An accurate prediction of the ozone concentration profile requires the application of the correct ozone kinetics involved. By measuring total organic carbon (TOC) as a surrogate for NOM, experimentally determined rate constants can be calculated to account for the effects of ozone doses and water quality.
NOMENCLATURE
CFD CO D
RANS
GLO SSARY
INTROD UCTION
- Demand on sustainable access to drinking water
- Project background
- Static mixer
- Motivation of the study
- Ove r aU obj ecti ves
- Thesis outUne
- References
This parameter is important in the control and operation of the contactor as it ensures that sufficient ozone is added to the water. One of the ways to alleviate this is by effectively using the current water treatment works.
LITERATURE
Ozonation process
- Ozone destruction
From (a-I) to (a.3) the gas flow is identified to be countercurrent to the water flow, co-current with thc water flow, or both co-current and countercurrent to the water flow; whereas (a-4) shows a horizontal arrangement of the water flow. An example of the use of this equipment is the Choisy·le·Roi water treatment where the contact column is equipped with an emulsifier, i.e. the injector is located at the top of the vertical digestion tubes (shown in Figure 2·2(d) .
Ozone chemistry
-1) where Pj is the partial pressure of the solute,}, in the gas phase, expressed in atmospheres (atm);. The application of the film layer concept makes it possible to determine the concentration profiles of ozone and the solute in the film layer.
Ozone reactor engineering
Thus, the system of equations is reduced to a conservation of mass Eqn. 2.16) and three moment equations in the X-, Y-, and z-directions in Eq. conservation of mass or also known as the continuity equation in the Canesian·tensor fonn is:. where p is the density of the fluid, XI is the length in the i dimension, and UI is the velocity in the j direction. The convective derivative is physically the rate of change of the flow variable due to the motion of the fluid element.
Conclusions
Despite the large knowledge base, the accuracy of the numerical solution is still uncertain (De Clercq, 2003). In some cases, validation and verification of the CFD simulated results is difficult or may not be possible. Errors and uncertainties in the conceptual and computational models are identified and assessed during the validation process (De Clercq, 2003).
The use of CFD modeling improves the understanding of fluid dynamics in a system.
HYDRODYNAMIC MODEL OF THE OZONE CONTACTOR
The efficiency of different target and inactivation reactions depends on this exposure time of the target pollutants to ozone. The hydrodynamics of an ozone contactor is a strong function of both the contactor configuration and the system operating conditions. In these tests, a quantity of tracer is induced as a pulse or a step function at the inlet of the contactor, marking the fluid elements as they enter the contactor.
The tracer concentration C(t) is monitored over time at the contactor outlet.
JIC(I)dl
Hydrodynamic model description
- Geometry and meshing
The contactor examined is one of four in the pre-ozonation system at Wiggins Waterworks (Figure 3-1). The outlet weir was shown as a rectangular trench. the height of which was set to the measured height of the liquid flowing over the open, broad-crested weir. The importance of RTD is reflected in the requirements issued by the US Environmental Protection Agency.
For a given flow rate and contactor volume, T10 decreases as the degree of dispersion increases (i.e., the RID becomes wider).
Objectives
The literature found so far has not seen the application of the RNG model to a full-scale ozone contactor. The effect of different turbulence models on the predicted RTD of the ozone contactor is discussed in Section 3.5.3. As with uniform flow, constant profiles of turbulence quantities across the inlet are usually adopted.
This may be contributed by the large size of the model and the use of less powerful computers at the time (parallel processors.
Experimental verification
Therefore, the mass diffusion coefficient of the tracer in the mixture was set to an arbitrarily low value, thereby suppressing the first term in Eq. The low detection threshold of Lt is an advantage, allowing the identification of diluted samples at the beginning and end of tracer assays (Do-Quang et al., 2000; Cockx et al. 1999). Due to the large amount of LiCI required and the time planned for the tracer tests.
The subsequent samples were taken at 3 min intervals until the 24'" min and then at 6 min intervals until the end of the trace test.
Results and discussion
- Simulated results
- Compariso n using normalised RTD functions
- Scenario study
- Simulated contours
This means that the uncertainties in the response measurements are compounded with the uncertainties in the measurement of the concentrate. The density functions of the experimental and the simulated tracer reactions were calculated using Eq. 3. A higher concentration of tracer is observed on the left side of the lower compartment compared to that on the right side.
View of the contactor from above. Figure 3-13 (a) shows that the tracer is stored only on the right side of the lower space.
Conclusions
The turbulent intensity of the incoming flow is a required boundary condition for the turbulence model. Even without gas injection, its value was not known due to the effect of the static mixer blades. For the operation of the contactor, it was more important to match the overall RTD.
The effect of the gas was manifested in the shift in the left-right distribution of flow in the contactor.
OZONATION OF NATURAL WATERS
- Introduction
- Raw water reaction kinetics
- Ozone-consuming substances and surrogates
- Experimental characterisations
- Conclusions
The basic assumption of this approach is that such a residual ozone concentration should be maintained throughout the contactor (eg: the outlet concentration is then considered to be the appropriate average value). -2) can be rewritten in terms of the rate of disappearance of dissolved ozone as follows:. -7) can explain the effects of ozone dose and raw water quality with an appropriately chosen substitute for OCS.
Modeling the kinetics of the reaction of ozone with natural organic matter in Huron River water.
