Water & Wastewater Mixing: Lighting Up A Dark Art (or cramming a quart into a pint pot!) Dr Mick Dawson Process Director mdawson@bhrgroup.co.uk 25th October 2011 BHR Group 2011 BHR Group is a trading name of VirtualPiE Limited www.bhrgroup.com
Aims To answer the questions: What is WWM? Why was it started? What has it achieved? Who has been involved? Where is it going? BHR Group 2011 2
Content The need for WWM WWM Work Areas WWM Deliverables WWM Case Studies Future needs BHR Group 2011 3
Need for WWM: Cramming a quart into a pint pot Historically, the design and construction of water, wastewater and sludge (biosolids) treatment facilities has been civil engineering dominated. The large volumes to be processed led to large surface area, land intensive plants principally constructed from concrete. In more recent times, pressure for change has resulted in adoption of a range of new and more intensive processes resulting in a greater chemical engineering involvement. Process intensification therefore required the transfer of mixing and reactor design know-how from the chemical to the water sector BHR Group 2011 4
MIXING RATE: Lighting up a dark art Mixing rate describes the rate at which concentration fluctuations are removed Conventional water industry design parameter is G factor actually a shear rate From flocculation theory Does not quantify mixing rate Limited use in liquid blending design BHR Group 2011 5
Potable Mixing Applications Source blending Recycle blending Coagulation ph correction Polymer dosing Flocculation Disinfectant dosing Sulphonation Ozonation BHR Group 2011 6
Wastewater Mixing Applications Chemical Assisted Sedimentation Dosing for P-removal ph correction Anoxic zones Activated Sludge Recycle blending BHR Group 2011 7
Sludge Mixing Applications Sludge storage & blending tanks Anaerobic & Aerobic Digesters Inline blending & Sludge Conditioning Hydrolysis, Pasteurisation & Chemical Treatment BHR Group 2011 8
General benefits of well designed mixing Improved treated water/wastewater quality Capital cost saving: reduced plant footprint, easier plant start-up and commissioning. Operating cost saving: reduced additive chemical consumption, reduced process power demand, maximized throughput, reduced process downtime and lighter load on downstream processes BHR Group 2011 9
WWM is A well focused collaborative research project. Supported and steered by Water PLCs, Consultants, Mixer & Chemical Suppliers. Aimed at improving process efficiency and profitability. Live: Phases 1-6: 1996-2009, Phase 7 ongoing BHR Group 2011 10
Current WWM MEMBERS WWM 7 2009 2011 United Utilities Severn Trent Water MWH Black & Veatch Hidrostal ITT Flygt Monsal Statiflo CAMBI Other Members 1996 2009 RAS inlet Thames Water Yorkshire Water Northumbrian Water SNF Fleurger 14.92m Settled solids inlet Alternate RAS inlet (closed) 11.79m Outlet 3.5m BHR Group 2011 11
Inline Blending Research Pipes Potable Water: Turbulent flow T-mixers, jet mixers, static mixers, orifice plates Sludge: Laminar to turbulent flow, non-newtonian, high fouling T-mixers, static mixers, orifice plates, valves, pumps Channels Potable Water: Turbulent flow, low fouling T-mixers, jet mixers, static mixers, weirs, Sewage: Turbulent flow, high fouling T-mixers, jet mixers, weirs, air mixers, impellers BHR Group 2011 12
Pipe Blending with T-mixers & Jets Potable Water: CoV measured @100mm also CFD Variables Additive momentum flux [N] Feed pipe diameter, d Q/q L/D Dose arrangement BHR Group 2011 13
Pipe Blending with T-mixers Sludge: CoV measured @100mm Variables Shear thinning rheology (K,n) Re: 100-10,000 Additive momentum flux [N] Q/q Dose arrangement BHR Group 2011 14
Pipe Blending with Static Mixers Potable Water: CoV & F d measured (LIF). Data shared with HILINE/FMP Variables Q Mixer Type: Kenics, HEV, SMV, STM Mixer Scale Element number Q/q Dose arrangement Energy efficiency compared BHR Group 2011 15
