72 Questions
EASY What is a primary reason for the deposition of solids in cooling towers?
The increased concentration of dissolved solids due to evaporation
What is the byproduct of the breakdown of calcium bicarbonate in cooling towers?
Calcium carbonate
What is a consequence of scaling in cooling towers?
Increased operating costs and risk of under-deposit corrosion
What is a common source of impurities in cooling water?
Raw make-up water
Corrosion in cooling systems can lead to what?
Equipment failure and loss of heat transfer efficiency
What is biological fouling?
Growth of microorganisms on surfaces
What increases the rate of calcium bicarbonate breakdown and scaling?
Rise in pH and temperature
What is a consequence of under-deposit corrosion?
Increased risk of equipment failure
What is the result of biological attack on cooling tower wood?
The cellulose deteriorates.
What is the recommended pH range for cooling tower water?
6 to 8
What is the maximum recommended limit of Total Dissolved Solids in cooling tower water?
< 2500 mg/L
Why is it important to control the growth of microorganisms in cooling towers?
To protect the environment and human health
What is the purpose of the guidelines published by the Canadian Council of Ministers of Environment?
To provide water quality guidelines for cooling towers
What is the visible result of the cooling tower operation?
A large white 'cloud' of water vapour
What is the primary cause of steel corrosion in cooling towers?
Dissolved oxygen in the cooling water
What happens to the rate of corrosion when the concentration of dissolved oxygen in the water increases?
It increases
What is the approximate concentration of dissolved oxygen in water at 20°C?
9.1 ppm
What is the effect of acidity on corrosion?
It promotes corrosion
What is the effect of temperature on corrosion rates?
Corrosion rates increase with increasing temperature up to 70°C
What is a common problem in cooling towers due to airborne dust and debris?
Plugging
What is biological fouling caused by in cooling towers?
Algae, fungi, and bacteria growth
What can biofilms do in cooling towers?
Reduce flow rates in tubes and channels
What is a critical biological growth that can appear in cooling towers?
Legionella bacteria
What causes wood deterioration in cooling towers?
Biological and chemical attack
MEDIUM What is the primary source of carbon for microorganism growth in cooling towers?
Cellulose deterioration
What is the recommended limit for manganese in cooling tower water?
< 0.5 mg/L
What is the purpose of keeping the pH of cooling tower water between 6 and 8?
To minimize corrosion
What is the consequence of not controlling microorganism growth in cooling towers?
Increased corrosion rates
What is the maximum recommended limit for total iron in cooling tower water?
< 0.5 mg/L
What is the visible result of the cooling tower operation?
A large cloud of water vapor
What is the primary reaction that occurs between steel and oxygen in cooling towers?
Rust formation through electrochemical reaction
At what temperature does the concentration of dissolved oxygen in water decrease significantly?
30°C
What is the effect of a neutral pH of 7.1 on steel corrosion?
It increases the corrosion rate
What is the primary source of plugging in cooling towers?
Airborne dust and debris
What is the effect of biofilms on heat exchanger efficiency?
It decreases the efficiency
What is the primary mode of transmission of Legionella?
Inhalation of contaminated water droplets
What is the primary component of wood that gives it strength?
Cellulose
What is the primary agent of delignification in wood?
All of the above
What is the effect of temperature on corrosion rates above 70°C?
It has relatively little effect on the corrosion rate
What is the primary reason why Legionella is a significant concern in cooling towers?
There is no vaccine for it
Why is scaling less severe in cooling towers compared to boilers?
Because the operating temperatures are much lower in cooling towers
What is the primary source of the impurities in cooling water that leads to deposition of solids?
Raw make-up water
What is the consequence of under-deposit corrosion in cooling towers?
Increased operating costs and plant downtime
What is the chemical reaction that leads to the deposition of solids in cooling towers?
Ca(HCO3)2 ⇌ CaCO3 + CO2 + H2O
What is the effect of an increase in pH and water temperature on the deposition of solids in cooling towers?
It increases the rate of scaling
What is the consequence of corrosion in cooling systems?
Loss of heat transfer efficiency and equipment failure
What is the primary source of impurities in cooling water that leads to biological fouling?
Microorganisms in the water
What is the consequence of plugging or erosion of equipment in cooling towers?
Increased operating costs and plant downtime
HARD What is the approximate concentration of dissolved oxygen in water at 30°C?
7.6 ppm
Which of the following is NOT a factor that enhances biological fouling in cooling towers?
Oxygen-poor environment
What is the primary component of wood that gives it strength?
