Pilot-scale Fluidized Bed Reactor Research Articles

Process Optimization and Robustness Analysis of Ammonia–Coal Co-Firing in a Pilot-Scale Fluidized Bed Reactor

A computational fluid dynamics (CFD) model was coupled with an advanced statistical strategy combining the response surface method (RSM) and the propagation of error (PoE) approach to optimize and test the robustness of the co-firing of ammonia (NH3) and coal in a fluidized bed reactor for coal phase-out processes. The CFD model was validated under experimental results collected from a pilot fluidized bed reactor. A 3k full factorial design of nine computer simulations was performed using air staging and NH3 co-firing ratio as input factors. The selected responses were NO, NH3 and CO2 emissions generation. The findings were that the design of experiments (DoE) method allowed for determining the best operating conditions to achieve optimal operation. The optimization process identified the best-operating conditions to reach stable operation while minimizing harmful emissions. Through the implementation of desirability function and robustness, the optimal operating conditions that set the optimized responses for single optimization showed not to always imply the most stable set of values to operate the system. Robust operating conditions showed that maximum performance was attained at high air staging levels (around 40%) and through a balanced NH3 co-firing ratio (around 30%). The results of the combined multi-optimization process performance should provide engineers, researchers and professionals the ability to make smarter decisions in both pilot and industrial environments for emissions reduction for decarbonization in energy production processes.

Co-gasification of plastics waste and biomass in a pilot scale fluidized bed reactor

Co-gasification of plastics waste and biomass in a pilot scale fluidized bed reactor

Significance of temperature and pressure on minimum fluidization velocity in a fluidized bed reactor: An experimental analysis

ABSTRACT This investigation addresses the minimum fluidization velocity (U mf ) determination in a refractory insulated fluidized bed reactor (FBR) of 200 mm ID. Umf is determined with respect to different particle sizes and operating parameters like temperature and pressure up to 900 °C and 1 MPa respectively. This study has the main thrust into the establishment of U mf at elevated temperature and pressure during the thermochemical process, involving uniform mixing of gas-solid by fluidization phenomena at a pilot scale FBR. So, to understand the significance and impact of temperature along with pressure on Umf , a set of fluidization experiments have been demonstrated in FBR. Two waste materials are abundantly available, similar to Geldart’s group-B type bed materials, i.e. Calcined-clay and Coal-ash of an average size of 1.04 and 0.92 mm respectively, and apparent density of 883 and 850 kg/m3 respectively, have been selected as bed material. Experimental results revealed that Umf directly relates to particle size and inverse relationship with operating temperature and pressure. Results revealed that U mf decreases by 59.7% and 59.2% for both bed materials such as Calcined-clay and Coal-ash respectively as the temperature increases from 30 to 900°C at atmospheric pressure. Similarly, U mf also decreases by 63.3% and 66.0% for bed materials such as Calcined-clay and Coal-ash respectively as the pressure increases from atmospheric pressure to 1 MPa at room temperature. An empirical model has been developed for predicting Umf at elevated temperature and pressure during fluidization phenomena. The experimental Remf shows a good agreement with the predicted Remf by using the developed model proving its robustness.

Heterogeneity analysis of gas–solid flow hydrodynamics in a pilot-scale fluidized bed reactor

Mesoscale drag model is of crucial significance for the reliability and accuracy in coarse-grid Eulerian–Eulerian two-fluid model (TFM) simulations of gas–solid flow hydrodynamics in fluidized bed reactors. Although numerous mesoscale drag models have been reported in the literature, a systematic comparison of their prediction capability from the perspective of heterogeneity analysis is still lacking. In this study, in order to investigate the effect of several typical drag models on the hydrodynamic behaviors, the nonuniformity analysis and the sensitivity to material properties, extensive coarse-grid TFM simulations of a bubbling pilot-scale fluidized bed reactor are carried out. The results demonstrate that the mesoscale drag models outperform the empirical drag model in terms of nonuniformity due to the consideration of the influence of the mesoscale structures on the drag force in the bubbling region. Furthermore, the results reveal that our previously developed three-marker gradient-based drag model considering the solid concentration gradient exhibits satisfactory performance in predicting the bubbling flow hydrodynamics. Besides, the material-property-dependent drag model considering the explicit effect of material properties on drag corrections is most sensitive to the particle diameter. This work provides guideline for possible future improvements of mesoscale models to simulate gas–solid flow more accurately and universally.

