undefined | unit 1 water conditioning

CHEM

UNIT-1Water Conditioning Q1) List the units of Hardness?A1) Units of Hardness

Parts Per million (ppm): It is defined as the number of parts by weight of CaCO3 equivalent present in per million (106) parts by weight of water.

1 ppm = 1 part of CaCO3 equivalent hardness in (106) parts of water.

Milligrams per litre (mg/l): It is defined as the number of milligrams of CaCO3 equivalent hardness present in one litre of water.

1 mg/L = 1 mg of CaCO3 equivalent hardness present per litre of water.It can be easily proved that 1mg/L = 1 ppm, for waterWeight of 1 litre of water = 1kg = 103g = 106mg= 1000*1000g= 106mg1mg/L = 1mg of CaCO3 equivalent hardness per 106 parts of water. 1mg/L = 1 part of CaCO3 equivalent hardness per 106 parts of water.1mg/L = 1ppm

Degree Clark (0Cl): It is defined as the parts of CaCO3 equivalent hardness per 70,000 parts of water or it is number of grains (1/7000lb) of CaCo3 equivalent hardness per gallon (10lb or 70,000 grains) of water. 10 Clark= 1 part of CaCo3 per 70,000 part of water.

Degree of French (0Fr): It is defined as the parts of CaCO3 equivalent hardness per Lac (100000) parts of water.

10Fr = 1 part of CaCO3 equivalent hardness per (105) parts of water.

Milli equivalent per litre (meq/L): It is defined as the number of milli equivalents of hardness present per litre.

1 meq/L = 1 meq of CaCO3 per L of water = 10-3 * 50g of CaCO3 eq. per litre of water = 10-3 * 1000 * 50 mg of CaCO3 eq. per litre of water = 50mg of CaCO3 eq. per litre of water = 50mg/L of CaCO3 eq. per litre of water = 50 ppm = 50mg of CaCO3 eq. per 106 litre of water = 1 mg of CaCO3 eq. per 106 /5 mg litre of water = 1 part of CaCO3 equivalent per 20,000 parts of water. Q2) Define Principle and Reaction of water softening?A2) Principle Water softening refers to the removal of magnesium, calcium and certain other metal cations in hard water, water softening is Water softening is usually accomplished by using lime softening or ion exchange resin, but in recent times the softening is attained with nanofiltration of reverse osmosis.ReactionThe softening of water is attained by either adding chemicals that form precipitates that are insoluble or by ion exchange method. The chemicals usually added are borax, ammonia, calcium hydroxide (slaked lime) or trisodium phosphate, in the lime soda method, filtration and sedimentation processes are carried out to remove precipitates. Q3) Differentiate between the Lime soda and the Zeolite process?A3)

Sl no	Lime soda process	Zeolite process
1	The water treatment plant occupies more area or place	Water treatment plant occupies less area.
2	Water after treatment has lesser dissolved solids	Water after treatment has much more dissolved solids.
3	This method of treatment of water is very economical and the material is also cheap.	This method of water treatment is expensive, and the material used for softening is also very expensive.
4	It cannot operate under pressure	It can operate under pressure
5	This method can be applied to acidic water also	This method cannot be applied to acidic water
6	There is a problem of Settling, coagulation and removal of sludge	In this method, no problems arise due to coagulation, sludge and settling.
7	Residual Hardness is low about 15 to 50 ppm	Residual hardness is low about 10-15ppm
8	In order to meet the changes in hardness of incoming water, frequent control and adjustments is required.	Control test comprises of only testing the hardness of treated water.

Q4) Define Priming and Foaming and its prevention?A4) Foaming:This occurs inside the boiler Foaming is the formation of thick layer of steam bubbles on the top of water surface inside the boiler due to:

High concentration of Impurities

Presence of vegetable or animal fats in feed water (Carryover from Oil Heaters)

Increase in level of dissolved & suspended solids (TDS level)

Increase in Boiler water level

Prevention of FoamingTo prevent foaming, scum or surface blow down shall be carried out frequently to expel any floating impurities from boiler. Also, no lube oil (or oil) shall be allowed to enter the boiler.Priming:Priming is the condition of Boiler in which large amount of water is carried along with steam into the steam line. It is Caused by:

Excessive Foaming

Insufficient steam space

Because of sudden rush of steam (This may happen if steam stop valve is opened suddenly)

Prevention of Priming

Never keep boiler water level too high &

Open steam stop valve slowly

Actions to be taken during Priming & Foaming of Boiler

Scum blows down

Reduce boiler burner firing rate

Check weather boiler chemical added in excess?

Detection of source of contamination present in boiler feed water by oil.

