Bench-scale Fluidized Bed Reactor Research Articles

Kinetic Model Implementation of Fluidized Bed Devolatilization

Computational modeling is a powerful tool for studying and investigating the behavior of fluidized bed gasifiers and the modeling of the initial devolatilization step is necessary to provide a reliable description of the whole process involving the feedstock decomposition and the subsequent gasification reaction. In this work, a bench-scale fluidized bed reactor was used to examine the devolatilization of different carbonaceous materials within the temperature range from 650 to 850 °C. The experimental test campaign was used to derive the linear correlation factor to describe the devolatilization in terms of product distribution as a function of temperature and highlight the different behavior between lignocellulosic and plastic feedstocks. Furthermore, the experimental data were used to develop concise kinetic expressions able to fit the experimental devolatilization times ranging from 75 in the case of poplar at a lower temperature and 22 s for the Organic Fraction of Municipal Solid Waste (OFMSW) at a higher temperature. The obtained model produces a simple kinetic expression where the size of the particle is enclosed in the kinetic parameters. The kinetic model sided by the application of linear correlations describes the overall thermal decomposition in a fluidized bed, simplifying its modeling in commercial simulation software, even when particles are considered as point-like bodies.

An experimental investigation into the fate of fuel-bound N-species during fluidised bed combustion of a dried coal slime in O2/Ar mixtures

The formation of NO, NO2, N2O and N2 from fuel-bound nitrogen species during the combustion of a coal slime (CS) and its char (CS char) were investigated in a laboratory bench-scale fluidised bed reactor by tracking the N-containing gas species using a gas chromatograph and an electrochemical gas analyser. Quartz sand with a particle size fraction of 0.3–0.38 mm was used as the bed material. A stream of an Ar/O2 mixture of varying O2 concentration was used as the oxidant and fluidisation gas. The effect of operating temperature (900–1300 K), initial O2 concentration (3–8%), fuel feed rate (0.0041 g min−1 for CS, 0.0036 g min−1 for CS char) and C/O2 mole ratio (0.14–0.78) on carbon burnout, NOx, N2O and N2 formation were systematically studied. It was found that the oxidation process of CS in the fluidised bed is controlled by mass diffusion under the tested conditions. N2, N2O and NO concentrations in the flue gas during CS combustion were higher than during CS char combustion under the same experimental conditions due to the presence of the greater N content in CS (1.56%) than in CS char (1.34%). At low combustion temperatures of 900 K and 1000 K, the fuel-N was mainly converted to NO and N2O. However, as the operating temperature increased, NO and N2 became the dominating species in both the CS and CS char combustion experiments. The NO concentration increased with increasing initial O2 concentration due to enhanced oxidation of char-N. Comparing the N2 formation data during CS and CS char combustion, it is inferred that in the presence of volatile, fuel-N was preferentially converted to N2.

Devolatilization of Polypropylene Particles in Fluidized Bed

Gasification of plastic waste is an emerging technology of particular interest to the scientific world given the production of a hydrogen-rich gas from waste material. Devolatilization is a first step thermochemical decomposition process which is crucial in determining the quality of the gas in the whole gasification process. The devolatilization of polypropylene (a key compound of plastic waste) has been investigated experimentally in a bench-scale fluidized bed reactor. Experimental tests were carried out by varying two key parameters of the process—the size of the polypropylene spheres (8–12 mm) and temperature (650–850 °C). Temperature shows the highest influence on the process. Greater molecular cracking results were more pronounced at higher temperatures, increasing the production of light hydrocarbons along with the formation of solid carbon residue and tar. The overall syngas output reduced, while the H2 content increased. Furthermore, a pseudo-first-order kinetic model was developed to describe the devolatilization process (Eapp = 11.8 kJ/mol, A1 = 0.55 s−1, ψ = 0.77).

