(a) Explain the causes and effects of Oxides of Nitrogen (NOx)
(b) Explain the causes and effects of Oxides of Sulphur (SOx)
(c) Describe ONE method by which the level of the NOx emission may be reduced.
(d) Explain how the effects on engine components of Sulphur in the fuel may be minimized?
(a) Causes and effects of Oxides of Nitrogen(NOx)
- Nitrogen is normally regarded as an inert gas.
- During the combustion, nitrogen reacts with oxygen to form Nitric Oxide (NO).
- Between 5 and 10% is further oxidized in the exhaust stream to form Nitrogen Dioxide (NO2).
- About 1% of Nitrous Oxide (N2O) is also formed.
- The rate of NOx formation is a function of temperature.
- Nitrogen Oxides (NOx) react with other chemicals in the atmosphere, in strong sunlight to form ozone, a principal component of Smog.
- The NOx also reacts with water and oxygen to form nitric acid which is one of the constituents of acid rain.
- NO2 also causes damage to lung and other delicate tissue.
(b) Causes and effects of Oxides of Sulphur(SOx)
- when burning, fuel containing Sulphur, Sulphur dioxide (SO2) produced.
- About 5% is further oxidized to form Sulphur trioxide (SO3).
- Sulphur oxides (SOx) are the primary causes of acid rain.
- SOx react with water, oxygen, and other chemicals in atmosphere to form various acidic compounds.
- Sunlight increases the rate of the reactions.
- Result is a mild solution of sulphuric acid which are absorbed in the cloud and fall down as acid rain.
- Sox controlled either by removing sulphur from fuel or by removing Sox from exhaust gas by scrubbing.
(c) Method of reduction of NOx emission
- Remove oxides of nitrogen form exhaust gas. (selective catalytic reduction or SCR) 98% reduction claimed
- Catalyst material is titanium dioxide doped with vanadium pentoxide
- Urea (NH2,2CO) or Ammonia(NH3) inject into exhaust stream
- NOx reacts with urea and ammonia to form nitrogen and water
(d) How to minimize the effects of Sulphur in the fuel on engine components
- SOx combined with water to form sulphuric and sulphurous acid which can deposit on cylinder liners and exhaust gas economizers causing corrosion when the temperature falls below the dew point.
- To minimize these effects, keep cylinder liner temperatures as high as possible cylinder lubrication use correct grade to neutralize acid deposition.
- In economizer, if temperature of exhaust gas fall below the acid dew point, acid corrosion occurs.
- At low load running and during maneuvering, bypass economizer to avoid this happening.
(a) Sketch and describe vacuum sewage system using on board?
(b) What is Biochemical Oxygen Demand (B.O.D)?
(c) What is Coliform Count?
(a) Vacuum sewage system
Based on vacuum created by an eductor, used to pull the sewage into the sewage tank.
- A pressure switch maintains vacuum in line, from toilets by auto start/stop of centrifugal pumps.
- Water in sewage tank is used as driving water for the eductor.
- Float switches used to control discharge from holding tank to sewage treatment plant or overboard, maintain vacuum in system.
- The holding tank is at atmospheric pressure.
- Calculations based on a daily flow, 10 liters per person- using 1.2 liters of water per flushing operation.
- The sewage tank capacity varies from 2.5~10 m3.
(b) Biochemical Oxygen Demand (B.O.D)
- Amount of oxygen taken up by sewage sample in mg/l or ppm is termed as Biochemical Oxygen Demand.
- Measure of strength of sewage.
- Identifies biological decomposable substances and is a test on the activity of bacteria,
- Presence of oxygen feed on and consume organic matter.
- Test results are expressed as amount of oxygen taken by one litre sample (diluted with aerated water)
- when incubated at 20°C for five days. It gauges the effectiveness of sewage treatment process.
- B.O.D of raw sewage is 300 to 600 mg/litre.
- I.M.O recommends a B.O.D of 50 mg/litre after treatment.
(c) Coliform Count
- Coliform organisms are recognized as the indicator Organisms of sewage pollution.
- Numbers present in sewage are large. Each person contributes between 125 billion, in winter to 400 billion, in summer.
- Coliform are present in human intestine and presence in water is taken as an indication of the pathogen count.
- Responsible for Typhoid, Dysentery, Polimyelitis, Cholera disease.
