Marine Boiler: Types of Burner

In a marine boiler, oil fired burner is normally used. Diesel or heavy fuel oil is used as burning fuel. The fuel to be used has to be clean and in correct temperature and viscosity for rapid combustion. This is to ensure the fuel to be at right atomization that will turn the fuel into micro droplets for efficient combustion.

Temperature is a critical factor as a lower than the normal temperature will lead to increase in the size of droplet resulting in poor combustion producing soot and smoke. If the fuel temperature is too high, the droplets can be too small leading to rapidly burning of the fuel near the burner tip. For a Marine Boilers, three basic types of burners are used.

1. PRESSURE JET BURNER
2. AIR OR STEAM BLAST ATOMISER
3. ROTARY CUP BURNER

PRESSURE JET BURNER:

The main purpose of boiler burner is to break the oil into fine droplets i.e. to atomize the fuel in correct manner so that efficient combustion can be achieved. In pressure jet burner, an orifice or nozzle is fitted at the end of a pressure tube which atomizes the fuel in to fine droplets.

Atomization of fuel also depends mainly on the flow rate of the fuel from the burner’s end. The difference in the pressure of the fuel before and after the nozzle controls the flow-rate of the fuel from burner. Hence, if the flow rate of the fuel from burner is reduced to 50%, it will affect the atomization by a drop of 25%. To overcome this problem, this type of burner is supplied with different size of nozzle (having different diameter of orifice), which can be interchanged as per the flow rate of the fuel which mainly depends on the boiler load.

The fuel pressure required for pressure jet burner may vary from 7 bar to 15 bar depending upon the design of burner and load of the boiler. The maximum required viscosity at the burner inlet is normally 15 cst and both diesel and heavy oil can be used as a fuel.

Advantage of Pressure jet burner:

• Simple in construction
• Economical in maintenance
• Variety of sizes for different boiler load
• Can be accommodated in all type o furnca
• Produces variety of flame: short and fat, long and thin

Disadvantage:

• Limited turndown ratio for some nozzle size- 2:1
• Nozzle hole prone to frequent clogging
• This burner requires highest oil- pre heat treatment
• Nozzle cleaning to be carefully done as it can be damaged easily
• Requires frequent maintenance
• Inefficient at high load boilers

AIR OR STEAM BLAST ATOMISER:

This type of burner is similar in working as pressure jet, with an addition of high pressure steam supply arrangement incorporated in it.  The oil is thus sprayed in the path of this high pressure air r steam which helps the fuel for atomization. Normally air is used during the initial starting of burner and then steam take over the operation. A convergent divergent nozzle is used to convert the pressure energy to kinetic energy which results in a high velocity jet of steam which enables atomization of oil which is sprayed in its path.

The steam side have tangential nozzle which provides rotatory motion to the fuel to ensure efficient combustion.

The fuel pressure required for pressure jet burner may vary from10 bar to 21 bar depending upon the design of burner and load of the boiler. The maximum required viscosity at the burner inlet is normally 15 cst and both diesel and heavy oil can be used as a fuel

Advantages:

• Robust construction
• High Turndown ratio of 4:1
• Efficient combustion over whole firing range
• Air fuel ratio can be adjusted for achieving efficiency
• Good combustion of heavy fuel oil

Disadvantages:

• combustion depends on steam/ air supply
• Additional maintenance of connections and piping for air and steam

ROTARY CUP BURNER

As the name suggest, this burner comprises of a burner nozzle which is covered by a rapidly rotating cone. The fuel oil is carried on to a nozzle which is centrally located within the rotating cone. As the fuel oil moves along the cup due to absence of centripetal force, the oil film becomes thinner in its course as the circumference of the cup increase. Ultimately, the fuel is discharged from the tip of the rotating cone in the form of fine atomized spray.

The atomization achieved in the rotating cup burner has very high turndown ration as compared o pressure jet burner because atomization is produces by rotating cup rather than pressurizing the fuel supply to nozzle.

Advantages:

• Good turndown ratio of better than 4:1.
• Good atomization of heavy fuel oils.
• Lowest oil pre-heat temperature required 
for atomization.
• No high pressure fuel in the line
• Disadvantages:

Complex in construction

Costly to maintain.

Electrical consumption and connections required for the 
cup drive.

