Residence time and contact volume in sloped compost and compost/vegetated filter beds

2011 ◽  
Vol 63 (6) ◽  
pp. 1093-1098
Author(s):  
K. Coulson ◽  
R. J. Petrell ◽  
D. Chiu
Keyword(s):  
Residence Time ◽  
Flow Rate ◽  
Pore Space ◽  
Plug Flow ◽  
Concentration Data ◽  
Filter Width ◽  
In Series ◽  
Free Drainage ◽  
Bed Slope ◽  
The Ideal

Little is known about transport mechanisms in sloped dormant vegetated and compost only filters for roadway runoff. Residence time experiments were carried out in triplicate in 0.254 m wide × 0.65 m long by 0.10 m deep beds using a bromide tracer. Bed slope was 12°. Only at the lowest flow rate tested (0.276 l/min per m of filter width) were mean residence times in compost beds with and without dormant grasses different. Pools formed ahead of beds at higher flow rate, and pool depth reached bed depth at 3.54 l/min/m. The ideal model of a well-mixed pool in series with a plug flow porous bed was a good predictor of effluent concentration data at flows ≥2.66 l/min/m. Theoretical contact volume within the beds increased with flow rate to reach approx. 30% of available pore space, while free drainage volume declined. Data shows that designs for sloped compost filter beds must consider flow, bed depth and length, and whether or not areas for pooling are needed.

scholarly journals Explicit Residence Time Distribution of a Generalised Cascade of Continuous Stirred Tank Reactors for a Description of Short Recirculation Time (Bypassing)

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 615 ◽  
Author(s):  
Peter Toson ◽  
Pankaj Doshi ◽  
Dalibor Jajcevic
Keyword(s):  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Flow Reactor ◽  
Plug Flow ◽  
Stirred Tank ◽  
Stirred Tank Reactors ◽  
Delayed Impulse ◽  
In Series ◽  
Back Mixing

The tanks-in-series model (TIS) is a popular model to describe the residence time distribution (RTD) of non-ideal continuously stirred tank reactors (CSTRs) with limited back-mixing. In this work, the TIS model was generalised to a cascade of n CSTRs with non-integer non-negative n. The resulting model describes non-ideal back-mixing with n > 1. However, the most interesting feature of the n-CSTR model is the ability to describe short recirculation times (bypassing) with n < 1 without the need of complex reactor networks. The n-CSTR model is the only model that connects the three fundamental RTDs occurring in reactor modelling by variation of a single shape parameter n: The unit impulse at n→0, the exponential RTD of an ideal CSTR at n = 1, and the delayed impulse of an ideal plug flow reactor at n→∞. The n-CSTR model can be used as a stand-alone model or as part of a reactor network. The bypassing material fraction for the regime n < 1 was analysed. Finally, a Fourier analysis of the n-CSTR was performed to predict the ability of a unit operation to filter out upstream fluctuations and to model the response to upstream set point changes.

RTD Measurement, Modeling, and Analysis of Liquid Phase of Three-Tube Industrial Pulp Digester

2019 ◽  
Vol 17 (4) ◽  
Author(s):  
Meenakshi Sheoran ◽  
Avinash Chandra ◽  
Sanjeev Ahuja ◽  
Haripada Bhunia ◽  
Harish J. Pant
Keyword(s):  
Liquid Phase ◽  
Flow Regime ◽  
Residence Time ◽  
Dispersion Model ◽  
Flow Behavior ◽  
Plug Flow ◽  
Hydrodynamic Performance ◽  
Concentration Data ◽  
Tracer Concentration ◽  
Dispersion Number

Abstract Residence-time distribution (RTD) experiments were performed to analyze an industrial scale three-tube series continuous pulping digester’s hydrodynamic performance. An impulse of radiotracer 82Br (γ energy source) was introduced at the inlet of the first tube. The radiotracer concentration in the liquid phase was traced at the outlet of each tube. The input behavior of the radiotracer converted to a non-ideal pulse tracer input for the second and third tubes of the digester. Numerical convolution is adopted to deal with the non-ideal pulse input of the radiotracer. A modeling procedure for determining the RTD from the outlet tracer concentration data is proposed. A plug flow component followed by axial dispersion model is considered, and is adjusted after its convolution with the inlet tracer concentration data to obtain the RTD of the individual tubes. The obtained RTD data are analyzed to explain the flow behavior, degree of dispersion, and flow abnormalities existing in the digester. The mean residence-time (MRT), and dispersion number are estimated for the model components for the three tubes. The vessel dispersion number is found to decrease from tube 1 to tube 3. Overall, the conversion of the highly dispersed flow regime into the plug-flow regime is observed in the whole digester.

