Patent Publication Number: US-2011068062-A1

Title: System for removing contaminants from a water circulation stream

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a system for removing contaminants from hydrocarbon-containing liquids, and more particularly to a system of controlling operation of a circulation pump in such system. 
     Rigorous environmental regulations require multi-stage treatment of all hydrocarbon-containing liquids, including drilling waste, storage tank contents and the like. The industry employs primary treatment systems, such as heater treatment devices, gun barrels, separators, and the like. Oil pumped from a well usually contains significant quantities of salt water that is removed with the help of oil-water separators. Separated oil is transferred to an oil storage tank, while the water is collected in a separate vessel. However, modern oil-water separators still leave a small quantity of loosely emulsified water in the removed oil, as a consequence of which water and small solid particles tend to accumulate on the bottom of the oil storage tank. 
     Conventionally, a recirculation system is employed for removing the remaining water from the oil storage tank and for returning removed water to the oil-water separator. A pump is usually connected to the oil storage tank to provide the power necessary for moving the remaining water away from the oil storage tank and into the separator or water reservoir. The pumped water stream carries the suspended contaminants through the pump, which creates a significant problem, particularly if the level of oil in the storage tank is low. 
     The present invention contemplates provision of a system of water recirculation, which protects the circulation pump and removes contaminants from the system before they have an opportunity to damage the pump. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a system of removing contaminants from a water recirculation stream. 
     It is another object of the invention to provide a system of protecting a recirculation pump from damage by small particulate matter. 
     These and other objects of the invention are achieved through a provision of a system for removing contaminants from a water stream in a circulation line, where salted water is removed from an oil storage tank and delivered into a water reservoir. The storage tank is configured for retaining a pre-determined quantity of fluid containing unrefined oil, water and suspended solid contaminants. A water circulation conduit is connected to the storage tank for removing water using a powered circulation pump from the storage tank. A filter assembly is mounted between the storage tank and the circulation pump for collecting suspended solids from the water stream. 
     A control unit is mounted in the circulation conduit between the filter assembly and the circulation pump, said control unit being configured to detect an out-of-range pressure in the circulation conduit before the water stream reaches the circulation pump. The control unit has a pressure sensor and a transducer that is operationally connected to the power supply. Upon detection of low level of oil in the storage tank or a clogged filter, the transducer de-activates the pump and sends an alarm signal to an operator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made to the drawings, wherein like parts are designated by like numerals, and wherein 
         FIG. 1  is a schematic view of the system of the present invention. 
         FIG. 2  is a detail exploded view of the filter device of the system of the present invention. 
         FIG. 3  schematically illustrates the step of cleaning of the filter basket of the filter assembly. 
     
    
    
