Water Softeners – Answers to the Top 25 Asked Questions:

We’ve listed the top 25 asked questions about water softeners with answers below. You can also get more water softener facts, reviews & comparisons by clicking this link.

Be sure to also check out our salt and salt free Water Softener Sale going on right now!

The Top 25 Questions & Answers:

How does a Water Softener work?

Will a Water Softener make my water safe to drink?

Why does soft water feel slimy or slick in the shower?

When do the resins in the softener tank need to be changed?

I see ads for “No Salt” needed water conditioners.

How do they work without using salt?

How often do I need to add salt to the Brine Tank?

How much salt should my softener use?

What kind of salt do you recommend using and do your softeners also use Potassium Chloride in place of salt?

My valve appears to be operating but the salt is not going down. What could cause this problem?

I have a working Water Softener, but I am still getting Iron Staining. Why is that?

I have a Water Softener, but I still have odor in my water. Why is that?

I have very hard water and high Iron. What kind of softener do I need?

How Can I find out what is in my water…or where can I have My Water Tested?

How can I determine what kind of unit, and what size I will need?

How can I tell what my flow rate is?

What kinds of Iron could be in my water?

Can the softener cause pressure loss, if so what do I look for, and what do I need to fix it?

What is a water softener?

What is Hydrogen Sulfide?

What is hard water?

What is meant by scaling or fouling?

What is ion exchange?

What is a Backwashing Filter?

1. How does a Water Softener work?Basically, the resin or mineral inside the mineral tank is specially designed to remove “hard” particles of lime and calcium, by a simple ion exchange process. The resin beads inside the softener tank have a different or opposite electrical charge than the dissolved particles of the incoming water. Because of this electrical charge difference, the dissolved particles suspended in your water will cling to the resin beads on contact, thereby ridding the water of these particles, causing the water exiting the unit to be “soft”. The resin has a limit to how much of these hardness particles it can hold, which is why there are many different sizes of softeners and also why regeneration or brining is required.

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2. Will a Water Softener make my water safe to drink? No. Your water must be safe to drink before you condition the water with a softener. If you are concerned about the safety of your drinking water, contact your local health department about getting a bacteria test, or full lab analysis on your water.

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3. Why does soft water feel slimy or slick in the shower?The minerals that make water hard usually contain calcium and magnesium. Calcium and magnesium in water interfere with the cleaning action of soap and detergent. They do this by combining with soap or detergent and forming a scum that does not dissolve in water. Because these minerals react with soap and detergent, they remove the soap and detergent, thereby reducing the effectiveness of these cleaning agents. You can overcome this by adding more soap or detergent. However, the scum that is formed can adhere to what is being washed, making it appear dingy. An automatic water softener connected to water supply pipes removes magnesium and calcium from water and replaces them with a trace amount of sodium. Sodium does not react with soap or detergents. This will reduce the amount of soap you would need to use, and insures it will not remain in or on the item being washed, whether the item is tile, glassware, clothes, skin or hair.

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4. When do the resins in the softener tank need to be changed?

With the proper pretreatment and maintenance, the average water softener will not need its resins replaced in its lifetime (20 + years). It is impossible to accurately determine the life of resin since so many factors contribute to the degradation of the resin itself. Note: Proper pretreatment can be a simple as a sediment filter or as complex as chemical injection system combined with a multimedia bed, this is determined by having your water tested.

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5. I see ads for “No Salt” needed water conditioners. How do they work without using salt?

There are 2 immediate answers you need to know:

1. Many dealers will advertise a no salt water conditioner in a misleading way. Any brand of water conditioner can be operated without using salt. This is done by using a salt substitute, potassium chloride. It is generally more expensive compared to regular salt (sodium chloride), and can be difficult to find in some areas. Also, it is generally recommended you increase the salt setting on your control valve by about 10%, when using a salt substitute. This is usaully not the method being referred to as a “No Salt” water softener today, but be sure!

2. NEW TECHNOLOGY SALT FREE WATER SOFTENERS are a recent and reliable alternative that make perfect sense in most applications. There are multiple methods (many products & claims are hype & a waste of money) however, the only reliable one is a process called template assisted crystallization (TAC).

