144 Questions
EASY What happens to the hardness of water in a sodium zeolite system?
It becomes essentially nonexistent
What is the purpose of backwashing in a zeolite softener?
To remove entrained dirt and expand the bed
What is the purpose of brining in a zeolite softener?
To regenerate the zeolite
What is the concentration of sodium in the softened water?
105 - 108 ppm CaCO3
What happens when the hardness of the softened water rises to a set point?
The bed is considered depleted and must be regenerated
What is the purpose of a slow rinse in a zeolite softener?
To displace the brine solution
What is the concentration of calcium in the raw water?
66 ppm CaCO3
What is the purpose of a fast rinse in a zeolite softener?
To remove any remaining salt and minerals
What is the concentration of sodium in the raw water?
24 ppm CaCO3
What factors affect the capacity of a zeolite softener?
Quantity and type of exchange material, amount of dissolved minerals in the water, and regenerating solution
What is the primary concern for consumers when using hard water?
Poor lathering and white residue on faucets and dishware
Why do calcium and magnesium ions precipitate out of the solution as the water temperature increases?
Their solubility decreases with temperature
What is the primary purpose of removing calcium and magnesium ions from water?
To prevent the formation of scale and its consequences
Which of the following techniques is NOT used to soften water?
Clarifiers
What is the pH at which the reactions in Lime-Soda softeners occur?
11
What is the residual amount of hardness that remains after treatment?
50-85 mg/L as CaCO3
What is the product of the reaction between lime and impurities that cause carbonate hardness?
Calcium carbonate (CaCO3)
What are the two categories of lime-soda softeners?
Hot and cold
What is the purpose of adding soda ash to the water in Lime-Soda softeners?
To react with impurities that cause non-carbonate hardness
What happens to the calcium and magnesium ions after they react with lime and soda ash in Lime-Soda softeners?
They become suspended solids and can be removed
What is the typical temperature of the hot process in lime-soda softeners?
95-100°C
What is the purpose of the sludge blanket in lime-soda softeners?
To filter out suspended precipitate
What is the advantage of zeolite softeners compared to lime-soda softeners?
They require less capital costs
What is the purpose of ion-exchange systems in water softening?
To remove magnesium and calcium ions
What is the typical structure of zeolites?
Open cage-like structure
What is the result of the chemical reactions in zeolite softeners?
The formation of sodium bicarbonate and sodium sulfate
What is the advantage of zeolite softeners over lime-soda softeners in terms of hardness removal?
Zeolite softeners can bring the hardness down to zero
What is the typical lifespan of synthetic zeolites?
15-20 years
What is the purpose of the first unit in a demineralizer?
To exchange hydrogen ions for other cations
What is the result of the reactions in the cation exchanger?
Acidic solution
What is exchanged for hydroxide ions in the anion exchanger?
Anions
What is the typical conductivity reading of the water after treatment?
Lower than 15 μS/cm
How are the ion exchangers regenerated?
By passing a diluted solution of sulfuric acid through the bed
What is the purpose of reverse osmosis?
To remove dissolved solids and organic matter from water
What is the principle behind reverse osmosis?
A pressure is applied to the side with the impurities, allowing water to pass through a membrane
What is the typical total dissolved solids of sea water?
Around 38,000 mg/L
What is the purpose of a demineralizer?
To remove ions and other minerals from water
What materials are used to build demineralizers?
Corrosion-resistant materials
What happens to the brine during the fast rinse step?
It is completely removed from the zeolite bed
What indicates the completion of the regeneration process?
The hardness in the discharge stream drops to 1 ppm
What is the purpose of the multi-ported valve in a softener?
To control the operation of the softener
What is a common cause of incomplete softening?
Improper flow rates during operation
What is the recommended solution for a fouled exchange material?
Pre-treat the hard water influent to remove impurities
What is the function of the cation exchanger in a demineralizer?
To remove cations from the water
What is the approximate percentage of zeolite resin lost per year due to attrition?
3%
What is the purpose of the ejector in a demineralizer?
To supply pressure to the system
What is the recommended frequency for inspecting and maintaining a softener?
