WO1995010345A1

WO1995010345A1 - Oil/water separation process

Info

Publication number: WO1995010345A1
Application number: PCT/CA1994/000572
Authority: WO
Inventors: Wayne W. Hesse; Howard T. Marles
Original assignee: Hesse Wayne W; Marles Howard T
Priority date: 1993-10-13
Filing date: 1994-10-13
Publication date: 1995-04-20
Also published as: AU7850794A; CA2108297A1

Abstract

A relatively simple apparatus includes an elongated horizontal casing (23) divided by a transversely extending partition (26) into an inlet (28), heating chamber (24) and a coalescing chamber (25), a pair of elongated, tubular heaters (44) extending into the heating chamber for heating the oil and water in such chamber to facilitate separation of the oil and the water, an inlet trough (34) at the inlet end of the casing with a downcomer tube (40) attached thereto for introducing an oil water emulsion into the casing, whereby a water stream (47) is established at the bottom of the casing with an oil stream (48) thereabove in the heating chamber and a gas stream (39) at the top of the casing, a weir (88) attached to the partition (26) for receiving oil separating from the water in the heating chamber, distributors extending from the bottom of the partition into the coalescing chamber (25) for receiving oil overflowing the weir (88) and distributing the oil in the coalescing chamber near the bottom thereof, an elongated, horizontal coalescing bed (106) completely spanning the coalescing chamber, whereby the entire oil stream passes through the bed, the bed being completely filled with spheres for promoting separation of residual water from the oil stream, a water outlet (122) at the outlet end of the casing remote from the inlet end, an oil outlet (121) in such outlet end, and a gas outlet (125) in the top of the casing proximate the outlet end. The water stream discharged from the coalescing chamber is fed directly to a hydrocyclone for the separation of residual oil from the water stream.

Description

OIL/WATER SEPARATION PROCESS

This invention relates to an apparatus and method for treating an oil field emulsion, and in particular for separating water from oil contained in an oil and water emulsion which may contain sand and gas.

The treating of oil field emulsions is presently performed in vertical or horizontal treaters. The treaters in question are intended to process field production fluids containing up to 30% water in the form of free water and emulsified water. A common conventional apparatus for

treating such emulsions include vertical treaters which utilize heat combined with chemical additives for separating water from oil and water. Vertical treaters are primarily intended for use in low volume situations, and perform at pressures from atmospheric to 50 psi in standard systems and up to 100 psi or higher in special systems. When using vertical emulsion treaters, the emulsions are broken using heat and baffle trays containing a filter medium in which large water droplets are formed. The water, being heavier than oil settles to the bottom of the treater and the oil rises to the top.

A second type of treater, which is the type proposed in this application is a so-called horizontal style treater, i.e. a treater which is elongated horizontally. Produced fluids enter the treater above a firetube, and flow downwardly for distribution beneath the firetube. Liberated gases pass through a gas equalizer into a heating compartment. Oil and emulsion flow upwardly around the firetube, while free water falls to the bottom of the vessel for discharge. Examples of horizontal treating apparatuses are described in Canadian Patents Nos. 1,146,901, issued to H.R. Bull on May 24, 1983; 1,296,263, issued to G.G. Ayroong on February 25, 1992 and 1,314,490, issued to K. McCants on March 16, 1993, and U.S. Patents Nos. 4,233,154, issued to C.L.

Presley on November 11, 1980; 4,722,800, issued to G.G. Aymong on February 2, 1988; 4,824,579, issued to h . L . George on April 25, 1989 and 4,995,495, issued to S.V. Krynski on February 26,

1991.

Many conventional horizontal treaters are somewhat complicated and expensive to fabricate. Moreover,

conventional treaters often require large water handling vessels and equipment such as free water knockouts, filtration systems and atmospheric settling tanks. Perhaps of even greater significance is the fact that conventional treaters are designed to operate at low pressures.

An object of the present invention is to overcome the disadvantages of existing apparatuses by providing a treater which can operate in the pressure range of above 40, preferably 75 to 200 psi, and which does not rely on large water handling vessels or auxiliary equipment such as free water knockouts.

Another object of the invention is to provide a treater, which being adapted to operate at high pressures, allows a relatively large volume of fluid to be processed in a small vessel.