Hydrotalcite as a deoxygenation catalyst in fast pyrolysis of biomass for the production of high quality bio-oil

Commercially available MG70 hydrotalcite (HT) has been investigated for its influence on the in-situ catalytic fast pyrolysis of beechwood. The investigations were performed both with an analytical Py-GC/MS (pyroprobe) and on a bench scale fluidized bed reactor at a pyrolysis temperature of 500 °C. The semi qualitative pyroprobe analysis was carried out for different catalyst to biomass (C/B) ratios and a ratio of 4 was found to be optimum. At this C/B ratio, the acids, anhydro-sugars and methoxy phenolics were more or less eliminated and HT facilitated the formation of alkylated cyclopentenones, cresols, methly furans and hydrocarbons. The application of HT in the bench scale fluidized bed reactor allowed for further analysis of the pyrolysis products: bio-oil, char, and gas. The semi qualitative GCMS analysis of bio-oil was in general agreement with the volatiles detected from Py-GC/MS analysis. In addition the catalyst was characterized by BET, XRD and TGA analysis. Overall an organic rich bio-oil with a yield of 9.5 wt%, higher heating value of 29.3 MJ/kg (as received) was obtained. The pH of the bio-oil increased from 3.2 to 6.0 and oxygen content reduced from 46.3 to 20.5 wt% (as received). The substantial increase in CO2 concentration in the pyrolysis gas also supported these findings. Overall, HT facilitated the formation of moderately deoxygenated compounds and they are of interest as they can be further processed downstream to produce bio-fuels.

Regeneration of pristine HZSM-5 extrudates during the production of deeply deoxygenated bio-oil fromex situcatalytic fast pyrolysis of biomass in a bench-scale fluidised-bed reactor

Deeply deoxygenated bio-oil with ∼1 wt% oxygen is produced inex situcatalytic fast pyrolysis applying an unmodified HZSM-5 with good regeneration performance.

Role of dolomite as an in-situ CO2 sorbent and deoxygenation catalyst in fast pyrolysis of beechwood in a bench scale fluidized bed reactor

The dual effect of dolomite as a CO2 sorbent and deoxygenation catalyst in fast pyrolysis of beechwood was investigated. Investigation was performed on a bench scale fluidized bed reactor at an pyrolysis temperature of 500 °C and at different WHSV. CO2 breakthrough curves and bio-oil samples were produced simultaneously. The results show that dolomite is both a feasible catalyst and a CO2 sorbent as it produced a moderately deoxygenated bio-oil and a CO2 free and H2 rich gas. Acids were eliminated, whereas the concentration of methylated phenols and methylated cyclopentanones were enhanced. These results were achieved when rapid carbonation stage was prevailing throughout the experimental run. An organic rich bio-oil with 9.46 wt% yield and a HHV of 28.0 MJ/kg (as received) was obtained. The pH of the catalytic bio-oil increased from 3.2 to 6.0 and the oxygen content reduced to 21.5 wt% from 47.3 wt%. Moreover, the moderately deoxygenated bio-oil is of interest as it can undergo downstream reforming into wide range of liquid fuels with reduced H2 consumption. Calculations show that the H2 generated as a result of CO2 sorption can suffice the requirement for hydrodeoxygenation. In addition the catalysts were also characterized by BET, XRD and SEM analysis.

Sewage Sludge Gasification in a Fluidized Bed: Experimental Investigation and Modeling

Fluidized bed gasification is a promising process technology to manage the growing amount of sewage sludge (SS) requiring disposal. Two samples of SS, produced in different seasons of the year by a municipal wastewater treatment plant, were subjected to gasification at 850 °C in a bench-scale fluidized bed reactor using, as a gasification agent, a nitrogen/air mixture at different values of oxygen/fuel equivalence ratio (ER = 0.1–0.2). The starting materials and the output streams (syngas, tar, and solid residues) were thoroughly characterized. The fate of specific SS constituents and the characteristics of bottom ashes were addressed, so contributing to the problem of a proper SS management approach in the context of the circular economy. Computer-aided simulations were also performed, which allowed us to predict the composition of the syngas from SS gasification under operating conditions different from those experimentally investigated (i.e., reactor temperature and ER).

