Solids Separation System for Natural Gas Wells

The present invention relates generally to separator apparatus employed for processing natural gas wellhead effluent, and in particular, to a separator system which will separate solids such as coal, gas and water at the wellhead site.

When processing natural gas at the wellhead site to produce sales gas, it is conventional practice to provide a system for separation of water and hydrocarbons which may include conventional high or low pressure separator apparatus as generally described in my prior U.S. Pat. Nos. 4,579 565 and 4,198,214 the disclosures of which are incorporated herein by reference. In general, such separator apparatus comprises a horizontal vessel having a gas-operated heater associated with a fire tube located in the vessel to provide heat and pressure during the separation process whereby light end hydrocarbons are separated from heavy end hydrocarbons and water to produce sales gas. Such apparatus and systems are designed to be continuously operable at the wellhead site without the necessity for the presence of operator personnel and are intended to be continuously operable by use of self-generated supply gas used for heater fuel and for operation of controls.

In some situations, such as a natural gas well located in a coal field, the wellhead effluent may contain relatively large amounts of water and solid materials such as coal pieces, particles and dust, which can cause problems in production of sales gas and also create environmental problems in connection with disposal of waste material.

A primary object of the present invention is to provide continuously operable separator apparatus which will separate gas, water and solids such as coal in wellhead effluent at the wellhead site in an efficient low cost manner.

Another object of the invention is to provide separator apparatus which will be non-polluting in operation, prevent loss of gas, and enable recovery of the solids.

These and other objects will become apparent throughout the following description of the invention.

In general, the system of the present invention comprises an elongated cylindrical separator tank means mounted in a vertical attitude for receiving relatively high pressure (e.g. 100 to 1000 or more psig) wellhead effluent. Liquids are collected in a lower portion of the separator tank means and gas is collected in an upper portion thereof. Liquids and solids are removed through a bottom portion of the tank means. A vertically disposed cylindrical elongated hood means of relatively small diameter, less than the inside diameter of the tank means, is coaxially mounted within a lower portion of the tank means containing the wellhead effluent liquids so as to be surrounded by the liquids and enable upward flow of gas bubbles between the outer wall of the hood means and the inside wall of the tank means. The hood means has an effluent inlet means located between a closed top end portion and an open bottom end portion to initially separate the gas from the liquids and solids and create a pocket of trapped gas therein. A relatively large diameter cap means is coaxially mounted on the top end portion of the hood means to provide a gas trap chamber for upwardly flowing gas bubbles and a relatively narrow width annular flow channel between the side wall of the tank means and the cap means and also to provide a gas trap means adjacent to the flow channel. The hood means may include a plurality of outwardly and downwardly extending gas discharge scrubber means in communication with the gas pocket in the interior of the hood means to enable downward gas discharge into the liquids surrounding the hood means to cause downward flow of fine solid particles relative thereto. A solids collection means is mounted below the hood means and has a slurry discharge outlet means leading therefrom for removal of the solids in a liquid slurry. A mist extraction means is situated in the upper portion of the tank means to entrain liquid droplets prior to discharge of gas through a gas outlet means at the top of the tank means.

An illustrative and presently preferred embodiment of the invention is shown in the accompanying drawing wherein:

FIG. 1 is an elevational schematic view partially in section showing a separator apparatus; and

FIG. 2 is an enlarged elevational view of a hood means with bubble column means and gas dispersion means.

In general, the present invention comprises an elongated cylindrical tank means 10 as shown in FIG. 1 mounted in a vertical attitude for receiving natural gas wellhead effluent containing water and/or liquid hydrocarbons and solids, such as coal particles, through an inlet means 12 and a centrally located cylindrical hood means 14. A conventional liquid level control means 16 is provided in an intermediate portion of tank means 10 for maintaining a body of water and other liquids 17 in the tank means 10 at a level 18 above the hood means 14 and below the upper end portion 19 of the tank means 10 and to provide an elongated gas collection chamber 20 in the upper portion of tank means 10.