Pilot or Ignition Burner:

In some marine boiler with main burner firing in heavy fuel oil, it is very difficult to initially start the boiler with main burner. For start up of the boiler, a separate pilot or ignition burner is provided which uses diesel oil as a fuel. This enables the pilot burner to ignite even at the coldest condition the ship faces at sea.

The Pilot burner has a separate diesel oil piping and pump. The heat source is provided by two electrodes igniting the pilot flame, which are fitted to a high voltage ignition transformer. The pilot burner is allotted with a limited period of ignition during which it acts as a source of heat for main burner and once the time is over, the pilot flame goes off.

A pilot burner consists of a detachable nozzle with fine holes to atomize the diesel fuel for instant ignition. The nozzle to be cleaned at regular interval and operation of pilot burner checked for atomization.

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Reference:

learn.marineinsight.com

Boiler Safety Valve

Boiler Safety Valves:

One of the most critical automatic safety devices in a steam system is the safety valve. It protects lives, equipment and property from potentially dangerous levels of temperature and forces caused by excessive steam system pressure.
The main purpose for a safety valve is to prevent the pressure in a system to exceed certification pressure.
Above certification pressure no one can guaranty the systems safety - and especially for a steam system with a very hot gas with a huge amount of latent heat the consequence with a failure can be dramatically.

Design:

The size of a safety valve depends primarily on the maximum boiler output and the operation pressure of the system. The safety valve must as minimum have the evacuation capacity of all the vapor the boiler can produce running at full power at the working (or certification) pressure.

1. For a higher pressure the steam is compressed and requires less volume and the size of the valve can be reduced
2. for a lower pressure the steam is expanded and requires more volume and the size of the valve is increased
3. Although the principal elements of a conventional safety valve are similar, the design details can vary considerably. 
4. The DIN style valves (commonly used throughout Europe) tend to use a simpler construction with a fixed skirt (or hood) arrangement whereas the ASME style valves have a more complex design that includes one or two adjustable blow down rings. 
5. The position of these rings can be used to fine-tune the over pressure and blow down values of the valve.
6. For a given orifice area, there may be a number of different inlet and outlet connection sizes, as well as body dimensions such as centreline to face dimensions. 
7. Furthermore, many competing products, particularly of European origin have differing dimensions and capacities for the same nominal size.

Safety Valve Operation:

1. When the inlet static pressure rises above the set pressure of the safety valve, the disc will begin to lift off its seat.
2. However, as soon as the spring starts to compress, the spring force will increase.
3. This means that the pressure would have to continue to rise before any further lift can occur, and for there to be any significant flow through the valve.
4. The additional pressure rise required before the safety valve will discharge at its rated capacity is called the over pressure.
5. The allowable over pressure depends on the standards being followed and the particular application.
6. For compressible fluids, this is normally between 3% and 10%, and for liquids between 10% and 25%.
7. In order to achieve full opening from this small over pressure, the disc arrangement has to be specially designed to provide rapid opening.
8. This is usually done by placing a shroud, skirt or hood around the disc.
9. The volume contained within this shroud is known as the control or huddling chamber.
10. As lift begins and fluid enters the chamber, a larger area of the shroud is exposed to the fluid pressure.

Safety Valves Regulation:

1. Each boiler (including exhaust gas boiler) and steam generator is to be fitted with at least one safety valve and where the water-heating surface is more than 46.5 m2 (500 ft2), two or more safety valves are to be provided. The valves are to be of equal size as far as practicable and their aggregate relieving capacity is not to be less than the evaporating capacity of the boiler under maximum operating conditions.
2. In no case,

- The inlet diameter of any safety valve for propulsion boiler and superheaters used to generate steam for main propulsion and other machinery to be less than 38 mm (1.5 in.) nor more than 102 mm (4 in.).

- For auxiliary boilers and exhaust gas economizers, the inlet diameter of the safety valve must not be less than 19 mm (3/4 in.) nor more than 102 mm (4 in.).

3. In all cases, the safety-valve relieving capacity is to be determined on the basis of the boiler heating surface and water-wall heating surface along with the fuel-burning equipment.

SAFETY VALVE   - PRESSURE ACCUMULATION TEST:

1. Safety valves are to be set under steam and tested with pressure accumulation tests in the presence of the Surveyor.
2. The boiler pressure is not to rise more than 6% above the maximum allowable working pressure when the steam stop valve is closed under full firing condition for a duration of 15 minutes for fire tube boilers and 7 minutes for water tube boilers.
3.During this test, no more feed water is to be supplied than that necessary to maintain a safe working water level.
4. The popping point of each safety valve is not to be more than 3% above its set pressure.