Dual-functional witherite in improving chemical looping performance of iron ore and simultaneous adsorption of HCl in syngas at high temperature

The synergetic effect in using witherite (BaCO3) and iron ore (IO) for simultaneous dechlorination and chemical looping combustion (CLC) of municipal solid waste (MSW) derived syngas was studied on a bench-scale fluidized bed reactor at the temperature range of 800–900 °C. For comparison, limestone a widely used HCl sorbent was also tested. It was found that the pristine IO had negligible HCl sorption capacity during CLC of syngas. The IO-witherite mixture demonstrated much higher HCl adsorption capacity than the pristine IO and IO-limestone mixture in the temperature range of 800 to 900 °C with the presence of 25–35 vol% H2O in syngas. At the loading ratio 10 wt% of sorbent, the HCl removal capacity of IO-witherite was 3 times higher than that of the IO-limestone at 900 °C. Though IO and sorbent were physically mixed, a strong solid-solid interaction between IO and witherite surface occurred to form interstitial solid solution, BaFe12O19. The hexagonal structure of the BaFe12O19 facilitated the lattice oxygen mobility and thus improved greatly the redox performance of the IO. With increasing the inlet HCl concentration, the CLC performance of IO-Ba was further improved mainly because the chlorination process made the witherite particles more porous, which benefits the solid-solid interactions. The bulk spent witherite particles after processing could be separated easily from the IO particles by magnetic separation to realize the recovery of the used sorbents, while IO particles could be refilled into the CLC process. This research highlights that the IO-witherite mixture could be a promising OC for the CLC of HCl containing syngas to accomplish cleaner combustion.

Oxygen carriers from incineration bottom ash for chemical looping combustion of syngas: Effect of composition on combustion efficiency

Incineration bottom ashes (IBA) were investigated as oxygen carriers (OCs) for their application in chemical looping combustion (CLC). The OCs were prepared by mixing the magnetic separated fraction of IBA (IMF) with its non-magnetic fraction (NMF) at various ratios. Additionally, a synthesized iron oxide supported on the pre-washed IBA (0, 25, 50 and 75 wt%), termed as synFe, were also investigated for comparison with the investigated IMF. Thermogravimetric analysis (TGA) combined with elemental analysis unveiled that Fe2O3 and CaSO4 in IMFs were the major sources of the available lattice oxygen in the investigated oxygen carriers. A synergistic effect was observed among the complex components in IMF-based OCs causing the experimental oxygen transport capacity to be larger than the theoretically expected, calculated based on the metal oxides (including Fe2O3, CuO, Mn2O3 and NiO) and CaSO4 redox couples. A syngas (H2 + CO) combustion tests with the IMF-based OCs in a bench-scale fluidized bed reactor were conducted, where the100-IMF demonstrated the most pronounced and stable combustion performance (95% for H2 and 90% for CO), comparable to those delivered by 50% and 75% synFe. Based on this study, the IMF compounds from the raw IBA without any further treatment carry a high potential for CLC process, which provides possible option of a cost-effective OCs and sustainable application of IBA.

CO2 methanation in a bench-scale bubbling fluidized bed reactor using Ni-based catalyst and its exothermic heat transfer analysis

CO2 methanation, as a power-to-gas technology, is considered to be an important method to secure energy supply by utilizing CO2 and H2 gases. In this study, a 0.2 kW CH4 bench-scale fluidized bed reactor was used for CO2 methanation using approximately 13 kg nickel-based catalyst to investigate the effect of temperature, gas velocity, and H2/CO2 ratio on CO2 conversion, CH4 purity, and CH4 selectivity. Response surface methodology (RSM) was employed to design the experimental conditions to statistically evaluate the effect of operating variables. Reduced quadratic model equations for CO2 conversion and CH4 purity were derived, which determined the optimal conditions within the experimental conditions. The suggested conditions for the highest CO2 conversion were 297 °C, 4.66H2/CO2, and 4.0 Ug/Umf (velocity ratio), whereas different conditions were determined for the highest CH4 purity. Among the operating variables, temperature was the most influential factor, followed by the gas ratio. The highest CO2 conversion and CH4 purity were 98% and 81.6%, respectively. Additionally, the heat transfer coefficient (ho) was found to be 115 W/m2∙°C during a 10-h continuous CO2 methanation experiment, which is an important design factor for the further scale-up of the process.

