Dual Fluidized Bed Gasifier Research Articles

Development of a CFD-DEM Model for a 1 MWth Chemical Looping Gasification Pilot Plant Using Biogenic Residues as Feedstock.

Chemical looping gasification (CLG) is a novel dual fluidized bed gasification process that enables the conversion of solid feedstocks to a nitrogen-free syngas through in situ air separation, avoiding a costly air separation unit. While there have been recent advances in experimental studies, modeling of CLG is almost exclusively restricted to lab-scale units or 1D models. In this study, a 3D CFD-DEM model of a 1 MWth fuel reactor for the conversion of solid biomass was developed. Due to the high computational demand of the DEM method, a coarse-grained approach was used in combination with a simplified reaction network. The hydrodynamics were modeled with an EMMS drag model. Simulations were conducted for two woody biomasses and wheat straw based on experimental data of a 1 MWth CLG reactor. The model was able to predict the pressure profile over the reactor accurately, with a mean error below 10%. Carbon conversion and oxygen carrier oxidation were in good agreement with the experimental data with mean deviations below 5%, while reasonable values below 8 mol % mean error were achieved for the gas composition. Discrepancies in the gas composition as well as temperature profile indicate that further work is needed in the pyrolysis step of the model.

Low-emission hydrogen production from gasification of Australian coals – Process simulation and technoeconomic assessment

Although renewable energy-based technologies such as water electrolysis and biomass gasification for hydrogen production are cleaner than fossil energy-based routes, there are still prevailing challenges associated with the high cost and operational challenges in the scale-up of those technologies in the short term. Considering the abundance of coal as a current primary source of energy in Australia, the use of coal to produce hydrogen is not only in line with Australia's resource endowment but is also expected to become a supplement to the other hydrogen production pathways during the global energy transition period. This paper presents a comprehensive techno-economic assessment of low-emission hydrogen production from Australian coal gasification integrated with carbon capture and storage (CCS). The study explores four cases of hydrogen production, comparing Australian brown coal (Victorian brown coal) and black coal (Queensland black coal) gasification. Variations in gasifiers, gasification agents, and associated operating conditions contribute to differences in energy efficiency, costs, and CO2 emissions among the cases. The findings reveal a levelized cost of hydrogen from coal gasification ranging between A$4.12–4.90 per kg of hydrogen. Notably, entrained flow gasification of Victorian brown coal in a mixture of oxygen and steam environment demonstrates advantages under the current market conditions. However, less mature technologies like dual fluidized bed gasifiers could emerge as viable alternatives if deployed on a commercial scale. The study also addresses direct carbon emissions from the process, indicating a CO2 emission intensity range of 16.3–20.9 kg CO2/kg H2 without CCS and 0.1–1.1 kg CO2/kg H2 with CCS for the four cases. These insights contribute valuable information for decision-making in the pursuit of sustainable and economically feasible hydrogen production methods during the ongoing energy transition.

MFIX–DEM simulation of gas-solid flow dynamics in a dual fluidized bed system

Abstract To overcome the operational difficulties associated with bubbling and circulating fluidized bed gasifiers, a new gasification technology termed dual fluidized bed gasification (DFBG) has evolved. To strengthen the understanding of the gasification and combustion processes in the DFBG system, a thorough analysis of bed hydrodynamics is of paramount importance. Furthermore, the complexity of the hydrodynamics escalates while incorporating diverse fuels like biomass and coal, along with bed materials fluidized in a single reactor due to its nonlinearity and transience. As a result, the study of hydrodynamics in such a system is indispensable. The present study focuses on the discrete element model (DEM) simulation of the bed hydrodynamic behaviour within the gasifier of a DFBG system. The simulation was conducted using Multiphase Flow with Interphase eXchanges (MFiX) software. The influence of superficial velocity on the number of particles in a gasifier was analyzed using the 2-D discrete element model (DEM). In this numerical investigation, transient variation of pressure drop, axial and radial solid volume fraction, and particle velocity was evaluated, and the data were analyzed using the ParaView software. The simulation results of the gasifier indicated an increase in the bed pressure drop with the rise in inlet air velocity. The effective height of solid volume fraction also increased with the surge in superficial velocity. The solid velocity profile and streamlines were also investigated to understand its variation pertaining to the location within the fluidized bed.