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References: 

marineengineeringonline.com

www.marineinsight.com

www.youtube.com

Marine Engineers' World (Facebook)

Starting & Stopping : ( Boiler -- Water Tube)

This article we will explain starting and stopping boiler during normal and emergency working conditions.

Precautions on Starting Boiler

Before start-up of the boiler plant, following general work and check procedures must be considered.

·         Check that the main steam valve, by-pass valve and circulation valves if provided scum valve, and blow-down valves are closed.

·         Open the feed water valves and the air valve. Fill the boiler with feed water to approximately 50 mm below normal water level. The water level rises due to expansion when the boiler is heated. If the temperature difference between the boiler and feed water exceeds approximately 50ºC, the boiler must be filled very slowly.

·         When filling a pressure less boiler, the shut-off valve after the feed water pump must be throttled. Otherwise the pump motor will be overloaded.

·         Check the water level in the water level gauges. Check frequently during the complete start-up. The water level gauges should be blown down several times to ensure a correct indication.

·         Check that the water level control system is connected and operational.

·         Check the oil system and start the fuel oil supply pump. Pre-heat the fuel oil if the burner should operate on heavy fuel oil.

·         Check the burner and the safety functions according to the manufacturer instruction.

Points to note while starting a boiler from cold condition :( with no super heater)

·         Check that the boiler is properly closed-up (especially after repairs).

·         Check (physically) that all appropriate valves are shut or open for safe starting of the boiler.

·         Boiler water filled to slightly below normal level.

·         Starting treatment chemicals may now be added to the boiler water.

·         Check and clear the furnace of any flammable materials.

·         Ensure that the boiler uptake passage is clear.

·         Pre-purging of furnace for a specified amount of time is necessary to clear the gas-side of flammable gases, to avoid a starting explosion!

·         On a cold boiler, the firing-up must not be speed up too much in order not to over strain the boiler material unnecessarily by quick, uneven temperature raises.

·         Keep the boiler vents open until a heavy steam jet is flowing out (until a boiler pressure of about 1 bar is reached).

·         Before the boiler is put on load, blow-through the gauge glasses, test the safety valves using easing gear and try out the safety cutouts.

Starting Boiler and Pressure Rise

1.      The following work procedures must be followed during start-up of the boiler.

2.      Check that the gauge board valve and pressure gauge valves are opened.

3.      Check that the air valve is open if the boiler pressure is below 1.0 bar.

4.      Check the water level & others parameters are normal.

5.      The forced draft fans should be started to purge the system to remove any trapped exhaust gases or oil vapors

6.      Start the burner on manual control and on low load. Check that the water level does not rise too high during the pressure rising period.

7.      If the air valve was opened close it when only steam blows out. A pressure reading should be indicated on the boiler pressure gauge before the air valve is closed.

8.      Tighten all covers such as manholes, hand holes, inspection doors, etc. during the pressure rising period. If required, check all flange joints on the plant.

9.      Change to automatic control of the burner when the boiler pressure is 0.5 bar lower than the working pressure of the boiler.

10.  Open the by-pass valve slowly to heat-up and pressurize the steam system. If the boiler is not provided with a by-pass valve, the main steam valve should be used to heat-up and pressurize the steam system.

11.  Open the main steam valve and close the by-pass valve.

12.  Open the valves to the steam consumers carefully in order to avoid water chocks.

13.  When the boiler is in normal operation, check that the water level control system and the gauge board functions are fully operational.

Stopping Boiler

Normal boiler shut down

If necessary, the boiler can be shut down at any load without special preparations.

When the boiler is stopped, sudden temperature and pressure drops should be avoided as they might expose mountings, pipe lines, and the boiler plant to inadmissible temperature gradients.

1.      When minimum load is obtained, stop the burner.

2.      Keeps the water level at normal level until the boiler stops producing steam.

3.      Stop the feed water pump and close the feed water valves.

4.      Close the main steam valve.

Emergency shut down

The boiler must be taken out of service immediately if parts of the heating surface have been glowing or the boiler shows recognizable deformations.

