Questions and Answers
Which of the following types of water is considered corrosive?
What is the main issue associated with cooling water systems?
Corrosion is a process that converts a refined metal into a more chemically stable form.
True
What is the estimated direct loss in the U.S. due to corrosion each year?
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Which corrosion control technique uses chemicals to protect metal surfaces?
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The process of forming hard, dense crystals from minerals in cooling water is known as _____.
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What are common scales found in cooling systems?
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___ are chemicals dosed to cooling waters to prevent scaling and deposition.
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Which mechanism is capable of preventing the precipitation of salts from a supersaturated solution?
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What does the Crystal Distortion Mechanism produce?
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What is the purpose of the Dispersion of Crystal Mechanism?
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What type of tests can the Veolia R&D team support in laboratory studies?
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What is biofouling primarily caused by?
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Match the type of fouling with its definition:
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What causes dense drift droplets to hit the eliminator walls?
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Louvers are made up of asbestos sheets.
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The ______ is the flow of cooling water being pumped through the entire plant cooling loop.
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What are the three factors affecting evaporation rate?
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What is the purpose of the blow down in cooling towers?
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What is windage in the context of cooling towers?
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The ______ temperature is the lowest temperature that can be reached by the evaporation of water under current ambient conditions.
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What does the Cycle of Concentration (COC) indicate?
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What is the formula for calculating Liquid Gas (L/G) ratio?
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Which of the following is a typical consequence of increased COC?
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What does the Langelier Saturation Index (LSI) indicate?
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Which of the following are types of cooling water systems? (Select all that apply)
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What is the purpose of a cooling tower?
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Closed recirculating cooling water systems allow air contact.
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What is a Chilled Water System used for?
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Which component is NOT part of a chilled water system?
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What are Drift Eliminators used for?
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What defines a Natural Draft Cooling Tower?
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What is the primary benefit of Closed Cooling Systems?
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1 ton of refrigeration (TR) is equivalent to ______ Btu/h.
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What type of cooling system is usually used in data centers?
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Mechanical Draft Cooling Towers do not use power-driven fans.
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Study Notes
Water Treatments in Cooling Systems
- Cooling systems utilize various types of water for cooling processes in chemical production, steel manufacturing, and other applications.
- Cooling water systems are categorized as:
- Open recirculating
- Closed recirculating
- Indirect cooling
- Once-through cooling
Cooling System Types
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Closed Cooling Systems:
- Circulate water in a closed loop, minimizing air exposure.
- Advantages include no water loss, constant water quality, and reduced corrosion and scaling.
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Open Cooling Systems:
- Use water that comes into direct contact with air.
- Features include significant water loss through evaporation, high salt concentration, and increased biofouling potential.
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Once-through Cooling Systems:
- Water is used once and discharged, commonly used in coastal installations due to their simplicity.
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Chilled Water Systems:
- Designed for large buildings to control air conditioning temperatures, using components like condensers, compressors, and cooling towers.
Cooling Towers
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Definition:
- A device that rejects waste heat through water cooling, employing either evaporative or dry cooling methods.
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Types of Cooling Towers:
- HVAC Cooling Towers: Remove unwanted heat from chillers, optimizing energy efficiency.
- Industrial Cooling Towers: Used for machinery heat removal in industries like power and petrochemicals.
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Heat Transfer Methods:
- Wet Cooling Towers: Rely on evaporation to cool the water.
- Dry Cooling Towers: Use air only for cooling, minimizing water usage.
- Closed Circuit Cooling Towers: Combine air and water systems for efficient heat transfer.
- Hybrid Cooling Towers: Switch between wet and dry operations.
Cooling Tower Components
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Key Components:
- Cold Water Basin
- Drift Eliminators: Prevent water loss by capturing water droplets from exhaust air.
- Spray Nozzles: Enhance heat transfer by dispersing water into droplets.
- Louvers: Control water retention and air distribution.
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Fills:
- Splash Type: Breaks water streams, increasing air contact.
- Film Type: Spreads water into thin films for improved heat exchange.
Thermal Energy and Measurements
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British Thermal Units (BTU):
- A measurement of heat, specifically the energy required to raise the temperature of one pound of water by one degree Fahrenheit.
- 1 ton of refrigeration is equivalent to 12,000 BTU per hour.
Environmental Considerations
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Thermal Pollution:
- The introduction of heated water into natural water bodies can disrupt local ecosystems and requires management strategies in cooling processes.
Mass Balance in Cooling Systems
- Essential parameters include:
- Make-up water (M), circulation rate (COC), temperature differential (ΔT), and evaporation rate (E).
- Understanding water and salt balances is crucial for optimizing cooling tower operations and maintaining system efficiency.### Mass Balance - Water & Salts
- Make-up water compensates for evaporation, blowdown, and windage losses.
Circulation Rate (CR)
- CR refers to the flow of cooling water in the entire cooling loop.
- Pumps arranged in series increase total head while maintaining flow rate.
- Pumps arranged in parallel increase flow rates with a common head.
Evaporation Rate (ER)
- ER is the volume of water evaporating for cooling.
- Influenced by surface area, ambient temperature, and air velocity.
- Formula: EC = evaporation constant (0.85%-1.0% of CR per 10°F).
Seasonal Impact on Evaporation
- Evaporation rates vary by season due to temperature differences:
- Summer: 90-100% efficiency
- Spring/Autumn: 70-80% efficiency
- Winter: 50-60% efficiency
Windage (W)
- Windage represents water evaporated as droplets carried by air from the cooling tower.
