Abstract:
The dewatering system for oil storage tanks includes a dewatering pipe or line extending from the bottom of the oil tank, and a recirculation or return line teed into the dewatering pipe and extending back to the tank. The return line may include multiple branches to the tank, which permit return flow across the bottom of the tank to flush scale, sediment, and/or other residue from the bottom of the tank. A sensitive oil/water sensor is installed at the tee. When a minute fraction of oil is detected in the water, a valve downstream of the tee and sensor is automatically closed to return the oil and water mix back to the tank before any oil can leave the system. The system may include a timer mechanism to operate the recirculation system automatically on a periodic basis.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to the separation of different liquids from one another, and particularly to a dewatering system for oil storage tanks wherein an automated system provides for the removal of collected or trapped water from an oil storage tank. 
         [0003]    2. Description of the Related Art 
         [0004]    The collection of at least some small fraction of water in petroleum (oil) storage tanks is a chronic problem in the petroleum industry. Water can accumulate in such storage tanks due to entrainment with oil as it is pumped from the ground or from some other source, and water can condense within the airspace in a partially filled tank. As water is more dense than the oil or other petroleum product within the tank, the water will settle to the bottom of the tank. 
         [0005]    Accordingly, various systems have been developed in the past for the removal of water residue from oil storage tanks. Most earlier systems relied upon a human operator opening a drain valve at the bottom of the tank, and monitoring the appearance of the water as it flowed from the tank and drain valve. When oil was observed in the water, the operator would close the drain valve. Obviously this technique can be somewhat wasteful, as it generally requires a fair amount of oil mixed with the water in order for the operator to observe the water and react by shutting off the valve. Aside from the direct economic loss of the oil that escapes with the water, the oil entrained with the drained water must be removed from that water before the water can be used for other purposes or drained back into a clean natural water source. 
         [0006]    Thus, a dewatering system for oil storage tanks solving the aforementioned problems is desired. 
       SUMMARY OF THE INVENTION 
       [0007]    The dewatering system for oil storage tanks includes a dewatering pipe or line having a recirculation or return line extending therefrom and back to the oil tank. The return line preferably includes a plurality of branches extending to the lower portion of the tank in order to provide flow across the bottom of the tank to wash scale, sludge, and/or other debris from the bottom of the tank. An oil/water sensor is installed in the tee of the dewatering pipe and the return line. The sensor is an electronic ppm sensor providing a high degree of resolution, being capable of detecting amounts of oil in the water down to fifty parts per million. The system is completely automated. When the sensor detects an oil fraction of more than fifty parts per million in the water outflow, the system automatically shuts off the outgoing water flow and returns the entire flow back to the oil tank by means of a pump in the recirculation or return line. The shutoff valve is downstream of the sensor and tee. Any oil in the water is captured upstream of the shutoff valve before leaving the system. An electronic timer maintains the pump in operation and holds a solenoid valve open in the return line for a predetermined amount of time to ensure that the water containing an oil fraction is completely returned to the tank. The system may also be operated by an automatic timer to close the dewatering pipe and actuate the pump for recirculation on a periodic basis. 
         [0008]    These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic plan view of a dewatering system for an oil storage tank according to the present invention, illustrating its various components. 
           [0010]      FIG. 2  is a schematic side elevation view of the oil storage tank of the dewatering system for an oil storage tank according to the present invention, illustrating various components associated therewith. 
       
    
    
       [0011]    Similar reference characters denote corresponding features consistently throughout the attached drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    The dewatering system for oil storage tanks provides an automated system for removing water that has collected in an oil storage tank, and returning any water having oil therein back to the oil storage tank. The system is also configured to provide a periodic flow of water back into the bottom of the tank to flush scale, sediment, and/or other impurities from the bottom of the tank. 
         [0013]      FIG. 1  of the drawings provides a schematic view of the dewatering system  10 . The system extends from an oil storage tank  12  having a sump  14  therein. As water has a higher specific gravity than most oils, any water will tend to collect in the bottom portion of the tank  12 , beneath the oil, as shown in  FIG. 2  by the water W beneath the oil O in the tank. Accordingly, the dewatering pipe or line  16  has an inlet  18  extending from its oil tank connection end  20  (e.g., at the butt flange shown in  FIGS. 1 and 2 ). The inlet  18  extends down into the sump  14  of the oil tank  12  to draw water therefrom. The dewatering line  16  further has an outlet end  22  opposite its oil tank connection end  20 . It should be noted that the dewatering line  16  is not intended to deliver oil from the tank  12 , but is strictly configured for the purpose of removing water from the tank  12 . Any oil that is drawn into the dewatering line  16  will be in no more than trace amounts, as described further below. 
         [0014]    The dewatering line  16  includes a tee  24  installed therein between the oil tank connection end  20  and the outlet end  22 . The stem of the tee  24  comprises one end portion of a water return line  26  extending therefrom, the opposite end of the return line  26  having an oil tank connection end. While the return line  26  may comprise a single continuous pipe having a single connection to the oil tank  12 , the preferred embodiment illustrated in  FIG. 1  includes a plurality of water return line branches  28   a  through  28   c,  respectively. Each of the branches has an oil tank connection end  30   a  through  30   c.  Each of the branches  28   a  through  28   c  preferably includes a manually operated shutoff valve  32   a  through  32   c,  adjacent to its oil tank connection end. An additional manually operated first shutoff valve  34  is installed in the dewatering line between the outlet end  22  of the line and the tee  24 . Another manually operated second shutoff valve  36  is installed in the dewatering line adjacent its oil tank connection end  20 , e.g., external to the tank  12  between the butt flange and the inlet end  18  of the line  16  inside the tank. 
