Reactor Height Research Articles

Effect of compressibility factor on the hydrodynamics of naphtha catalytic-reforming reactors

A detailed steady-state catalytic-reforming unit (CRU) reactor process model is simulated in this work, and for the first time, different compressibility Z factor correlations have been applied using gPROMS software. The CRU has been modeled and simulated with the assumption that the gas phase behaves like an ideal gas. This is assumed for the four reactors in series and for different conditions of hydrogen–hydrocarbon ratio (HHR), operating temperature, and pressure. The results show that the Z factor varies at every point along the height of the reactors depending on reaction operating pressure, temperature, and HHR ratio. It also shows that the magnitude of deviation from ideal gas behaviour can be measured over the reactor height. The Z factor correlation of Mahmoud (J Energy Resour Technol Trans ASME 136:012903, 2014) is found to be suitable for predicting the Z factor distribution in the reactors.

Design scenarios of outdoor arrayed cylindrical photobioreactors for microalgae cultivation considering solar radiation and temperature

Advancing microalgae biotechnologies requires the design of high efficiency, large scale outdoor photobioreactor systems. Here we present a predictive biomass productivity model to define system design parameters yielding high biomass productivities for a facility encompassing arrays of cylindrical photobioreactors (PBRs) in a sub-tropical location (Brisbane, Australia). The model analyses the temperature and the light distributed through the culture medium as a function of PBR height, diameter, spacing distance between reactors, biomass concentration and cultivation regime (continuous vs. batch; fixed vs. capped temperature control). Temporal changes in light and temperature were used to predict volumetric and areal productivities (Pvol and Pareal respectively) for three Chlorella strains (C. vulgaris, C. sp. 11_H5 and C. pyrenoidosa). A simple empirical relationship was derived to rapidly predict Pvol in PBR arrays based on the ratio of spacing distance and reactor height (L/H) if the Pvol of a single, unshaded PBR was known. For C. vulgaris under a continuous operation and variable temperature (within its maximum growth threshold), the highest Pvol in the range analysed was obtained at the smallest diameter (0.1 m), highest biomass concentration (1.5 g L−1) and largest L/H, (Pvol ~0.3 g L−1 d−1). In contrast, the highest Pareal (~50 t ha−1 yr−1) was found at higher diameters (0.15 and 0.3 m), a lower biomass concentration (0.3 g L−1) and low L/H (0.2–0.4); this was attributed to a higher overall culture volume per PBR and per area. Our predictions, based on light and temperature effects on productivity, suggest that attaining a high Pvol could reduce costs, energy and materials associated with water usage, harvest loads and PBRs; whereas attaining a Pareal toward its maxima could reduce costs associated with land. The model supports effective PBR array design and process optimisation to help minimise production cost.

Performance Analysis of Air and Oxy-Fuel Laminar Combustion in a Porous Plate Reactor

Greenhouse gas emissions from the combustion of fossil fuels pose a serious threat to global warming. Mitigation measures to counter the exponential growth and harmful impact of these gases on the environment require techniques for the reduction and capturing of carbon. Oxy-fuel combustion is one such effective method, which is used for the carbon capture. In the present work, a numerical study was carried out to analyze characteristics of oxy-fuel combustion inside a porous plate reactor. The advantage of incorporating porous plates is to control local oxy-fuel ratio and to avoid hot spots inside the reactor. A modified two-steps reaction kinetics model was incorporated in the simulation for modeling of methane air-combustion and oxy-fuel combustion. Simulations were performed for different oxidizer ratios, mass flow rates, and reactor heights. Results showed that that oxy-combustion with an oxidizer ratio (OR) of 0.243 could have the same adiabatic flame temperature as that of air-combustion. It was found that not only does OR need to be changed, but also flow field or reactor dimensions should be changed to achieve similar combustion characteristics as that of air-combustion. Fifty percent higher mass flow rates or 40% reduction in reactor height may achieve comparable outlet temperature to air-combustion. It was concluded that not only does the oxidizer ratio of oxy-combustion need to be changed, but the velocity field is also required to be matched with air-combustion to attain similar outlet temperature.

