US3564527A - Alarm scheme for waste fluid drain - Google Patents

Abstract

A SAMPLING CONDUIT SAMPLES THE FLUID FLOWING IN THE DRAIN PIPE OF A WASTE WATER PIPING SYSTEM FOR A FLOATINGROOF STORAGE TANK. THE ELECTRICAL CONDUCTIVITY OF THE FLUID IN THE SAMPLING CONDUIT IS MONITORED CONTINUOUSLY, AND AN ALARM IS GIVEN WHEN A PREDETERMINED CHANGE IN THIS CONDUCTIVITY OCCURS.

Description

Feb. 16, 1971 J. LERNER ETAL I 3,5 7

' ALARM SCHEME FOR WASTE FLUID DRAIN T Original File'doct, 11, 1966 5 Sheets-Sheet 1 'vi'f FIGURE"I INVENTORS JULIUS LERNER BY ROBERT AYER ATTORNEY Feb.16, 1971 LERNER ETAL 3,564,527

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Feb. 16, 1971 J. LERNER ET AL I ALARM SCHEME FOR WASTE FLUID DRAIN 5 Sheets-Sheet 4 Original Filed Oct. 11, 1966 INVENTORS JULIUS LERNER ROBERT MAYER EM f ATTORNEY W Feb. 16, 1971 LERNER ETAL 3,554,527

ALARM SCHEME FOR WASTE FLUID DRAIN JULIUS LERNER ROBERT MAYER United States Patent ALARM SCHEME FOR WASTE FLUID DRAIN Julius Lerner, Broomall, and Robert Mayer, Delaware, Pa., assignors to Sun Oil Company, Philadelphia, Pa.,

a corporation of New Jersey Continuation of application Ser. No. 585,933, Oct. 11,

1966. This application May 28, 1969, Ser. No. 831,261

Int. Cl. G08b 21/00 US. Cl. 340-242 4 Claims ABSTRACT OF THE DISCLOSURE A sampling conduit samples the fluid flowing in the drain pipe of a waste water piping system for a floatingroof storage tank. The electrical conductivity of the fluid in the sampling conduit is monitored continuously, and an alarm is given when a predetermined change in this conductivity occurs.

This application is a continuation of application Ser. No. 585,933, filed Oct. 11, 1966, now abandoned.

This invention relates to an alarm scheme for a waste fluid drain, and more particularly to an arrangement for providing an alarm in response to the fortuitous leakage of a valuable liquid such as a hydrocarbon into a waste water drain system.

In petroleum refineries, tanks having floating roofs are often used to store hydrocarbons. In order to carry off atmospheric precipitation falling on such roofs, the upper faces of such roofs ordinarily slope downwardly toward a central drain, from which point a drain pipe (made in sections connected together by swing joints, in order to accommodate the movement of the floating roof as the tank is filled and/ or emptied) extends downwardly through the interior of the tank to the bottom thereof and thence outwardly to the ground outside the tank, through a drain valve.

There have been instances where the swing joints have failed, permitting hydrocarbon from the inside of the tank to leak into the drain pipe and out to the ground through the drain valve. This is both dangerous and wasteful. Because of this fortuitous leakage, it has been common practice to keep the drain valve (on the outside of the tank) closed, letting the water level build up on the floating roof during a rain or other atmospheric precipitation. According to this practice, the drain valve is opened some time later, the water drained, and the valve again closed. (Obviously, if any hydrocarbon leaks out through the valve at this time, it can be properly handled, e.g. by closing the drain valve to prevent any undue loss of hydrocarbon.) However, this practice has the considerable disadvantage of requiring a man to make the rounds in order to drain the water from the various tank roofs. Also, it allows, in the case of heavy rains, the buildup of a considerable load on the tank roof, and (if the water level becomes high enough) may allow the water to overflow the roof. If there is any flaw in the flexible seal around the floating roof, water then runs into the hydrocarbon storage tank; this is of course undesirable.

This invention provides an arrangement for detecting and indicating the presence of hydrocarbon in the drain piping system, adjacent the aforementioned drain valve. Then, the drain valve may be left open, so that any rain water on the floating roof may be immediately drained; thus, no repeated manual operation of the valve is necessary, and there can be no buildup of water on the roof. The indication provided may be in the form of an audible or visual alarm, or it may be used to close a suitable valve at the tank.