Cellulose
What is the effect of acidity on corrosion rates in cooling towers?
Increases corrosion rates
Which of the following is a consequence of corrosion in cooling systems?
Equipment failure
What is the primary mode of transmission of Legionella?
Inhalation of contaminated mist
What is the primary agent of delignification in wood?
Oxidizing agents
What is the effect of biofilms on heat exchanger efficiency?
Reduces efficiency
What is the primary reason why Legionella is a significant concern in cooling towers?
It can cause serious lung infections
What is the consequence of plugging or erosion of equipment in cooling towers?
System failure
What is the primary reason why the Canadian Council of Ministers of Environment developed water quality guidelines for cooling towers?
To regulate the environmental impact of cooling towers on human health
What is the significance of the recommended pH range of 6 to 8 for cooling tower water?
It reduces the risk of corrosion
What is the primary consequence of not controlling the growth of microorganisms in cooling towers?
Biological fouling
What is the primary role of non-oxidizing biocides in controlling microorganism growth in cooling towers?
To prevent the growth of microorganisms
What is the primary source of carbon for the growth of microorganisms in cooling towers?
Cellulose from wood
What is the primary reason why the total dissolved solids limit is set at 2500 mg/L in cooling tower water?
To reduce the deposition of solids
What is the primary reason why the concentration of dissolved solids increases in cooling towers?
Water evaporates in the towers, leaving behind dissolved solids
What is the effect of an increase in both pH and water temperature on the rate of calcium bicarbonate breakdown?
It increases the rate of calcium bicarbonate breakdown
What is the primary consequence of corrosion in cooling systems?
It increases the operating costs and results in more plant downtime
What is the primary source of impurities in cooling water that leads to plugging or erosion of equipment?
All of the above
What is the primary consequence of biological fouling in cooling towers?
It leads to wood deterioration
What is the chemical reaction that leads to the deposition of solids in cooling towers?
Ca(HCO3)2 ⇌ CaCO3(scale deposit) + CO2(gas) release) + H2O
What is the primary reason why scaling is less severe in cooling towers compared to boilers?
The operating temperatures are much lower in cooling towers
What is the primary consequence of under-deposit corrosion in cooling towers?
It increases the operating costs and results in more plant downtime
Study Notes
Cooling Tower Impurities and Their Effects
- Impurities in cooling tower water can lead to increased operating costs and equipment failure.
- Sources of impurities include:
- Avian waste
- Contact with the atmosphere
- Raw make-up water
Deposition of Solids (Scaling)
- Water evaporation in cooling towers increases the concentration of dissolved solids, leading to deposition of solids (scaling) on condensers and evaporative surfaces.
- Scaling primarily results from dissolved calcium bicarbonate, which breaks down when heated.
- Factors influencing scaling include:
- Concentration of calcium and bicarbonate ions
- pH of the cooling water
- Water temperature
Corrosion
- Corrosion can cause:
- Equipment failure
- Loss of heat transfer efficiency
- Loss of structural integrity of concrete walls and basins
- Principal cause of steel corrosion is dissolved oxygen in the cooling water.
- Factors influencing corrosion include:
- Concentration of dissolved oxygen
- Acidity
- Temperature
Plugging or Erosion of Equipment
- Airborne dust and debris, dirt, sand, corrosion products, natural organics, and aluminum phosphates can enter the water and plug up the system.
- Plugging can lead to increased operating costs and equipment failure.
Biological Fouling
- Biological fouling occurs due to growth of algae, fungi, avian waste, and bacteria in recirculating cooling towers.
- Factors enhancing biological fouling include:
- Warm water
- Abundant sunlight
- Oxygen-rich environment
- Biological fouling can lead to:
- Reduced flow rates
- Corrosion of metals
- Destruction of wooden portions of the tower
Legionella and Waterborne Diseases
- Legionella bacteria can cause serious lung infections and flu-like infections.
- Legionella growth is enhanced in cooling towers and other human-made systems.
- Prevention is the only option, as there is no vaccine.
Wood Deterioration
- Wooden components in cooling towers are susceptible to biological and chemical attack, leading to deterioration.
- Chemical attack occurs mainly through delignification.
- Biological attack occurs through cellulose deterioration.
Water Quality Guidelines
- Guidelines for cooling tower water quality include:
- pH range of 6 to 8
- Total dissolved solids less than 2500 mg/L
- Limits for calcium, iron, manganese, copper, aluminum, sulfide, silica, and suspended solids.
Cooling Tower Impurities and Their Effects
- Impurities in cooling tower water can lead to increased operating costs and equipment failure.