Q5) Explain Sludge and Scale formation in Boilers?A5) Sludge formation , scale formation

In boiler water evaporates continously and the concentration of salts left behind goes on increasing . After the saturation point they get precipitated.

If the precipitate remains in boiler tube as loose and slimy matter is called sludge.

If some of the precipitated matter adhers strongly and forms strong bad conducting layer on their inner side of boiler tube , then it is known as scale.

Sludge :-( formation of sludge )

The loose slimy mass of salts precipitated in boiler water is the sludge.

They are generally formed at cooler portion of boiler and they loosely deposit in the parts of boiler tube where flow rate is slow e.g vlves bends

Sludges are easy to remove by using brushes detergent solutions blow down opreation e.t.c .

Disadvanatages of sludges :-

They tend to waste some portion of heat.

Edcessive sludge formation distrub working of boiler and sometimes may choke up the pipe .

Prevention of sludges :-

Use of water contaning very low quantity of total disolved solids.

Frequently making blow down opreation i.e replacing salts concentrated water with fresh water.

Scales formation Scale is the hard and strongly adhered coating to the inner surface of boiler and it is a bad conductor of heat. It is the main source of boiler trouble.It is caused due to :-

Decomposition of bicarbonates :-

At high temprature bicarbonates decompose into sticky water insolube material.Ca ( HcO3)2 ----------------- CaCO3 + H2O + CO2Mg ( HCo3)2 - - -------------- Mg (Oh)2 + 2CO2 2. Hydrolsis of magnesium salts :- At higher temprature magnesium salts undergo hydrolysis.MgCl2 + 2H2O ---------------------- mg ( OH)2 + 2HCl3. Presence of silica :- The source of ssilica is ( form) from sand and filter .silica may be in the form of colloidal particles. And it can be deposite as calcium silicate or magnesium silicate as firmly adhering materials. 4. Decreased solublity of CaSO4 :- CaSo4 has lesser solublity at higher temprature hence at high temprature CaSo4 present in boiler feed water will precipitate as hard scale forming materials.

Fig:1 Scale and Sludge formation in Boilers B] Disadvantages of scale :-1. waste of fuel :- Scales are bad conductors of heat and resultes in the reduction of heat transfer to the boiler . higher the thickness of scale greater than the wastage of fuel there by . it has been reported that 0.25 cm . scale would increase fuel consuption by aboyut 2 to 3 percent.

Thickness of scale	0.325 mm	0.625mm	1.25mm	2.5 mm
Wastage of fuel	10 percent	15 percent	50 percent	80 ercent

3. over heating of boiler :- Scale being pooe conducter of heat it reduces transfer of heat from boiler to boiler water . to keep the required steam pressure we need to overheat the boiler . 4. boiler saftey :- due to the scale formation the overheating of boiler is done in order to maintain constant stream supply with required pressure . this overheating makes boiler metal to become soft and weak . this cause distortation of boiler tube and becomes dangerous in morden high pressure boiler . 5. Danger of Explosion :- When thick scale cracks due to uneven expansions the water come suddenly suddenly in contact with the overhead boiler metal. This cause large amount of steam formation suddenly and sudden high pressure is developed . due to sudden high pressure is devloped . due to sudden high pressure the softer boiler metal may burst with explosion. C] Removal of scales :- Scales are removeed from time by different ways.

By use of suitable chemicals the scale can be dissolved and removed.

Use of scraper or wire brush for thin scales to remove.

Thick s ales may br removed by hammer and chisle.

The thermal shocks technique is used to remove hard brittle scale . in this method empty boiler is heated and cooled by cold water suddenly . while sudden cooling the contracting boiler metal excerts pressure on scale to crack them.

Blow down opreation used if scales are loosely adhering.

D] prevention of scales :- It is better to minimize scales formation and reduce the problems in steam generation.

Use of softened water.

Adding sodium phosphate to the water

Frequent blow down operations to remove the scales when they are thin.

Adding sodium aluminate which can trap the scale forming particles.

Adding organic chemicals like tannin which forms coating on the scale forming particles . this matter becomes easily removable by blow down operation.

Q6) Write a note Caustic Embrittlement?A6) This phenomenon occurs in boilers; the caustic materials accumulate in boiler materials. The phenomena can also be described as the cracking of mild steel riveted boiler plates. The process occurs at a temperature of 200°-250°C resulting in the local deposition of concentrated hydroxide.In Caustic embrittlement the main things that are focussed are the parts of the boiler like bends, cracks, rivets and joints. At high temperature and pressure sodium hydroxide is formed from residual sodium carbonate which undergoes hydrolysis.Caustic embrittlement is also known as stress corrosion cracking.There are many causes of caustic embrittlement, including the combined action of the following three components:

A susceptible material

A given chemical species

Tensile stress

Caustic embrittlement can be prevented through several methods, including:

Controlling the temperature and potential

Controlling the stress levels and hardness

Materials are used that do not crack when placed in a given environment.