Established schedule
What is the purpose of the spent brine?
To be discharged to the sewer
Why do operators consider hard water a problem?
Because it can cause scale buildup in boiler systems.
What is the purpose of adding lime and soda ash to the water in Lime-Soda softeners?
To react with impurities that cause hardness.
MEDIUM What happens to calcium and magnesium ions as the water temperature increases?
Their solubility decreases.
What is the typical result of not removing calcium and magnesium ions from water?
Scale builds up in high heat areas.
What happens to the calcium and magnesium ions after they react with lime and soda ash in Lime-Soda softeners?
They are removed from the water.
What is the purpose of softening water?
To remove calcium and magnesium ions from the water.
What is the main difference between Lime-Soda softeners and Zeolite softeners?
The type of ion exchange material used.
Why do calcium and magnesium ions need to be removed from water before it enters a boiler system?
Because they can form scale in high heat areas.
What happens to the sodium concentration in the softened water compared to the raw water?
It increases dramatically
What is the purpose of the gravel or anthracite at the bottom of the zeolite softener?
To support the zeolite material
What is the purpose of the slow rinse step in the regeneration process?
To remove the remaining brine solution
What happens to the calcium and magnesium ions during the brining step?
They are removed and replaced with sodium
What is the result of the backwashing step?
The zeolite material is expanded
What is the purpose of the computer screen control system in the zeolite softener?
To control the regeneration process
What is the typical concentration of calcium in the softened water?
0 - 1.5 ppm
What is the purpose of the fast rinse step in the regeneration process?
To remove the remaining brine solution
What happens to the zeolite material when it reaches its capacity?
It is regenerated with brine solution
What is the purpose of the service inlet valve in the zeolite softener?
To allow hard water to enter the softener
What is the primary difference between hot and cold lime-soda softeners?
Temperature
What is the purpose of recycling sludge in a hot process lime-soda softener?
To aid in precipitation
What is the advantage of zeolite softeners over lime-soda softeners?
All of the above
What is the typical temperature of the hot process in lime-soda softeners?
95-100°C
What is the function of the sludge blanket in lime-soda softeners?
To filter out suspended solids
What is the result of the chemical reactions in zeolite softeners?
Calcium and magnesium ions are removed
What is the typical structure of zeolites?
Open cage-like structure
What is the advantage of zeolite softeners in terms of hardness removal?
Can bring hardness down to zero
What is the typical lifespan of synthetic zeolites?
20 years
What is the purpose of ion-exchange systems in water softening?
To remove hardness-causing ions
What happens to the brine during the fast rinse step?
It is flushed to the sewer
What is the purpose of the slow rinse in a zeolite softener?
To create a slow moving plug of water that forces the remaining brine into areas it may not have penetrated earlier
What is the indication that the regeneration process is complete?
When the hardness in the discharge stream during the fast rinse drops to 1 ppm
What is the purpose of the multi-ported valve in a softener?
To control the various operations of the softener
What is a common cause of incomplete softening?
All of the above
What is the recommended solution for a fouled exchange material?
Pre-treat the hard water influent to remove impurities
What is the approximate percentage of zeolite resin lost per year due to attrition?
3%
What is the function of the cation exchanger in a demineralizer?
To remove cations from the water
What is the purpose of the ejector in a demineralizer?
To create a vacuum to draw water through the system
What is the recommended frequency for inspecting and maintaining a softener?
Establish an inspection and maintenance schedule
What is the primary function of the hydrogen zeolite cation exchanger in a demineralizer?
To exchange cations for hydrogen ions
What is the resulting effluent of the cation exchanger in a demineralizer?
An acidic solution
What is the purpose of the anion exchanger in a demineralizer?
To exchange anions for hydroxide ions
What is the typical conductivity reading of the water after treatment in a demineralizer?
Less than 15 μS/cm
How are the ion exchangers in a demineralizer regenerated?
With a diluted solution of sulfuric acid and a diluted solution of caustic soda
What is the primary purpose of reverse osmosis?
