Technical field of the present invention

The present invention relates to methods for removing water from natural gas. Technological background of the present invention

Natural gas is normally transported from supply stations to end users at higher pressures of 50 bar to 100 bar. This higher pressure gas must be depressurized in regulator stations prior to being used by the end users. The energy generated by this pressure release in the regulator stations is normally wasted. If fed to expansion turbines, the energy could be utilized for power generation.

After expansion of the gas, the temperature of the gas will drop below 0°C. In order to avoid water in the natural gas from icing after expansion, the natural gas needs to be preheated before being fed to the expansion turbines.

Disclosure of the present invention: object, solution, advantages

Starting from the disadvantages and shortcomings as described above as well as taking the prior art as discussed into account, an object of the present invention is to overcome the limitations and problems that earlier methods have experienced.

These objects are accomplished by a method comprising the features of claim 1 as well as by a method comprising the features of claim 5. Advantageous embodiments and expedient improvements of the present invention are disclosed in the respective dependent claims.

The present invention basically provides for removing water by feeding the natural gas to at least one molecular sieve prior to the natural gas being fed to the expansion turbines thereby removing the need to preheat the natural gas. By avoiding this preheating of the natural gas, several advantages are realized. With no preheating, thermal energy is saved. The overall economics are improved and the process is less complicated. Further, there is no cold energy captured after expansion.

Basically, a method for removing water from natural gas is disclosed. Water is removed from the natural gas before it is fed to an expansion turbine, in particular by passing the natural gas through at least one molecular sieve.

This will inhibit ice formation in the natural gas stream after it has been expanded in the expansion turbine so that additional heat need not be applied.

The energy that results from the expansion of the natural gas can be used in refrigeration or other activity, and the natural gas can be fed to storage or an appropriate end use.

In one embodiment of the present invention, there is disclosed a method of feeding natural gas to an expansion turbine to generate energy comprising removing water from the natural gas before the natural gas is fed to the expansion turbine.

In a second embodiment of the present invention, there is disclosed a method for inhibiting formation of ice in a natural gas stream prior to the natural gas stream being fed to an expansion turbine comprising removing water from the natural gas stream, in particular by feeding the natural gas stream through at least one molecular sieve.

The natural gas that is treated may advantageously be at a purity of more than ninety percent methane.

The amount of water in the natural gas may expediently range from about 30 mg/m ³ to about 70 mg/m ³ .

The molecular sieve material may favourably be any molecular sieve material that can adsorb water. Typical molecular sieve materials may preferably be selected from the group consisting of zeolites such as type 3A, 5A, ZSM-5 and 13X.

The molecular sieve may advantageously be contained in an adsorbent bed or adsorption bed which can expediently comprise at least one adsorbent bed, and more preferably two adsorbent beds. This adsorption process can favourably be a cyclical process that is preferably a temperature swing adsorption (TSA) process.

The natural gas when fed into the adsorption process may preferably be at a pressure from about 50 bar to about 100 bar.

After the natural gas has been subjected to the adsorption process, the resulting natural gas which is free from water may typically be at ambient temperature and/or may typically be at a pressure of about 50 bar to about 100 bar.

The expansion turbine may advantageously be a typical expansion turbine that will produce energy from a gas feed. The energy generated by the expansion turbine can expediently be fed to a generator where the output of the generator can favourably be used for refrigeration or dry ice production. The natural gas that is recovered from the expansion turbine can preferably be fed its intended to storage depending upon the operator's needs. Brief description of the drawing

For a more complete understanding of the present inventive embodiment disclosures and as already discussed above, there are several options to embody as well as to improve the teaching of the present invention in an advantageous manner. To this aim, reference may be made to the claims dependent on claim 1 and on claim 5; further improvements, features and advantages of the present invention are explained below in more detail with reference to the following description of a preferred embodiment by way of non-limiting example and to the appended drawing figure taken in conjunction with the description of the embodiments, of which: FIG. 1 shows a schematic of a process of the present invention for removing water from a natural gas stream prior to the natural gas stream being fed to an expansion turbine.

Detailed description of the drawings; best way of embodying the present invention

Before explaining the present inventive embodiment in detail, it is to be understood that the embodiment is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the present invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

In the following description, terms such a horizontal, upright, vertical, above, below, beneath and the like, are used solely for the purpose of clarity illustrating the invention and should not be taken as words of limitation. The drawings are for the purpose of illustrating the invention and are not intended to be to scale.

Turning to FIG. 1 , a schematic showing a process for removing water from natural gas prior to it being fed to an expansion turbine, according to the present invention is described.

Natural gas which is typically ninety percent methane is fed through line 1 to adsorbent beds A and B. The natural gas stream will typically contain water in an amount ranging from 30 mg/m ³ to 70 mg/ ³ .

The natural gas is split between two lines 2 and 3 which feed the natural gas containing the water to the molecular sieve containing beds A and B respectively depending upon the step of the cycle.

The molecular sieve material will adsorb water in the beds A and B and the now water-free natural gas will be fed to lines 4 and 5 from beds A and B respectively depending upon the step in the adsorption cycle to line 6. Typically the adsorbent material in the beds A and B will be a zeolite such as a 3A, 5A, ZSM-5 or 13X type zeolite.

The preferred adsorption cycle is a temperature swing adsorption (TSA) cycle. Typically the methane gas stream containing the contaminant water is passed through the first bed A through the feed of natural gas 1 to line 2 where water is adsorbed on the adsorbent material present in the bed A. The gas stream being treated is typically at ambient temperatures and will be at a feed pressure of 50 bar to 100 bar.

Once adsorption is complete as determined by measuring breakthrough, water-free natural gas is fed through line 4 to line 6 for entry into the expansion turbine C. The feed stream of natural gas containing water switches to line 3 and the second bed B where water will be adsorbed on the adsorbent material present therein.

The temperature of bed A will be raised by purging with a hot inert gas stream through line 4. This will desorb water from the adsorbent material in bed A while bed B is undergoing the adsorption step and producing water-free natural gas which is fed through line 5 to line 6 and into the expansion turbine C.

When bed B is near breakthrough, feed of the natural gas stream is stopped in line 3 and its flow is diverted into bed A again through line 2 where the adsorption cycle begins anew. Bed B is then subjected to a hot inert gas stream feed through line 5 which will desorb the water from the adsorbent material in bed B and preparing it to again receive natural gas for treatment.

The water-free natural gas stream produced by either bed A or bed B which is at a pressure of about 50 bar to about 100 bar and ambient temperature will be fed through line 6 to the expansion turbine C where it will be expanded and the energy produced by this expansion will be captured and fed through line 8 to a generator D. The natural gas can be significantly reduced in temperature without any icing occurring due to the removal of the water by the inventive methods.

The natural gas which is now at temperatures as low as -50°C once it has been through the expansion turbine is fed through line 9 to a process requiring natural gas chosen by the operator or to a storage unit.

It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result. List of reference signs

1 line for water-containing natural gas

2 line for water-containing natural gas to adsorbent bed or adsorption bed A

3 line for water-containing natural gas to second adsorbent bed or adsorption bed B

4 line for water-free natural gas from adsorbent bed or adsorption bed A

5 line for water-free natural gas from second adsorbent bed or adsorption bed B

6 line for water-free natural gas to expansion turbine C

8 line for energy from expansion turbine C to generator D

9 line for natural gas from expansion turbine C

A adsorbent bed or adsorption bed, in particular first adsorbent bed or first adsorption bed, of molecular sieve or molecule sieve

B second adsorbent bed or second adsorption bed, of molecular sieve or molecule sieve

C expansion turbine

D generator