Contents
1.Question.Sr 4 2009 ... 5
State why compressor suction and delivery valves should seat promptly. ... 5
2.Question.Sr 1 2011, ... 7
Sketch a static oily water separator intended to handle large-quantities of heavily contaminated water. Label the principal components, how the internal arrangement of sub-division, baffles and fittings, indicate the direction of fluid flow in all parts; and - ... 7
(a) Describe how it operates. ... 7
(b) Give two reasons why oil might be carried over the water. ... 7
(c) How the level of oil separated is controlled? ... 7
3.Question.Sr 12 2010 ... 11
With reference to tubular heat exchangers explain: ... 11
a. how differential movement between tubes and body is accommodated when the tube plates are rigidly located in the body. ... 11
b. how and why turbulence is imparted to fluid flow through the tubes ... 12
c. why it has become possible to discard sacrificial anodes ... 13
d. what is meant by the term 'guided flow', with particular reference to oil heaters ... 14
4.Question ... 14
Sketch and explain the parts of a shell and tube type lubricating oil cooler showing how the oil and water flow path and material for each part ... 14
Explain how expansion and contraction of the tube stack of the cooler is accommodated ... 14
5.Question. ... 17
Draw line diagram of a feed water system for an auxiliary boiler, labeling all the principal items and showing the direction of flow. ... 17
Explain how water level to the boiler is regulated? ... 17
Indicate how the risk of oil contamination may be reduced. ... 17
6.Question ... 25
(i) In plate type heat exchanger, fluid press. & temp, do not normally exceed 10 bar and 150°C respectively. ... 25
(ii) Titanium & stainless steel finding increasing acceptance, ... 25
(iii) Carrying bar & clamping bolts are often much larger than pack thickness. ... 25
(iv) State how it can be ascertained that plate stack is correctly tightened and the likely result of excessive tightness. ... 25
7.Question ... 27
Describe the checks you would make while taking over a E\R. watch at sea ... 27
Under what condition would you refuse to ... 27
Take over ... 27
Hand over ... 27
8.QuestionSr 8 2006 ... 29
With regards to keeping the gas side of a boiler in good condition discuss each of the following ... 29
The mechanism of combustion stating the factors which are important for good combustion .... 29
Fuel oil treatment ... 29
Soot removal equipment ... 29
9.Question ... 32
Describe the following conditions are prevented in auxiliary boilers ... 32
Feed contamination by oil heating coil drains ... 32
Internal corrosion ... 32
Furnace blowback ... 32
Uptake fire ... 32
With reference to hydraulic deck machinery: ... 37
(a)State the sources for contamination of the system; ... 37
(b) Describe possible effects due to contamination, ... 37
(c) Explain how the oil can be monitored by ships staff. ... 37
11.Question ... 39
Name method of F.W. generation on board ship ... 39
Sketch and describe any one method what treatment is give to render it fit for drinking ... 39
12.Question. ... 43
(a) For Freon-22 vapor compression refrigeration machine, state how each of the following faults arc indicated and how they arc remedied; ... 43
(i) Air in the system ... 43
(ii) Moisture in the system ... 43
(iii) Undercharge ... 43
(iv) Overcharge ... 43
(b) Describe with a diagram detailing the devices incorporated into the refrigeration system to protect the machinery and equipment against malfunction. ... 43
13.Question ... 49
Describe the boiler fuel burning system and indicate the effect of the following ... 49
Air supply insufficient ... 49
Air supply excessive ... 49
Presence of water in oil ... 49
Excessively high oil temperature ... 49
14.QuestionSr 3 2009, ... 52
Explain the operation of automatic self cleaning centrifuge. Detailed sketches should be used for your explanation. Labeling principle component and indicating directional flow of all fluid. .... 52
Explain how dam ring contribute to efficient centrifuging with reference to oil of different specific gravity. ... 52
15.QuestionSr. No. 4 APRIL 2007 ... 57
(a) Draw a line diagram of the engine room section of a bilge system for a passenger or cargo vessel including the connection of oily-water separator; label the principal items. ... 57
(b) State-... 57
(i) What type of valves are fitted in the bilge system and why? State the material of construction of the valves. ... 57
(ii) The means used in passenger vessel-to reduce flooding risk by way of bilge system in the event of collision, ... 57
(iii)The type of pump ideally used to discharge through the oily-water separator. ... 57
16.Question ... 61
Sketch an automatic sprinkler system for combating fire in passenger spaces on a ship and state – ... 61
(a) The safety devices incorporated in the system. ... 61
(b) How the system is charged? ... 61
(c) The parameters governing the volume of the pressure tank. ... 61
(d) Means provided to prevent the passage of seawater into the pressure tank. ... 61
17.Question ... 65
With reference to electro-hydraulic steering gears: ... 65
Explain in terms of control parlance the function of the "Hunting gear" ... 65
Explain the consequences if the standby pumping unit is motored; ... 65
State TWO methods employed to prevent the standby hydraulic pump being motored by the operating unit ... 65
18.QuestionDEC, Emergency set 2006... 68
Explain why each of the following features is considered desirable for air compressors: ... 68
(a) A single-throw crank for a multi-stage compressor; ... 68
(b) Minimum clearance volume; ... 68
(d) Generous size of suction filter ... 68
19.QuestionSr 11 2008, ... 71
State why each of the following are fitted to ships steering gear system ... 71
Brake or locking devices. ... 71
Shock buffer relief valve. ... 71
Steering gear stops or cut-outs. ... 71
Rudder stop. ... 71
Describe the routine testing of steering gear... 71
20.QuestionEmery 2007-2008 ... 73
What is the purpose of a fusible plug on an air receiver and at what temperature is it designed to melt. ... 73
What inter locks are there on the starting air system ... 73
What is the pressure of a starting air receiver? ... 73
Explain how would you start an air compressor and stop it after overhaul. ... 73
What safety devices are fitted to a start air line? ... 73
1.Question.Sr 4 2009
State why compressor suction and delivery valves should seat promptly.
If a suction valve does not reseat promptly at the end of the suction stroke, due to a weak spring or due to carbon deposit, part of the air drawn into the cylinder will be returned through the defective suction valve during the first part of the delivery stroke.
If a delivery valve is slow in reseating, for the same reason, part of the air compressed and delivered during the delivery stroke will return to the cylinder during the first part of the suction stroke.
Explain the effect on the compressor if the air induced into the cylinder at a temperature higher than normal.
The higher the temperature of the air drawn into the cylinder, the less will be the weight of air discharged by the compressor in a given time, since the higher the temperature of the air the greater will be the volume occupied by a given weight.
What would be the effect of the suction valves having too much lift?
The valves would be late in closing and this would reduce the volumetric efficiency of the machine.
Valves with too much lift reach the end of their travel with greater force and therefore are more liable to break.
Explain why pressure relief device are fitted to the water side of cooler casing.