To remove dissolved solids from water
What is the typical total dissolved solids of seawater?
38 000 mg/L
What is the principle behind reverse osmosis?
A membrane allows water molecules to pass through, but not impurities
What is the advantage of demineralizers over other water treatment methods?
They can remove up to 99% of dissolved solids
What materials are used to build demineralizers?
Corrosion-resistant materials
What is the primary effect of hard water on boiler operations?
Formation of scale in high heat areas
What is the main difference between lime-soda softeners and zeolite softeners?
Lime-soda softeners use chemical precipitation, whereas zeolite softeners use ion exchange
What is the purpose of soda ash in Lime-Soda softeners?
To react with impurities that cause non-carbonate hardness
HARD What happens to the solubility of calcium and magnesium ions as the water temperature increases?
It decreases
What is the common problem faced by consumers when using hard water?
Difficulty in lathering soap
What is the primary purpose of removing calcium and magnesium ions from water?
To prevent scale formation in boilers
What is the result of the chemical reactions in Lime-Soda softeners?
Formation of suspended solids
Why do operators consider hard water a problem?
Because it causes scaling in boilers
What is the primary mechanism by which zeolite softeners remove hardness from water?
Ion exchange
What is the benefit of hot process lime-soda softening over cold process?
All of the above
What is the purpose of the sludge blanket in lime-soda softeners?
To filter out suspended solids
What is the typical residual amount of hardness in water after lime-soda softening?
50 - 85 mg/L
What is the advantage of zeolite softeners over lime-soda softeners?
All of the above
What is the typical structure of zeolites?
Open cage-like
What is the result of the chemical reactions in zeolite softeners?
All of the above
What is the typical lifespan of synthetic zeolites?
Up to 20 years
What is the purpose of the recirculation pump in lime-soda softeners?
To recycle part of the sludge to the top of the unit
What is the advantage of hot process lime-soda softening over zeolite softening?
None of the above
What is the primary cause of incomplete softening in a zeolite softener?
Improper flow rates during operation
What is the purpose of the anion exchanger in a demineralizer?
To remove anions from the water
What is the typical concentration of chlorides in spent brine?
40 000 mg/L
What is the purpose of the multi-ported valve in a softener?
To control the various operations of the softener
What is the approximate percentage of zeolite resin lost per year due to attrition?
3% per year
What is the purpose of the ejector in a demineralizer?
To mix the regenerant solutions
What is the recommended solution for a fouled exchange material?
Pre-treat the influent water
What indicates the completion of the regeneration process?
The hardness in the discharge stream drops to 1 ppm
What is the purpose of the cation exchanger in a demineralizer?
To remove cations from the water
What is the purpose of the slow rinse in a zeolite softener?
To remove the remaining brine from the zeolite bed
What is the primary reason for the regeneration of a zeolite softener?
To restore the capacity of the softener
During brining, what is the primary function of the sodium chloride?
To replace calcium and magnesium ions with sodium ions
What is the primary advantage of using a zeolite softener in parallel?
To ensure soft makeup water is always available
What is the primary consequence of not backwashing the zeolite bed?
Compaction of the zeolite bed
What is the primary function of the slow rinse step during regeneration?
To displace the brine from the softener
What is the primary factor that affects the amount of salt required for regeneration?
Type of zeolite material used
What is the primary consequence of not controlling the backwash flow rate?
Carrying out of zeolite resin with the backwash effluent
During operation, what happens to the zeolite bed due to the force of the flowing water?
It gets compacted
What is the primary function of the computer screen in Figure 8(b)?
To control the softener operation
What is the primary reason for the use of a bed of gravel or anthracite in a zeolite softener?
To support the zeolite material
What is the primary function of the cation exchanger in the first unit of a demineralizer?
To exchange cations with hydrogen ions
What is the purpose of the anion exchanger in a demineralizer?
To exchange anions with hydroxide ions
What is the typical conductivity reading of the water after treatment in a demineralizer?
Lower than 15 μS/cm
What is the purpose of regenerating the ion exchangers in a demineralizer?
