Tank Reactor Research Articles

Venting of a runaway organic peroxide decomposition in viscous solvents on pilot scale

AbstractRunaway reactions continue to occur in polymerization reactors, which are widely used in the chemical industry. Those of greatest concern include highly viscous multiphase mixtures. Considerable uncertainties exist in the design of emergency pressure‐relief systems for such reactors because there are only limited experimental data available on the flow of such fluids in relief systems.Venting experiments are reported here that have been carried out in a 350 L pilot‐scale reactor for the runaway decomposition of an organic peroxide in xylene solvent, with batch volumes of 150 and 200 L and with a range of concentrations of polystyrene dissolved in the xylene to modify the viscosity. Measurements were made of pressures in the reactor, vent line, and catch tank; temperatures at different levels in the reactor and in the vent line and catch tank; viscosity in the reactor; mass in the catch tank; and two‐phase density in the vent line.Analysis of the results shows that the venting behavior of a high‐viscosity reaction system is complex. There is no simple relationship between maximum pressure and viscosity. The results indicate that the flow regime in the reactor is influenced by the fluid viscosity and that this is of primary importance in explaining the effects on maximum pressure. © Crown Copyright 2006. Published with the permission of the Controller of HMSO and the Queen's printer for Scotland. Process Saf Prog, 2006

A modified Activated Sludge Model No. 3 (ASM3) with two-step nitrification–denitrification

A common limitation of the Activated Sludge Models (ASM) [Henze, M., Gujer, W., Mino, T., van Loosdrecht, M.C.M., 2000. Activated Sludge Models ASM1, ASM2, ASM2d, and ASM3. IWA Scientific and Technical Report No. 9. IWA Publishing, London, UK] is the representation of the nitrification dynamics as a single-step process and the consequent denitrification on nitrate alone. This generally acknowledged simplification may represent a serious limitation in specific applications where nitrites become important, either as a target final product or an unwanted intermediate. This paper proposes an enhancement to the basic ASM3 model, introducing a two-step model for the process nitrification and, consequently, considering denitrification on both nitrite and nitrate. After introducing the relevant process kinetics and adapting the stoichiometric matrix accordingly, the model implementation in the Matlab/Simulink™ platform is described with reference to the benchmark setting. To obtain a fast implementation, the process units (reaction tanks and secondary settler) have been implemented as DLLs linked to the Simulink blocks, whereas the model parameters and stoichiometric matrix remain accessible to the user. The new model is compared with the standard ASM3 and checked for consistency and mass conservation. It is also shown that with the default kinetic parameters nitrite may represent a considerable fraction of the nitrified effluent, thus revealing a design limitation in the benchmark sizing. In the last part, an optimization of the benchmark plant volumes has been attempted in order to minimize such violations, resulting in a moderate increase of the overall reaction volume. The pertinent software is freely available for research purposes.

Characterization of nutrient leaching rates from settled rainbow trout ( Oncorhynchus mykiss) sludge

The leaching of nutrients from settled rainbow trout ( Oncorhynchus mykiss) sludge into overlying water was evaluated over a 7-day period. Nutrient leaching was assessed in a stagnant reaction tank and one agitated by aeration to simulate turbulent conditions in stocked production raceways. Leaching of total phosphorus (TP), ortho-phosphate (OP), total Kjeldahl nitrogen (TKN), total ammonia nitrogen (TAN), and total organic carbon (TOC) occurred rapidly during the first 24 h in both stagnant and agitated conditions. The highest 24 h leaching occurred in the agitated tank, and power regression equations accurately described the varying rates of increasing TP, OP, TAN and TKN. In the stagnant tank, linear increases of TP, OP, TKN and TAN concentrations occurred during the first 24 h. These linear increases continued from days 2 to 7, but at slower rates than occurred during the first 24 h. Average nutrient leaching rates (mg leached/g sludge-h); (dry weight basis) were calculated based on linear concentration increases. In the agitated tank, nutrient concentrations decreased after 60 h, as aerobic bacterial uptake and/or chemical precipitation was suspected. Therefore, average leaching rates could not be determined. These findings reveal that daily cleanout of settling areas could eliminate the release of TP, OP, TAN, TKN, and TOC from settled solids by 66%, 65%, 39%, 76%, and 51%, respectively, as compared to weekly cleanout schedules. Sustained leaching rates indicate nutrient release will likely continue beyond 7 days. This information suggests aggressive and continuous sludge management is most beneficial for maintaining high water quality and regulatory discharge compliance in fish production.

