Fluidized Bed Gasifier Research Articles

Hydrogen Production by Fluidized Bed Reactors: A Quantitative Perspective Using the Supervised Machine Learning Approach

The current hydrogen generation technologies, especially biomass gasification using fluidized bed reactors (FBRs), were rigorously reviewed. There are involute operational parameters in a fluidized bed gasifier that determine the anticipated outcomes for hydrogen production purposes. However, limited reviews are present that link these parametric conditions with the corresponding performances based on experimental data collection. Using the constructed artificial neural networks (ANNs) as the supervised machine learning algorithm for data training, the operational parameters from 52 literature reports were utilized to perform both the qualitative and quantitative assessments of the performance, such as the hydrogen yield (HY), hydrogen content (HC) and carbon conversion efficiency (CCE). Seven types of operational parameters, including the steam-to-biomass ratio (SBR), equivalent ratio (ER), temperature, particle size of the feedstock, residence time, lower heating value (LHV) and carbon content (CC), were closely investigated. Six binary parameters have been identified to be statistically significant to the performance parameters (hydrogen yield (HY)), hydrogen content (HC) and carbon conversion efficiency (CCE) by analysis of variance (ANOVA). The optimal operational conditions derived from the machine leaning were recommended according to the needs of the outcomes. This review may provide helpful insights for researchers to comprehensively consider the operational conditions in order to achieve high hydrogen production using fluidized bed reactors during biomass gasification.

Thermodynamic analysis of novel methanol polygeneration systems for greenhouses

This work presents the modeling and thermodynamic analysis of two novel small-scale polygeneration systems that are capable of simultaneously converting residual biomass to methanol (MeOH), electricity, heat and a CO2-rich stream for agricultural greenhouses. The first system is based on a downdraft gasifier, while the second relies on a dual fluidized bed (DFB) gasifier. Both configurations leverage the H2, O2, and electricity generation capabilities of reversible solid oxide cells (RSOCs). The Aspen Plus process simulator is used to model the thermodynamic performance of the proposed polygeneration systems, which operate at total efficiencies ranging from 83.9 to 85.0%. From a biofuel and electrical efficiency perspective, the system based on a DFB gasifier is superior, providing the added benefit of enabling carbon capture and storage, as a N2-free stream with a molar purity exceeding 90% CO2 is generated, which could be readily liquefied or sequestered.

Effect of Tar-adsorbing Particles on Tar Components Generated by Lignite Gasification in a Fluidized Bed Gasifier

In a dual fluidized bed gasifier suitable for gasification of lignite, tar is generated as the raw material is gasified because the gasification reaction has at 1073-1173 K, which is a relatively low temperature, and there is a problem such as tar adhering to the piping of the cooling system in the subsequent stage. In this study, in order to reduce tar in the gasification of lignite, porous alumina particles were applied as a tar adsorbent to the upper stage of a laboratory-scale two-stage fluidized bed gasifier, and the gasification characteristics of the produced gas and the tar components were analyzed and its effect was investigated. From the analysis results of tar components using gas chromatograph mass spectrometry (GC/MS) and field desorption mass spectrometry (FD-MS), the tar components obtained under the respective gasification conditions of pyrolysis and steam were almost no difference, and the main components of tar were polycyclic aromatic hydrocarbons without substituents. It was also found that the main components of tar can be sufficiently identified by GC/MS analysis alone. The application of the porous alumina particles increased the gas yields due to the cracking effect of tar. Furthermore, it was confirmed that the gas yields increased under the steam gasification condition rather than pyrolysis condition, and the gasification reactions were promoted by steam. From these results, it is considered that the porous alumina particles are effective in reducing tar, and as a reformer using this, a dual-type reformer capable of using the tar adsorbent for a long period of time is suitable.

Investigation of hydrodynamics and segregation characteristics in a dual fluidized bed using the binary mixture of sand and high-ash coal

The cold flow hydrodynamics and segregation characteristics of a binary mixture of high-ash coal and sand have been investigated in a dual fluidized bed(DFB) gasifier. A short riser, maintained in the fast-fluidized bed regime by different combinations of primary and secondary aerations, is used. The influence of fluidization velocities, secondary-to-primary aeration ratio (φ), particle mixture properties has been examined on the full-loop pressure profile, solids circulation rate (Gs), and segregation characteristics. A substantial influence on DFB pressure profiles is observed for the polydisperse binary mixture compared to unary sand particles having a narrow particle size distribution. Coarse particle fractions measured at loop-seal and pot-seal indicates significant segregation in the riser and the BFB, which reduces as fluidization velocities increase. Variations in Gs and φ show a minimal impact on particle segregation. No reverse gas bypass is detected for the designed operating parameters through solids recycle valves, namely loop-seal and pot-seal. Except for some discrepancies observed at high superficial velocities and Gs, the values of axial solids holdup in the riser yield a reasonable agreement between experiments and a hydrodynamic model based on empirical correlations.