An object of this invention is to provide an arrangement Patented Feb. 16, 1971 ICC for detecting and indicating the presence, in a piping system for removing a waste fluid, of a valuable fluid.

Another object is to provide an alarm system for indicating a hydrocarbon leak in a water drain system for a hydrocarbon storage tank.

A further object is to provide an arrangement for continuously monitoring the waste water drain system of a floating-roof hydrocarbon storage tank.

The objects of this invention are accomplished, briefly, in the following manner: A drain pipe is connected into the waste water piping system of a floating-roof storage tank, to form a part of such system, this drain pipe having coupled thereto a sampling conduit which samples the fluid flowing in the drain pipe. The conduit is constructed and arranged to contain fluid at all times. The electrical conductivity of the fluid in the sampling conduit is monitored continuously, and when a predetermined change (e.g., a decrease) in this conductivity occurs, an alarm device is energized to provide an alarm indication.

A detailed description of the invention follows, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a somewhat schematic cross-section of a piping system for carrying off water resulting from atmospheric precipitation falling on the roof of a hydrocarbon storage tank, illustrating certain features of the invention;

FIG. 2 is a somewhat schematic cross-section of a portion of the drain system of FIG. 1, illustrating certain other features of the invention;

FIG. 3 is a diagram of the electrical circuitry employed in the detecting and indicating arrangement of the invention;

FIG. 4 is a side view of the piping arrangement used in the invention;

FIG. 5 is a view looking at the right-hand side of FIG. 4; and

FIG. 6 is a cross-section of a T assembly mounting a sensing electrode.

In petroleum refineries, a type of tank having a floating roof is often used as a hydrocarbon storage tank. FIG. 1 illustrates certain features of such a tank with which the present invention is concerned. The diameter of the floating roof 1 is somewhat smaller than the inside diameter of the tank 2. A flexible seal 3 is provided around the outer edge of roof 1, sealing against the inner cylindrical wall of tank 2 to keep vapors from escaping from the tank and to keep rain water from running into the tank. The roof 1 is shaped (e.g., its upper surface may be of inverted conical shape, as illustrated) in such a manner that any atmospheric precipitation falling on the roof will flow to the center and into the central drain 4. The rain water (which is waste water, insofar as this invention is concerned) enters drain 4 and flows down the drain pipe 5 (which latter extends from drain 4 down through the interior of the tank, to the bottom thereof) and out onto the ground through a flanged drain valve 6, which is located outside of the tank.

Since the roof 1 floats on the liquid hydrocarbon 7 within the tank 2, it rises and falls as the tank is filled and emptied. In order to accommodate this motion, the drain pipe 5 is made in sections which are coupled together through swing joints 8. This system of pipes and joints acts like a pantograph.

The piping system so far described (for carrying off waste water )is known in the art as a Gallagher drain.

There have been instances where the swing joints 8 have failed, permitting the hydrocarbon 7 stored in the tank to leak into the drain pipe 5 and out to the ground through the drain valve 6. This is both dangerous (due to the flammable nature of the hydrocarbon) and wasteful (since the hydrocarbon is a valuable fluid). Because of this fortuitous hydrocarbon leakage, prior practice was to keep valve 6 closed, letting the water level build up on roof 1 during a rain. Then, at some later time, the valve 6 was opened, the water drained, and the valve again closed. As stated hereinabove, this practice requires a man to make the round of the tanks in order to drain the water, and also permits (in the case of heavy rains) the buildup of a considerable load on roof 1, with the possibility of the water overflowing the roof and flowing into the tank if there is any flaw in seal 3. The flow of water into the storage tank is of course undesirable.

The present invention provides a means whereby a hydrocarbon leak may be detected adjacent valve 6, outside the tank 2. Using this means, the valve 6 may be left open, permitting any rain water on roof 1 to be immediately drained therethrough; the said means maintains a continuous watch for the presence of hydrocarbon in the Gallagher drain system, enabling the valve 6 to be safely left open.

