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13th February 2019 2. OPTIMIZATION OF WASTE HEAT AND CLOSED FEED SYSTEM With the ever increasing costs of oil fuel there is an increasing need to optimize on the use of available waste heat from main engine exhaust gases. This is particularly adaptable to large ships powered by slow speed Diesel engines having powers over 10000 KW. In such engines the mass flow of the gases is sufficient to power a turbo-alternator sufficient to supply the full electrical sea load. By this process the overall efficiency of the power plant i considerably increased. Auxiliary steam turbines: Auxiliary steam turbines are used in turbo-generator sets and also for cargo pump and fan drives. Power outputs vary up to about 1.5MW for generator sets. The single cylinder turbines can be arranged horizontally or vertically. Both condensing and back pressure turbines have been used, being designed for steam conditions ranging from about 6bar to about 6.2 bar at 5100C. Turbo-generators are also fitted in many motor ships in conjunction with waste heat recovery schemes, based on using the exhaust from very large and powerful slow-speed diesels. Diesel engine builders have developed engines with greater powers in response to the ship owners demand and also in competition with steam turbines, for propulsion. Diesels are now used almost exclusively for modern ships. Only for liquefied gas carriers where the gas boil- off can be burned in the boilers, steam turbines are still being installed.

Closed feed system :- (Fig.60) The closed feed system ensures that air is eliminated from the feed system so that air does not enter the boiler. This ensures that air and oxygen are eliminated from the feed water, thereby preventing corrosion of the boiler internal steam and water space. The extra feed needed is taken into the regenerative condenser, where air within the condenser is being continuously being removed by the three stage air ejector. The water from the condenser is extracted by the condensate pump and utilised to cool the drains from gland steam and feed heaters and in exchange is heated as it enters the feed pump through the feed filters. Further heat is added to the feed by the feed heater. Steam for feed heating is taken from

the steam bled from an intermediate pressure stage of the turbine. Feed heating is used to maximum advantage, thereby improving plant efficiency.

Advantages of superheating steam :- In the operation of steam turbines it is essential that the steam is superheated to an optimum condition such that the steam temperature at the superheater outlet is lower than the exhaust temperature at the superheater tubes region sufficient enough to transfer the heat from the exhaust gases to the superheated steam. The main advantages are : (1) Increase in overall plant thermal efficiency (2) The dry condition of the steam prevents erosion of the turbine blades .

3. Function 4 Oral Questions:-

(1) What are the advantages of the closed feed system.

(2) State the advantages of superheating.

3. TYPICAL EXAMINATION QUESTIONS WITH ANSWERS (1)Question(2) S.NO 1EKG2014:- (a) Describe the procedure to be adopted for the inspection of a safety valve fitted to an exhaust gas fired auxiliary boiler stating,with reasons, which parts should receive particularly close attention. (b) Describe the procedure for setting of safety valves of exhaust gas fired auxiliary boilers. (c) Explain the action taken after the setting of safety valves as in(b).

Answer :- (a)With the safety valves completely dismantled , the following parts need close inspection. (1) Valve spindle:- generally inspect the spindle for any damage particularly cracks on the surface. Particularly check for bends if any and this can be done by verification of trueness by centering on the lathe. (2) Springs:- the permanent set or deformity can be checked by comparing their heights with the spare spring on board. Springiness may be checked by bouncing them on the floor. Ring the springs to detect for any cracks. (3) Valve and valve seats.;- Check the valve and valve seats for any indentation or grooving marks. If so the valves and valve seats will need machining. Valve and valve seat need lapping with very fine emery paste or jewellers rouge since they very rarely come into operation. (4) Valve chest, spring casings and covers:- Check for cracks by tapping

them and listening to the metallic sound. (5) Compression nut:- Try the compression nut on the cover and check

for radial and axial play. (6) Check the drain from bottom of chest is clear, as well as the connecting pipe up to scupper is clear. (7) Other parts require close inspection for deformity and cracks. (b) The valves have to be set as soon as the ship moves into full -away mode and the boiler is pressurised by the heat of the exhaust gas from main engine. The valves should be assembled without the caps and easing gear. The

procedure is as follows :- (1) Keep the steam stop valve from the exhaust gas boiler shut. This will enable the steam pressure to be built up fast(2) One of the valves should be gagged using gagging tool (3) When the pressure comes up to the set value listen to the hissing sound from the valve as steam is escaping. If not slightly slacken the compression nut till sound is heard. (4) Change over the gagging tool to the other valve and repeat the same operation with this valve. (5) When both have been set go outside and observe the flow of steam from waste steam pipe, which must be a full flow. Come to the boiler platform and note the steam pressure on boiler. It should show a slightly higher pressure than set value. The important point is that the pressure shown on the gauge is steady and not fluctuating . It should also be understood that the set value can have an error of + or - 3%.

Refer to the boiler manual for the safety valve set pressure. This pressure is normally about 0.5 kg/cm2 lower than the auxiliary boiler working pressure. The exhaust boiler may now be connected to the steam range or connected to the steam space of the auxiliary boiler as the case may be. (c) The exhaust gas boiler safety valves cannot be set by the class surveyor when the ship is sailing, hence this activity is delegated to the chief engineer to be carried out. A documentary proof has to be provided to the class to update their records. Hence the chief engineer should send a letter to the office to be forwarded to class stating that the exhaust gas boiler safety valves have been set to the pressure as per the manual. A copy of this letter will be forwarded to the class. (2)Question (8) EKG S. NO1 2014:- Describe how the following conditions can be avoided in auxiliary boiler (a) Furnace distortions. (b) Uptake fires (c) Difficulty in maintaining normal level.