Research reactor KAMINI

KAMINI is a 30 kW, 233U fuelled research reactor located at Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam. The reactor functions as a neutron source with a flux of 10 12 n/cm 2/s at the core center. KAMINI uses plate type of fuel in a reactor tank. Demineralized water is used as moderator, biological shield and coolant. Reflectors are made of beryllium oxide with Zircaloy-2 sheath. Cadmium is used as the absorber material in the safety control plates (SCP) provided for power control and shutdown of the reactor. There are three beam tubes and three irradiation locations within the reactor tank facilitating neutron radiography of radioactive and non-radioactive objects, sample irradiation for neutron activation analysis, physics and shielding experiments. The reactor attained first criticality in October 1996 and nominal power of 30 kW in September 1997. This article covers the design description, facilities available for experiments and their utilization for research and development. Seven years of operating experience of KAMINI, which is the only reactor using 233U as fuel, are also highlighted.

Dynamic optimization of electrochemical reactors for the exact optimal control of consecutive electrochemical reactions

The kinetics, mass transfer, surface dynamics and double layer charging of consecutive electrochemical reactions have been investigated so as to set up a complete formulation and dynamic optimization of its performance in batch electrochemical reactors. The dynamic optimization problem statements are exclusively put together to represent the behavior of both Faradaic and non-Faradaic processes and consequently the formulated dynamic problems have been solved using the maximum principle. The results of applying the optimal time-varying profiles of electrode potential are compared between the two different modes of batch electrochemical reactor and also with those resulting from the tradition-operating style of these reactors. Despite the effect due to double layer charging, an enhanced selectivity result has been obtained even in the presence of significant mass transfer resistance by determining the best transient operating profile of control variable. Besides these, this paper also discusses on the methodology of dynamic optimization in continuous stirred tank and plug flow electrochemical reactors.

Small-scale domestic wastewater treatment using an alternating pumped sequencing batch biofilm reactor system

An alternating pumped sequencing batch biofilm reactor (APSBBR) system was developed to treat small-scale domestic wastewater. This laboratory system had two reactor tanks, Reactor 1 and Reactor 2, with two identical plastic biofilm modules in each reactor. Reactor 1 of the APSBBR had five operational phases--fill, anoxic, aerobic, settle and draw. In the aerobic phase, the wastewater was circulated between the two reactor tanks with centrifugal pumps and aeration was mainly achieved through oxygen absorption by microorganisms in the biofilms when they were exposed to the air. This paper details the performance of the APSBBR system in treating synthetic domestic wastewater over 18 months. The effluent from the APSBBR system satisfied the European Wastewater Treatment Directive requirements, with respect to COD, ammonium-nitrogen and suspended solids. The biofilm growth in the two reactor tanks was different due to the difference in substrate loadings and growth conditions.

Novel Process for Recycling Waste Plastics To Fuel Gas Using a Moving-Bed Reactor

The conventional pyrolysis of waste plastics, carried out in a tank reactor or kiln, yields fuel oil with a wide boiling range. To improve the economic process of feedstock recycling of waste plastics, a new thermal process for fuel-gas production is proposed. Considering the role of sand as an effective heating medium and by using a reactor structure for suitably controlling the reaction temperature and reaction time, a new type of reactor equipped with a screw conveyor has been developed; this reactor is termed the moving-bed reactor. The formation of gaseous hydrocarbons was achieved at 82 wt % (pyrolysis) and 94 wt % (catalysis) in the operations research of the new process using polypropylene as feed.

Processes Governing Flow and Chemical Characteristics of Discharges from Free-Draining, Underground Coal Mines

In the Uniontown Syncline of Southwestern Pennsylvania, discharges from unflooded, free-draining coal mines are acidic with high sulfate concentrations. Flow and water quality data obtained in 1998–2000 for an unflooded mine discharge in the Uniontown Syncline were evaluated using a tank reactor fill-and-draw model to describe seasonal variations in outflows over time observed for the mine as well as to simulate discharge water quality. The hydraulic model was coupled to a chemical mass balance using estimates of recharge water quality and in-mine chemical production∕loss. Field data indicated that the concentrations of sulfate, iron, and acidity were fairly constant even when flow varied greatly. Flow-related mass production functions for these constituents were obtained by fitting the field data. The hydraulic–chemical model was used to simulate sulfate and acidity production from pyrite dissolution and total carbonate loss in the mine. Model simulations indicated that in-mine acid production correlated with recharge rate, due to the sustained presence of oxygen which drives pyrite dissolution, and that recharge water chemistry had a significant influence on discharge characteristics. For the mine studied, alkaline recharge water mitigates the acidity of the discharges.