Refer now to FIG. 2, which schematically illustrates certain structural features of the detecting arrangement of the invention. The mechanical assembly of FIG. 2 is provided with a flange 9 for mounting on a similar flange on the valve 6. One end of a drain pipe 10, which carries the flow from the valve 6 (and which extends substantially horizontally away from the valve, as shown schematically in FIG. 1), is welded to flange 9. The other end of pipe 10 may be left open as shown in FIG. 2, or it may be coupled to a suitable sump. For simplicity in illustration, only the pipe 10 is shown in FIG. 1; also, the flanged couplings mentioned are not shown in detail, since these are entirely conventional.

Pipe 10 has a hole 11 in the bottom thereof, and centered at this hole is a threaded coupling 12 which is welded to the outside of the large pipe 10. A sampling conduit assembly 13, to be described in more detail here inafter, is threadedly connected to coupling 12. Assembly 13 forms in effect a U tube, one of the legs of the U being connected to the coupling 12, and thus coupled to the hole 11 at the bottom of pipe 10. The other leg of the U has a reverse bend portion coupled thereto to provide a downwardly-facing outlet 14 which is left open.

Under normal conditions (to wit, no hydrocarbon leakage into the drain system), when water flows in the system including drain pipe 10 the metallic U-tube 13 will fill with water (via hole 11) until it flows out of the outlet 14. A water level will be established at 15. This water level having been established, if more water flows the new water will displace some of the water already in the sampling conduit (U-tube) 13, and the water level 15 will remain constant.

If there is fortuitous leakage of hydrocarbon 7 from the tank 2 (FIG. 1) into the waste (drain) piping sys tem, this hydrocarbon will enter the pipe 10, and at least a portion of it will flow through the hole 11 and into the U-tube 13. Since the hydrocarbon has a lower density than the water already in the U-tube, it will remain on top of the wafer and have its own free surface indicated by the dotted line 16. This will unbalance the forces in U-tube 13 and some of the water will flow out of the outlet 14 until the system comes to equilibrium.

If the inflow of hydrocarbon into tube 13 is small, this equilibrium will result in the hydrocarbon level 16 being higher than the original water level 15, the new water level 17 being lower than the old water level 15.

A metallic electrode 18 is mounted in the vertical leg 20 of the U-fu be 13, this mounting being effected by means of a combination insulator and packing gland 19. As will be described more fully hereinafter (with reference to FIG. 3), one terminal of an alternating current (A.C.) source is connected to electrode 18 and the other terminal thereof is connected to ground 22 (the metallic tube 13 itself). Since the bare tip (inner end) of the electrode 18 is exposed to the liquid in the U-tube, it will be appreciated that the AC. conductivity of the liquid in the U- tube may be measured by means of the electrical connections described.

As long as the water lever 17 in the vertical leg 20 is above the bottom edge 21 of the electrode 18, current flow can take place through the relatively high-conductivity water (between electrode 18 and the U-tube wall), and a circuit is in effect completed. The A.C. conduc tivity of the hydrocarbon is much lower than that of the Water. When enough hydrocarbon flows into the vertical leg 20 to lower the water level 17 to a point just below the electrode bottom edge 21, the relatively high-conductivity circuit (through the water) will be broken, in effect opening the circuit, and the alarm will be activated. That is to say, the reduction in current flow which takes place between electrode 18 and ground 22 (the wall of tube 13), when the high-conductivity water path is no longer present, results in the activation of the alarm.

Refer now to FIG. 3, illustrating an electrical circuit (connected to electrode 18 and ground) which can be used for continuously monitoring the electrical conductivity of the fluid in the sampling conduit 13, and for providing an alarm in response to a change in such conductivity. Alternating current from a suitable source 45 (e.g., the ordinary -volt commercial supply) is sup plied through a switch 46 and a fuse 47 to the primary winding of a power transformer 23. The combination of a resistor 24 and two back-to- back Zener diodes 25 and 26 is connected across the secondary winding of transformer 23. The lower end of the secondary of transformer 23 is connected to the grounded side of the source 45, and the alternating voltage used for measuring conductivity is taken between this end of the secondary and the common junction 51 of resistor 24 and Zener diode 26. An A.C. conductivity measurement is used in order to minimize the polarizing of the electrode (probe) 18 and the consequent electrolysis, which would damage the probe. The voltage applied to electrode 18 (and used for monitoring the. conductivity of the liquid in tube 13, as previously mentioned) is prevented from exceeding a safe limit under normal conditions by the use of the transformer 23 and the Zener diodes 25 and 26, which perform a voltage-limiting function; the current through these diodes is limited by resistor 24.

