US3318223A - Method and means for disposal of waste gas - Google Patents

Description

May 9, 1967 J. L. MAHER METHOD AND MEANS FOR DISPOSAL OF WASTE GAS 3 Sheets-Sheet 1 Filed Aug. 6, 1965 INVENTOR JOSEPH L. MAHER ATTORNEY y 1967 J. L. MAHER I 3,318,223

METHOD AND MEANS FOR DISPOSAL OF WASTE GAS Filed Aug. 6, 1965 3 Sheets-Sheet 2 GAS INLET I N VEN TOR JOSEPH L. MAH R 1 ,03 2 BY 1 May 9, .1967 I J. 1.. MAHER METHOD AND MEANS FOR DISPOSAL OF WASTE GAS Filed Aug. 6, 1965 3 Sheets -5heet 5 II I His- ATTORNEY I United States Fatent C 3,318,223 METHOD AND MEANS FOR DISPOSAL OF WASTE GAS Joseph L. Maher, Tulsa, Okla., assignor to Crest Englueering, Inc., Tulsa, Okla, a corporation of Oklahoma Filed Aug. 6, 1965, Ser. No. 477,728 8 Claims. (Cl. 98-1) The present invention relates to disposal of waste gas without combustion. More specifically, the invention relates to dilution of Waste gas with atmospheric air so that release of the mixture will not result in a hazard.

It is presently customary to dispose of waste gas, from petroleum production, by burning such waste gas. On shore installations it is generally practical to locate a burner well above ground level and supply waste gas for combustion at the burner. However, the location of a flare in proximity to ofishore installations can be a formidable problem. It is often sensible to limit the location of flares to minimum distances from platforms on which production and storage [facilities are located. The provision of a separate platform on which to mount a flare can loom as an expense out of proportion to the flare support function of the platform. It has become feasible to study extensively methods and means of disposing of waste gas from production platforms without ignition of the gas.

In general, flammable gas comes from two sources within the initial production installation. Separator gas evolves continuously. Vapors originating from overpressured vessels, and released through relief valves, flow in unsteady volumes. Any equipment utilized to dispose of the calculable volumes from separators and/or the unsteady flow from relief valves must be operated continuously, sized to be ready ifOl the maximum instantaneous rate of flow of relief gas. The present invention provides a method and means for disposing of gas within this requirement.

In evolving the present invention, it was observed that natural gas may be safely dispersed in the atmosphere provided it is first mixed with sufficient air to dilute it below the combustible concentration. For pure methane, the lower limit of combustion is approximately five percent gas by volume, The lower limit decreases to 3.22 percent for ethane. Therefore, for a natural gas having methane as the major component, dilution with air should be carried down to a gas concentration of approximately three percent.

A principal object of the present invention is to dilute waste gas with air prior to dispersing the mixture in the atmosphere.

Another object is to mix waste gas with air quickly to dilute the gas.

Another object is to mix waste gas with air while increasing the flow of the mixture very little more than either the flow of waste gas or the flow of air.

Another object is to continuously detect the dilution of the gas with air and terminate the flow of gas at a predetermined percentage of dilution.

Another object is to provide a positive draft for the mixture regardless of the strength of air flow transverse the entrance for air to the mixing which obtains the desired dilution.

The present invention contemplates flowing waste gas to a predetermined area and distributing the gas over the area. It is then contemplated that air will be flowed to and distributed over the area in quantities sufficient to dilute the gas a predetermined percent. The gas and air are then mixed and dispersed to the atmosphere.

The invention further contemplates waste gas being distributed over an area from a conduit with multiple open- 'ice in-gs. Air is conducted over this same area and the two fluids mechanically mixed to dilute the gas to a nonhazardous percentage.

The mixing can be carried out with a fan of such diameter and speed as to impart a low velocity of flow to the dispersed mixture, a velocity only a little more than the separate velocities of the air and gas.

