Closed oil liquid ring gas compression system with a suction injection port

TECHNICAL FIELD

This invention relates to gas compression systems, and more particularly to a closed oil gas compression system utilizing a liquid ring pump.

BACKGROUND OF THE INVENTION

Many of the existing hydrocarbon formations have been produced to such a point that the natural gas available in these reserves is at low pressures or below atmospheric pressure. To produce natural gas from these reserves, the gas must be pumped from the formation and compressed for sale. The cost to pump and compress gas can be substantial; therefore, cost saving measures are important in making retrieval of the gas economically viable.

Generally a self contained compression system is used to extract natural gas from low or below pressure reserves, and is located on the well site. The compression system comprises a variety of apparatus, including a compressor. Typically, prior art compression systems employ a screw type compressor to draw gas from the formation and compress it for sale. However, screw compressors are expensive and require relatively high energy inputs to compress the gas. Further, these compressors have parts with metal-to-metal contact which require a constant oil source. The oil is deposited into the pump and eventually is carried away by the compressed gas, thus the screw pumps use oil and the oil source must regularly be replenished. Other compressor types commonly used in these applications also require a constant oil feed.

The gas extracted from some low or below pressure formations contain vapors and entrained liquid. Typical compression systems used with these wells must dry the gas before it can be compressed, because screw and other typical compressors cannot handle the liquid. In these systems, when the compressor encounters liquid or vapor the compressor will overload and shut down.

Therefore, there exists a need for a compression system which can handle gas having vapors and entrained liquid. Also, a closed oil system is desirable because the oil reserves need not be refilled as often. Finally, the compressor system should compress efficiently and at low cost.

SUMMARY OF THE INVENTION

The present invention is drawn to a closed oil compression system employing a liquid ring pump. The invention is an apparatus for compressing a gas from a well. The gas has entrained liquid and vapor. The apparatus has a scrubber vessel for receiving the gas and separating at least a portion of the liquid and vapor. A storage vessel stores a seal liquid. A liquid ring pump is connected to the scrubber vessel and storage vessel. Seal liquid is mixed with the gas before it enters the pump, and the liquid is used to compress the gas. A separator vessel is connected to the pump and the storage vessel for separating at least a portion of any seal liquid entrained in the gas and returning the separated seal liquid to the storage vessel.

The storage vessel is integral with the scrubber vessel. The scrubber has an internal partition which divides the scrubber vessel into a first and second chamber, wherein the second chamber is the storage vessel. The separator vessel has a coalescing filter that further separates seal liquid from the gas. The separator vessel has a cylindrical splash guard surrounding the coalescing filter. A scavenger line runs from the coalescing filter to a condition between the scrubber and the pump. The liquid ring pump is single stage having a single inlet and single outlet. Further the apparatus has a heat exchanger and temperature responsive valve. The temperature responsive valve routes seal liquid from the storage vessel through the heat exchanger before mixing with the gas if the temperature of the seal liquid is above a given temperature.

Further, the present invention encompasses a method of compressing wet gas from a well, the wet gas having entrained liquid and vapor. The method includes the steps of providing a suction scrubber, a storage vessel containing seal liquid, a liquid ring pump, and a discharge separator. At least a portion of the liquid and vapor are separated from the gas with the suction scrubber. The seal liquid is injected into the gas before it enters the liquid ring pump. The gas is compressed with the seal liquid in the liquid ring pump. At least a portion of any seal liquid from the gas is separated in the discharge separator and the separated liquid is fed back into the storage vessel.

Further steps include cooling the seal liquid before injection into the gas. A coalescing filter with a splash guard is provided in the discharge separator and the coalescing filter separates at least a portion of any seal liquid from the gas. A partition is provided in the suction scrubber to form the storage vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic of the gas compression system of this invention.

FIG. 2

is an elevation view of the suction scrubber of the system of FIG.

1

.

FIG. 3

is an elevation view of the discharge separator of the system of FIG.

1

.