Influencing the solid fraction distribution in a circulating fluidized bed system using differently shaped internals

Solids distribution and gas–solid contact gain in importance for new and alternative energy conversion processes realized with fluidized bed systems. The so-called dual circulating fluidized bed (DCFB) system represents a reactor concept proposed for these novel processes. This concept is based on the interconnection of two circulating fluidized beds via two loop seals. In this work, a cold flow model, designed according to the DCFB system, is used to investigate the influence of constrictions placed along the height of the secondary reactor. Experiments were performed with differently shaped constrictions, aperture ratios, varying distance between the constrictions and different length of the horizontal section at the smallest cross section in the constriction. In general, the mean solid fraction in the upper part of the secondary reactor benefits from the constrictions (mean solid fraction up to +1800% compared to a straight reactor without any constriction). The mean solid fraction in the reactor increased with the solid circulation rate between the reactors and the superficial gas velocity in the secondary reactor. Further, investigations showed substantial deviations for the solid fraction in the upper part of the reactor for the investigated geometries of the constrictions. Fluid dynamic limitations restricting the operating range of the cold flow model could be observed. These limitations depend on combinations of solid circulation rate and superficial gas velocity in the secondary reactor and differ for the investigated geometries. Solid fraction distribution in the secondary reactor showed high solid fractions in the constricted sections (up to 60%) while it remained low between the constrictions.

Assessing the effects of intra-granule precipitation in a full-scale industrial anaerobic digester.

In this paper, a multi-scale model is used to assess the multiple mineral precipitation potential in a full-scale anaerobic granular sludge system. Reactor behaviour is analysed under different operational conditions (addition/no addition of reject water from dewatering of lime-stabilized biomass) and periods of time (short/long term). Model predictions suggest that a higher contribution of reject water promotes the risk of intra-granule CaCO3 formation as a result of the increased quantity of calcium arriving with that stream combined with strong pH gradients within the biofilm. The distribution of these precipitates depends on: (i) reactor height; and (ii) granule size. The study also exposes the potential undesirable effects of the long-term addition of reject water (a decrease in energy recovery of 20% over a 100-day period), caused by loss in biomass activity (due to microbial displacement), and the reduced buffer capacity. This demonstrates how both short-term and long-term operational conditions may affect the formation of precipitates within anaerobic granules, and how it may influence methane production and consequently energy recovery.

Dual fluidized bed steam gasification: Change of product gas quality along the reactor height

The impact of the counter-current column of the gasification reactor of a 100 kWth dual fluidized bed steam gasification pilot plant on the product gas quality was investigated. Through the advanced design of the gasification reactor by operating the lower part as bubbling bed and the upper part as counter-current column, the gas-solid interactions between downward flowing hot bed material particles with upwards flowing product gas could be enhanced. This was realized by equipping the counter-current column with constrictions, which increase the residence time and the bed material hold-up. Thus, the conversion efficiency of the fuel including the tar was improved. For the investigations three different experimental campaigns converting softwood pellets using a mixture of olivine and limestone (50/50 wt.-%), a mixture of feldspar and limestone (50/50 wt.-%), and 100 wt.-% quartz as bed materials were conducted. Higher H2 contents and lower contents of higher hydrocarbons could be detected along the height of the counter-current column. Especially heavy tar compounds could be reduced significantly. These two effects are explained by enhanced water gas shift and steam reforming reactions. In case of catalytically inactive quartz, only thermal effects are available and therefore lower effects on tar reduction could be obtained.

Experimental characterization of turbulent mixing performance using simultaneous stereoscopic particle image velocimetry and planar laser-induced fluorescence

