BEntropy Production of Moving Bed Reactors

We present an entropy production formulationn for a gas-solid moving bed reactor,which we have not seen in any published reference. Apart from the traditional “flows” and “forces”,e. g., those for heat conduction and mass diffusions in each phase , we introduced the heterogeneouseffects: gas-solid heat and mass transfer, which lead to some new flows and forces in the entropyproduction formulation.

Continuous Production of Carbon Nanotubes by Using Moving Bed Reactor

High-quality carbon nanotubes were continuously produced by using moving bed reactor. The studies of scanning electron microscopy and transmission electron microscopy reveal their homogeneity both in inner (similar to 10 nm) and outer diameter (20-40 nm) of the tubes. The studies of X-ray photoelectron spectroscopy and the oxidation of carbon nanotubes in air demonstrate that the tubes have good graphitic degree.

Thermochemical Conversion of Coal and Coal-Biomass Blends in an Autothermal Moving Bed Gasifier: Experimental Investigation

A unique laboratory scale auto-thermal moving bed gasifier was designed for studying the thermochemical conversion of coal-biomass blends. For this purpose, two coals (lignite and sub-bituminous), two biomass materials (corn stover and switchgrass), and their respective blends were used. Gasification characteristics of the fuels were evaluated with an emphasis on improving the producer gas composition. The efficiency and product gas compositions reveal that utilizing the inner stainless-steel tubing better promotes heat transfer upwards in the axial direction when compared to utilizing quartz insulation. The H2/CO ratio at the same operating conditions is much higher due to the increase in bed temperature and heat transfer upwards in the axial direction. This improved the overall efficiency by at least 20%. Using pure oxygen and steam, efficiency greater than 50% was obtained for blends with corn stover at steam to oxygen ratio of 2:1. Also, using air as the gasifying agent greatly improved the H2/CO ratios and overall efficiency in blends with corn stover. In contrast, blends with switchgrass were not very effective with respect to the overall gasification characteristics. Blending switchgrass with coal may not be viable option from the viewpoint of generating high quality producer gas for downstream operations.

Heat Transfer within Direct Heating Integrated Moving Bed Torrefier by Method of Lines

This work deals with the determination of the temperature profile within a direct heating moving bed torrefier in order to determine its minimum column height. A thermal model based on eulerian-eulerian two-phase solid-gas theory was performed and solved with the method of lines. In addition, this study allows to investigate the effect of the biomass particle size on the minimum torrefier column height. This investigation was performed by changing, simultaneously, the diameter of particles and the minimum fluidization velocity of the bed. Then, the calculations were made for a counter-current torrefaction reactor of 30 cm in diameter and for 5 kg/h of the feed rate of raw sugarcane bagasse. Results show that the height of the reactor column must be at least 30 cm for that are 1 mm in diameter and 108 cm for particles that are 2 mm in diameter.

Experimental study on filtration performance of the moving bed granular filter with axial flow

The filtration performance of the moving bed granular filter with axial flow (MBGF-AF) is investigated through a large cold experiment. The effect of different operation parameters on the filtration performance (collection efficiency, pressure drop) of the axial-flow moving bed filter is investigated in combination with the dust deposition effect and the mechanism of trapping dust by the capturing particles. The results show that the collection efficiency of MBGF-AF is enhanced by decreasing the superficial gas velocity, increasing the inlet dust concentration properly, or decreasing the moving velocity of the capturing particles. A model covering the above operation parameters is established to calculate the collection efficiency of the moving bed granular filter. It is used in a wide range of operating parameters for the MBGFs.

