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Liquid Cargoes > Cargo Handling Systems > Flashcards

Cargo Handling Systems Flashcards

1
Q

What are the advantages of double hulled tankers?

A

offer a degree of protection against collision and stranding damage by protectively locating the cargo tanks

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2
Q

what degree of longitudinal sub-division of cargo tanks is in the earlier double hull tankers?

A

none

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3
Q

what degree of longitudinal sub-division of cargo tanks is in the newer and larger double hull tankers?

A

either 1 or 2 sub-divisions

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4
Q

where are most of the longitudinal strength members located?

A

in the segregated ballast tanks

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5
Q

why are most of the longitudinal strength members located in the segregated ballast tanks?

A

gives flush cargo tanks - easier to drain + clean

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6
Q

how do you segregate different grades or types of chemical in cargo tankers?

A
  • smaller tanks
  • more tanks
  • more complex pipeline system
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7
Q

how are tanks separated?

A
  • some by cofferdams

- more sophisticated ships each cargo tank will be served by its own pump + pipeline

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8
Q

what are the three basic pipeline systems used on tankers?

A
  1. direct line
  2. ring main
  3. free flow
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9
Q

what is the function of the pipeline system?

A

to direct the oil to and from the terminal and within the cargo tanks

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10
Q

what controls the flow of oil?

A

valves located within the system

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11
Q

what is the Manifold?

A
  • the interface between the ship and shore pipelines

- runs athwartships, usually amidships

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12
Q

what are ‘Chiksans’?

A
  • the actual connection of the Manifold

- usually made of flexible rubber hoses or metal arms

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13
Q

why do modern systems use hydraulic clamps as a connection to the ships Manifold?

A

allows fast decoupling in the event of an emergency

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14
Q

what part of the Manifold allows for the vertical movement of the ship whilst loading at a terminal?

A

the Chiksans

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15
Q

how is seawater ballast drawn to the pumps through sea?

A

suction valves located in the pumproom

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16
Q

why is a double valve segregation used in drawing seawater ballast to the pumps from the sea?

A

prevent leakage to the sea - especially important if the ballast system is connected to the cargo system

17
Q

what determines the bottom line layout in a ship?

A
  • which trade the ship is to be operated in
  • ship size
  • economic factors
18
Q

what is a direct line layout of pipes in a tanker?

A
  • crude tankers
  • typically three pipe lines
  • each serve its own group of cargo tanks
  • allows three grades of oil to be carried with total segregation
  • if only carrying one grade, you can open the crossover valves between the lines
19
Q

what is a ring main line layout of pipes in a tanker?

A
  • not a common system used now!!
  • product tankers where a high degree of segregation is required
  • system is more complex, hence more expensive
  • great flexibility is achieved
  • usually any of the ships cargo pumps can serve any cargo tank
  • crossover lines interconnecting each side of the ‘loop’ due to segregation valves on branch lines
20
Q

what is a free flow system line layout of pipes in a tanker?

A
  • simple system
  • some crude oil tankers
  • doesn’t rely on pipelines to direct oil to the tanks
  • uses a series of sluice valves to adjoin tank bulkheads are fitted
  • reduced costs
  • cargo is loaded through a simple ring main line
  • sluice valves located at adjoining cargo tank bulkheads are opened to discharge cargo
  • oil flows from forward to aft and the cargo pump suctions, in the after most centre cargo tank
  • discharge the cargo via the deck lines
  • as the cargo flows from one tank to the next - mixing occurs
  • high discharge rates are achievable + very little residues are left
  • this reduces the stripping time at the end of discharge
21
Q

what does the term stripping time mean?

A

the removal of the small quantities of oil remaining after the main cargo pumps have discharged as much of the cargo as possible

22
Q

If stripping lines aren’t fitted, what else can be used and why?

A
  • main lines

- due to the advent of self-priming units fitted to main cargo pumps

23
Q

how do centrifugal pumps work?

A
  • imparting energy to the liquid in the form of increased velocity
  • centrifugal force is imparted to the liquid by rotation of a single, or possibly double, impeller rotating at about 1200 rpm
  • the velocity produced is converted to a discharge pressure by slowing it down in a suitably shaped casing known as a volute
  • the impeller blades are curved and operate to fine tolerances within the pump casing
  • the drive mechanism for the pump is via a drive shaft from the engine room into the pump room
  • pumps are usually driven from the ships boilers
24
Q

what are the advantages of using a centrifugal pump system?

A
  • capable of pumping large bulk quantities > 5,000 m (cubed)

- relatively compact size - allows for small pump rooms therefore larger cargo carrying capacity

25
Q

what are the disadvantages of using a centrifugal pump system?

A
  • not good at handling gas/air/liquid mixtures (can be overcome by fitting a self-priming device
  • not good at creating pressures below atmospheric
26
Q

what are positive displacement pumps?

A
  • known as a reciprocating pump where the standard main cargo pump for many years until the increase in ship size rendered them redundant for this purpose
  • still used on oil tankers as stripping pumps
  • steam driven
  • consists of two pistons in separate chambers
  • steam forces the steam piston up
  • the linkage connecting the two pistons forces the oil chamber piston to the left displacing the oil in the chamber out to the discharge pipe
27
Q

what are the advantages of the positive displacement pumps system?

A
  • simple construction, therefore easy maintenance

- very good suction characteristics

28
Q

what are the disadvantages of the positive displacement pump system?

A
  • not suitable for high flow rates
  • pumping capacity is directly related to the size of the cylinders
  • not good for pumping against high back pressures
  • may result in having to strip internally to the slop tanks + using a centrifugal pump to discharge ashore from there
29
Q

what are submerged pumps?

A
  • essentially these are centrifugal pumps
  • usually hydraulically driven (have their impeller located in the bottom of the tank)
  • typically found on chemical tankers where total segregation is required
  • each tank has its own pump, load/discharge line + manifold connection
  • as pumps are submerged in the cargo, good stripping performance is achieved
  • air or nitrogen is blown into the top of the stack + cargo is force out through the small-bore line forward of teh (closed) discharge valve
30
Q

what are the advantages of the submerged pump line system?

A
  • eliminates the need for a pump room, so increasing space available for cargo
  • if individual pumps and lines total segregation is achieved
  • reduced piping in cargo tanks
  • good stripping performance
31
Q

what are the disadvantages of the submerged pump line system?

A
  • initial high installation costs
  • bulk discharge rate may not be as high as with conventional centrifugal pumps
  • how to deal with pump failure while cargo is still in the tank (can supply the ship with a portable pump that can be lowered into the tank)
32
Q

what is the Eductors pump system?

A
  • used for stripping tanks during discharge + tank cleaning
  • pump with no moving parts
  • relies on Bernoulli’s principle to function
  • a suction is created by a constriction in part of the eductor
  • this increases flow velocity + creates a low pressure (suction)
33
Q

what are the advantages of the Eductor pump system?

A
  • no moving parts, hence reliable
  • simple construction
  • self-priming
34
Q

what are the disadvantages of the Eductor pump system?

A
  • requires a motive liquid to ‘drive’ it
  • during discharge, the two liquids combine and so must be of the same grade
  • efficiency depends on driving pressure and low back pressure
  • usually used for internal stripping + not directly ashore

Liquid Cargoes (11 decks)

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