Simultaneous measurements of velocity and concentration using stereoscopic particle image velocimetry (stereo-PIV) and planar laser-induced fluorescence (PLIF) were used to investigate the mixing performance of a scaled-up multi-inlet vortex reactor (MIVR). Data were collected in three measurement planes located at different heights from the reactor bottom (¼, ½, and ¾ of the reactor height) for Reynolds numbers of 3250 and 8125 based on the reactor inlet velocity and hydraulic diameter. The collected data were analyzed to determine turbulent flow statistics such as turbulent viscosity, turbulent diffusivity, and turbulent Schmidt number. When analyzed across 16 different azimuth angles and radial positions (r) normalized by the reactor radius (Ro), the turbulent viscosity was found to be nearly axisymmetric. In the free-vortex region (r/Ro > 0.2), the turbulent viscosity results were nearly constant. Near the center of the reactor in the forced-vortex region (r/Ro < 0.1), the turbulent viscosity significantly increased, with peak values occurring near the center. The turbulent viscosity and Reynolds shear stress were highest near the reactor exit at the ¾ plane. The dominance of high turbulent fluxes and low concentration gradients near the reactor center led to high turbulent diffusivity. Away from the center, the turbulent diffusivity was reduced because of large concentration gradients and low turbulence intensity in the spiral arm region. The turbulent Schmidt numbers were also found to correlate with concentration gradients. The turbulent Schmidt number values were found to vary from 0.1 to 1.2. The highest spatial variation in $$S{c_t}$$ was observed in the spiral arms region, where the concentration gradients are also the highest. This spatial variation in Schmidt number contrasts with the common assumption of constant $$S{c_t}$$ in Reynolds-averaged CFD models. A typical stereo-PIV/PLIF simultaneous instantaneous measurement for Re = 8125. The color and vectors represent the instantaneous mixture fraction and in-plane velocity field, respectively. (a) ¼ Plane. (b) ½ Plane. (c) ¾ Plane.

A monolith CuNiFe/γ-Al2O3/Al catalyst for steam reforming of dimethyl ether and applied in a microreactor

Structured CuNi/γ-Al2O3/Al catalyst exhibited a good stability in steam reforming of dimethyl ether (DME SR) system, but there was a high CO concentration in outlet gas (about 25%). For the problem, a series of CuNiFe/γ-Al2O3/Al catalysts with different Fe content were prepared through impregnation method. It is found that the CO concentration obviously decreased after the addition of Fe. When the loading amount of Fe was 12.5 wt%, the catalyst presented the best performance: the conversion of DME reached 100% and the H2 yield was over 0.9 in both the microreactor and fixed-bed reactor. Furthermore, cross-flow channels and parallel-flow channels were built respectively by mesh-type catalyst and plate-type catalyst in the microreactor. The gas/solid mass transfer limitations in both flow channels were investigated by Damköhler number (Da). The results showed that the Da values of cross flow were always <0.01, while the values of parallel flow were >0.01. It indicated that the diffusion over mesh-type catalyst was less influenced by temperature and reactor height, making it a more appropriate choice for the microreactor.

Experimental Investigation of Combustion Characteristics and Emissions for a Pilot-Scale Bubbling Fluidized Bed Combustor Fueled by Biomass Chips of Sesame and Broad Bean Stalks

ABSTRACTThe study work investigated the combustion characteristics and gaseous emissions during burning chips of sesame and broad bean stalks in a pilot-scale Bubbling Fluidized Bed Combustor (BFBC). The effects of the startup temperature, excess air percentage, moisture content, and injection location of secondary air on axial temperature profiles along the combustor and flue gas emissions were studied. The results indicated that biomass fuel characteristics have a significant role in the distribution of axial temperature along the reactor height. A great effect on the axial temperature profile was detected when the startup temperature was changed. The 30% and 100% excess air represent the near percentages for better combustion characteristics for burning the stalks of broad bean and sesame, respectively. Enhancement was observed in the combustion behavior when using the dried samples compared to the as-received samples. Higher values of axial temperature and lower concentrations of flue gas emissions are a result of rising injection location of the secondary air. The combustion efficiency reached to 92.4% for burning the sesame stalks and 96.6% for the broad bean stalks. Based on an energy balance performed on the BFBC, the thermal efficiency was ranged from 28.2% to 59.4% for SS and from 17.2% to 42.1% for broad bean stalks.

A decentralized biomass torrefaction reactor concept. Part I: Multi-scale analysis and initial experimental validation

A new, simplified biomass torrefaction reactor concept that operates under oxygen-lean conditions is proposed as a potential way to downscale torrefaction reactors for small- and medium-scale applications. To verify the feasibility of the concept, a multi-scale analysis was conducted to understand the design requirements, underlying chemistry, intra-particle effects, and overall reactor-scale heat transfer. We demonstrate that the heat transfer within the reactor and the appropriate reactor height is largely determined by gas-phase advection. Finally, by implementing a laboratory-scale reactor and operating it under diverse conditions, we show that such a design can indeed satisfy the requirements for torrefaction. This lays the basis for the second part of this two-part paper, where we develop a detailed mathematical model for this concept. In future studies, we will also systematically define and map the performance metrics and reaction conditions in order to understand the scaling laws for potential commercialization of this concept.