Numerical study of fluid dynamics and heat transfer property of dual fluidized bed gasifier

In this work, the Eulerian-Lagrangian multiphase particle-in-cell approach is adopted to track the reactive gas-solid motion in the biomass gasification of dual fluidized bed gasifier. Firstly, the mole fraction of dry gaseous products obtained at the gasifier outlet is evaluated and compared with the experimental measurement to prove the accuracy and adaptability of numerical model. Then, the gasification properties of biomass together with the influence of operating parameters in the full-loop system are studied. The results demonstrate that the gas-solid flow with a large particle Reynolds number and vertical flux is relatively fast in the combustor. The combustible gaseous species generated in the biomass gasification mainly locate in the upper part of bubbling fluidized gasifier. Particle temperature is the largest in the standpipe of the full-loop apparatus. Vigorous heat exchange between gas and solid phase occurs in the combustor. Moreover, the heat transfer coefficient of solid phase in the combustor is apparently higher than that in the gasifier. Increasing the steam/biomass ratio and biomass flow rate enlarges the heat transfer coefficient of particles in the bubbling fluidized gasifier but slightly impacts that in the combustor. The results obtained provide meaningful insights for further study of the complex dual fluidized reactor.

Circulating fluidized bed gasification of solid recovered fuels - Results from gasification and gas filtration tests

Fluidized bed gasification technology offers an attractive way to use inhomogeneous biomass residues and various waste-derived feedstocks in power and heat production as well as in various circular economy concepts based on the synthesis gas route. A fluidized bed gasification process development (PDU) plant of 200 kW capacity was operated with Solid Recovered Fuels (SRFs) and demolition wood. In part of the tests carried out with SRF, deposits were formed in the gas lines, and the pressure drop of the filter increased as well. However, optimal combination of gasification, gas cooling and filtration conditions were found to achieve a stable pressure drop, avoid deposit formation and to achieve efficient removal of gas contaminants. The effects of the operating conditions on the achieved carbon conversion and formation of tars and other gas contaminants were studied. The produced gas was filtered at 370-500 °C using two alternative filtration systems applying ceramic bag filters or ceramic fiber filters. The removal efficiency of waste-derived trace metals and chlorine was determined at different filtration temperatures.

Production of synthesis gas from biomass residues by staged fixed-bed gasification - results from pilot test campaigns

Fluidized-bed and entrained-flow gasification systems are developed for large-scale synthesis gas applications with at least 100 MW biomass input. However, there is also a market need for smaller-scale plants, which could be better integrated into energy production systems and local biomass logistics. The staged fixed-bed (SXB) gasifier described in this paper targets a size range of 10-50 MW of feedstock input. The primary gasification stage occurs in an updraft fixed bed. The tar-containing updraft gas is further processed in the secondary gasification zone, where gas temperature is raised from 200-500 °C to 750-900 °C by feeding secondary oxygen through a specially designed catalytic distributor zone. The composition and tar content of the resulting raw gas is similar to that of fluidized-bed gasifiers. Consequently, hot gas filtration, catalytic reforming and final gas cleaning technologies, similar to those recently developed and demonstrated for fluidized-bed gasifiers, can be applied. The results from the 0.5 MW pilot gasification tests carried out with wood, bark and sunflower husk pellets are presented in this paper.

Release Behavior of Sulfur during Fluidized Bed Gasification

Release Behavior of Sulfur during Fluidized Bed Gasification

Catalytic gasification of coal in a decoupled dual loop gasification system over alkali-feldspar

The catalytic gasification of Yuyang coal for the production of hydrogen-rich syngas has been performed in a novel decoupled dual loop gasification system using alkali-feldspar as an in-situ catalytic bed material. This experimental setup is comprised of a fluidized bed gasifier (FBG), a moving bed reformer (MBR), a riser combustor (RC) and a particle grading cyclone (PGC). By the PGC, two loops, i.e. a gasification loop with quartz sand as circulating bed material between the FBG and the RC and a reforming loop with alkali-feldspar as circulating bed material between the MBR and the RC, are formed. The effects of process parameters such as reformer temperature (700–850 °C), steam/coal ratio (S/C) (0.6–1.5) and air equivalence ratio (ER) (0.15–0.30) on the composition of product gas, lower heating value (LHV), tar content, yield of product gas, the carbon and water conversions and the cold gas efficiency were investigated. At the reformer temperature of 850 °C, the lowest tar content 5.8 g/Nm3 and the maximum yield of product gas 1.0 Nm3/kg daf were obtained. The addition of steam increased the H2 yield. The maximum hydrogen concentration of 65.1 vol% in product gas was attained at the S/C ratio of 1.5. Oxygen as a part of gasification agent led to the rise of CO2 concentration from 24.3 to 46.3 vol% and the reduction of H2 concentration from 54.4 to 33.0 vol% with the increase of ER from 0.15 to 0.30.