     DETAIL DESCRIPTION OF THE INVENTION 
     Turning now to the drawings in more detail, numeral  10  designates the system of removing contaminants according to the present invention. The system  10  comprises an oil storage tank  12 , which receives a quantity of unrefined oil that may or may not have undergone a primary treatment, for instance in an oil-water separator vessel  14 . In such separators, oil is separated from heavier material, in this instance water. The oil may also be deposited into the stock tank  12  from a field truck that sucks it up from a spill in the oil field by vacuum or from a pipeline that is run to the stock tank from a producing well. 
     In the oil-water separator vessel  14 , oil  16 , as a lighter liquid, rises, to the top of the separator vessel, while heavier emulsified water  18  settles, by gravity on the bottom. A water pump  20  connected to a lower portion of the separator vessel  14  transfers the salt water to a salt water reservoir  22 . The recovered water is treated (flocculation, filtration, etc.) to local charge standards. This portion of the liquid phase of the oil stream is not re-circulated through the system of the instant invention. 
     Since the liquid oil leaves the oil-water separator  14  still retaining some of the water and solid particulate matter, heavy salt water and tiny particles tend to settle as a layer  30  in the lower portion of the oil storage tank  12 , which may or may not receive the influx of fluid from the separator  14 . A conduit  32  with a control valve  34  is connected to the oil storage tank  12  a distance above the bottom wall  36  of the tank  12 . A sight glass  38  allows visual inspection of the level of oil in the storage tank  12 . A transport truck (not shown) can be connected to the oil removal conduit  32  for removing oil from the storage tank  12  and delivering oil to another location. 
     A circulation pump  40  is fluidly connected to the oil storage tank  12  via a circulation conduit  42 . An inlet of the conduit  42  is located adjacent the bottom wall  38 , close to the area where the contaminant layer  30  is located. 
     A filter assembly or scrubber  50  is mounted in fluid communication with the circulation line  42  between the circulation pump  40  and the oil storage tank  12 . The filter assembly  50  comprises a hollow filter body  52 , which can be a cylindrical vessel having a closed bottom  54  and an open top  56 . A peripheral flange  58  is secured to the top  56 , with the flange  58  having a greater diameter than the body  52 . A lid or cover  60  fits over the flange  58  and is secured thereto by a plurality of bolts  62  fitted into through openings (not shown) formed in the flange  58 . Threaded ends of the bolts  62  are secured on the underside of the flange  58  by nuts  64 . The cover  60  can be moved in relation to the flange  58  by removing some of the bolts  62  and nuts  64 , allowing the cover  60  to swing away from the open top  56 , as shown in  FIG. 3 . 
     A mesh basket, or filter member  70  is configured for removable positioning in the body  52 . The filter member  70  has a generally cylindrical body having a diameter at least slightly smaller than the inner diameter of the body  52  and vertical dimensions less than the vertical dimensions of the filter body  52 . The basket  70  fits into the filter body  52 , with the top edge of the filter member  70  being located below the open top of the filter body  52 . 
     The filter member  70  has a plurality of perforated openings  72  formed about the circumference of the filter member to allow water to pass through the perforated basket into the body of the filter, while preventing debris from leaving the basket  70  with the flow of fluid. A handle  74  is secured to the top edge of the filter member  70  to facilitate removal of the basket  70  from the filter body  52  and emptying of the solid contaminants collected in the basket  70 , as schematically shown in  FIG. 3 . 
     A filter inlet portion  76  of the conduit  42  is connected to the filter body  52  at a level above the top edge of the basket  70  (see,  FIG. 1 ) to ensure that all intake water and suspended sediment is directed through the filter. A filter outlet is formed adjacent a bottom portion of the filter body  52 . The filter outlet is connected to a filter outlet portion  78  of the conduit  42 . A first filter shut-off valve  80  is mounted in the filter inlet portion  76 , and a second filter shut-off valve  82  is mounted in the filter outlet portion  78 . The valves  80 ,  82  are closed when the filter basket  70  is emptied of the collected debris. 
     A circulation pump control valve  84  is mounted upstream from the circulation pump  40  and downstream from the filter assembly  50  and the second filter shut-off valve  82 . The control valve  84  is provided with a control unit  86 , which detects an out-of-range pressure condition in the conduit portion  87  connecting the shut-off valve  82  with the control valve  84 . The control unit  86  is provided with a pressure sensor and a transducer  89 , which is activated by low level of liquid in the oil tank storage  12  or by a blockage in the filter assembly  50 . 
     The control unit  86  is operationally connected to a power supply  90 , which operates the pump  40 . The transducer  89  of the control unit  86  shuts down power to the circulation pump  40  upon detection of the out-of-range condition. If desired, the transducer may be equipped with a wireless signal transmitter to inform a remote control station or an operator that the circulation pump has been de-activated. 
     By placing the control unit  86  at the intake of the pump  40  the system of the present invention protects the pump  40  from burning up because of no flow of fluid through the pump or too low pressure in the stock tank  12 . The pressure switch of the control unit  86  is upstream of the pump  40 , which allows it to sense the hydrostatic head in the oil stock tank  12 . 
     The filter  50  catches debris that accumulates at the bottom of the oil storage tank  12  before any foreign matter is allowed to reach the recirculation pump  40 . All solid materials that normally accumulate at the bottom of an oil tank in the field can be captured before they reach the impeller of the pump  40 . Clogged pump impellers have a negative impact on total production. The system of the present invention alleviates the need for field maintenance that entails cleaning the impeller, which requires generally shutting down the entire collection process. 
     The catch basket  70  allows for easy cleaning and removal of the trash, thereby reducing the potential for pump downtime. The scrubber  50  also works to produce the low suction pressure when it is clogged such that a down stream pressure switch of the control unit  86  senses the low pressure and through a series of relay switches shuts down the pump  40 , thereby protecting it from burning up because of no flow of fluid through the pump. 
     Normally, the removed filtered water is re-circulated through a conduit line  92 , which connects the output of the pump  90  with the oil-water separator  14 , from which it can be removed via a water pump  20  to a water reservoir  22 . Alternatively, the conduit line  92  can be directly connected to the water reservoir  22 . The pressure on the suction to the pump is created by the hydrostatic head of the oil in the stock tank  12 , which may be blocked off because of the debris that accumulated in the basket  70 . 
     Once the circulation pump receives the low pressure signal signaling that the basket in the scrubber is full of debris, an alarm signal generated by the transducer  89  of the control unit  86  is sent off to alert the operator to close the shut off valves  80 ,  82  on both sides of the scrubber  50 . The operator then unbolts the lid  60  from the filter  50 , removes the basket  70  from the filter body  52  and empties the trash out of the basket  70 . The alarm signal may be a visual or audio signal, as well as a wireless signal sent to a remote location, computer, telephone and the like. 
     Once the basket  70  is clean, the operator places the basket back into the filter body  52 , bolts the lid  60  back onto the filter body  52 , opens the valves  80 ,  82  and manually overrides the pressure cutoff switch by the relays until such time as circulation is restarted. The circulation pump  40  continues re-circulation of the salt water until such time as sufficient debris is collected in the basket  70 , which diminishes the pressure on the suction part of the circulation pump, as detected by the control unit  86 . 
     The control unit  86  has a secondary protection feature, a 24-volt pressure micro switch with a reset button to ensure protection of the circulation pump  40 . Should the flow of oil be reduced before reaching the pump, the micro switch will cut power to the pump until maintenance is initiated to restore flow to the system. 
     Many changes and modifications can be made in the design of the present invention without departing from the spirit thereof. I, therefore, pray that my rights to the present invention be limited only by the scope of the appended claims.