TAC is a process in which calcium ions in the water are converted to calcium crystals. These crystals now lose any binding, or scaling ability and are washed down the drain w/ the rest of the water. Any residential, industrial, or commercial setting will benefit substantially with one of these systems.

They stop scale build up in the water system and appliances. These systems also eliminate any salt costs and save a considerable amount of space. Additionally, they do not require a control valve and because of this there is no wasted backwash water, and there is very little maintenance.

We specialize in this new technology. Be sure to check our water softener sale page for more info.

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6. How often do I need to add salt to the Brine Tank?

It depends on how often your system needs to regenerate. The more your softener regenerates the more salt you will consume. As for the salt level in the brine tank, you can let the salt get down to the point inside the tank where you can see the water just above the salt. When you see water above the salt, it is time to add more! Generally, you will add salt to your brine tank about every 8 weeks.

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7. How much salt should my softener use?

1. An average softener with 1 cu. ft. of resins (30,000 grain, 10 ” x 44 ” tank) should use about 6-8 lbs. per regeneration to achieve an economical 24,000 grain capacity (hardness in grains divided into grains of capacity results in the gallons of water that can be treated before resins is exhausted).

2. We sell only metered valves with our Watts brand softener packages, since they tend to use less salt than a non-metered unit (i.e. one set to regenerate every so many days with no regards for actual water used).

3. The national average is 60 lbs. per month, but that can vary depending upon the quantity and the quality of water being treated.

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8. What kind of salt do you recommend using and do your softeners also use Potassium Chloride in place of salt?

We recommend buying salt for your water softener that is very clean; around the 99.5% salt content and up. All softeners can use Potassium Chloride in place of salt. Potassium Chloride tends to melt when it gets wet, sometimes forming a “bridge” inside the salt tank, so we recommend filling the Brine tank only halfway or a bit more when using Potassium Chloride, so you can easily monitor it going down inside the tank after the unit regenerates.

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9. My valve appears to be operating but the salt is not going down. What could cause this problem?

The salt not going down could be due to many different reasons.

1. Valve is not regenerating due to a mechanical problem.

2. Salt may be bridged (become solid) above water that is at the bottom of the salt tank.

3. If you have been using pellet salt for many years you could have a lot of undissolved residue at the bottom. This residue will not dissolve and also can block water flow in and out of the salt tank.

4. The valve could be failing to draw the brine solution out and if you have a float shut off in the brine tank, it would be prevent the salt tank from overflowing (which it would do if the float shut off was not there).

5. The brine refill control could be clogged, prevent water to refill the salt tank.

(Note: It is highly recommended that you contact an experienced water quality specialist to trouble shoot any problem with your equipment.)

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10. I have a working Water Softener, but I am still getting Iron Staining. Why is that?

There are several things that could cause you to still be getting staining.

1. It is critical that your system never run empty of salt.

2. It is important that the time of day be kept correct and that no one uses water between 2 a.m. – 3 a.m. when the system is regenerating. While the system is in regeneration, any water used would be unconditioned (coming straight from the well).

3. It could be your resin tank is too small to handle all the iron.

A. What size is the resin tank?

B. What is the level of Iron and Hardness of the water?

4. It could be you are not regenerating often enough, or using enough salt per regeneration.

A. How often does your softener regenerate?

B. How many people are using the water? C. How much salt are you using per month?

5. It could be that your iron content exceeds the recommended maximum. (1 cu.ft. of resin can effectively remove up to 3 parts per million iron with out additional treatment.)

6. On rare occasions the iron could be coming from just the hot water tank. If it is more than 20 years old it could be rusting out on the inside, thus putting iron back into the water. This is also true in older homes, again over 20 years old, that used galvanized plumbing.

Above are the common reasons a working water softener might still be allowing you to get staining. For additional help and recommendations, call or contact an experienced water quality specialist.

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11. I have a Water Softener, but I still have odor in my water. Why is that?

Water softeners do not remove most taste and odor problems (although they can remove the metallic taste of iron in water).