Photocatalytic Oxidation of Toluene on Fluorine Doped TiO2/SiO2 Catalyst Under Simulant Sunlight in a Flat Reactor

Improving the capacity of TiO2 semiconductors for visible light response is a key problem for utilization of solar energy in photo-catalytic degradation of organic pollutants. Both catalyst character and reactor conditions are important for the reaction efficiency. The fluorine ion doped TiO2/SiO2 catalyst was prepared by sol-gel method using HF solution as fluorine source. The activity test and UV–vis results indicated that this catalyst was superior to TiO2 P25 in photocatalytic oxidation of gaseous toluene under simulant sunlight irradiation due to the enhancement of visible and ultraviolet light absorbance. GC-MS results indicated that the main intermediates accumulated on active sites included benzoic acid, benzaldehyde, and phenol. A flat interlaid reactor was designed for continuous treatment of the stream with F-TiO2/SiO2 film. The results showed that coating the catalyst on the surface of both top and bottom glass substrates, through the knife coating method with an optimal reactor height, attained the highest efficiency. In addition, the presence of water and oxygen enhanced the oxidation of toluene due to the generation of hydroxyl radicals and peroxy radicals, respectively. The toluene oxidation rate increased with the increase in water vapor concentration in the range of 0~60 vol.%.

Determining the effects of aeration intensity and reactor height to diameter (H/D) ratio on granule stability based on bubble behavior analysis.

Aerobic granular sludge was considered as a leading wastewater technology in the next century. However, the loss of granule stability limited the application of this promising biotechnology. Increasing aeration intensity and height to diameter (H/D) ratio were conventional strategies to enhance granule stability. In this study, hydraulic effects of aeration intensity and H/D ratio were explored basing on bubble behavior analysis. However, results revealed that due to viscous resistance, increasing aeration intensity and H/D ratio had limited effects on enhancing hydraulic shear stress, not to mention the extra operation and construction cost. A deflector component was further applied to regulate hydraulic shear stress on large granules under low aeration intensity and H/D ratio. Hydraulic shear stress of large granules was constantly around 3.0 times higher than that in the conventional reactor, resulting in higher percentage of granules within optimal size range (81.95 ± 5.13%). A high abundance of denitrifying bacteria was observed in reactors, which led to high TN removal efficiency of 88.6 ± 3.8%.

Stratification of microbial communities throughout a biological sulphate reducing up-flow anaerobic packed bed reactor, revealed through 16S metagenomics

Biological sulphate reduction (BSR) is a promising low-cost treatment of acid rock drainage effluents. In this paper, the system performance and microbial ecology of a lactate supplemented BSR up-flow anaerobic packed bed reactor (UAPBR) are evaluated across reactor height and compared to a continuous stirred tank reactor (CSTR). The biomass concentrations of planktonic and biofilm communities were quantified and subsequently characterised by 16S rRNA gene amplicon sequencing. The defined microbial communities were shown to correlate with differing availability of lactate, volatile fatty acids produced from lactate degradation and sulphate concentration. The UAPBR was able to achieve near complete sulphate conversion at a 4-day hydraulic residence time (HRT) at a sulphate feed concentration of 10.41 mM (1 g/L). The high volumetric sulphate reduction rate of 0.184 mM/L.h achieved in the first third of the reactor was attributed to OTUs present in the planktonic and biofilm communities. While the scavenging of sulphate within the final third of the UAPBR was attributed to an acetate oxidising genus of SRB which was not detected in the lactate-fed CSTR. The detailed analyses of the microbial communities throughout the UAPBR and CSTR contribute to the growing understanding of the impact of the microbial communities of BSR reactors on system performance.

Full-Scale Experimental Study of Groundwater Softening in a Circulating Pellet Fluidized Reactor.