The invention also contemplates the percentage of dilution being detected continuously by an instrument which is connected to shut off the supply of gas to the dilution process where the dilution reaches a predetermined percent.

Finally, the invention contemplates at least one deflecting vane in the conduit for air, the vane being in a plane oriented to deflect air flowing transverse the air conduit so at least a portion of the air is deflected toward the mixing zone.

Other objects, advantages and features of this invention will become apparent to one skilled in the art upon consideration of the written specification, appended claims, and attached drawings, wherein;

FIG. 1 is an elevation of an ofi-shore production platform on which a dispersal unit including the present invention is embodied;

FIG. 2 is a sectioned elevation of the dispersal unit; and

FIG. 3 is a sectioned plan view along lines 33 of the unit of FIG. 2.

Reduction to practice In reducing the present invention to practice, a relatively small test unit was first designed. The test unit was sized to dilute in the order of one million standard cubic feet per day (s.c.f.d.) of waste gas. Following successful tests of this first unit, a facility for handling seven million s.c.f.d. of gas became the first commercial embodiment of the invention.

The original concept of mixing sufiicient air with waste gas to produce a mixture which is not hazardous is readily understood. The specific form of a structure capable of mixing air with waste gas may be given many variations. However, the rotary multi-bladed fan has several attractive practical considerations. It was decided to utilize a fan of this type which was originally developed for use with cooling towers. The waste gas and air conducted to the rotating fan would be mixed to form the non-hazardous mixture.

The waste gas was provided with a manifold conduit to the fan and from this conduit the gas was distributed at a plane from which it would be fed into the fan blades. The distribution was made by branch pipes connected to the waste gas manifold conduit with their outlets terminated in a common plane parallel to the rotating fan blades. Air was drawn into the fan, along with the distributed waste gas, the rotating fan blades mechanically mixing these two fluids.

In sizing the waste gas distribution branch conduits, the velocity of the gas from the conduits had to be carefully considered. The velocity could reach a value which would cause resonance as the gas stream is interrupted by the fan blades rotating above the point of discharge of the gas. Controlling the maximum velocity by proper sizing of the branch conduits obviated this source of noise.

It was discovered in testing the first unit that satisfactory mixing took place in a very short length of travel by the mixture from the fan discharge. However, it was desirable to provide a stack of some length for travel of the mixture to a point of discharge. If the fan power should fail, a stack of some length would act as a chimney with a natural draft capable of drawing in enough air to provide a fair degree of mixing with the waste gas by mixing process.

natural turbulence. This mixture could then be ejected from the stack high enough in the air to greatly reduce the possibility of its becoming a hazard.

Another of the many considerations of the function by the unit included the effects of surface winds on the Winds traveling transverse to the axis of the stack could create negative pressures in the stack which would cause the waste gas to be drawn from its branch conduits and away from the mixing process at the fan. It was conceived that deflector plates at the mixing end of the stack provided an impact surface for winds which would deflect at least a part of the winds up into the mixing area and insure against negative pressure development in the stack.

Obviously instrumentation can be provided to sample the mixture at various points along the length of the stack to determine the degree of dilution at such points. No such system has been shown in order to not encumber the disclosure with elements which would detract from the invention. However, it is to be understood that the applicant is well aware that an analyzing system could include the function of flashing a visual warning if the dilution pattern deteriorated. Further, it is evident that such a system could include means of controlling the flow of waste gas to the unit, limiting it as desired in view of any deterioration in the efliciency of the mixing process.

Overall production installation 1 be conducted toshore facilities or storage on the platform.

Many andlvaried arrangements have been used and considered. However, the waste gas at this location has been a problem;

' It has been customary to burn waste gas. On land this burning equipment is not difiicult to provide, sufficiently remote from the production facility to eliminate the hazard. But how about these off-shore installations? If the burning is removed to a safe distance from platform 1, a separate platform for this one function could become extremely expensive. In water hundreds of feet deep a platform for this single function could cost many hundreds of thousands of dollars. The present invention provides a process and apparatus for simply disposing of this waste gas right on the production platform 1 itself. Unit 2 receives this waste gas, mixes it with air and disperses the mixture high in the air. Without its being burned, the gas is'rendered harmless to the production facility and personnel.