Should Waste Stabilization Ponds be Designed for Perfect-Mixing or Plug-Flow?

1991 ◽  
Vol 23 (7-9) ◽  
pp. 1495-1502 ◽  
Author(s):  
Marcelo Juanico
Keyword(s):  
Flow Pattern ◽  
Residence Time ◽  
Plug Flow ◽  
Weekend Effect ◽  
Waste Stabilization Ponds ◽  
Hydraulic Loading ◽  
Stabilization Ponds ◽  
Waste Stabilization ◽  
In Series ◽  
Two Parameters

The effect of the hydraulic flow pattern on the performance of Waste Stabilization Ponds is analyzed by modelling. The analysis is made on two parameters with different removal constants (Bacteria and BOD) and for the cases of steady hydraulic loading and when hydraulic loading changes on weekends. Plug-flow ponds perform much better than perfect mixed ones for removal of parameters with high removal constants such as bacteria. Plug-flow and perfect mixed ponds perform very similarly when the removal constant is low as for BOD. Changes in the hydraulic loading regime due to weekend effect do not modify the variability of outflow quality from plug-flow ponds. These changes do affect the variability of outflow quality from perfect mixed ponds only in the case of parameters with high removal constants such as bacteria. Polishing ponds Intended for bacterial removal should be designed for plug-flow. Facultative ponds intended for BOD removal may be designed for perfect mixed, partial mixed or plug-flow. Several small ponds with short residence time located In series, or the parcellation of a single big pond with widely spaced baffles, would avoid short circuiting of effluents between inlet and outlet. However, this design does not assure a plug-flow pattern, and it may lead to the formation of dead areas and the reduction of the actual residence time of effluents within the system.

scholarly journals Assessing the degree of plug flow in oxidation flow reactors (OFRs): a study on a potential aerosol mass (PAM) reactor

2018 ◽  
Vol 11 (3) ◽  
pp. 1741-1756 ◽  
Author(s):  
Dhruv Mitroo ◽  
Yujian Sun ◽  
Daniel P. Combest ◽  
Purushottam Kumar ◽  
Brent J. Williams
Keyword(s):  
Flow Rate ◽  
Cfd Simulation ◽  
Plug Flow ◽  
Volumetric Flow Rate ◽  
Flow Patterns ◽  
Space Time ◽  
Flow Reactors ◽  
Tracer Testing ◽  
Aerosol Mass ◽  
In Series

Abstract. Oxidation flow reactors (OFRs) have been developed to achieve high degrees of oxidant exposures over relatively short space times (defined as the ratio of reactor volume to the volumetric flow rate). While, due to their increased use, attention has been paid to their ability to replicate realistic tropospheric reactions by modeling the chemistry inside the reactor, there is a desire to customize flow patterns. This work demonstrates the importance of decoupling tracer signal of the reactor from that of the tubing when experimentally obtaining these flow patterns. We modeled the residence time distributions (RTDs) inside the Washington University Potential Aerosol Mass (WU-PAM) reactor, an OFR, for a simple set of configurations by applying the tank-in-series (TIS) model, a one-parameter model, to a deconvolution algorithm. The value of the parameter, N, is close to unity for every case except one having the highest space time. Combined, the results suggest that volumetric flow rate affects mixing patterns more than use of our internals. We selected results from the simplest case, at 78 s space time with one inlet and one outlet, absent of baffles and spargers, and compared the experimental F curve to that of a computational fluid dynamics (CFD) simulation. The F curves, which represent the cumulative time spent in the reactor by flowing material, match reasonably well. We value that the use of a small aspect ratio reactor such as the WU-PAM reduces wall interactions; however sudden apertures introduce disturbances in the flow, and suggest applying the methodology of tracer testing described in this work to investigate RTDs in OFRs to observe the effect of modified inlets, outlets and use of internals prior to application (e.g., field deployment vs. laboratory study).

