LNG weight

[John Connor]

I was reading about the weight of LNG and CNG and CNG weighs more. Why is that? You would think being in a liquid state NG would weigh more.

 

[sm625]

LNG is "frozen", but not compressed. CNG is, well, compressed. Methane has a low expansion ratio, unlike steam.

 

[Mark R]

CNG at 200 bar pressure has a density of about 180 g/litre. LNG at atmospheric pressure has a density of about 450 g/litre.

CNG tanks are heavy. Even carbon fiber reinforced plastic (CRP) tanks will typically have a tare weight about 3-4x of the net weight. By contrast an LNG tank has a tare weight about 1.5x the net weight.

 

[John Connor]

I don't care about tank weight...

 

[dave_the_nerd]

I don't care about tank weight...

You'd probably ought to. Because if this is true:

CNG at 200 bar pressure has a density of about 180 g/litre. LNG at atmospheric pressure has a density of about 450 g/litre.

Then the premise in your OP is false:

I was reading about the weight of LNG and CNG and CNG weighs more.

You _can_ reconcile those two statements if you assume that whatever you read was taking tank weight into consideration. (And assuming the same volume of gas.) Or we could assume that whatever you read was backwards. Or that you misunderstood it. Either way, probably needs a re-read.

 

[John Connor]

http://www.midwestenergysolutions.net/cng-resources/energy-volume-weight

 

[RU482]

http://www.midwestenergysolutions.net/cng-resources/energy-volume-weight

notice the E in those figures

 

[John Connor]

Okay, so GGE seems to fit the NIST standard that shows up for CNG.


So WTH is the actual weight of CNG anyway?

 

[giantpandaman2]

LNG is denser. You're comparing apples to oranges when you say CNG "weighs more." The weights on that website compare an LNG gallon to a CNG equivalent which have different BTU's. To have differing BTU's means that they have differing amounts of of natural gas...hence the "weights" are not equivalent.

CNG and LNG have differing storage requirements, hence weight of their tanks matters when it comes to transporting them when comparing equivalent energy.

Really, I think you need to understand that density is not the same as weight and a gallon one thing (LNG) doesn't equal an "equivalent" of another (CNG) that's comparing itself to gasoline not LNG.