Relief v/v to protect against over pressure on air side
If the valve was not fitted and should a tube fail in the intercooler or after cooler, then the cast iron compressor casing would be subjected to the pressure of the air at that particular stage. Failure of the casing could occur which, in the past has caused serious injury and death.
2.Question.Sr 1 2011,
Sketch a static oily water separator intended to handle large-quantities of heavily contaminated water. Label the principal components, how the internal arrangement of sub-division, baffles and fittings, indicate the direction of fluid flow in all parts; and -
(a) Describe how it operates.
(b) Give two reasons why oil might be carried over the water.
Operation of the Simplex Turbulo Separator
The unit is first completely filled with clean water, the oily water mixture is men pumped into the coarse separating compartment Depending upon the type of oil to be separated, heating coils are often incorporated to assist me separation process, particularly if the oil is highly viscous and dense) In the coarse separating compartment some of the oil due to the density differential will separate and rise into an upper collection space. The oil / water mixture then flows down into the fine separating compartment moving slowly between the catch plates. The oil separates from the water onto the underside of the plates and travels outwards until it is free, where it then rises upwards and into the upper collecting space.
The oil that gathers in the collecting space is discharged by an automatic dump valve controlled by a capacitance type level detector, into an oil storage tank.
The water remaining in the separator at this point is has an oil content of approximately 100 ppm, the water now passes through into the second stage coalescer unit
The coalescer unit causes the surface tension of the oil droplets and the water to breakdown resulting in the small globules of oil to join together forming larger globules. The large globules of oil rise upwards into the upper oil collection space where it is then manually drained to the oil storage tank- Due to the smaller volume of oil in this unit the drain off is much less frequent than in the first stage of the separator.
The remaining effluent will now have an oil content of less than 15 ppm and can therefore be legally discharged overboard The effectiveness of the operation is continuously monitored for oil content and should the designed throughput of the system be exceeded the overcarried oil will be detected and an alarm will activate, shutting down the unit
After the pumping of bilges is complete the unit should be shut down and drained, then flushed through with fresh water so as to recover all the oil. It also leaves the separator clean for the next time it is used and so reducing the risk of contamination on start up. Flushing through will also minimise the risk of corrosion.
Some systems have the overboard valve fitted below the level of the separator unit, in which case it is possible for the contents of the separator to be siphoned overboard it is therefore usual to have an anti-vacuum valve fitted to the highest point in the overboard discharge line. This valve must be regularly inspected and maintained to ensure its correct operation
Oil catch plate of primary column damaged.
Strainer between primary and secondary column clogged or damaged. First stage filter element in secondary column damaged or heavily clogged.
AUTOMATIC CONTROL OF OIL DISCHARGE
It is effected by means of a vertical capacitance probe in the top of 1st stage vessel, the probe being normally salt water finding. When oil completely surrounds the probe, altering its capacitance, it energises the solenoid of the pilot valve which in turn opens the oil valve. This causes a partial loss of pressure in the vessel and the water valve will close. On completion of oil discharge the capacitance of the probe will again alter to de-energise the pilot valve solenoid and so close the oil valve, when the pressure will build up again and the water valve will open. An alarm probe is fitted to warn of an oil build up should the control system malfunction.
The water discharge from the 1st stage enters the 2nd stage at the bottom and passes vertically through a coalescer bed or filter. The coalesced up oil is removed from the top of the vessel and the water discharge to the 3rd stage.
The 3rd stage is similar to the 2nd stage, where further coalscing takes place, oil goes on top and removed. The water discharge from this stage can be passed overboard after monitoring.
3.Question.Sr 12 2010
With reference to tubular heat exchangers explain:
a. how differential movement between tubes and body is accommodated when the tube plates are rigidly located in the body.
One plate is fixed at one end whereas the tube plate at the other end is free to move with the expansion of the tubes.
The tube stack is fitted with alternate circular disc and ring baffles made of brass to give radial flow to the fluid and also supports the tube stack.
The fixed end tube plate is sandwiched between the shell and water box with jointing material. Synthetic rubber 'O' rings for the sliding tube plate permit free expansion.
If the joints leak at the face end, special tell - tale hole indicates leakage and the 'tell - tale' ring will allow the liquids to escape without mixing.
The toroidal expansion joint in the center of the shell accommodates differential thermal expansion between the tubes and the shell.
Baffles are used in shell and tube heat exchangers to direct fluid across the tube bundle. They run perpendicularly to the shell and hold the bundle, preventing the tubes from sagging over a long length. They can also prevent the tubes from vibrating. The most common type of baffle is the segmental baffle. The semicircular segmental baffles are oriented at 180 degrees to the adjacent baffles forcing the fluid to flow upward and downwards between the tube bundle. Baffle spacing is of large thermodynamic concern when designing shell and tube heat exchangers. Baffles must
be spaced with consideration for the conversion of pressure drop and heat transfer. For thermo economic optimization it is suggested that the baffles be spaced no closer than 20% of the shell’s inner diameter. Having baffles spaced too closely causes a greater pressure drop because of flow redirection. Consequently having the baffles spaced too far apart means that there may be cooler spots in the corners between baffles. It is also important to ensure the baffles are spaced close enough that the tubes do not sag.
b. how and why turbulence is imparted to fluid flow through the tubes
Turbulence is beneficial in a heat exchanger, because it rotates particles of the liquids so that they tend to break up the boundary layer and remove heat by direct contact with the heat transfer surfaces.
A second advantage of turbulent flow, is that the scouring action tends to keep cooler surfaces clean.
Disadvantages
The price for the benefit of turbulence along a heat exchange surface is that at tube entrances, or the entry area between pairs of plates in plate type coolers, the turbulence is more extreme and damage from corrosion/erosion occurs. This type of attack is termed impingement.
c. why it has become possible to discard sacrificial anodes in sea water coolers
Steel is cheaper, but prone to corrosion. It may be cast or fabricated. The presence of corroding iron or steel confers benefits in sea-water systems. The metal acts as a sacrificial anode and additionally delivers iron ions which are carried through and give protection to other parts of system where they deposit.
[MGPS system is used onboard ship. Description and working of MGPS is as follows.
Basic principle on which MGPS runs is electrolysis. The process involves usage of copper, aluminum and ferrous anodes. The anodes are normally fixed in pairs in the main sea chest or in such place where they are in the direction of the flow of water.
The system consists of a control unit which supplies impressed current to anodes and monitors the same. While in operation, the copper anode produces ions, which are carried away by water into the piping and machinery system. Concentration of copper in the solution is less then 2 parts per billion but enough to prevent marine life from settling.
Due to the impressed current, the aluminum/ferrous anode produces ions, which spread over the system and produce a anti corrosive film over the pipes, heat exchanger, valves, refrigeration and ac unit etc, internally.