DISCLOSURE OF THE INVENTION

Referring to

FIG. 1

, the system of this invention described in general terms accepts a feed stream

10

from a well, generally referred to as wet gas because it contains a vapor constituent and sometimes a small liquid constituent entrained in the gas. Feed stream

10

is supplied at a relatively low pressure and is drawn into suction scrubber

12

which removes by gravity heavier vapor and liquid portions and enables the gaseous and lighter vapors to be drawn out of scrubber

12

through suction line

14

. The separated liquid falls to the bottom and is stored in a primary chamber

16

of scrubber

12

.

Scrubber

12

has a secondary chamber

18

separated from primary chamber

16

in which seal liquid, preferably a conventional SAE 10W or higher viscosity grade hydraulic oil, is stored. Seal liquid is removed from secondary chamber

18

through seal liquid line

20

and routed to a single stage liquid ring pump

22

as needed. En route to pump

22

, seal liquid is combined in metered portions with the gas and lighter vapors from suction line

14

. Liquid ring pump

22

uses the seal liquid to compress the gas from line

14

and draws a vacuum on line

14

and chamber

16

. A mixture of compressed gas, vapor, and any seal liquid and condensed liquid entrained in the gas is then routed through discharge line

24

to discharge separator

26

. Separator

26

removes any liquids, including entrained seal liquid, and the compressed gaseous product, including hydrocarbon vapor, discharges through discharge outlet

28

. Discharge outlet

28

leads to a natural gas pipeline for further processing. The separated liquid portion, which is predominantly seal liquid, falls to the bottom of separator

26

and is routed back to secondary chamber

18

through seal liquid fill line

30

as needed. The entire system, including scrubber

12

, pump

22

, separator

26

, and all piping, sensors, and valves are held on a single skid

32

(FIGS.

2

and

3

).

More specifically, scrubber

12

, as shown in

FIG. 2

, is a generally cylindrical pressure vessel with a partition

34

separating the primary chamber

16

above and secondary chamber

18

below. Wet gas from feed stream

10

is drawn into the interior of primary chamber

16

near an upper end. The heavier vapors disperse and liquid portions fall to the bottom of primary chamber

16

, while the gaseous and lighter vapor portions are sucked upward through suction line

14

. Suction line

14

intersects primary chamber

16

above feed stream

10

. Eventually, the dispersed heavier vapor condenses and falls to the bottom and combines with the separated liquid portion. A seal liquid drain line

36

is positioned in the lowest point of scrubber

12

in secondary chamber

18

, and a scrubber drain line

38

is positioned above and adjacent to partition

34

in primary chamber

16

. The separated liquid collects in and fills the bottom of primary chamber

16

and scrubber drain line

38

allows the liquid to be periodically removed. Seal liquid is stored in secondary chamber

18

, and seal liquid drain line

36

allows the seal liquid to be periodically removed. A liquid level controller

40

is mounted in a side of scrubber

12

to sense the liquid level in primary chamber

16

and report to a central control panel

42

(FIG.

1

). Liquid level controller

40

is set to shut off pump

22

when the liquid level reaches a predetermined height and indicates a liquid level shut down on panel

42

.

Referring again to

FIG. 1

, seal liquid exits secondary chamber

18

through seal liquid line

20

and is routed to a temperature responsive valve

44

. An intermediate valve

46

is positioned between temperature responsive valve

44

and scrubber

12

to allow the flow in line

16

20

to be restricted or entirely shut off. Temperature responsive valve

44

is a thermostatic coil valve responsive to temperature to route liquid through a heat exchanger

48

and to a metering valve

50

if its temperature is above a given value, preferably 160° Fahrenheit, or straight to the metering valve

48

50

if its temperature is below that given value. Heat exchanger

48

is sized to cool the liquid to the given value, in this case 160° Fahrenheit. A temperature sensor

52

is positioned at the entrance of valve

50

to sense the temperature of entering liquid and report to control panel

42

.