The supervising authorities must be informed, and the boiler must not be used until approval from these authorities is available a substantial loss of water is noted the feed water system is unable to provide the necessary amount of feed water, e.g. due to failure of parts the safety valve cannot function sudden cracks or damage are noted in the refractory, and if steam or moisture is coming out of the refractory oil in the feed water is detected too high salinity level is detected.

If an emergency shut down must be carried out, the fuel supply should be stopped. The main steam valve should be closed gradually, and the boiler must be cooled. The safety valves must not be operated. Parallel working boilers should be disconnected at once.

Stop for repair or inspection

The following describes the measures to be taken when the boiler is shut down for repair or inspection.

1.       Clean the boiler from soot with water.

2.       Operate the burner for at least 15 minutes after the soot removal to dry out the remaining water.

3.       Stop the boiler as mentioned previously.

4.       Check the furnace and the pin tubes with regard to cleanliness.

5.       Empty the boiler from water and clean it. Check if lime stone appears.

6.       Check and clean the outer fittings. Change gaskets where required.

7.       Clean the feed water tank and feed water pipes.

8.       Clean and grease the bearings of motor, pump, and fan.

9.       Check and align the burner, if necessary.

10.   If the boiler is shut down for a long period of time, the pin tubes must be thoroughly cleaned.

11.   Check that the necessary spare parts are available. Order complementary parts in time.

It is of extreme importance that the boiler is NOT operated without water when the oil burner is in operation, e.g. due to disconnection of the water level safety devices. This will immediately cause complete breakdown of the boiler.

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 Reference:

1. brighthubengineering.com

2. marineengineeringonline.com

3. Manual (AALBORG INDUSTRIES)

4.  Marine Engineers' World (Facebook)

5. Bangladesh Marine Academy

Questions & Answers (Boiler) Part-1

1. What is boiler?

It is a pressure vessel in which the water is heated to evaporate and generate the steam and the unit is so arranged that the generated steam accumulated in it.

2. Types of boiler:

          A. Water Tube Boiler

          B. Fire Tube Boiler.

3.Types of boiler by pressure:

1. Low pressure boiler up to 10 kg/cm².
2. Medium pressure boiler 10 to25 kg/cm².
3. High pressure boiler over  25 kg/cm².

4. Explain the difference between fire tube & water tube boiler.

                          Difference between water tube & fire tube boiler

Water tube boiler	Fire tube boiler
1. Water flows through the tube.	1. Water flows around the outside of the tube.
2. Hot gasses pass around the outside of the tube	2. Hot gas passes through the tube.
3. Lighter in comparison with capacity	3. Robust 8 heavier.
4. High pressure & high capacity	4. Less pressure & less capacity.
5. Complex, cleaning difficult	5. Simple, easy maintenance
6. More efficient	6. Less efficient.
7. Distilled water to be used.	7. Normal water to be used.

5. What are the advantages & disadvantages of water tube boiler?

Advantage of water tube boiler: 

·                     Lighter.

·                     Simple to construction

·                     Safer.

·                     Efficient over 85%, Hence reduce fuel consumption.

·                     Steam can be produced within shorter time.

·                     Greater evaporation rate.

·                     High pressure and temp. steam is produce.

Disadvantage:

           1) Little reserve of water and steam in the boiler, so efficient control of water level is required.

           2) the high rate of heat transfer across those tube walls together with small bores required positive circulation of water.

          3)The small bore tubes demand  pure feed condition to prevent scale formation which could lead to blow and over heating.

          4)The thin tubes give little resistance for corrosion, Cleaning difficult.

6. What are the functions of steam drum?

    (a) steam separation, 

    (b) steam-water circulation and 

    (c) purifying steam.

7. What is the function of super-heater?

Super-heater is used to super heat the steam and get higher thermal Efficiency of the plant.

8. Why large boilers are top supported?

        (a) avoid buckling of furnace walls, 

       (b) allow thermal expansion and 

       (c) reduce thermal loads.

Q. Name of Aux. boiler Mounting & major parts:

1) Main steam stop v/v (non return type)
2) Two safe v/vs.
3) Two gauge glass
4) Air vent cock.
5) Feed check v/v (non return type)
6) Automatic feed water regulator. (Not mounting)
7) Scum blow down v/v.
8) Blow down v/v (non return type).
9) Salinometer cock / sampling cock.
10) Man-hole door.
11) Mud-hole door
12) Pressure gauge connector.
13) Root v/v for level indicator.
14) Root v/v for pressure gauge glass.
15) Circulating p/p suction v/v
16) Soot blower.  (Not mounting)

9. Sketch a vertical auxiliary boiler

Save the images for clear view.  