Alkali is avoided wherever necessary

Softening agents such as sodium sulphates can be used in place of sodium carbonates

Hairlines can be prevented by adding lignin, tannin or sodium sulphate they also prevent infiltration of sodium hydroxide into the areas

Q7) Explain the three methods of internal water conditioning?A7) The residual salts that are not removed by external methods can be removed by adding some chemicals directly into the boiler water. These chemicals are known as ‘Boiler compounds. This method is known as ‘Internal treatment’ E.g.) Carbonate conditioning, Phosphate conditioning, Calgon conditioning, etc., a) Carbonate conditioning: Used for low pressure boilers. Here the salts like CaSO4 are converted to easily removable CaCO3. But sometimes it produces NaOH, CO2 and hence Carbonic acid. So, it is less preferred. CaSO4 + Na2CO3 ------> CaCO3 + Na2SO4 b) Phosphate conditioning: Used for high pressure boiler. No risk of CO2 liberation. 3CaSO4 + 2 Na3PO4 ---------> Ca3(PO4)2 + 3 Na2SO4 Three types of Phosphate salts are used:

Na3PO4 Tri sodium Phosphate highly acidic water

Na2HPO4 Di sodium hydrogen Phosphate slightly acidic water

NaH2PO4 Sodium di hydrogen phosphate highly alkaline water

c) Calgon conditioning: Calgon is the trade name of sodium hexa meta phosphate- Na2 [ Na4 (PO3)6]. With calcium ions it forms a soluble complex and prevents scale and sludge formation. It is used for high- and low-pressure boilers. 2CaSO4 + Na2[ Na4 (PO3)6] --------> Na2 [Ca2(PO3)6] + 2 Na2SO4 Q8) Define Breakpoint Chlorination?A8) Breakpoint chlorination is defined as the point where sufficient chlorine has been added to a quantity of water to enable disinfection. In other words, it is at this point that all the undesirable contaminants are removed from the water. It is at this breakpoint that, all the chlorine that is added to the solution gets consumed by the chemical reactions of the contaminants, that results in water having no free availed chlorine (FAC).In waste water treatment, breakpoint chlorination involves removing of ammonia from a solution, that changes to an oxidised volatile form. Increased amounts of chlorine residue are produced by adding chlorine to water that contains ammonia or organic matter that contains nitrogen.This process involves the continuous addition of chlorine to water, till a point where chlorine brings about a suppression in the rate of corrosion successfully., that makes the diffusion process difficult due to rust.Excessive amount of chlorine causes defragmentation to the human tissues. In a reaction Chlorine can undergo strong oxidation causing hydrogen to separate from water, this hydrogen combines with chlorine to form hydrogen chloride and nascent oxygen, that causes damage in tissues.Generally, in swimming pools, breakpoint chlorination has a certain amount of free chlorine that is used to fully remove combined chlorine from the pool water. It is necessary to avoid the unsuccessful termination Q9) Describe any two methods of water purification for domestic uses?A9) Ozone Ozone are also potent germicides and powerful oxidizers apart from being gooddisinfectants, ozone is an unstable gas and can kill bacteria and viruses effectively, they are powerful oxidizers, with no build-up immunity or toxic residues. Ozone is most effective disinfectant compared to chlorine and other commonly used disinfectants. ozone is short-lived, they return to their normal form when it breaks. When ozone destroys bacteria or any organic compound, the free atoms liberated attack any foreign particle that are present in air or water, however during this process ozone does not produce any toxic compounds unlike chlorine compounds.For the decontamination of water or air, ozone is considered the most effective and a safe disinfectant, at the right levels and safety standard they can be used effectively in hospitals, industries and homes. ChlorineOne of the commonly used disinfectants is Chlorine, it is known to be very effective in deactivating the pathogenic microorganisms, Chlorine is easily applicable, measured and controlled, they are relatively cheap and very persistent in nature.Chlorine has been used for applications, such as the deactivation of pathogenicmicroorganisms in waste water, drinking water and swimming pools.The mode of action is that chlorine kills bacteria and viruses by breaking thechemical bonds in their molecules Chlorine kills pathogens such as bacteria andviruses by breaking the chemical bonds in their molecules. Chlorine can exchange atoms with other, like enzymes in bacteria and other cells. When the enzymes come in contact with chlorine, hydrogen atoms are replaced by chlorine in the molecule, resulting in the change in the shape of the compound and they may also fall apart, as the enzymes lose their activity the bacteria or the cell dies.

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