What is the energy content of natural gas on an LNG transporter?

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Discussion Overview

The discussion centers around determining the energy content of liquefied natural gas (LNG) being transported on an LNG carrier. Participants explore various aspects of the composition of the gas, the calculations involved in estimating energy content, and the implications of different heating values.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant provides the composition of the LNG, indicating the mole percentages of various components, primarily methane.
  • Several participants inquire about the total amount of methane in the tanks and suggest looking up combustion energy values for calculations.
  • There is a discussion about whether to consider the energy from liquid water or water vapor in the combustion process, with references to higher and lower heating values.
  • Another participant mentions the need to convert LNG to gas phase methane, noting that this conversion absorbs energy and could affect calculations.
  • A question is raised about whether the goal is to determine the amount of BTUs delivered at the destination.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the calculations and the specific energy content based on the provided gas composition. There is no consensus on the best approach to determine the energy content or the relevance of different heating values.

Contextual Notes

Participants mention the need for specific mass or volume data to perform calculations, as well as the potential impact of different heating values on energy content estimations. The discussion does not resolve these complexities.

Teodor Xypolitidis
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My brother is working on an LNG transporter and I would like to know how much energy there is in the LNG the ship is transporting, here is the info I got :
Methane ISO6974 99.8518 mole%
ethane 0.0137 mole%
propane 0.0000 mole%
i-butane 0.0000 mole%
n-butane 0.0000 mole%
i-Pentane 0.0000 mole%
n-Pentane 0.0000 mole%
c6+ 0.0000 mole%
Nitrogen 0.1345 mole%
Carbon Dioxide 0.0000 mole%
Oxygen 0.0000 mole%
The pressure in the tank is 160 mbar and the ambient pressure is 116 mbar.
 
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Liquid water or water vapor?
 
How much methane is in the tanks? You can Google for the combustion energy (per pund, kg, et,). If you want, you can add the energy to liquefy it, but that's a small fraction.
 
russ_watters said:
How much methane is in the tanks? You can Google for the combustion energy (per pund, kg, et,). If you want, you can add the energy to liquefy it, but that's a small fraction.
I have written the info about the consistency of the natural gas the % of methane etc but I don't know how to calculate it, I want to know about this exact percentages and these pressures
 
Bystander said:
Liquid water or water vapor?
what do you mean by that ?
 
Teodor Xypolitidis said:
I have written the info about the consistency of the natural gas the % of methane etc but I don't know how to calculate it, I want to know about this exact percentages and these pressures
No, I mean total volume or mass - you may as well assume it is 100% methane. It is a simple multiplication exercise if you have the mass and the energy per unit mass.
 
Teodor Xypolitidis said:
what do you mean by that ?
If you burn something and then condense the water out of the combustion products, you get about 20% more energy. That's referred to as the higher (as opposed to lower) heating value.
 
The energy of combustion of gas phase methane is available in a reference book - look it up. But you first have to covert the LN2 in the tanks into gas phase methane. That is energy absorbe, and a loss. There are tables with that info, too. The combustion products are gaseous H2O and CO2. Forget about condensation.
 
  • #10
What are you trying to actually determine, is it the amount of BTU's that will be delivered at the vessel's destination?
 

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