CHAPTER-01(BOILER)
Q: With reference to an auxiliary Boiler.
a) Explain the difference between fire and water tube boiler.
b) What is the advantage of water tube boiler over smoke tube boiler?
c) Sketch a vertical Water tube boiler (aux) name all major parts.
Ans a
NO
Water tube boiler
Fire tube boiler
1
Water flow through the tube.
Hot gases passes through the tube.
2
Lighter in compare with capacity.
Robust and heavy.
3
High pressure and high capacity.
Less pressure and less capacity.
4
Not liable to explosion.
Most suspect able to explosion.
5
Distilled water can be used.
Normal water can be used.
6
Complex cleaning is difficult.
Easy to maintenance.
Ans b)
Efficiency over 85% hence reduces fuel consumption.
It can produce high pressure and high temperature steam.
Steam can be produced within short time.
Greater evaporation rate.
Not liable to explosion.
Compact and light weight compare with capacity.
Name of the mountings fitted to the boiler.
Feed check V/V.
Safety V/V.
Water gauge glass.
Hot well tank.
Air vent cock.
Scum V/V.
Blow down V/V.
Fig: 01/A
Q. Purpose of the mountings fitted to the boiler.
01. Feed check V/V:
Allow feed water to boiler.
Non return V/V prevents to back the water from boiler.
Double shut off V/V reduce rise of leakage into feed line while it is in repair.
02. Safety V/V: At list two safety V/Vs have to be fitted of a boiler.
The function of safety V/V to prevent/protect the boiler against over pressure.
It release out steam by more than 10% over of set pressure.
03. Water gauge glass. At list two gauge glasses have to be fitted of a boiler.
It indicates the correct water level in boiler.
04. Hot well tank:
Compensate leakage water and expel vapor of air.
Allow to observe any oil/foreign matter in feed water.
To warm up feed water.
05. Air vent cock:
To release the air when initially raising steam or prevent vacuum when emptying.
06. Scum V/V:
A shallow dish positioned at the normal level and connected to the V/V which is use to remove scum from the water surface.
07. Blow down V/V:
A valve which enables water to be blow down completed from a boiler by partially or completely.
Q. What is the safety of safety of safety V/V?
Drain line without any V/V.
Easing gear.
Pad lock on the cotter.
Dia more than 38 mm.
Lift ¼ dia.
Should not accumulated 10% excess pressure.
A compression ring is fitted after final adjustment to ensure no further movement take place.
Q. What is easing gear?
Easing gear: In case of safety V/V stuck up easing gear operate manually to prevent excess pressure.
Q. What is feathering?
Feathering: The release of small amount of steam by a safety V/V at a pressure below the blow off V/V.
Q. What is the purpose of soot blower?
Soot blower enables the tube surfaces to be cleaned of loose sooty deposits without shutdown of boiler.
To prevent overheating.
To prevent scale formation.
To increase boiler heat transfer.
To prevent uptake fire.
Q. Explain boiler gauge glass blow down procedure?
Take proper personal safety precaution.
Close steam and water cocks, open drain. Water will be drained and there is nothing else indicates steam and water cocks are not leaking.
Open steam cock. A clear sound, close steam cock.
Open water cock. A clear sound, close water cock and drain cock.
Open water cock again water fills up glass.
Open steam cock and water level drops to boiler water.
After blowing through, when V/Vs opened again the water level raises and gradually drops to former position.
Q. Safety of boiler gauge glass.
Two gauge glasses.
Guard to protect from accidental damage.
Water side ball and steam side orifice.
Drain cock.
Handles are vertical downwards in normal working position.
Remote operation system to be provided with gauge glass.
A board painted with diagonal black and white.
Q. What is boiler water treatment (BWT)? Why it is necessary?
The testing of boiler feed water and the addition of chemicals as required to maintain the water in a particular condition is known as boiler water treatment.
It is necessary
To maintain the condition of boiler water.
Prevention of scale formation.
Control of sludge formation.
To reduce the total dissolved solid.
Q. Range of chemical value in boiler water.
PH value ………………………… 9.5 to 10 (Feed system)
10.5 to 11(Drain water)
P – Alkalinity …………………… 100 – 150 ppm
T– …………………….. 200 – 300 ppm
Chloride ……………………….. 300 ppm
Phosphate ………………………………..
Hydrazine …………………………………..
