Drainage Services Department Research & Development Forum 2017 - - PowerPoint PPT Presentation

Drainage Services Department Research & Development Forum 2017 –

Smart Primary Sedimentation Tanks Design using Three-Dimensional Computational Fluid Dynamic Modeling

Date: 14th November 2017 By: Professor Kin-Man Ho Kingsford Environmental

CONTENTS

1. Uses of 2/3D CFD Modelling for Smart STW Flow & Process Hydraulic Design in HK 2. Smart PST Design Using 3D CFD Modelling 3. Process Hydraulic Enhancement Features by 3D CFD PST Modelling 4. Technical Background of the 3D CFD PST Model 5. Application of the 3D CFD PST Model 6. Full-Scale R&D Trial – Shatin STW 7. Recommendations & Further R&D Studies 8. Acknowledgement 9. Q&A

Uses of 2/3D CFD Modelling for Smart STW Flow & Process Hydraulic Design in HK

CFD Modelling has been extensively used in STW Flow & Process Design in Hong Kong since 1996: - ➢ The Shek Wu Hui STW – Upgrading Existing and New FSTs with 2D CFD only in 1996 and 2009; ➢ The Tai Po STW– Upgrading Existing and New FSTs with 2D CFD only in 2007 and 2013; ➢ The Sai Kung STW – Existing FSTs with 2D CFD only for Operation and Performance Evaluation

• nly in 2005;

➢ The Shatin STW – Upgrading Existing and New FSTs with 2D CFD only in 1998 and 2006; ➢ The Stonecutters Island STW – Upgrading Existing and New CEPT Tanks with Integrated 2D PST and 3D Flow Distribution CFD Modelling in 2008 ➢ The Shatin & Tai Po STWs – Enhance the hydraulic performance of the new effluent UV Channels with 3D CFD Model in 2009 ➢ The Shatin STW – Existing PSTs 3D CFD only in 2016 - 17

Uses of 3D CFD Modelling for Smart STW Flow & Process Hydraulic Design (cont’)

Role of 3D CFD Models

➢ Very powerful commercial packages, FLOW3D, FLUENT etc., are now available for flow distribution modelling ➢ For Solids separation, integrated with sub-routine(s) of proprietary Liquid-Solids Separation Equations/Program ➢ To design and or evaluate Grit Channel, PST/FST, CEPT, Mixing and Anaerobic Digestors ➢ To simulate the flow hydraulic and process hydraulic (with solids) performance ➢ To facilitate the design and upgrading & allow evaluation of options to optimize the system/process hydraulics or to relieve any capacity constrains identified ➢ To investigate likely overflow and maintenance events under different development scenarios during dry & wet seasons ➢ To serve as a planning tool for investigation options to modify, improve & operate the new/existing systems for better performance & power consumption

Smart PST Design Using 3D CFD Modelling

Why these works are important in Smart PST Design and upgrading?

➢ Higher PST TCOD, TSS & TKN removal to cope with variations

• f influent sewage characteristics lead to

➢ lower aeration power consumption ➢ more biogas production ➢ larger process capacity

➢ Less MLSS concentration increases the capacity of the FSTs which is the bottle-neck of the biological process ➢ More compact PST design/upgrade with simple in-tank hydraulic enhancement features simulated and designed by the 3D CFD PST Model ➢ Target to increase TCOD removal of ~20 - 25%.

Process Hydraulic Enhancement Features by 3D CFD PST Modelling

Inlet Zone Transitional Zone Uniform Velocity Zone Effluent Zone

Inlet Energy Dissipating & Flocculation Baffles Mid-Tank Baffles Settled Primary Sludge Protection Baffles In-Board Launders Lamella Plates/Tubes

Technical Background of the 3D CFD PST Model

➢ Powerful 3D PST Model

➢ To give complete & precise representation of water & solids movements in the PST in terms

• f flow, energy/velocity & solids concentration contours,;

➢ The flocculation & settling patterns from the inlets to the outlets of both settled sewage & sludge lines.

➢ Incorporates a special technique, known as the FAVORTM (Fractional Area Volume Obstacle Representation) method, which is used to define general geometric regions within the rectangular grid. ➢ Uses special numerical method to track the location of surfaces & to apply the proper dynamic boundary conditions at those surfaces. ➢ Offers multi-block meshing, which add more flexibility & efficiency to the finite difference meshing technique.

Application of the 3D CFD PST Model

➢ 1st Step -Development and Calibration

➢ Review the design and operation details of the new or existing PSTs to develop & calibrate the 3D CFD PST model. ➢ Prepare 3D CAD drawings of the PSTs & convert to Standard Triangle Language (STL) format as input to the commercial 3D CFD package. ➢ Check the numerical stability & convergence of the built model. ➢ Use water surface elevation measurements to calibrate the model.