Effect of seeding biofloc on the nitrification establishment in moving bed biofilm reactor(MBBR)

In recirculating aquaculture systems,nitrification is usually accelerated by inoculating nitrifier or mature biocarriers.In this study,the performance of the establishment of nitrification in the MBBR according to three different strategies:conventional method(Control group A),inoculation with biofloc recovered from a tilapia biofloc culture system(Group B),and addition with extra nitrite(Group C)in the Moving bed biofilm reactor(MBBR)was compared.Among them,the biofloc-inoculated group considerably accelerated the nitrification process in the MBBR(38 d),which is roughly 18 d faster than the control group(A)(56 d)and 21 d faster than group C(59 d).Less ammonia(8 mg/L NH_(4)^(+)-N,10 mg/L in other groups)and external nitrite(2 mg/L NO_(2)􀀀^(-)N)in the influent caused effluent ammonia to drop more slowly(5 d slower than the control group,8 d slower than the B group),which is detrimental to the nitrification process’development.Notably,the influent’s hydraulic retention time(HRT)was reduced from 12 h to 6 h following the successful establishment of nitrification.During the adaptation to reduced HRT,the MBBR inoculated with biofloc experienced short-term changes in the water quality index of the effluent water,whereas the other groups did not.The biofilm seeded with biofloc had the highest mean gray value ratio(1.42)of live/dead cell fluorescence,which grew better and could cover the entire groove under multiple microscope observations.However,the other groups did not demonstrate a similar trend.In summary,the research found that seeding biofloc use as nitrification bioaugmentation into the MBBR of the recirculating aquaculture system(RAS)to greatly speed up the nitrification process.

Inhibition and recovery of nitrification in treating real coal gasification wastewater with moving bed biofilm reactor

Moving bed biofilm reactor （MBBR） was used to treat real coal gasification wastewater. Nitrification of the MBBR was inhibited almost completely during start-up period. Sudden increase of influent total NH 3 concentration was the main factor inducing nitrification inhibition. Increasing DO concentration in the bulk liquid （from 2 to 3 mg/L） had little effect on nitrification recovery. Nitrification of the MBBR recovered partially by the addition of nitrifying sludge into the reactor and almost ceased within 5 days. Nitrification ratio of the MBBR achieved 65% within 12 days by increasing dilute ratio of the influent wastewater with tap water. The ratio of nitrification decreased to 25% when influent COD concentration increased from 650 to 1000 mg/L after nitrification recovery and recovered 70% for another 4 days.

Effect of alkalinity on nitrite accumulation in treatment of coal chemical industry wastewater using moving bed biofilm reactor

Nitrogen removal via nitrite （the nitrite pathway） is more suitable for carbon-limited industrial wastewater. Partial nitrification to nitrite is the primary step to achieve nitrogen removal via nitrite. The effect of alkalinity on nitrite accumulation in a continuous process was investigated by progressively increasing the alkalinity dosage ratio （amount of alkalinity to ammonia ratio, mol/mol）. There is a close relationship among alkalinity, pH and the state of matter present in aqueous solution. When alkalinity was insufficient （compared to the theoretical alkalinity amount）, ammonia removal efficiency increased first and then decreased at each alkalinity dosage ratio, with an abrupt removal efficiency peak. Generally, ammonia removal efficiency rose with increasing alkalinity dosage ratio. Ammonia removal efficiency reached to 88% from 23% when alkalinity addition was sufficient. Nitrite accumulation could be achieved by inhibiting nitrite oxidizing bacteria （NOB） by free ammonia （FA） in the early period and free nitrous acid in the later period of nitrification when alkalinity was not adequate. Only FA worked to inhibit the activity of NOB when alkalinity addition was sufficient.

The effect of bubble plume on oxygen transfer for moving bed biofilm reactor

The movement of the bubble plume plays an important role in the operation of a moving bed biofilm reactor （MBBR）, and it directly affects the contact and the mixture of the gas-liquid-solid phases in the aeration tank and also the oxygen transfer from the gas phase to the liquid phase. In this study, the velocity field is determined by a 4-frame PTV as well as the time-averaged and timedependent velocity distributions. The velocity distribution of the bubble plume is analyzed to evaluate the operating efficiency of the MBBR. The results show that the aeration rate is one of the main factors that sway the velocity distribution of the bubble plumes and affect the operating efficiency of the reactor.

