Chapter 6G

6E. Hydrate Inhibition Calculations Back to Main

This page is used to predict the necessary inhibitor concentration. The Positive manner to prevent hydrates (and corrosion) is to keep the lines and equipment "dry" of liquid water. When the decision is made to operate a line containing liquid water and the minimum line temperature is below the hydrate point inhibition of this water is necessary. Many materials may be added to water to depress both hydrate and freezing temperatures. The following equation has been found reliable for prediction of the necessary inhibitor concentration in the water phase to lower the hydrate point a given amount.

(Equation 6.5)

Where: d = ° C depression of hydrate point

XR = weight percent inhibitor in the liquid water phase

M = mol wt of inhibitor

Ki = Constant 1297° C [2335° F]

Correlations other than Equation 6.7 have been proposed. For methanol concentrations up to about 50 wt% the following equation may be more accurate.

(Equation 6.7)

Where: d = ° C depression of hydrate point

xm = mol fraction of methanol in the liquid water phase

A = constant -72° C [-129.6° F]

Most experienced operators will adjust the injection rate by trial-and-error following initial start-up. This is one of many process calculations that provide a little more than a "safe" or "ballpark" estimate to guide operations.

##### How do I carry out this calculation?

To calculate the hydrate inhibition calculation an inhibitor must be decided. Choose methanol, ethylene glycol, or diethylene glycol by clicking on and shading the circle provided for that selection.

Once the inhibitor has been chosen, the inlet pressure, minimum flowing pressure, hydrate formation temperature, minimum flowing temperature, inlet inhibitor concentration wt%, saturation temperature, gas flow rate, water content at saturation temperature, and water content at minimum flowing temperature must be entered into their entry spaces. To do so use the mouse to click the cursor in the entry spaces and input the data. Once this has been done, select Run to execute the solution.

##### Definitions of the variables and where to obtain the unknown data

Inlet pressure is the pressure at which the gas flows into the system.

Minimum flowing pressure is the lowest expected pressure in the system.

Hydrate formation temperature can be determined by calculations on Chapter 6 Screens C and D.

Minimum flowing temperature is the lowest expected temperature in the system.

Inlet inhibitor concentration Wt% is the amount of inhibitor present in the liquid water. This value is a percentage.

Saturation temperature designates the temperature at which vaporization takes place at a given pressure. This pressure is called saturation pressure for the given temperature. (This value is not needed if the water content is known)

Gas flow rate is the flow capacity.

Water content at saturation temperature is the amount of liquid water present at the saturation temperature. This can be determined using the water dewpoint at that temperature and a suitable water content correlation. This can also be calculated using Chapter 6 Screens A and B.

Water content at minimum flowing temperature is the amount of liquid water present at the minimum flowing temperature. This can be determined using the water dewpoint at that temperature and a suitable water content correlation. This can also be calculated using Chapter 6 Screens A and B.

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