- Sources of impurities include:
- Avian waste
- Contact with the atmosphere
- Raw make-up water
Deposition of Solids (Scaling)
- Water evaporation in cooling towers increases the concentration of dissolved solids, leading to deposition of solids (scaling) on condensers and evaporative surfaces.
- Scaling primarily results from dissolved calcium bicarbonate, which breaks down when heated.
- Factors influencing scaling include:
- Concentration of calcium and bicarbonate ions
- pH of the cooling water
- Water temperature
Corrosion
- Corrosion can cause:
- Equipment failure
- Loss of heat transfer efficiency
- Loss of structural integrity of concrete walls and basins
- Principal cause of steel corrosion is dissolved oxygen in the cooling water.
- Factors influencing corrosion include:
- Concentration of dissolved oxygen
- Acidity
- Temperature
Plugging or Erosion of Equipment
- Airborne dust and debris, dirt, sand, corrosion products, natural organics, and aluminum phosphates can enter the water and plug up the system.
- Plugging can lead to increased operating costs and equipment failure.
Biological Fouling
- Biological fouling occurs due to growth of algae, fungi, avian waste, and bacteria in recirculating cooling towers.
- Factors enhancing biological fouling include:
- Warm water
- Abundant sunlight
- Oxygen-rich environment
- Biological fouling can lead to:
- Reduced flow rates
- Corrosion of metals
- Destruction of wooden portions of the tower
Legionella and Waterborne Diseases
- Legionella bacteria can cause serious lung infections and flu-like infections.
- Legionella growth is enhanced in cooling towers and other human-made systems.
- Prevention is the only option, as there is no vaccine.
Wood Deterioration
- Wooden components in cooling towers are susceptible to biological and chemical attack, leading to deterioration.
- Chemical attack occurs mainly through delignification.
- Biological attack occurs through cellulose deterioration.
Water Quality Guidelines
- Guidelines for cooling tower water quality include:
- pH range of 6 to 8
- Total dissolved solids less than 2500 mg/L
- Limits for calcium, iron, manganese, copper, aluminum, sulfide, silica, and suspended solids.
Cooling Tower Impurities and Their Effects
- Impurities in cooling tower water can lead to increased operating costs and equipment failure.
- Sources of impurities include:
- Avian waste
- Contact with the atmosphere
- Raw make-up water
Deposition of Solids (Scaling)
- Water evaporation in cooling towers increases the concentration of dissolved solids, leading to deposition of solids (scaling) on condensers and evaporative surfaces.
- Scaling primarily results from dissolved calcium bicarbonate, which breaks down when heated.
- Factors influencing scaling include:
- Concentration of calcium and bicarbonate ions
- pH of the cooling water
- Water temperature
Corrosion
- Corrosion can cause:
- Equipment failure
- Loss of heat transfer efficiency
- Loss of structural integrity of concrete walls and basins
- Principal cause of steel corrosion is dissolved oxygen in the cooling water.
- Factors influencing corrosion include:
- Concentration of dissolved oxygen
- Acidity
- Temperature
Plugging or Erosion of Equipment
- Airborne dust and debris, dirt, sand, corrosion products, natural organics, and aluminum phosphates can enter the water and plug up the system.
- Plugging can lead to increased operating costs and equipment failure.
Biological Fouling
- Biological fouling occurs due to growth of algae, fungi, avian waste, and bacteria in recirculating cooling towers.
- Factors enhancing biological fouling include:
- Warm water
- Abundant sunlight
- Oxygen-rich environment
- Biological fouling can lead to:
- Reduced flow rates
- Corrosion of metals
- Destruction of wooden portions of the tower
Legionella and Waterborne Diseases
- Legionella bacteria can cause serious lung infections and flu-like infections.
- Legionella growth is enhanced in cooling towers and other human-made systems.
- Prevention is the only option, as there is no vaccine.
Wood Deterioration
- Wooden components in cooling towers are susceptible to biological and chemical attack, leading to deterioration.
- Chemical attack occurs mainly through delignification.
- Biological attack occurs through cellulose deterioration.
Water Quality Guidelines
- Guidelines for cooling tower water quality include:
- pH range of 6 to 8
- Total dissolved solids less than 2500 mg/L
- Limits for calcium, iron, manganese, copper, aluminum, sulfide, silica, and suspended solids.
This quiz covers the sources of impurities in cooling tower water, including avian waste, atmospheric contact, and raw make-up water, and the resulting problems of scaling, corrosion, and plugging.
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