- I.M.0 recommends a Coliform count of 250/100 ml. of effluent after treatment.
- It gauges the effectiveness of disinfection
Enumerate the following fire, fighting appliance required in the machinery space of 5000 BHP sea going ship regarding SOLAS regulations as the following.
(a) Portable fire extinguisher
(b) Non portable fire extinguisher
(c) Fire hydrant, hose and nozzle
(d) Fixed Fire Fighting installation systems
(a) PORTABLE FIRE EXTINGUISHERS
For machinery space containing Internal Combustion Engine and oil fire boiler.
1. Portable fire extinguisher approved type and design.
2. Capacity not more than 13.5 Ltrs and not less than 9 Ltrs.
3. For every 746 KW, require one portable fire extinguisher suitable for oil fire
4. For 5000 BHP machinery space, require at least 5 number
5. At every entrance one number to be located and not more than 10 mtr apart between each and every extinguisher.
6. In boiler room, at least 2 portable foam extinguishers or equivalent to be located.
7. Near main switch board, at least one portable extinguisher suitable for electric fire to be located.
8. For each boiler room and machinery space one set of portable foam applicator unit with spare cartridge.
(b) NON-PORTABLE FIRE EXTINGUISHERS
1. At least 45 Ltrs capacity of foam extinguisher or equivalent enable to deliver any point of F.O & L.O pressure system and other fire hazards.
2. A 135 Ltrs capacity of foam extinguisher or equivalent, enable to any part of the boiler room.
3. A receptacle containing at least 0.3 m3 of sand or other approved materials and hand scoop.
(c) FIRE HYDRANT, NOZZLE AND HOSE
1. At least 2 fire hydrants with complete hose and nozzle, to be located with container at port and starboard side each.
2. Hose must be non-perishable material and sufficient length to reach any part of machinery space.
3. All nozzles approved dual purpose type incorporating with a shut off. Standard size of nozzle-12,16,19mm.
(d) FIXED FIRE FIGHTING INSTALLATIONS
For machinery space total power is 746 KW and above,
- FIRE MAIN SYSTEM -At least 2 fire pumps and one emergency fire pump and
- A fixed fire, fighting installation system must be provided with any one of the following.
(1) CO2 FLOODING SYSTEM
- Most suitable due to its fire extinguishing efficiency, cleanliness and easy for application.
- CO2 bottles to be installed are calculated depend on required free volume of CO2
(2) HIGH EXPANSION FOAM SYSTEM
- Mostly used on Tanker’ cargo space.
- The foam layer could not be disturbed too easily to avoid re-ignition occur due to residual heat.
(3) HIGH PRESSURE WATER MIST (HIGH FOG)
- Provided with approved type spray nozzle, fitted above the High potential fire hazard places such as ME, GE and Boiler.
- This system consists of water tank, high-pressure pump and control system.
(a) Sketch and describe the coupling which is essential to withdraw propeller shaft from aft.
(b) Explain fitting and removal procedure.
(c) Where they are used onboard?
(d) What are the advantages of muff coupling?
(a) Muff coupling
- Consists basically of two steel sleeves.
- Thin inner sleeve has a bore slightly larger than shaft diameter and its outer surface is tapered to match taped bore of outer sleeve.
- Nut and sealing ring close annular space at end of sleeves.
(b) Fitting and removal procedure
- When coupling is in position, outer sleeve is hydraulically driven onto tapered inner sleeve.
- At same time, oil is injected between contact surfaces to separate them and overcome friction between them.
- Separation oil is supplied by hand pump (two points for forced lubrication).
- Drive oil is supplied by another hand pump or power pump.
- When outer sleeve reaches predetermined position, forced lubrication pressure is released and drained.
- Drive oil pressure maintained in hydraulic space until oil between sleeves drains and normal friction is restored.
- After disconnecting hoses, plugs fitted and rust preventive is applied to protect exposed seating.
- A sealing strip is pressed into groove between end of sleeve and the nut.
- Grip of coupling is checked by measuring diameter of outer sleeve before and after tightening.
- The diameter increased should agree with the figure stamped on the sleeve.
- Some makers recommend value by specified travel of outer sleeve.
- To disconnect coupling, oil pressure is applied into hydraulic space with set value.
- With the shafts supported, oil is forced between the sleeves.