Hood means 14, as shown in Figs. 1 and 2, comprises an elongated cylindrical member 21 having an open bottom end portion 22 for discharging the water and solids portion of the well effluent into a lower portion 23 of tank means 10 at a location spaced upwardly a substantial distance from the bottom 23B of tank means 10. Hood means 14 also has a closed upper end portion 24 providing a closed chamber 25 above inlet opening 26. A baffle and gas trap mean 28 is mounted on the upper end portion of hood means 14 for collecting upwardly moving gas bubbles in the liquid and radially discharging collected gas back into the liquid in a narrow width channel between the baffle and gas trap means 28 and the side wall of the separator tank means 10. Baffle and gas trap means 28 comprise a conical cap member 29 having a diameter substantially larger than the diameter of cylindrical member 21 fixed to the upper end portion 24 of hood means 14 and an annular side wall member 31 having a plurality of circumferentially spaced circular gas discharge openings 32. A plurality of circumferentially spaced gas discharge means 34 are mounted on the outer periphery of hood means 14 with radially outwardly extending gas inlet openings 35 connected to gas collection chamber 25. Downwardly facing gas discharge openings 36 are located in an enlarged diameter discharge member 37 having a plurality of circumferentially spaced gas discharge slots 38 and a cylindrical gas discharge opening 39 at the lower end portion thereof. A baffle plate 40 may be centrally mounted in member 37 to cause flow of gas thereabout.

In normal continuous operation, the natural gas wellhead effluent is discharged at wellhead pressure, e.g. 1000 psig, into hood means 14 through inlet opening 26. Liquids and solids flow downwardly toward the bottom portion 23 of tank means 10 through discharge opening 22 to form a slurry of water indicated by wave lines and solid particles and dust. The heavier particles will settle toward the bottom of the tank means by gravity. The lighter particles and dust may be carried upwardly with the gas which rises toward the top portion 20 of tank means 10 as bubbles indicated by circles. Wellhead gas under pressure is trapped in chamber 25 and maintains a liquid level in member 21 and members 37 below radial gas discharge inlet openings 35 and adjacent the upper end portions of slots 38 as illustrated by dotted line 41. Tank means 10 is filled with a body of liquids which is primarily water and extends between tank bottom portion 23B and liquid level control means 16 so that hood means 14 is completely immersed in the liquids. A relatively large width annular gas flow channel 42 is provided between the outside of hood cylinder 21 and the inside of the tank wall 43. Gas entrained in the liquids is carried into the body of liquids as liquids are supplied through central main effluent discharge opening 22. Small bubbles of gas are also discharged from chamber 25 into the body of liquids in gas flow channel 42 through circumferentially spaced gas discharge means 34. The small gas bubbles are washed by the water to remove and reduce upward movement of solid particles and dust. In this manner, gas bubbles in the body of liquids continuously rise through the body of liquids toward the gas collection chamber 20 in the upper end portion of tank means 10 while solid particles in the body of liquids continuously descend toward the bottom portion 23B of tank means 10. In order to further reduce upward movement of solid particles and dust, baffle and gas trap means 28 provide a relatively narrow width annular flow channel 44 between annular side wall member 31 and side wall portion 43 of tank means 10. Baffle and gas trap means 28 also provide an annular gas trap chamber 45 which receives upwardly rising gas bubbles and from which gas flows radially outwardly into flow channel 44 through circular openings 32 in annular side wall member 31. In this manner, dust and very fine particles are removed from the gas during flow through circular openings 32 and flow channel 44. The cap member 29 has a conical shape so that any particles carried upwardly beyond flow channel 44 will settle toward the inclined upper surface 46 and move downwardly toward and through flow channel 44.