10. Feed check v/v: (Short Note) 

Pair of non return valves, one main and other auxiliary v/v fitted with stop/close indicator. Double shut off reduces the risk of boiler water leakage into the feed water line and if the feed water line fractures or a joint in the line blows then boiler contents will not be discharged out.

11.Main steam stop v/v: (Short Note) 

Main steam stop v/v is fitted on top of the boiler and connected with the main steam pipe-line. It is usually screw down non return type v/v. Its purpose is to isolate the boiler from the main steam line.

12. Safety v/vs :  (Short Note) 

Safety v/vs are fitted to a boiler to prevent boiler over pressure. At least two safeties must be fitted to a boiler. Safety values should be capable to release all steam, the boiler can produce without raising the pressure by more the 10% over a set valve.

13. Where air vent cock is located and its purpose?

The air vent cock is fitted at the top of the steam space of the boiler.

Its purposes are-

1. To release air from the boiler either filling the boiler water or raising the steam.

2. To allow air to enter in the event of boiler cooling down or blowing down .( to prevent vacuum effect)

14.Boiler safety devices :

1} Safety valves (Two)

2} Low / high water level alarm

3} Too low water level alarm and shut down

4} Water level indicators

5} Pressure gauge

6} Low fuel oil pressure alarm

7} Low / high fuel oil temperature alarm

8} Flame failure alarm

9} Smoke density alarm

10} Easing gear arrangement

11} Air vent

12} Force drought fan stop alarm

13} Low / high steam pressure alarm

15. Why we need to blow down the gauge glass?

Gauge glass blow down is made to know the boiler and gauge glass connection is clear or not. And to give the exact water level in the boiler.

16. Boiler gauge glass blow down procedure:

1} Shut steam and water cocks than open the drain cock.

2} After draining water from the sight glass,if nothing comes out, both steam and water cocks are good in order.

3} Open the steam cock side, blow out the steam.

4} Close the steam cock side, the steam connection is clear.

5} Open the water cock side, blow out the water.

6} Close the water cock side, the water connection is clear.

7} Close the drain cock.

8} Open the water cock, water should then gradually come rise up to the top of the gauge glass.

9} Open the steam cock, the water in the glass should fall to the level of the water in the boiler.

Note: Working position - all cocks handle are in downward position.

17. Why we need to blow down the boiler water?

Boiler blow down is made to reduce the density of salt and to remove the dissolved and suspended solids, also the floating solid impurities in the boiler system.

If these are not removed from the boiler water system, foaming, priming, corrosion will occur in the boiler steam space and feed water system.

18. What check should be carried out on a boiler during watch?

1. Steam pressure & temperature.
2. Boiler water level.
3. Blow down gauge glass.
5. F.O. Pressure and temp.
6. Check the flow gas temp.
7. Check the flame shape.
9. Feed water press and temp.
10. Feed water regulator
11. Check safety level devices.
12. Cascade tank water level and temp.
13. Observation tank check for oil.
14. Condenser sea water outlet temp.
15. Check any leakage of valves.
16. Blow down the boiler
17. Soot blow

19. Alarm fitted in boiler system.

1. Steam press, high / low.
2. Boiler water level high/low.
3. Flame failure
4. High salinity.
5. Fuel temp. high or low

20. Indication of soot blow is done.

1. Shoot will come out through the funnel.
2. If steam is used for soot blowing steam press. Will suddenly comedown.
3. Exhaust back press will reduce.
4. Exhaust gas outlet temp at the uptake (after the EGB) will reduce because of boiler heat transfer.
5. After soot blow is finished within short time steam press will come up.

21. Why do you perform scum blow down and bottom blow down?

Scum blow down ( surface blow down):

To remove accumulated, suspended and floating solids, impurities and also remove dissolved solid concentration, they hinder the formation of steam.

Bottom blow down: 

To remove suspended solids and residual sludge that have settled at the bottom.

If these contaminants are not removed regularly they will build up until they hinder the

circulation patterns.

To be continue................. 