Answer:- The main cause of furnace distortion is overheating of the furnace, making it sufficiently malleable to deform according to the stress direction. Over heating can be caused by shortage of water in extreme conditions. It can also be caused by heavy scale formation on the water side adjoining the furnace plating, since scale is a bad conductor of heat leading to overheating and subsequent distortion Overheating is avoided by ensuring that the gauge glasses are in optimum condition by maintaining them ie by regular

blowing of the glasses so that no conditions of false readings and difficulty in reading the levels is avoided. Overheating by scale formation is avoided by regularly testing the boiler water and ensuring the treatment is in accordance to the standards stipulated for the type and pressure range of the boiler. Uptake fires :- Uptake fires in forced circulation economisers are caused by accumulation of oily soot in the spaces between the tube fins which being saturated with oil will catch fire by a burning piece of soot from the engine exhaust. When the main engine is running at full power the excess air supply is enough to aid the fire started and will continue till all the accumulated soot is burnt. Such fires are avoided by regular use of sootblowers where provided. Apart from this periodical water washing of the economiser must be carried out since just soot blowing is not sufficient. Difficulty in maintaining normal water level.:- In auxiliary boilers on motor ships where steam usage is limited maintaining safe water level in the boiler is not difficult since usage of heating steam is limited and does not vary very much, provided the feed controllers are working satisfactorily and the gauge glasses are in good condition. In steam ships using water tube boiler whose water storage capacities are limited, high variations of water level do occur caused by variations in steam demand for the main turbines during manoeuvring. The feed controllers are not able to sense the changes required at the rate the changes occur and this difficulty leads to a condition o f ‘shrink’ equivalent to low level and ‘ swell’ high level. To overcome these difficulties modern boilers are fitted with sensitive controllers using proportional plus integral controllers. (3)Question(1) Sno (2) EKG 2014 :- Sketch and describe a boiler water level controller of the

float operated type. State the reasons for having this mechanism on the boiler and using the controller and boiler for analogy explain the following terms: (a) Detecting element (b) Servomotor (c) Desired value.

A feed controller of the float type is as sketched above. (Fig.61) This controller controls the speed of the pump by a variable resistance in the current supplied to the pump motor. The variation in resistance is controlled by the float . When the difference in the water level is low in the boiler the command signal is difference between the desired value(half level in float chamber) and the actual level in the boiler. When this

difference is high the resistance is cut out or reduced so the motor turns faster bringing up the level quickly. When the actual level in the boiler is higher than the desired level in the boiler the resistance increases slowing down the pump or in the extreme condition the motor stops because the current connection is cut off. This is the principle of operation of the controller. This type of controller is a proportional plus integral controller. The desired value is the half level in the float chamber corresponding to half the gauge glass level. The amplifier is the adjustable rheostat which controls the current. The detecting element is the float. (4)Question (2) S no (2) EKG 2014:- Discuss the causes of corrosion and the means by which corrosion of the following may be limited by manufacturers and ship’s personnel respectively: (a) Internal and external surfaces of auxiliary steam lines. (b) External surfaces of auxiliary boilers. (c) Water boxes of seawater coolers and condensers. (d) Main sea water inlet pipes.

Answer:- (a) The internal surfaces of steam lines are affected by air corrosion caused by condensed water remaining inside with air, when the steam is shut off. Corrosion is caused by a warm and moist atmosphere within the pipes. Hence the pipes should be internally coated with a good polymer paint which is coated over the galvanized surface. To maintain this surface in good condition , it is the function of the ship’s staff to ensure that the lines are drained properly when not in use. The external surfaces are to be coated with a strong heat resistant primer paint and then properly insulated and further protected by metal cladding to protect the

insulation. The function of the manufacturer / fabricator is the internal coating and external coating as well as the insulation. When pipes are renewed the ship staff should ensure that the pipes are properly protected in the manner stated above. (b) The external surfaces of auxiliary boilers are to be coated with at least two coats of good quality heat resistant paint and then covered with an adequate thickness of insulation. The insulation is further protected with steel cladding of at least 3 mm thickness with binding steel straps. This is the job of the manufacturer. The ship staff function is to ensure that during boiler surveys followed by repairs the damaged portions of the insulation are properly restored. (c) The internal surfaces of water boxes are coated with atleast two coats of bitumastic slow drying anti corrosive paint and further fitted with adequate size of zinc slab to prevent galvanic corrosion. This is the job of the manufacturer when the cooler or condenser is new. Subsequently during service when cooler boxes are opened by ship staff for cleaning, they should ensure that the boxes are restored to the same standard as mentioned above. (d) Main sea water pipes leading from the sea chest to the sea filter and up to the intermediate valve are internally coated with a thick layer of good quality polymer paint by the manufacturer when the ship is new. Subsequently during every dry-docking it is recommended that ship owners follow this procedure if sea water pipes are to last longer.

Question(1) S no X (EMER) 2014:- Sketch a high lift safety- valve lid and seat detailing their special features. Describe how such valve is overhauled and any clearances that should be measured and noted.

