CA2205670C

CA2205670C - Pipeline transmission method

Info

Publication number: CA2205670C
Application number: CA002205670A
Authority: CA
Inventors: Ian Morris; Glen Perry
Original assignee: JL Energy Transportation Inc
Current assignee: JL Energy Transportation Inc
Priority date: 1996-11-18
Filing date: 1997-05-16
Publication date: 1999-11-16
Anticipated expiration: 2017-05-16
Also published as: CA2205670A1

Abstract

At pressures over 1000 psia, it is advantageous to add to natural gas an additive which is a C2 C3 and C4 hydrocarbon compound, CO, NH3 or HF or a mixture of such additives. Above a lower limit (which varies with the additive being added and the pressure), this results in a smaller Z factor, or (M w.Z) product, representing increased packing of molecules, and therefore leading to a decrease in the amount of power needed to pump the mixture or to compress it.

Claims

1. A method of transporting natural gas by pipeline, which comprises:
(a) adding to such natural gas sufficient of at least one C2 or C3 hydrocarbon or a mixture of C2 and C3 hydrocarbons such so the hydrocarbon, together with the C2 and C3 hydrocarbon (if any) originally in the natural gas, forms a resulting mixture with a total C2 or C3 hydrocarbon content which is sufficient, at the pressure and temperature to be used for transporting, to reduce the product of the z factor and the average molecular weight of the resulting mixture to a level lower than the product of the z factor and the average molecular weight of the untreated natural gas, and (b) transporting such resulting mixture by pipeline at a temperature of between -40° and +120° Fahrenheit and pressure greater than psia, said pressure and temperature being chosen so the resulting mixture has no coherent liquid phase at the temperature and pressure of transmission.

2. A method as claimed in claim 1, where the hydrocarbon is selected from (a) between 26 and 40% of at least one C2 compound if the pressure is about 1000 psia, declining smoothly to about 6% to 15% of said C2 compound if the pressure is about 2200 psia, or (b) between 12% and 5% of a C3 compound, if the pressure is about 1000 psia, declining smoothly to the C3 amount which will not cause liquefaction at the pressure used when the pressure is above 1000 psia.

3. A method as claimed in either claim 1 or claim 2, in which there is not more than 1% by volume of carbon dioxide in the resulting mixture.

4. A method as claimed in claim 1 or claim 2, in which there is not more than 2% nitrogen in the resulting mixture.

5. A method as clamed in any of claims 1-4, in which the temperature at which the resulting mixture is transmitted is between -20°F and +120°F.

6. A method as claimed in any of claims 1-4, in which the pressure at which the resulting mixture is transmitted is between 2160 psia and 1150 psia.

7. A method as claimed in any of claims 1-6 in which the C2 hydrocarbon added to the natural gas is ethane.

8. A method as claimed in any of claims 1-7, in which the C3 hydrocarbon added to the natural gas is propane.

9. A gas mixture, for use in a pipeline at a pressure greater than 1,000 psia and a temperature of from -40 degrees F to +120 degrees F, which comprises:
(a) from 68 to 92% by volume of methane;
(b) from 6 to 35% by volume of ethane;
(c) from 0 to 9% by volume of propane;

(d) from 0% by volume of C4 hydrocarbons to a percentage of C4 hydrocarbons which does not liquify at the pressure used;
(e) not more than 1 % of carbon dioxide;
(f) not more than 2% of nitrogen, the total being 100%, and such mixture being completely gaseous with no liquid phase at the temperature and pressure of intended operation.

10. A gas mixture as claimed in claim 9, said gas mixture being at a pressure of 1000-2200 psia and a temperature of from -20 degrees F
to +120 degrees F.