1. Odors are typically caused by hydrogen sulfide (“rotten egg smell”) in wells or “bleach” smell in chlorine treated water; both of these causes can be resolved using an activated carbon filter in conjunction with a water softener.

2. The self-sacrificing rod installed in your hot water heater can sometimes be the cause of your odor in the hot water. Having a qualified plumber replace this rod could solve this problem.

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12. I have very hard water and high Iron. What kind of softener do I need?

To offer a proper and accurate recommendation for any system(s) needed to correct your water problems, we need current and accurate water test results. Public water suppliers have the information available to you by simply calling them and requesting to know the level of Hardness, Iron and pH of your water. If you have a private well, simply obtain a water test kit from a local hardware store, of you can purchase one of our test kits through a qualified water quality specialist.

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13. How Can I find out what is in my water…or where can I have My Water Tested?

If you have public water, simply contact the office where you pay your water bill. They should have current water testing records on file. If you are on a private water system, then contact your county health department to see about having your water tested, or you can buy a Home Water Test kit available from us at this link! Your water test results should show levels of hardness, Iron (what type of Iron you have), pH, Hydrogen Sulfide (for rotten egg odor), Nitrates and Total Dissolved Solids (TDS).

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14. How can I determine what kind of unit, and what size I will need?

Filter systems are sized based on a couple of factors: (1) type and amount of dissolved mineral present in your water; (2) your home’s flow rate, which is typically based on the number of people present in the home. For filter systems, this information simply tells us what the fastest rate your water will travel through our units would be, and how much water in gallons per day is being used. Water softeners are sized based on the total hardness of your water, and the number of people in the home. Most all-residential applications have around an average 5 GPM flow rate. Typically, the higher the flow rate of your water going through the unit, the larger the mineral tank will be to handle the larger water flow rate. With a larger tank, the filtering media or resin will be physically deeper thereby permitting the water flowing down through it to be in contact with the media longer. Contact time is important, as the media/resin inside the tank needs to be in contact with your water for a long enough period of time, ensuring all dissolved impurities are removed before it leaves the tank.

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15. How can I tell what my flow rate is?

You can get a fairly close idea of your water flow rate by simply running water at full open position through either an outside garden hose faucet or with your bathtub faucet. Example: Turn the faucet on to the full open position… then quickly put the gallon container under the full flow of water. Immediately start timing how many seconds it takes to fill the container all the way up. If it fills the container up in 15 seconds, you simply divide 60 seconds (1 minute)…by 15 seconds (the amount of time it took to fill the container up). The answer is 4, so your flow rate would be very close to 4 GPM! We recommend that you order a unit that would handle at least 4 GPM. It would be over size the unit to ensure you are getting a unit with plenty of GPM flow capacity.

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16. What kinds of Iron could be in my water?

There are basically four types of iron found in water, they are:

* Oxidized Iron contains red particles easily visible as the water is drawn from the faucet.

* Soluble or “Clear Water Iron” is very common, and will develop red particles in the water after water is drawn from the faucet, and is exposed to the air for a period of time. The iron particles actually “rust” once they are exposed to air.

* Colloidal Iron consists of extremely small particles of oxidized iron particles suspended in water. This type iron looks more like cloudy, colored water, instead of being able to actually see small red particles of iron. This type iron will not filter well because of the extremely small particle size. (Chlorination may be required).

* Bacterial Iron consists of living organisms found in the water and piping of the well and house. You can tell if you have Bacterial Iron by looking in your toilet flush tank, and finding a reddish/green slime buildup. To confirm this, you should take a sample of this slime to your local health department for testing. This kind of iron is the hardest to get rid of. To completely eliminate this form of bacterial iron requires chlorination of the entire water system, starting with the well casing, well pump, pressure tank and the home plumbing system. (Chlorination may be required).

* Hydrogen Sulfide causes water to have a pungent “rotten egg” odor, and is easily removed using a Manganese Greensand filer.

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17. Can the softener cause pressure loss, if so what do I look for, and what do I need to fix it?

Yes, a softener will cause some pressure loss due to the resistance from the resin bed, but excessive pressure loss can be caused by one or a combination of the following.