MGPS anodes are fitted with specially designed safety cap which helps in removing the anode for replacement on board ship. Normally MGPS have a design life which coincides with the dry dock of the vessel.]
d. what is meant by the term 'guided flow', with particular reference to oil heaters In more recent designs of tube type heaters and coolers, the guided flow concept has been introduced, i.e. a secondary heating, or cooling, surface in the form of radial fins integral with the tubes between which flow is guided radially, alternately out and in from section to section. This gives (1) greater heat transfer surface (2) better heat transfer (3) lower metal surface temperature (4) in the case of oil heaters less risk of oil cracking and hence fouling. GUIDED FLOW FUEL OIL HEATER
4.Question
Sketch and explain the parts of a shell and tube type lubricating oil cooler showing how the oil and water flow path and material for each part
SHELL: The shell or cylinder is usually made of close grained alloy cast iron, with surfaces machined as required. Gun metal or fabricated steel may be used as alternatives depending upon requirements. Shell is normally is in contact with the liquid being cooled, which may be either oil or fresh water, as such there is no corrosion problem with the shell.
END COVERS AND WATER BOXES: The covers and water boxes are commonly of cast iron or fabricated from mild steel. Sacrificial anodes in the rod or plug form and an electrical contact strip are fitted to minimise corrosion due to galvanic action.
Where the end covers are coated with rubber or a bitumastic type coating or made of gunmetal, then it can provide protection for itself but makes the tubes and tube plates vulnerable for corrosion.
Easily removable covers on water boxes permit repairs and cleaning easier.
TUBE PLATES AND TUBE STACK : The tube stack is made up of stress relieved aluminium brass tubes (76% copper, 22% zinc, and 2% aluminium) expanded into Naval Brass tube plates, (62% Cu, 37% Zn, 1% Sn, Tin reduces corrosion)
All material used in H\E have different rates of thermal expansion when subjected to heat In shell and tube type H\E this expansion must be taken care of hence
The tube stacks are made up to have a fixed tube plate at one end and a tube plate at the other end which is free to move when the tubes expand or contract.
The tube stack is constructed with baffles of the disc and ring, single or double segmental types. The fixed end tube plate is sandwiched between the shell and water box, with jointing material. The expansion end is fitted with Synthetic rubber 'O' rings with telltale hole which will allow for free expansion
5.Question.
Draw line diagram of a feed water system for an auxiliary boiler, labeling all the principal items and showing the direction of flow.
Explain how water level to the boiler is regulated?
State how solid impurities are removed from feed water, which is pumped into the boiler.
Indicate how the risk of oil contamination may be reduced. Answer.
The water level in a boiler is critical. If it is too low damage may result from overheating; if too high priming can occur. It is therefore desirable to maintain the level in the boiler within the limits of the water level indicator.
In the case of water tube boilers with their high evaporation rates and small water reserves, the classification societies demand that some form of automatic feed water control be fitted, to maintain the water level in the boiler drum within the desired limits. These control systems may be grouped into the following types.
A single element feed water control system (below) will respond to a change in the level of water in the boiler drum as mentioned above and the suitability is therefore limited to boilers where the steam release water storage ratio is low, i.e. where the amount of water contained in the boiler relative to the steam output is reasonably high and also where load variations are of limited magnitude.
The level of water in the boiler drum is referred to a constant head with the resulting differential being applied to a differential transmitter, which converts the measurement to a proportional pneumatic signal. This signal is passed to a controller as the measured variable signal where it is compared with a desired value and any deviation between the two causes the controller output to change and pass the changed signal, via an auto/manual station, to the feed water control valve.
The primary control element in this system is initiated from the steam flow and from this
measurement a control signal can be generated to position the feed water regulating valve so that the inflow of feed water will equal the outflow of steam. This system in itself will be insufficient to satisfactorily maintain the level in the boiler drum at a desired value since during the period of time that elapses between the change in the steam flow and the repositioning of the feed water valve to bring the inflow of feed water into alignment with the outflow steam, the level in the boiler drum could change to any position. It is therefore necessary to introduce another element, i.e. water level control, so that the level in the boiler drum can be maintained at its proper value. The steam flow is measured by an orifice plate in the main steam line, between the drum and the primary superheater, using a differential pressure transmitter to convert the steam flow into a proportional pneumatic signal. This signal is introduced to the control system via the averaging relay which also accepts the signal from the water level controller. Therefore, with a change in steam flow there is an immediate corrective action on the feed regulating valve via the averaging relay, with the level controller being used as a trimming device to ensure the boiler water level returns to the correct position during stable conditions.
Three Element Feed Water Control
In the three element system, the basic control is carried out by a comparison of steam flow and water flow (below). In a closed feed system the water flow will equal the steam flow when the system is in equilibrium and any change in this condition will result in a control signal being applied to the feed water control valve. The signal from the water level will also effect the re-adjustment of the feed water valve to trim the level back to the desired value when the stability is achieved.
In addition to moving the feed water valve in the correct direction on a change in steam demand, the water flow signal adjusts the control system to ensure that the position of the valve is such that the water input equals the steam output from the boiler. Therefore, any variations in feed water pressure ahead of the feed water valve causing a change in water flow will immediately be detected by the flow meter and the valve will be repositioned to maintain the correct water flow before this effects the level in the boiler drum.
Three Element Feed water Control:
For automatic control of the feed water flow to the boiler, following three (elements) primary inputs are normally being considered.
Drum level. Main Steam flow. Feed water flow.
In addition, measurements of Drum Pressure, Main Steam Pressure and Main Steam temperature are also taken for correction/compensation purpose as detailed below.
Following paragraphs briefly explains how the feed water flow is regulated to match the steam demand from the boiler
Drum level measurement:
Two numbers of level transmitters (dP transmitters) one on left hand side and the right hand side of the Boiler Steam Drum are provided to measure drum level.
The two level signals from these transmitters are averaged and connected to a manual three-way selector switch. The other two inputs for the three-way selector switch are directly from the two transmitters. Normally the average signal is selected for the control. In case any problem with
any one of the transmitters; the healthy transmitter is selected in the three-way selector switch for the control.
The functioning of two level transmitters is continuously monitored through a deviation monitor. In case of difference between the two level transmitters is higher than the preset value, and then the control is automatically transferred to Manual with an annunciation.
The selected drum level signal is compensated for density variation in the drum water due to pressure changes (actually due to temperature changes) in the drum, through a function generating with drum pressure signal.
Drum Level Control:
The compensated drum level signal fed to a reverse acting P I controller as process variable. This measured drum level is compared with set point and a correcting signal (with proportional plus integral action) is generated in the controller according the deviation between the measured process variable (drum level) and the set point.
Main steam flow measurement:
The dP Transmitter measures the dP across the ventury nozzle, provided in the main steam line (The dP measured is proportional to the square of the flow through the ventury nozzle and hence the square root of the dP taken as proportional to flow.) The measured dP is square rooted and compensated density variations due to change of Pressure and Temperature.
Feed water flow measurement:
The dP Transmitter measures the dP across the orifice fitting is provided in the Feed water line. The measured dP is square rooted to arrive at the feed water flow.