Enriched hydrogen production over air and air-steam fluidized bed gasification in a bubbling fluidized bed reactor with CaO: Effects of biomass and bed material catalyst

Gasification is one of the methods of generating biopower or biofuels from biomass waste. In this study, a bench-scale fluidized bed reactor was used for biomass air and air-steam gasification. Gasification was performed under constant operating conditions (~780 °C, equivalence ratio = ~0.32) to investigate the effect of biomass (switchgrass, pine residues) and bed materials (sand, CaO+ sand, Al2O3, and CaO + Al2O3). All gasification products, such as synthesis gas (syngas), contaminant gases, tar, and biochar (solid) were comprehensively analyzed. The composition of biomass significantly impacted CO and H2 yield from volatile combustible matter and fixed carbon. Further, the presence of CaO made the condition favorable for the water-gas shift (WGS) reaction combined with the CO2 carbonation reaction, which increased H2 concentration. Additional steam with CaO increased H2 concentration closer to 50% (N2 free condition) through the combination reactions of steam hydrocarbon reforming and WGS by producing 44 gH2/kgdry biomass and 143 gCO/kgdry biomass. The usage of steam reduced the overall yield of contaminant gases, whereas the usage of CaO or Al2O3 decreased the amount of gasification tar by approximately 5.8–6.5 gtar/kgdry biomass. This study can provide valuable experimental data for biomass waste to produce better quality syngas.

Steam Gasification of Lignite in a Bench-Scale Fluidized-Bed Gasifier Using Olivine as Bed Material

The gasification of lignite could be a promising sustainable alternative to combustion, because it causes reduced emissions and allows the production of syngas, which is a versatile gaseous fuel that can be used for cogeneration, Fischer-Tropsch synthesis, or the synthesis of other bio-fuels, such as methanol. For the safe and smooth exploitation of syngas, it is fundamental to have a high quality gas, with a high content of H2 and CO and minimum content of pollutants, such as particulate and tars. In this work, experimental tests on lignite gasification are carried out in a bench-scale fluidized-bed reactor with olivine as bed material, chosen for its catalytic properties that can enhance tar reduction. Some operating parameters were changed throughout the tests, in order to study their influence on the quality of the syngas produced, and pressure fluctuation signals were acquired to evaluate the fluidization quality and diagnose correlated sintering or the agglomeration of bed particles. The effect of temperature and small air injections in the freeboard were investigated and evaluated in terms of the conversion efficiencies, gas composition, and tar produced.

Bench scale analysis of the physical attrition properties for copper-ferri-aluminate oxygen carriers during chemical looping combustion

Abrasion and fragmentation related attrition has been deemed as one of the major design challenges for the development of oxygen carriers for chemical looping process concepts and their implementation. Since the technology seeks to replace conventional power generation, oxygen carrier lifetime is a critical parameter as it can impact the potential competitive nature for the implementation of the process concept. In this study, attrition propensity is examined for two novel carrier materials CuFeAlO4 and CuFe1.5Al0.5O4 in a bench scale fluidized bed reactor unit under reacting conditions. Bench scale outcomes were compared to attrition outcomes from a sub pilot operation to determine comparability of scale. Routes by which attrition performance can be improved are proposed and validated through examining the solid-state chemistry of the carrier system and evaluation method. The study suggests that material structure, maturation and microstructure can play a major role in physical attrition propensity.