KINETIC MODEL OF THE OZONE CONTACTOR
- Introduction
- Objectives
- Kinetic model description
- Experimental verification
- S Results and discussion
The first term on the right side of the equation describes the ozone self-decomposition reaction, the second the reaction with oes. The laminar finite-rate model in FLUENT was chosen for the kinetic modeling study. Finally, the flow passes points 5 and 6, which are again located on each half of the contactor (Figure 5-4 (c»).
From a previous study (Brouckaert et al., 2000) it was found that the dispersion in the bottom compartment was increased by the asymmetry of the contactor.
0 , OCS
Ozone mass balance
In order to measure the exit ozone concentration, a sample was taken before the gas reached the final destructor unit (mu). The measurements proved difficult because the gas flowing from above into the mu was greatly affected by the air drawn by the vacuum interrupter at the top of the contactor. The loss of ozone from the gas phase was assumed to be equal to the mass dissolved in water, ie: all other losses were assumed to be negligible.
In dozens of modeling works to date, the mass transfer efficiency of phorone to water using a static mixer was assumed to be complete.
Conclusion
A simple o:wne balance was performed and the mass transfer efficiency of the static mixer was calculated to be over 970/0, assuming that all the o:wne that disappeared from the gas phase went into solution. This additional test was necessary to check the assumption used by the model that the o:mne transfer is complete with negligible loss.
Refe rences
1983a) Rate constants of reactions of ozone with organic and inorganic compounds in water - p. 1994) Characterization 0/ water quality criteria for ozonation processes. 1985) Rate Constants o/ozone Reactions with Organic and Inorganic Compounds in Water - Ill Inorganic Compounds and Radicals. Kilham LB (2002) Measurement of dissolved o/ozone and development of a new gauge. 1990) Effects of %zone, chlorine dioxide, chlorine and monochloramine on Cryptosporidium parvum oocyst viability.
1998) The relationship between the structure of natural organic matter and its reactivity to molecular ozone and hydroxyl radicals. 2001) Mode/Jing Kinetics of the Reaction of Ozone with Natural Organic Maller in Huron River Water.
WIGGINS WATERWORKS' OZONE KINETICS EXPERIMENTS
- Introduction
- Objectives
- Assumptions
- Equipment and methods
- Conclusions
- References
The room was also conditioned to minimize the effect of ambient temperature on ozone formation. Figure 6·2 shows the initial setup of the ozonation column in (a) and when the dose calibration was almost complete in (b). This was achieved by performing laboratory ozonation on samples of the raw water and ultrapure Milli-Q water (Millex, Millipore).
This point is also applied when calculating the boundary conditions of the kinetic model from the previous chapter.
CONCLUSIONS
General comments
The study of the ozone contactor at Wiggins Waterworks began with a simplified hydrodynamic model to predict the RTO and progressed to a more complex, physical modeling of reaction kinetics. During the course of the investigation, it became clear that a suitable method for characterizing raw water was needed. It was clear from the experience of many researchers that long-term monitoring is necessary for optimal performance of an ozone contactor.
However, the focus of the experimental work on kinetics in Chapter 6 was on identifying such a method and not on the accuracy of the method.
Recommend a tion s and future work
It should be noted that, as with any modeling, a virtual model represents a close resemblance to reality at its best, and is never the physical process itself. Therefore, the characterization method should be as simple as possible and easily incorporated into a routine analysis. The monitoring point should be moved from the current position at the outlet to the proposed position at point 4, which is at the end of the second room.
A long-term monitoring system should be established to evaluate the effects of changing water quality due to seasonal fluctuations.
APPENDICES
TURBULENCE THEORY FUNDAMENTALS
- References
The eddy viscosity is therefore assumed to be isotropic, i.e.: invariant with respect to direction (Landahl and Mollo-Christensen, 1986) and is the same for all Reynolds stresses. A popular alternative to the standmd l-t: model is the Ie-t: model based on the reset group (RNG) proposed by Yakhot and Orszag (1986). Many studies have shown that the wall flow can be divided into three layers (Chung, 2002), as shown in Figure A-I, usually in the nondimensional form of velocity, u', and distance, y·. A-IS) where the distance is perpendicular to the wall and u is known as the friction velocity (with TJP and Tw is the surface shear stress).
Standard weight The functions proposed by Launder and Spalding (1974) are chosen for the CFD model of.
RTD EXPERIMENTAL AND SIMULATED DATA
- Plant operation records on tbe ozone contactor no. 2
- Error analysis - Monte Carlo Method .1 Matlab code calculation
The calculation of the mass balances can be found on the worksheet labeled IracerMB in the spreadsheet file, Tracer tests,xls. Lowercase letters (a or b) indicate experimentally measured values or a calculation using these values;. Calculation details can be found on the worksheet labeled IracerMB in the Tracer spreadsheet file lesls.xls.
SourcelII o(uncertainties Unit Std MeaD Adjusted variance Cak "ar. volume of the contactor Inlet.. analysis of the concentrate dilution of the cone sample.. ace elTect on measurements mg Li*1L scale for weighing dosage soln kg density of dosage soln kg /L mass oruacer at the inlet.
MONITORING EXPER IMENTAL AND SIMULATED DATA
I Steady state data
- Step test data
- Ozone ma ss balance
RAW WATER CHARACTERISATION DATA
CFD MODELS OF THE OZONE CONTACTOR