Feed water flow control:
The compensated steam flow is added with the corrected signal generated in the drum level controller. This sum is taken as the demand of feed water flow (cascade set point) for the boiler and compared with the actual feed water flow to the boiler. The deviation between the demand and the actual feed water flow, fed to the P & I controller. The processed out put from the controller is given to the final control element through a 'Hand selector switch' and an 'Auto – Manual station' – the Feed water control valve as positioning signal.
Single Element Control:
During low load operation, three-element control is not required. Drum level measurement with it's set point is adequate. Hence the output of the Drum Level Controller is directly given to the Feed water Control Valve through the selector switch provided after Cascade P & I Controller. [Auto Manual Operation:
An Auto Manual Control Station is provided as the last element of control system. Auto or Manual operation can be selected from the Auto Manual Selector Switch in this Control Station. If auto selected, the positioning signal from the selected controller (through Hand selector switch) will go to the Final control Element – Feed water Control Valve. If manual is selected, the controller's outputs are isolated and the Feed water Control valve can be positioned from this control station.
Raise/Lower push buttons are provided in this control station through which Feed water Control valve can be opened or closed as desired by the operator. Bump less transfer facility shall be built in as part of the Control Station to avoid sudden jump of control valve position during change over from auto to manual or vice versa.
Indications:
Normally Set point value indication, Deviation indication, Final Control element (Feed water Control valve) position indication and Process value indication are provided either part of the Auto Manual Control Station or separately.
Alarm and Trip signals: Low and high level alarm signals are generated from one for the transmitters output through software switches. However very Low and very high level trip signals (software switches) from both the transmitters output and also from the
averaged/compensated signals are considered through an 'OR' gate. Signals from transmitters are also checked for the healthiness of the respective transmitters before connecting to the 'OR' gate. Following are the Trip/Alarm Signals generated.
Transmitter deviation Alarm. Drum level – Low Level Alarm Drum level – High Level Alarm Drum level – Very Low Level Trip Drum level – Very High Level Trip]
Removing impurities from boiler feedwater
Feedwater is filtered to remove suspended matter and if the suspended solids are very fine, a flocculation step may be needed to enable effective filtration. The water is then subjected to other treatments to make it suitable for the boiler. Depending on the quality of water, it may be subjected to one or more treatments like chemical precipitation, lime-soda softening, ion exchange, deaeration, and reverse osmosis.
The feed water/hot well/cascade tanks have to have filters installed, filled with lofa sponges, coconut fibres or similar, which effectively take up small amounts of oil. The filter inserts have to be exchanged regularly according to demand. The cascade tank can easily be equipped with a continually measuring oil detecting device which monitors if oil is present in the condensate. By locating the sensor in the cascade tank, it can be assured that oil is detected before it enters the feed water section, which means that no part of the feed water is being contaminated.
A more comprehensive system for preventing oil from entering the boiler would be to transmit a signal to an air- or electrically operated three-way valve switching over the condensate flow to the bilge until the oil source is pinpointed and eliminated. An investment in such equipment pays off quickly because it prevents the boiler from serious damage by burnt down tubes and furnace room plates.
Hot well is provided with filter observation tank.
Fill hot well and scum the oil from funnel and put in drain tank Towel filter will get coated with oil which escaped scumming Pump takes suction from bottom oil remains on top of hot well
Every drain line has steam trap with drain, check drain of coil to detect leaking return line Scum blow down if oil enters boiler
Maintain high alkalinity [pH = 11 to 12] 14 is maximum add coagulant with pH high hydroxyl of oil are formed coagulant will make ball of that
Some ships are provided with oil sensing alarm and oil in feed water alarm Find out leak and rectify leak
Glass has light behind it oil can be seen here then drain or skim oil from observation tank Toweling filter are provided in hot well
Hotwell has overflow connection with oil it can be overflowed Skim oil from hotwell by means of newspaper absorption mat
Hotwell suction to pump is from lower part therefore oil is not sucked In feed water line oil in water alarm is provided
If oil goes in boiler then scum blowdown Chemical treatment in extreme condition
6.Question
(i) In plate type heat exchanger, fluid press. & temp, do not normally exceed 10 bar and 150°C respectively.
(ii) Titanium & stainless steel finding increasing acceptance,
(iii) Carrying bar & clamping bolts are often much larger than pack thickness.
(iv) State how it can be ascertained that plate stack is correctly tightened and the likely result of excessive tightness.
Answer.
Plate type heat exchangers are made up of thin identical metal pressing plates with corrugation of dashboard type, chevron pattern or herring-bone pattern, each with nitrile rubber gasket.
The plates are supported beneath and located at the top by parallel metal bars and held together against an end plate by clamping bolts.
The arrangement facilitates addition of plates in pairs to increase capacity as well as damaged plates can easily be removed and cleaning can be done without removing the plates from
position. For this reasons, carrying bars and clamping bolts are made larger than plate pack thickness.
Nitrile rubber seals around the inlet and outlet passages and between plates are so arranged that one fluid flows in alternate passages between plates and the second fluid in the intervening passages usually in opposite counter flow directions. Since nitrile rubber is fitted inside a groove between the plates with an adhesive (plibond) and forms the seal, pressure of fluids generally restricted to 10 bar to avoid possibility of leakage. At high temperature, the rubber hardens and: loses its elasticity, so the fluid temperature is also restricted within 110°C .
The plate corrugations promote turbulence in the flow of both fluids to encourage efficient heat transfer. Turbulence as opposed to smooth laminar flow causes more of the liquid passing between the plates to come into contact with them. It also breaks up the static boundary layer which tends to adhere to the metal and act as heat barrier when flow is laminar. The corrugations make the plates stronger and stiff, so permitting the use of thin material. The increase in plate area also contribute to heat exchange efficiency. However, turbulence causes impingement erosion and so titanium or stainless steel plates are used which are extremely hard and strong and corrosion and_ erosion resistant.
The plate stack is tightened by clamping bolts to compress the rubber joints to prevent leakage. However, overtightness is avoided by checking through the tell-tale hole arrangement at the side of gaskets which indicate leakage through rubber seals. Correct tightness of bolts will just stop any leakage from tell-tale holes.