Feasibility Study of an Activated Sludge/Contact Aeration Combined System

The activated sludge/contact aeration combined system (AS/CA) is created by adding biological contact filters into the rear section of the activated sludge tank. The system contains both suspended micro-organisms and fixed micro-organisms. This system combines the advantages of both single systems, and avoids disadvantages particular to the individual systems. A special feature of AS/CA is its enhanced ability to remove oil and grease, and improve the color of treated water. A pilot treatment plant was constructed and located in a slaughterhouse generating 2000 m 3 /day of wastewater. The test results were as follows operating with a 6-h hydraulic retention time (HRT): effluent COD = 145.6 mg/L (86% removal rate), effluent BOD 5 = 46 mg/L (85% removal rate), effluent SS = 66 mg/L (85% removal rate), effluent oil and grease dropped from 68.6 mg/L to 21 mg/L (70% removal rate), effluent true color = 50 (83% removal rate). These values just met the minimum requirements in Taiwan's effluent standards. The pilot plant results for operating with 8-h HRT were as follows: effluent COD = 71 mg/L (94% removal rate), effluent BOD 5 = 29 mg/L (91% removal rate), effluent SS = 43 mg/L (86% removal rate), effluent oil and grease dropped from 54.6 mg/L to 7 mg/L (87% removal rate), effluent true color = 47 (84% removal rate). These test results proved that the oil and grease removal rate increased with an increase in HRT, and reduced the likelihood of other effluent parameters exceeding effluent standards. Denatural Gradient Gel Electrophoresis (DGGE) analysis was performed on the samples. Analytical results check that compared to both a single activated sludge system and contact aeration system, the AS/CA system had relatively high level of microbe diversity and a high number of microbes. Scanning Electron Microscope (SEM) analysis also revealed degradation of oil and grease in each reaction tank.

Hybrid Process for Heavy Metal Removal from Wastewater Sludge

Bioleaching processes have been demonstrated to be effective technologies in removing heavy metals from wastewater sludge, but long hydraulic retention times are typically required to operate these bioprocesses. A hybrid process (coupling biological and chemical processes) has been explored in laboratory pilot-scale experiments for heavy metals (cadmium [Cd], copper [Cu], chromium [Cr], and zinc [Zn]) removal from three types of sludge (primary sludge, secondary activated sludge, and a mixture of primary and secondary sludge). The hybrid process consisted of producing a concentrate ferric ion solution followed by chemical treatment of sludges. Ferric iron solution was produced biologically via oxidation of ferrous iron by A. ferrooxidans in a continuous-flow stirred tank (5.2 L) reactor (CSTR). Wastewater sludge filtrate (WSF) containing nutrients (phosphorus and nitrogen) has been used as culture media to support the growth and activity of indigenous iron-oxidizing bacteria. Results showed that total organic carbon (TOC) concentrations of the culture media in excess of 235 mg/L were found to be inhibitory to bacterial growth. The oxidation rate increased as ferrous iron concentrations ranged from 10 to 40 g Fe2+/L. The percentage of ferrous iron (Fe2+) oxidized to ferric iron (Fe3+) increased as the hydraulic retention time (HRT) increased from 12 to 48 h. Successful and complete Fe2+ oxidation was recorded at a HRT of 48 h using 10 g Fe2+/L. Subsequently, ferric ion solution produced by A. ferrooxidans in sludge filtrate was used to solubilize heavy metals contained in wastewater sludge. The best solubilization was obtained with a mixture of primary and secondary sludge, demonstrating a removal efficiency of 63, 71, 49, and 80% for Cd, Cu, Cr, and Zn, respectively.

Characteristic time series and operation region of the system of two tank reactors (CSTR) with variable division of recirculation stream

Abstract The paper deals with a system of a cascade of two tank reactors, being characterized by the variable stream of recirculating fluid at each stage. The assumed mathematical model enables one to determine the system’s dynamics for the case when there is no time delay and for the opposite case. The time series of the conversion degree and of the dimensionless fluid temperature, characteristic for the system considered as well as the operation regions—the latter—basing on Feingenbaum diagrams with respect to the division ratio of the recirculating stream are presented.

