressure. With an increasing A/C ratio or decreasing S/C ratio, the combustion products (CO2 and H2O) increase, whereas the gasification products (CO and H2) decrease due to the increase in the O2 concentration. In addition, temperature increases with an increase in the A/C ratio or a decrease in the S/C ratio. The feed velocity increases with an increasing A/C or S/C ratio, and, accordingly, the pressure increases and bed height decreases. The CH4 decreases in all of the cases as it is being consumed in gasification as well as combustion reactions.

Study on the structure characteristics and gasification activity of residual carbon in biomass ashes obtained from different gasification technologies

The structure characteristics and gasification activity of residual carbons in two rice husk (RH) gasification ashes, a fly ash (FAC) obtained from industrial circulating fluidized bed gasifier (CFBG) and a bottom ash (BAU) obtained from industrial updraft fixed bed gasifier (UFBG), were investigated. Results show that the residual carbon content of FAC (15.93%, dry basis) is much lower than that of BAU (40.27%, dry basis), and the carbon conversion efficiencies of RH in CFBG and UFBG are 93.09% and 74.44%, respectively. The dominant carbon species in RH is oxygen-linked aliphatic carbon (ca. 80%), which disappears in the residual carbons of FAC and BAU. Consequently, the nonprotonated aromatic carbon in RH increases significantly from about 3% to 66–68% during gasification processes, leading to the aromaticity of carbon increases from about 15% to 88–90%. The surface area and pore volume of carbon in RH increase significantly during gasification processes, especially those of FAC, while the gasification activity of carbon in RH decreases slightly due to the increased aromaticity of carbon.

Sulfur conversions during coal char gasification with a two-stage air supply in a pilot-scale circulating fluidized bed gasifier

ABSTRACTThis paper aims at studying sulfur conversions in a pilot-scale circulating fluidized bed (CFB) gasification system of two-stage air supply. The effects of different air supply approaches, secondary air supply heights and gasification agent compositions on gasifier temperature, sulfur conversions and the release of hydrogen sulfide (H2S) and carbonyl sulfide (COS) were investigated. Two-stage air supply approaches optimized CFB gasifier temperature profile and enhanced sulfur conversions to gas. Sulfur conversions to gas decreased with the increase of secondary air supply nozzle location height. The increased steam-to-carbon ratio promoted sulfur release, leading to more H2S and less COS release.

Genetic algorithms and neural networks in optimization of sorbent enhanced H2 production in FB and CFB gasifiers

The paper introduces artificial intelligence (AI) approach for the optimization study of a hydrogen concentrations in syngas via CaO Sorption. The performed model allows estimating the hydrogen content in the syngas produced from biomass in different types of facilities. Bubbling fluidized bed (FB) and circulating fluidized bed (CFB) are taken into account in the study. Comparing with the previous FB gasification results, CFB gasification was capable of producing syngas with higher hydrogen concentration.The model considers and covers a broad range of conditions, influencing the hydrogen rich-gas production. The presented non-iterative approach gives quick and accurate results as an answer to the input data sets. The H2 concentration in the gas, estimated using the developed model, is in good agreement with the experimental data. Maximum relative error between measured and calculated data is lower than ±8%.The model allows also studying the influence of operating parameters on the hydrogen concentration in the gas. The method constitutes an easy to employ and useful complementary technique in relation to the other ways of data handling, including experimental procedures. The model can be used by scientists and engineers for optimizations purposes and can be applied as a submodel oraseparate module in engineering calculations, capable to predict the H2 concentration in the syngas from biomass via the CaO sorption both in FB and CFB gasifiers.

A hydrodynamic model for biomass gasification in a circulating fluidized bed riser

This study presents a three-dimensional Computational Fluid Dynamic (CFD) model and experimental measurements of the hydrodynamics in the riser section of a Circulating Fluidized Bed (CFB) biomass gasifier consisting of a binary mixture of polydisperse particles. The model is based on multi-fluid (Eulerian-Eulerian) approach with constitutive equations adopted from the Kinetic Theory of Granular Flow (KTGF). The study first presents an assessment of the various options of the constitutive and closure equations for a binary mixture followed by sensitivity analysis of the model to the solution time step, cell size, turbulence and the alternative formulations of the granular energy equation. Accordingly, a robust and reliable hydrodynamic model is recommended and validated using conventional pressure measurements and Positron Emission Particle Tracking (PEPT) technique. Furthermore, the model predictions and experiments revealed evidence of the particle re-circulation within the lower part of the riser, which is an important feature contributing to rapid mass and heat transfer in a CFB gasifier. The present hydrodynamic model can be further developed; by incorporating appropriate reactions and heat transfer equations, in order to fully predict the performance and products of a CFB biomass gasifier.

Experimental investigation of a triplet ash valve for circulating fluidized bed

In a circulating fluidized bed (CFB), the ash discharge process is challenging due to poor reliability of the solid or mechanical valve at high temperatures and pressures, particularly for a CFB gasifier. This work proposed a novel triplet ash valve for solids discharge in CFB. It resembles a loop seal. The ash valve is comprised of three supply chambers and one discharge chamber. The hydrodynamics and operation characteristics of the ash valve were investigated using Geldart B particles in a cold flow model. The effects of chamber aeration, pressure drop of the standpipe and back pressure on the performance of the ash valve were analyzed. A wide linear operation range of solids flow rate can be achieved by adjusting the aeration of the three supply chambers and the discharge chamber. The specific feasible operation scheme of the ash valve was discussed. An increase of pressure drop in the standpipe promoted the solids flow rate of the ash valve, whereas a higher back pressure of the ash valve decreased the solids flow rate. Finally, a correlation was presented to predict the solids flow rate of the ash valve.