The Maximum Mixedness Model Applied with Detailed Reaction Mechanisms

2017 ◽  
Vol 15 (3) ◽  
Author(s):  
R. Barat ◽  
D. Cedio-Fengya ◽  
J. Stevens
Keyword(s):  
Residence Time ◽  
Reaction Mechanisms ◽  
Concentration Data ◽  
Species Concentration ◽  
Stirred Reactor ◽  
In Series ◽  
Residence Time Distributions ◽  
Chemical Reaction Mechanisms ◽  
Energy Balances ◽  
Detailed Chemical

Abstract The Zwietering maximum mixedness model (MMM) is extended for use with detailed chemical reaction mechanisms in a combustion setting. Both MMM species and energy balances are offered with a Chemkin-consistent nomenclature. The solution algorithm is discussed. Several reactor residence time distributions are currently offered for use with the MMM program. The MMM is used here to simulate observed literature species concentration data in a turbulent, jet-stirred combustor. For comparison, the results are also compared to simulations from perfectly stirred reactor (PSR) and partially stirred reactor (PaSR) models. The MMM model predicts the observed higher-than-PSR fuel conversions using a residence time distribution based on two unequal CSTRs-in series.

scholarly journals Application Of Sabo Technology In The Togurara River At Gamalama Volcano Area To Control Of Lahar Flow In The Ternate City

2019 ◽  
Vol 10 (2) ◽  
Author(s):  
Ardian Alfianto ◽  
Jati Iswardoyo ◽  
Cosmas Bambang Sukatja
Keyword(s):  
Flow Rate ◽  
Field Survey ◽  
Mathematical Approach ◽  
Management Agency ◽  
Volcano Eruption ◽  
River Bed ◽  
Field Assessment ◽  
In Series ◽  
Local Residents ◽  
Bed Slope

The lahar flow  that occurred after the 2012  Gamalama Volcano  eruption, leading to the eastern valley flowing downstream  through the Togurara River to the center of Ternate City and Sultan Babullah Airport. To overcome the potential of  lahar  flow in the river since 2013 - 2016, several sabo dams and building facilities have been built. Based on the results of the calculation of deposits that potentially become lahar flows in 2016, the built-in capacity of the Sabodam has not been able to control the volume of sediment in the upstream of the river, then in the year 2017, 2018 constructed several additional Sabodam.  In order to determine the effectiveness, feasibility and conditions of the completeness of Sabodam, is done field assessment on 25 ~ 27 September 2018, the method used was a mathematical approach based on sabo technology. The assessment was in the form of a field survey, simple measurements, interviews with the Sabodam management agency and local residents related to the lahar flow that had occurred. With the capacity of several additional Sabodams built in series, the average river bed slope was originally 9.09% to 6.83%. After the construction of Sabodam, the maximum lahar flow was once as high as 7 m, but now it decreases do 4.2 m.   As the slope of the Togurara River slopes progressively, the lahar flow rate and its destructive power are reduced, so that Ternate City and Sultan Babullah Airport are spared from lahar disaster.Keywords: Lahar flow, sabodam, sabo technology, slope of riverbed, Togurara River.

scholarly journals RTD Modeling of a Non-Ideal Coiled-Tube Reactor Through Experimental Investigation for Pulse Input Using Methylene Blue Dye

2020 ◽  
Vol 8 (3) ◽  
pp. 1220-1231
Keyword(s):  
Methylene Blue ◽  
Residence Time ◽  
Flow Behavior ◽  
Plug Flow ◽  
Deep Understanding ◽  
Blue Dye ◽  
Coiled Tube ◽  
Pulse Input ◽  
Tube Reactor ◽  
In Series

This paper focuses on the grasp of a deep understanding of flow behavior in a coiled tube reactor through Residence Time Distribution (RTD) studies. The reactors, in general, are classified ideally: mixed and plug-flow patterns. Unfortunately, in the real world, it has been observed that they show very different behavior from that expected. Thus, the characterization of the nonideal coiled tube reactor is needed to carry out. The calculations were carried out in the Matlab for distribution of residence time of the coiled tube reactor that is used in the Chemical Reaction Engineering Laboratory at MIET College. Pulse input tests were used significantly to analyzed the flow behavior using methylene blue (MB) tracer. A significant disparity in RTD curves in the presence of the secondary flow was examined and data were recorded. Finally, a suitable mathematical model was selected from the Tank in Series (TIS) and Axial Dispersion Models (ADMs) based on residual error and was used to validate these outcomes. The deconvoluted of the signal was used to get Cin for the verification of the pulse input behavior. The results were compared with the experimental data that concluded the modeling of the reactor is in good agreement.