Q. Describe with reason the test carried out on feed water of a low pressure auxiliary boiler.
01. PH test: 1,2,3,4,5,6=Acid 7,8,9,10,11,12,13,14=Alkaline
Reason: To determine PH value. i.e. The degree of acidity or alkalinity of the water.
Test:
A litmus strip is submerged in the complex water.
Colour of strip change according to the condition of water.
Blue colour indicates alkaline.
Red means acidic.
The degree of coloration compared with the data sheet to indicate the possible range of PH value.
02. Alkalinity test:
Reason : To ensure about the alkaline condition of boiler feed water.
Test for P-alkalinity:
100 ml sample of boiler water is taken.
10 drops of phenolphthalein is added sample will turn to pink colour.
N/50 Sulphuric acid is added to clear the sample.
Calculation: ml of N/50 acid used × 10 = PPM of caco3.
Test for Total alkalinity:
Sample after P-alkalinity test is taken.
10 drops of methyl orange is added result is yellow.
N/50 H2SO4 is added until it turn to pink.
Calculation: ml of N/50 acid used for both test × 10 = PPM of caco3
03. Chloride test:
Reason: To measure the chloride value. Which indicate of sea water leakage into the system.
Test:
100 ml of boiler water sample is taken.
10 drops of phenolphthalein is added sample will turn to pink colour.
N/50 H2SO4 is added to clear the sample.
2 ml H2SO4 is added.
20 drops of potassium chromate indicator is added.
N/35.5 nitrate solution is added until the solution will brown.
Calculation: ml of N/35.5 solution used × 10 = PPM of chloride.
4. Phosphate test:
Reason : To determine the amount of phosphate content as a reserve.
Test:
Take 5 ml of sample water.
Add 5 ml molybdate.
Add stannous chloride.
Mix and compare with standard blue colour.
Q. What are the tests are normally carried out for boiler water?
Alkalinity test.
Chloride test.
Phosphate test.
Sulphite test.
Hydrazine test.
Hardness test.
Dissolved O2 test.
Total dissolved solid test.
PH test.
Q. How many types of corrosion may take place in a boiler?
Galvanic corrosion→ When two dissimilar metals are present in a saline solution galvanic action may occur resulting the corrosion of base metal.
Fretting corrosion→ Its occur due to slight oscillatory motion.
Pitting corrosion.→
Electro chemical corrosion.→ When there is relatively a large cathodic and a small anodic area.
Caustic creaking→ Caustic creaking is caused by the action of strong NaOH solution on steel which is under stress.
Scale formation.
External corrosion.
Q. What is the PH value?
Logarithm of reciprocal of hydrogen ion concentration.
Q . What is the result of scale deposition?
Efficiency of boiler reduce due to poor heat transfer.
Poor heat transfer causes over heating of tubes distortion and failure.
Q. Water treatment recommendation.
To prevent scale→ Coagulant are of sodium aluminates, starch, taningels and casein etc.
To give alkalinity and minimize corrosion→ NaOH, Ca(OH)2 and Na2CO3 .
To condition sludge→ Sodium aluminates.
To remove oxygen→ Na2SO4(Sodium sulfite), N2H4(Hydrazine)
To reduce foaming→ anti foam (polyonides/polyamides)
Q. Scale deposits.
Hard scales: CaSO4 Ca & Mg silicates.
Soft scales: CaCO3 Mg hydroxide.
Q. With reference to boiler water quality how oxidation and acid corrosion level of boiler internal parts are prevented.
Prevention of oxidation: Oxidation which is responsible for metal corrosion can be prevented by preventing any ingress of dissolved oxygen. This can be done by two ways.
Mechanically → It is done by deaerating equipment.
Chemically →Add chemical in the boiler water. Such as sodium sulphite or hydrazine.
2Na2SO3 + O2 = 2 Na2SO4
N2H4 + O2 = 2H2O + N2
Prevention of acid corrosion: Acid corrosion occur due to magnesium chloride and carbon dioxide (MgCl2 , CO2) with continuous supply of dissolved O2 in the boiler water. This can be prevented by lime Ca(OH)2 and soda ash (Na2CO3) treatment and also scavenging the O2.
MgCl2 + Ca(OH)2 = Mg(OH)2 + Ca Cl2
Ca Cl2 + Na2 CO3 = CaCO3 + 2NaCl
Q. What is steam trap?
Steam trap is a special type of v/v which prevents the passing of the steam but allows condensate to pass. It works automatically and put into drain line. They are three types .
Mechanical
Thermostatic
Thermodynamic
Q. Purpose of blowing down a boiler.
Reduce water level to prevent carryover or priming.