Recycling of product gas does not affect fast pyrolysis oil yield and composition

It has been reported that a deoxygenated bio-oil (ca. 0.12 kg kg−1 O on bio-oil basis) can be obtained simply by recycling the non-condensable gases (NCG) of biomass fast pyrolysis to a fluidized-bed reactor operated at atmospheric pressure [Mullen et al., 2013, Energy Fuels, 27, 3867–3874]. Such an unprecedented effect would (i) complicate the use of lab-scale research results obtained typically under inert gas (N2, He, Ar) atmosphere for the design of commercial scale pyrolysis units projected to utilize a recycle gas atmosphere (ii) obviate the need for catalytic pyrolysis or mild hydrotreatment processes. Considering these implications, further validation or refutation of the claimed deoxygenation effect of recycle gas atmosphere is needed.Therefore, fast pyrolysis experiments with pine wood were performed in a bench-scale fluidized bed reactor under N2 atmosphere, recycle gas atmospheres (75 % and 90 % recycle gas volume fraction) at reactor temperatures of 430 °C and 500 °C. Mass balances were obtained and the bio-oils were analyzed using GC/MS, GPC, elemental analysis and Karl Fischer titration. No significant differences were observed in product yield and bio-oil composition (e.g. oxygen content) when going from a nitrogen gas atmosphere to a recycle gas atmosphere for both pyrolysis temperatures.

Evaluation of performance of copper converter slag as oxygen carrier in chemical-looping combustion (CLC)

In this study, copper converter slag sample was utilized as oxygen carrier (OC) for Chemical Looping Combustion (CLC) of synthetic syngas. The CLC cycles were substantiated in a bench-scale fluidized bed reactor by altering the inlet atmosphere between fuel and air consecutively. The tests were conducted at 4 times the minimum fluidization velocity, and 1123 K (850 °C) reduction half-cycle temperature (TRHC) for 50 cycles. The mean fuel gas conversion values obtained during 30 s of RHC time (tRHC) were as; 78% for 1:1 CO in nitrogen, 84–89% for syngas, and 97% for 1:1 H2 in nitrogen. Copper converter slag sample was stable and sufficiently reactive throughout the tests, moreover, the reactivity increased substantially by the consecutive CLC cycles. The increase of the porosity and the formation of the copper ferrite during the CLC cycles were found to be the main contributors to the activation of the copper converter slag. It is concluded that the evaluation of copper converter slag in the CLC process is both an economical option for OC supply (especially in coal-fueled CLC processes where some OC loss is inevitable), and an environmentally favorable alternative for recycling copper converter slag unless wasting the precious metals in it.

Characteristics of the pyrolytic products from the fast pyrolysis of palm kernel cake in a bench-scale fluidized bed reactor

Palm kernel cake (PKC) was pyrolyzed in a bench-scale pyrolysis plant equipped with a bubbling fluidized bed reactor, char separation system, and bio-oil recovery system under various reaction temperatures. Experiments were conducted to evaluate the effects of reaction temperature and observe the behavior of nitrogen in pyrolysis products. The maximum yield of bio-oil from PKC was approximately 63 wt.% at a reaction temperature of 401 °C. The main chemical compounds of bio-oils obtained from PKC were acetic acid, levoglucosan, nitrogen-containing compounds, and fatty acids such as dodecanoic acid, octanoic acid, tetradecanoic acid, and oleic acid. At reaction temperatures above 401 °C, the nitrogen content of bio-oils does not depend on reaction temperature. It is suggested that the resulting bio-oil requires additional treatment for use as a clean fuel.

Effect of upflow velocity on the performance of a fluidized bed reactor to remove phosphate from simulated swine wastewater

This study investigated the effect of upflow velocity (200–500 cm/min) on the performance of a bench-scale fluidized bed reactor to remove phosphate from simulated swine wastewater. Experiments were conducted at an inflow pH of 9, a phosphate concentration of 89 mg P/L, a Mg:P ratio of 1:1 adjusted using MgCl2 and a recycle ratio of 20. Decreasing upflow velocity enhanced the phosphate removal efficiency. Thermodynamic simulations showed that the struvite crystallization did not reach equilibrium at high velocity. The phosphate reduction inside the reactor (SOPin) showed two crystallization periods, of which the quick period was well fitted with a linear model. High upflow velocity promoted the phosphate reduction rate, but it reduced the crystallization time inside the reactor. Hence, the crystallization did not reach equilibrium, decreasing the phosphate removal efficiency. Low upflow velocity did not affect the nutrient release behaviour of struvite pullets despite yielding low crushing strength and purity. The nutrient release was determined by the solubility of struvite rather than the product quality. Furthermore, kinetics of SOPin reduction provides a basis for the design of FBR aiming to optimize the removal of phosphate and yield struvite products with good quality.