Method is as follows: The easing gear cable is disconnected from the easing gear. The easing gear is dismantled by opening the lever bearing keeps. The cotters connecting the caps to the spindles are removed after opening their locking devices and the caps taken out. Note position of both compression nuts by counting the counting the number of exposed threads and noting the same for future reference when assembling the valves.

Unscrew both compression nuts to relieve the springs of their compression. Dismantle the top cover along with compression nuts. Dismantle the Bonnet holding nuts and take out the bonnets along with spindles, springs, spring plates and attached valves. The valves can be dismantled from the spindles . the valves are in complete dismantled condition for inspection Inspection of parts:- The inspection of the parts and suitable corrective action is as follows: The spindle should be checked for any bends and this can be verified exactly by centring and truing on the lathe. The springs should be checked for any deformity or permanent set and this can be done by comparing their heights and also comparing with the spare spring. Springs should be renewed if they are deformed or permanently set. The compression nut should be tried on the cover and checked for radial and axial play. If the nut is slack it should be renewed. Check the valve and valve seat for any cuts or ridges. Normally such defects do not occur since the valves very rarely open due to excessive pressure The valve requires light lapping using jeweller’s rouge. Ensure the drain hole and connecting drain pipe to the funnel scupper are both clear. The inspection being completed and suitable corrective action taken, the valves can be assembled after survey and compression nuts tightened to the original settings, The caps and easing gear will be assembled after he valves are floated(set) by the surveyor. The clearance normally measured is the compression ring clearance for setting the valve before final floating of the valves. However there can be situations where the valve and/ or valve seat are damaged by groove formation. The

valve and/or valve seat will need machining to remove the groove. This operation will alter the lip clearance and hence the lip clearance has to be measured. The method to find the altered lip clearance is not directly possible using a feeler gauge. Hence an indirect method is used whereby 4 lead balls made from lead wire available on board for clearance measurements is used. The balls are placed in four locatons under the lip as shown in the sketch (Fig.63) and compressed by the valve using the spindle , cover and gagging tool. The 4 balls are then taken out and their thickness measured using a vernier gauge. The average thickness is obtained which is the existing clearance. Assume this clearance is 2.7 mm. This clearance is to be increased to 3.2 mm which is done by adequately machining the valve lip accordingly

(5) Question (5) Sno X EKG 2014:- Sketch suitable welded joints indicating the approximate plate thickness dimensions, preparation for the following purposes: (a) End plate connection to the shell of an unfired pressure vessel. (b) Longitudinal seam of an unfired pressure vessel. (c) Prefabricated combustion chamber for an auxiliary boiler.

The details of the welding preparation showing penetration allowance and edge preparation are as per classification rules conforming to double “Vee “ uniform bevels standard of welding joint. (Fig.64) (6) Question (6) S no 1 EKG 2013 :- With reference to boiler feed water regulation : (a) Describe, with aid of sketches, the operation of a boiler feed water regulator controlled by at least two other parameters besides the water level in the drum.

(b) Give reasons for the inclusion of other elements besides the water level in controlling feed flow. (c) Deduce the possible effects on the system when the drain valve on the constant head leg in the level transmitter starts to leak. Answer:-

(a) There element control gives the highest value of performance. Feed flow is compared to steam flow for the correct 1: 1 ratio. If the ration is incorrect then an out of balance signal is given to the controller. Drum level again acts as a trimming device on a wide proportional band with integral action. Three element actions are illustrated in Fig.65 (b) The reason for including the other elements steam flow and level is to make the feed controller sufficiently sensitive to prevent the effects of “shrink ”and “swell” Which occur during manoeuvring periods. (c) If the drain in the constant leg of the level transmitter leaks, the level seen in the level indicator

will be false and erroneous because of the steady leakage from the constant head leg.

(7)Question(3) S no3 EKG 2013 :- Discuss with reference to the super heater outlet temperature of a main boiler operating at a constant load, the following statements: (a) An increase in excess air will tend to cause a decrease in super heater outlet temperature due to the cooling effect of more air being introduced. (b) A decrease in economiser inlet temperature will tend to cause a decrease in super heater outlet temperature due to the cooling effect of more water being introduced. (c) Badly fouled generating tube banks will cause an increase in the super heater outlet temperature. (d) Excessive amounts of total dissolved solids in the boiler water will cause variations in the super heater outlet temperature.

Answer:- (a) This statement is not entirely correct. If the combustion is not optimal, then excess air helps in improving the combustion thereby increasing the combustion temperature thereby increasing the flue gas inlet temperature to super heater. But if the combustion is in optimum condition, the excess air supplied for combustion will reduce the resultant temperature of combustion due to increase in mass flow of air which becomes the inlet temperature of flue gases to the super heater.

(b) This statement is not correct, since the boiler is supplying wet steam at the corresponding generated pressure which is constant. If feed inlet emperature is lower more fuel oil will be consumed to make up to the required saturation temperature of the water in the boiler. (c) This statement is not correct. Badly fouled generator tubes will not entirely convert all the water to steam and this results in lower dryness fraction of steam generated. The higher temperature of flue gas at super heater is utilised to completely dry the steam before the steam is superheated to the required temperature. (d) This is not entirely true. Total dissolved solids are not carried with the steam during evaporation, but settles inside the boiler, thereby increasing the density of the boiler water. At the same time there is a small carry over of solids with the steam during evaporation because of the wetness of the steam. In general it may be accepted that there is an increase in scale deposition on super heater tube internal walls causing a decrease in heat transfer resulting in slightly lower superheat temperature (8)

Question(1) S no x-3 EKG 2013:- (a) State the standing instruction you, as second engineer would issue with

respect to the action to be taken in the event of a boiler uptake fire. (b) State how the incidence of uptake fires may be minimized (c) State the reasons for blow back from the furnace of an auxiliary boiler.