MFiX-TFM simulation of hydrodynamics of a dual fluidized bed system

The abundance and replenishable nature of biomass make it a suitable fuel for power generation. Among the various technologies, dual fluidized bed gasification (DFBG) is a suitable technology to generate high-quality syngas from biomass. However, the complexity of hydrodynamics and heat transfer with bed geometry, flow conditions as well as feedstock demands effective research for the design of such system. This study, therefore, focuses on the simulation of hydrodynamics of a dual fluidized bed gasification system. The 2-D two-fluid model (TFM) simulations were performed using Multiphase Flow with Interphase eXchanges (MFiX) software by varying the superficial air velocities for both the gasifier and riser. The influence of superficial air velocity on static pressure, pressure drop, axial and radial voidage, solid velocities, and granular temperature was evaluated. From the simulations, it was observed that with the increase in superficial air velocities, there was an increase in the effective height of pressure drop (66%), voidage, and solid velocities of the gasifier. For the simulation of the riser, similar trends in the profile of hydrodynamic parameters were also observed. The optimum velocity for the gasifier and riser has been suggested to be between 0.15 and 0.35 m/s and 6–7 m/s, respectively.

Techno-Economic Potential of a Polygeneration System Integrated with Conventional or Hybrid Solar Dual Fluidized Bed Gasification Technology in an Australian Sugar Mill

Techno-Economic Potential of a Polygeneration System Integrated with Conventional or Hybrid Solar Dual Fluidized Bed Gasification Technology in an Australian Sugar Mill

Techno-economic analysis of small-scale ammonia production via sorption-enhanced gasification of biomass

Biomass gasification is a green and efficient pathway for lowering the carbon footprint of ammonia production. Decentralized, small-scale biomass gasification plants (<150 t NH3/day output) are more practical than large plants due to sustainable large-scale biomass supply constraints. Small-scale biomass gasification for ammonia production faces the challenges of high energy consumption and production costs. Process intensification through sorption-enhanced gasification (SEG) integrates steam gasification and in-situ CO2 separation using regenerable CaO sorbents, directly producing hydrogen-rich syngas (∼70 vol%), which streamlines syngas conditioning and increases cost-effectiveness. Two SEG process configurations for small-scale biomass-to-ammonia (∼45000 t of agricultural residues/year) were proposed: SEG process A, which produced low-carbon ammonia without air separation, and SEG process B, which employed an air separation unit to deliver carbon-negative ammonia by capturing CO2. The two processes were compared against a dual fluidized bed gasification (DFBG) process, which generated green ammonia without an air separation, like SEG process A. Of the three cases, SEG process B showed the lowest biomass (2.14 t biomass/t NH3) and water consumption (0.47 t H2O/t NH3) and avoided 2.8 t CO2/t NH3, making it carbon-negative. While the DFBG process and SEG process A had higher energy efficiencies, SEG process B posted the lowest net energy consumption (36.6 GJ/t NH3). Furthermore, SEG process B had the lowest ammonia production cost ($692/t NH3) and payback time (9.4 years), making it the most economically viable. Sensitivity analysis showed that favorable carbon credit policies could boost the economics of SEG process B to match large-scale plants.

Simulation of Olive Pomace Gasification for Hydrogen Production Using Aspen Plus: Case Study Lebanon

Biomass is a renewable energy source gaining attention for its potential to replace fossil fuels. Biomass gasification can produce hydrogen-rich gas, offering an environmentally friendly fuel for power generation, transportation, and industry. Hydrogen is a promising energy carrier due to its high energy density, low greenhouse gas emissions, and versatility. This study aims to develop a hydrogen generation plant using a dual fluidized bed gasifier, which employs steam as a gasifying agent, to convert olive pomace waste from the Lebanese olive oil industry into hydrogen. The process is simulated using Aspen Plus and Fortran coding, and it includes a drying unit, gasification unit, gas cleaning unit, steam methane reformer unit, water–gas shift reactor unit, and a pressure swing adsorption unit. The generated gas composition is verified against previous research. Sensitivity analyses are conducted to investigate the impacts of the steam-to-biomass ratio (STBR) and gasification temperature on gas composition, demonstrating a valid STBR range of 0.5 to 1 and a reasonable gasification temperature range of 700 °C to 800 °C. Further sensitivity analyses assess the impact of reformer temperature and the steam-to-carbon ratio (S/C) on the gas composition leaving the steam methane reformer.