According to one aspect, the present invention relates to an apparatus for separating oil from water comprising elongated horizontal casing means; partition means dividing said casing means longitudinally into a heating chamber and a coalescing chamber; heater means extending into said heating chamber for heating an oil and water emulsion in said heating chamber to facilitate separation of the oil and water; inlet means at an inlet end of said casing means for introducing an oil and water emulsion into said heating chamber, whereby a water stream is established in the bottom of said casing means, with a gas stream at the top of said casing means, and an oil stream between said water and gas streams in said heating chamber; weir means attached to said partition means for receiving oil separating from water in said heating chamber; distributor means extending from said partition means into said coalescing chamber for receiving oil overflowing said weir means and distributing the oil in the coalescing chamber near the bottom thereof; elongated

horizontal coalescing bed means completely spanning the coalescing chamber, whereby the entire oil stream passes through said bed, said bed means including a plurality of spheres for promoting separation of residual water from the oil stream in said coalescing chamber; water outlet means at an outlet end of said casing means opposite said inlet end; oil outlet means in said outlet end; and gas outlet means in the top end of the casing means proximate said outlet end.

According to a second aspect, the invention relates to a method of separating water from an emulsion containing oil, water and gas comprising the steps of introducing the emulsion into a trough in the top of a heater chamber in a closed tank under a pressure of 75 to 200 psi, whereby gas is separated from the emulsion to form a gas stream in the top of the tank; passing the emulsion downwardly through a downcomer tube to the bottom of the tank heater chamber; heating the emulsion in the heater chamber to promote the separation of water from the oil creating a water stream in the bottom of the heater chamber and an oil stream above the water stream; passing the gas stream over a vertical partition in the tank to a gas outlet for discharge from the tank; passing the water stream beneath the partition to a water outlet for discharge from the tank; passing the oil stream over a weir in the heater chamber of the tank beneath the top of said partition and through said partition proximate the bottom thereof into a coalescing chamber; distributing the oil stream over the water stream in said coalescing chamber; passing said oil layer upwardly through a coalescing bed of plastic spheres extending the length and width of said coalescing chamber; and

overflowing the oil stream above said coalescing bed into a discharge box for discharging the oil stream from the tank.

The invention will be described in greater detail with reference to the accompanying drawings, which illustrate a preferred embodiment of the invention, and wherein:

Figure 1 is a schematic flow diagram of the system used in carrying out the process of the present invention;

Figure 2 is a schematic, longitudinal sectional view of a treater used in the system of Fig. 1;

Figure 3 is a cross section taken generally along line III-III of Fig. 2; Figure 4 is a side view of an inlet for introducing an oil and water emulsion into the treater of Fig. 2;

Figure 5 is a side view of an inlet trough for use in the treater of Fig. 2;

Figure 6 is an end view of the inlet trough as seen from the right of Fig. 5;

Figure 7 is an end view of the treater as seen from the left of Fig 2;

Figure 8 is a cross section of the lefthand end of the treater taken generally along line VIII-VIII of Fig. 7;

Figure 9 is a plan view of desand or flush headers used to clear solids from firetubes and the bottom of the treater of Fig. 2;

Figure 10 is a schematic side view of one of the flush headers of Fig. 9;

Figure 11 is a cross section taken along line XI-XI of Fig. 10;

Figure 12 is a side view of another of the headers of

Fig. 9;

Figure 13 is a cross section taken along line

XIII-XIII of Fig. 12;

Figure 14 is a plan view of a desand baffle used in the treater of Fig. 2;

Figure 15 is a side view of the baffle of Fig. 14;

Figure 16 is a cross section taken generally along line XVI-XVI of Fig. 15;

Figure 17 is a bottom view of a portion of the baffle of Figs. 14 and 15;

Figure 18 is a perspective view of a weir and partition used in the treater of Fig. 2;

Figure 19 is a plan view of oil distributors used in the treater of Fig. 2;

Figure 20 is a side view of one of the oil distributors of Fig. 19;

Figure 21 is a cross section taken generally along line XXI-XXI of Fig. 20;

Figure 22 is a perspective view of a length of the distributor of Fig. 20;

Figure 23 is a partly sectioned, plan view of grates used in the treater of Fig. 2;

Figure 24 is a schematic side view of the grates of Figs. 23;

Figure 25 is a cross section taken generally along line XXV-XXV of Fig. 2;

Figure 26 is a cross section taken generally along line XXVI-XXVI of Fig. 24;

Figure 27 is a longitudinal sectional view of a gas outlet used in the treater of Fig. 1;

Figure 28 is a cross section of a mounting frame taken generally along line XXVIII-XXVIII of Fig. 27; and

Figure 29 is a cross section of a second mounting frame used in the gas outlet taken generally along line

XXIX-XXIX of Fig. 27.