Reference:

1. Bangladesh Marine Academy

2. Hand Notes of Mr. Min Zar Tar

3. Manual Book: AALBORG MISSION OM 1200

4.Marine Engineers' World (Facebook)

Questions & Answers (Boiler) Part-2

22. Explain why water testing is essential in boiler water management?

1. To prevent scale formation in the boiler & feed water system. 

2. To prevent corrosion in the boiler & feed water system.
3. To control the sludge formation & prevention of carry over with the steam.
4. To prevent entry of foreign matter such as oil, waste, sand copper particles, iron oxide in the boiler.

23. Test carried out on feed water of a low pressure aux boiler: 

Ph Test: 

Reason:
To determine the ph value i.e. the degree of acidity or alkalinity of the water.

Procedure:
· A litmus strip is submerged in the sample water.
· Color of the strip change accordingly to the condition of the water.
· Blue color indicates alkaline & Red means acidic.
· The degree coloration compared against the datasheet to indicate the possible range of ph value.
Alkalinity test:
Reason: To ensure about alkaline condition of the sample.
Test for P-alkalinity:
100 ml of boiler water is taken as a sample.
10 drops of phenolphthalein is added, then sample will twin in pink color.
N/50 sulfuric acid is added to clear the sample.
Calculation: ml of N/50 acid used X 10 = PPM CaCO3.
Test for total alkalinity:

1. P-alkalinity test is taken. 
2. 10 drops of methyl orange is added, result yellow coloration. 
3. N/50 sulfuric acid is added until it turn to pink. 

Calculation: ml of N/50 acid used for both test x 10 = PPM CaCO3.
Chloride test:
Reason: To measure the chloride value to make an indication of sea water leakage in feed water system.
Test:

1. 100 ml of boiler water taken as sample. 
2. 10 drops of phenolphthalein is added sample will turn into pink 
3. N/50 H2SO4 is added to clear the sample. 
4. 2ml of H2SO4 is taken again. 
5. 20 drops of potassium chromate indicator is added. 
6. N/35.5 Silver nitrate solution is added until a brown coloration results.

Calculation: ml of N/35.5 solution used x 10 = P.P.M. Cl.
Phosphate test:
Reason: To determine the amount of phosphate content as a reserve. 

Test:
· 25 ml filtered boiler water is taken as a sample.
· 25 ml vanadomolybdate reagent is added.
· Comparator tube is fitted with this solution z is placed in night hand compartment of the comparator.
· A blank prepared by mixing equal volume of vanadomolybdate reagent and demonized water is placed in left hand compartment
· At least three minutes is allowed to develop the color then compared with disc.

Calculation: Phosphate reserve in P.P.M from the disc reading. 

24. How feed water treatment keeps the boiler scale free?

1) By using distilled water.
2) By keeping the hardness salts in suspension in the solution, to prevent scale formation.
3) By stopping the suspension salt and impurities from sticking on the heat transfer surface.
4) By providing anti foam to prevent water carry over.
5) By eliminating dissolved gases and providing some degree of alkalinity to prevent corrosion.

25.Enumerate the boiler water test

1. Alkalinity test

• a. Phenolphthalein ( p) alkalinity test
• b.Total ( T ) alkalinity test (2 x P)

1. Chloride test
2. Condensate PH test
3. Amerzine test ( Hydrazine test)
4. Excess phosphate test
5. Conductivity test (Total dissolve solids test)
6. Hardness test

26.Purpose of Boiler water test?

1. Alkalinity test:

This is to ensure that the boiler water prevents corrosion by neutralization of acidic gases.
(a) Phenolphthalein ( p) alkalinity
This test is carried out to prevent acidic corrosion.
(b) Total ( T ) alkalinity test
To determine the amount all of hydroxide, all of the carbonate, and two thirds of the phosphates.
Note: Hydroxides and carbonates can co-exist together in a solution but hydroxides
and bi-carbonates can not.
2. Chloride test

1. To know the amount of salt in boiler water.
2. To minimize chloride level and to adjust the blow down.

3.Condensate PH test

1. To control condensate PH value within a limit. 
2. To minimize corrosion in steam and condensate system.

4. Amerzine test ( Hydrazine test)

1. To test for dissolved Oxygen content ****
2. To know reserve hydrazine (N2H4) ppm and to prevent corrosion and aeration.
3. To minimize oxygen pitting and corrosion in boiler, steam and condensate system.

5. Phosphate test

1. To control the scale formation due to hardness (presence of Phosphate in sample means no hardness salts).
2. A reserve of phosphate should be maintained in the boiler water ready to neutralize any hardness salts which may enter.