Conversion of Coal in a Fluidized Bed Chemical Looping Combustion Reactor with and without Oxygen Uncoupling

Chemical looping combustion (CLC) is a carbon capture technology that involves circulating metal-based oxygen carrier particles between two reactors, where the metal is alternately oxidized by air and then reduced by fuel as the fuel combusts. In the variant of CLC known as chemical looping with oxygen uncoupling (CLOU), the oxygen carrier releases gaseous O2 in the fuel reactor, allowing for a rapid reaction with solid fuels. This study focuses on improving the understanding of mechanisms responsible for carbon conversion of coal and coal char in a bench-scale fluidized bed reactor using oxygen carriers with and without oxygen uncoupling properties. Effects of coal particle size and temperature on the rate of carbon conversion are evaluated in order to quantify performance and to aid in design and modeling of large-scale fully circulating chemical looping systems. The data confirms that conversion with a copper-based CLOU carrier is faster and results in lower CO and CH4 concentrations than the natural o...

Deactivation kinetics for lignite gasification in a fluidized bed reactor

Lignite gasification may be characterized by the active site restriction result from deactivation. As was aimed here, a deactivation model (DM) can be developed by “pseudo-steady-state” mass balance, i.e. describing variation of available surface with time. For this purpose, bench-scale fluidized bed reactor (FBR) was operated for obtaining gasification product profiles. Gas samples were taken from the reactor effluent stream, and fed continuously to the gas analyzers for on-line simultaneous measurements of H2, CO2, CO, CH4 and O2. Data were used for extracting model parameters (k// and kD) from the linear form of DM. Experiments at temperature range of 973–1173 K were conducted. Fluidizing mixture (air and steam) entered the bed through a distributor of a 200-mesh stainless steel sieve and fluidized the single charge of lignite with a mean particle diameter approximately 250 µm. The agreement between the experimental and predicted carbon concentrations was confirmed for DM. The latter may be successfully used to design the fluidized bed combustors or gasifiers.

Effects of supports on reduction activity and carbon deposition of iron oxide for methane chemical looping hydrogen generation

Chemical looping hydrogen generation is a promising technology which has the potential to efficiently produce hydrogen and capture CO2 with the aid of iron-based oxygen carriers. The properties of the iron-based oxygen carrier, such as carbon resistance, redox activity, and cycle stability, are critical factors for the development of CLHG process. In this study, four different supports, MgAl2O4, CeO2, ZrO2, and CeZrO4, were incorporated with iron oxide by a co-precipitation method. The reduction activity, carbon resistance and redox stability of the oxygen carriers with methane were investigated in a bench-scale fluidized bed reactor. The redox activity and oxygen transfer capacity were also tested by temperature programmed reduction (TPR) and temperature programmed oxidation (TPO). Carbon formation was observed during the reduction period through the methane decomposition reaction. It was revealed that the carbon resistance of the oxygen carriers was partially determined by the oxygen transfer capacity. For the fresh oxygen carriers, the incorporation of MgAl2O4 led to a better carbon resistance because more lattice oxygen can be released compared to the other supports before carbon deposition. After 10 redox cycles, the Fe2O3/CeZrO4 oxygen carrier performs the best oxygen transfer capacity, but the oxygen transfer capacity of the Fe2O3/MgAl2O4 oxygen carrier reduced obviously. In addition, the specific surface area could dramatically affect the reduction activity of the oxygen carriers. Crystalline graphite was observed on the reduced oxygen carriers, which posed a negative effect on the reduction activity, leading to sintering of the oxygen carriers.