1. On well water, this is usually due to fine sand coming from the well.

2. On softeners installed in the open sunlight (mostly in Florida), a layer of algae can grow and thick pieces of this growth clog the lower distributor tube screen when they start peeling off the inside of the resin tank.

3. On chlorinated water supplies, sand can get into the tank from new construction or work on water lines in the area. All of these situations are rare.

4. The most common cause of pressure loss occurs on chlorinated water. The resin can be damaged by high chlorine levels and turn to mush. This has the same effect as having fine sand at the bottom of the resin tank.

The solution for all of the above problems is to dump the resin tank, clean and rebed with new resins. One cubic foot of softening resins is enough to properly fill the average residential softener. We can calculate the amount for you, if you provide exact resin tank dimensions.

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18. What is a water softener?

A water softener reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion concentration in hard water.

These “hardness ions” cause three major kinds of undesired effects. Most visibly, metal ions react with soaps and calcium-sensitive detergents, hindering their ability to lather and forming a precipitate—the familiar “bathtub ring”. Presence of “hardness ions” also inhibits the cleaning effect of detergent formulations. Second, calcium and magnesium carbonates tend to precipitate out as hard deposits to the surfaces of pipes and heat exchanger surfaces. This is principally caused by thermal decomposition of bi-carbonate ions but also happens to some extent even in the absence of such ions. The resulting build-up of scale can restrict water flow in pipes. In boilers, the deposits act as an insulation that impairs the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this can lead to failure of the boiler.[1] Third, the presence of ions in an electrolyte, in this case, hard water, can also lead to galvanic corrosion, in which one metal will preferentially corrode when in contact with another type of metal, when both are in contact with an electrolyte. However the sodium (or Potassium) ions released during conventional water softening are much more electrolytically active than the Calcium or Magnesium ions that they replace and galvanic corrosion would be expected to be substantially increased by water softening and not decreased. Similarly if any lead plumbing is in use, softened water is likely to be substantially more plumbo-solvent than hard water.

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20. Can the softener cause pressure loss, if so what do I look for, and what do I need to fix it?

Yes, a softener will cause some pressure loss due to the resistance from the resin bed, but excessive pressure loss can be caused by one or a combination of the following.

1. On well water, this is usually due to fine sand coming from the well.

2. On softeners installed in the open sunlight (mostly in Florida), a layer of algae can grow and thick pieces of this growth clog the lower distributor tube screen when they start peeling off the inside of the resin tank.

3. On chlorinated water supplies, sand can get into the tank from new construction or work on water lines in the area. All of these situations are rare.

4. The most common cause of pressure loss occurs on chlorinated water. The resin can be damaged by high chlorine levels and turn to mush. This has the same effect as having fine sand at the bottom of the resin tank.

The solution for all of the above problems is to dump the resin tank, clean and rebed with new resins. One cubic foot of softening resins is enough to properly fill the average residential softener. We can calculate the amount for you, if you provide exact resin tank dimensions.

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21. What is Hydrogen Sulfide?

Hydrogen sulfide (or hydrogen sulphide) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence.

It often results from the bacterial break down of sulfates in organic matter in the absence of oxygen, such as in swamps and sewers (anaerobic digestion). It also occurs in volcanic gases, natural gas and some well waters. The odor of H2S is commonly misattributed to elemental sulfur, which is in fact odorless. Hydrogen sulfide has numerous names, some of which are archaic.

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22. What is hard water?

Hard water is the type of water that has high mineral content (in contrast with soft water). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg(CO3)2). Hard water is generally not harmful.

The simplest way to determine the hardness of water is the lather/froth test: soap or toothpaste, when agitated, lathers easily in soft water but not in hard water. More exact measurements of hardness can be obtained through a wet titration. The total water ‘hardness’ (including both Ca2+ and Mg2+ ions) is read as parts per million or weight/volume (mg/L) of calcium carbonate (CaCO3) in the water. Although water hardness usually only measures the total concentrations of calcium and magnesium (the two most prevalent, divalent metal ions), iron, aluminium, and manganese may also be present at elevated levels in some geographical locations.