With reference to Fig. 1, the system employed to carry out the process of the present invention includes a treater generally indicated at 1 for receiving an emulsion of oil and water which could also contain gas and solids. The emulsion is introduced into the treater 1 via an inlet 2. The treater is used to separate the constituents of the emulsion which are discharged separately from the treater. The gas is discharged from the top of the treater 1 via a line 3

containing a valve 4. Oil is discharged through an line 5 from one end of the treater 1 and a valve 6. Solids are discharged from the treater 1 via lines 7 and 8, respectively, valves 9 and 10 in such lines, and a drain line 11. The water separated from the emulsion in the treater 1 contains residual oil. In order to remove water the residual oil, the latter is fed via line 12 and valves 13 and 14 to a hydrocyclone 15.

The water can bypass the hydrocyclone and be discharged from the system via valve 16 and line 17. The residual oil

separated from the water in the hydrocyclone 15 is discharged via line 18. The water is discharged via line 19 to the line 17, and out of the system through valve 20.

With reference to Figs. 2 and 3, the treater 1 is an elongated cylindrical tank 23, which is divided longitudinally into a preliminary treatment or heating section 24 and a coalescing section 25 by a vertical partition 26. An emulsion of oil and water containing gas and solids is introduced into the tank 23 via an inlet 28. As best shown in Fig. 4, the inlet 28 is in the form of a pipe 29 with a flange 30 on top thereof. A semi-cylindrical extension 31 is provided on the bottom end of the pipe 29, and a disc-shaped deflector 33 is provided on the bottom end of the extension 31. The deflector 33 is perpendicular to the direction of flow of the emulsion through the pipe 29. In effect, the deflector sprays the emulsion entering the tank 23 into an inlet trough 34.

As best shown in Figs. 5 and 6, the inlet trough 34 is generally triangular in cross section, including downwardly converging side walls 35 with flanges 36 extending outwardly from the top edges thereof. Gas separates from the mixture entering the trough 34, and forms a gas stream 39 (Fig. 2) at the top of the tank 23. The emulsion flows downwardly from the end of the trough 34 opposite the inlet 28 through a downcomer pipe in the form of an inclined, square cross section tube 40, which is connected to the body of the trough by flanges 41 and 42. The tube 40 extends downwardly between a pair of generally U-shaped tubular firetubes or heaters 44 for discharging the emulsion through the open bottom end 45 towards the bottom of the tank. Due to gravity emulsion discharged from the tube 40 forms a continuous water layer 47 and an oil layer 48. Of course, the water layer 47 contains residual oil, and the oil layer contains some water.

Each of the heaters 44 (Fig. 8) includes an

elongated tubular body 50 extending into the tank 23 through a convex head assembly 51. The head assembly 51 includes a convex shoulder 53 tapering inwardly through a concave radius to a narrow neck 54. An annular flange 55 is mounted on the neck 54, and a thick plate 56 is connected to the flange 55 by bolts or studs 58. The plate 56 is used to support the firetubes 44, which are cantilevered inwardly from the plate. Flanges 59 are provided on the outer ends of the arms of the firetube 44. The bottom flanges 59 are used to connect the firetubes 44 to burners (not shown), and the top flanges 59 connect the firetubes to flues (not shown) for discharging the products of combustion.

Any solids contained in the emulsion discharged from the downcomer 40 begin to settle to the bottom of the tank 23, or remain suspended between the oil and water layers. As mentioned above, the solids are discharged through lines 7 and 8. The lines 7 are connected to desand outlets 61 in the bottom of the tank 23. Desanding of the bottom portion of the tank 23 is expedited by flushing headers 63 and 64 containing a plurality of nozzles 66 (Figs. 9 to 11). Suitable nozzles 66 are available under the trade-mark "Veejet". The headers 63 and 64 are similar, including inlet tube 67 in the bottom of the tank 23, and U-shaped pipes 68. The pipes 63 and 64 are suspended above the bottom of the tank 23 from cross bars 70 using U-brackets 71. The flushing headers 65 which are located outside of the firetubes 44 are attached to a pair of inlet pipes 72 connected by vertical extensions 73 and T- joints 74. The headers 76 and 77 also contain a plurality of nozzles 66. The headers 65 are supported by posts 78 and U- brackets 79. By spraying water through nozzles 66 in the in the headers 63, 64 and 65, solids deposited on the tank bottom and on the heater surfaces are moved downwardly.

The solids pass beneath baffles 81, which are spaced from the bottom of the tank 23 by feet in the form of small crossbars 82. The baffle 81 includes a generally triangular casing 83, which is maintained in position by posts 85 (Fig. 16) welded to the bottom of the tank. The top ends of the posts 85 are threaded for receiving nuts 86.

