Fluidized Bed Material Research Articles

Two-fold advancement in LDPE Pyrolysis: Enhancing light oil output and substituting sand with kaolin in a fluidized bed system

Low-density polyethylene (LDPE) is the second most prevalent waste plastic globally, followed by polypropylene. The pyrolytic conditions required to obtain light oil(≤C12) from LDPE are more stringent than those for polypropylene, water plastics, acrylonitrile, butadiene, styrene, and other materials. Consequently, numerous researchers have underscored the necessity of employing catalysts in LDPE pyrolysis. This study explored the pyrolysis characteristics of LDPE at various temperatures in a non-catalytic fluidized bed reactor. The experiments employed a mixture of sand + kaolin, one of the Si-Al catalysts, to investigate the pyrolysis of LDPE in a fluidized bed reactor at different temperatures. The findings demonstrated that using sand + kaolin as a fluidized bed material significantly enhances the yield of pyrolysis oil while concurrently reducing the gas yield compared to using sand alone. Moreover, a higher light oil fraction was obtained using kaolin (16.67 wt%) at 560 °C compared with 8.6 wt%. In addition, the study revealed that elevated temperatures (520 °C, 560 °C, and 600 °C) led to a reduction in olefins and paraffin, coupled with an increase in the formation of naphthenes, aromatics, and ketones in the pyrolysis oil. Overall, the findings underscore the promising potential of kaolin as an alternative to sand, facilitating the enhanced production of valuable light oil fractions. The insights garnered from this study are invaluable for devising effective waste management strategies.

Alkali desorption from ilmenite oxygen carrier particles used in biomass combustion

Oxygen-carrying fluidized bed materials are increasingly used in novel technologies for carbon capture and storage, and to improve the efficiency of fuel conversion processes. Potassium- and sodium-containing compounds are released during biomass combustion and may have both negative and positive effects on conversion processes. Ilmenite is an important oxygen carrier material with the ability to capture alkali in the form of titanates. This is a desirable property since it may reduce detrimental alkali effects including fouling, corrosion, and fluidized bed agglomeration. This study investigates the interactions of alkali-containing compounds with ilmenite particles previously used in an industrial scale (115 MWth) oxygen carrier aided combustion system. The ilmenite samples were exposed to temperatures up to 1000 °C under inert and oxidizing conditions while the alkali release kinetics were characterized using online alkali monitoring. Alkali desorption occurs between 630 and 800 °C, which is attributed to loosely bound alkali at or near the surface of the particles. Extensive alkali release is observed above 900 °C and proceeds during extended time periods at 1000 °C. The release above 900 °C is more pronounced under oxidizing conditions and approximately 9.1 and 3.2 wt% of the alkali content is emitted from the ilmenite samples in high and low oxygen activity, respectively. Detailed material analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were conducted before and after temperature treatment, which revealed that the concentrations of potassium, sodium and chlorine decrease at the outermost surface of the ilmenite particles during temperature treatment, and Cl is depleted to a deeper level in oxidizing conditions compared to inert. The implications for ilmenite-ash interactions, oxygen carrier aided combustion and chemical looping systems are discussed.

Experimental study on effect of temperature and equivalence ratio on biomass syngas generation for fluidized bed gasifier techniques

ABSTRACT This paper presents a comparative study of selected woody biomass for the potential of fuel gas generation that can be used for heat and power generation using a Fluidized Bed Gasifier (FBG). The characteristics of produced energy gas using the thermochemical Bubbling Fluidized Gasification Technique for selected woody biomass feedstock materials were studied for selected temperatures. Initially, the CFD analysis has been implemented to determine the feasible equivalence ratio (ER) for the selected biomasses. Using CFD ANSYS solver studied gas-solid interaction and gasification process inside a fluidized bed biomass gasifier. Experimental investigations were conducted on the FBG reactor for a feeding rate of 10 kg/hr of biomass materials. Experimental investigations were conducted on the FBG reactor for a feeding rate of 10 kg/hr of biomass materials. The work characteristics of produced gas were investigated by the experimental process for bagasse, groundnut shell, and wooden shavings as feedstock biomass materials for the gasification bed temperature at 500ºC, 550ºC, and 600ºC and Equivalence Ratio (ER) ratio of 0.30. Air was employed as a gasifying agent, and sand with limestone was used as the fluidized bed material. The results show that the fluidized bed has higher temperatures of 600ºC and above, generating higher Calorific Value (CV) syngas. Among all three feedstocks, groundnut shells produced gas HHV of 4.21 MJ/m3. The lowest HHV for bagasse at 500ºC of 3.01 MJ/m3. The effect of bed temperature on Carbon Conversion Efficiency (CCE) shows maximum CCE for bagasse is 60.86%, noted at 550ºC, and the minimum for wooden shaving at 550ºC is 57.69%.