Suction line

14

has a check valve

54

to prevent back-flow of gas and vapor into primary chamber

16

of scrubber

12

. A suction shutdown sensor

56

is positioned in suction line

14

to shut pump

22

off when the vacuum in line

14

reaches a predetermined point and indicates a suction shutdown on panel

42

. Line

14

converges with seal liquid line

20

after metering valve

50

and before liquid ring pump

22

. Metering valve

50

meters the amount of seal liquid introduced into the gas in suction line

14

.

Liquid ring pump

22

is conventional single-stage liquid ring pump which uses the seal liquid to compress the gas and light vapor stream from suction line

14

. It has a single inlet, suction line

14

, and a single outlet, discharge line

24

; wherein a two-stage liquid ring pump would have separate inlets and outlets for the gas and the seal liquid. Liquid ring pumps are unique in that they can compress gas with significant amounts of vapor to high pressures without damage to the pump. Pump

22

creates a vacuum in suction line

14

, thus drawing gas into suction scrubber

12

and through suction line

14

. The gas and seal liquid mixture entering pump

22

is separated and compressed, then routed through discharge line

24

to separator

26

. Discharge line

24

has a temperature shutdown sensor

58

which reports to central control panel

42

and can shut pump

22

down if the temperature of the gas and liquid mixture is over a predetermined temperature. A discharge shutdown sensor

60

is positioned in discharge line

24

to shut down pump

22

if the pressure in line

24

is above a predetermined pressure.

Referring to

FIG. 3

, discharge separator

26

is similar to scrubber

12

in that it is a generally cylindrical pressure vessel, and the compressed mixture is drawn in near an upper end. As the compressed mixture from line

24

enters separator

26

the heavier liquids fall to the bottom. A cylindrical baffle or splash guard

62

joined to the top of separator

26

and extending downward in front of the entrance of line

24

contains a cup-shaped coalescing filter

64

. The cylindrical sidewalls of splash guard

62

are impermeable and spaced inward from the sidewalls of separator

26

. This creates an annular space between the sidewalls of splash guard

62

and separator

26

. The discharge of line

24

strikes the sidewall of splash guard

62

. The sidewall of coalescing filter

64

is smaller in outer diameter than the diameter of splash guard

62

creating an annular space. The bottom of splash guard

62

has a cover

66

with holes that allow gas and light vapor to be drawn into the coalescing filter

64

. Most of the entrained liquid coalesces on filter

64

and falls to the bottom of separator

26

as liquid, while the final gaseous portion which has now been compressed is removed through discharge outlet

28

. Note that liquid vapor and lighter hydrocarbons produced from the well along with the gas is not significantly separated by separator

26

and remains in the discharge gas. The liquid separated by separator

26

is primarily seal liquid.

A scavenger line

72

runs from the bottom of coalescing filter

64

out of discharge separator and into suction line

14

downstream of check valve

54

(FIG.

21

). Scavenger line

72

crates a lower pressure within coalescing filter

64

to increase flow through the filter

64

, and thus increase the amount of seal liquid captured. Separator

26

has a fill line

68

through which seal liquid can be added to the system, and a pressure relief valve

70

.

The apparatus of this invention has several significant advantages over the prior art. The system is a closed oil system; therefore does not require a continuous oil feed. The guard in the discharge separator boosts its separating efficiency and increases the life of the coalescing filter. Therefore, more of the seal liquid is recovered and the product discharged through the discharge outlet is dryer. The two chambered suction scrubber allows seal liquid to be stored in the bottom of the scrubber without the need for a separate storage vessel. Seal liquid is also stored in the discharge separator. The use of a hydraulic oil as seal fluid as opposed to water and glycol allows a majority of the seal fluid to be recovered in the discharge separator. The use of a single stage liquid ring compressor, wherein the gas and seal liquid are combined before the compressor, allows the system to operate at a much greater flow rate and compress to a greater pressure. Because of the liquid ring compressor, the system can handle much higher liquid content in the feed stream. Also the liquid ring compressor costs less and requires a lesser energy input to operate at the same or higher compression as other systems.

While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes and modifications without departing from the spirit thereof.