Numerical modelling of the coal phase-out through ammonia and biomass co-firing in a pilot-scale fluidized bed reactor

The co-firing of ammonia (NH3) with coal has raised awareness, boosting NH3 research and development on its use and deployment as a sustainable fuel. Recent advancements point towards the co-firing of coal with biomass and NH3 as a state-of-art strategy to phase-out coal from coal-based power stations. The implementation of NH3 to the coal-biomass fuel mix allows not only to decarbonize coal-fired processes but also reduces biomass exploration costs to avoid feedstock availability disruption while increasing the power station production efficiency. Moreover, such a strategy brings an alternative player into the environmentally friendly power mix portfolio, accelerating the coal phase-out from electricity production. However, the use of NH3 for power generation still presents some research gaps. Thus, this study delivers a 2D Eulerian-Lagrangian numerical model to describe the co-firing of coal with biomass and NH3 in a pilot-scale fluidized bed reactor. The numerical model is validated against experimental data on coal and biomass combustion to assess the model's accuracy. The coal, biomass, and NH3 co-firing ratios are varied to the point where coal is gradually reduced from the fuel mix, and its effect on the combustion processes is broadly investigated to determine the biomass and NH3 impact on the reactor's emissions. Overall, the use of both biomass and NH3 showed to broadly reduce carbon and NO emissions from coal-fired energy systems, emphasizing the potential addressed to biomass as an alternative to coal and NH3 as an effective carbon-neutral fuel of the future.

Numerical modelling of ammonia-coal co-firing in a pilot-scale fluidized bed reactor: Influence of ammonia addition for emissions control

The co-firing of coal and NH3 is a sustainable solution allowing the retrofitting of coal power facilities without major modifications while contributing to global decarbonization goals. However, the use of NH3 for power generation still presents some research gaps. This study delivers a 2D Eulerian-Lagrangian numerical model describing the co-firing of coal-NH3 in a pilot-scale fluidized bed reactor. The numerical model is validated against experimental data on coal combustion to assess the accuracy of the model·NH3 co-firing ratio is varied between 0 and 80% (by mass) and the effect on the combustion process is broadly investigated to determine the impact on heat release, and carbon, NO, and NH3 emissions. The effect of NH3 injection position into the reactor and air staging on NO formation is studied. Also, the impact of NH3 on the reactor temperature distribution and radiative flux is evaluated. Results indicate that NH3 co-firing delivers CO2 emissions decrease of up to 26% compared to pure coal firing. For a co-firing fraction of 10% NH3, NO emissions level was identical to that of coal firing alone, yet between 20 and 80% ratio NO emissions gradually decreased by up to 40%. The NH3 injection location had a substantial effect on NO emissions, with injection points further downstream the bed surface leading to increased NO concentrations. Air staging also proved to have a dominant effect on NO formation, with a 50% reduction of NO emissions obtained for a 20% air staging alone. Lower gas temperatures and decreased radiative flux were predicted as the NH3 ratio increased. Given the similar heat transfer rates measured between 10 and 20%, a 20% NH3 operation would be possible without a detrimental effect on temperature and radiative flux.

Minimizing gas leakages in a system of coupled fluidized bed reactors for chemical looping combustion

Chemical Looping Combustion (CLC) is a technology to generate a pure stream of CO2 during the combustion of fossil or renewable fuels for power generation. This is carried out in a system of interconnected fluidized bed reactors, at least one so-called air reactor and a fuel reactor. Gas leakages are a major problem in those CLC systems as undesired gases in the exhaust can make the later sequestration more expensive and might lead to further gas cleaning. Therefore, the off-gas of the fuel reactor, where the fuel is mainly converted, should be as pure as possible. In those interconnected fluidized beds, the loop seals or so-called siphons should prevent the gas leakage from one side to the other. The present work focuses on the pressure conditions inside an experimental 25 kWth pilot scale fluidized bed reactor system for CLC to minimize gas leakage between the single reactors. The system consists of a riser air reactor and a two-stage bubbling fluidized bed fuel reactor system. By using CO2 as tracer gas at different positions, the gas distribution from the two loop seals through the system as well as the leakage flow from the air reactor via the cyclone and loop seal to the fuel reactor is analyzed. From a detailed experimental and sensitivity analysis of the system behavior in different operation conditions, measures to minimize gas leakage are developed. A key factor for the understanding of the gas leakages in the system was derived from pressure drop analysis of 23 pressure ports. Each process unit is examined and design criteria for such systems of interconnected fluidized beds are derived.