(d) State the standing instruction you, as second engineer, would issue with respect to the avoidance of boiler furnace blow back.

Answer:- (a) STANDING INSTRUCTIONS: (1) An uptake fire is recognized by the sounding of the uptake

temperature alarm. (2) When this alarm is sounded and recognised. Go to the Fiddley deck or upper platform where the forced circulation exhaust gas economiser is located, feel the casing plates or observe if the paint is blackening indicating existence of a fire. (3) Confirm from Bridge if any flame or sparks leaving the economiser

uptake. (4) Slow down main engine, inform C/E and 2/E, and stop M/E.. (5) stop circulation pump to economizer 6) Start boundary cooling of economiser casing plates. (7) When sufficiently cool , open inspection door on casing plate to for

inspection. (b) Incidence of uptake fires may be minimised by regularly water washing the finned tubes in the economiser every six months or annually. Thisis to be done apart from the regular usage of sootblowers if provided. (c) The reasons for furnace blow back from auxiliary boiler are: (1) Purging of air insufficient.

(2) Water in the oil causing steam lock in the oil and making flow

discontinuous and subsequent blow back. (3) Oil overheated causing gas lock and subsequent blow back. (d) STANDING INSTRUCTIONS for avoidance of boiler furnace blow back: (1) When starting the boiler combustion system, start on manual mode

so that long air purge can be given (2) Ensure the fuel oil is sufficiently heated and this may require circulating the oil through the heater sufficiently till the oil temperature reaches the right temperature. (3) Ensure the fuel oil is free of water and this can be verified by operating the spring loaded drain valve on the oil service tank and ensuring the oil is free of water. (4) Change over to auto-mode only when steady state conditions are achieved. (9)Question(3) S noX-3 EKG2013:- With regard to the safety valves fitted to a boiler: (a) (1) State why an easing gear is fitted. (2) Discuss the conditions under which easing gear may be used. (3) state any precautions that may have to be taken during the use of easing gear. (b) Explain why corrosion occurs in wet steam lines and in condensate systems.

Answer:- (a) (1) An easing gear is fitted to a boiler to manually open the valves in

emergency conditions. (2) The conditions under which the easing gear is to be used are: (a) In case the valves are struck and the Pressure has reached a dangerous level, the easing gear must be used to relieve the excess pressure. (b) If it is confirmed that the water level in the boiler is dangerously low or high after blowing through the gauge glasses, the easing gear must be used to avoid a dangerous situation. (c) The precautions to be observed are that the following operations

have also to be carried out: (1) The fire or burner should be switched off. (2) The feed pump or the feed check valves should be stopped/shut. (3) The main steam stop valve shut. (b) Corrosion occurs in wet steam lines because of air and moisture existing in steam pipe lines when the steam lines are shut, causes air corrosion or corrosion caused by oxygen. Hence steam lines must be thoroughly drained of condensed water when they are not in use and the drains kept shut so that no air enters the lines. This is also applicable to condensate lines. (10)Question(1) S no 4EKG 2012:- A fire in the exhaust gasboiler on a motor ship may develop in two or three stages . With reference to such situations, discuss: (a) The factors which could be a cause for initiation and development of : (1) Ignition of soot. (2)Small soot fires.

(3)High temperature (b) State the standing instructions you, as second engineer officer would issue with respect to the action to be taken in the event of a boiler uptake fire.

Answer :- The spaces between the fins in the finned tubes of the exhaust boiler are thickly covered by oily soot having accumulated there for a considerable period. This oily soot when heated up by the exhaust gas during full service speed of the engine causes the oil to vapourise and form a halo around the fins. With the engine operating at service speed the excess air supply and its high temperature (3500C) are favourable to start ignition of the soot. All it needs is a flying cinder to ignite the oil vapour –air mixture. This is the genesis of a soot fire. (2) The soot adhering to the fins catch fire and this is the initiation of a soot fire. (3) As the fire develops onwards by burning the accumulated soot the temperatures reached are high and capable of burning and melting the thin walled fin tubes allowing water in circulation through the tubes to leak out. The leaking water quickly converts to steam because of the excessive heat of the fire, the steam gets superheated to a very high temperature when it disassociates into hydrogen and oxygen. The liberated hydrogen feeds the soot fire which now intensifies into a high temperature fire also named hydrogen fire. (b) STANDING INSTRUCTIONS: (1) An uptake fire is recognized by the sounding of the uptake

temperature alarm. (2) When this alarm is sounded and recognised. Go to the Fiddley deck or upper platform where the forced

circulation exhaust gas economiser is located, feel the casing plates or observe if the paint is blackening indicating existence of a fire. (3) Confirm from Bridge if any flame or sparks leaving the economiser

uptake. (4) Slow down main engine, inform C/E and 2/E, and stop M/E. (5) stop circulation pump to economizer (6) Start boundary cooling of economiser casing plates. (7) When sufficiently cool, open inspection door on casing plate to for

inspection. (11)Question (1) S no 9 EKG 2012 :- (a) Discuss the possible reasons for the following changes in boiler water test results and state what action should be taken in each case. (1) Reduction of total dissolved salts and chemical reserves. (2) Reduction in phosphate reserve, with increase in chlorides and total dissolved solids. (3) Reduction in alkalinity reserve only. ) Increase in oxygen levels only