Model predictive control of a dual fluidized bed gasification plant

Dual fluidized bed (DFB) gasification is a promising method for producing valuable gaseous energy carriers from biogenic feedstocks as a substitute for fossil fuels. State-of-the-art DFB gasification plants mainly rely on manual operation or single-input single-output control loops, and scientific contributions only exist for controlling individual process variables. This leaves a research gap in terms of comprehensive control strategies for DFB gasification. To address this gap, we propose a multivariate control strategy that focuses on crucial process variables, such as product gas quantity, gasification temperature, and bed material circulation rate. Our approach utilizes model predictive control (MPC), which enables effective process control while explicitly considering process constraints. A simulation study is given demonstrating how different MPC parametrizations influence the behavior of the closed-loop system. Experimental results from a 100kW pilot plant at TU Wien demonstrate the successful control achieved by the proposed control algorithm.

Numerical Study on the Steam Gasification of Biomass in a 100 kW Dual Fluidized Bed Gasifier

Numerical Study on the Steam Gasification of Biomass in a 100 kW Dual Fluidized Bed Gasifier

Thermodynamic analysis of small-scale polygeneration systems producing natural gas, electricity, heat, and carbon dioxide from biomass

Agricultural greenhouses are still heavily dependent on fossil fuel-based products despite the abundant residual biomass at their disposal. This paper presents two novel decentralized systems that can convert biomass simultaneously into synthetic natural gas (SNG), electricity, useful heat, and a CO2-rich stream. To do so, the electricity and H2/O2 production features of reversible solid oxide cells (RSOCs) are exploited. A steam dual fluidized bed (DFB) gasifier is used in the first proposed system, while the second one adopts a simpler oxygen/steam-blown downdraft gasification approach. Thermodynamic simulations using Aspen Plus software reveal that the total polygeneration process efficiency could reach 86.6%, with a CO2 generation capacity exceeding 275g per kilogram of biomass input. If not used inside the greenhouse atmosphere to enhance crop growth, this high-purity CO2 stream could be sequestered/liquefied to render the process carbon negative. The flexibility of the polygeneration systems is investigated through parametric analysis, where maximum SNG efficiencies that are on par with large-scale plants are obtained. The possibility of storing surplus electricity from intermittent sources as chemical energy in SNG is also highlighted.

Gaussian Process Regression-Based Control of Solids Circulation Rate in Dual Fluidized Bed Gasification

Gaussian Process Regression-Based Control of Solids Circulation Rate in Dual Fluidized Bed Gasification

Enrichment of fuel properties of biomass using non-oxidative torrefaction for gasification

The abundance and replenishment nature of solid biomass prompt fuel substitution for gasification and thermal power plants. However, many challenges are encountered while utilizing raw biomass, such as seasonality, strong hydrophilicity, low bulk and energy density, excess oxygen content, less compositional homogeneity, and poor grindability. It is, therefore, indispensable to augment the thermo-chemical properties of the solid biomass by performing suitable pretreatment. Among the various pretreatment techniques, non-oxidative torrefaction effectively upgrades solid biomass to coal-like fuel altering its physico-chemical properties. Therefore, in this work, torrefaction of rice husk and sugarcane bagasse have been performed in a fixed bed reactor by varying temperatures from 210–330 °C and residence time from 30–60 min under a non-oxidative environment. The experimental investigation illustrates a decrease in mass and energy yield of the biomass with a rise in temperature and residence time. Conversely, the higher heating value of rice husk and sugarcane bagasse has improved by 119.4% and 128.9%, respectively. The hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C) ratio of the torrefied biomass has reduced to enriched fuel variety as indicated by the van Krevelen plot. The decomposition and structural modifications were assessed using Fourier transform infrared spectroscopy, x-ray diffraction, and morphology analysis. Based on the experimental observations, it has been found that torrefaction of rice husk at 290 °C and 30 min and sugarcane bagasse at 270 °C and 30 min would generate enriched syngas using a dual fluidized bed gasification system. Furthermore, water gas shift reactions will be promoted to enhance the percentage of hydrogen in the gas mixture.