Design and thermal characterization of an induction-heated reactor for pyrolysis of solid waste

A small-scale induction heated reactor (IHR) was specifically developed to study fast pyrolysis, here investigated as the first step of gasification process, representing some of the reaction conditions encountered in a fluidized bed reactor. First, the thermal response of the system was characterized at transient and steady state, and CFD calculations were performed to have a complete description of the temperature profiles inside the reactor. The novel device can handle a few grams of solid at temperatures up to 900 °C, allowing high heating rates (near 80 °C/s) and a uniform distribution of temperature in the sample. Secondly, the pyrolysis of a solid recovered fuel (SRF) sample was carried out at 800 °C, and the distribution and composition of reaction products were analyzed and compared with tests performed in a pilot scale fluidized bed reactor (FBR). The results obtained in the IHR showed a good reproducibility. The same main gas and tar species were measured in the IHR and FBR, with some differences in gas and tar composition that were attributed to the extent of secondary reactions, enhanced by higher heat transfer rates and the presence of bed material in the FBR.

Exergetic study of beech wood gasification in fluidized bed reactor using CO2 or steam as gasification agents

The study of energy and exergy balance in the gasification of beech wood was performed using a pilot-scale fluidized bed reactor at different operation conditions. The temperature range studied was from 600 °C to 900 °C, with the use of CO2 and steam as gasification agents and biochar and sand as bed materials. The singularity of this work was the combination of an experimental work and a complete evaluation of the exergy distribution of beech wood gasification based on strict use of the same experimental set-up, but varying the operating conditions. Also, a detailed analysis of pyrolysis products was taken into consideration. Temperature increase had a negative influence on exergy destruction. When sand was used as the bed material, the exergy destruction rate increased from 9 to 13% of the total exergy entering the system. Comparing pyrolysis and gasification with CO2 under the same conditions, it was found that the pyrolysis reaction destroyed more exergy than gasification. Steam showed lower exergy destruction rate than CO2 gasification when biochar was used as bed material for tar cracking. This means that more exergy was conserved in steam gasification reaction, even though syngas efficiency was to 65% for both set-ups.

Quantitative study of mixing/segregation behaviors of binary-mixture particles in pilot-scale fluidized bed reactor

In this study, a three-fluid Eulerian model coupled with the kinetic theory of granular flow was developed to investigate the mixing/segregation behaviors of binary-mixture particles in a pilot-scale fluidized bed reactor. The proposed model was validated by comparing predictions with the classical calculated data and the experimental data. A new mixing index was defined by counting the mixing information in each mesh, and then it was applied to evaluate quantitatively the effects of the key model parameters (i.e., restitution coefficient, friction coefficient) and operating conditions (i.e., inlet gas velocity, particle size ratio) on the mixing characteristics of binary-mixture particles. The hydrodynamic characteristics of binary-mixture particles in semi-continuous feed mode were also obtained. Numerical results demonstrate that the size segregation of particles can be easily realized under the conditions of high air velocity and large particle size ratio when the binary-mixture particles differ only in size.