To recharge the ion exchangers with hydrogen and hydroxide ions
What is the primary mechanism behind reverse osmosis?
Applying pressure to force water molecules through a membrane
What is the typical total dissolved solids of sea water?
38 000 mg/L
What is the purpose of the waste from the regeneration process in a demineralizer?
To dispose of impurities collected during operation
What is the advantage of demineralizers compared to other water treatment methods?
They can handle changes in influent water quality
What is the purpose of building demineralizers with corrosion-resistant materials?
To protect the demineralizer from acidic and basic regeneration solutions
What is the primary advantage of reverse osmosis compared to other water treatment methods?
It can desalinate sea water
Study Notes
Hard Water and Its Effects
- Hard water is water that contains high levels of calcium and magnesium ions, typically above 120 ppm (parts per million) or 120 mg/L (milligrams per liter).
- Hard water is usually found in groundwater sources.
- Hard water can cause problems for consumers, including:
- Difficulty lathering soap and shampoo
- Leaving white residue on faucets and dishware
- For boiler operators, hard water can cause more severe problems, including:
- Scale formation, which can lead to under-deposit corrosion and local metal failure
- Decreased heat transfer efficiency
Methods of Water Softening
- Four common methods of water softening:
- Lime-soda softening
- Sodium zeolite softening
- Demineralization
- Reverse osmosis
Lime-Soda Softening
- Uses chemical precipitation to remove calcium and magnesium ions
- Lime (calcium hydroxide) and soda ash (sodium carbonate) are added to the water
- The lime reacts with impurities that cause carbonate hardness, forming insoluble calcium carbonate
- The soda ash reacts with impurities that cause non-carbonate hardness, forming magnesium hydroxide
- The resulting solids are removed through clarification, flocculation, or filtration
- Two types of lime-soda softeners:
- Hot process (95-100°C)
- Cold process (25-30°C)
Sodium Zeolite Softening
- Uses ion exchange to remove calcium and magnesium ions
- Zeolite material is used to exchange sodium ions for calcium and magnesium ions
- The zeolite material is regenerated with a brine solution to remove the trapped calcium and magnesium ions
- Can remove up to 99% of hardness-causing ions
- Typical performance:
- Calcium: 0-1.5 ppm
- Magnesium: 0-1.5 ppm
- Total hardness: 0-3 ppm
- Sodium: 105-108 ppm
Demineralization
- Uses ion exchange to remove most ions, including calcium and magnesium
- Two exchange units are used in series: a cation exchanger and an anion exchanger
- Cation exchanger replaces calcium, magnesium, and sodium ions with hydrogen ions
- Anion exchanger replaces anions of acids with hydroxide ions
- Can remove up to 99% of dissolved solids, organic matter, and colloidal matter
- Typically used for desalination of seawater
Reverse Osmosis
- Uses membrane technology to remove up to 99% of dissolved solids, organic matter, and colloidal matter
- Based on the principle of osmosis, where a membrane separates two fluids and allows water molecules to pass through, but not impurities
- Pressure is applied to the side with the impurities to create pure water, while concentrating the impurities
- Typically used for desalination of seawater
Hard Water and Its Effects
- Hard water is water that contains high levels of calcium and magnesium ions, typically above 120 ppm (parts per million) or 120 mg/L (milligrams per liter).
- Hard water is usually found in groundwater sources.