         [0015]    An oil/water sensor  38  is installed in the tee  24  of the dewatering line  16 . The oil/water sensor  38  is a sensitive electronic device, capable of detecting only a few parts per million of oil mixed with the water flowing through the dewatering pipe  16 . Such sensors are conventional, and are known as “ppm” (parts per million) sensors. A recirculation pump  40  is installed in the return line  26 , to pump any water having even trace amounts of oil therein back to the oil storage tank  12 . 
         [0016]    The dewatering system is controlled by a conventional microprocessor-based programmable logic controller or other electronic controller  42  that communicates electronically with the oil/water sensor  38  and other components. The electronic controller  42  receives signals from the oil/water sensor  38  to control the operation of the recirculation pump  40 , a first solenoid valve  44  disposed in the dewatering line  16  between the outlet end  22  and the tee  24 , and an electronic timer  46  that, in turn, communicates with the recirculation pump  40  and with a second solenoid valve  48  disposed in the return line  26  between the pump  40  and the oil tank connection end(s)  30   a,    30   b,  and  30   c  of the return line. The electronic controller  42  is driven or operated, in turn, by a programmable timer  50 . The programmable timer  50 , the electronic controller  42 , the electronic timer  46 , the recirculation pump  40 , and the two solenoid valves  44  and  48  ultimately receive their operating power from a power supply  52  (e.g., power grid, generator, wind power, solar power, etc.). 
         [0017]    The normal operation of the system is controlled according to signals received by the electronic controller  42  from the oil/water sensor  38 . When no oil (or at least no oil above a predetermined small fraction) is detected by the sensor  38 , the electronic controller  42  opens the first solenoid valve  44  in the dewatering line  16  and closes the second solenoid valve  48  in the return line  26 . The first manual valve  34  between the outlet  22  and the tee  24  of the dewatering pipe  16 , the second manual valve  36  at the oil tank connection end  20  of the dewatering pipe  16 , and at least one of the three manually operated shutoff valves  32   a,    32   b , and/or  32   c  in the return line branches  28   a  through  28   c  that connect to the oil tank  12 , are normally open to permit normal operation. They may be closed to permit maintenance or repair of the system. 
         [0018]    Preferably, the oil/water sensor  38  is set to provide a signal when a very small amount of oil is detected in the water, e.g., fifty parts per million (50 ppm), or 0.005 percent, although the system may be set to operate at other detected fractions of oil. When such an oil fraction (or greater) is detected by the oil water sensor  38 , the electronic controller  42  sends a signal to the first solenoid valve  44  to close the valve, thus shutting off water outflow (and any oil fraction therein) from the dewatering pipe  16 . Simultaneously with the above valve closure, the electronic controller  42  sends a signal to the electronic timer  46  to cause the timer  46  to actuate the recirculation pump  40  and to open the previously closed second solenoid valve  48 . This results in all water (and oil mixed therein) in the dewatering line  16  between the tee  24  and the tank  12 , and all water (and any oil therein) in the return line  26  being recirculated back into the oil tank  12 . The electronic timer  46  may be set to hold the second solenoid valve  48  open and to operate the recirculation pump  40  for a predetermined period of time, after which the valve  48  is closed and the pump  40  is shut down. The recirculation procedure begins anew if the sensor  38  detects more oil in the dewatering pipeline  16 , after the first solenoid valve  44  is reopened to allow flow through the line  16 . 
         [0019]    The programmable timer  50  may be set to actuate the system independently of the detection of oil in the water by the sensor  38 . If the programmable timer  50  is set to do so, it sends a signal periodically to the electronic controller  42  to close the first solenoid valve  44  and a corresponding signal to the electronic timer  46  to open the second solenoid valve  48  and actuate the pump  40 . The water recirculation operation is identical with that described further above, excepting that it was not initiated by receipt of a signal from the oil/water sensor  38 . 
         [0020]    The multiple return line branches  28   a  through  28   c  extending into the bottom of the oil tank  12  provide additional benefit, in that the water flowing back into the bottom of the tank  12  during recirculation will tend to create turbulence in the bottom of the tank to flush any scale, sediment, and/or debris from the tank bottom. This benefit will occur at each time the recirculation system is actuated, whether by a signal from the oil/water sensor  38  to the electronic controller  42  or by a periodic signal to the controller  42  from the programmable timer  50 . The various manual valves  32   a  through  32   c  may be opened or closed as desired to direct the return flow into the bottom of the tank  12 , e.g., two of the three valves may be closed with only one remaining open to direct a stronger flow through that single open valve, or a crossflow may be set up by opening two of the three valves, etc. 
         [0021]    The above-described dewatering system results in a completely automated system that virtually assures that no appreciable amount of oil will escape with water removed from the oil storage tank. The system is economical and quite reliable, in that it does not rely upon human intervention for its operation other than for the occasional opening or closure of manually operated valves for periodic maintenance or the like. The dewatering system provides the additional benefit of scale and sludge removal from the bottom of the oil storage tank, which results in additional economies of operation for the oil storage system. 
         [0022]    It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.