Application of the 3D CFD PST Model (cont’)

➢ 2nd Stage Design and Capacity Evaluation and Optimization

➢ Further stimulations to evaluate the effectiveness of hydraulic enhancement feature(s) for optimizing the process & hydraulic performance could then be commenced. ➢ Use the modified PST model to test different “what if” (extreme) operational scenarios.

➢ 3rd Stage Full-Scale Validation

➢ Conduct full-scale tests with dye distribution method combined with water surface elevations measurements to validate & fine-tune the model.

Full-Scale R&D Trial – Shatin STW

The existing Shatin STW has been selected for the trial. Flow-3D integrated with HACM was selected for this project. This Study aims to confirm the applicability of the 3D CFD Model for Smart PST Design in Two (2) Phases: -

1st Phase (This Presentation): -

To develop the 3D CFD Model; To quantify the performance improvement of the existing PSTs with and without SAS co-settling; To identify most optimal upgrading option with different combinations of the hydraulic improvement features; To evaluate the economic viability of these features in OPEX savings.

2nd Phase (If Proceeded): -

Full-scale upgrading of a selected PST; Performance comparison of the PSTs with and without upgrading; Validation of the 3D CFD PST Model Applications for new PST (and FST, others) design for future projects

1st Stage of the 3D CFD PST Model

To develop and calibrate the 3D CFD PST Model

➢ As-built 2D drawings of Unit 3 PSTS  3D drawings & STL CFD Model input files; ➢ 12 months historical operation data of the crude sewage, & settled sewage (Jan to Dec 2015); ➢ On-Site Data Collection of the primary sludge characteristics

3-D AutoCAD Drawing of Existing PST No. 9

On-site Data Collection (with & without co-settling)

➢ 5-day raw & settled sewage characterization study ➢ Flocculation tests with determination

• f the non-settleable solids

concentration ➢ Solids profile tests ➢ Sludge settling velocity distribution tests

1st Stage of the 3D CFD PST Model (cont’)

To determine the optimal achievable performance improvement in terms of COD, TSS & TKN removal using the 3D CFD PST Model, with the process hydraulic enhancement features & combination(s) below: -

➢ Inlet Energy Dissipating & Flocculation Baffles ➢ Sludge Hopper Protection Baffles ➢ Mid-Tank Re-flocculation Baffles ➢ In-Board Launders ➢ Lamella Plates/Tubes (Not considered due to limitation of their applications in the existing PST geometry).

2nd Stage of the 3D CFD PST Model

Inlet Zone Transitional Zone Uniform Velocity Zone Effluent Zone Inlet Baffles Mid-Tank Baffles Settled Primary Protection Braffles In-Board Launders Lamella Plates/Tubes

Inlet Energy Dissipating & Flocculation Baffles

➢ Improve the energy dissipation at the inlet & solids flocculation & hence the solids removal performance. ➢ Solids settled gradually along the full length of the PST ➢ Settled solids re-suspended close to the effluent launder

Application of the 3D CFD Model in Configuring the Process Hydraulic Enhancement Modification

Without Inlet Baffle

Inlet Energy Dissipating & Flocculation Baffles + Mid-Tank Re-Flocculation Baffles

➢ A set of Mid-Tank Re-Flocculation Baffles introduced & simulated. ➢ Significant removal of solids was evident. ➢ Mid-Tank Baffles provided sufficient quiescent velocity distribution on its downstream side to promote rapid settling of the remaining solids. ➢ 2nd set of Mid-Tank Baffles was not considered. ➢ Existing effluent launders do not need to be modified.

Application of the 3D CFD Model in Configuring the Process Hydraulic Enhancement Modification (cont’)

Inlet Energy Dissipating & Flocculation Baffles + Mid-Tank Re-Flocculation Baffles + Sludge Hopper Protection Baffles

➢ High velocity near the sludge hopper at the PST front end caused the sludge blanket to re-suspend. ➢ Sludge Hopper Canopy introduced & simulated. ➢ Highly beneficial for separating the bottom velocity near the settled primary sludge layer.

Application of the 3D CFD Model in Configuring the Process Hydraulic Enhancement Modification (cont’)

With flow distribution considerations, the pollutant removal efficiencies of the existing & modified PSTs w/ & w/o co-settling under 4 flow conditions were predicted & summarized below:

Quantification of the Enhanced PST Performance & Capacity

Flow Condition Time Units 3 & 4 Flow (m3/hr/4PSTs) Lowest Flow Rate 2:00 – 6:00 ~2,900 NH4-N Peak 6:00 – 10:00 ~4,500 Average Flow 10:00 – 14:00 ~4,500 COD Peak 20:00 – 23:00 ~6,300 Without Co-settling % increase With Co-settling % increase Existing PST Modified PST