Modeling of Vortex-Flow Solar Reactor via Ideal Reactors in Series Approach

2010 ◽  
Author(s):  
Nesrin Ozalp ◽  
Vidyasagar Shilapuram ◽  
D. Jayakrishna
Keyword(s):  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Vortex Flow ◽  
Flow Reactor ◽  
Flow Behavior ◽  
Plug Flow ◽  
Flow Reactors ◽  
In Series ◽  
Sweeping Gas

In this work, we present a thorough reaction engineering analysis on the modeling of a vortex-flow reactor to show that commonly practiced one-plug reactor approach is not sufficient to explain the flow behavior inside the reactor. Our study shows that N-plug flow reactors in series is the best approach in predicting the flow dynamics based on the computational fluid dynamics (CFD) simulations. We have studied the residence time distribution using CFD by two different methods. The residence time distribution characteristics are calculated by approximating the real reactor as N-ideal reactors in series, and then estimated the number of ideal reactors in series for the model. We have validated our CFD model by comparing the simulation results with experimental results. Finally, we have done a parametric study with a different sweeping gas to identify the best screening gas to avoid carbon deposition inside the vortex-flow reactor. Our results have shown that hydrogen is a better screening gas than argon.

Removal of trichloroethylene and trichloroethane using a novel hollow-fibre gas-permeable membrane

2003 ◽  
Vol 3 (5-6) ◽  
pp. 67-72
Author(s):  
S. Takizawa ◽  
T. Win
Keyword(s):  
Boundary Layer ◽  
Flow Regime ◽  
Removal Efficiency ◽  
Residence Time ◽  
Flow Rate ◽  
Air Flow ◽  
Hollow Fibre ◽  
Permeation Rate ◽  
Permeable Membrane ◽  
Diffusional Boundary Layer

In order to evaluate effects of operational parameters on the removal efficiency of trichloroethylene and 1,1,1-trichloroethene from water, lab-scale experiments were conducted using a novel hollow-fibre gaspermeable membrane system, which has a very thin gas-permeable membrane held between microporous support membranes. The permeation rate of chlorinated hydrocarbons increased at higher temperature and water flow rate. On the other hand, the effects of the operational conditions in the permeate side were complex. When the permeate side was kept at low pressure without sweeping air (pervaporation), the removal efficiency of chlorinated hydrocarbon, as well as water permeation rate, was low probably due to lower level of membrane swelling on the permeate side. But when a very small amount of air was swept on the membrane (air perstripping) under a low pressure, it showed a higher efficiency than in any other conditions. Three factors affecting the permeation rate are: 1) reduction of diffusional boundary layer within the microporous support membrane, 2) air/vapour flow regime and short cutting, and 3) the extent of membrane swelling on the permeate side. A higher air flow, in general, reduces the diffusional boundary layer, but at the same time disrupts the flow regime, causes short cutting, and makes the membrane dryer. Due to these multiple effects on gas permeation, there is an optimum operational condition concerning the vacuum pressure and the air flow rate. Under the optimum operational condition, the residence time within the hollow-fibre membrane to achieve 99% removal of TCE was 5.25 minutes. The log (removal rate) was linearly correlated with the average hydraulic residence time within the membrane, and 1 mg/L of TCE can be reduced to 1 μg/L (99.9% removal).

Sorption and desorption of phosphorus by shale: batch and column studies

2010 ◽  
Vol 61 (3) ◽  
pp. 599-606 ◽  
Author(s):  
Johnsely S. Cyrus ◽  
G. B. Reddy
Keyword(s):  
Residence Time ◽  
Flow Rate ◽  
Nutrient Release ◽  
Phosphorus Sorption ◽  
Column Studies ◽  
Desorption Process ◽  
Low Concentrations ◽  
Sorbent Materials ◽  
High Concentrations ◽  
The Cost

Constructed wetland systems have gained attention as attractive solutions for wastewater treatment. Wetlands are not efficient to treat wastewater with high concentrations of phosphorus (P). In order to remove high soluble P loads by wetland, sorbent beds can be added prior to the discharge of wastewater into wetlands. Sorption by sorbent materials is identified as a method for trapping excess P in wastewaters. In the present investigation, shale has been identified as a sorbent material for removal of phosphate (PO4-P) due to the cost effectiveness, stability and possibility of regeneration. The study focuses on the removal of PO4-P from wastewater using shale and the feasibility of using the P-sorbed material as slow-release fertilizer. Phosphorus sorption experiments were conducted by using shale (2 mm and 2–4.7 mm). Results indicate that Shale I (particle size = 2 mm) showed the highest sorption of PO4-P (500 ± 44 mg kg−1). Breakthrough point was reached within 10 h in columns with flow rates of 2 and 3 ml min−1. Lower flow rate of 1 ml min−1 showed an average residence time of about 2 h while columns with a higher flow rate of 3 ml min−1 showed a residence time of about 40 minutes. Variation in flow rate did not influence the desorption process. Since very low concentrations of PO4-P are released, Shale saturated with PO4-P may be used as a slow nutrient release source of P or as a soil amendment. The sorbent can also be regenerated by removing the sorbed PO4-P by using 0.1 N HCl.

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