Computational Fluid Dynamics (CFD): Smart Use of Advanced Modelling - - PowerPoint PPT Presentation

Computational Fluid Dynamics (CFD): Smart Use of Advanced Modelling Tools

Dr Anna M. Karpinska Portela Birmingham, 28 Jan. 2020

Senior Process Scientist - Asset Performance Optimisation

What is CFD?

2

▪ “If we know what is happening within the vessel, then we are able to predict the behaviour

• f the vessel as a reactor. Though fine in principle, the attendant complexities make it

impractical to use this approach.”–Octave Levenspiel (1972) ▪ “Computational fluid dynamics (CFD) changes this picture. Using CFD, we can compute three dimensional velocity fields and follow interactions of reactants and products through a tank. We can use this information to optimize tank geometry and operation.“ – Randal W. Samstag (2015) ▪ CFD is a powerful numerical modelling tool, which allows for flow visualisation with detailed characterisation of the special phenomena under varying process conditions.

CFD for Wastewater – Art and Science

3

▪ Since over two decades – application of CFD extended to civil and environmental engineering ▪ Recent developments in multiphase flow – steady increase of the use of CFD in wastewater engineering ▪ To date, CFD has been primarily used for evaluation of hydraulic problems at wastewater and sludge treatment streams level ▪ More advanced application of CFD is increasingly studied- simulation of the integrated flow field and physical, chemical and/or biological processes for optimized process design and plant operation

CFD for Wastewater – Opportunities

4

▪ Analysis of the multiphase flow behaviour ▪ Prediction of the impact of wide range of operating conditions on the local-scale phenomena:

▪ Flow field + interfacial mass transfer + chemical reactions

▪ High-precision technique for evaluation of the engineering systems, which are expensive and difficult to reproduce in lab- and pilot-scales ▪ Robust tool for:

▪ Unit process design ▪ Troubleshooting ▪ Optimisation (“tune for benefit”)

▪ Enhanced process performance ▪ Energy-optimised operation

▪ Elimination of “Build, Test & Correct” and “The Rule of Thumb” approaches

CFD for Wastewater- Examples

5

Headworks Flow splitters PSTs

Samstag and Wicklein, 2015

ASPs

Karpinska and Bridgeman, 2017

Lagoons

Current and Future Added Value of CFD

6

Wicklein et. al, 2016

▪ Flow Field and few Internal Processes- well established, but require some care and effort for quality solution ▪ Many Internal Processes are emerging and requiring significant care and effort in the CFD Model

Future Added Value of CFD

7

▪ Use of CFD to build knowledge (input, output, backmixing, recirculation) for improved simpler models (Compartmental Models -CM)

Alvarado et al., 2012

Challenges to be addressed?

8

▪ No guidance document with regard to “Good Modelling Practice” (GMP) covering state-of- the-art, knowledge gaps and future needs ▪ Lack of educational support and targeted training

▪ Users rely on either self-training or very limited training courses provided by CFD manufacturers (lacking problem specifics as water/wastewater treatment is hardly their core business) ▪ Frequent CFD software misuse by inexperienced users

▪ Incorrect problem statement ▪ Poor model choice ▪ Wrong setup assumptions ▪ Misinterpretation of the results

▪ Reduced confidence in outcomes of CFD analysis (decreased usage of the software)

▪ Lack of handbook dedicated to CFD applied to wastewater practice

Challenges – CFD for ASP

9

▪ Complete CFD simulation of ASP is challenging

▪ No unequivocal CFD modelling guideline for ASPs ▪ Biologically active liquid- gas- solids system ▪ Complex hydrodynamics (interactions between the phases) ▪ Biochemical conversion rates ▪ High mesh resolution required for solution accuracy ▪ Massive computational costs (RAM & CPU) and long simulation run times ▪ Data collection for calibration and validation- time consuming and resource expensive (ADV, ADCP, LDV, tracer testing, spatial profiling) ▪ Overall cost of CFD analysis is high, yet cheaper than capital costs of a new asset !

Rehman et al., 2014 Karpinska and Bridgeman, 2017

Common ASP Modelling Pitfalls

10

▪ Model oversimplification - use of the most computationally inexpensive modelling scenario

▪ Steady-state analysis & turbulence modelled with standard k-epsilon model ▪ Neutral density (clean water set as a working fluid, no solids transport) ▪ Fixed bubble size (rigid spheres)- neglecting Bubble Size Distribution (no coalescence and breakup) ▪ Coarse mesh ▪ Lack of calibration

▪ Errors in the results and validation

Karpinska and Bridgeman, 2017

Overestimation of the turbulent interactions (wrong initial assumption & inappropriate model)

Who are we?

11

Working Group on Computational Fluid Dynamics (CFD) for Unit Processes

Management Team (MT):

▪ Julien Laurent, Engees Strasbourg, France - Chair ▪ Randal Samstag†, Civil and Sanitary Engineer, USA - Secretary ▪ Jim Wicks, The Fluid Group, UK – Vice-Chair ▪ Ingmar Nopens, Ghent University, Belgium ▪ Ed Wicklein, Carollo Engineers, USA ▪ Anna Karpinska Portela, Southern Water, UK ▪ Alonso Griborio, Hazen and Sawyer, USA ▪ Steve Saunders, Ibis Group, USA ▪ Olivier Potier, Université de Lorraine, France ▪ Damien Batstone, University of Queensland, Australia ▪ Nelson Marques, Blue Cape, Portugal ▪ Usman Rehman, AM-TEAM, Belgium

https://iwa-connect.org/

IWA Working Group for CFD – Current Activities

12

▪ Papers/Books

▪ Papers available on

▪ GMP for CFD in wastewater engineering ▪ State-of-the-art on CFD modelling of the unit processes ▪ A protocol for the use of CFD as a supportive tool for wastewater treatment plant modelling

▪ IWA Scientific and Technical Report- GMP CFD for Wastewater - book in preparation (expected July 2020)

▪ Dissemination

▪ Platform presentations in conferences (IWA events, IWA/WEF WRRFMod Seminars, WEFTEC, Watermatex, Water&IT, ..) ▪ Workshops and Webinars to promote GMP for CFD ▪ WaterWiki, IWA-Connect, LinkedIn

https://www.wrrmod2020.org/ https://iwa-network.org/all-events/ https://weftec.org/

Good CFD Modelling Practice – 4 Steps

13

Wicklein et al., 2016

▪ Define Problem ▪ Gather Data ▪ Solve Problem ▪ Show Results

Complete Flow of a CFD Modelling Process for Quality Output

14

Wicklein et al., 2016.

▪ Dimensions ▪ Model selection for problem ▪ Geometry & meshing ▪ Boundary Conditions ▪ Physics ▪ Solution Methods ▪ Convergence

Dedicated CFD GMP Book –available soon!

15

▪ Dedicated chapters covering

▪ Fundamentals

▪ Multiphase modelling

▪ Individual unit treatment processes

▪ State-of-the-art ▪ GMP – with case study ▪ Knowledge gaps ▪ Research needs ▪ Future trends

Thank you for your attention!

16

anna.karpinska-portela@southernwater.co.uk

Rehman et al., 2017