Medium frequency induction‐heated chemical reactor with cooling metallic envelope of the tank

Purpose – Analysis and development of a high efficiency, induction heated chemical reactor, medium frequency supplied (1,000‐2,000 Hz), able to be equipped with efficient cooling circuits.Design/methodology/approach – The numerical investigations of the technical solutions proposed in this paper are based on 3D finite element models that are experimentally validated.Findings – Solutions to increase the transparency of the cooling envelope of the reactor tank with respect to magnetic field. The positions of envelope regions characterized by high values of power losses are experimentally confirmed by infrared temperature measurements.Practical implications – The numerical analysis and the experimental investigations, show the possibility to implement efficient cooling circuits in chemical reactors without affecting the performances of the induction heating process. By designing properly the metallic envelope of the tank the global efficiencies of the chemical reactors increase at around 90 percent with redu...

Responsive brushes and gels as components of soft nanotechnology

Progress in the development of generic molecular devices based on responsive polymers is discussed. Characterisation of specially synthesised polyelectrolyte gels, "grafted from" brushes and triblock copolymers is reported. A Landolt pH-oscillator, based on bromate/ sulfite/ferrocyanide, with a room temperature period of 20 min and a range of 3.1 < pH < 7.0, has been used to drive periodic oscillations in volume in a pH responsive hydrogel. The gel is coupled to the reaction and changes volume by a factor of at least 6. A continuously stirred, constant volume, tank reactor was set-up on an optical microscope and the reaction pH and gel size monitored. The cyclic force generation of this system has been measured directly in a modified JKR experiment. The responsive nature of polyelectrolyte brushes, grown by surface initiated ATRP, have been characterised by scanning force microscopy, neutron reflectometry and single molecule force measurements. Triblock copolymers, based on hydrophobic end-blocks and either polyacid or polybase mid-block, have been used to produce polymer gels where the deformation of the molecules can be followed directly by SAXS and a correlation between molecular shape change and macroscopic deformation has been established. The three systems studied allow both the macroscopic and a molecular response to be investigated independently for the crosslinked gels and the brushes. The triblock copolymers demonstrate that the individual response of the polyelectrolyte molecules scale-up to give the macroscopic response of the system in an oscillating chemical reaction.

대구성서산업단지 발생원부지경계 대기 중 휘발성유기화합물질의 농도수준

The concentrations of volatile organic compounds(VOCs) in the ambient air were measured at various point(Source, source boundary) in Seongseo industrial complex during May to November 2003. Air samples were collected in Silcocan canister and analyzed using a cryogenic preconcentration system and GC/MSD. We identified 37 species by the US EPA(TO-14 method). The result showed a variety distribution of the con­centration, Higher concentrations of BTX, Styrene, 1,3,5-Trimethylbenzene, 1,2,4-Trimethylbenzene were observed at the sampling sites. They seemed to be emitted from the facility of wastewater treatment, reaction tank of chemistry factory and facility of Tenter. The concentrations of VOCs contents in Seongseo industrial complex were generally higher than those in Yeosu complex and Ulsan complex, although those were similar in Sihwa­Banwol complex.

Effect of powdered activated carbon type on the performance of an adsorption-microfiltration submerged hollow fiber membrane hybrid system

This study highlights the importance of the type of powdered activated carbon (PAC) on the performance of an adsorption-MF hollow fiber membrane hybrid system. Submerged UF hollow fiber membrane with pore size of 0.4 Μm was used along with the PAC in a single reaction tank to treat the wastewater. This procedure is different from the commonly adopted practice of having adsorption with PAC as a pretreatment step to membrane operation. This system is helpful in containing the PAC within one system, allows certain variation in feed characteristics and improves the efficiency of the hybrid system. The overall performance of the membrane hybrid system was evaluated based on TOC removal, UV254 absorbance, turbidity removal and flux development. It is important to select a right PAC type to be used in the hybrid system in order to minimize the PAC dose and to enhance the performance. The adsorption capacity of the activated carbon had a greater influence on the overall performance of the hybrid system than other physical properties of the PACs and must be given greater consideration when selecting the PAC for the membrane hybrid system. Scanning electron micrograph (SEM) analysis of the cake deposit over the membrane helps to support the reason for moderate retention of organics.