6. Conductivity test

1. Measure of the total amount of dissolved solids (T.D.S) including the treatment chemicals. (Excessive density leads to priming and or deposits)
2. To remove dissolved and suspended solid by blowing down.

7. Hardness test

1. To check for salt causing "hardness"
2. Hardness test of boiler water are not necessary when the phosphate is above the lower limit of the control range.

27. Describe the correct procedure of blowing down boiler water (partial blow down).

Blowing down procedure of boiler (partial blow down)

1. Put notice
2. Take permission from the port authority if the ship at port.
3. At first close all the steam requirement v/v to purifier, F.O tanks etc.
4. Wear proper clothing.
5. Blow down the gauge glass by taking feed water in the boiler.
6. Stop the water p/p and keep it to normal mode.
7. Maintain sufficient pressure in the boiler.
8. Stop firing of the boiler.
9. Cutoff the F.O system of the boiler.
10. Keep one person standby near the gauge glass.
11. Ensure that the ship side v/v outside of the ship nobody is working or no fishing boat is there.
12. First open the ship side v/v fully.
13. Remove the scum by scumming.
14. Finally crack open the boiler blow down v/v to avoid thermal shock & water hammering.
15. Keep eye on gauge glass.
16. Close the blow down v/v & then ship side v/v before low water level of the boiler.

28. Significance of regular blow down:

1) To reduce the water level in the boiler to prevent carry over or priming.
2) To reduce corrosion.
3) To remove sludge or mud from the boiler.
4) To reduce solid particles.
5) To reduce the dissolved solid.
6) To reduce oil by scum blow down.
7) To reduce chloride.

29. What is foaming in boiler and how to prevent it ?

It is the formation of thick layer of steam bubbles on the top of the water surface inside the boiler due to:

1. High concentration of impurities.
2. By the animal or vegetable fats in feed water carryover from the oil heaters.
3. Increase in level of dissolved & suspended solid TDS level.
4. Increase in water level.

To prevent foaming , surface or scum blow down should done frequently to expel any floating impurities for the boiler and no lube oil should be allowed to enter the boiler.

30. What is boiler priming and how to prevent it ? 

It is condition in which large amount of water are carried along with the steam into the steam line.
It is caused by:

1. Excessive foaming 

2. Improper amount of steam space 

3. By a sudden rush of steam such as is produced when steam stop valve is suddenly opened.
To prevent priming: 

1. Never keep the water level too high.
2. Open steam stop valve slowly.

31. Why are boiler manholes elliptical in shape?

The boiler manhole-lids are mounted from the inside of the boiler so that the boiler pressure will help to keep them tight. Hence the manholes have to be elliptical in shape to make it possible to take the lid out from the boiler.

32. Describe the procedure followed to raise steam from a cold boiler.

Procedure to raise steam from a cold boiler:

1)            Wear proper clothing.

2)            Ensure all piping involving water; steam and fuel are in order.

3)            Make sure that uptake cover is removed safety v/vs are in order.

4)            Ensure boiler plant in operational order.

5)            Shut main steam stop v/v.

6)            Take water to the boiler at 1/4 rd of the gauge glass.

7)            Blow down the gauge glass to check it.

8)            Check the F. O. tank temp & system.

9)            Make sure that air vent of steam drum and super heaters are open.

10)          Start the blower to make the combustion chamber gas free.

11)          Start the boiler F.O. circulating p/p/ booster p/p.

12)          Inject the fuel and light up the burner.

13)          According to the manufacturer warm up the boiler by continue firing for 5 minutes every half an hour.

14)          Take personal safety from back fire.

15)          Shut the vent of steam drum when white steam come out.

16)          Ensure the sufficient quantity of water is available in boiler.

17)          Take normally 18-24 hours for complete operation.

18)          Thus the boiler is ready for work.

32. What action will you take in case of foaming and priming?

1. Scum blow down.

2. Reduce boiler fire rate.

3. Check whether boiler chemicals added are in excess.

4. Detect the source of contamination.

5. In case of bad priming the boiler may have to be taken out of service, shut down.

6. For contamination due to oil have to be chemically cleaned.

33. Boiler blow down procedure ( cool down):

1. Change the fuel oil burning system from HO to DO and then shut down the burning system.
2. Stop feed pump close feed check valve.
3. Drain down the boiler after allowing it to cool down.
4. If no sufficient time to do this, lower the boiler pressure to 3 to 4 bar.
5. Shut the main steam stop valve.
6. Open the ship side valve then open the blow down valve.
7. Banging noise will appear when boiler is empty.
8. Close the boiler blow down valve and ship side valve.
9. Then release the steam pressure through safety vlv by means of easing gear.
10. When pressure is off, open the air vent and the boiler to cool down.