7.Question
Describe the checks you would make while taking over a E\R. watch at sea
Under what condition would you refuse to
Take over
Hand over Answer
Report to duty 20min earlier Start with the funnel
Check smoke condition in the day, at night check for sparks Check expansion tank water level
Blow through gauge glass of auxiliary boiler
Check oil level, suction pr, discharge pr, vibration, amperes, feel motor of A\C, Fridge compressors
Check air comp, drain air bottle
Cylinder head platform Exhaust temp
f.O. Leakages [fire hazard]
turbocharger oil level J.C.W. temp startingair line check for temp rise check air cooler pressure drop fuel pump leak
rack position
lubricators are injecting uniformly scavenge drain to be kept open purifier room
check ampere, temp oil level vibration F.W.G. vacuum temp salinity
Bottom platform
Feel all running pumps, check pr temp noise Check S.W. pump for leakage
Lighting of bilges, bilge should be dry Check sump sounding
Stern tube fwd seal
Take rounds of steering gear room and check all parameters no leaks oil level grease Take round of generators
Check all parameters
When completely satisfied come to the engine room
Check alarm panel when alarm had come what action was taken by previous watch keeper Check if the condition has improved or detoriated
Check all remote temp and pressure Check any standing instruction from C\E. Check for any instruction from bridge If all is satisfied then take over watch
Refusal to take over watch
Severe abnormality in engine room machinery
Bilges are full and its not possible to find out the ingress of water or oil Alarms are present on the panel and there is no improvement
Irrespective of the action taken by previous watch keeper Inform 2nd eng and C\E.
Maneuvering about to start do not leave the previous engineer If you your self are not confident of keeping watch independently if sufficient rest period is not completed then do not take over watch if person is incompetent then do not hand over watch
8.QuestionSr 8 2006
With regards to keeping the gas side of a boiler in good condition discuss each of the following
The mechanism of combustion stating the factors which are important for good combustion
Fuel oil treatment
Soot removal equipment Answer
To a degree necessary for good combustion. Time is required for combustion air and fuel to mix and to burn completely within the confines of the combustion chamber. Modern marine boiler plant provides for this with larger furnaces than were previously found.
High temperature is needed to vaporise the fuel and to ensure rapid ignition.
Turbulence is necessary to aid mixing of fuel and air so that complete combustion can be achieved without the need for more air than that required to consume the combustibles carbon, hydrogen and sulphur. The arrangement of the air admission apparatus is important.
Of further importance for efficient, complete combustion of heavy fuel oil is the design and performance of the fuel atomiser.
[Combustion of Fuel in Boilers.
The combustion of a residual fuel oil in a boiler furnace takes in a number of stages, which are described as follows.
The oil is first heated in steam or electric fuel oil heaters. This reduces its viscosity and makes it easier to pump, filter, and finally to atomize. However it must not be overheated at this stage, otherwise a process known as cracking' occurs,-leading to carbon deposits, and the formation of gas in the fuel oil lines, etc. The gas, due to its large volume, reduces the mass of oil passing through the burners, which in turn leads to a possible reduction in the steaming rate of the boiler owing to the reduced amount of fuel actually burnt. This gasification can also cause instability in the combustion process itself, resulting in a fluctuating flame formation.
The heated oil is now passed through the burners where it is atomized; this process breaks it up into a fine spray of droplets, so presenting a very large surface area of oil to the combustion processes. The droplets formed are .of two main types, i.e. very fine particles consisting of the lighter fractions of the fuel, which form a fine mist, and slightly larger droplets formed by the heavier fractions of the residual fuel.
Heated combustion
Another important factor for the formation of the primary flame is that it must be supplied with primary air in the correct proportion and at the right velocity. In the case of air registers using high velocity air streams this is done by fitting a tip plate which spills the primary air over into a series of vorticesrasindicated . This ensures good mixing of the air and fuel and, by reducing the forward speeds involved, helps to maintain the primary flame within the refractory q'uarl. SECONDARY FLAME
The larger oil droplets, heated in then passage through the primary flame zone, then vaporize and begin to burn. This, although a rapid process, is not instantaneous, and so it is essential that oxygen is supplied steadily and arranged to mix thoroughly with the burning particles of oil. An essential feature for the stability of this suspended secondary flame is that the forward velocity of the air and oil particles must not exceed the speed of flame propagation. If it does the flame front moves further out into the furnace and the primary flame will now bum outside the quad with resulting instability due to overcooling.
As indicated careful design of the swirl vanes in the air register can be used to create the required flow patterns in the secondary air stream. The secondary flame gives heat to the surrounding furnace for the generation of steam.]
Fuel oil treatment
The fuel which is used in boiler i.e. HFO contains many impurities such as water, asphaltin, sludge, sodium and vanadium and metal particles such as alumina silica and catalytic fins
If these impurities are not removed combustion process gets disturbed and efficient combustion does not take place and soot formation takes place
Presence of water in oil causes fluctuation in flame or flame failure
Asphaltin will cause the deposition of hard carbon in form of honey comb on heating surface as well as on burner and swirler plate
Sodium and vanadium will cause high temperature corrosion of heat transfer surface of gas side If it has metal particle leads to damage of burner with damaged burner injection pattern will change – improper combustion
These metal particle form ash and get deposited over heating surface
Treatment settling and service tank to be drained for efficient removal os sludge Better to purify oil, removal of water and asphaltin in form of sludge and catalytic fins
Soot removal equipment
Soot blower where steam is blown out by use of steam or air pressure
Soot sticks which are thrown in furnace and burnt in furnace these form chemical gas which release the soot
Infrafone in which high frequency sound waves are admitted into combustion gases this causes fine vibration of tube and it releases the soot
Water washing in port Manual cleaning by brushing
9.Question
Describe the following conditions are prevented in auxiliary boilers
Feed contamination by oil heating coil drains
Internal corrosion
Furnace blowback
Uptake fire Answer.
Feed contamination by oil from heating coil drain Heating coil to be checked for leakage regularly Material \ design.
Material to be suitable for maintaining pressure and temp of the steam Expansion allowance to be given to coils
Anchor holding brackets coil to be properly secured
Coils to be kept at elevated platform at least 6 inches from bottom or tank bottom to prevent corrosion
Should be easily accessible.
Operation.
Should be pressure tested during inspection
Before admitting the steam coils to be drained properly to prevent water hammer this may crack the coil
Steam to be admitted slowly
If leakages do take place oil will find its way to observation tank
Oil must be drained out from observation tank or cascade tank by overflowing the tank Skim the oil from top or use newspaper to skim from top
Rectify leakage first then skim it Note- if oil reaches inside boiler Only scum or surface blowdown
Maintain high alkalinity and pH value of feed water
If no scum blowdown add coagulant and high alkalinity this will form oil globules This will have coalescence effect due to condition of coagulant
Then it will form non adhesive oil sludge at bottom then blow down
Internal corrosion
This is due to corrosion and dissolved oxygen
Use closed boiler feed water system so that air inclusion is minimum
Use dearators [mechanical]
Add hydrazine as oxygen scavenger or add sodium sulphide
Dissolved Co2
This will form H2Co3 – weak acid This will cause corrosion
Prevent entry of Co2 by way of dissolving air in system While cold start makes sure all air is vented
Add alkaline compound to neutralize acid
Corrosion due to dissolved chlorides This forms HCl which is corrosive Regular blow down
Addition of alkaline compound
Corrosion – dissolved solid such as sodium and magnesium sulphate and bicarbonates Use phosphate treatment and maintain it in alkaline condition and regular blow down At regular interval boiler water should be tested for alkalinity dissolved solids reserved phosphate so as to make sure that boiler water is maintained in good condition
Furnace blow-back:
This occurs due to insufficient purging of the Furnace, during burner firing. The blow-backs occur due to an accumulation of oil and its vapour within the furnace, which is ignited by a re-lit burner, i.e. sudden application of heat. The effect can also occur when a sudden admission of air occurs into a fuel-rich flame.