Flow characteristics of mixed particles with a simulated cold state in moving bed reactor

The funnel flow of high-temperature circulating ash and coal in moving bed with height restrictions directly influences the efficiency of coal pyrolysis and scale-up design of reactor.It is one of the technical bottlenecks in the use of moving bed.In order to provide data support for the particle flow and pyrolysis model close to the actual working conditions in the future,this study describes the flow characteristics of solid-solid mixed particles in a cold two-dimensional moving bed.The results indicate that flow char-acteristics of mixed particles in the quartz sand-coal system are better than those in the cold circulating ash-coal system.The optimized conditions were obtained,the insert half angle is 20° and a heat carrier to coal ratio of 6:1.As the mixture progressed downstream,secondary separation of the heat carrier and coal become apparent.Furthermore,mixture residence time has been investigated to explore the relationship between regional residence time and to predict accurately the actual pyrolysis progress in pyrolyzer.

Modeling and analysis of oil shale refinery process with the indirectly heated moving bed

China is rich of oil shale as one of alternative fossil energy resources.The exploitation and utilization of oil shale are strategically important in alleviating the shortage of oil and gas resources in China.However,low utilization rate of raw material,low oil yield,and high content of heavy components in the oil are the main problems in current Fushun type oil shale refinery technology.An indirectly heated moving bed is developed to de-bottleneck Fushun type technology.The oil shale refinery process with the indirectly heated moving bed is modeled and simulated in this work.Based on the simulation,a techno-economic analysis is performed and compared with the conventional Fushun oil shale refinery process.Results show that:for a shale refinery of 3.0 Mt/y scale,375 t/h oil shale retorting requires 149.6 MW of heat,in which 60%of the heat is produced by combustion of the oil shale pyrolysis gas,while remaining 40%from the coal gasified gas.In consideration of investment and operation,the cost of product shale oil of the new process is 2636 CNY/t,which is 12%lower than that of the conventional Fushun refinery process.This benefit comes from higher utilization of raw material and oil yield of the new process.The competitive crude oil price of the indirectly heated moving bed refinery process is about 51$/bbl,while that of the Fushun refinery process is 58$/bbl.During 2017 year,the crude oil price fluctuates at around 50$/bbl,thus the new indirectly heated moving bed refinery process shows better economic competitiveness.

Influence of the pressure drop and the air lock on the solid flux in a cross-flow moving bed

The gas-solid flow pattern in a rectangular cross-flow moving bed is simulated by the multiphase particle-in-cell(MP-PIC)model with the Barracuda software.The computed results are verified by the experimental data.In the bed,the actual solid flux generally equals the solid flow rates in the solid feed and discharge tubes.However,these two flow rates are greatly influenced by the air lock and the pressure drop in the solid feed and discharge tubes,namely,the negative and positive pressure gradients,respectively,rather than the traditional opinion that they are merely controlled by the valve openings.The pressure drops in these tubes are calculated by the proposed“common pressure pool with multiple outlets”(CPPMO)and the“common pressure pool”(CPP)methods.It is found that the local gas resistance dominates the pressure drop in the solid discharge tubes,while the gas frictional resistance determines the pressure drop in the solid feed tube.In addition,when the solid flow rate nearly tends to zero in the solid feed tube,the air lock forms.A solid flux equation is then given by considering both the air lock and the pressure drop factors in the cross-flow moving bed.