(b) State why the complete results of boiler water tests are logged or entered into data retrieval system rather than a note being made of any particular result which may be outside set limits. Answer:- (1) The only possibility for the reduction in TDS and chemical reserves is that there can be some

tubes leaking by which the water from the boiler is escaping to ythe atmosphere along with dissolved salts and chemicals. Hence the reduction in chemical reserves also. It is wrong to assume water can leak to the sea as this can happen only in the most rarest occasion when all the three valves namely the boiler blow down valve, the intermediate valve and the shipside blow down valve are all leaking at the same time. (2) Reduction in phosphate reserves and increase in chlorides can occur when sea water enters the boiler most probably through leaky condenser tubes or a priming fresh water generator. (3) For only alkalinity reserve to reduce indicates that oil is leaking into the boiler caused by oil finding its way into the boiler through leaky steam heating pipes in oil tanks. Oil combines with caustic soda to form a soapy emulsion and this method is used for chemical cleaning of the boiler water space if contaminated by oil. (4) Increase in oxygen levels can occur if air finds its way into the condenser through leaky drains or exhaust pipes on the low pressure side of the steam system. This defect is restricted only to closed feed system where air from the feed water is removed by the deaerators and air ejector fitted to the condenser, which is operating continuously under vacuum.

Remedial action :- (1) The leaky tubes can be found out during a routine smoke side cleaning activity and the defective tubes suitably plugged. (2) The water boxes of the dump condenser should be opened up. The tubes should be cleared of mud using a suitable cane rod and then brushed with a nylon rotary brush. The tubes should be checked for leakage by filling fresh water in the condenser steam space

through inspection door of steam space and the leaky tubes can be found out from the two end tube plates by water falling out of the leaky tubes. The leaky tubes are plugged by wooden plugs made on board. F/W generator is priming, this will Cause the salinity alarm to sound. Priming may be caused by lower vacuum indicating defect in the air ejector ventury. This may need to be changed. (3) The defective steam heating pipe in the oil tank must be identified by testing the drains from the return pipes leading to the observation tank. The defective steam pipe in the oil tank should be suitably repaired (4) The defective exhaust pipe or drain should be identified and suitably

repaired. If the air ejector is faulty it should be suitably repaired (b) Boiler water test results change gradually considering the mass of water in boiler as well as the mass of water in circulation and makeup. Hence the results are to be observed on a regular basis and hence the need for data logging. (12)Question(1) S no 6 EKG 2012:- Describe how you as, as second engineer, would prepare an auxiliary boiler for survey by a classification society. Answer:- To carry out the survey the boiler has to be blown down completely according to the blowing down procedure. After blowing down and before commencing the cleaning operation the boiler must be safely isolated to prevent any accidents occurring and for this the steam outlet connection to the main steam line must be blanked using a strong spoon flange at the connection to the main steam manifold. Similarly the common feed line must be blanked to prevent

accidental entry of feed water in the boiler under survey. These precautions are necessary to be observed in ships where there are two or three boilers connected to a common steam manifold. Cleaning procedure:- The boiler’s fire side smoke side and water/steam side have to be thoroughly cleaned and made free of all deposits so that the bare metal surface is exposed. In water tube boilers rotary descaling heads mounted on a flexible shaft is very effectively used for descaling the internal surfaces of the water tubes where scaling occurs. In smoke tube boilers the external surfaces are descaled manually. In small package boilers where entry into the boiler is not possible, chemical cleaning or descaling is done by warming up the boiler with a very weak acid solution which loosens the scale and breaks it. The scale collected is flushed out. All the 10 listed mountings are dismantled, overhauled and surveyed. The furnace lining is suitably repaired by renewing broken bricks, the fire cement wherever cracked is suitably excavated and fire cement mortar mix made and filled up.

(13) Sno9 EKG 2012:- with reference to auxiliary boiler safety valves: (a) Describe with the aid oif a sketch, the safety valve for an auxiliary boiler. (b) Identify, with reasons, the parts that require particularly close attention during overhaul. (c) Describe how the safety valves are reset after an overhaul, ensuring no feathering.

Answer:- (a) The sketch given below is a ordinary spring loaded high lift safety valve as fitted in marine auxiliary boilers. This valve gives uninterrupted constant lift of D/24 and is suitable for low pressure auxiliary boilers. The lift of the valve is resisted by the spring

compression which can be set to lift to the required pressure.

(b) With the safety valves completely dismantled, the following parts need close inspection. (1) Valve spindle:- generally inspect the spindle for any damage particularly cracks on the surface. Particularly check for bends if any and this can be done by verification of trueness by centering on the lathe.