The mainly oil portion of the emulsion rises in the heater section 24 of the tank 23 and passes over a weir 88 (Fig. 18) which is mounted on the partition 26. The partition 26 is in the form of a circular plate 89, with segments removed from the top and bottom thereof, so that the gas stream 39 can pass over the top of the partition, and the water stream 47 can pass beneath the partition. The weir 88, which is generally L-shaped in cross section, including a vertical arm 90, which is similar in shape to the partition plate 89, but shorter than such plate, and a rectangular horizontal arm or baseplate 92 extending between the plates 89 and 90 and the sides of the tank 23.

A pair of truncated, triangular openings 93 (Figs.

18 and 21) are provided near the bottom of the partition 26 above the baseplate 92 for discharging oil from the heater section 24 to the coalescing section 25 of the tank. Oil flowing through the openings 93 flows across the top of the water layer 47, and is distributed in the coalescing section 25 by generally triangular distributors 95. As best shown in Fig. 22, each distributor 95 includes a generally triangular body defined by inclined side walls 96, a horizontal top wall 97 and short vertical bottom ends 99 on the side walls 96. An end wall (not shown) is provided on the outer free end of each distributor 95. The distributors 95 are mounted on crossbars 101 defined by angle irons extending across the tank 23. L- shaped brackets 102 connect the distributors 95 to the crossbars 101. A plurality of spaced apart holes 104 are provided in each of the side walls 96 near the top end thereof for discharging oil into the coalescing section.

Oil rising in the coalescing section 25 must pass through a coalescer bed defined by a plurality of beads 106. The beads 106 are for example plastic spheres which serve to separate residual water from the oil. The beads 106 are mounted between a pair of grates 107 and 108. The beads 106 entirely fill the space between the grates 107 and 108, except at the discharge end, the centre of which is occupied by an oil discharge box 110. The grates 107 and 108 are defined by a plurality of longitudinally and transversely extending bars 111 and 112, respectively supported by a plurality of

transversely extending crossbars 114. The oil box 110 at the outlet end of the coalescing section includes a bottom wall 116, side walls 117, and an inner end wall 119. A level control 120 (Fig. 2) is used to control the level of the oil in the box 110. Oil is discharged from the box 110 via an outlet 121 to line 5 (Fig. 1). Water is discharged from the water layer 47 through an outlet 122 to the line 12. Inlet ducts 123 are provided in the discharge end of the tank 23 for receiving level controls (not shown).

With reference to Figs. 2 and 27 to 29, any gas separating from the emulsion in the heating section 24 or from the oil in the coalescer section 25 of the tank 23 is

discharged via a large diameter outlet 125 containing a demister pad 126. A suitable demister pad is available from Otto H. York Company, Inc. The outlet 125 includes a tubular casing 127 connected to a large diameter cover 128 containing a small diameter flanged outlet pipe 130. The pad 126 is suspended in the tube 127 by means of top and bottom frames

132 and 133, respectively. The top frame 132 is generally H-shaped, including crossbars 134 extending between opposite sides of the tube 127, and a centre bar 135. The bottom frame

133 includes an outer ring 137 and a pair of crossbars 138 at 90° to each other. A rod 140 extends downwardly from the centre of the top frame 132 through a sleeve 141 in the centre of the bottom frame 133. Complimentary threads are provided at the bottom end of the rod 140 and in the sleeve 141.

During operation, fluid enters the inlet 2 of the tank 1 and is distributed into the inlet trough 34. In the trough 34 solution gas is liberated from the liquid phases, and the liquid phases are directed through the downcomer tube 40 to a level below the heating elements defined by the firetubes 44 and an established liquid interface level, i.e. the interface between the water stream 47 and the oil stream 48. At this point, the fluid phases are coalesced and separated by gravitational forces, fluid turbulence from additional solution gas breakout and the co-mingling between liquid phases. An interface level between the water and the oil streams is established by the bottom end of the weir 88. The interface is established with the lighter fluid (oil) assuming the upper layer and the heavier layer (mainly water) being below the interface. The gas phase rises to form a gas stream 39 at the top of the tank 1. The gas phase is

discharged through the outlet 125. The gas outlet flow is controlled by the gas back pressure valve 4 (Fig. 1), which maintains a back pressure on the process. The liquid phase or stream passes beneath the partition 26 and is ultimately discharged via outlet 123.