34.Describe the maintenance procedure of a cascade tank.

Maintenance procedure of cascade:

1. Changing the filter periodically which protects the boiler system from any                   contamination.
2. Maintaining the cascade tank water level.
3. Maintain the water temp. around 600C.
4. Maintaining the correct operation of flat v/v.
5. Keeping clean the tank and sight glass.
6. Always supply clean drain return to the cascade tank.
7. Always drain the tank for scum out.
8. Tank should be covered to prevent entry of any dirt or foreign matters.
9. Tank surface should be scale and deposit free.

35. 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.

1. Mechanically 
2. Chemically. 

• Mechanically it is done by de-aerating equipment. 
• Chemically add chemical to boiler water such as sodium sulphite or hydrazine. 2Na2SO3+O2 = 2Na2SO4 

        N2H4 + O2 = 2H2O + N2

36. Prevention of acid corrosion: 

Acid corrosion occurs due to magnesium chloride & carbon dioxide with continuous supply of dissolved oxygen (MgCl2, CO2) in the boiler water.

• This can be prevented by lime (Ca(OH)2) and soda ash (Na2CO3) & scavenging the oxygen. 

MgCl2 + Ca(OH)2 = Mg(OH)2+CaCl2 

CaCl2 + Na2CO3 = CaCO3 + 2NaCl

37. Opening up and Inspection Procedure

After making sure no vacuum in it, Then---
1. To remove top man hole door, slacken the dog holding nuts but do not remove them until first broken the joint.
2. Remove nuts and dogs and take out the door.
3. The bottom door can be removed after warning personnel to keep clear of the top door.
4. Make ventilation before entering. Do not allow naked light near the boiler.
5. Preliminary internal inspection carried out before cleaning, to check scale deposits and any special points.
6. Plug orifice to blow down valve to prevent choke, place guards over the manholes landings to prevent damage.
7. Carried out cleaning and internal works.
When all works completed, a full internal examination must be carried out:

1. Cleanliness, all openings are clear, water level gauge connection clears from deposits.
2. All internal pipes and fittings have been replaced correctly and securely attached.
3. Remove plug from the blow down valve orifice.
4. The face of manhole doors and landings inspect to clean and undamaged).
5. Replace manhole doors by using new joints.
6. Operate all boiler mountings. Open air vent cock and fill the boiler with water to sufficient level.

38. How external and internal treatment of boiler feed helps to reduce the scale formation inside the boiler? 

Scale is formed inside the boiler due to presence of salts in the feed water. This scale formation can be reduced by reducing the content of salt. 

This is achieved externally by:
- Using evaporated fresh water or evaporated sea water.
- Proper filtering of feed water.
- Maintaining the correct feed temp.
- De-aeration.
Internally this is done by:
- Ensuring a chemicals reserve dissolved in the feed water in the boiler.

39. How do take action if gauge glass showing low water level?

If water level has not yet dropped completely out the sight glass, water may be put into the boiler.
If water drops completely out of sight glass, check another sight glass, if both disappear water; do not add water until the boiler is cool enough to prevent any possible damage due to rapid cooling of over heated plate.
1. The fire must be immediately stopped.
2. The main steam stop valve must be closed.
3. Blow down and cool down the boiler.
4. Check leakage, drum outside, Located the cause of trouble and make necessary repair.
5. Enter the boiler after it has cooled and examined any possible damage.
6. After repair, water fill up slowly and restore to normal operation.
7. If no damage occurred, inject the water slowly into the boiler and restore it to operation.

40. What are the possible causes if gauge glass shows no water?

1. One gauge glass defective.
2. Boiler tube crack and leaking.
3. Feed regulator jammed.
4. Fail feed pump (Air in feed water line or pump).
5. Level controller malfunction.
6. Steam consumption is too much.

References: 

1. Marine Engineers' World (Facebook)

2. Bangladesh Marine Academy 

3. Hand Notes of Mr. Min Zar Tar

4. Manual Book: AALBORG MISSION OM 1200

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