Techno-economic analysis of forest biomass blends gasification for small-scale power production facilities in the Azores

The present work assesses the energetic valorisation of forest biomass blends in the archipelago of the Azores, to do so, a multiphase 2-D Eulerian-Eulerian model was employed to simulate forest biomass gasification in a pilot-scale fluidized bed reactor. The numerical model was validated under experimental gasification runs performed in a 250 kWth quasi-industrial biomass gasifier. The potential use of the produced syngas as a complementary energy source for small-scale power production in the Azores was assessed based on the results. The exergy efficiency and tar production of the process were determined. A techno-economic study combining the net present value (NPV), internal rate of return (IRR), and payback period (PBP) followed by a Monte Carlo sensitivity analysis was comparatively performed for two distinct application sizes (100 and 1000 kW) so to gauge which unit size carries enhanced operative feasibility and foresee the main investment risks in conducting forest biomass blends gasification for power production in small facilities. Results revealed that the 100 kW unit was economically impracticable under current market conditions, while the 1000 kW unit showed to be economically feasible with an NPV of 486 k€, IRR of 17.44% and PBP of 7.4 years. The sensitivity analysis predicted a higher risk of failure in the NPV, being highly sensitive to the electricity sales tariff and electricity production. Indeed, forest biomass gasification projects carry great potential when applied to small facilities with economic viability in some economies of scales, withal, special concerns must always be considered regarding the project attractiveness to potential investors.

Fluidized bed fast pyrolysis of corn stover: Effects of fluidizing gas flow rate and composition

ABSTRACT Fast pyrolysis of corn stover was carried out in a pilot scale fluidized bed reactor in nitrogen atmosphere. The effects of varying gas flow rates at optimum reaction temperature of about 500ºC and feed size of < 1.0 mm on yield and composition of bio-oil, char and gas were investigated. The results for three runs with flow rate of gas of 45, 80 and 70 L/min, respectively, were obtained. The distribution of pyrolysis products was calculated gravimetrically by mass balance and corrected with optimization mass model using proximate and ultimate analysis of feedstock and pyrolysis products. The maximum yield of bio-oil (52 wt%) was obtained in run 3 with flow rate of gas of 70 L/min having heating value of 21.20 MJ/kg. GC-MS analysis identified the major chemical compounds present in the bio-oil which were levoglucosan, hydroxyl acetaldehyde, acetol, acetic acid, phenols, 2-methyl-2-cylopenten-1-one, guaiacol, 2(5H)-furanone, fufuryl alcohol, p-cresol and 2-ethyl alcohol. The bio-oil produced from run 3 had higher amounts of aromatic hydrocarbons, non-methoxylated phenolics, levoglucosan and smaller amounts of acids. On the other hand, bio-oil obtained from TGRP experiments had low value of total acid number (57.73 mg of KOH/g) indicating less oxygenating compounds with greater heating value in the product.

Conventional and autothermal pyrolysis of corn stover: Overcoming the processing challenges of high-ash agricultural residues

The high ash content of agricultural residues and other kinds of herbaceous biomass makes it a challenging feedstock for fast pyrolysis to bio-oil. Using corn stover as a representative feedstock, this study investigates fast pyrolysis of high ash, herbaceous biomass in a pilot-scale fluidized bed reactor using both conventional, nitrogen-blown and autothermal, air-blown operation. Initial efforts to pyrolyze corn stover were challenged by bed fouling, which prevented steady reactor operation. Substitution of coarser bed material allowed operation at higher superficial velocities, which promoted attrition and elutriation of recalcitrant biochar particles from the reactor. This resulted in dramatic improvement in stable reactor operation for both conventional and autothermal pyrolysis with bio-oil yields among the highest reported for pyrolysis of corn stover. The oxygen-to-biomass equivalence ratio required for autothermal operation was 6.8%. Autothermal operation also resulted in significant process intensification, increasing corn stover throughput from 7.8 kg hr−1 to 21.9 kg hr−1 for this 8.9 cm diameter reactor. Air-blown, autothermal operation did not significantly reduce bio-oil yield despite the presence of partial oxidation reactions. Carbon balances indicate carbon yields of biochar and aqueous, bio-oil light ends decreased by 18.5% and 4.7%, respectively, during autothermal pyrolysis compared to conventional pyrolysis while the more valuable, organic-rich heavy ends of the bio-oil were essentially preserved.