- Outer sleeve slides off inner sleeve with a rate controlled by release of drive oil pressure.
(c)
- Used onboard as flange couplings for tail shaft. It allows the shaft to be withdrawn outboard.
- Also, used for ME camshaft connections.
(d) Advantages
- To withdraw propeller shaft to outboard.
- saving in man power and time
- To transmit full power with rigidity
- Good alignment.
(a) How to fit and withdrawal of Pilgrim propeller nut with aids of sketches?
(b) What are the advantages of Pilgrim propeller compare to conventional type?
(a) The pilgrim propeller nut is a threaded hydraulic jack, designed to use for keyless propeller.
- It provides a predetermined friction grip between the propeller and tail shaft
- It has circumferential slot with groove, O-ring, drilled oil passage cooperating with oil resistance Nitrile tyre and steel loading ring.
Fitting
1. Propeller is mounted on tail shaft. Pilgrim nut is screwed onto the shaft.
2. Hydraulic pump is connected to the nut, purge air and gradually set up pressure.
3. Steel ring receives thrust from hydraulically pressurized nitrile rubber tyre and pushes up propeller onto tapered tail shaft.
4. Hydraulic pressure is gradually raised until the predetermined push-up length is achieved.
5. Pressure is released and locking plate is fitted.
6. Shaft and propeller boss temperature/ Final push-up length/ applied hydraulic pressure to be recorded.
Withdrawal
1. Nut is taken off and screwed back in reverse order steel loading ring is facing outwards.
2. A wood block is placed between nut and propeller boss, leaving some clearances.
3. Long studs are screwed into the aft face of the propeller boss and withdrawal plate is fitted over the studs.
4. Nuts are fitted on the studs plate contacts the propeller nut and steel ring.
5. Hydraulic pressured is applied; propeller pulling off from the taper end of the shaft.
(b) Its advantages over conventional type
1. Without key, no stress raisers associated with shaft key and key way.
2. Shaft is stronger and has greater resistance to fatigue failure.
3. Even and sufficient frictional coefficient between surfaces of the propeller and shaft.
4. Cast iron (CI) sleeve has a similar thermal expansion to the steel shaft. reduces the slackness in the hot water.
5. Fitting at sub-zero temperatures gives no problem.
6. The nut used to fit or to remove the propeller; no special hydraulic tool is required.
7. Saving in man power and time
(a) State the situations when need to check shaft alignment.
(b) How many methods of checking shaft alignment?
(c) How to carry out optical sighting methods
(d) Explain about Jack up method?
(a) Shaft alignment needs to be checked due to the following situations
1. Bearings running hot. wiped
2. After bearing repair and/ or replacement.
3. Major vibration problems in shafting
4. Damage to shafting due to collision, grounding
5. After replacement of stern tube
(b) Methods of checking shaft alignment
(1) Optical sighting method
(2) Piano wire method
(3) ‘Gap’ and ‘Sag’ method
(4) Jack up method.
(c) Optical Sighting Method
- This method uses optical sighting or laser equipment to establish a reference line for the shafting.
- This reference line is commonly projected off a gear or engine flange and the stern tube bored relative to this line.
- Pin-hole lamp is mounted on the forward coupling and sighting boards are positioned at each coupling by viewing along the line of the shafting.
- The boards are adjusted vertically and horizontally until all the holes are in line.
- Then measurements are taken from the holes to each coupling flange.
- Laser beam of optical telescopes can be used for better accuracy.
- These methods are usually used when the new ship shaft alignment is checking.
(d) Jack-up method
- This method is used to check the bearing reactions after coupling the shafting.
- Hydraulic jacks are placed as close as possible to a bearing and the load is slowly transferred from the bearing to the jack as the jack is raised.
- A plot made of the jack load versus the shaft deflection gives determination of the actual bearing load.
- When the shaft is clear of the bearing, the plotted curve will show a distinct change in slope.
- A similar curve is plotted when lowering the shaft; corresponding reaction loads lower.
- Take actual jack load as the average between the two curves.
- Take bearing reaction as the point where the extrapolated line crosses the load axis on the graph.
- Theoretically bearing load is checked by jacking only at one angular position.
- But in general practice, it is done at four angular positions.
- Any bends in the shaft detected by a load variation in the four positions.
- This method is used after ship grounding and suspect the shaft is bent.