Pipe Blending with Static Mixers Sludge: CoV & F d measured Variables Shear thinning rheology (K,n) Re: 100-10,000 Mixer type: Kenics, SMF, Statiflo Element number Q/q Energy efficiency compared Fouling tendency assessed on-site BHR Group 2011 16
Pipe Blending with Orifice Plates Potable: CoV & F d measured Variables d/d Dose arrangement Q/q Energy efficiency compared Sludge:CoV & F d measured Variables Shear thinning rheology (K,n), Re: 100-10,000 d/d Dose arrangement Q/q Energy efficiency compared Fouling tendency assessed on-site BHR Group 2011 17
Blending with Pumps & Valves Pumps: CoV measured Variables Shear thinning rheology (K,n), Re: 100-10,000 Stroke rate Q/q Energy efficiency compared Valves: CoV & F d measured Variables Shear thinning rheology (K,n), Re: 100-10,000 Valve position Dose arrangement Q/q Energy efficiency compared BHR Group 2011 18
Channel Blending with T-Mixers, Spargers & Jets Potable Water: Turbulent CoV measured using W=300mm, H=400mm channel Variables H/W Additive momentum flux [N] Feed pipe/hole diameter, d and number Q/q L/D Dose arrangement Dose position Additive Density BHR Group 2011 19
Channel Blending with Jet Mixers Potable Water & Sewage: CoV measured On-site & laboratory Variables H/W Q Feed pipe diameter Jet momentum flux [N] Q/q L/D Jet position Additive dose arrangement Energy efficiency compared BHR Group 2011 20
Channel Blending with Static Mixers Potable Water: CoV & F d measured Variables Q Mixer Type: HEV, SMV, STM, DIY Baffles H/W L/D Element number Q/q Dose arrangement Energy efficiency compared BHR Group 2011 21
Channel Blending with Gas Mixers Potable Water & Sewage: CoV measured On-site & laboratory Variables Q g Q H/W L/D Sparge position Sparge Arrangement BHR Group 2011 22
Blending with Weirs & Flumes Potable Water, Sewage:Turbulent CoV measured Variables H/W Additive momentum flux [N] Weir height Feed pipe/hole diameter, d and number Q/q L/D Dose arrangement Dose position BHR Group 2011 23
Tank Mixing Research CSTRs Potable water ( Flash Mixers, Flocculators) Impellers, jets Batch or Semi-Batch Sewage (Anoxic Zones) Impellers, submersible mixers Sewage Sludge (Digesters, Blend Tanks etc.) Impellers, jets, gas mixers, submersible mixers BHR Group 2011 24
CSTR Blending Flash Mixers Potable Water, Sewage: Turbulent CoV, RTD measured Variables Impeller type N C/D Q Inlet shape Dose position Energy efficiency compared BHR Group 2011 25
Tank Mixing Research Anoxic Zone Mixing Sewage: Turbulent CFD modelling of Base & surface velocities RTD Blending of inlet streams Variables Tank geometry Inlet geometry Mixer type & number Mixer power Mixer position & orientation BHR Group 2011 26
Tank Mixing Research Impellers Sludge, Transitional, non-newtonian CFD & physical modelling of Velocities Blending Caverns Variables Tank geometry Sludge rheology Inlet location Impeller type & number N Comparison with full scale measurements BHR Group 2011 27
Tank Mixing Research Jets Sludge, Laminar & Turbulent, non-newtonian CFD & physical modelling of Velocities Blending Caverns Variables Tank geometry Sludge rheology Jet location, type & number Jet diameter & Q Additive density BHR Group 2011 28
Tank Mixing Research Submersible Mixers Sludge, Laminar & Turbulent, non-newtonian Physical modelling of Velocities Blending Caverns Variables Tank geometry Sludge rheology Mixer location, type & number Mixer diameter & Q BHR Group 2011 29
Tank Mixing Research Gas Mixers Sludge, Laminar & Turbulent, non-newtonian Inlet position (b) Sparger B 6 7 Physical modelling of Velocities Blending 5 11 12 x 9 8 Variables 4 10 1 Tank geometry Scale 3 x 2 Inlet posi Sludge rheology Q g Nozzle location, type & number Nozzle operation BHR Group 2011 30
WWM Deliverables Dosing & Mixing in WTW & STW CR8240 Design Guide for Liquid Blending in Pipes & Channels CR8238 Chemical Dosing & Mixing for Sewage Treatment Sludge Tank and Digester Mixing CR8237 Digester & Sludge Tank Mixing Design Guide CR8239 Sludge Tank & Digester Mixing Research Report Digester & Sludge Tank Mixing Software Energy Saving in Flash Mixing & Flocculation CR8250 Energy Saving in Flash Mixing & Flocculation Calculation Spreadsheets BHR Group 2011 31