Detection of Agglomeration by Analysis of Vibration Signatures in a Pilot-Scale Fluidized Bed Reactor of Propylene Polymerization

Abstract Polymerization of propylene was performed in a pilot fluidized bed reactor, resembling an industrial unit. In order to detect agglomeration in this reaction process, wall vibration signatures of the bed, which contains useful information about its hydrodynamics, were measured by an accelerometer. This approach is non-intrusive and can be easily applied in industry. Different methods employed to analyze the measured vibration signatures. Average cycle frequency of the signatures showed that agglomerates were formed and settled down in the reactor during the process. Plot of the power spectral density function of vibration signals showed that the peak corresponding to the dominant frequency generated by bubbles is located around 2,000 Hz. Energy of the signal among the three hydrodynamic structures in the bed (i. e., micro, meso and macro-scales) showed a decrease in share of macro-scale and a slight increase in share of micro and meso-scales due to the formation of agglomerates. The principal component analysis was performed to characterize the hydrodynamic changes occurred in bed due to formation of agglomerates during the polymerization reaction. Using the S-statistic test, changes in the hydrodynamics of the bed due to formation of agglomerates were detected about 20 minutes before defluidization.

Comparative 2D and 3D analysis on the hydrodynamics behaviour during biomass gasification in a pilot-scale fluidized bed reactor

Abstract 2D and 3D simulations were carried out to predict the whole gasification process behaviour in a pilot-scale bubbling fluidized bed reactor. Special concern for the complex hydrodynamics phenomena within the fluidized bed was undertaken. The implemented multiphase Eulerian-Eulerian mathematical model was validated by comparison to experimental gasification runs and fluidization curves gathered from the pilot-scale fluidized bed. Appropriate 2D and 3D computational domains were achieved by applying a mesh sensitivity study. Solids distribution within the fluidized bed, mixing and segregation phenomena and binary mixture heat transfer were comparatively studied for both configurations. 3D simulations showed improved predicting performance with the experimental results. Also, 3D simulations presented improved segregation degree, while 2D simulations showed improved mixing index, alongside with a tendency to underestimate the reactor heat transfer behaviour. Main findings point to a general good agreement with some close resemblances in the solids distribution between the 2D and 3D simulations whenever quantitative values were considered, while in absolute terms larger discrepancies were seen. The bed expansion was misrepresented at higher superficial gas velocities to a great extent by the 2D configuration. Moreover, it was found that higher superficial gas velocity will induce higher differences between both configurations. Lastly, both configurations successfully described the general tendencies, however, 2D simulations are appropriate every time accuracy is not demanding, whereas 3D simulations should be considered for accurate predictions.

Selection of cost-effective magnesium sources for fluidized struvite crystallization

Struvite crystallization has been considered a promising approach to recover phosphorus from wastewater. However, its practical application is limited, probably because of the high cost of magnesium (Mg). In this study, a comprehensive economic analysis was conducted using five Mg sources (MgCl2, MgSO4, MgO, Mg(OH)2, and bittern) during the operation of a pilot-scale fluidized bed reactor (FBR), using swine wastewater as the case matrix. First, the economic operating conditions were investigated, and subsequently, the performance and the costs of the five Mg sources were compared. The results indicated that the FBR could be operated most economically at pH of 8.5 and Mg to phosphorus (Mg/P) molar ratio of 1.5. Under these conditions, no significant differences in phosphorus removal and product quality could be found between the five Mg sources. Selecting the most economical Mg source was thus highly dependent on the prices of the reagents and Mg sources. Low-solubility Mg sources were preferable when NaOH was priced higher, while high-solubility Mg sources proved more economical when HNO3 was expensive. The bittern was the most economical choice only when the distances for total inorganic orthophosphate removal and struvite recovery were shorter than 40 and 270km, respectively. The current study provides an overview of the economic selection of an Mg source, which can help reduce the cost of struvite crystallization.

