Water Treatment Final

What is condensate treatment?

Treating the water with chemicals and heat to be sent and reused from the condensate tank since it’s much cheaper than using 100% make up water.

What are reasons for treating condensate?

Impurities can plug or corrode the condensate system and feedwater system, or cause scale or corrode the boiler.

What is carbon dioxide?

Carbonates and bicarbonates break down in the boiler to carbon dioxide. Enters system as alkalinity in the raw water supply or because of poorly functioning deaerators. CO2 reacts with condensate to create carbonic acid.

What can carbonic acid cause?

Can cause thinning of metal parts in condensate return system or localized grooving

What is oxygen?

Enter through contact with air in makeup water or condensate. If DA is not working correctly oxygen won’t be removed. Can cause pitting of the metal

What is hardness?

Can cause scale which reduces heat transfer and can overheat the boiler metal.

What is mechanical inspection and maintenance?

Inspecting piping and fittings and repairing any leaks, improperly working steam traps will minimize the amount of make up water that is required.

What is dealkalization equipment?

When using sodium zeolite ion exchange softeners the hardness is reduced to zero from exchanging the Ca and Mg ions with Na.

What do neutralizing amines do?

Are used to increase PH of the condensate. Vaporize and travel with the steam. when the steam condenses the neutralizing amines will raise the PH of the condensate. Reacts with carbonic acid

Why shouldn’t you add to much neutralizing amine?

Will raise PH too much and can cause corrosion problems as well. Amount injected should keep PH level around 8.8 - 9.2

Why is ammonium hydroxide bad?

Attacks and corrodes copper or copper alloy parts

What are filming amines?

Creates protective films on metal surfaces. Are effective against the corrosive effects of both CO2 and O2.

What is condensate polishing?

Mixed bed of ion exchangers. Used if the condensate becomes contaminated. Filters out particulate and suspended matter, and ion exchange to remove hardness and chlorides.

What is a fluorometer?

Can be used to monitor the amine concentration.

What are corrosion coupons?

Used to check corrosion rates. Takes time to get a reading and see how corroded a system is becoming. They are the same or very similar metal used in the system. Immersed in condensate tank in a coupon rack.

What are problems in cooling towers due to impurities?

Deposition of solids (scaling), corrosion, plugging or erosion of equipment, biologic fouling, and wood deterioration.

What is deposition of solids scaling?

As water evaporates, impurities stay behind and concentrate. Higher concentrations can cause scale in condensers and on cooling tower surfaces. The amount of scale depends on concentration of calcium and bicarbonate ions dissolved and PH of the water.

What can corrosion cause in cooling towers?

Equipment failure, loss of heat transfer efficiency due to heat exchanger fouling, and loss of structural integrity of concrete walls and basins. Caused by dissolved oxygen in cooling tower.

What is plugging or erosion of equipment from cooling towers?

Most towers are open to atmosphere, so airborne dust and debris can enter water and then piping system

What is biologic fouling?

Algae, fungi, and avian waste and bacteria growth all cause it. Enhanced by warm water, abundant sunlight and oxygen rich environment. Slime and biofilm can reduce flow rates in tubes an channels, release organic acids, and attack and destroy wooden portions of tower

What are biofilms?

Reduce heat exchanger efficiency and increases operating costs

What is legionnaires disease?

Natural bacteria that can cause serious lung infections. Water temp needs to be above 50 celcius to kill them. Keep under 20 celcius to prevent multiplication.

What is cellulose?

Long fibres and gives wood its strength

What is lignin?

Cements the cellulose fibres of wood together

What are solutions to cooling tower problems?"

Most can be addressed with water treatment.

How is scaling prevented in cooling towers?

Chelates are used to keep solids in suspension so they can be blown down. Remove calcium hardness from water with softening process, keep scale forming salts in solution, and precipitate the calcium as a removable soft sludge rather than a hard scale.

How do you soften the water to prevent scaling?

Either with ion exchange softeners, or cold lime softening.

What is cycle control?

Maintain a ratio of dissolved solids in the circulating water, to the dissolved solids in the make up feedwater.

What can a higher cycle of concentration do?

Greater chance of scale deposition

What is make up proportional blowdown?

Directly related to the amount of make up water added (100 litres of make up added but at 4 cycles = discharge 25 litres of total amount that entered)

What is conductivity blowdown?

Blowdown is opened when conductivity gets up to a set value.

What are methods of corrosion control?