(2) Springs:- the permanent set or deformity can be checked by

comparing their heights with the spare spring on board. Springiness may be checked by bouncing them on the floor. Ring the springs to detect for any cracks. (3) Valve and valve seats :- Check the valve and valve seats for any indentation or grooving marks. If so the valves and valve seats will need machining. Valve and valve seat need lapping with very fine emery paste or jewellers rouge since they very rarely come into operation. (4) Valve chest, spring casings and covers:- Check for cracks by tapping

them and listening to the metallic sound. (5) Compression nut:- Try the compression nut on the cover and check

for radial and axial play. (6) Check the drain from bottom of chest is clear, as well as the connecting pipe up to scupper is clear. (7) Other parts require close inspection for deformity and cracks. BOILER SAFETY VALVE SETTING PROCEDURE: 1) A Gagging tool is used alternatively on the valve to prevent simultaneous lifting of the valves at the set pressure. 2) Use the standard boiler gauge brought by the surveyor if the boiler pressure gauge is not calibrated. 3) Remove the caps keep the valve spindle of one valve (port) gagged. The other valve will be se first (stbd). 4) Keep the compression nut screwed down, on the valve to be set, till the previous marks.

5) Raise steam pressure slowly and bring pressure to set pressure. 6) A slight hissing sound will be heard. This is the floating condition of the valve. In this condition the valve will sit on its seat by slight pressure on the spindle with the palm of the hand and will not come back unless tapped.

7) Reduce pressure, remove gagging tool and fit out the other valve. Repeat above operation on this valve for setting. 8) When both valves are set remove gagging tool. Fire the boiler at maximum capacity. Note full flow of waste team from waste steam pipe. Note pressure on gauge. The pressure should not exceed 10% of the set pressure. On satisfactory completion of setting, refit caps, cotters, locks and easing gear. Test easing gear and following safety alarms and cut outs: - (a) H.P cut off and alarm (b) Low water alarm and cut off (c) High water alarm and cut off

NOTE:- For purpose of answering in the examination the sketch reproduced from Reed’s vol 8 may be drawn. (Fig.70)

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Question(1) S no X-MG EKG 2010:- A rating has been badly burnt by a “Blow- back” from the oil fired auxiliary boiler. As second engineer make a full report to Head office explaining the circumstances of the incident and the precautionary means now taken to reduce the possibility of a similar occurrence in the future. Answer:- To The Engineering superintendent, British petroleum, LONDON (UK) Subject :- Accident report. Dear sir, I wish to report on the accident which occurred yesterday the 15th October 2012 at the port of Glasgow where we were discharging crude. There was a request from the chief officer for inert gas as the inert gas pressure in the tanks had fallen down. Accordingly the fourth engineer started the combustion equipment on the auxiliary boiler on manual mode after taking due precautions and having given a long purge of air through the furnace. The ignition relay was defective as the arcing was not sufficient for the oil to ignite. He therefore intended to dismantle the arcing contacts to have them cleaned and while dismantling the contact Oil under pressure leaked out of the burner tip and caused a blow back. The rating who was assisting the fourth Engineer was in the path of the flame and the flame hit his chest scalding the skin of his chest. The rating was immediately escorted out of the machinery space, given first aid and sent to the local hospital on the port ambulance. He is out of danger and recovering and we hope he will join the ship at the next port. This accident could have been avoided if a safety interlock was provided between the arcing relay and

solenoid fuel stop valve and to be doubly safe a stop valve fitted between oil fuel pump and solenoid valve. I suggest you issue a suitable fleet notice on this incident with instructions that whenever any work is being carried out on the oil fuel burner, especially during boiler operation, the fuel system must be completely shut off to prevent any such incidents. Yours faithfully, Second Engineer.

NOTE :- Most of the candidates answer with the concept of improper purge causing blow back. Normally blow back due to improper purging can be violent causing rupturing of the air register. In the case mentioned above the blow back need not be violent but strong enough to burn an individual because the air register is partly opened to deal with the arcing contacts. (15) Question (7) Sno9 EKG 2011:- With regard to keeping the gas side of boilers in good condition discuss each of the following : (a) The mechanism of combustion stating the factors which are important to good combustion. (b) Oil fuel treatment. (c) Soot removal equipment.

Answer :- (aWith reference to the combustion of oil fuel, the mechanism of combustion is the chemical process by which the constituents of the oil fuel are burnt completely. Oil fuel is a blend of residual fuel and some diesel oil to reduce the viscosity of the mixture. The constituents are carbon, hydrogen and sulphur (limited to about 4.5%). Sufficient excess air is required for god combustion, whereby the oxygen in the air will chemically combine with the elements to form their oxides and in this process heat is liberated to heat the water in the boiler.

Combustion Equipment :- Good combustion is essential for the efficient running of the boiler, it gives the optimum heat release and the minimum amount of deposits on the heating surfaces. To ascertain the quality of combustion observe the following and grade the combustion as stated : If colour of smoke at the funnel is black, the colour of the flame seen through the observation glass is red with a smoke fringe, the quality is poor--- lacks air for combustion. If colour of flame is golden or orange and colour of smoke seen at the funnel is, it indicates bad combustion---over excess air for combustion. If colour of flame is amber and the smoke is colour less with a haze, indicates good combustion. Quantitatively when the combustion is good, the percentage of carbon- di-oxide in the flue gas by volume is between 12 % and 14%. Condition of burners, oil condition pressure and temperature, condition of air registers, air supply pressure and temperature are factors which can influence combustion. Burners:- If these are dirty, or the sprayer plates are damaged, then atomisation (spray) of the fuel is affected. Oil:- If oil is dirty , it can foul up the burners . Filters are provided on the oil supply lines , but these can get dirty or damaged. Ideally the last filter should have its mesh size smaller than the diameter of holes in the burner. Water in the oil can affect combustion, it could lead to the burners getting extinguished and a dangerous situation arising. It could also produce panting which can result in structural damage of the air register.