1. Boiler furnace to be sufficiently ventilated before firing the boiler- start the FD Fan. (Pre purge).
2. In case of failure to fire the boiler cause of failure to be investigated and then only another attempt to be taken to fire the boiler.
3. While shutting down the boiler furnace to be well ventilated (post purge).]
There should be an adequate period of time (of air purge) with the air registers (flaps) fully open, and the forced draught fan 'On'.
While lighting up, minimum fuel should be admitted, to maintain a 'minimum flame', to avoid an excessive build-up of oil, before ignition occurs.
Proper maintenance of burners should be carried out, to prevent oil dribbling, while the burner is off.
Regular inspection of the colour of the flame - a deep yellow colour indicates a fuel-rich flame. A correct air/fuel ratio should always be maintained.
2. Soot emanates from main engine and therefore combustion in main engine to be maintained at best level.
3. Uptake temp, to be monitored closely. (If reqd. high temp alarms may be fitted for exh.Gas IN and OUT temperatures for exh.gas. boiler)
4. Physical water washing, soot cleaning and its inspection, periodically is of great help in keeping it clean.
Uptake Fires can be avoided by carrying out regular soot blowing and maintaining full water circulation.
Likewise, if a rise in the exhaust gas temperature differential across the boiler occurs, it could indicate fouling of the tubes. If a fire does occur the engine should be stopped immediately and the turbocharger air intakes covered to starve the fire of air. The soot blowers should not be used as this could fan the fire.
Check to ensure full water circulation is maintained. A small fire may burn itself out as the heat will be conducted away by the circulating water.
If a water washing system is fitted it could extinguish a small Fire. If there is a tube leak, the circulation should be stopped and the boiler drained.
If the circulation stops it causes a risk of tube failure which can cause a hydrogen fire.
Without circulation the tubes will rapidly increase in temperature and may eventually rupture if under pressure. The resulting water vapour dissociates releasing hydrogen which will burn reaching temperatures as high as 2000°C. The heat sustains the reaction causing the iron to oxidise which can melt the complete tube stack. In case of a high temperature fire the engine
should be stopped immediately. The boiler circulation should be stopped and the boiler drained. Boundary cooling should then be carried out until the fire is extinguished.
Any fire should be dealt with quickly to prevent a small fire becoming a large one which could destroy the boiler.
10.QuestionSr 3 2006
With reference to hydraulic deck machinery:
(a)State the sources for contamination of the system;
(b) Describe possible effects due to contamination,
(c) Explain how the oil can be monitored by ships staff.
Possible cause of contamination in the hydraulic system are ingress of water, metal particles from general wear, dirt, grease, also oxidation products from overheated oil , air in the system. Contaminants
Foreign particles
Metal particles – magnetic – wear down of pump gears, bearing [bush bearing] Abrasion of piping
Sand and dust Sludge
Cargo residue Rust
Moisture \ water content
Sources of contamination From breathers of tanks From header tanks left open Wear down of pumps gears
Oxides dark appearance
Water ingress due to hole on tank tops leading to rain water entry
Cooling water line leakage in cooler tubes and cooling water pump is kept on with out starting the oil pump
Entry of water into topping up oil kept in drums on the deck due to holes on them Due to different oil qualities – of wrong grade of oil leading to deterioration of quality Due to condensation of air in tanks
Contaminants in a hydraulic; system can lead to three types of failure.
Catastrophic failure - This is where a component ceases to operate. If the damage is severe the oil will be contaminated with debris and more
components in the system could become damaged.
Intermittent failure - This is perhaps the most common problem and is caused when dirt or wear debris is large enough to prevent a valve
from seating or causing an obstruction to a small orifice, the dirt may eventually wash away and the system will function normally. This type of intermittent fault results in an unreliable system, with ship's staff wondering when the next breakdown will occur.
Degradation failure - Wear and erosion of components increases clearances and damages valve seats and seals. This causes imprecise
control and a reduction in efficiency. If wear is occurring this will escalate and eventually cause catastrophic failure.
Oil monitoring by ship staff.
Visual inspection- with water presence, water will become milkfish white. With oxidation colour will become dark yellow. Water content can be checked by calcium carbide method. Sprinkling water on
Hot plate, with water presence crackling noise can be heard. Check viscosity of oil with oxidation, viscosity will increase. By flow stick method.
Contamination can be monitored by testing regularly i.e. LO tests, filters cleaned regularly, if of the magnetic type, build up metal particles should be noted as it could give an indication of bearing failure.
11.Question
Name method of F.W. generation on board ship
Sketch and describe any one method what treatment is give to render it fit for drinking Method of F.W. generation on board ship
Distillation, Reverse Osmosis (RO), flash distillation Distillation
The most commonly used form of shipboard freshwater generation is evaporative distillation, which uses engine jacket cooling water or steam heat from exhaust or gas fired boilers to evaporate sea water, which is then condensed into fresh water
Simple single effect evaporator
The single effect, high vacuum, submerged tube evaporator shown in Figure is supplied with diesel engine cooling water as the heating medium. Vapour evolved at a very rapid rate by boiling of the sea-water feed, tends to carry with it, small droplets of salt water which must be removed to avoid contamination of the product. The demister of knitted monel metal wire or polypropylene collects the salt-filled water droplets as they are carried through by the air, These coalesce forming drops large enough to fall back against the Vapour flow.
Figure High vacuum, submerged tube evaporator
Evaporation of part of the sea water leaves a brine the density of which must be controlled by continual removal through a brine ejector or pump. Air and other gases released by heating of the sea water, but which will not condense, are removed by the air ejector. The evaporator shown has a single combined ejector for extraction of both brine and air.
The system above shows an evaporator typically heated by Main Engine Jacket water means to supply steam when the engine is shut down.
To start this evaporator
Open sea water cooling to the coiling coils
A take off line from the outlet of the cooler goes to the ejector booster pump. After shutting any vents the booster pump is started. The vacuum in the shell should begin to drop.
A take off from the educator booster pump is led to the shell via a flow control valve. This should be cracked to fill the unit increasing to a design level gradually as the vacuum increases. It should be noted that it is possible on some systems to increase feed to a point where the educator can no longer cope and the shell is overfilled.
This should be avoided as the possibility exists of getting saltwater on the demister mesh arrangement designed to remove wetness from the steam.
The system above shows an evaporator typically heated by Main Engine Jacket water means to supply steam when the engine is shut down.