Hardness
Hardness in water is defined as the presence of multivalent cations. Hardness in water can cause water to form scales and a resistance to soap. It can also be defined as water that doesn’t produce lather with soap solutions, but produces white precipitate (scum).
Example : 2C17H35COONa + Ca2+ → (C17H35COO)2Ca + 2Na+
Types of hard water
In the 1960’s, scientist Chris Gilby discovered that hard water can be categorized by the ions found in the water. A distinction is also made between ‘temporary’ and ‘permanent’ hard water.
Temporary hardness
Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. It can be removed by boiling the water or by the addition of lime (calcium hydroxide). Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon cooling.
Upon heating, less CO2 is able to dissolve into the water (see Solubility). Since there is not enough CO2 around, the reaction cannot proceed from left to right, and therefore the CaCO3 will not dissolve as rapidly. Instead, the reaction is forced to the left (i.e. products to reactants) to re-establish equilibrium, and solid CaCO3 is formed. Boiling the water will remove hardness as long as the solid CaCO3 that precipitates out is removed. After cooling, if enough time passes the water will pick up CO2 from the air and the reaction will again proceed from left to right, allowing the CaCO3 to “re-dissolve” into the water.

For more information on the solubility of calcium carbonate in water and how it is affected by atmospheric carbon dioxide.

Permanent hardness
Permanent hardness is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence of calcium and magnesium sulfates and/or chlorides in the water, which become more soluble as the temperature rises. Despite the name, permanent hardness can be removed using a water softener or ion exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column.
Hard water causes scaling, which is the left over mineral deposits that are formed after the hard water had evaporated. This is also known as limescale. The scale can clog pipes, ruin water heaters, coat the insides of tea and coffee pots, and decrease the life of toilet flushing units.

Similarly, insoluble salt residues that remain in hair after shampooing with hard water tend to leave hair rougher and harder to untangle.

In industrial settings, water hardness must be constantly monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that comes in contact with water. Hardness is controlled by the addition of chemicals and by large-scale softening with zeolite and ion exchange resins.

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23. What is meant by scaling or fouling?

Fouling refers to the accumulation of unwanted material on solid surfaces, most often in an aquatic environment. The fouling material can consists of either living organisms (biofouling) or be a non-living substance (inorganic or organic).

Other terms used in the literature to describe fouling include: deposit formation, encrustation, scaling, scale formation, crudding, and deposition. The last four terms are less inclusive than fouling; therefore, they should be used with caution.

Fouling phenomena are common and diverse, ranging from fouling of ships, natural surfaces in the marine environment (marine fouling), fouling of heat-transferring components through ingredients contained in the cooling water or gases, and even the development of plaque or calculus on teeth, or deposits on solar panels on Mars, among other examples.

This article is mostly devoted to the fouling of industrial heat exchanger systems, although the same theory is generally applicable to other varieties of fouling. In the cooling technology and other technical fields, a distinction is made between macro fouling and micro fouling. Of the two, micro fouling is the one which is usually more difficult to prevent and therefore more important.

