Ch3- Cargo handling (c) Flashcards
Why are most tankers double hull?
To avoid pollution in case of collision or grounding
Why are tankers equipped with vapour recovery manifolds (MARPOL Annex VI)?
To reduce the emissions of volatile organic compounds (VOCs)
Why are tankers fitted with slop tanks?
Collect oil residues from the tank cleaning operation
What are bottom line and deck line systems used for?
To allow cargo to be loaded from a terminal into the designated tanks, and to transfer the oil from the tanks to the ships pumps to pump out the oil to a terminal.
How does the terminal connect to the ships manifolds?
Via Chiksans
What do chiksans do?
Offer a secure connection to the ships manifold
Define manifold.
A fluid or gas distribution system that serves to bring many valves into one place or a single channel into an area where many points meet
Name an advantage of ring line systems.
Any tank can be discharged by any pump.
Thus, different grade of cargo can be loaded
Name 3 disadvantages of ring line systems
- Expensive to build, due to extra length of piping required
- Extra bend is required, thus decreasing rate
- Risk of leakage from radius of bend
Name 4 advantages of direct line systems
- Easy to operate
- Less training of personnel is required
- Takes less time to set up before commencing cargo operation (less valves)
- Contamination is unlikely, as it is easy to isolate each system
Name 2 disadvantages of direct line systems
- Layout is not as versatile
- Very rigid system, making it difficult to plan
Into which tanks does oil first flow into in free flow systems?
Aft tanks
What are each tanks provided with in free flow line systems?
Small stripping lines
Name 2 advantages of free flow line systems
- Having lesser and less complicated piping systems in the tanks
- Is suitable for large tankers (which do not carry many grades of oil)
How many types of oil can be carried in free flow line systems?
1
Name a disadvantage of free flow line systems
Flexibility of operations is comparatively less as compared to other piping systems
Which has a pump room:
Deck line only systems or bottom line systems
Bottom line systems
Describe the layout of a bottom line system (draw)
- Bottom lines run from the pumps in the pumproom forward with branch lines connecting to each of the cargo tanks
- Bottom line is connected to the deck lines, via the drop line or pumproom riser, which are then connected to the manifolds
Describe the process of loading cargo (bottom line system)
cargo is pumped from the shore into the ships manifold
Then down the drop line into the bottom line and then into the required cargo tanks via the branch lines
What controls which tanks are filled?
Valves
What is isolated during loading of cargo in bottom line systems?
Ships pumproom
Describe the cargo discharge process (bottom line systems)
required tank valves are opened
Cargo runs through the branch line into the bottom line, through the ships pump
The cargo is then guided up the pumproom riser, along the deck line to the manifold and then to the terminal via the Chiksan arm
What is kept closed during discharge (bottom line system)
Drop line valve
Describe the layout of a deck line only system
3/4 deck lines which connect to cargo tanks via branch lines.
Each tank has a loading line and discharge line, with respective valves.
The discharge line has a cargo pump attached.
Describe the cargo loading process (deck line only system)
Terminal pump the cargo through the Chiksan arm into the ship’s manifold and then into the deck line.
What valves are opened and which are closed during loading on deck line only systems?
Loading valves on tanks to be loaded are left opened, and discharge valves are to be kept closed
Describe the cargo discharge process (deck line only system)
Cargo pump in each tank to be discharged is started, and the cargo pumped up through the discharge line and through the discharge valve into the deck line
later, to the manifold and then into the terminal via the Chiksan arm
What valves are closed during discharge (deck line only systems)
Loading valves
What are the four types of cargo pumps?
Centrifugal pumps
Submerged pumps
Eductors
Positive displacement pumps
Why are there usually more than one type of pump fitted?
To deal with the different stages of a pumping operation
What does VLCC stand for?
Very large crude carrier
What is a VLCC capable of pumping?
12000 m3 per hour
Two advantages of a centrifugal pump
- Capable of pumping large bulk quantities per hour possible
- Relatively compact size
Two disadvantages of centrifugal pumps:
- Not good at handling gas/air/liquid mixtures which is an issue when trying to remove low levels of liquid in the tanks
- Unable to create its own vacuum when the oil level is low in the tank
What are submerged pumps?
Centrifugal pumps that are installed in the cargo tank and submerged in the cargo
How are submerged pumps usually driven?
Hydraulically
Name 5 disadvantages of submerged pumps
- Eliminates the need for a pumprrom
- If the ship has individual pumps and lines, then total segregation is achieved
- Reduced piping in cargo tanks
- Good stripping performance
- Eductors are not required
Name 3 disadvantages of submerged pumps
- Initial high installation costs
- Bulk discharge rate may not be as high as with conventional centrifugal pumps
- How to deal with a pump failure with cargo still in the tank
What do eductors require?
A motive oil (oil, water, steam, air)
What systems are fitted with eductors?
Bottom line systems
What happens in an eductor?
The motive liquid and liquid being ‘pumped’ mix at the discharge side
The nozzle and pipe constriction increases velocity creating a low pressure on the suction side
What are three advantages of eductors?
- No moving parts, hence reliable
- Simple construction
- Self-priming, will suck liquid and gases
What are two disadvantages of eductors?
- Requires a motive liquid to ‘drive’ it (during cargo 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 and not directly ashore)
What is a positive displacement pump used for (also known as a reciprocating pump)?
Stripping out the last of the liquid cargo from the tanks and the pipelines
What is the difference between positive displacement pumps and eductors?
PDPs don’t require a motive liquid, unlike eductors
PDPs capacity is usually much lower than an eductor (so they are only used for small quantities at the end of discharge operation)
What are two advantages of positive displacement pumps?
- Very good suction characteristics
- Doesn’t require a motive liquid to drive it
What are two disadvantages of positive displacement pumps?
- The pump speed is slow (typically 30-35 double strokes per minute)
- Not good for pumping against high back pressures
What is a screw pump?
Often found on ships with deck line systems, and is used to drain the lines at the end of the discharge
What are four types of pipeline valves?
- Globe valves
- Gate valves
- Ball valves
- Butterfly valves
Name Ballast Water Management methods (7)
- BW exchange
- Heat treatment
- FIltration
- Ultraviolet
- Hydro cyclones
- Bio-degradable chemicals
- Electrochemical control