Recovery and removal of fluoride from fluorine industrial wastewater by crystallization process: a pilot study

Recovering fluoride from wastewater has large economic and environmental significance within the fluorine industry. A novel crystallization process was proposed for the recovery and the removal of fluorine-containing industrial wastewater by steps. A pilot-scale reaction-separation integrated reactor was used to recover the sandy cryolite via crystallization. A pilot-scale fluidized bed reactor was used to recover the sandy calcium fluoride via crystallization. The results showed that the recovery rate of cryolite was greater than 70%, with a purity of more than 89%. The qualities of cryolite products could meet the national standard for synthetic cryolite in China. The purity of the calcium fluoride was greater than 71%, with a particle size of 153.1 μm, and a water content of 27%. The qualities of calcium fluoride products could meet the national standard of comminuted fluorspar in China. Both the cryolite products and the calcium fluoride products could be reused as raw materials. The fluoride concentration of the wastewater was less than 10 mg/L, which met the national discharge standard in China.

Biochar Gasification: An Experimental Study on Colombian Agroindustrial Biomass Residues in a Fluidized Bed

The effect of lignocellulosic biomass composition on gasification of biochar in a pilot-scale fluidized-bed reactor was studied. First, three biomass samples from agroindustrial sectors of Colombia were pyrolyzed. These biochars were then subjected to gasification. The biomasses, biochars, and gasification residues were subjected to various physicochemical and morphological analyses to study the evolution of the carbonaceous structure and syngas composition. In the case of sugar cane bagasse and rice husk, the high contents of cellulose and hemicellulose promoted the thermochemical conversion of the biochar into syngas; however, in the palm kernel shell, its high lignin content made thermochemical pyrolysis and gasification difficult as a result of the recalcitrance of the lignitic structure, which forms a more organized carbonaceous structure.

Pilot Scale Production of Activated Carbon Spheres Using Fluidized Bed Reactor and Its Evaluation for the Removal of Hexavalent Chromium from Aqueous Solutions

Large scale production of activated carbon is need of ongoing research due to its excellent adsorption capacity for removal of heavy metals from contaminated solutions. In the present study, polymeric precursor polystyrene beads [Brunauer Emmett Teller (BET) surface area, 46 m2/g; carbon content, 40.64%; crushing strength, 0.32 kg/sphere] were used to produce a new variant of activated carbon, Activated Carbon Spheres (ACS) in a pilot scale fluidized bed reactor. ACS were prepared by carbonization of polymeric precursor at 850 °C followed by activation of resultant material with steam. Prepared ACS were characterized using scanning electron microscope, CHNS analyzer, thermogravimetric analyzer, surface area analyzer and crushing strength tester. The produced ACS have 1009 m2/g BET surface area, 0.89 cm3/g total pore volume, 92.32% carbon content and 1.1 kg/sphere crushing strength with less than 1% of moisture and ash content. The ACS were also evaluated for its potential to remove hexavalent chromium [Cr(VI)] from contaminated solutions. The chromium removal is observed to be 99.1% at initial concentration 50 mg/l, pH 2, ACS dose 1 g/l, contact time 2 h, agitation 120 rpm and temperature 30 °C. Thus ACS can be used as an adsorbent material for the removal of Cr(VI) from contaminated solutions.

Multi-fluid reactive modeling of sorption enhanced steam reforming of coke oven gas in fluidized bed

A three-fluid Eulerian approach, which couples structure-dependent kinetic models of catalysis and carbonation reactions, is used to model sorption-enhanced steam reforming of coke oven gas (SER-COG) in a pilot-scale fluidized bed reactor. Three pellet models (PM-I, PM-II, PM-III) in terms of methodologies coupling hydrodynamics of multiple fluids with multi-scale reactions were comparatively studied. Pellet model PM-I, which dealt with catalyst and sorbent as separate dispersion phases and linked reaction kinetics closely with micro-structures of pellets in corresponding disperse phase, well reproduced the reformed gas compositions observed in experiments. With pellet model PM-I incorporated with the three-fluid Eulerian approach, numerical studies demonstrated that high H2 or CO inlet fraction would suppress conversion of CH4, and decreased CO selectivity because of the reduced reforming rates of steam and methane. High initial H2 fraction in COG also amplified the suppression of high operational pressures on SER-COG. To achieve CH4 conversion>90%, products with H2>95% and CO<1%, a C/A (mass) of 0.2–1, steam/CH4 around 3.3–4.3 were suggested for atmospheric SER-COG at 580°C when a mixture of H2/CH4/CO (0.3:0.6:0.06, molar) was fed as fuel.