- Hard water can cause problems for consumers, including:
- Difficulty lathering soap and shampoo
- Leaving white residue on faucets and dishware
- For boiler operators, hard water can cause more severe problems, including:
- Scale formation, which can lead to under-deposit corrosion and local metal failure
- Decreased heat transfer efficiency
Methods of Water Softening
- Four common methods of water softening:
- Lime-soda softening
- Sodium zeolite softening
- Demineralization
- Reverse osmosis
Lime-Soda Softening
- Uses chemical precipitation to remove calcium and magnesium ions
- Lime (calcium hydroxide) and soda ash (sodium carbonate) are added to the water
- The lime reacts with impurities that cause carbonate hardness, forming insoluble calcium carbonate
- The soda ash reacts with impurities that cause non-carbonate hardness, forming magnesium hydroxide
- The resulting solids are removed through clarification, flocculation, or filtration
- Two types of lime-soda softeners:
- Hot process (95-100°C)
- Cold process (25-30°C)
Sodium Zeolite Softening
- Uses ion exchange to remove calcium and magnesium ions
- Zeolite material is used to exchange sodium ions for calcium and magnesium ions
- The zeolite material is regenerated with a brine solution to remove the trapped calcium and magnesium ions
- Can remove up to 99% of hardness-causing ions
- Typical performance:
- Calcium: 0-1.5 ppm
- Magnesium: 0-1.5 ppm
- Total hardness: 0-3 ppm
- Sodium: 105-108 ppm
Demineralization
- Uses ion exchange to remove most ions, including calcium and magnesium
- Two exchange units are used in series: a cation exchanger and an anion exchanger
- Cation exchanger replaces calcium, magnesium, and sodium ions with hydrogen ions
- Anion exchanger replaces anions of acids with hydroxide ions
- Can remove up to 99% of dissolved solids, organic matter, and colloidal matter
- Typically used for desalination of seawater
Reverse Osmosis
- Uses membrane technology to remove up to 99% of dissolved solids, organic matter, and colloidal matter
- Based on the principle of osmosis, where a membrane separates two fluids and allows water molecules to pass through, but not impurities
- Pressure is applied to the side with the impurities to create pure water, while concentrating the impurities
- Typically used for desalination of seawater
Hard Water and Its Effects
- Hard water is water that contains high levels of calcium and magnesium ions, typically above 120 ppm (parts per million) or 120 mg/L (milligrams per liter).
- Hard water is usually found in groundwater sources.
- Hard water can cause problems for consumers, including:
- Difficulty lathering soap and shampoo
- Leaving white residue on faucets and dishware
- For boiler operators, hard water can cause more severe problems, including:
- Scale formation, which can lead to under-deposit corrosion and local metal failure
- Decreased heat transfer efficiency
Methods of Water Softening
- Four common methods of water softening:
- Lime-soda softening
- Sodium zeolite softening
- Demineralization
- Reverse osmosis
Lime-Soda Softening
- Uses chemical precipitation to remove calcium and magnesium ions
- Lime (calcium hydroxide) and soda ash (sodium carbonate) are added to the water
- The lime reacts with impurities that cause carbonate hardness, forming insoluble calcium carbonate
- The soda ash reacts with impurities that cause non-carbonate hardness, forming magnesium hydroxide
- The resulting solids are removed through clarification, flocculation, or filtration
- Two types of lime-soda softeners:
- Hot process (95-100°C)
- Cold process (25-30°C)
Sodium Zeolite Softening
- Uses ion exchange to remove calcium and magnesium ions
- Zeolite material is used to exchange sodium ions for calcium and magnesium ions
- The zeolite material is regenerated with a brine solution to remove the trapped calcium and magnesium ions
- Can remove up to 99% of hardness-causing ions
- Typical performance:
- Calcium: 0-1.5 ppm
- Magnesium: 0-1.5 ppm
- Total hardness: 0-3 ppm
- Sodium: 105-108 ppm
Demineralization
- Uses ion exchange to remove most ions, including calcium and magnesium
- Two exchange units are used in series: a cation exchanger and an anion exchanger
- Cation exchanger replaces calcium, magnesium, and sodium ions with hydrogen ions
- Anion exchanger replaces anions of acids with hydroxide ions
- Can remove up to 99% of dissolved solids, organic matter, and colloidal matter
- Typically used for desalination of seawater
Reverse Osmosis
- Uses membrane technology to remove up to 99% of dissolved solids, organic matter, and colloidal matter
- Based on the principle of osmosis, where a membrane separates two fluids and allows water molecules to pass through, but not impurities
- Pressure is applied to the side with the impurities to create pure water, while concentrating the impurities
- Typically used for desalination of seawater
Learn about hard water, its causes, effects on daily life, and severe problems it can cause for boiler operators. Understand the issues with soap lathering, residue, and scale formation.
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