Open sea water cooling to the coiling coils
A take off line from the outlet of the cooler goes to the ejector booster pump. After shutting any tarted. The vacuum in the shell should begin to drop.
A take off from the educator booster pump is led to the shell via a flow control valve. This should be cracked to fill the unit increasing to a design level gradually as the vacuum increases.
d be noted that it is possible on some systems to increase feed to a point where the educator can no longer cope and the shell is overfilled.
This should be avoided as the possibility exists of getting saltwater on the demister t designed to remove wetness from the steam.
The system above shows an evaporator typically heated by Main Engine Jacket water with
A take off line from the outlet of the cooler goes to the ejector booster pump. After shutting any tarted. The vacuum in the shell should begin to drop.
A take off from the educator booster pump is led to the shell via a flow control valve. This should be cracked to fill the unit increasing to a design level gradually as the vacuum increases.
d be noted that it is possible on some systems to increase feed to a point where the
Should this happen then it can take considerably longer before the salinity of the distillate falls to an acceptable level.
Treatment chemical in the feed should now be added
When the water reaches working level in the shell the heating coils may be warmed through. It should be noted that it is rarely the case the educator is able to provide all the vacuum required, instead as the unit begins to steam, the condensing of this steam assists to pull the down the shell pressure.
The heating should be increase as the shell pressure reduced. The maximum temperature in the shell is governed by design and to a maximum of 85'C to reduce scaling
The salinometer may be switched on once condensate is detected in the distillate pump suction. The distillate pump control may be switched to auto. On some installations a recirc is fitted which dumps the outlet from the distillate pump back to the evaporator. This may take the form of an automatic three way valve operated by the salinometer. In addition a manual dump to bilge may be fitted to dump the initial charge of distillate out of the unit reducing the time to on-line
Initial treatment (Figure) involves passing the distillate through a neutralite unit containing magnesium and calcium carbonate.
Some absorption of carbon dioxide from the water and the neutralizing effect of these compounds, removes acidity.
The addition of hardness salts also gives the water a better taste.
The sterilizing agent chlorine, being a gas, is carried into the water as a constituent of sodium hypochlorite (a liquid) or in granules of calcium chloride dissolved in water.
The addition is set to bring chlorine content to 0.2 ppm.
While the water resides in the domestic tank, chlorine should preserve sterility. In the long term, it will evaporate so that further additions of chlorine may be needed. The passage of water from storage tanks to the domestic system is by way of a carbon filter which removes the chlorine taste.
Figure Chlorine sterilization and conditioning
12.Question.
(a) For Freon-22 vapor compression refrigeration machine, state how each of the following faults arc indicated and how they arc remedied;
(i) Air in the system
(ii) Moisture in the system
(iii) Undercharge
(iv) Overcharge
(b) Describe with a diagram detailing the devices incorporated into the refrigeration system to protect the machinery and equipment against malfunction.
Moisture in the system
If there is air in the system, water or moisture will also be present as the atmospheric air contains a large percentage of moisture. If no ice has formed the indications are similar to those of the presence of air, but if ice has formed as it is most likely to do at the regulator, it can cause a complete stoppage at this part. This is liable to happen if evaporator gauge reading is below 82° F. It is necessary to thaw the ice to remove the moisture and if it is in small quantity the moisture can be absorbed by a “drier" inserted into the liquid line.
In putting the first charge of refrigerant into a machine, great care is taken to ensure all pipe lines are exhausted of atmospheric air and free from moisture, an air pump being used for this
purpose.
Air in the system
Air in the system is indicated by an abnormally high condenser gauge reading accompanied by very small bubbles in the liquid in the sight glass. The remedy is to close the liquid stop valve or regulator, and pump the entire charge into the condenser and receiver until the evaporator gauge registers 1Ib/sq. inch, when the machine is stopped. The compressor delivery valve is now dosed and the condenser contents allowed to cool to the surrounding temperature. The air is now
expelled from the condenser and receiver through the vent plug at the top until the condenser gauge reading, using the temperature scale, is reduced to that of the cooling water temperature.
Having got rid of the air it will most likely be necessary to top up the charge of refrigerant. This will be done after opening the discharge valve from compressor and resetting the regulator to its normal working position.
Air can only find its way into the system by leakage from the atmosphere, at a defective pipe joint or compressor crank-shaft gland seal, for example. It is undesirable as it lowers the efficiency and leads to corrosion.
Indication:
Condensing pressure is high.
Bubbles in the sight glass
Compressor runs hot and tong time.
Jumping of the gauge pointer
Causes
During charging air enters into the system.
If Freon - 12 b used air teaks into suction line (WP is less than atmospheric pressure).
Pump down the refrigerant (air will not condensate- but remain on top of the condenser above the liquid refrigerant).
Connect the collecting cylinder to the purging tine, open the valve and collect air in the cylinder.
After purging shut the valve completely
Check the level of the refrigerant, if required charge it.
Restart the compressor with all safety precautions.
Undercharge
If the system is undercharged, either the condenser or the evaporator may be short of gas. An undercharge in the condenser is denoted by a low condenser gauge reading and the appearance of large bubbles in the liquid sight glass. If evaporator is short of gas, then compressor delivery temperature will be high. Another indication of undercharge is the necessity to run the machine for longer periods between cut-outs, to maintain the cold room temperatures, assuming no change in the cold room conditions. Undercharge is generally due to leakage of gas from the system and will cause a rapid fall in efficiency.
The remedy is to add refrigerant to the machine until all bubbles disappear from the sight glass with the regulator set to give correct gauge readings.
Compressor runs hot and performance falls off
Low condenser gauge reading
Bubbles in the sight glass
Causes:
Partial blockage at the filter or drier
Expansion valve blocked at the strainer.
Leakage at the shaft seal, flange coupling, valve gland etc.
Remedy:
Identify and rectify leakage.
Clean filter and drier.
Add more gas.
Overcharged
An overcharge will be indicated by a high condenser gauge reading, together with a full sight glass reading, and a tendency for compressor delivery to become cold.
This can only be rectified by discharge of gas from the machine, which can be done by
discharging slowly through the purge plug fitted on top of condenser, until the condenser gauge reading returns to normal. Discharge should be to the open atmosphere and never to the engine-room or an enclosed space. In the case of an ammonia machine, considering its toxic properties, discharge may be made through a pipe into a vessel containing water, in which the ammonia is absorbed. It is claimed that one part of water by volume, will absorb 800 parts of ammonia.
An overcharge of refrigerant can take place when using the compressor to draw from the storage bottle when topping up, and particularly if gauges are defective.
Indication.
High condenser gauge reading.
Sight glass full of liquid refrigerant
High-pressure switch activates to stop compressor
Causes
Excess refrigerant has been charged in the system
Ice on the regulator
Remedy:
Remove the refrigerant from the system. This is done by connecting a cylinder-to the liquid line-charging valve, starting the compressor and operating the line-charging valve. Purge air and maintain effective cooling. Remove ice from the regulator.