Components subject to fouling
The following lists examples of components that may be subject of fouling and the direct effects of fouling:
  • heat exchanger surfaces – reduces thermal efficiency, increases temperature, creates corrosion, increases use of cooling water
  • piping, flow channels – reduces flow, increases pressure drop, increases energy expenditure, may create flow oscillations
  • ship hulls – increases fuel usage, reduces maximum speed
  • turbines – reduces efficiency, increases probability of failure
  • solar panels – decreases the electrical power generated
  • reverse osmosis membranes – reduces efficiency of water purification, increases pressure drop, increases energy expenditure
  • electrical heating elements – increases temperature of the element, increases corrosion, reduces lifespan
  • nuclear fuel in pressurized water reactors – axial offset anomaly
  • injection/spray nozzles (e.g., a nozzle spraying a fuel into a furnace) – incorrect amount injected, malformed jet, component inefficiency, component failure
  • venturi tubes, orifice plates – inaccurate or incorrect measurement of flow rate
  • pitot tubes in airplanes – inaccurate or incorrect indication of airplane speed
  • teeth – promotes tooth disease, decreases aesthetics
Macro fouling
Macro fouling is caused by coarse matter of either biological or inorganic origin, for example industrially produced refuse. Such matter enters into the cooling water circuit through the cooling water pumps from sources like the open sea, rivers or lakes. In closed circuits, like cooling towers, the ingress of macro fouling into the cooling tower basin is possible through open canals or by the wind. Sometimes, parts of the cooling tower internals detach themselves and are carried into the cooling water circuit. Such substances can foul the surfaces of heat exchangers and may cause deterioration of the relevant heat transfer coefficient. They may also create flow blockages, redistribute the flow inside the components, or cause fretting damage.
Examples
  • Manmade refuse
  • Detached internal parts of components
  • Algae
  • Mussels
  • Leaves, parts of plants up to entire trunks
Micro fouling
As to micro fouling, distinctions are made between:
  • Scaling or precipitation fouling, as crystallization of solid salts, oxides and hydroxides from water solutions, for example calcium carbonate or calcium sulfate.
  • Particulate fouling, i.e., accumulation of particles, typically colloidal particles, on a surface
  • Corrosion fouling, i.e., in-situ growth of corrosion deposits, for example magnetite on carbon steel surfaces
  • Chemical reaction fouling, for example decomposition or polymerization of organic matter on heating surfaces
  • Solidification fouling – when components of the flowing fluid with high-melting point freeze onto a subcooled surface
  • Biofouling, like settlements of bacteria and algae
  • Composite fouling, whereby fouling involves more than one foulant or fouling mechanism.

Precipitation fouling

Temperature dependence of the solubility of calcium sulfate (3 phases) in pure water.

Scaling or precipitation fouling involves crystallization of solid salts, oxides and hydroxides from solutions. These are most often water solutions, but non-aqueous precipitation fouling is also known.

Through changes in temperature, or solvent evaporation or degasification, the concentration of salts may exceed the saturation, leading to a precipitation of salt crystals. Precipitation fouling is a very common problem in boilers and heat exchangers operating with hard water and often results in limescale.

The calcium carbonate that has formed through this reaction precipitates. Due to the temperature dependence of the reaction, and increasing volatility of CO2 with increasing temperature, the scaling is higher at the hotter outlet of the heat exchanger than at the cooler inlet. In general, the dependence of the salt solubility on temperature or presence of evaporation will often be the driving force for precipitation fouling. The important distinction is between salts with “normal” or “retrograde” dependence of solubility on temperature. The salts with the “normal” solubility increase their solubility with increasing temperature and thus will foul the cooling surfaces. The salts with “inverse” or “retrograde” solubility will foul the heating surfaces. An example dependence of the solubility on temperature is shown in the figure. Calcium sulfate is a common precipitation foulant of heating surfaces due to its retrograde solubility.

Precipitation fouling can also occur in absence of heating or vaporization. For example, calcium sulfate decreases it solubility with decreasing pressure. This can lead to precipitation fouling of reservoirs and wells in oil fields, decreasing their productivity with time.[1] Similarly, precipitation fouling can occur on mixing of incompatible fluid streams.

The following lists some of the industrially most common phases of precipitation fouling deposits observed in practice to form from aqeous solutions:

  • Calcium carbonate (calcite, aragonite usually at t > ~50 °C, or rarely vaterite);
  • Calcium sulfate (anhydrite, hemihydrate, gypsum);
  • Calcium oxalate (e.g., beerstone)
  • Barium sulfate;
  • Magnesium hydroxide (brucite);
  • Silicates (serpentine, acmite, gyrolite, gehlenite, amorphous silica, quartz, cristobalite, pectolite, xonotlite);
  • Aluminium oxide hydroxides (boehmite, gibbsite, diaspore, corundum);
  • Aluminosilicates (analcite, cancrinite, noselite);
  • Copper (metallic copper, cuprite);
  • Phosphates (hydroxyapatite);
  • Magnetite from extremely low-iron water.
Particulate fouling
Fouling by particles suspended in water (“crud”) or in gas progresses by a mechanism different than precipitation fouling. This process is usually most important for colloidal particles, i.e., particles smaller than about 1 μm in at least one dimension (but which are much larger than atomic dimensions). Particles are transported to the surface by a number of mechanisms and there they can attach themselves, e.g., by flocculation or coagulation. Note that the attachment of colloidal particles typically involves electrical forces and thus the particle behaviour defies the experience from the macroscopic world. The probability of attachment is sometimes referred to as “sticking probability”, which for colloidal particles is a function of both the surface chemistry and the local thermohydraulic conditions. Being essentially a surface chemistry phenomenon, this fouling mechanism can be very sensitive to factors that affect colloidal stability, e.g., zeta potential. A maximum fouling rate is usually observed when the fouling particles and the substrate exhibit opposite electrical charge, or near the point of zero charge of either of them. With time, the resulting surface deposit may harden through processes collectively known as “deposit consolidation” or, colloquially, “aging”.
The common particulate fouling deposits formed from aqueous suspensions include:

 

  • iron oxides and iron oxyhydroxides (magnetite, hematite, lepidocrocite, maghemite, goethite);
  • Sedimentation fouling by silt and other relatively coarse suspended matter.

Corrosion fouling

Corrosion deposits are created in-situ by the corrosion of the substrate. They are distinguished from fouling deposits, which form from material originating ex-situ. Corrosion deposits should not be confused with fouling deposits formed by ex-situ generated corrosion products. Corrosion deposits will normally have composition related to the composition of the substrate. Also, the geometry of the metal-oxide and oxide-fluid interfaces may allow practical distinction between the corrosion and fouling deposits. An example of corrosion fouling can be formation of an iron oxide or oxyhydroxide deposit from corrosion of the carbon steel underneath.

Chemical reaction fouling

Chemical reactions may occur on contact of the chemical species in the process fluid with heat transfer surfaces. In such cases, the metallic surface sometimes acts as a catalyst. For example, corrosion and polymerization occurs in cooling water for the chemical industry which has a minor content of hydrocarbons. Systems in petroleum processing are prone to polymerization of olefins or deposition of heavy fractions (asphaltenes, waxes, etc). High tube wall temperatures may lead to carbonizing of organic matter. Food industry, for example milk processing, also experiences fouling problems by chemical reactions.

Fouling through an ionic reaction with an evolution of an inorganic solid is commonly classified as precipitation fouling (not chemical reaction fouling).

Solidification fouling
Solidification fouling occurs when a component of the flowing fluid “freezes” onto a surface forming a solid fouling deposit. Examples may include solidification of wax (with a high melting point) from a hydrocarbon solution, or of molten ash (carried in a furnace exhaust gas) onto a heat exchanger surface. The surface needs to have a temperature below a certain threshold; therefore, it is said to be subcooled in respect to the solidification point of the foulant.
Biofouling or biological fouling is the undesirable accumulation of micro-organisms, algae and diatoms, plants, and animals on surfaces, for example ships’ hulls, or piping and reservoirs with untreated water. This can be accompanied by microbiologically influenced corrosion (MIC).

Bacteria can form biofilms or slimes. Thus the organisms can aggregate on surfaces using colloidal hydrogels of water and extracellular polymeric substances (EPS) (polysaccharides, lipids, nucleic acids, etc). The biofilm structure is usually complex.

Bacterial fouling can occur under either aerobic (with oxygen dissolved in water) or anaerobic (no oxygen) conditions. In practice, aerobic bacteria prefer open systems, when both oxygen and nutrients are constantly delivered, often in warm and sunlit environments. Anaerobic fouling more often occurs in closed systems when sufficient nutrients are present. Examples may include sulfate-reducing bacteria (or sulfur-reducing bacteria), which produce sulfide and often cause corrosion of ferrous metals (and other alloys). Sulfide-oxidizing bacteria (e.g., Acidithiobacillus), on the other hand, can produce sulfuric acid, and can be involved in corrosion of concrete.

Composite fouling
Composite fouling is common. This type of fouling involves more than one foulant or more than one fouling mechanism working simultaneously. The multiple foulants or mechanisms may interact with each other resulting in a synergistic fouling which is not a simple arithmetic sum of the individual components.

 

 

24. What is ion exchange?

 

Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic ‘ion exchangers’.