All of the circuit components contained within the dotted-line rectangle 48 are located at a control house (which is the alarm or indicating location, where an operator is present), while the components contained within the dotted-line rectangle 49 are all at the Gallagher drain (field) location of FIGS. 1 and 2, adjacent the tank 2. A cable 36 interconnects the two locations 48 and 49.

The cold or grounded connection for the alternating voltage for the conductivity measurement comprises a lead 50 (one of the conductors in cable 36) connected to the lower or grounded end of the secondary of transformer 23 and extending to the ground connection 22 (see also FIG. 2) at the U-tube 13.

The other connection for the alternating voltage is taken from the junction point 51, the alternating voltage being coupled essentially unchanged through a diode network 52 (to be later described) to a lead 53 which is another one of the conductors in cable 36. The hot side of the AC. supply, at the tank location 49, is coupled trough a protective network including components 37-43 to the insulated electrode 18 (see also FIG. 2). Resistor 37, resistor 40, and choke 41 are connected in series in that order between lead 53 and the probe or electrode 18. From the common junction of resistors 37 and 40, a pair of Zener diodes 39 and 38 are connected in backto-back relation to ground connection 22, and from the common junction of choke 41 and electrode 18, a pair of Zener diodes 43 and 42 are connected in back-to-back relation to ground connection 22. In case of abnormal conditions such as a lightning surge on the cable 36, the voltage at electrode 18 is limited by the resistor-Zener diode-choke network 3743.

By means of the circuitry previously described, an alternating voltage is applied between the electrode or probe 18 and ground (the metal wall of tube 13 in FIG. 2), thereby to cause an alternating current to flow through the fluid in this tube. The magnitude of this current depends upon the alternating current conductivity of the fluid through which the current is flowing. The network 52 comprising diodes 29, 30, 31, and 32 rectifies the alternating current flowing in the system including leads 50 and 53, the direct current output of this network being taken from a diagonal of the bridge-type diode network 52, across which diagonal is connected a filtering capacitor 34. A sensitive direct current relay 33 is connected across this same diagonal, to be energized by the rectified output current of network 52.

The relay is illustrated in its deenergized position, in which its movable contact 54 rests on its (normally closed) contact 55. In this deenergized position of the relay 33, a circuit is completed from the ungrounded terminal of the AC. source 45, through contacts 54 and 55 and an unsafe signal lamp 28, to the opposite or grounded terminal of source 45. This lights the lamp 28. When relay 33 is energized, the relay contact 54 energizes its (normally open) contact 56, completing a circuit from the ungrounded terminal of the source 45, through contacts 54 and 56 and a safe signal lamp 27, to the opposite terminal of source 45. This lights the lamp 27.

When the water level in tube 13 (FIG. 2) is above the bottom edge 21 of the electrode 18, sufficient current flows (due to the relatively high A.C. conductivity of the water) in the AC. conductivity-monitoring circuit to cause energization of relay 33, closing its contact 56 and lighting the safe lamp 27. When the conductivity of the fluid in U-tube 13 becomes low (due, for example, to the hydrocarbon, which has a much lower conductivity than water, replacing the water above level 21), relay 33 is deenergized, closing its contact 55 and lighting the unsafe lamp 28. This provides an indication (alarm) that hydrocarbon has leaked into the water drain system (Gallagher drain).

An audible alarm may be used instead of, or in parallel with, the unsafe lamp 28.

A resistor 35, connected in parallel with capacitor 34, is used to adjust the sensitivity of the indicating portion (relay portion) of the system. The sensitivity is set so that relatively high-conductivity material such as water (in the U-tube 13) will cause energization of relay 33, but conductivity due to leakage from the electrode 18 to ground (which may develop under field condit ons) will not energize the relay and will thus not provide a false safe indication when a low-conductivity material such as a hydrocarbon is present in the U-tube.