A slurry solids collection means 50 is mounted below hood means 14 to collect and concentrate solids which are continuously removed as a relatively dilute water-solids slurry through discharge conduit means 52, 54. Collection means 50 is cone shape with an upper annular inlet portion 60 having a relatively large diameter so as to extend radially a substantial distance beyond discharge opening 22 and provide an annular rim portion 61 located closely adjacent tank side wall portion 62. Inlet portion 60 is located directly beneath and in relatively closely spaced axial relationship to hood discharge opening 22 so that most of the solids will descend into and be contained by the collection means 50. An annular relatively small diameter lower discharge portion 64 is connected to discharge pipes 52, 54 by a coupling member 65. In order to remove solid materials which may accumulate in the tank bottom portion 23B, a drain means 66 and a clean-out opening means 67 are provided.

A conventional mist extractor means 70 is located at the top of tank means 10 to remove fine mist droplets of moisture from the gas prior to discharge into a gas outlet line means 72 for delivery to a sales gas line or to additional processing apparatus. In addition, a conventional gas dryer column means 74 may be mounted on the top of tank means 10 to receive some of the gas and to provide a source of control and supply gas for operating various conventional gas operated flow control means as hereinafter explained in detail. The tank means 10 is provided with a conventional relief valve means 75, pressure gauge means 76 and rupture head means 77.

The inlet means 12 is provided with a conventional inlet control valve means 80 and a bypass pipe means 82 with an automatic bypass control means 84. Slurry discharge conduit means 52, 54 have associated conventional automatic control valve means 85, 86 and manual valve means 87, 88. Discharge conduit 66 has a conventional manual control valve means 89. Liquid level control means 16 comprises a float means 90 and conventional level responsive controller unit 91.

In the illustrative embodiment, the automatic control devices are gas operated so as to enable automatic continuous operation at the wellhead site by gas supplied from gas drier means 74 or any other suitable source through a supply line 92 to conventional control gas supply means 93 providing variable pressure control gas to supply lines 94, 95, 96, 97. Control gas supply line means 93 comprises various conventional devices such as a shut-off valve means 100, a strainer means 101, a pressure controller means 102, a flow regulator means 103, a relief valve means 104, a pressure gauge means 105, a drip pot means 106 and a regulator means 107.

In operation, initial separation of effluent components occurs as a result of the change of velocity during discharge into the hood means as well as gravitational forces on the gas, liquids and solids. The effluent comprises gas and solids such as coal (granules, particles and dust), as well as water which is present in a large amount. When the effluent is discharged into the tank means 10 from the hood means 14, most of the solid components thereof are carried downwardly toward the collection means 50. The construction and operation is such that most of the gas is initially collected in the gas trap chamber 25 in the hood means above the water level 41 therebeneath and exits downwardly from the hood means 14 through each of the discharge means 34 whereby the water acts to scrub particles such as fine coal dust from the gas and force its descent to the solids collection means 50. All of the gas rises through the water surrounding the hood means 14 for eventual travel to the top portion of the tank means 10. A substantial portion of the gas rises into the gas trap chamber space 45 under the trap means 28 for final dispersion therefrom through the screen means 31 and upward travel through the water to the upper gas chamber portion 20 of the tank means 10. The cover means 29 of the hood means 14 can be conical so that any solids components which may deposit thereon from the surrounding water will slide off for gravitational travel to the solids collection means 50. The gas in elongated gas chamber 20 travels through the conventional mist extractor means 70 to remove fine droplets of moisture therefrom before being discharged through the gas outlet line means 72. Some of the gas enters the gas dryer column means 74 to provide supply gas for the various gas operated control devices.

The separator apparatus herein described is continuously automatically operable at the wellhead site by pressure of the wellhead effluent and gravity for efficient and effective separation of gas, solids and water contained in natural gas well effluent. Gas operated control means are provided so that the apparatus may be operated by supply gas obtained from the apparatus. The apparatus can operate on a continuous schedule with minimal requirements for monitoring and for down-time maintenance. The solids are removed in a water slurry which may be conveniently discharged to any suitable storage means and the solids may be recovered.

It is to be understood that the above description of a preferred embodiment is meant to be illustrative and not limiting, and that it is intended that the appended claims be construed to include various alternative modifications and embodiments of the invention except insofar as limited by the prior art.