Transformation of inorganic matter in poultry litter during fluidised bed gasification

This work investigates the transformation, release and fate of inorganic matter during fluidised bed gasification of poultry litter and also poultry litter mixed with limestone as an additive. The poultry litter, the cyclone and bed ash were characterised by means of chemical fractionation analysis, as well as X-ray diffraction. Concurrently, the release of inorganic species during gasification of the feedstock was measured in separate laboratory experiments using molecular beam mass spectrometry. In addition, FactSage was used to predict the formation of gaseous species and the composition of solid residues from gasification under equilibrium conditions. On average, the cyclone ash accounts for 4.6 wt% and the bed ash 12.4 wt% of the total poultry litter fed into the reactor. All phosphorous (P) was present in the cyclone ash as stable phosphates, while potassium (K) in both cyclone and bed ash was mainly present as H2O leachable KCl, organically associated and stable phosphates and silicates. Furthermore, an assessment was made against the appropriate criteria, whether the ashes from gasification can be categorised as component materials for EU fertiliser products.

CFD study of the thermochemical characteristics of mesoscale bubbles in a BFB gasifier

Using the computational fluid dynamic model based on the multiphase particle-in-cell approach, reactive gas-solid flows in a three-dimensional bubbling fluidised bed gasifier regarding coal gasification is simulated. The predicted results of gas components are firstly validated with experimental measurements. Subsequently, the dynamics (e.g. chord length, aspect ratio, velocity, volume) together with the essential thermal features (e.g. temperature, pressure, density, viscosity, conductivity, specific heat capacity) of mesoscale bubbles are explored. Bubbles in the central part of the gasifier have a large lateral chord length and volume. The restriction effect of the gasifier wall elongates the vertical chord length and enlarges the aspect ratio of bubbles close to the wall. The density and pressure of bubbles decrease along with the bed height, and the thermochemical properties of bubbles are strongly related to bubble temperature. A large content of the CO2 exists for those bubbles close to the bed surface. The gas velocity, operating pressure and gasifying agent obviously affect the bubble property, while the effects of inlet gas temperature and coal flow rate are relatively weak. The results obtained provide meaningful insight regarding the mesoscale structures involved in fluidised bed coal gasification.

Evolution of carbon microstructure and gasification activity during rice husk gasification

In order to investigate the evolution of carbon microstructure and gasification activity during circulating fluidized bed gasification, the simulated circulating gasification of a rice husk was carried out in a laboratory fixed bed reactor, and the pore structure, carbon microstructure and gasification activity of char during gasification were investigated. The results show that the BET surface area of char increases firstly and then decreases with an increase in gasification cycle times, and the surface areas of rice husk chars obtained from circulating gasification process are much higher than that of original char. The ID1/IG values of char decrease monotonously with an increase in gasification cycle times, indicating that the graphitization degree of carbon structure in char increases. Meanwhile, the relative content of AD3+D4 of char decreases firstly and then increases slightly with the progress of circulating gasification, and the relative contents of AD3+D4 of all chars obtained from a circulating gasification process are lower than that of original char. Moreover, the gasification activity of char increases gradually with an increase in gasification cycle times, and the gasification activity of all chars obtained from a circulating gasification process are higher than that of original char.

Replacement of Palm Methyl Ester to Rapeseed Methyl Ester for Tar Removal in the Nong Bua Dual Fluidized Bed Gasification Power Plant

The blockage problem of tar in a biomass power plant is a main problem and it must be removed. Rapeseed methyl ester (RME) was imported and used as scrubbing solvent to scrub tar at a 1 MWel Nong Bua prototype Dual Fluidised Bed (DFB) gasifier in Nong Bua district, Nakhonsawan province, Thailand. Using local oil in Thailand is an attractive choice from economic viewpoint. Pervious lab test study on naphthalene solubility in different local oils in Thailand was investigated. Local palm methyl ester (PME) shows the competitive performance to the RME. In this research, PME was tested to scrub tar in an oil scrubber at the Nong Bua DFB gasifier plant. Gravimetric tar content after passed a PME scrubber was measured and compared to that from a RME oil scrubber. The results show that both solvents have similar tar removal performance due to their contents of ester, methanol, and glycerin are similar. In addition, viscosity of both solvents has no significant effect on tar removal. From the current research, therefore, PME has been used as solvent in an oil scrubber at 1 MWel Nong Bua prototype DFB gasifier with technical and economic reasons.