The hydrocarbon detecting and indicating arrangement of this invention is fail safe, which is desirable. If the AC. power fails, relay 33 will of course be deener gized, lighting the unsafe lamp 28, or at least extinguishing the safe lamp 27. Also, if the water in sampling conduit 13 evaporates during prolonged dry spells, and the water level therefore falls below the bottom edge 21 of the electrode 18, the current flowing drops to substantially zero, resulting in the deenergization of relay 33 and the lighting of the unsafe lamp 28.

Referring again to FIG. 3, an immersion heater 44 (located at the Gallagher drain location 49, and referred to further hereinafter) is used to keep the water in U- tube 13 from freezing during cold weather. In this con nection, it will be remembered that this invention involves the continuous monitoring of the electrical conductivity of the fluid in conduit 13, and the continuous presence of water in such conduit. One end of heater 44 is grounded (and thus connected to one terminal of the AC. power source 45) at location 49, and the other end of this heater is connected by means of a lead 57 (which is one of the conductors in cable 36) to the ungrounded or hot side of source 45.

Now refer to FIGS. 4-6, which illustrate a structural and piping arrangement which may be used for the alarm scheme of the invention, at the tank location 49. FIG. 4 is a side view corresponding more or less to the schematic of FIG. 2, while FIG. 5 is a view looking at the right-hand side of FIG. 4. The vertical leg 20 of the U-tube 13 comprises the straight portion of the T assembly 58 illustrated in cross-section in FIG. 6. The upper end of the T assembly 58 is threaded at 59 and screws into the threaded coupling 12, which latter is welded to the bottom of drain pipe 10 at hole 11. The lower end of T assembly 58 is threaded at 60 and screws into the side arm of a T fitting 61. The fitting 61 forms a horizontally-extending portion of the U-tube 13 and is threadedly connected by means of a short nipple 62 to one of the in-line couplings of another T fitting 63. From the side arm of fitting 63, the U-tube 13 is continued upwardly by means of a nipple 64 whose lower end is threaded into the side arm of the T and whose upper end is threaded into one end of an elbow fitting 65. Fitting 65 forms the initial section of the reverse bend portion which is coupled to the free leg of the U. One end of a nipple 66 is threaded into the other end of L 65, and the other end of nipple 66 is threaded into one end of an elbow fitting 67; the other end of L 67 faces downwardly, is open, and provides the downwardlyfacing U-tube outlet 14.

It will be appreciated, from the foregoing description, that the items 58, 61, 62, 63, 64, 65, 66, and 67 together make up the U-tube-plus-reverse-bend tube 13.

The immersion heater 44 (see FIG. 5) is positioned within the horizontally-extending lower portion of U- tube 13 that is formed by the in-line couplings of Ts 61 and 63, and by nipple 62. The heater is mounted in the U-tube by means of a threaded coupling 68 which is secured to one end of the heater and which threads into the in-line coupling of T 63 opposite to nipple 62. Electrical connection is made to the heater through a housing (not shown) which is attached to the coupling end of the heater.

FIG. 6 illustrates the detailed construction of the elec trode 18 and insulating packing gland arrangement 19. A longitudinally-bored metallic boss member 69 is secured to the side wall of a hollow metallic tube to form the T assembly 58. The said hollow tube, as previously described, is threaded externally at both ends and forms the vertical leg 20 of the U-tube 13. A cylindrical metallic electrode or probe 18 is positioned centrally in the bore of boss 69 and the inner end of this probe extends into the interior of the hollow tube forming the vertical U- tube leg 20, through an aperture in the wall of this tube which is aligned with the boss bore. A short length of the extreme inner end of the rod electrode 18 (adjacent the longitudinal center line of the vertical U-tube leg 20) is left bare or uncovered, to serve as an electrical conductivity sensing electrode, as previously described in connection with FIGS. 2 and 3. That is to say, this bare inner end of probe electrode 18 is in electrical contact with the fluid contained in the vertical leg 20 of the U-tube 13.