Continuous size fractionation of magnetic nanoparticles by using simulated moving bed chromatography

The size fractionation of magnetic nanoparticles is a technical problem,which until today can only be solved with great effort.Nevertheless,there is an important demand for nanoparticles with sharp size distributions,for example for medical technology or sensor technology.Using magnetic chromatography,we show a promising method for fractionation of magnetic nanoparticles with respect to their size and/or magnetic properties.This was achieved by passing magnetic nanoparticles through a packed bed of fine steel spheres with which they interact magnetically because single domain ferro-/ferrimagnetic nanoparticles show a spontaneous magnetization.Since the strength of this interaction is related to particle size,the principle is suitable for size fractionation.This concept was transferred into a continuous process in this work using a so-called simulated moving bed chromatography.Applying a suspension of magnetic nanoparticles within a size range from 20 to 120 nm,the process showed a separation sharpness of up to 0.52 with recovery rates of 100%.The continuous feed stream of magnetic nanoparticles could be fractionated with a space-time-yield of up to 5 mg/(L∙min).Due to the easy scalability of continuous chromatography,the process is a promising approach for the efficient fractionation of industrially relevant amounts of magnetic nanoparticles.

Industrial application of the technique of removing Mo by a combination of moving packed bed and fluidized bed ion exchange

The application of the technique of removing molybdenum by moving packed bedand fluidized bed ion-exchange in a factory was described. The data showed that the Mo removalefficiency is above 99 percent, and the Mo content in APT (Ammonium Paratungstate) is controlledsteadily below 18 X l0^(-6), in the case of treating the feed liquor containing Mo 1.4 g/L. Thetechnique is simple and convenient in operation, good reusability of resin, loss consumption ofdesorption reagent and little pollution on environment. The loss of tungsten is less than 0.5percent. The technique bas been proved to be an economical and efficient process for Mo removal.

Fate of Parent and Substituted Polycyclic Aromatic Hydrocarbons in SBR/MBBR Treatment Process:Experimental Value Against Model Prediction

The knowledge of the existence,distribution and fate of polycyclic aromatic hydrocarbons(PAHs)and substituted polycyclic aromatic hydrocarbons(SPAHs)in wastewater treatment plants(WWTPs)was vital for reducing their concentrations entering the aquatic environment.The concentrations of 13 SPAHs and 16 PAHs were all determined in a WWTP with styrene butadiene rubber(SBR)in partnership with the moving bed biofilm reactor(MBBR)process.SPAHs presented a higher concentration lever than PAHs in nearly all samples.The total removal efficiencies of PAHs and SPAHs ranged from 64.0%to 71.36%and 78.4%to 79.7%,respectively.The total yearly loads of PAHs(43.0 kg)and SPAHs(73.0 kg)were mainly reduced by the primary and SBR/MBBR biological treatment stages.The tertiary treatment stage had a minor contribution to target compounds removal.According to a synthesis and improvement fate model,we found that the dominant processes changed as the chemical octanol water partition coefficient(K_(ow))increased.But the seasonal variations of experimental removal efficiencies were more obvious than that of predicted data.In the primary sedimentation tank,dissolution in the aqueous phase and sorption to sludge/particulate matter were controlling processes for the removal of PAHs and SPAHs.The sorption to sludge and biodegradation were the principal removal mechanisms during the SBR/MBBR biological treatment process.The contribution of volatilization to removal was always insignificant.Furthermore,the basic physicochemical properties and operating parameters influenced the fate of PAHs and SPAHs in the WWTP.

Anaerobic-aerobic processes for the treatment of textile dyeing wastewater containing three commercial reactive azo dyes:Effect of number of stages and bioreactor type

In this study,the effect of number of stages and bioreactor type on the removal performance of a sequential anaerobic-aerobic process employing activated sludge for the treatment of a simulated textile dyeing wastewater containing three commercial reactive azo dyes was considered.Two stage processes performed better than one stage ones,both in terms of overall organic and color removal,as well as the higher contribution of anaerobic stage to the overall removal performance,thereby making them a more energy efficient option.The employment of a moving bed sequencing batch biofilm reactor,which uses both suspended and attached biomass,for the implementation of the anaerobic stage of the process,was compared with a sequencing batch reactor that only employs suspended biomass.The results showed that,although there was no meaningful difference in biomass concentration between the two bioreactors,the latter reactor had better performance in terms of chemical oxygen demand(COD)removal efficiency and rate and color removal rate.Further exploratory tests revealed a difference between the roles of suspended and attached bacterial populations,with the former yielding better color removal whilst the latter had better COD removal performance.The sequential anaerobic–aerobic process,employing an aerobic membrane bioreactor in the aerobic stage resulted in COD and color removal of 77.1±7.9%and 79.9±1.5%,respectively.The incomplete COD and color removal was attributed to the presence of soluble microbial products in the effluent and the autoxidation of dye reduction metabolites,respectively.Also,aerobic partial mineralization of the dye reduction metabolites,was experimentally observed.

