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Dow — Technical Presentation (February 2017)
31 slides from Dow's technical presentation, February 2017
Slide 1: Cooling Tower Blow Down Water Treatment for Reuse
Cooling Tower Blow Down Water Treatment for Reuse Kai-Uwe Hoehn Dow Water & Process Solutions DOW RESTICTED
Slide 2: Agenda
Agenda 1. What is Cooling Tower Blow Down (CTBD)? 2. Why reuse CTBD water? i. Typical volumes, trends and drivers ii. Reuse opportunities targets and criteria 3. What are the reuse limitations with CTBD water? i. Typical contaminants, water chemistry of CTBD water and ii. Challenges for treatment of
Slide 3: Open-Recirculating Cooling Towers
Open-Recirculating Cooling Towers Drift & Evaporation Hot Fluid Cooling Make-Up Water Tower Exchanger With ongoing recirculation Cold Fluid the water quality deteriorates to a point where make up water additions and blow Blowdown Re-Circulating down are required. Pump
Slide 4: Typical Blow Down Volumes and Concentration Ratios
Typical Blow Down Volumes and Concentration Ratios 700MW coal-fired power plant - Cooling Tower Circulation Volume 71,600m3/h 40,000 metric tons of crude oil – Cooling Tower Circulation Volume 80,000m3/h ---- Water Digest, Mar-Apr. 2008, Vol. Blow 2, No. 5, P. 22-31 down Power Generation Capacity Bl
Slide 5: Typical Composition of CTBD from Surface Water
Typical Composition of CTBD from Surface Water Item Unit Make-up Blowdown Range • Can vary substantially by region Water Water as feed source for cooling tower is pH - 7.43 8.47 8.47-8.85 surface water or secondary SS mg/l 11.1 26 municipal waste water Turbidity NTU 8 26 15--30 Total Solid mg/l 241.
Slide 6: CTBD Water
CTBD Water CTBD Water typically is a brackish, has high TDS and contains some: • Suspended particles • Scalants • Inorganic foulants • Corrosion products • Organic matter • Bio-active material
Slide 7: Why Reuse Cooling Tower Blow Down?
Why Reuse Cooling Tower Blow Down ? • Water Scarcity • Discharge Limits • Cost Reduction • Environmental • Increased Water Scarcity • Population growth into more arid areas, increased water stress, competing use of water for municipal and agriculture demands vs. industrial processes. • Which results
Slide 8: Water Chemistry / Composition
Water Chemistry / Composition • Analysis should be BALANCED when expressed in meq/l or ppm as CaCO3 Ca Alk • Temperature (HCO3) • TDS • Suspended solids • Bacteria Mg • Organics Cl • ppm KMnO4 , TOC, (BOD) • Residual biocides • Scale and corrosion inhibitors Na SO4 • pH value K • pH < 7 (free CO2) ,
Slide 9: Technologies to Remove Key Contaminants
Technologies to Remove Key Contaminants Turbidity Hardness Alkalinity Silica Dissolved Solids Suspended Solids Sulfate/Chloride Colloids Lime WAC WAC Softening Strainer MF/UF Fibrous Weak Acid RO Filter Cation resins Acid Coagulation/Fl Dosing occulation Strong 2B3T/MB Strong Acid Base MMF Cation re
Slide 10: Existing Practice for Blowdown Reuse: Chemical Softening
Existing Practice for Blowdown Reuse: Chemical Softening Cooling Tower Make Up EDI MMF RO ~75% Lime/Soda Balance Softening Boiler Tank Clarification Make SAC SBA MB Up Pros 2nd Pass • High hardness/alkalinity Removal Efficiency RO MB ~90% • Removes Silica, high MW organics, Ba, Sr • Usually dose coa
Slide 11: Existing Practice for Blowdown Reuse: IEX WAC and SAC Softening
Existing Practice for Blowdown Reuse: IEX WAC and SAC Softening Cooling Tower Make Up EDI RO NaOH HCl NaOH >80 % Boiler Make Softener Degasifier Crystallization SAC SBA MB Up WAC Cartridge (SAC) Filter RO Pros >90 % MB • Complete hardness removal (more than 99.5%) Cons • Higher RO recovery without s
Slide 12: Existing Practice for Blowdown Reuse
Existing Practice for Blowdown Reuse Coag/Floc/Clarification+MMF+MF/UF+RO Cooling Tower Make Up (popular in China) EDI Boiler RO ~ 70-75% Make Coag/Flocc Up SAC SBA MB Clarification MMF MF/UF RO >90 % MB Cons Pros • No removal for hardness/alkalinity in • High suspended solids removal efficiency pre
Slide 13: Two-Stage RO at 80% Recovery
Two-Stage RO at 80% Recovery concentrate = ~20% 20 of feed flow @ ~ 5x feed concentration Stage 2 RO Feed 50 Flow 100 % Stage 1 80 % low TDS 50 30 permeate 80 flow for reuse Pretreatment e.g. UF
Slide 14: Typical RO Element Selection for CTBD
Typical RO Element Selection for CTBD • For cooling tower makeup reuse, brackish water low energy RO elements or even NF can be used (NF, LE, XLE) ‒ These element types achieve the salinity quality requirement for cooling tower makeup water at very low operating pressure / low energy consumption • I
Slide 15: Example: Two-Stage 80% Recovery CTBD RO
Example: Two-Stage 80% Recovery CTBD RO 120 100 80 Feed 60 Concentrate 40 20 Permeate 0 % Flow ~5x
Slide 16: Operational Risk and Concentration Factor