General structural arrangement of unit 2 Referring specifically to'FlG. 2, the waste gas dispersal A unit, embodying the present invention, is illustrated as a skid-mounted stack 3 mounted to extend vertically up into the air. Stack 3 is supported by structural members 4 which extend up from a skid 5 base to support the lower end 6 of the stack well above the horizontal plane of the skid. A flared skirt 7 extends downward from the periphery of the stack lower end 6. A conduit 9 brings the waste gasto the stack and also forms a convenient structural mount for a motor 10 which is linked to rotate fan blades 11 at the lower end 8 of the stack. Air flows Fan and distributi n system FIG. 3 is a section of FIG. 2 along lines 3-3 to provide a plan view of the fan blades 11 and distributor branches 13 from waste gas conduit 9. Motor 10 is also disclosed'to further advantage, together with its linkage to gearing at the central hub of blades 11. Motor 10 is located outside of skirt 7 to provide convenient access for maintenance and servicing of the motor.

Taking FIGS. 2 and 3 together, it is clear how the branch conduits terminate in a common plane which is parallel to the plane of fan blade rotation and on a circle about the center of blade rotation above which a high degree of turbulence is generated by the rotating blades. The number and sizing of branch conduits 13 are selected to give a predetermined maximum velocity to the waste gas discharged from these branches.

The release of gas from branch conduits 13, in the plane beneath fan blades 11, is a distribution of the gas from conduit 9 into a zone of high turbulence generated by the rotating blades. The gas is directed upward, toward the blades 11 at a seletced distance from their center of rotation. The rotating blades cut these streams of upflowing gas and mechanically distribute the gas over the cross-section of stack 3. 7

Air is drawn into the lower end -6 of the stack 3. The

characteristics of the flow of fluids under the mechanical force of fan surfaces dictate the funnel approach provided by flared skirt 7. Air will flow smoothly from the surrounding atmosphere, up into skirt 7, and approach the mixing process at the fan uniformly. Both this air, and gas from conduits 13, will flow together into the space swept by the blades 11 and be mixed thoroughly in the turbulence generated by the selected section of the blades by the time they have traveled a short distance up the stack 3 on the upper side of the fan.

If winds occur, traveling transverse the axis of stack 3, they could tend to draw gas from conduits 13 down toward the air directly above the skid 5. Gas would then flood this area above the skid and spread over surrounding equipment and personnel on the latform. This could be a very hazardous condition- I The negative pressures in stack 3, which could be created by transverse winds, are obviated by arranging at .least one vertical barrier directly below stack 3 for the transverse traveling winds to strike. These winds, striking this barrier, will be deflected, at least partially, up the stack 3 and preclude the development of negative pressures within the stack.

The deflecting barrier is provided by plates 15 and I 16 which divide the cross-sectional area of stack 3 into quarters. This arrangement is more readily understood from'the plan view of FIG. 3.

The plates 15 and 16'extend from skid 5 up to the entrance formed by skirt 7. Winds, sweeping across the skid, strike the vertical surfaces of these plates and are at least partially deflected up into the fan and lower end 6 of stack 3.

' From the foregoing it will be seen that this invention is 'one well adapted to attain all of the ends and objects 'hereinabove set forth, together with other advantages which are obvious and which are inherent to the method and apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to beunderstood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The present invention having been described, what is claimed is:

1. A method of dispersing waste gas of petroleum production through a vertical stack which is supported Well above a horizontal surface, including,

conducting waste gas of petroleum production to the lower end of the vertical stack,

distributing the waste gas at predetermined positions in a horizontal plane at the lower end of the stack,

flowing air through the plane in which the gas is distributed,

creating a predetermined turbulence in zones above the positions of gas distribution to form a mixture which is non-hazardous,

and discharging the mixture from the top of the stack.