Use corrosion resistant metals and materials, apply protective coatings, use sacrificial anodes, and form protective films with chemicals

What are cathodic inhibitors?

Coat the cathodic surfaces of a system. Examples are bicarbonate polyphosphates, zinc.

What are anodic inhibitors?

Coats the anodic surfaces. Has to be enough chemicals to cover all anodic regions otherwise corrosion effects can worsen. Examples are molybdate, orthophosphate, nitrite

What are film forming chemicals.

Traditional ones are polyphosphates, chromates and zinc. Forms a thin film on metal which prevents dissolves oxygen and carbon dioxide in the water from coming in direct contact with the metal.

What are disadvantages of using chromates for corrosion control?

Can cause environmental damage when released through blowdown or system drainage.

Why are heavy metals good to prevent biological fouling?

Penetrates cell wall and destroys protein groups that are essential to life support

Why are oxidizing chemicals good for biological fouling?

They oxidize protein groups resulting in a loss of enzyme activity in the cell and cell dies. Chlorine is an example.

Why are non oxidizing chemicals good for biological fouling?

These pass into cells and cause precipitation of proteins out of solution inside the cell and kill the cell.

What are biocides?

Usually shock fed to system to kill microbiological growth.

What are conductivity tests used for?

Used to determine the dissolved solids concentrations. Higher conductivity = more dissolved solids.

What is a DMA (differential microbial analysis)?

Differential microbial analysis used off site to determine various microorganisms. Dip slides are dipped in cooling water and then incubated to see what or how much grows

What is galvanic corrosion?

Occurs when dissimilar metals are in physical contact with each other and exposed to a fluid. Fluid transfers electrons and metal ions between 2 metals. Difference of electrochemical potential cause electrons to flow from more negative metal (anode) to more positive metal (cathode)

What can high flow cause in regards to corrosion?

Erosion can occur at piping turns and can strip protective chemical coatings and leave the pipe unprotected and susceptible to galvanic corrosion.

What can low fluid flow do in regards to corrosion?

Too low, suspended material can drop out and deposit on metal surface and galvanic corrosion cells can form under the deposits.

What is sodium nitrite?

Used as a corrosion inhibitor. Anodic corrosion inhibitor that forms protective iron oxide surface film. Good for ferrous metals, not for copper or copper alloys, but also promotes biological growth.

What is molybdate?

Another corrosion inhibitor. Used for systems with mixed metallurgy. Provides best corrosion protection

What is selective leaching?

Can happen in cooling systems. One particular metal is preferentially attacked.

What determines how much galvanic corrosion occurs?

The voltage difference between the 2 metals. The greater the potential difference between 2 metals, the greater the corrosion.

How can you prevent closed system corrosion?

Replace dissimilar piping with piping of similar materials, install dielectric pipe fittings, install sacrificial anodes, or add corrosion inhibitor and oxygen scavenger

Why is glycol used in closed loop systems?

Used to prevent freezing. Colourless and odourless.

What is glycol?

Reacts with oxygen to form organic acids that will increase corrosion. Factory blended with corrosion inhibitors. PH of a system is a good indicator of whether the glycol has enough inhibitor.

What are characteristics of glycol systems?

They require less monitoring, relatively trouble free when inhibitor is used. but will transfer less heat than water does, so more heating coils are needed.

What are the 5 common reasons for boiler water treatment?

Prevents scale on boiler tubes, prevents sludge from forming, prevents corrosion, prevents carryover and ensures that required level of steam purity is achieved

What does properly treated water provide?

Efficient equipment operations, increased boiler life expectancy, reduced fuel use, optimized water use, reduced waste and savings on maintenance and labour

What are the 3 main impurities?

Suspended solids, dissolved solids and dissolved gases

What is soluable?

Dissolves easily in water

What is insoluble?

Doesn’t dissolve easily in water

What is a solute?

What is being dissolved (eg, sugar in water)

What is a solvent?

What the solute is being dissolved in (eg, water)

Suspended solids are:

Substances that are held or suspended in the water and are insoluble in the water and are carried along in the flow of water

What problems can arise from high suspended solids?

Deposits that build up on tubes and heat transfer spots, erosion of piping or plug up equipment, and foaming.

What are dissolved solids?

Ionic compounds with calcium and magnesium cations are calcium and magnesium salts

What is hardness?

Higher amount of calcium and magnesium ions in water = scale and reduced heat transfer causing tube overheating.

How is silica removed?