A novel fluidized-bed-electrode solid-oxide-fuel-cell reactor for N2O catalytic decomposition

Global warming potential (GWP) of N2O is 310 times that of CO2. However, conventional solid oxide fuel cell (SOFC) cathode catalytic N2O decomposition has been observed to have a low conversion rate, leading to uneven temperature distribution on the cathode surface. To address this issue, we proposed a novel gas–solid phase fluidized bed catalytic electrode for N2O decomposition in a SOFC system. The fluidized bed material was prepared using cerium oxide particles coated with lanthanum, strontium, and iron (CeO2-LSF). The N2O conversion rate was 99.78% at 720 °C. By assisting particle fluidization with argon, compared to the case of fixed bed electrode, the peak power density improved by a maximum of 39.86% at 670 °C. This improvement was due to mass transfer enhancement by particle fluidization, thereby reducing the concentration polarization of the SOFC. Furthermore, the maximum temperature difference inside the reactor decreased significantly from 92 °C to 42 °C when the cathode particles were fluidized. The reactor can achieve high-efficiency decomposition of N2O while simultaneously improving fuel cell power density and operational reliability.

Kinetics of Natural Kaolinite as a Catalyst for Toluene Dry Reforming

This study aims to develop a kinetic model for natural kaolinite as a potential tar removal catalyst in biomass gasification processes. The catalyst was crushed, sieved (0.2mm), and analyzed using TGA, BET, and XRF. The apparent first-order kinetic parameters of the dry reforming reaction at temperatures ranging from 750 to 900°C under 1atm were used to determine kaolinite's catalytic activity. It was found that both dry reforming and thermal cracking reactions occurred simultaneously. Furthermore, the raw kaolinite catalyst significantly removed toluene (80% at 900°C), at activation energy and frequency factor of 209 kJ/mol and 5.86×109s−1, respectively. Capitalizing on its catalytic activity in its natural form and its high efficacy as fluidized bed material, kaolinite can have great potential in primary and secondary tar reduction measures.

Effects of used bed materials on char gasification: Investigating the role of element migration using online alkali measurements

Online alkali measurements using surface ionization are employed to study alkali release during heating of used industrial fluidized bed materials and gasification of biomass-based char and bed material mixtures. The alkali release from the bed materials starts at 820 °C and increases with temperature, the time a bed material has experienced in an industrial process, and in the presence of CO2. Online alkali measurement during heating of char mixed with used bed material shows significant alkali uptake by the char. Complementary SEM-EDS studies confirm the alkali results and indicate that other important inorganic elements including Si, Mg, and Ca also migrate from the bed material to the char. The migration of elements initially enhances alkali release and char reactivity, but significantly reduces both during the final stage of the gasification. The observed effects on char gasification become more pronounced with increasing amount of bed material and increasing time the material experienced in an industrial process. The ash-layer on the used bed material is concluded to play an important role as a carrier of alkali and other active components. The char and bed material systems are closely connected under operational conditions, and their material exchange has important implications for the thermal conversion.