The softening effect of a new type of circulating pellet fluidized bed (CPFB) reactor on groundwater was studied through a full-scale experiment. The operation of the CPFB reactor in the second water plant in Chang’an District in Xi’an China was monitored for one year, and the results were compared with those for the Amsterdam reactor in The Netherlands. The removal efficiency of Ca2+ in the CPFB reactor reached 90%; the removal rate of total hardness was higher than 60%; effluent pH was 9.5–9.8; the turbidity of the effluent and the turbidity after boiling were lower than 1.0 NTU; the unit cost was less than €0.064 per m3; and the softened effluent was stable. The pellets in the CPFB reactor were circulated, providing higher crystallization efficiency. The diameter of the discharged pellets reached between 3–5 mm, and the fluidized area height of the CPFB reactor was 4 m. The performance parameters of the CFPB reactor were optimized.

Scaling-up of an up-flow anaerobic sludge blanket incorporated with a bio-filter liner system for treating kitchen wastes

A bottom biofilter liner incorporated to an Up-flow Anaerobic Sludge Blanket Reactor (UASBR) was designed, developed and evaluated for food wastes for 47 days as a semi-batch set-up with intermittent up-flow circulation (very infrequent) to simulate the start-up. This study was conducted to scale-up already developed UASBR. In the mineralization process, the surface area at the bottom of the reactor is the most critical parameter. Thus, it has been found that total dissolved solids (TDS) of bottom, middle and top strata seem to follow first order rate reactions. The TDS was divided by the feeding that took place at different times to give a unit production of TDS at time. The average unit value of the bottom strata was then divided by the lowest experimental TDS value, thus yielding a ratio equating the two areas of desired to that of the experimental value. Therefore, a diameter (or area) could be found for any loading rate. The height of the reactor was found by considering ratios of the volumes to that of the predicted maximum TDS concentration obtained from the learning curve of the first order reactions and the maximum experimental value. The total height of reactor is 3.4 m, which is optimum for kitchen wastes, would remain constant for different loading rates. A prototype would be constructed and performance would be evaluated to reconfirm the hypothesis that a biofilter liner system is effective in reducing inhibitions often encountered in UASB reactors.

The Integration of Gasification Systems with Gas Engine to Produce Electrical Energy from Biomass

The need for energy especially biomass-based renewable energy continues to increase in Indonesia. The objective of this research was to design downdraft gasifier machine with high content of combustible gas on gas engine. Downdraft gasifier machine was adjusted with the synthetic gas produced from biomass. Besides that, the net energy ratio, net energy balance, renewable index, economic analysis, and impact assessment also been conducted. Gas engine that was designed in this research had been installed with capacity of 25 kW with diameter and height of reactor were 900 mm and 1000 mm respectively. The method used here were the design the Detailed Engineering Design (DED), assembly, and performance test of gas engine. The result showed that gas engine for biomass can be operated for 8 hours with performance engine of 84% and capacity of 25 kW. Net energy balance, net energy ratio, and renewable index was 30 MJ/kWh-electric; 0.89; 0.76 respectively. The value of GHG emission of Biomass Power Generation is 0.03 kg-CO2eq/MJ. Electrical production cost for Biomass Power Generation is about Rp.1.500,/kWh which is cheaper than Solar Power Generation which is about of Rp. 3.300,-/kWh.

Post-treatment of anaerobic effluent containing 1,4-dioxane and heavy metals via auto-aerated down-flow hanging luffa (ADHL) system

Abstract Biodegradation of anaerobic effluent containing 1,4-dioxane and heavy metals via auto-aerated down-flow hanging luffa (ADHL) system was extensively investigated. The oxygen was naturally supplied to the consortium bacterium through windows located along the reactor height creating favorable aerobic conditions. The bioreactor efficiently removed 1,4-dioxane and total chemical oxygen demand (CODt) from anaerobic effluent without significant inhibitory effects. Removal efficiencies of CODt and 1,4-dioxane were significantly increased from 31.3 ± 10 to 59.5 ± 5.9% and from 43.7 ± 11.9 to 90 ± 4.9% at increasing the hydraulic retention time (HRT) from 5.7 to 17.3 h, respectively. Moreover, ADHL system was very effective for removal of heavy metals (Cr6+, Cu2+, Fe3+, Mn2+, Ni2+) where the extracellular polymeric substances (EPS) concentrations were quite high and amounted to 12.3 ± 1.3 g/g biomass at an HRT of 17.3 h. The nitrification efficiency was 3.0, 46.8 and 56.3% at HRTs of 5.7, 11.5 and 17.3 h, respectively. Batch experimental results showed that the key removal mechanism of 1,4-dioxane was adsorption followed by biodegradation process.