Polyethylene terephthalate (PET) recycling via steam gasification - The effect of operating conditions on gas and tar composition.

Polyethylene terephthalate (PET) is widely used in textile fiber, film, and bottles. Although PET bottle recycling has made great progress, other PET waste is still not recycled. Gasification could be an option for recycling or recovering energy and chemicals from PET waste. However, single stream PET steam gasification in fluidized bed is seldom investigated. In this paper, individual PET gasification experiments were then conducted in a lab-scale bubbling fluidized bed to investigate how gasifying agents, temperature, residence time and steam/fuel ratio affect the product composition. The results showed that, in steam gasification, steam was the main source of H2, but increasing the steam to fuel ratio cannot increase the H2 yield remarkably. Temperature was an essential parameter. Increasing temperature from 750 to 800°C improved the yields of H2 (+87.7%), the dominant gas product CO2 (+40.3%), and biphenyl (+123%) notably. In contrast to other common thermoplastics, high concentrations of CO2 and biphenyl are the prominent characteristics of PET steam gasification. In addition, plastic steam gasification optimizations for syngas applications were discussed.

CFD analysis of biomass steam gasification in fluidized bed gasifier: A parametric study by the assessment of drying stage

ABSTRACT In this study, CFD analysis was performed based on a comprehensive pyrolysis chemical reaction model to simulate the gasification process of biomass in a fluidized bed gasifier using almond shells as the biomass feedstock. A novel multi-phase CFD model consisting of 33 chemical reactions that cover all of the drying stages, detailed primary and secondary pyrolysis stages, as well as gasification stage, was adopted for the first time. Gasification temperature and steam-to-biomass ratio were selected as the main parameters and their effects on produced gas composition, lower heating value, char yield, tar content, and tar components were evaluated. The obtained results of the base case agreed to a reasonable extent with the results of the previous experimental works. According to the results, an increase in gasification temperature enhanced the mole fractions of H2 and CO. Therefore, it was recommended to use higher temperatures and steam-to-biomass ratio for production purposes of H2 and CO. The lower heating value decreased by a factor of 14.7% and 1.86% for increased values of gasification temperature and steam-to-biomass ratio, respectively. It was also observed that CH4 mole fraction has a strong effect on the lower heating value of the produced gas. Furthermore, char yield was found to have a declined trend with increasing gasification temperature; however, the reverse was valid with increasing steam-to-biomass ratio.

Performance investigation of a non-combustion heat carrier biomass gasifier for various reforming methods of pyrolysis products

ABSTRACT Conventional biomass gasifiers such as fixed bed gasifiers, fluidized bed gasifiers, and entrained flow gasifiers have been widely studied in the literature covering biomass gasification systems. However, there are few published studies on non-combustion heat carrier biomass gasifier technology in the literature. Therefore, further studies are needed to reveal potential advantages, disadvantages, and possible improvement opportunities for this gasifier type. In this work, we investigate the effects of various operating parameters: reformation temperature, steam-to-biomass ratio, and steam-to-oxygen ratio on important performance indicators of non-combustion biomass gasifiers. To estimate the pyrolysis products, we use stoichiometric methods based on published data in the literature. The reforming of pyrolysis products is estimated using the Gibbs free energy minimization method using Aspen Plus. In addition, calculator blocks, sensitivity blocks, and design specifications are used to obtain the results. The results reveal that the desired hydrogen to carbon monoxide ratio can be obtained for steam reforming and autothermal reforming of pyrolysis products while a low hydrogen-to-carbon ratio (less than 1.5) is obtained for partial oxidation of pyrolysis products. However, partial oxidation can be beneficial in increasing the heating value of the syn-gas. The results presented in this study will be useful in improving the current configuration of non-combustion heat carrier biomass gasifiers. In future studies, the effects of gasifying agents on the tar content of the syn-gas, impurities in the syn-gas, start-up time of the gasifier, and size of the gasifier should be investigated.

