The various sources of water can be broadly
• The various sources of water can be broadly classified as • Rain water • Surface water (Rivers, Streams, Ponds, Lakes and reservoirs) • Ground Water (Springs, Shallow Wells and Deep Well)
Impurities of Water Non-Ionic Impurities This includes salt, mud, dirt, micro-organisms, bacteria and other organic matter, oil and corrosion products Ionic Impurities This includes salts which dissociates into cations such as calcium, magnesium, sodium, iron etc. and anions such as bicarbonates, hydroxides, chlorides, sulphates etc. Dissolved Gases This mainly includes oxygen and carbon dioxide
INDEX • • PART - III PART - IV PART - VI PART - V 1 I THE COOLING TOWERS WATER PARAMETERS THE NEED CORROSION SCALING MICROBIOLOGY TREATMENT CHEMICALS & METHODS
COOLING TOWER DESIGNS AIR WATER CONTACT • Forced Draft • Induced Draft • Natural Draft • Cooling Pond
INDUCED DRAFT Most common.
SOME BASIC DEFINITIONS: • Recirculation = Amount • Drift + Windage = any • • of water flowing throughout the system. Evaporation = Water lost from system as vapour, TDS left back. Hold - Up = Line +basin volume+any other. Delta T = Difference in inlet and outlet temp. oc CT. • • water loss due to air draft in the system. Leaks = Any other loss of water! Blowdown = Water drained purposely from the systemto reduce TDS. COC = Circulation water impurity/make-up water impurity
BASIC CALCULATIONS • Recirculation rate = No. of pumps running! • Evaporation rate M 3/Hr = R. R (M 3/Hr) * delta T • • • 675 Blowdown M 3 / Hr = Evaporation M 3/Hr (COC - 1) Delta T = Inlet to CT - Outlet to CT Drift + Windage Loss M 3/Hr = 0. 05 to 0. 2 % of Recirculation Rate. • COC = As per make up water quality
PARAMETER DEFINITION W A T E R PH Chlorides Measure. Acid / Alkali Value of Acid/ Alkali Measure of Ca & Mg - Sulphates - Silica Metals Iron, Cu TDS - Alkalinity Hardness IMPLICATION High: Will Precipitate Ca, Mg, Low: Corrosive. Presence = Scale, Absence = Corrosive Low: Good! High: Pitting, corrosive. Low: Good! High: Scale Presence means corrosion & Fouling. High - Will aid scale. Low - aid Corrosion. P A R A M E T E R S
OTHER ENTRANTS. . . PARAMETER TURBIDITY / SS DEFINITION Insoluble Foulants IMPLICATION Deposition, Fouling, Create zone for biofouling & Corrosion Microbes TBC / SRB / Fouling, Corrosion, Algae Hazardous BOD / COD Organics Will Support Biogrowth, Organic Fouling OTHERS CONTAMINATION FROM IMPACT Oil & Grease Leaks Cause Corrosion, Ammonia Leaks, Air Fouling, Biofouling, scrubbing Interfere with treatment Gases Air, Leaks, Scrubbing Ash, Coal Surrounding, Soot Blow Alcohols Vapours Process Fluids Leaks
Cooling Water Problems • Corrosion • Scaling • Microbial fouling
WATER TREATMENT: COMMERCIAL ASPECTS CORROSION: • Greater initial capital • • • Investment to Provide Corrosion Resisttsnt Equipment. Overdesign of Equipment: With adequate protecttion, wall thickness can be reduced by 2535 %. A 360 km, 20 cm piping reduced wall thickness from 0. 818 cm to 0. 635 cm, saves 3700 Tons STEEL. Process Leaks-Losses. Production time loss. Equipment replacement costs. Saftey measures, Inventory for Replacements Maintainace costs SCALE & FOULING: • Reduced Heat tranfer, affecting • • • Day-to-Day Production. Flow blockages. 1/16” thick fouling reduces flow by 40 -50 % for half inch I. D. Frequent Stoppages of Plant; Loss of Production: (for POWER): Every 0. 1 mm scale = 4 % POWER LOSS. Promotes Pitting, Off oudors, Health Hazard. Production downtime, Quality and Quantity, Unscheduled maintainance costs. Hazards by Product Loss to air.
CORROSION CAUSES: A SUMMARY UNDERDEPOSIT Organic Ingress Anaerobic Conditions Poor Control NO 2, NH 3 Slime/Algae BIOLOGICAL Cracking Metallurgy Galvanic INADEQUATE INHIBITOR TYPE / CONC. Erratic Demand Poor Control Overfeed Organics NO 2, NH 3 CHLORINE LOW p. H Overfeed of ACID CHLORINE Contamination Poor Control HIGH p. H CORROSION Low Flow < 2 Ft/Sec. High Temp. High TSS/Fe Contamination Insufficent dispersant Blowdown control GENERAL
How Corrosion Affected By • Scale Under deposit Corrosion • Microbio Under deposit , S-producing bacteria, Fe deposit bacteria • Fouling Under deposit
How control the Corrosion • Use corrosion-resistant materials • Apply inert barriers/film • Use sacrificial anodes • Adjust water chemistry • Apply chemical Inhibitors
Deposition of Ca, Mg, Fe, Cu, Al Mud, Dirt, Ash, Coal Suspended Solids Salts With CO 3, PO 4, SO 4 Including Si. O 2, OH CORROSION INHIBITORS ITSELF! Organics REDUCED HEAT TRANSFER EFFECIENCY ENVIRONMENT FOR SRB GROWTH-PROMOTES PITTING.