Numerical investigation on the influence of immersed tube bundles on biomass gasification in industrial-scale dual fluidized bed gasifier

Immersed tubes play a pivotal role in enhancing fluidization quality within fluidized beds by effectively disrupting bubbles. However, the effect of such internals within a large-scale gasification apparatus remains unclear. Consequently, this study focuses on numerically simulating biomass steam gasification within an industrial-scale dual fluidized bed gasifier that features immersed tube bundles using the multiphase particle-in-cell method. In this method, particles with identical properties are grouped, and the interparticle collisions are model via the solid stress to improve computational efficiency. The numerical model has been well verified with experiment in terms of bed pressure drop, solid recirculation and chemical reactions. Some main conclusions are shown as follows. Immersed tubes significantly alter the motion of gas and particles in the gasifier. The presence of immersed tubes can ameliorate solid entrainment and avoid excess particles escaping from the gasifier. The asymmetrical structure of the gasifier results in asymmetrical distribution of gas temperature and gas species. Increasing the number of immersed tubes slightly enhances particle temperature near the loop seal outlet. The radial biomass dispersion coefficient and axial sand dispersion coefficient decrease about 40.9 % and 28.9 % when increasing the immersed tube number from three to nine. The results provide enhanced understanding of the role of immersed tubes in altering gas-particle interactions and fluidization dynamics in industrial-scale fluidized bed gasifier.

System Hydrodynamics of a 1 MWth Dual Circulating Fluidized Bed Chemical Looping Gasifier

Chemical looping gasification (CLG) is a novel dual-fluidized bed gasification technology that allows for the production of high-calorific syngas from various solid feedstocks (e.g., biomass). Solid circulation between the two coupled fluidized bed reactors, serving the purpose of heat and oxygen transport, is a key parameter for the CLG technology, making system hydrodynamics the backbone of the gasification process. This study serves the purpose to provide holistic insights into the hydrodynamic behavior of the dual-fluidized bed reactor system. Here, special focus is placed on the operational principles of the setup as well as the entrainment from the circulating fluidized bed (CFB) reactors, the latter being the driving force for the solid circulation inside the entire reactor system. Using an elaborate dataset of over 130 operating periods from a cold flow model and 70 operating periods from a 1 MWth CLG pilot plant, a holistic set of ground rules for the operation of the reactor setup is presented. Moreover, a novel easily-applicable approach, solely relying on readily-available live data, is presented and validated using data from the 1 MWth chemical looping gasifier. Thereby, a straightforward estimation of solid entrainment from any CFB setup is facilitated, thus closing a crucial research gap.

Experimental investigation of hydrogen-intensified synthetic natural gas production via biomass gasification: a technical comparison of different production pathways

A sustainable and secure energy supply requires alternative concepts for energy generation. Utilizing biomass to produce synthetic natural gas (SNG) allows the synthesis of a currently widely used energy carrier on a renewable basis. The additional integration of hydrogen increases the carbon utilization of the biomass. This study experimentally investigates and compares the production of raw-SNG in three novel process chain configurations combining the advanced dual fluidized bed (DFB) gasification technology, gas cleaning units, and a fluidized bed methanation reactor. The three process chains comprise the direct methanation of DFB product gas, a hybrid route with hydrogen addition to the DFB product gas, and the methanation of a hydrogen-enriched product gas generated through DFB gasification with in situ CO2 removal (SER process). The direct methanation of the DFB product gas yielded a raw-SNG CH4 content of 40 vol.-%db at 360 °C and atmospheric pressure conditions. Through the integration of external hydrogen in a hybrid process, the carbon utilization of the biomass could be increased from 37% to around 70% at an unchanged cold gas efficiency of 58–59%. Via the SER process, a high raw-SNG CH4 content of 70 vol.-%db was achieved at an increased cold gas efficiency of 66% without the need for external hydrogen. Finally, a comparison points out the main advantages of the process configurations and provides a decision basis for novel SNG production pathways.

Numerical study of the biomass gasification process in an industrial-scale dual fluidized bed gasifier with 8MWth input

In the present numerical study, biomass steam gasification in industrial-scale dual fluidized bed gasifier with 8MWth input is numerically simulated via the multiphase particle-in-cell (MP-PIC) method, where the gas turbulence is controlled via large eddy simulation (LES), and the solid phase is tracked under the Lagrangian framework. This model has been well validated with experimental measurement. The gas and solid fluxes, gas distribution, gas and solid thermal properties together with the effect of solid inventory and steam-to-biomass ratio on the system performance are discussed in detail. Results show that the asymmetrical structure of the gasifier leads to a nonuniform distribution of gas phase. Product gases released in the gasifier have similar distributions. The vertical gas flux is much higher than those along radial directions, due to the fluidization characteristics. A decrease of the vertical gas temperature in the combustor and an increase of that in the gasifier are observed due to the improvement of solid circulation rate and heat transfer raised by increasing the solid inventory. Enlarging the solid inventory can increase the particle mean temperature at gasifier outlet while decreases that at gasifier inlet, and decrease the sand temperature and heat transfer coefficient along the combustor height. Moreover, the impact of inventory height and S/B on gas thermal properties in both reactors is discussed.