Fluid dynamic analysis of dual fluidized bed gasifier for solar applications

A hydrodynamic model of a dual fluidized bed gasifier (DFBG) is developed and its predictions are compared with measurements of solids flux and pressure profiles from a cold flow model (CFM). Then, the performance of a DFBG gasifier is theoretically analyzed in terms of solids circulation and solids distribution under changes in riser and loop seal aeration, solids inventory and particle size, and a sensitivity analysis is made to delimit the model prediction capability. Furthermore, the model is applied to analyze the effects of key design aspects of DFBG, such as the relative size of riser and gasifier, the connection between both units, the circulation rate of solids and their distribution around the system. The model is further used to extend the DFBG operation with external solar energy carried by heated solid particles, i.e. to design solar DFBG (SDFBG). The analysis is focused on the performance with high solids inventory in the gasifier to increase the char conversion (operation with a large solar share) and the control of solids circulation to meet the heat demand of the gasifier with the availability of solar energy. The operation with large solids inventory in the gasifier requires the size of the gasifier to increase considerably compared to that of the conventional DFBG. The substitution of the connection pipe between the riser and the bubbling bed (current design in commercial DFBG) by a lower loop seal enables better control of the solids circulation, thus, benefiting the solar design.

Influence of Gasification Operating Parameters on Performance of the Nong Bua Dual Fluidized Bed Gasification System in Thailand

Gasification system performance generally depends on feed moisture content, activity of bed material, gasifier and combustor temperatures, and scrubber media. The tar concentration and gas composition of product gas are two indicators of the gasification system performance. In this research, the effects of gasifier temperature and the activity of bed material on the tar concentration and gas composition of the product gas produced from a dual fluidized bed (DFB) gasification system power plant were investigated. The DFB gasification system power plant is located in Nong Bua district, Nakhon Sawan province, Thailand. Two periods of gasification operation were examined. These two periods were when the olivine was freshy activated and then after a period of operation. The gasifier temperature had several peaks during the operation, which caused the product gas composition to fluctuate. When the olivine had been used for a period, the percentage of hydrogen was approximately 3% higher than when the olivine had been freshly activated, and a lower heating value was observed, which was probably due to lower heating value of hydrogen. The tar concentration was substantially lower when compared with the freshly activated olivine. When the olivine was used for a period, the average tar concentration was 56±22 mg/Nm3 (this is after 95 h continuous operating time) while the average tar concentration of the freshly activate olivine was 872±125 mg/Nm3 (which was after 34.5 h continuous operating time). It was concluded that the average tar concentration and gas composition were influenced by the activity of the bed material and the gasification temperature.

Development of Oxygen Transport Properties by Olivine and Feldspar in Industrial-Scale Dual Fluidized Bed Gasification of Woody Biomass

In dual fluidized bed (DFB) gasification, the interaction of the bed material with the fuel ash leads to the development of a bed catalytic activity toward tar-abating reactions. However, the formation of ash layers may also be detrimental to the process, especially in terms of the uncontrolled transport of oxygen from the combustor to the gasifier. A few previous studies investigating the development of catalytic activity in bed materials have also reported the development of oxygen transport, although the latter was not the focus of these studies. This work verifies that olivine and feldspar, which are bed materials with limited and no intrinsic oxygen transport capacities, respectively, develop the capacity to transport oxygen by interacting with the fuel ash. We correlate this development in oxygen transport to the development of bed catalytic activity. Our results imply that the volatile species that are released by the bed material to the gas phase in the gasifier contribute to the developed oxygen transport. Sulfur is proposed as one of the components of these volatile species, and its potential contribution is investigated. For feldspar, the results support the notion that sulfur is involved in the transport of oxygen, both as a volatile species and as a species remaining within the ash layer. The results also suggest that other species, including volatile ones, are involved. These aspects are investigated based on experimental results obtained from the Chalmers gasifier—a semi-industrial-scale DFB gasifier—and are isolated in laboratory-scale experiments.

Iron-based catalyst (Fe2-xNixTiO5) for tar decomposition in biomass gasification

In this study, a novel Fe2-xNixTiO5 catalyst for potential applications in biomass gasification gas cleaning/upgrading was investigated. The material was successfully synthesized through combined mechanical activation and microwave firing. Catalytic steam reforming was studied in a fixed bed tubular reactor, using a mixture of toluene and naphthalene as model tar compounds as well as downstream a fluidized bed gasifier. Fe2-xNixTiO5 catalyst showed high activity in converting the model compounds at temperatures higher than 700 °C. The catalyst exhibited a tar conversion of 78% at 800 °C when exposed to biomass-derived gas from a bubbling fluidized bed gasifier. Nevertheless, the catalytic activity declined with increased time on stream due to structural changes in iron active phases, caused by redox conditions of the producer gas. Furthermore, thermodynamic calculations suggest that sulfur chemisorption on the nickel surface, may also contribute to the catalyst deactivation.