13.Question
Describe the boiler fuel burning system and indicate the effect of the following
Air supply insufficient
Air supply excessive
Presence of water in oil
Excessively high oil temperature Answer.
This refers to a semi automatic fuel oil system
Oil is pumped into the settling tank and any water allowed to settle out This can then be drained off by means of spring loaded drain cock
When required for use the high suction valve on the settling tank is opened and oil is allowed to pass to the cold filters fitted on the suction side of the FO service pump
Due to high viscosity of the unheated residual oil only a coarse filter just sufficient to prevent damage to the pump can be used @ this stage. This consist of a positive displacement pump operating at a constant delivery pressure
A spring loaded relief valve fitted on the discharge side of the pump allows only excess oil to spill back to the suction side of the pump in the event of over pressure
After leaving the pump, the oil temp is raised in the FO heater. This is done ion order to lower the viscosity of oil making it easier to filter and finally to atomize
The correct oil temp is maintained by means of a thermostat placed in the outlet from the FO heater, which controls the supply of seam to hater
The hot filters are fitted after the heater are normally of an auto clean type in some cases they are constantly rotated by electric motors
These filters provide a fine filtration
This prevent wear and chokage of the fine passages in the atomizing tip of the fuel oil burner The heated and filtered oil now passes through an automatic pneumatically operated valve which varies the oil supply pressure to the burner in response to variation in the main steam pressure transmitter to the master pressure controller
The combustion air controller also varies in order to maintain the correct ratio between the amount of fuel and air supplied to the furnace
Two emergency valves are now fitted the 1st is manually operated quick closing shut off valve which enables the FO to be shut off by hand from the boiler very rapidly in case of emergency The second is a shut off v\v with a steam actuator operates to shut off the fuel in the event of loss of water in the boiler
The oil is now ready to enter the individual dead legs supplying oil to the burners An isolating v\v and a safety cock or similar device fitted to each leg
To enable oil temp in the system to be brought quickly up to and then maintained @ desired operating value a recirculating valve is fitted which enables oil to be circulated through the ring main back to the pump suction
This valve is closed as the burner are brought in operation
The system uses gas oil to flash up from cold. Air pressure is supplied to gas oil storage tank is used to force oil through the burner. The use of this oil continues until sufficient steam pressure
has been generated to enable the FO heater to be put into operation so as to raise the temp of residual FO to a value required for its combustion
Safety fitting include quick closing valve operated from outside of E\R fitted to the suction lines from the settling tanks which enable fuel to be shut off from the system in case of emergency. There is also emergency stops fitted to the fuel service pump
The system can easily be changed to manual control by simply bypassing the automatic control v\v and controlling oil supply pressure by means of hand jacking wheel on the spring loaded relief v\v governing the discharge pressure from the fuel oil service pump
Air supply insufficient
Will cause bad combustion causing carbon monoxide to be formed resulting in black smoke and loss of heat
The risk of accumulating a dangerous collection of unburnt fuel in the plant this may cause back fire
Unburnt fuel and carbon gets deposited on the tube surface and affects the heat transfer which may lead to overheating
Air supply excessive
Will cause a grey white smoke also a loss of heat as extra air is heated in going through the furnace and carries the heat up the funnel
It might cause fire in exhaust trunking and uptake where carbon deposit and unburnt residue of fuel is present
Burner flame may be distorted and may get extinguished due to turbulence The flue gases will contain more O2 which is undesirable for IG on tankers
Water in fuel
Spluttering @ the burner will take place accompanied by hissing sound and white smoke will appear @ the funnel
Fire is likely to be damaged
Sodium salts dissolved in water are highly corrosive at high temp and will lead to corrosion at burner tip, tube nest etc
Sodium can also cause damage to brick work
Water may evaporate at high temp and they can cause vapour lock in the fuel system, which will cause fluctuation in the fuel pressure
Boiler efficiency drops due to loss of calorific value of fuel
Fuel oil high temperature
To high an oil temp results in carbonization and chocking of the tips
Because due to high temp viscosity decreases and hence fuel broken into very small particle and hence burns near nozzle
High temp could also lead to vapour lock in the system causing improper supply of fuel to burner and can trip the boiler
Oil may crack at high temp in the heater causing asphalt and carbon deposits on heater tubes
14.QuestionSr 3 2009,
Explain the operation of automatic self cleaning centrifuge. Detailed sketches should be used for your explanation. Labeling principle component and indicating directional flow of all fluid.
Explain how dam ring contribute to efficient centrifuging with reference to oil of different specific gravity.
Answer
1 Conditioning and displacement water 2. Oil In, 3. Clean oil out, 4. Water Out
5. Disk stack 8. Flow control disk, 6. Hydraulic Pressure & Spring Force keeps bowl closed. Hydraulic Pressure overcomes spring force to open bowl for sludging
Describe an automatic self-sludging centrifuge suitable for dealing with fuel of density up to 1O1Okg\m3 at I5deg C.
ANS
As the density of the oil approaches that of water (above 991 kg\m3) the hydraulic equilibrium in the bowl becomes unstable, and a gravity disc will no longer maintain a water seal.
As the density of the oil approaches that of water (above 991 kg\m3) the hydraulic equilibrium in the bowl becomes unstable, and a gravity disc will no longer maintain a water seal.
To overcome this problem, Alpha Laval has developed the Alcap separator, the principle of which is illustrated,
Oil is fed into the high speed rotating bowl which basically operates as a clarifier, but water and solids are separated and are thrown to the outside of the bowl by centrifugal force,
At regular intervals a sludge cycle will take place.
Water is admitted into the bowl to soften the sludge and displace the oil in the bowl.
When a transducer in the oil discharge line detects water the bowl is opened and the sludge and water discharged.
The bowl opens and closes very rapidly and oil loss is minimal.
If the fuel contains water it will build up in the bowl and start to be discharged with the clean oil. The transducer in the discharge line will detect this and if this occurs after the minimum sludge cycle time, a sludge cycle will be initiated; if the water is detected before the minimum sludge cycle time, then water discharge valve will open.
The start up procedure for the centrifuge described
Ensure purifier has been fully assembled, that the bowl cover locking dogs are in position, and the brake is off.
The purifier pump suction should be closed, the pump discharge valve open to the heaters, and the recirc valve open back to the purifier suction.
The discharge from the purifier should be open to the settling tank. The feed regulating valve to the purifier should be set to zero.
Start the purifier watching the ammeter, which should fallback as the purifier speed increases. Ensure the purifier does not vibrate. In case of vibration or excessive current shut down immediately and investigate.
Open the fuel suction from the settling tank to the purifier pump.
Warm through and open heating steam to and from heaters. Ensure heater control set to 95deg C. Continue to recirc fuel until purification temperature is reached.
Open operating water and set bowl operating water to close.
Open feed regulator to purifier and shut recirc valve. Set purifier oil feed to minimum. Ensure sludge cycle is set to x hours.
