In-term project presentation by

Kanish Jindal

Modeling of chlorine contact Modeling of chlorine contact chamber at West Lafayette chamber at West Lafayette

treatment planttreatment plant

Problem StatementProblem Statement

Modeling of chlorine disinfection contact chamber and predicting the effluents residence time distribution (RTD) curve

Model : Model : FLUENT

CFD : Computational fluid dynamics

Dynamics of things that flow

Computational model that represents a system or device that you want to study

Fluid flow behavior

Insight Insight Foresight Foresight EfficiencyEfficiency

Fluent Fluent Provides numerical solution for

given domain under given flow conditions

Graphic user inter phase for generation of model

Can write your own codes (User defined functions)

Solver to converge solution

Post processing to analyze results

Gives a foresight to flow physics

Blending time

Solution methodSolution method

Divides the domain into discrete control volumes using a computational grid

Solve the governing integral equations for the conservation of mass and momentum

Solves for energy, turbulence and chemical species if appropriate

Solution contd….Solution contd….

Integration of the governing equations on the individual control volumes

Linearization of the discretized equations and solution of the resultant linear equation system to yield updated values of the dependent variables

West Lafayette Wastewater West Lafayette Wastewater Treatment PlantTreatment Plant

Originally constructed in 1958

Expanded in 1970, upgraded in 1997

Treats 9 millions gallons of waster water every day (3.3Billions/year)

Chlorination –before discharging into Wabash river

Located at 500 South River Road, the Wastewater Treatment Utility serves 29,000 residents, plus 38,000-student Purdue University and the old regional sewer district.

ApproachApproach

EPA determines effectiveness of contactors by CT method

Residence time distribution (RTD) is used to predict the overall microbial inactivation level

Contactor can be modeled as a box system and its RTD can obtained using FLUENT

The RTD obtained from the model is compared with the actual results

Model DescriptionModel Description

Chlorine

Treated Effluent

Hydraulic Jump

Chamber I

Chambers II/III

Disinfected Effluent

Chlorine & Treated Effluent

Chamber I

Chambers II/III

Disinfected Effluent

Hydraulic Jump

• Length 41.41m

• Depth of water = 2.58m

• Width = 1.93 m

Model OutlineModel Outline

•Boundary conditions

•Inlet

•Flow = 9.91 MGD

• Velocity Inlet = 0.096m/s

•k = 2.3E-5

•€ = 9.50E-8

• Domain default fluid

•Mass Balance

Numerical AnalysisNumerical Analysis

Preprocessing: Gambit

Geometric model: From top down approach

Interval Size = 0.4 Hex/wedge

elements Cooper Meshing

MethodMethod

Segregated Model

RNG k- € Model

Based on Navier-Stokes equation

k = kinetic energy = 0.0025(vel)2 *

€ = Energy dissipation rate = 0.1643 (k)3/2/(0.1 * entrance width)*

Inlet

Outlet

Point of injection

* Source : Modeling of Disinfection contactor

ResultsResults

Mean residence time = 1628sec27.13 min

Mean residence time = 55.5min

Residence time distribution

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100 120

Time (mins)

F(t)

min

s

F(t)

Contd..Contd..

Turbulence 0.5%

Length 0.025m

Min time 1476 sec

Max time 1626 sec

Mean time 1556 sec

Std Dev 54.53 secFrom actual 2400 secdata (1st observation)Mean value 56.2 min

= 3360 sec

Velocity profileVelocity profile

Velocity in x direction

Velocity decreases at corners

Sensitivity AnalysisSensitivity Analysis

Effluent RTD was insensitive to uncertainty in the influent turbulent intensity and turbulence length scale

The variation was consistent with respect to variation in turbulence intensity and turbulent length scale

ConclusionConclusion

There is some variation in the effluent RTD curve due to input parameter uncertainties

RNG k- € model was used which might not represent the true flow regime inside the contactor

The assumptions for mixing condition of chlorine to treated influent might have caused some deviations

The deviations between the modeled and experimental results might be due to narrow thickness between the boundary walls resulting in a plug flow regime