Minimum-Variance Model Predictive Control for Dual Fluidized Bed Circulation Control

Dual fluidized bed steam gasification enables the production of gaseous energy carriers from woody biomass or biogenic residues. The circulation of bed material in dual fluidized bed gasifiers strongly affects the process behavior. Therefore, precise control of the bed material circulation is desired. This paper presents a control algorithm addressing two aspects of the given problem setting: On the one hand, redundant control actuators are available. Typically, there are several air streams to the reactors influencing the bed material circulation. On the other hand, only black box models with uncertainties in their model parameters are available for model-based control design. The presented control algorithm uses a model predictive controller considering known uncertainties in the model parameters and drives the process in a region with the lowest model uncertainties. This results in an improvement of the closed-loop performance when the actual plant deviates from the internal model used for the model predictive control predictions. Simulations show 66 % less offset from the design trajectory with the presented algorithm when compared to a standard model predictive controller.

Effect of biomass ash on preventing aromatization of olefinic cracking products in dual fluidized bed systems

In this work, the effect of ash activated olivine on olefinic products cracking and aromatization was assessed. The experiments were carried out in the Chalmers 2–4 MWth dual fluidized bed gasifier, where the feedstock was cracked using steam as fluidization agent, at a reaction temperature of ca. 780–790 °C. Three activation states of the olivine, representing three consecutive days of the campaign, were evaluated. The changes of the permanent gas composition along with the reduction in aromatic species with the time of exposure to biomass ash demonstrate a clear effect of the ash activated olivine on the conversion of olefinic cracking products. The ash activation of the olivine clearly promoted the reactions involving steam. As a consequence, higher yields of permanent gases, mainly H2, CO and CO2, were produced at expenses of the yields of the total aromatic compounds and C4 hydrocarbons and larger. It is concluded that the biomass ash activated olivine promotes the steam reforming path of the C4 and larger hydrocarbon fragments, while avoiding the alternative aromatization route. The results presented here provide useful insights on the opportunities and limitations of ash activated materials in DFB systems when steam cracking linear hydrocarbon feedstocks, e.g., polyolefin-based materials.

Design and performance analysis of a solar dual fluidized bed gasifier

The potential to conduct allothermal steam-gasification of biomass using a dual fluidized bed gasifier (DFBG) assisted by solar energy has already been conceptually proposed. In this paper the design and operation of a solar DFBG (SDFBG) device to deal with this concept is assessed by modeling, considering thermodynamic, kinetic and fluid-dynamic issues. The challenges identified in previous works, as well as the modifications required in the current state-of-the-art technologies of (no-solar) DFBG for implementing the new solution using heated particles as heat carriers, are worked out. Two SDFBGs, considering different arrangements for integrating the solids carrying the solar energy into the system, are designed. The operation of both under different solar-external heat loads, from autothermal operation (no external heat) to 3 MJkgbio,daf−1 of external heat, is assessed and compared. This work shows how the technology can be implemented and scaled up.

Dynamic modeling of dual fluidized bed steam gasification for control design

Dual fluidized bed steam gasification allows the production of high-value product gas from woody biomass or biogenic residuals. Advanced control concepts such as model predictive control are promising approaches to improve the process performance and efficiency. These control techniques require dynamic models of the process that can predict the plant’s behavior as a function of the manipulated variables. This paper presents a gray-box modeling approach based on mass and energy balances to obtain a mathematical description of the temperatures inside the two reactors and the total mass flows leaving the reactors. The model incorporates data-driven components where first-principle modeling is hardly possible with reasonable effort. An artificial neural network is utilized to model the bed material circulation between the two reactors. Experiments were carried out at a 100 kW pilot plant to generate measurement data both for system identification and model validation. Simulations verify that the model achieves reliable predictions for the dual fluidized bed gasification process.