The electrode 18 is electrically insulated 'from the metallic wall of vertical leg 20, and from the metallic boss 69, by means of the combination insulator and packing gland arrangement 19, which will now be described. Arrangement 19 includes a bushing 70 of electrical insulating material which surrounds the shank of electrode 18, this bushing extending from a point immediately adjacent the bare inner end of the electrode to a point within the boss 69. An electrically-insulating packing gland 71, which is urged into sealing position around rod 18 by means of an externally-threaded nut 72 acting on a follower 73, abuts the outer end of bushing 70 and extends to a point outwardly beyond the outer ends of boss 69 and nut 72, to complete the electrical insulation of electrode 18 from the metallic members through which it passes.

An electrical lead 74, secured by means of nuts to the threaded outer (and bare) end of electrode 18, provide a means 'for connecting the electrode 18 to the circuitry of FIG. 3; the other (or grounded) electrical connection (for the AC. conductivity measurement) is made to the metallic wall of vertical leg 20, as indicated at 22 in FIG. 2.

The outer end of boss 69 is externally threaded at 75, to enable the bottom of a housing 76 (FIGS. 4 and 5) to be secured thereto. The lead 74 passes into the interior of housing 76. Housing 76 has integral therewith a pair of opposite side couplings 77 and 78. A rod 79 is secured to coupling 77, to mount the U-tube assembly be ow pipe by means of a bracket 80 secured to rod 79 and welded to the outside of pipe 10. A conduit (not shown) is secured to coupling 78, to permit connection of lead 53 and various electrical components at location 49 (see FIG. 3) to the lead 74, and thus to electrode 18. The last-mentioned conduit extends to suitable housings (not shown), which provide for connection of the cable 36 to the heater lead 57 and to the remaining leads at location 49.

As previously stated, an unsafe indication is given (by the lighting of lamp 28) if and when the water level is sampling conduit 13 drops to a certain extent (as a result of evaporation during prolonged dry spells). When this occurs, water may be purposely added to the sampling conduit 13, to replace that which has evaporated. This water may be added through an internally-threaded aperture (normally closed by a pipe plug 81) provided in the top of pipe 10, in vertical alignment with hole 11. Thus, when the addition of water becomes necessary, plug 81 is removed and water is poured through the open aperture until a sufficient amount has been added (indicated, for example, by water running out of the outlet 14). As stated hereinabove, the alarm scheme of this invention calls for the continuous presence of water in sampling conduit 13.

The invention claimed is:

1. In a piping system for carrying off waste liquid from a drain located in the roof of a tank, said waste liquid comprising water resulting from atmospheric precipitation falling on said roof and said system being subject to the fortuitous leakage thereinto of valuable liquid: an arrangement for detecting and indicating the presence in such system of such valuable liquid comprising a horizontally-extending drain pipe coupled to the drain, a continuous U-shaped sampling pipe with one leg of the U coupled to the bottom region of said drain pipe and with a reverse bend portion coupled at one end to the other leg of the U, the other end of said reverse bend portion being open to the atmosphere and said sampling pipe being constructed and arranged to contain liquid at all times; and means energized from an external electrical power source for continuously monitoring the electrical conductivity of the liquid in said sampling pipe.

2. System according to claim 1, wherein the tank is a hydrocarbon storage tank, and wherein the valuable liquid consists of hydrocarbon stored in the tank.

3. System recited in claim 1, wherein said detecting and indicating arrangement includes also means controlled by said monitoringmeans-and operating to provide an alarm indication in response to a change in the electrical conductivity being monitored.

4. System recited in claim 1, wherein said monitoring means includes an electrode extending into the interior of said sampling pipe but electrically insulated from the metallic wall of said pipe, means connecting a source of alternating current between said electrode and the wall of said sampling pipe, and means responsive to the flow of current between said electrode and said sampling pipe wall through the liquid in said pipe.

References Cited UNITED STATES PATENTS 545,550 9/1895 Symons 137-179X 1,172,116 2/1916 Devericks 137179 2,573,172 10/1951 Ennis et al. 137172 2,677,964 5/1954 Engelder 73-304 2,839,742 6/ 1958 Sumner. 3,074,587 1/ 1963 Jennings.

3,333,258 7/1967 Walker et al 340244 FOREIGN PATENTS 256,289 8/ 1926 Great Britain 73-301 DONALD J'. YUSKO, Primary Examiner D. tMYER, Assistant Examiner US. Cl. X.R.

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