In-term project presentation by Kanish Jindal Modeling of chlorine contact chamber at West Lafayette treatment plant

Problem Statement Problem 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 Foresight Efficiency Insight Foresight Efficiency

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 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…. 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 Treatment 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.

Approach 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 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 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 Analysis Preprocessing: Gambit Geometric model: From top down approach Interval Size = 0.4 Hex/wedge elements Cooper Meshing

Method Segregated Model RNG k- € Model Based on Navier-Stokes equation k = kinetic energy = (vel) 2 * € = Energy dissipation rate = (k) 3/2 /(0.1 * entrance width)* Inlet Outlet Point of injection * Source : Modeling of Disinfection contactor

Results Mean residence time = 1628sec min Mean residence time = 55.5min

Contd.. Turbulence 0.5% Length 0.025m Min time 1476 sec Max time 1626 sec Mean time 1556 sec Std Dev sec From actual 2400 sec data (1 st observation) Mean value56.2 min = 3360 sec

Velocity profile Velocity in x direction Velocity decreases at corners

Sensitivity 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

Conclusion 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