- Concentration of impurities in drift droplets is similar to incoming water.
- W varies by cooling tower type:
- Natural draft: 0.3%-1.0% of CR
- Induced draft: 0.1%-0.3% of CR
- With drift eliminators: 0.005%-0.0005% of CR
Cooling Tower Temperatures
- Key temperature terms in cooling towers:
- Range (ΔT): Difference between cooling water inlet and outlet temperatures.
- Dry-bulb temperature (DBT)
- Wet-bulb temperature (WBT)
- Approach temperature
- Performance metrics include cooling efficiency, effectiveness, cycle of concentration, and blowdown loss.
Wet Bulb Temperature (WBT)
- Indicates the lowest temperature air can achieve via evaporation of water.
- WBT is lower than DBT and equal at 100% relative humidity.
- Lower WBT translates to more effective evaporation, enhancing cooling performance.
Blow Down
- Blow down is the intentional discharge of concentrated water to maintain water quality in cooling systems.
Cycles of Concentration (COC)
- COC indicates the ratio of dissolved solids concentration in circulating water to make-up water.
- Can be calculated using total dissolved solids (TDS), conductivity, or other trace elements.
- A higher COC helps save water and chemicals and improves cooling efficiency.
Liquid Gas (L/G) Ratio
- The L/G ratio is the balance between water and air mass flow rates in cooling systems.
- Heat transfer is represented by the equation L(T1 - T2) = G(h2 - h1).
Parameters for Calculations
- Key parameters for calculating water consumption in cooling towers include make-up rate, blowdown rate, recirculation rate, differential temperature, evaporation rate, and windage.
Holding Time Index (HTI)
- HTI is the time required for a chemical's concentration to dilute to 50% of its original level in the cooling tower.
Langelier Saturation Index (LSI)
- LSI measures water's saturation concerning calcium carbonate.
- Influences corrosion and scaling tendencies in cooling systems.
- Calculated using pH values and factors such as calcium hardness and water alkalinity.### Water Types Comparison
- Brackish water: Available, stable quality, high scaling, corrosive, and limited coefficient of capital (COC).
- Potable water (Reverse Osmosis - RO): Available, stable quality, low corrosivity, high COC, and expensive.
- Treated Sewage Effluent (TSE): Not consistently available, variable quality, high cycles of concentration (COC), requires special treatments.
- Seawater: Not consistently available, stable quality, highly corrosive, and highly brackish.
Cooling Water Treatments and Importance
- Essential for the efficient operation and longevity of cooling tower equipment.
- Major concerns in cooling systems include microbial induced corrosion (MIC), under-deposit corrosion, and scaling.
Frequency of Water-Related Problems
- Corrosion: Significant issue across once-through, closed, and open cooling systems.
- Scale: Occurs in all system types, with increasing severity in open cooling systems.
- Bio-slime: Major concern in once-through and open cooling systems, less so in closed systems.
Common Issues in Cooling Systems
- General corrosion and under-deposit corrosion lead to shortened operation life of components.
- Reduced thermal efficiency results from scale and sludge accumulation.
- Increased energy consumption and pressure drop due to scale and sludge causing circulation issues.
- Leakage can occur from corrosion or under-deposit corrosion.
- Waste of water treatment chemicals due to corrosion products and sludge presence.
Understanding Corrosion
- Corrosion converts refined metals to more stable forms (e.g., oxides, hydroxides).
- Results in significant economic loss globally ($3 trillion in 2022).
- Direct losses in the U.S. estimated at over $300 billion annually.
Corrosion Mechanisms
- Involves oxidation (anode) and reduction (cathode) reactions within electrical circuits.
- Environment, temperature, and water chemistry significantly impact corrosion rates and types.
Factors Affecting Corrosion
- pH levels: A critical factor; varies by metal types.
- Temperature: Higher temperatures increase corrosion rates, roughly double for every 18°F increase.
- Water chemistry: Varies effects on corrosion.
- Water velocity: Complex mechanisms influence corrosion behavior.
- Metallurgy: Base factor impacting how materials respond to corrosion.
Corrosion Control
- Corrosion inhibitors: Chemicals like anodic and cathodic inhibitors are used to protect metals from corrosion.
- Dual corrosion inhibitors recommended for enhanced protection.
Monitoring Techniques
- Online corrosion monitoring systems provide rapid corrosion measurements.
- Corrosion coupons allow for cost-effective monitoring of system corrosivity.
Scaling in Cooling Systems
- Scaling occurs when dissolved minerals precipitate to form solid deposits, reducing efficiency and flow.
- Common scales found include calcium carbonate, calcium sulfate, magnesium silicate, and zinc carbonate.
Importance of Scale Control
- Prevents blockage of tubes and pipes that would impair heat transfer and increase flow resistance.
- Scale inhibitors used to maintain clear systems and prevent the formation of deposits.
Factors Influencing Scaling Tendency
- Water pH, total dissolved solids (TDS), temperature, and water alkalinity all play crucial roles in scaling potential.
- Scale inhibitors work through mechanisms like threshold inhibition to manage scaling effectively.
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Description
Test your knowledge on the various water treatments used in cooling systems. This quiz covers topics such as cooling towers, treatment principles, and issues like corrosion and scaling. Enhance your understanding of how Veolia contributes to efficient water management.