Numerical and experimental studies of microcapsules phase change material in a pulsating fluidized bed as an energy storage medium

Phase change materials (PCMs) and particularly microencapsulated phase change materials (MPCM) have introduced new ways to enhance the energy storage capacity of a system due to the high latent heat and high storage density of these materials. This experimental and numerical research aims to investigate the process in a pulsating fluidized bed with MPCMs operating as an energy storage device. Experiments were carried out with MPCM (PX52) in a pulsating fluidized bed with the 0.2 m ID and 1 m height. Numerical simulation was performed using the Eulerian-Lagrangian approach in a symmetric two-dimensional model. Pulsating gas flow at a temperature of 60 °C with a frequency range of 1–10Hz for 200 μm mean diameter was used in the experiment and simulation. The effect of pulsating on the efficiency of the energy storage was examined at 1.5, 2, and 2.5 of the minimum fluidization velocity (Umf). Also, simulation and experiment were performed in the continuous mode for comparison with the published research of others. Results of simulation and experimental data of this study and others were noticed in close agreement. The simulation and experimental results revealed an optimal pulsating frequency, at which the energy storage in the fluidized bed is highest for 2 Umf in 7Hz, which is 92% for pulsating and 64% for continuous flow. Besides, using 7Hz and 10Hz frequencies enhanced the charging time with higher efficiency and reached the stabilized temperature in a shorter time.

A Novel Method for On-Line Characterization of Alkali Release and Thermal Stability of Materials Used in Thermochemical Conversion Processes

Alkali metal compounds are released during the thermal conversion of biofuels and fossil fuels and have a major impact on the efficiency of conversion processes. Herein, we describe a novel method for the simultaneous characterization of alkali release and mass loss from materials used in combustion and gasification processes including solid fuels, fluidized bed materials, and catalysts for gas reforming. The method combines the thermogravimetric analysis of selected samples with the on-line measurement of alkali release using a surface ionization detector. The technique builds on the careful treatment of alkali processes during transport from a sample to the downstream alkali monitor including the losses of alkali in the molecular form to hot walls, the formation of nanometer-sized alkali-containing particles during the cooling of exhaust gases, aerosol particle growth, and diffusion losses in sampling tubes. The performance of the setup was demonstrated using biomass samples and fluidized bed material from an industrial process. The emissions of alkali compounds during sample heating and isothermal conditions were determined and related to the simultaneous thermogravimetric analysis. The methodology was concluded to provide new evidence regarding the behavior of alkali in key processes including biomass pyrolysis and gasification and ash interactions with fluidized beds. The implications and further improvements of the technique are discussed.

Hydrodynamics of gas-solid fluidization at ultra-high temperatures

The interest in processing granular materials in fluidized beds at ultra-high temperatures has grown recently to reduce energy consumption and CO2 emissions in relation to numerous high-temperature solid-state reactions. The present research focuses on understanding the hydrodynamics of gas-solid fluidization at temperatures up to 1650 °C to aid the development of ultra-high temperature fluidized bed reactors. Experiments are conducted in a fluidized bed of 30 mm diameter at temperatures up to 1650 °C with corundum and magnesite oxide particles. The fluidization stability is examined based on bed pressure drop measurements using a non-isothermal experimental method. The results demonstrate that stable fluidization of these particles at ultra-high temperatures can be attained by using particles of large and broad size distribution and operating at sufficiently high gas velocities. This article also discusses the bed pressure drop fluctuation, minimum fluidization velocity, and pressure drop offset at ultra-high temperatures.

Design of a gas-solid-solid separator to remove ash from circulating fluidized bed reactors

Cyclones are one of the most common types of gas-solid separators used in circulating fluidized bed boilers. However, cyclones typically do not allow ash to leave the system through the cyclone exit, causing ash to build up in the fluidized bed and necessitating additional systems to remove ash that builds up in the bed. In this study, an alternative “disengager” gas-solid separator is proposed as a way of inherently separating small and large solids, resulting in a gas-solid-solid separation system where ash is allowed to leave the system along with gas while the desired fluidized bed material is retained. Unlike cyclones, which rely on centrifugal force to separate solids and gas, the disengager separates based on entrainment velocity of the particles. Upwards-flowing gas and particles strike a deflection plate and enter the disengaging chamber where particles with low terminal velocity such as ash fines flow with the gas, while larger particles such as sand fall to the bottom of the separator and are returned to the fluidized bed.In this study, several different proposed disengager configurations are simulated and compared to a typical cyclone using computational fluid dynamic (CFD) simulations. It was found that separation efficiency in the disengager is strongly influenced by the size of the deflection plate, rather than by the size of the unit itself. The predicted separation efficiency showed that compared to a cyclone, the disengager design allows significantly more ash to exit the system but retains a similar amount of desirable material. Additionally, the disengager was predicted to not suffer significantly more erosion that a cyclone.