Gas visualization of industrial hydrocarbon emissions

Gases leaking from a polyethene plant and a cracker plant were visualized with the gas-correlation imaging technique. Ethene escaping from flares due to incomplete or erratic combustion was monitored. A leakage at a high-pressure reactor tank could be found and visualized by scanning the camera system over the industrial site. The image processing methods rely on the information from three simultaneously captured images. A direct and a gas-filtered infrared image are recorded with a split-mirror telescope through a joint band-pass filter. The resulting path-integrated gas concentration image, derived from the two infrared images, is combined with a visible image of the scene. The gas-correlation technique also has the potential to estimate the flux in the gas plume by combining a wind vector map, derived by cross-correlating the images in time, with a calibrated gas path-integrated concentration image. The principles of the technique are outlined and its potential discussed.

Oxygen and carbon dioxide kinetic challenges for thermophilic mineral bioleaching processes.

Agitated bacterial tank bioleaching reactors are currently sparged with air to satisfy both oxygen and CO(2) requirements of microbial cells. Under high-sulphide loading conditions, as is the case with high-grade metal sulphide concentrates, the microbial and chemical demand for oxygen is significantly increased during the bioleaching process. Sparging with enriched oxygen gas may offer an alternative process option to increased agitation and sparged aeration, to overcome the mass transfer difficulties at elevated temperatures where thermophilic Archaea, rather than Bacteria, are used. In the case of air sparging, the DO (dissolved oxygen) concentration in tank reactors could not be increased to a point where it would become inhibitory due to the limited oxygen content of air (20.9% O(2)). The use of enriched oxygen in such reactors at large scale does, however, pose its own set of process risks. The first aim of this investigation was, therefore, to determine the effects of various DO concentrations, in both the limiting and inhibitory ranges, on the microbial activity of Sulfolobus sp. U40813, a typical thermophilic mineral-leaching archaeon. Secondly, the effect of CO(2) concentration on the rate of ferrous iron oxidation was investigated. Both the oxygen and CO(2) kinetics were examined in controlled batch cultures at 78 degrees C, using ferrous sulphate and potassium tetrathionate as energy sources. The optimal DO concentration for iron oxidation was found to be between 1.5 and 4.1 mg.l(-1). The use of elevated DO concentrations (above 4.1 mg.l(-1)) inhibited the ferrous oxidation rates. The optimal gas CO(2) concentration for ferrous iron oxidation was found to be in the range 7-17% (v/v). The iron oxidation rates were, however, severely limited at CO(2) concentrations less than 7%, indicating that the CO(2) supply was limiting in this range and inhibited the microbial growth rate.

Partial oxidation of methanol for hydrogen production using ITO/Al 2O 3 nanoparticle catalysts

An indium tin oxide/alumina (ITO/Al 2O 3) nanoparticle catalyst was used for the selective oxidation of methanol to form hydrogen and carbon dioxide. At 68% methanol conversion, the hydrogen selectivity was 73%, and carbon monoxide was only 1–2% of the products. Four reactors were used, and the highest hydrogen selectivity was obtained in a tank reactor that contained a thin catalyst film. A packed bed reactor did not effectively remove the heat of reaction, but coating the catalyst as a thin film gave better control. The product selectivity dependence on temperature and the methanol/oxygen feed ratio was measured.

Simulation of Free Radical High‐Pressure Copolymerization in a Multizone Autoclave: Model Development and Application

A well‐mixed model has been formulated to study the steady‐state high pressure free‐radical homo‐ and copolymerization of ethylene and vinyl acetate in an industrial multi‐feed multi‐zone autoclave reactor system. Using a realistic set of kinetic mechanisms and coefficients, the multi‐zone system is modeled as a simple set of well‐mixed tank reactors in series. Results from this representation are compared to experimental data in order to estimate apparent initiator efficiencies in each zone. The model is used to calculate monomer conversion and initiator consumption rate, number and weight average molecular weights, and short and long chain branching frequencies at the exit point of each zone and the whole reactor. The effects of zone temperature, feed temperature, and initiator decomposition kinetics on the steady‐state reactor performance and polymer properties are considered and simulation results are compared with the industrial data. While estimated initiator efficiencies provide a clear indication ...

03/02697 Reaction tanks for manufacture of fuel gases from waste gases and waste heat and system for manufacture of fuels: Hiwata, K. Jpn. Kokai Tokkyo Koho JP 2003 104,701 (Cl. C01B3/06) 9 Apr 2003, Appl. 2001/297.733. (In Japanese)

03/02697 Reaction tanks for manufacture of fuel gases from waste gases and waste heat and system for manufacture of fuels: Hiwata, K. Jpn. Kokai Tokkyo Koho JP 2003 104,701 (Cl. C01B3/06) 9 Apr 2003, Appl. 2001/297.733. (In Japanese)