If the oil temperature is too low the oil does not readily atomise since its viscosity is high. This could cause flame impingement, overheating , tube and refractory failure.

If the oil temperature is too high the burner tip becomes too hot and excessive carbon deposits can then be formed on the tip causing spray defects. These could again lead to flame impingement on adjacent refractory and damage could occur on the air swirlers.

Oil pressure is also important since it affects atomisation and length of spray jets.

Air Registers :- Good mixing of the fuel particles with the air is essential, hence the condition of the air registers and their swirling devices are important. If they are damaged air flow will be affected. Air:- The excess air supply is governed by air pressure and if this is incorrect, combustion will be bad. (b) The oil fuel treatment does not suggest any chemical additives, but the need for proper filtration purification and heating to the correct temperature to give the required viscosity for good atomisation which in boiler oil combustion refers to length of spray.

(c) In order that the heating surfaces of any boiler, both smoke and water tube types, may be kept clean, and the boiler thus be constantly available for service in an efficient condition, it is imperative that in addition to off-load cleaning, it is periodically soot blown. Deposits are formed in all gas passage when burning any fuel, and the high ash contents of the heavier fuel oils can be troublesome unless efficient soot blows are installed and correctly operated.

Soot blowers are fitted in suitable positions so that all the heating surfaces, tubes, superheaters, economisers and air-heaters can be maintained in clean condition, provided, of course, that the equipment is properly maintained and regularly operated (usually every twelve hours).

The cleaning operation is performed by jets of high-pressure steam or air, the jets being caused to move

through an arc while in operation, so that they cover all parts of the heating surfaces.

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Question (9) S no 9 EKG 2011:- Explain why regular testing of water of auxiliary boilers is advisable. State what actions are necessary when measured values appreciably differ from desired values in each test. Give an interpretation of the situation when both alkalinity and chlorinity are found to have changed considerably.

Answer:- Regular testing of boiler water is essential for following reasons: (1) To ensure that the corrective action by chemical dosing or flash blowing

the contents are having the desired results. (2) To ensure and detect any contamination of seawater into the boiler or air contamination in closed feed systems (3) To ensure that the reserves such as alkalinity, phosphates and sulphites (in closed feed systems) are all within their limits (c) When measured values differ from acceptable standards, a corrective action chart is to be referred and suitable action taken accordingly. This chart is reproduced. (d)

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Question(1) S no 11 EKG 2011:-You have recently joined a vessel as second engineer officer. For the past several voyages it has been the practice on board to dispense with the use of the exhaust gas boiler and leave it to run dry. As part of an overall economy drive the company has requested you to re-commission the boiler. Write a letter to the superintendent engineer stating

how the boiler was brought on line and the safety valves adjusted. Answer:- From the question it is to be assumed that the exhaust gas boiler is a forced circulation exhaust gas economiser. In a dry bulk carrier about 1 to 1.5 tons /day is the normal consumption per day when the boiler is operated on oil fire. This oil can be saved during sea steaming. REPORT In accordance with your instructions we have today commissioned the exhaust gas boiler and the procedure adopted is as under. Washing procedure:- The casing covers were opened and the wash tray fitted in place. Using the fire hose and sea water connected to the hydrant in engine room, the finned tubes were thoroughly hosed with sea water till the fins were cleared of all the oily soot which had caked in between the fins of the tubes. A final hosing down with fresh water was carried out to rinse the tubes of any salt adhering to the surface of the tubes. Testing procedure :- The casing plates were fitted with new joints and the drain valve on the wash tray kept shut. Fresh water was filled to the top of the tubes through the inspection door in the casing plate. The inspection doors on the water and steam boxes were opened. Four tubes were found leaking, which were plugged using brass taper plugs made on board. Before fitting the casing doors finally, a leak test was carried out by circulating water from the boiler back to boiler using the circulating pump and no leaks found. Commissioning and floating the safety valves:- The ship left the port of Durban on 20th October 2012. When full away was rung, the engine speed raised to the full sea load condition. The safety valves were already overhauled and fitted without the easing gear for setting of the valves. The port valve was kept

gagged ready for setting. When engine speed came up to the full sea load condition, the pressure was rose up quickly inside the steam box as the steam stop valve was kept shut. With slight adjustment of the compression nut the valve was set at the pressure of 6.5 bar as recommended in the manual. The gagging tool was transferred to the starboard valve and the operation repeated. The flow of steam through the waste steam pipe noted and the accumulation of pressure was only 0.1 bar. The easing gear of the valves connected and the safety valves are now in operational mode. The boiler is not being fired now. For your ready reference the cleaning and testing rig is shown in sketch.

(18) Question EKG s NO 3 2007:- Give a description of an automatic soot blower system for a water tube boiler. Show on a diagram the layout of the system and the order of the operation you could expect the blower to follow. Answer :- The automatic sootblower is normally fitted on large water tube boilers of steam turbine driven ships. These sootblowers are air pressure operated. The use of air for soot blowing reduces the incidence of corrosion of the smoke side casing plates and tube

surfaces unlike steam sootblowers which cause wet steam to deposit on the surfaces leading to corrosion.