BHR Sludge Rheology Database Worlds largest body of sludge data 500+ Rheograms Predictive correlations for 12 sludge types Previously un-reported sludge types Polymer thickened sludges Potable sludges Iron dosed sludges Hydrolysed sludges SRDB available for use by WWM members via website BHR Group 2011 32
BHR System Losses Design Tool Estimate total pressure losses on suction and discharge side of pumps for alternative pipe diameters & velocities fitting types & diameters sludge types, concentrations and rheological properties laminar versus turbulent pipe flow Validated software tool against measured pressure losses Enables continued development as state of the art advances BHR Group 2011 33
Potable Coagulant savings example. The WWM Design Guide was applied to a large WTW. Installation of the recommended mixers resulted in... Consistent reduction in chemical consumption of 1.5kg/Ml Equating to an average daily saving on chemical of 150/day or 55,000/year Mixer cost was 15,600 + 3,600 installation Payback time 4 months Additional saving in reduced sludge production and processing BHR Group 2011 34
Potable Energy Saving examples.. The WWM Design Guide was applied to a WTW featuring mechanical flash mixing for coagulant. Improved coagulant mixing could best be achieved by installing the most efficient static mixer. The savings in electricity costs alone amounted to 7,000 p/a The WWM Design Guide was applied to a large WTW with turbine flocculators. Equivalent performance could be achieved using hydraulic flocculators. The savings in electricity costs would be 56,000 p/a BHR Group 2011 35
Potable Asset Design Standards.. United Utilities introduced chemical mixing Asset Standards in 2000 based on the WWM Design Guide mixer efficiency recommendations. Implementation of the standards for new builds and retrofits have saved UU 100,000s in chemicals, energy and smooth process operation. A new inlet works for a large WTW was designed with help from the WWM Design Guide for source blending and chemical mixing Effective blending of source waters with very different composition eliminated control problems that had been costing 10,000s per year BHR Group 2011 36
Waste Water Anoxic Zone Mixing The WWM Anoxic Zone Design Guide was used to evaluate rival bids for mixing a three chamber Anoxic Zone. The selected bid saved 6,300 per year in energy costs whilst achieving the specified mixing criteria at equal capital cost. BHR Group 2011 37
Waste Water Dosing Chemicals Application of the WWM Design Guide when dosing Fe or Al salts for P-Removal or CAS provides the only rapid mixing solution WWM currently provide the only non-ragging, low headloss rapid mixer Reducing chemical dose by 10%-50% results in Chemical cost savings of 100,000s company wide Reduction in sludge volumes Reduced scaling by Calcite & Struvite Lower coagulant residual in the final effluent BHR Group 2011 38
Sludge Thickening & Dewatering Application of the WWM Design Guide to polymer dosing on a large belt press sludge dewatering facility resulted in a 15% reduction in polymer consumption 20,000 per year saving in polymer costs an increase in cake DS of 1% to 4%. Reduced energy consumption for incineration plant of 150,000 per year Application of the WWM Design Guide to sludge mixer selection avoided serious ragging problems saving 1,000s in retro-fitting costs BHR Group 2011 39
Future Work Chemical Free Treatment Floc Strength Research Coagulation/Flocculation Dose Optimisation toolkit Polymer Dosing Optimisation Primary Settlement Software Design Guide Co-digestion and Digestion Technology Anaerobic Digester Design Energy Management Pipe Fouling Sludge Pumping Sludge Dewatering BHR Group 2011 40
Thank you Dr Mick Dawson. mdawson@bhrgroup.co.uk Water, Environment & Power (WEP) Fluid Systems Academy Process Enquiries: contactus@bhrgroup.co.uk BHR Group 2011 BHR Group is a trading name of VirtualPiE Limited www.bhrgroup.com