Typical ion exchangers are ion exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, and soil humus. Ion exchangers are either cation exchangers that exchange positively charged ions (cations) or anion exchangers that exchange negatively charged ions (anions). There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously. However, the simultaneous exchange of cations and anions can be more efficiently performed in mixed beds that contain a mixture of anion and cation exchange resins, or passing the treated solution through several different ion exchange materials.

Ion exchangers can be unselective or have binding preferences for certain ions or classes of ions, depending on their chemical structure. This can be dependent on the size of the ions, their charge, or their structure. Typical examples of ions that can bind to ion exchangers are:

• H+ (proton) and OH− (hydroxide)

• Single charged monoatomic ions like Na+, K+, or Cl−

• Double charged monoatomic ions like Ca2+ or Mg2+

• Polyatomic inorganic ions like SO42− or PO43−

• Organic bases, usually molecules containing the amino functional group -NR2H+

• Organic acids, often molecules containing -COO− (carboxylic acid) functional groups

• Biomolecules which can be ionized: amino acids, peptides, proteins, etc.

Ion exchange is a reversible process and the ion exchanger can be regenerated or loaded with desirable ions by washing with an excess of these ions.

Applications

Ion exchange is widely used in the food & beverage, hydrometallurgical, metals finishing, chemical & petrochemical, pharmaceutical, sugar & sweeteners, ground & potable water, nuclear, softening & industrial water, semiconductor, power, and a host of other industries.

Most typical example of application is preparation of high purity water for power engineering, electronic and nuclear industries; i.e. polymeric or mineralic insoluble ion exchangers are widely used for water softening, water purification, water decontamination, etc.

Ion exchange is a method widely used in household (laundry detergents and water filters) to produce soft water. This is accomplished by exchanging calcium Ca2+ and magnesium Mg2+ cations against Na+ or H+ cations (see water softening).

Industrial and analytical ion exchange chromatography is another area to be mentioned. Ion exchange chromatography is a chromatographical method that is widely used for chemical analysis and separation of ions. For example, in biochemistry it is widely used to separate charged molecules such as proteins. An important area of the application is extraction and purification of biologically produced substances such as amino acids and proteins.

Ion-exchange processes are used to separate and purify metals, including separating uranium from plutonium and other actinides, including thorium, and lanthanum,neodymium, ytterbium, samarium, lutetium, from each other and the other lanthanides. There are two series of rare earth metals, the lanthanides and the actinides, both of which families all have very similar chemical and physical properties. Ion-exchange is the only practical way to separate them in large quantities.

A very important case is the PUREX process (plutonium-uranium extraction process) which is used to separate the plutonium and the uranium from the spent fuel products from a nuclear reactor, and to be able to dispose of the waste products. Then, the plutonium and uranium are available for making nuclear-energy materials, such as new reactor fuel and nuclear weapons.

The ion-exchange process is also used to separate other sets of very similar chemical elements, such as zirconium and hafnium, which incidentally is also very important for the nuclear industry. Zirconium is practically transparent to free neutrons, used in building reactors, but hafnium is a very strong absorber of neutrons, used in reactor control rods.

Ion exchangers are used in nuclear reprocessing and the treatment of radioactive waste.

Ion exchange resins in the form of thin membranes are used in chloralkali process, fuel cells and vanadium redox batteries.

Others
In soil science, cation exchange capacity is the ion exchange capacity of soil for positively charged ions. Soils can be considered as natural weak cation exchangers.
In planar waveguide manufacturing ion exchange is used to create the guiding layer with higher index of refraction.

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25. What is a Backwashing Filter?

A backwashing filter is a tank with a specific filtration media filled inside, additional components for structure, and a control valve. The media is typically specific to the elements or components that need to be filtered from the water, such as but not limited to; Arsenic, Nitrates, Iron, Manganese, Chemicals, and Sediments. The water enters the tank, and the elements or components are stopped by the filtration media. The water then travels downwards and travels up through a stem at the bottom of the tank entering the household. During the backwash cleaning cycle, the control valve adjusts the pressure and water flow in the reverse direction, thereby purging the collected elements into a designated drain.

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