RESULT: REDUCED HEAT CONDUCTIVITY SCALE DEPOSITS Steel Iron Oxide Calcium Phosphate Magnesium phosphate Silicious material Initiation THERMAL CONDUCTIVITY 44. 7 2. 9 2. 3 2. 2 0. 1 Agglomeration Build-up REDUCED HEAT TRANSFER EFFECIENCY INDUCED DIFERENTIAL AERATION CELLS ENVIRONMENT FOR SRB GROWTH
FOULING IN HEAT EXCHANGER COOLING WATER PROCESS FLUID FLOW HIGH INLET PARTIAL TUBE BLOCKING TEMPERATURE LOW FLOW SCALE FORMATION FOULING DESIGN WATER FLOW AIR POCKET PRODUCT PROBLEMS EXCHANGER INSTRUMENT PARTIAL TUBE BLOCKING DUE TO WOOD ETC. . . OIL / GREASE FOULING REFER DESIGN. HIGH INLET TEMP. AIR INGRESS / LEAK HEAVY TUBE BLOCKING FAULTY GUAGE VACUUM/TEMP. FOULING / PRODUCTION LOSS PROCESS SIDE AIR INGRESS HIGH PRESSURE ON CW SIDE OBSERVE BASIN FOR RESIDUES COMPARE AND OPERATE ACCORDINGLY IDENTIFY AND SEAL LEAK SCALE & FOULING TREATMENT
How Scale affected by • Corrosion Surface roughness, M-OH Particles Localized High Ph • Fouling Corrosion, nucleation site • Microbio Corrosion, Nucleation site
How to control scale • Limit the concentration of minerals • Acid Injection : Ph & Alkalinity • Mechanical changes Increase flow, Side stream filter etc • Chemical Inhibitors
WATER PROCESS Contamination Scrubbing Inadequate Design Process side issues Low Flow On-Off operation Extended piping Source cont. Excess turbidity Organic load Ammonia etc MACROBIAL Pretreatment Control measures Environmental Tidal effect Sudden change SYSTEM microbial Oil & Grease OTHERS
• No MATERIAL / COATING Available Which • • Can withstand MICROBIAL COLONISATION RATE OF MULTIPLICATION: ONCE EVERY 20 MINUTES.
Bio fouling Build-up Cooling Water ① ② ③ ④ Micro organism and surrounding sticky matter (Slime) Inorganic matter
MONITORING METHOD 1) Bacteria Count Test 103 104 Target Comparison Chart 105 106 107
COOLING WATER TREATMENT PROGRAMME EXPECTED RESULTS: SCALE FREE PLANT COST EFFECTIVE PROGRAMME: HIGH C. O. C. EASE OF OPERATION PRODUCT- QUALITY PERFORMANCE. Shree’Power EXPECTATIONS: MS < 3 - 5 MPY Cu-ALLOY < 0. 5 MPY CORROSION CONTROL EFFECTIVE BIOCONTROL: TVC < 3 * 105 / Ml SRB < 100 / 100 Ml
Ion Exchange. Treatment • • • Indion 5863 - Scale inhibitor Indion 5515 - corrosion inhibitor Indion 9079 - Bio Dispercent Indion 1611 – Biocide Sodium Hypochlorite –Biocide
Dosages
Design Data • Re-circulation rate- 975 m 3/hr • Hold up- 350 m 3 • Δ T - 100 C • Evaporation loss- 14. 66 m 3/hr • Design COC- 5 • Design Blow down ~ 39 m 3/day
Control Limits PARAMETERS p. H TDS Total Hardness Chlorides Turbidity Phosphate Total Iron VALUES 7. 2 -7. 5 3000 500 ppm 800 ppm 20 NTU 4 -8 ppm < 1 ppm Max.
CONCLUSION • NECESSITY OF TREATMENT: – Avoid scale, corrosion and biofouling – To run plant w/o interruption – save water • NEED • Scale, corrosion inhibitors • Biocides for biocontrol • Biodispersants to ease up on treatment • Acid if water is too hard
Safety in WTP • Use of Safety suit while handling the Chemicals (Body Protection) • Use of Safety Goggles (For Eye Protection) • Use of Gum Boots • Use of Breathing Apparatus ( To Save form hazardous gases like Cl 2, SO 2 etc.
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