Reduced total dissolved solid.
Reduce chloride.
Remove sludge.
Empty boiler.
Remove oil by scum blow down.
Q. How to blow down a boiler in port?
Take the permission from local authority if the ship is in a port.
Take preeqution about personal safety.
Carry out soot blow.
Blow down the gauge glass to check it.
Fill fed water up to ¾ of gauge glass.
Stop feed p/p and keep it manual.
Maintain sufficient pressure in the boiler to avoid the contamination of sea water.
Stop firing the boiler.
Open the ship side v/v.
Scum blow down should be carried out.
Open the bottom blow down v/v to heat up the line.
When the noise reduced and the pressure will be low shut down the blow down v/v gradually.
Close ship side v/v.
Wait for boiler pressure near atmospheric and open the air vent to prevent the vacuum formation.
In port check ship side is clear and inform deck department.
Q. Why the scum and bottom blow down is necessary?
Scum or surface blow down is necessary to remove oil or floating particles and bottom blow down is necessary to remove heavy particles like salt.
Q. How external internal treatment of boiler feed helps to reduce the scale formation inside the boiler?
Scale formed inside the boiler due to presence of salts in feed water and this can be prevent by reducing the content of salt . This is achieved by …………..
Externally :
Using evaporated fresh water evaporated salt water.
Proper filtering of feed water.
Maintain the correct feed temperature.
Deaeration.
Internationally : Ensuring a chemical reserve dissolved in the feed of the boiler. Such as – Sodium aluminates , Stracktanin gel, Casein etc.
Q. What is the effect of oil in the feed water?
Oil Will adhere (jagia thaka) into the tubes and create one layer so that heat transfer will be interrupted which will create. Local over heating for ultimate failure, also decreasing the efficiency of the boiler.
Q. Explain the Back Fire.
If oil is permitted to accumulate inside the boiler furnace it will give off flammable vapour. When this vapour mixed up with air it will produce explosive mixture also be ignited and to rapid combustion of the mixture will cause sudden pressure. Build up inside the furnace and explosion will occur.
Q. Why steam pipe is usually insulated?
To protect heat radiator.
To keep cool the E/R environment.
To protect weak point of pipe line from damage.
To protect fire in case of fuel oil spray due to any leakage.
Safety of the personnel.
Q . Describe the maintenance procedure of cascade tank.
Proper water temperature should be maintained.
Maintain water level.
Cascade tank and sight glass should be washed periodically.
The surface of cascade tank should be scale and deposit free.
Tank should be covered to prevent entry of foreign particles.
Maintain the correct operation of float switch.
Q . What is a electro chemical corrosion?
When H+ from water come in contact with metal surface made Hydrogen atoms by taking electron from metal. So ion from metal surface come in contact with hydroxyl ion and farm metallic hydroxide which is soluble in water depending upon the pH value. Hence the metal is corroded
H2o → H+ + OH-
H+ + 2e- → 2H → H2
Fe++ +OH- → Fe (OH)2
Q. How sea water come into the boiler?
While cooling down the boiler if vent cock is not opened then vacuum will be created inside the boiler. If ship side valve is leaky or kept open then sea water will come into the boiler.
҉ Leaking condenser can cause the introducing of sea water.
Q. Describe the contamination of boiler feed water.
Feed water employed for marine boiler is usually……….
Unevaporated fresh water.
Evaporated fresh water.
Evaporated salt water.
All of above water can contain salt which could be harmful by scale formation and corrotion.
Salt water contained following solid……..
NaCl - 2500 ppm.
MgCl2 - 3000 ppm.
MgSO4 -2000 ppm.
CaSO4 -1200 ppm.
Ca(HCO3)2 – 200 ppm.
NaCl (Sodium Chloride) : This is common salt. Heavy contamination of this salt causes foaming and priming. NaCl could in conjunction with MgSO4 from sodium sulphate MgCl2 .
2NaCl + MgSO4 = MgCl2 + 2NaSo4
MgCl2 : Magnesium is soluble under boiler normal condition.
MgCl2 + 2H2O = Mg(OH)2 + 2HCl
Magnesium hydroxide has low solubility. So it can deposit and form scale.
Again HCl can causes corrosion according to the following relation.
2HCl + Fe = FeCl2 + H2
FaCl2 + 2H2O = Fe(OH)2 + 2HCl Corrosive: CaSO4 : This is very dangerous, because it can deposit and form of heard scale.
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