CLEAN PRODUCTION AND SMELTING REDUCTION TECHNOLOGY

Clean Production is the best method for iron-steel making industry to eliminate pollution thoroughly. In order to achieve this object, smelting reduction technology should play the key role. Furthermore, process integration method can be used to solve the problem of residual gas utilization by integrating smelting reduction process with direct reduced iron unit, gasoline, methanol or dimethyl ether synthesis unit, etc. A new smelting reduction process has been proposed which can be constructed on the present plant site. Since this process can directly treat the lump coal and iron ore fines, it reduces st6ps necessary in traditional blast furnace process and Corex smelting reduction process.

Simulation and Training Package on Corex Process

The flow behaviors in a gas solid contactor with inclined perforated plates that form a zigzag path were experimentally studied. In this contactor solid particles slide down along the inclined perforated plates by the upflowing gas. This structure, called as 'z path moving bed', has some of the advantages of both moving and fluidized beds. The discharge rate of solid particles, inclination angle of the perforated plate, aperture ratio of the perforated plate, size of particles and gas velocity were chosen as parameters for experimental conditions. The stable operation conditions were certained for the particles and apparatus used. The pressure drop, bed height and residence time distribution of particles were measured versus gas velocity.

Simulation of the effect of hydrate adhesion properties on flow safety in solid fluidization exploitation

During the solid fluidization exploitation of marine natural gas hydrates,the hydrate particles and cuttings produced via excavation and crushing are transported by the drilling mud.The potential flow safety issues arising during the transport process,such as the blockage of pipelines and equipment,have attracted considerable attention.This study aims to investigate the impact of hydrate adhesion features,including agglomeration,cohesion,and deposition,on the flow transport processes in solid fluidization exploitation and to provide a reference for the design and application of multiphase hydrate slurry transport in solid fluidization exploitation.We established a numerical simulation model that considers the hydrate adhesion properties using the coupled computational fluid dynamics and discrete element method(CFD-DEM)for the multiphase mixed transport in solid fluidization exploitation.An appropriate model to simulate the adhesion force of the hydrate particles and the corresponding parameter values were obtained.The conclusions obtained are as follows.Under the same operating conditions,a stationary bed is more likely to form in the transport process due to the hydrate adhesion forces;adhesion forces can increase the critical deposition velocity of the mixture of hydrate particles and cuttings.Hydrate adhesion lowers the height of the solid-phase moving bed,while the agglomeration and cohesion of particles can intensify the aggregation and deposition of hydrate debris and cuttings at the bottom of the pipe.These particles tend to form a deposit bed rather than a moving bed,which reduces the effective flow area of the pipeline and increases the risk of blockage.

THEORY OF NONFLUIDIZED GAS SOLIDS FLOW AND ITS APPLICATION

A theory of nonfluidized gas-solids flow, which combines the theory of multiphase flow with the mechanics of particulate media, was proposed on the basis of understanding that the particles contact each other, solids and gas are in movement, and the drag force on the particles caused by interstitial gas flow is similar to gravity force having the property of mass force. Then this theory was verified by experiments on vertical and inclined moving beds, and was applied to calculation and design of equipment and devices with moving beds, such as pneumatic moving bed transport, dipleg, V-value, L-valve, orifice flow, and arching prevention. It can be used to guide the design and operation of moving beds and fixed beds.