Process optimization of CNP removal from industrial soft drink wastewater in a single up flow A2O with continuous feed and intermittent discharge regime.

Simultaneous removal of carbon and nutrients (CNP) in a single laboratory-scale bioreactor is advantageous in terms of reactor volume and energy consumption. In this study, an innovative up-flow anaerobic/anoxic/aerobic (A2O) single bioreactor with continuous feed and intermittent discharge (CFID) regime equipped with a movable aerator in the reactor height for simultaneous removal of CNP from soft drinks wastewater was successfully designed, fabricated and operated. The effects of four independent variables, i.e. hydraulic retention time (HRT), aerator height, biomass concentration and nitrogen/soluble chemical oxygen demand (N/sCOD) ratio at three levels in the range of 4-8 h, 37-55.5 cm, 4,000-6,000-1, and 0.05-0.2, respectively, on eight process responses were investigated. The central composite design (CCD) and response surface methodology (RSM) were applied to design the experimental conditions, model the obtained data, and optimize the process. The bioreactor provides three conditions with different dissolved oxygen (DO) (anaerobic, anoxic and aerobic) in a single bioreactor by placing the aerator in the middle of the reactor. As a result, the maximum sCOD, total nitrogen (TN) and total phosphorus (TP) removal were about 100, 92 and 41%, respectively. The optimum region obtained was an HRT of 5-11 h, a mixed liquor suspended solids (MLSS) concentration of 4,000-4,700 mgL-1, and an aerator height of 46.25 cm, at the N/sCOD ratio of 0.1.

The Effect of COD Concentration Containing Leaves Litter, Canteen and Composite Waste to the Performance of Solid Phase Microbial Fuel Cell (SMFC)

This research is conducted to analyze and determine the optimum of COD concentration containing leaves litter, canteen and composite waste to power density and COD removal efficiency as the indicator of SMFC performance. COD as the one of organic matter parameters perform as substrate, nutrient and dominating the whole process of SMFC. Leaves litter and canteen based food waste were obtained from TPST UNDIP in Semarang and treated in SMFC reactor. Its reactor was designed 2 liter volume and equipped by homemade graphene electrodes that were utilized at the surface of organic waste as cathode and in a half of reactor height as anode. COD concentration was initially characterized and became variations of initial COD concentration. Waste volume was maintained 2/3 of volume of reactor. Bacteria sources as the important process factor in SMFC were obtained from river sediment which contain bacteroides and exoelectrogenic bacteria. Temperature and pH were not maintained while power density and COD concentration were periodically observed and measured during 44 days. The results showed that power density up to 4 mW/m2 and COD removal efficiency performance up to 70% were reached by leaves litter, canteen and composite waste at days 11 up to days 44 days. Leaves litter contain 16,567 mg COD/l providing higher COD removal efficiency reached approximately 87.67%, more stable power density reached approximately 4.71 mW/m2, and faster optimum time in the third day than canteen based food waste and composite waste. High COD removal efficiency has not yet resulted in high power density.

Effect of Moisture Content on Power Generation in Dual Graphene Anode Compost Solid Phase Microbial Fuel Cells (DGACSMFCs)

Moisture content which affects the decomposition of organic material is one of composting parameters. The optimum moisture content indicates the higher power generation. This research aims to determine the optimum moisture content toward power density during the composting process in DGACSMFCs. The reactor was designed with dual graphene anode placed on the base and a half of reactor height in 2 L effective volume. Moisture content was varied at 40%; 50%; 60%; with 4 turning frequency, C/N ratio 30:1, and the mixed waste-leaves litter and canteen based food waste, during 23 days of the observation time. Other parameters of the composting process such as pH, temperature, C-Organic, N-Total, P-Total, and K-Total were also observed as control parameters. The result shows that the optimum moisture content is 60% with power density 17.74 mW/m2, and the final compost characteristics are meet the compost requirement based on SNI 19-7030-2004 about the specification of compost from domestic waste..