The oil stream rises in the heating or inlet chamber

24, passes over the weir 88 and through the openings in the partition 26 into the coalescing chamber 25. Because the coalescing bed extends the length and width of the chamber 25, the oil stream is forced to pass through the plastic spheres 106, which assist in promoting the separation of residual water from the oil. When the oil level in the chamber 25 is sufficiently high, the oil stream overflows the into discharge box 110, and the oil is discharged from the tank through the outlet 121.

The water discharged through the outlet 123 is fed via line 12 and valves 13 and 14 to the hydrocyclone 15 where additional oil is separated from the water stream. A suitable hycrocyclone is the Krebs deoiler Model L2-M8 available from Krebs Engineers, Menlo Park, California.

Claims

WHAT WE CLAIM IS:-

1. An apparatus for separating water Iron oil comprising elongated horizontal casing means, partition means dividing said casing means longitudinally into a heating chamber and a coalescing chamber; heater means extending into said heating chamber to facilitate separation of the oil and water; inlet means at an inlet end of said casing means for introducing an oil and water emulsion into said heating chamber, whereby a water stream is established in the bottom of said casing means, with a gas stream at the top of said casing means, and an oil stream between said said water and gas streams in said heating chamber; weir means attached to said partition means foi receiving oil separating from water in said heating chamber; distributor means extending from said partition means into said coalescing chamber for receiving oil overflowing said weir means and distributing the oil in the coalescing chamber near the bottom thereof; elongated horizontal coalescing bed means completely spanning the coalescing chamber, whereby the entire oil stream passes through said bed, said bed means including a plurality of spheres for promoting separation of residual water from the oil stream in said coalescing chamber; water outlet means at an outlet end of said casing means opposite said inlet end; oil outlet means in said outlet end, and gas outlet means the top end o f the casing means proximate said out let end.

2. An apparatus according to claim 1, including parallel heaters extending into said casing means through the inlet end thereof; said inlet means including trough means for receiving the oil and water emulsion; and downcomer tube means at one end of said trough means for directing the emulsion downwardly between said heater tubes to a location beneath said heater tubes.

3. An apparatus according to claim 2, wherein said inlet means includes an inlet pipe, and diverter means on_ the bottom end of said inlet pipe for spraying the emulsion into said trough means.

4. An apparatus according to claim 1, wherein said partition means includes a wall extending across said casing means; a first gap between the top of the partition means and the top of said casing means permitting the passage of the gas stream thereover; and a second gap between the bottom of said partition means and the bottom of the casing means permitting the passage of the water stream therebeneath.

5. An apparatus according to claim 4, wherein said coalescing bed means includes a pair of vertically spaced apart grates for sandwiching said plastic spheres therebetween, said grates extending completely across the coalescing chamber and between inlet and outlet ends thereof.

6. An apparatus according to claim 5, wherein said oil outlet means includes a well on the outlet end of said casing means said well extending from the lower of said grates to a location above the uppermost grate.

7. An apparatus according to claim 6, wherein said distributor means includes a pair of open bottom distributor tubes extending from the partition means proximate the bottom end thereof for introducing the oil stream into the coalescing chamber immediately above the water stream passing beneath the partition means.

8. An apparatus according to claim 7, including header means for spraying water under pressure into said casing means on the surfaces of said heaters, and onto the bottom surface of the casing means to remove settled solids from the casing means.

9. An apparatus according to claim 8, including baffle means on the bottom of said casing means; and sand outlet means beneath said baffle means for discharging sand from the casing means.

10. A method of separating water from an emulsion containing oil, water and gas comprising the steps of introducing the emulsion into a trough in the top of a heater chamber in a closed tank under a pressure of 40 psi, whereby gas is separated from the emulsion to form a gas stream in the top of the tank; passing the emulsion downwardly through a downcomer tube to the bottom of the tank heater chamber; heating the emulsion in the heater chamber to promote the separation of water from the oil creating a water stream in the bottom of the heater chamber and an oil stream above the water stream; passing the gas stream over a vertical partition in the tank to a gas outlet for discharge from the tank; passing the water stream beneath the partition to a water outlet for discharge from the tank; passing the oil stream over a weir in the heater chamber of the tank beneath the top of said partition and through said partition proximate the bottom thereof into a coalescing chamber; distributing the oil stream over the water stream in said coalescing chamber; passing said oil layer upwardly through a coalescing bed of plastic spheres extending the length and width of a coalescing chamber; overflowing the oil stream above said coalescing bed into a discharge box for discharging the oil stream from the tank; and feeding the water stream directly to a hydrocyclone for the separation of residual oil from said water stream.