# What are the working condition(load case) of a LNG tanker?



## Fegor

I am going to calc. the power balance of a LNG tanker,and I have not done it before,so i just want to know how to define(divide) the load case of a LNG tanker?
Anyone experienced this type of ship?


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## janmike

Fegor
Spent 18 trips on LNG tankers as 2nd Mate. I am afraid never heard of the terms that you are using.


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## JRMacGregor

Fegor

I think what you want to know is the different operating modes of the ship. 

These would include;
- sailing in ballast - keeping tanks chilled
- sailing with cargo onboard (with or without boil off gas reliqufaction)
- in port discharging cargo
- in port while cooling down tanks
- sailing while cooling down tanks

Apart from the normal ship hotel and service loads, to complete the load balance you will need to calculate the power required by the cargo pumps and compressors. That depends on the specified discharge rate and the cool down rate.

It also depends on the propulsion system.

Until recently, LNG ship main propulsion was steam, with electric power produced by generators. This type of ship might need 6 to 10MW electrical power, which could be produced by two steam turbo alternators and one diesel. These ships can burn the cargo boil off gas (BOG) so less need for large electric plant to drive reliquefaction compressors when sailing.

Now there are medium speed diesel electric LNG ship designs which can also burn the BOG. You can select the total generator capacity to balance the propulsion and auxiliary loads in same way as any DE ship.

Also, there are slow speed diesel powered designs (cannot burn the BOG). These need larger electric plant for reliquefaction - could be up to 18MW depending on ship size.


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## Fegor

JRMacGregor said:


> Fegor
> 
> I think what you want to know is the different operating modes of the ship.
> 
> These would include;
> - sailing in ballast - keeping tanks chilled
> - sailing with cargo onboard (with or without boil off gas reliqufaction)
> - in port discharging cargo
> - in port while cooling down tanks
> - sailing while cooling down tanks
> 
> Apart from the normal ship hotel and service loads, to complete the load balance you will need to calculate the power required by the cargo pumps and compressors. That depends on the specified discharge rate and the cool down rate.
> 
> It also depends on the propulsion system.
> 
> Until recently, LNG ship main propulsion was steam, with electric power produced by generators. This type of ship might need 6 to 10MW electrical power, which could be produced by two steam turbo alternators and one diesel. These ships can burn the cargo boil off gas (BOG) so less need for large electric plant to drive reliquefaction compressors when sailing.
> 
> Now there are medium speed diesel electric LNG ship designs which can also burn the BOG. You can select the total generator capacity to balance the propulsion and auxiliary loads in same way as any DE ship.
> 
> Also, there are slow speed diesel powered designs (cannot burn the BOG). These need larger electric plant for reliquefaction - could be up to 18MW depending on ship size.


exactly what I want!

I have listed nine cases of various working conditions used for Power Load Calculation and how some of the major consumers work in those scenarios,I want to get your opinion.Thank you very much.







p.s.:GCU is Gas Combustion Unit,PSA is Pressure Swing Adsorption.


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## Fegor

janmike said:


> Fegor
> Spent 18 trips on LNG tankers as 2nd Mate. I am afraid never heard of the terms that you are using.


Sorry for my poor english.
and JRMacGregor's Answer is exactly what I want to get.
also thanks your reply.^_^


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## forthbridge

You may find the IEC60092 series of standards useful.
They cover almost every aspect of design of ships electrical systems.
If you are working for a company they probably have access but if not your local library will get them for you. 
To see a list go to www.iec.ch
click on webstore
type 60092 in to search
click on preview at the left hand side to see a summary of what is in each do***ent and note what ones you need. Ask your local library to obtain them for you, don't buy them unless you will be using them ofte as they are expensive.


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## david freeman

Fegor said:


> I am going to calc. the power balance of a LNG tanker,and I have not done it before,so i just want to know how to define(divide) the load case of a LNG tanker?
> Anyone experienced this type of ship?


I believe this to be the balance of cargo loaded at the loading port, and at the discharge port the amount of LNG sold to the importer. IE The revenue earned by the cargo owner. THE BOG costs will have to be appropriated and apportioned to the cargo consignee-Owner. This maybe a load of bunkum??? But them you may pick out the right bits.


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## Fegor

david freeman said:


> I believe this to be the balance of cargo loaded at the loading port, and at the discharge port the amount of LNG sold to the importer. IE The revenue earned by the cargo owner. THE BOG costs will have to be appropriated and apportioned to the cargo consignee-Owner. This maybe a load of bunkum??? But them you may pick out the right bits.


You mistook my point, I am an offshore ship designer .
As an electrical designer ,we have to analysis the electric power balance so to select proper power plant for a ship.
Before this ,I need to make clear of the operation modes (when which will run).


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