3 replies to this topic

[Max3008]

Dear all,

I have 2 problems and I really need your help:

1/ Could anyone tell me about the meaning of hydrate line in gas phase diagram? It can be used to predict the conditions (P, T) of the hydrate formation, can't it?

2/ A natural gas mixture has a dew point of -50 degree Cel. The problem is when this mixture is cooled down to -60 oC, the hydrate could not be formed. I wonder if the reason is it's composition ( methane with mole fraction of 0.7)? Methane molecules's active movement could make the hydrate formation more difficult, isn't it?

Thanks in advance. 

[Art Montemayor]

Hoang:

 

Your answers are:

 

1. Yes.  The hydrate line defines the temperature at which a hydrate will form for the gas in question, at the stated pressure.  However, the hydrate will form in the presence of liquid water.
2. You may have your gas at a temperature well below the given hydrate line, but it is not in contact with liquid water, the hydrate will have difficulty in forming.  Besides, what is the reference pressure for the “dewpoint” that you give for the gas?  Is it atmospheric pressure? Or is it operating pressure?  It makes a big difference.

Giving a dewpoint value without a pressure reference is like giving a temperature without stating if it is Fahrenheit or Celcius.

[Max3008]

1. I wonder if hydrate could be formed not only in the hydrate line but also in the left of the hydrate line, couldn't it?

2. The pressure is about 40 bar. I did not mention it because the pressure of dew point test and the mixture after cooling is the same.

[shan]

1.  Yes.  Hydrate is formed under any process conditions that are worse (higher pressure or lower temperature) than the initial hydrate conditions (hydrate line).

 

2.  To my knowledge, there is no correlation between natural gas hydrocarbon dew point (water is sold ice at -50C) and hydrate temperature.  Actually, methane is the most relevant composition to form hydrate.  Methane ice (methane hydrate) under sea may be one of next major energy sources for your generation to develop.