Characteristics of Air Gasification of 10 Different Types of Plastic in a Two-Stage Gasification Process

In this study, air gasification of 10 different types of plastic was conducted using a two-stage gasifier consisting of a fluidized bed gasifier and a tar-cracking reactor filled with activated carbon as a tar removal additive. The study aimed to show characteristics of the producer gases obtained from the two-stage gasification of individual plastics. Ten individual plastics were grouped into four according to their chemical compositional characteristics. In the experiment, product gases having tar contents in the range from 132 mg/Nm3 (ABS) to 0 mg/Nm3 (polyethylene and polyamide) were obtained. In the gasification of plastics having aromatic rings, the productions of char and tar in gas were higher than those of aliphatic plastics. The gasification of aliphatic plastics without heteroatoms, such as polyethylene and polypropylene, favored H2 production and had a maximum value of 26 vol %. Activated carbon played a significant role in lowering the tar content in gas and enhancing H2 production. Plastics having oxygen in their structures (PMMA, PA, PET, PU, and PC) enhanced the CO production. However, gasification of plastics having aromatic rings (PC, PET, and ABS) with sand as the bed material caused bed agglomeration and a severe coke buildup on an activated carbon bed. Dolomite as the fluidized bed material was found to be very effective in solving these operational problems.

Evaluation of the solar thermal storage of fluidized bed materials for hybrid solar thermo-chemical processes

Evaluation of the solar thermal storage of fluidized bed materials for hybrid solar thermo-chemical processes

Holistic assessment of oxygen carriers for chemical looping combustion based on laboratory experiments and validation in 80 kW pilot plant

By utilization of biomass for chemical looping combustion, negative CO2 emissions are possible, but with solid fuels also special requirements are immanent. In particular, the oxygen carriers an important process resource, must handle high temperature operation, while retaining good reaction kinetics and oxygen transport capacity. The focus of this work lies on the development of a fast and cost-effective characterisation scheme of oxygen carriers under operational conditions for dual fluidized beds in order to achieve an assessment for the comparability of different materials. For this purpose, three oxygen carrier were investigated in detail in a laboratory-fluidized bed and compared with operation in an 80 kW pilot plant. By classifying the oxygen carrier into fluidized bed material properties and carrier-properties, a ranking and assessment of ilmenite, braunite and a further manganese ore could be achieved. The tests showed that bed material properties such as attrition, density and bulk density must be given higher priority. These findings were confirmed by operation in an 80 kW pilot plant, where ilmenite achieved a carbon capture rate above 98% and a CO2 yield at almost 89%. The results show that the evaluation and estimation of operation in the 80 kW pilot plant is possible via the laboratory plant experiments.

External bed materials for the oxy-fuel combustion of biomass in a bubbling fluidized bed

This paper presents an experimental study of various bed materials for oxy-fuel combustion of biomass in a bubbling fluidized bed (BFB). A silica sand with three particle size distributions (PSDs) and a lightweight ceramic aggregate (LWA) made of thermally expanded clay with two particle size distributions were chosen as potentially suitable materials. The experiments of biomass combustion in oxy-fuel mode with these materials were carried out to study their suitability as fluidized bed materials. The experiments were performed using a 30kWth lab-scale BFB facility with A1 wood pellets as a fuel.The fluidized bed temperature was controlled at approx. 800°C and the volumetric fraction of O2 in dry off-gas at 10%. The resulting volumetric fraction of CO2 in dry off-gas was approximately 85%. At these conditions, there were no problems with sintering and forming of agglomerates. In the case of ceramic materials, it was possible to control the combustion process in a significantly wider range of operating parameters. Compared to silica sand, the experimental facility could be operated at a lower excess of oxygen (below 6% in dry off-gas) without significant influence on the temperatures in the facility. In terms of the consumption of the combustion facility itself, ceramic materials seem to be more suitable, as they are lighter. The pressure drop of the fluidized bed made of LWA is lower than that of the bed of the same volume made of silica sand, which means that less power is required to drive the fluidization fan.