2. The method of claim 1 wherein, the volume ratio of gas and air is maintained in :a range no greater than 3 to 97.

3. A method of dispersing waste gas of petroleum production through a vertical stack which is supported well above a horizontal surface, including,

conducting waste gas of petroleum production to the lower end of the vertical stack,

distributing the waste gas at a horizontal plane at the lower end of the stack,

m-ixing air with the distributed gas in a zone above the plane of gas distribution and in a volume ratio which produces a non-hazardous mixture,

and deflecting at least a portion of any wind which may be directed parallel to and below the plane of distribution up and into the lower end of the stack.

4. The method of claim 3 wherein, the volume ratio is maintained in a range no greater than 3 to 97 of gas and air.

5. A dispersal unit for waste gas of petroleum production, including,

a vertical stack supported from a horizontal surface with its lower end well above the horizontal surface,

a source of waste gas of petroleum production to be dispersed,

a manifold conduit connected between the source and stack so as to discharge waste gas through a series of branch conduit outlet means which are arranged in a predetermined pattern in a horizontal plane at the lower end of the stack,

and fan blades mounted to rotate in a plane above and parallel to the plane in which the waste gas is discharged to create a zone of predetermined turbulence above each branch conduit outlet means in which the gas and air will mix into a non-hazardous mixture and discharge from the upper end of the stack.

6. The unit of claim 5 in which the outlet means are arranged in a circle in their plane a predetermined distance from the center of fan rotation, the fan blades formed to generate turbulence at the circle greater than within the circle.

7. The unit of claim 5 in which the outlet means are sized to control the velocity of the gas discharged and obviate resonance when the fan blades create turbulence above the outlets.

8. A dispersal unit for waste gas of petroleum production, including,

a vertical stack supported from a horizontal surface with its lower end well above the horizontal surface,

a source of waste gas of petroleum production to be dispersed,

a conduit connected to the source and arranged to discharge the waste gas through a series of outlets arranged in a horizontal plane at lower end of the stack,

fan blades mounted to rotate in a plane above and parallel to the plane in which the waste gas is discharged,

and at least one flat plate mounted below the lower end of the stack perpendicular to the planes of gas distribution and blade rotation to receive any wind directed parallel the planes of distribution and rotation to deflect at least part of the air up and into the lower end of the stack.

References Cited by the Examiner UNITED STATES PATENTS 1,316,254 9/1919 Powell 98-115 1,732,315 10/1929 Ray 98-115 1,825,245 9/1931 Nitka 98-115 2,078,580 4/1937 Moore 98-1 2,593,702 4/1952 Schneible 98-115 2,772,625 12/ 1956 Clark 98-115 MEYER PERLIN, Primary Examiner.

Claims (1)

1. A METHOD OF DISPERSING WASTE GAS OF PETROLEUM PRODUCTION THROUGH A VERTICAL STACK WHICH IS SUPPORTED WELL ABOVE A HORIZONTAL SURFACE, INCLUDING, CONDUCTING WASTE GAS OF PETROLEUM PRODUCTION TO THE LOWER END OF THE VERTICAL STACK, DISTRIBUTING THE WASTE GAS AT PREDETERMINED POSITIONS IN A HORIZONTAL PLANE AT THE LOWER END OF THE STACK, FLOWING AIR THROUGH THE PLANE IN WHICH THE GAS IS DISTRIBUTED, CREATING A PREDETERMINED TURBULENCE IN ZONES ABOVE THE POSITIONS OF GAS DISTRIBUTION TO FORM A MIXTURE WHICH IS NON-HAZARDOUS, AND DISCHARGING THE MIXTURE FROM THE TOP OF THE STACK.

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