SOOTBLOWER CONTROL: The sootblower system utilises air for both control and blowing. Operational rotation of the blower head is achieved by means of an air piston ratchet mechanism. The sequence of operation is governed by the distributor operated by a similar air piston ratchet mechanism. The supply air to both pistons comes from the pilot valve whose operation is dependent on the charging and discharging rate of the air reservoir. Adjustable control orifices are provided entry to reservoir (charging) and on the atmosphere line (discharging). Each impulse or air puff blast rotates both ratchet gears by one tooth and gives a blowing blast for a few seconds.

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`Question (2) S no 9 MEP 2013 (a) Describe three different patterns of tube used in exhaust gas boilers. (b) Give two reasons why a tube is condemned.

(c) Describe how it is replaced by a spare tube. (d) Suggest with reasons the possible consequences of allowing an exhaust gas boiler to run dry, during full power operation of the main engine.

Answer :- (a)

he above sketches show three types of tubes used in composite boilers using waste heat from exhaust gas. SINUFLO type :- These are sinuous shaped tubes which improve heat transfer by retardation and being corrugated in shape are not thermally stressed since they are free to expand with increase of temperature. The corrugations are placed horizontally when fitting

them to avoid accumulation of soot in the troughs formed if the corrugations are placed vertically. SWIRLUFLO type:- The tubes are made with three lobes, the tubes are then twisted to give a helical pattern, whereby three helical paths of flow for the gases is obtained thereby increasing the retardation and thereby better heat flow. PLAIN TUBES WITH STRIP RETARDERS :-These are the oldest types of tubes made efficient for heat transfer by strips of steel twisted plating which give a helical path for the smoke flow and improve heat transfer. When cleaning the tubes the retarders are pulled out and replaced after the tubes are brushed out. (b) (1) A tube is condemned when it is fractured or develops a leak by being holed (2) a tube is condemned when the tube ends are corroded caused by fretting action because of faulty tube expansion or by forcing the boiler during warming up. Refer to sketch given below.

(c) In the case of a holed or leaky tube, the tube is cut at both ends after the tube plate in the water space and taken out of the manhole. The tube stubs are collapsed by grooving them with a half round chisel and then collapsed and drifted out. No flame cutting should be used for removing the tube stubs as that could burn the tube hole surface in the tube plate. The stubs collapse easily as the tubes are very ductile with a

carbon content of 0.1 % carbon. The tube holes in the tube plates are polished using emery paper so that all the burrs and material sticking on the surface are removed and the surfaces are polished to take in the new tube end. The tube is inserted as it is not tight fitting, adjusted in length and the extra portion cut off. This extra portion is then tested by collapsing it on a bench vice till the external diameter is reduced to half the original value. The surfaces at the longer ends are then examined for cracks. If surface cracks appear, the tube is rejected and another tube is taken for fitting. The tube is placed ends aligned and expanded using the tube expander. Modern tube expanders use an air motor to turn them so the work of tube expansion is speeded up. When replacing tubes damaged at the ends, the tubes are removed in the same manner as explained above. The holes on the tube plate are built up by welding using compatible electrodes and the operation carried out by class approved welder. Before fitting in a new tube the holes which have been built up must be reamed to remove the burrs. The procedure for fitting the new tubes is the same as stated above. (d) The maximum temperature of the exhaust gas at the exhaust boiler is 3500C, whereas the temperature of steel when metallurgical changes take place is 6000C. hence no damage can occur to the tubes if run for short periods in this condition. Damage occurs only when cold feed water is taken into the boiler in such conditions by thermal stressing. The boiler must be sufficiently cooled before taking in water. (20)Question (3) S no 12 EKG 2011:- Sketch and describe a suitable burner which can be used on gas and oil in a boiler of a LNG ship. Enumerate the normal attention required on such burners.

Answer:- his burner proved satisfactory in service and is still being fitted in some new installations, although for larger outputs but burner shown in figure has been developed. In this later type of burner the gas is introduced by means of ‘spuds’ or ‘Pokers’, and the oil and atomising steam via the central gun. The registers are of the axial flow type with slides operated pneumatically and turn- downs of 15:1 on oil and 5:1 on gas are normal, the latter being dependent on the available gas pressure. The firing equipment is to be of combined gas and oil type and be capable of burning both fuels simultaneously. The gas nozzles are to be so disposed as to obtain ignition from the oil flame which is to be present under all conditions of firing. A mechanical interlocking device is to be provided to prevent the gas supply being opened until the oil and air controls are in the firing position. Each burner supply pipe is to be fitted with a gas shut-off cock and a flame arrester unless the latter is incorporated in the burner. An audible alarm is to be provided giving warning of loss of minimum effective pressure in the oil fuel discharge line or failure of the fuel pump.Answer:-

(21)Question (4) S no 4 EKG 2011 :-An auxiliary boiler water level control system has a differential transmitter as the detecting element for water level. (a) Sketch and describe such an arrangement.

(b) If the transmitter was damaged, describe how a replacement unit would be calibrated.

Answer:- (a)

This level sensor could be used for a boiler level controller. Steam condenses in the reservoir maintaining a constant level therein. The pressure difference h acts on some form of differential pressure device (it could be a diaphragm type) which varies an air pressure signal which in turn would be used in a

control system. A balance leg is provided in order to avoid extreme pressure differences on the differential pressure device in the event of one of the terminal valves on the boiler being closed.

(b) When a new transmitter is to be fitted, it is calibrated taking reference from the level seen in the gauge glass. Normally the desired value will be half gauge glass.