In-Situ Catalytic Gasification of Rice Hull Using Municipal Solid Waste Incineration Bottom Ash

The demand for alternative energy is increasing rapidly because of global warming and the depletion of fossil fuels. Gasification is a technology that produces gaseous fuels through the incomplete combustion of waste or biomass. The introduction of a catalyst during gasification may increase the production of H₂ and reduce tar formation. In this study, the catalytic gasification of rice hulls was carried out using a fluidized gasifier. To improve the gas yield and reduce tar, municipal solid waste incineration bottom ash (IBA) having nanoporosity was introduced as a substitute for the fluidized bed material. Gasification was carried out at 800 °C, and the flow materials were silica sand, dolomite, and incineration bottom ash. The equivalence ratio, which is the ratio of oxygen supplied to oxygen required for complete combustion, was set to 0.3. The application of alternate fluidized bed materials (dolomite and incineration bottom ash) was effective in improving the hydrogen yield and tar reduction. This was attributed to the high Ca and Mg contents in dolomite and incineration bottom ash. Therefore, it is expected that IBA can be utilized as a catalytic fluidized bed material to replace silica sand.

Steam O2-enriched air gasification of lignite and solid recovered fuel in fluidized bed

Continuous steady-state gasification tests were performed, in which mixtures of lignite and solid recovered fuel (SRF) were fed to a bench-scale facility at atmospheric pressure, loaded with the bottom product of a high-temperature Winkler gasifier as the fluidized bed material. The O2/fuel and steam/fuel ratios were varied from 0.3 to 0.4 and from 0.25 to 0.35, respectively, and the effects of the temperature were examined at different levels (700, 750, and 800 °C). The objective of the experimental campaign was to evaluate the effects of above mentioned operating conditions on the (i) quality of syngas expressed in terms of gas yield (Ygas), cold gas efficiency (ηCG), and carbon conversion (XC); (ii) effectiveness in tar reduction; and (iii) improvement of the H2/CO molar ratio. Characterization analyses (grain-size distribution, scanning electron microscopy and energy-dispersive X-ray spectroscopy) were performed on the materials before and after the tests. Pressure-fluctuation signals were acquired during the tests to monitor the fluidization quality and diagnose the correlated incipient sintering or agglomeration of the bed particles. At 800 °C, the obtained results (Ygas=1.53;ηCG=79%;XC=92%;tar content = 7.35 g/Nm3; H2/CO molar ratio = 0.96) demonstrated the convenient feasibility of gasification with the SRF–lignite mixture as a fuel (SRF/lignite = 0.5 wt/wt) and helped define the operating conditions for future pilot tests aiming for liquid fuel synthesis, although the best results were obtained at 800 °C with SFR/lignite = 0.2 wt/wt (Ygas=1.79;ηCG=93%;XC=102%;tar content = 0.92 g/Nm3; H2/CO molar ratio = 0.84).

Prediction of coating uniformity in batch fluidized-bed coating process

Coating of particulate materials in fluidized beds is a widely used technique to eliminate particle agglomeration, provide slow release of an active substance, or protect active ingredients. When thin polymer shells are applied on a particle surface, it is important to determine the process parameters that provide coating uniformity. In this study, the degree of coverage, defined as the fraction of the coated surface of the particles, is proposed as a quantitative criterion of coating uniformity. A new model for the batch fluidized-bed coating process is presented. The model allows prediction of the function of particle distribution according to the degree of coverage at a given process time and thereby enables assessment of coating uniformity. An algorithm for the numerical solution of model equations for a batch fluidized-bed coater is described. The influences of the main process parameters on the coating uniformity were shown.