Operational Risk and Concentration Factor Concentration Factor (CF) CF = 1 / (1 – Recovery % ) 20 • High recoveries 18 >80% increase the 16 risk of scaling, 14 fouling and thus raise cleaning 12 frequency while 10 there is little extra 8 gain in water produced 6 4 • Use a brine 2 recovery unit to 0
Slide 17: RO Preventative Flush to Reduce CIP Frequency
RO Preventative Flush to Reduce CIP Frequency A short, 10 minute 1-3 x per day feed water or permeate flush ( high flow, low pressure, no permeate) is recommended to help half cleaning frequency Acid flushing every other day can further help to reduce cleaning frequency Flush Water Membrane leaf Per
Slide 18: RO Scale Prevention - Antiscalants
RO Scale Prevention - Antiscalants Name Methods How it works Acid dosing Convert bicarbonate to Carbon dioxide Carbonate scaling Antiscalant Slower scaling layer formation Softening Remove hardness Low Recovery Reduce ionic strength in RO concentrate Antiscalants Slower scaling layer formation Sulfa
Slide 19: RO Biofouling Prevention
RO Biofouling Prevention Operational Aspects • Intermittent or continuous DBNPA dosage • Chlorination / Dechlorination • Early detection - monitor pressure drop (dP) of each stage • Preventative cleanings • Clean at pH (12-13) when dP increased by 15% • Continuous 1-3 ppm pre-formed chloramines at p
Slide 20: Choosing the Right RO Cleaner & Sequence
Choosing the Right RO Cleaner & Sequence Right Cleaner • A wrong choice can aggravate a scaling/fouling problem • Acids for scaling • Alkaline for biological fouling • Alkaline with detergent for organic fouling • Frequently both alkaline and acid cleanings are required Cleaning Order • Alkaline cle
Slide 21: 3 Stage RO – 90% Recovery
3 Stage RO – 90% Recovery Stage 3 10 concentrate 20 Stage 3 = ~10% of feed flow Stage 2 50 Feed Flow 100 Stage 1 10 cbm/h 30 90 cbm/h 50 permeate 80 flow
Slide 22: 90% Recovery – RO: Main RO + Stage 3 Brine Recovery
90% Recovery – RO: 2 Stages Main RO + 1 Stage Brine Recovery Brine Recovery Stage 2 concentrate = RO unit ~20% of feed flow 10 20 Stage 3 Stage 2 at 50% 50 recovery Feed Flow 30 stage 3 can be 10 100 Stage 1 cleaned, serviced cbm/h 80 cbm/h and run independently permeate at suitable recovery -> flow
Slide 23: Case Study: CTBR in Gaojing Power Plant
Case Study: CTBR in Gaojing Power Plant
Slide 24: Reclaiming CTBD at World's Largest Thermal Power Plant
Reclaiming CTBD at World’s Largest Thermal Power Plant Plant: Datang Tuoketuo Power Station Location: Hohhot, Inner Mongolia, China Capacity: 6,600 MW Primary Fuel: Coal Application •Recovery of cooling tower blowdown •RO pre-treatment •Boiler feed at China’s largest coal-fired power plant Challenge
Slide 25: Challenge: Feed Water
Challenge: Feed Water Primary feed source: Cooling tower blowdown (CTBD) • High TDS • High alkalinity (HCO3-) Due to evaporation • High hardness process • High SO42- • High silica Secondary feed source: Pre-treated surface water from Yellow River (when insufficient CTBD available) • High TSS Na+ Ca2
Slide 26: CTBD Water Reuse Treatment Process
CTBD Water Reuse Treatment Process FILMTEC BW30-365 FR UF System Summary RO System Summary Number of trains 2 Configuration One pass, two stages (16:8) Number of modules per train 38 Type of module BW30-365 FR Type of module SFP-2880 Normalized 99% Module membrane area 77 m2 rejection (> 97% after 3
Slide 27: Maintenance
UF System Operating Parameters Item Step Duration Frequency Note Flux Operation Filtration 40min 62.2 lmh Air flow Air scour 60s Physical cleaning 8-10 Nm3/h Gravity drain 60s Backwash top 60s 40 min BW flux Maintenance Backwash bottom 60s 120 lmh Forward flush 120s NaOCl 20min 200 ppm CEB 10 days H
Slide 28: UF Operation: Flux & Permeability, TMP
UF Operation: Flux & Permeability, TMP Normalized Permeability • Constant flux; UF permeability is influenced by feed temperature • Stable permeability indicates Actual Operating Flux 60lmh is a reasonable design flux for feed source • Stable Trans Membrane Pressure (TMP) indicates: stable operation
Slide 29: UF Operation: Treated Water Quality
UF Operation: Treated Water Quality • Variable feed turbidity; average of 1.26NTU UF Feed • SFP-2880 produces filtrate with UF Permeate turbidity < 0.1NTU, most of the time • High resolution/accuracy online laser turbidimeter recommended
Slide 30: RO Operation: Flow and Rejection, dP
RO Operation: Flow and Rejection, dP • Stable normalized flux, no flux Normalized decline tendency and no rejection obvious fouling • Stable RO system Normalized flux rejection,99.2% in rejection (better than design!) • Stable pressure drop (dP) in the first stage means no obvious fouling • UF is hi
Slide 31: Thank You & Q&A
Thank You & Q&A NOTICE: Although the information and recommendations in this presentation (hereinafter "Information") is presented in good faith and believed to be correct, Dow makes no representations or warranties as to the completeness or accuracy of Information. Information is supplied upon the