Hydrogen and syngas production from biomass gasification for fuel cell application

ABSTRACTGasification process is being developed to produce a clean and efficient gas flue from fuels such as coal, biomass, and solid/liquid wastes for power generation. In this work, a biomass gasification kinetic model that can predict reaction temperature, gasification performance, and gas composition has been developed for a circulating fluidized bed (CFB). Experimental data from a CFB power plant have been used to validate the model. It is confirmed that the addition of steam is important for increasing the hydrogen concentration and syngas caloric value. Based on the predicted results, an optimal condition is suggested for air and steam gasification in the CFB gasifier.

Steam gasification reactivity of a high-sodium coal fly ash obtained from a pilot scale CFB gasifier

Circulating fluidized bed (CFB) gasification has several advantages for the utilization of low rank coals. However, the carbon content of fly ash is usually very high, which greatly influences the gasification efficiency. The purpose of this research is to investigate the gasification reactivity of a high-sodium Zhundong (ZD) coal fly ash obtained from a pilot-scale 2.5 t/d CFB gasification system. The experiments were carried out in a thermogravimetric analyzer with steam as gasification agent, and fast pyrolyzed ZD char was also investigated as a reference sample. The results show that increasing temperature accelerates the gasification rate both for fly ash and ZD char. Fly ash has higher gasification rate at the initial gasification stage. On the contrary, ZD char has higher reaction rate even at higher carbon conversion stage. Via distributed activation energy model, the average activation energy of ZD char and fly ash is calculated to be 94.4 and 91.2 kJ/mol, respectively. The integrated model study reveals that the reaction order of ZD char is about 0.74, whereas the reaction order of fly ash decreases from 1 to 0.59 when temperature increases from 900 to 1050 °C. The gasification reactivity of ZD coal fly ash is quite different with literature research on those fly ashes with rarely little catalytic elements in coal ashes. The interesting results are related with the unique properties of ZD coal fly ash and the transformation of sodium during gasification process.

Ash Fusion Properties and Mineral Transformation Behavior of Gasified Semichar at High Temperature under Oxidizing Atmosphere

The carbon conversion of fluidized bed gasification has been restricted by the entrainment of semichars with high carbon content. Recently, the disposal of the semichar has become an intractable problem. In this study, the ash fusion properties and mineral transformation behavior at high temperature of the semichar from an industrial circulating fluidized bed (CFB) gasifier were investigated under oxidizing condition. In comparison to the raw coal, the total base content increases from 27.92 to 29.45 after partial gasification, which results in a decrease in the ash fusion temperatures (AFTs) of the semichar. Kaolinite decomposed into quartz, alumina, and water via dihydroxylation reaction and anhydrite was transformed into oldhamite in the CFB gasifier. As the particle size increases, the AFTs of the semichar decrease first and then remain almost unchanged, which coincides with the variations in acid-to-base ratio; however, the disparity is relatively small, which favors its melting utilization. Quartz, ...

Characteristics of coal partial gasification experiments on a circulating fluidized bed reactor under CO2[sbnd]O2 atmosphere

Coal partial gasification experiments are carried out on a self-designed circulating fluidized bed (CFB) gasifier under CO2O2 atmosphere. The CFB gasifier system is mainly composed of a ceramic furnace, auger screw conveyor, gas supplier, gas-solid separation unit, temperature and pressure measuring system, and Distributed Control System (DCS). The experiments are conducted at temperatures between 800 and 930 °C. The coal with particle size of 0.45–0.9 mm is selected for experiments. Mixture of CO2 and O2 is adopted as reactant gas. The oxygen-coal ratio varies from 0.38 to 0.8. The results show that as oxygen-coal ratio increases, the concentration of CO + H2 first goes up and then declines. When the oxygen-coal ratio is 0.57, the concentration of CO + H2 reaches the maximum value. To a certain extent, the higher oxygen-coal ratio results in better gas composition. The volume fraction of combustible gas and the lower calorific value reach ∼40% and 5.58 MJ/Nm3. To explore the variety of char structure features, the Scanning Electron Microscope (SEM) and Raman Spectrometer are adopted. The results show that the pores of char are getting opened as the reactant gas enters the inside of char and new O-containing functional group and more aromatic rings are generated. It makes the chars become more disordered.

Impact of retrofitting existing combined heat and power plant with polygeneration of biomethane: A comparative techno-economic analysis of integrating different gasifiers

It is vital to identify and evaluate the optimal gasifier configuration that could be integrated with existing or new combined heat and power (CHP) plants to maximize the utilization of boiler operating capacity during off-peak hours with minimal effect on the boiler performance. This study aims to identify technically and economically most suitable gasification configuration and the reasonable operational limits of a CHP plant when integrated with different types of gasifiers. The selected gasifiers for the study are, (i) indirectly heated dual fluidized bed gasifier (DFBG), (ii) directly heated circulating fluidized bed gasifier (CFBG), and (iii) entrained flow gasifier (EFG). The gasifiers are selected on their ability to produce high-quality syngas from waste refused derived fuel (RDF). The syngas from the gasifiers is utilized to produce biomethane, whereas the heat and power from the CHP plant are consumed to run the gasification process. A detailed techno-economic analysis is performed using both flexible capacity and fixed capacity gasifiers and integrated with the CHP plant at full load. The results reveal that the integration leads to increase in operating time of the boiler for all gasifier configurations. The indirectly heated DFBG shows the largest biomethane production with less impact on the district heat and power production. Extra heat is available for biomethane production when the district heat and biomethane are prioritized, and the electric power is considered asa secondary product. Furthermore, the economic indicators reflect considerable dependency of integrated gasification performance on variable prices of waste biomass and biomethane.