So hello everyone I have been trying to learn on natural gas hydrates and problems on hydrate formation. So below content is only for academic point of view.
Hydrate formation is the major problem in offshore exploration which leads to flow blockage, loss of circulation and even abandonment of the well. This leads to lot of loss in form of dollars and time. The practical solution for preventing or delaying hydrate formations for a long pipeline subsea network is by adding inhibitors, any chemical which reduces the water potential can be used as an inhibitor but MEOH (Methyl alcohol is a universally accepted chemical inhibitor). Knowing the conditions (Pressure and Temperature) with and without inhibitors will help pipeline designing and pipeline operation. The most common hydrate forms structures (Structure I and Structure II) hydrates will be described.
Hydrate formation is the major problem in offshore exploration which leads to flow blockage, loss of circulation and even abandonment of the well. This leads to lot of loss in form of dollars and time. The practical solution for preventing or delaying hydrate formations for a long pipeline subsea network is by adding inhibitors, any chemical which reduces the water potential can be used as an inhibitor but MEOH (Methyl alcohol is a universally accepted chemical inhibitor). Knowing the conditions (Pressure and Temperature) with and without inhibitors will help pipeline designing and pipeline operation. The most common hydrate forms structures (Structure I and Structure II) hydrates will be described.
This study also shows how to dehydrate a wet gas using
glycols as a solvent which are generally available in offsite gas plant
facilities. Dehydration is a solution for reducing the water content before it
is sending to gas transportation.And Pressure has to be maintained with an objective of gas has to be in dew point conditions.
Basic substitute equations for calculating HFT.
·
1934, Hammerschmidt.
·
Makogon correlation.
·
1991, Motiee, 15 parameter T-Explicit Equation.
·
2005, Towler and Mokhatab and
·
Bahadori and Vuthaluru. Etc
In all the cases know the process pressure condition i.e. at
what pressure it is transporting and then calculate the temperature.
How to describe Type1
and Type2 Hydrates.
Actually we can easily describe Type I and Type II (or
Structure I and Structure II). Based on the below graph.
Graph -->Check Figure2.2
·
Less than 3.8 A it is difficult to form hydrate.
·
If the guest molecule are Ar,Kr,N2,O2 this is
Type II.
·
From 4.4 A methane, H2s, Xe, ethane, propane
will fall in Type I cages.
·
From 7A no Type I and Type II will form. There
is another type called TypeH.
Definition of
hydrates:
I am also going through the most common gas hydrate forms.
According to Von Stackberg and Muller, each of the structure contains two
types of cavities.
·
Structure I consists of 46 water molecules which
constitute 2 small pentagonal dodechahedra cavities and six tetrdecahedral
large cavities, having 2 opposite hexagonal faces and 12 pentagonal faces.
·
Structure II consists of 136 water molecules
comprising 16 small pentagonal dodechahedra cavities and 8
hexadecahedra large cavities, having 4 symmetrically arranged hexagonal faces
and 12 pentagonal faces.
The average cavity radiuses of 3 cavities are
3.9 A for pentagonal dodechahedra.
4.3 A for tetrdecahedral.
4.7 A for hexadecahedra.
Basically the reason why gas hydrates will form above the ice
point of water is, gases will diffuse in these cavities which will alter the
condition of formation of Ice. So this is the reason hydrates will form in
~10C.
References:
·
Empirical expressions for gas hydrate stability
law, its volume fraction and mass-density at temperatures 273.15 K to 290.15 KZhengquan
Lu1, 2, * and Nabil Sultan1
·
PREDICTION OF GAS-HYDRATE FORMATION CONDITIONS
IN PRODUCTION AND SURFACE FACILITIES A Thesis by SHARAREH AMERIPOUR
That's a great news about gas company. Thanks for sharing with us!
ReplyDelete