Colloidal (very very small) and ionic silica is removed by clarification and lime softening, reverse osmosis, and ion exchange

What causes foaming?

Bubbles or froth build up on surface of the boiler and pass out with the steam. Can also be caused by oils or suspended solids

How are dissolved solids removed?

Usually by some sort of ion exchange, and sometimes distillation and reverse osmosis.

What are dissolved gases?

Gases that are in solution (nitrogen, ammonia, CO2). As temperature increase, the solubility of gases in water decreases

Why is ammonia bad?

Can cause corrosion in copper and copper bearing alloys, especially if oxygen is also present.

Why is CO2 bad?

Forms carbonic acid when dissolved in water, which can cause grooving in return lines.

What is considered a neutral solution?

PH value of 7

What happens when PH level decreases?

Solution becomes more acidic

What happens when PH level increases?

Solution becomes more basic

What is the safe PH range for boiler water?

between 8.5 - 12.7 PH

What is magentite?

Naturally occurring that forms a protective layer over boiler metal to prevent further oxidation. Formed by iron being grabbed by the metal. High PH level dissolves this.

How is PH increased?

Caustic soda is usually added

How is PH reduced?

blowdown is usually used, removing the concentrated boiler water and new purer, lower PH make up water is added.

What is turbidity?

Measure of water cloudiness.

What is free chlorine used for?

Disinfect the water so biological impurities do not form or multiply during transportation.

Why would a settling pond be used?

Slows down the velocity of the water allowing the suspended solids to settle by gravity

What can bigger suspended particles cause (bigger than 2 microns?)

Can cause deposits, erosion and plugging of equipment

What is a clarifier?

A large settling tank that uses gravity to settle out particles. Solids are drained from the bottom. If particles are too small to settle (colloidal) a coagulant can be added to neutralize particles

Why is filtration used?

Used to get rid of the last of the suspended particles

What are pressure filters?

Water comes in through top and then goes through filter media then finally through a strainer. If differential pressure is too high then backwash is needed for cleaning.

What is backwash?

Reverses flow of water through the filter and frees trapped solids to waste

What is a filter and tubular filter?

Socks cover the tubes and a filter aid is added to coat the tubes/socks which helps the filtration.

What is a cartridge filter?

Similar to an oil filter in a car. Water flows around outer space of filter then through the filter to the outlet. As filter screens more solids, the pressure drop across the filter increases. Once too high it needs to be replaced.

What is adsorbed?

When things stick to something. Adhesive like velcro

What is an activated carbon filter?

Used to remove taste or odours from water. It is also used to remove chlorine. Organics are adsorbed into the filter

When happens to the solubility of calcium and magnesium ions when the temperature increase?

Solubility goes down making them harder to mix which precipitate out of solution and form scale.

How are calcium and magnesium ions removed?

By lime soda systems, sodium zeolite, demineralizers, and reverse osmosis

What are lime soda softeners?

Uses chemical precipitation to remove hardness ions. When solids form, they are now suspended solids instead of dissolved solids

What is a hot lime soda softener?

Has quicker reaction than cold version and solids are easier to remove. Removes silica as it attaches to the magnesium hydroxide solids

What is a sodium zeolite system?

Uses ion exchange. Usually cheaper than lime soda, easier to control, and chemicals are safer for operation. Used to remove 100% of calcium and magnesium ions which cause hardness

What is sodium zeolite?

The scale forming calcium and magnesium are exchanged with ones that do not produce scale (sodium), transforming the dissolved solid salts into sodium bicarbonate and sodium sulfate which are highly soluble.

What are demineralizers?

Uses ion exchange. Can remove most ions other than silica. Used for dissolved solids to get rid of hardness. Water comes in and cations (positive charge) exchange with hydrogen. Then goes to anion (negative charge) and exchanges negatives charges with hydroxide, making H2O, or clean and demineralized water to come out.

What is a cation exchanger?

Calcium, magnesium, sodium and all other cations are replaced with hydrogen ions. The incoming cations are transformed into acids, carbon dioxide and water.

What is an anion exchanger?

The outgoing (effluent) of the cation exchanger is an acidic solution. In the anion exchanger the acids are exchanged for hydroxide ions (OH = Hydroxide)

What is regeneration?

Resin will become exhausted and must be regenerated.

What is reverse osmosis?

If pressure is applied to say a body of water, it forces the water and impurities through a filter. Water gets through, but most impurities stay behind.