• Existing PST

Modified PST % TSS Removal ~56 ~65 ~16 ~55 ~64 ~17 % TKN Removal ~13 ~18 ~38 ~14 ~20 ~37 % COD Removal ~48 ~57 ~19 ~50 ~60 ~20

For TSS Removal - For the Design Flow of 340,000 m3/day ➢ For the modified PST, using 1.0 m3 Biogas/kg VSS destroyed for highly degradable primary TSS & 0.75 m3 Biogas/kg VSS destroyed for less degradable SAS, this leads to the increase biogas production:

✓ With Co-settling - ~3,550 m3 Biogas/day ✓ Without Co-settling - ~2,960 m3 Biogas/day ✓ (1m3 Biogas = HKD2.2)

Quantification of the Enhanced PST Performance & Capacity (cont’)

TCOD Removal - For the Design Flow of 340,000 m3/day ➢ A total of ~14,200 & ~12,000 kg/day of enhanced COD removed by the modified PSTs with & without co-settling, respectively. ➢ This corresponds to maximum savings in AOR per day from current aeration system (from IWA Model):

✓ With Co-settling – ~8,500 kgAOR/day ✓ Without Co-settling ~7,100 kgAOR/day

Quantification of the Enhanced PST Performance & Capacity (cont’)

For TKN Removal - For the Design Flow of 340,000 m3/day ➢ A total of ~890 & ~800 kg/day of additional TKN removed by the modified PSTs with & without co-settling, respectively. ➢ An O2 demand of 4.57 mgO/mgNO3-Noxidized & 2.86 mgO/NO3-N denitrified, corresponds to the following daily AOR savings from the current aeration system if sufficient COD is available (from IWA Model):

✓ With Co-settling – ~1,400 kgAOR/day ✓ Without Co-settling ~1,300 kgAOR/day

Quantification of the Enhanced PST Performance & Capacity (cont’)

Overall OPEX Savings – Modified PST With Co-settling

Modified PST w/ Co-settling Power Saving in % [1] ~16 ~16 ~16 Flow 226,076 [2] m3/day 82,517,920 [2] m3/year 340,000 [3] m3/day Electricity Cost [2] HKD 1.00 kWh HKD 1.00 kWh HKD 1.00 kWh Power Saving in Aeration ~4,430 kWh/day ~1,616,000 kWh/year ~2,430,000 kWh/year OPEX Saving together with the increase in biogas production

• ~HKD 3,512,000 per year

~HKD 5,282,000 per year

[1] A total power saving of ~16% can be conservatively achieved for the modified PST with co-settling by CFD Model. [2] Power consumption data extracted from 2015 Carbon Audit Report [3] STSTW design flow, summer DWF average.

Overall OPEX Savings – Modified PST Without Co-settling

Modified PST w/o Co-settling Power Saving in % [1] ~13 ~13 ~13 Flow 226,076 [2] m3/day 82,517,920 [2] m3/year 340,000 [3] m3/day Electricity Cost [2] HKD 1.00 kWh HKD 1.00 kWh HKD 1.00 kWh Power Saving in Aeration ~3,600 kWh/day ~1,300,000 kWh/year ~1,955,000 kWh/year OPEX Saving together with the increase in biogas production

• ~HKD 2,900,000 per year

~HKD 4,330,000 per year

[1] A total power saving of ~13% can be conservatively achieved for the modified PST without co-settling by CFD Model. [2] Power consumption data extracted from 2015 Carbon Audit Report [3] STSTW design flow, summer DWF average.

➢ This is the 1st trial using 3D CFD PST modeling to simulate the optimal combination of hydraulic enhancement features. ➢ Full-scale stress tests are recommended to be conducted for accuracy validation of the developed 3D CFD PST Model. ➢ Stress Validation Tests have 2 major components:

✓ Verify the hydraulic performance with dye tests ✓ Verify the TSS removal efficiency under the predicted or practically achievable maximum capacity

Recommendations & Further R&D Studies

➢ Stress Tests can be conducted by modifying 1 PST in the STSTW w/ a set of each of the Inlet Energy Dissipating & Flocculation Baffles + Mid-Tank Re-Flocculation Baffles + Sludge Hopper Protection Baffles. ➢ Validation Tests to verify & the previous 3D CFD Model predictions can then be conducted on the modified PST & performance then compared to an un-modified PST. ➢ Finally, for more compact PST configuration, it is recommended to incorporate Lamella Settlers in the PSTs from other DSD STW(s) (New or Existing) to quantify the exact benefit in solids removal enhancement as published in the literature.

Recommendations & Further R&D Studies (cont’)

➢ The opportunity to work on this R&D Project awarded by DSD. ➢ The great supports from the DSD/ST1 Team in organizing and supervising the on-site operation, sampling and analyses works for this R&D study. ➢ The tremendous efforts, round the clock, of the Kingsford Environmental R&D Team led by Ms. Maggie Chan.

Acknowledgement