Gas Hydrate Inhibitor Injection Calculations

Gas Hydrate Inhibitor Injection has been discussed previously on "Cheresources" in several posts. Besides the fact that the "Hydrate Utility" in HYSYS

can calculate inhibitor injection rates, there are other methods programmable in a simple excel sheet that can be utilized to provide fairly accurate

inhibitor injection rates. Equations provided by "Hammerschmidt" and "Nielsen-Bucklin" can provide good estimates for hydrate inhibitor rates and my

endeavour to find alternatives to sophisticated simulation software such as HYSYS has led to the development of several excel spreadsheets related

to equipment sizing and other calculations in the oil & gas field. On such effort on my part was dedicated to prepare a comprehensive calculation sheet for hydrate

inhibitor injection using both the "Hammerschmidt" and "Nielsen-Bucklin" method. Since the estimation of water content in natural gas is an essential part of this

calculation I had to integrate the water content calculation from the water content spreadsheet I had posted on "Cheresources" at:

http://www.cheresour...of-natural-gas/

Let us move on to the actual background and content of hydrate inhibitor injection and the related equations

Commonly used hydrate inhibitors are Methanol & Monoethylene Glycol (MEG) for depressing the hydrate formation temperature. The "Hammerschmidt" equation gives

the hydrate depression temperature as a function of the concentration (weight fraction) of the inhibitor in the final water phase & the molecular weight of the inhibitor. The

actual injection flow rate is a function of the water content which condenses in the pipeline from the source pressure & temperature conditions to the destination pressure

& temperature conditions. For a unboosted pipeline, this essentially means a drop in pressure & temperature.

Hammerschmidt Equation:

d = K*w / (1.8*MWinhib*(1-w))

where:

d = depression of the water dew point or gas hydrate freezing point, deg C

K = constant, dimensionless, Methanol = 2335; Monoethylene Glycol = 2700

w = mass fraction of inhibitor in final water phase

MWinhib = MW of inhibitor, Methanol = 32, Monoethylene Glycol = 62

Note:

The above equation is only applicable upto 25% by weight for Methanol & 70% for MEG in final water phase

i.e. w

where:

d = depression of the water dew point or gas hydrate freezing point, deg C (>13.5)

Vaporization losses are to be calculated as explained previously.

To conclude, hydrate inhibitor injection calculations can be set up using a spreadsheet and anybody interested can do so using the guidelines provided above. I would be

more than happy if somebody sets up an excel spreadsheet and requires me to check it.

Hoping to have a lot of comments from the members of "Cheresources".

Regards,.

Ankur

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