Mixing and segregation of binary mixtures of biomass and silica sand in a fluidized bed

In this work, mixing and segregation of binary mixtures involving biomass materials in a fluidized bed was experimentally investigated. A frozen bed method was employed to investigate both axial and radial distribution of biomass particles in silica sand. Three different biomass materials were studied: willow sawdust, pelletized soy and oat hull materials. Biomass loading investigated ranged from 5% to 30% by weight. The extent of mixing for each of the biomass composition was investigated using Lacey’s mixing index which is based on the standard deviations of the sample at different axial positions in the bed. The radial composition was also investigated by means of digital imaging analysis using a high-resolution digital camera. The experiments revealed the differences in the extent of particle distribution for pelletized biomass materials vs non-densified materials as a result of differences in particle size, density and importantly, the particle shape of the materials utilized. The results showed an increase in the extent of mixing as the fluidizing velocity increased for both pellet materials while the mixing index for sawdust decreased beyond a loading of 20%. With an increase in biomass loading, an increase in mixing index was found for the two pellet materials. A similar trend was observed for sawdust at the lower loading level. However, the mixing index started to decrease at higher loading level beyond 20%. The results greatly contributed to the understanding of the hydrodynamics of binary and multicomponent mixtures involving biomass materials, especially pelletized materials in fluidized beds.

Experimental study of heat transfer, hydrodynamics and drying kinetics in a centrifugal fluidized bed apparatus

This paper presents the test results of a prototype installation for drying dispersed materials in a centrifugal fluidized bed. The prototype is a batch apparatus with a vertical supply of a drying agent. A diagram of a test bench designed to study the hydrodynamics of the apparatus and the heat and mass transfer process during drying in a centrifugal fluidized bed is given and described. Silica gel with a particle diameter of 3.8 mm was used as a dispersed material. Hydrodynamic experiments were carried out on a “cold” model. Based on their results, the relationship of the hydraulic resistance of the apparatus at various values of the air velocity and mass of material in the working chamber is constructed. Experimental data have been obtained on low-temperature drying of silica gel in a centrifugal fluidized bed for various modes. The data are presented as time relationships of the temperature and humidity of the material and the drying agent. Analysis of the data obtained showed that the heat and mass transfer process in a centrifugal fluidized bed has a high intensity. A positive conclusion is made about the possibility of using this apparatus for low-temperature drying of capillary-porous bodies.

Experimental study of different materials in fluidized beds with a beam-down solar reflector for CSP applications

Fluidized beds are particularly suitable for integration into Concentrated Solar Power (CSP) plants with beam-down reflectors. Due to the high mixing rates and heat diffusion typical of fluidized beds, they enable the highly concentrated solar flux from the beam-down reflector to impinge directly on the particles. Depending on size, density, surface roughness, optical and mechanical properties, some granular materials are more appropriate than others to store thermal energy at high-temperatures in a fluidized bed. In this line, this work compares the experimental performance of three different granular materials: sand, carbo Accucast ID50 and SiC, considering different airflow rates, and two fluidization technologies: bubbling and spouted bed. Experimental tests were carried out in a facility specifically tailored for these type of tests that permitted different flow arrangements to apply different fluidization techniques using air as the working fluid, including a beam-down reflector with a 4 kWe lamp to simulate the concentrated solar radiation (peak radiation flux of 115 kW/m2).The temperature evolution and storage/recovery efficiencies for the different materials were compared using the two fluidization technologies, and varying the radiation level and airflow rate. Because of these tests, the influence of the airflow rate and radiation levels on the thermal efficiency of the beds was evaluated. The experimental results showed that SiC was the best candidate, as it exhibited the best thermal performance, reaching a peak storage efficiency of ηC=0.95, obtained with an airflow rate of 2.5Umf. Maximum temperatures of 250 °C were reached in a cylindrical bed with an aspect ratio of L/D≈1.