Underwater water treatment unit and method for cleaning said unit

Abstract

The invention concerns an underwater water treatment unit which has specific cleaning means which are suitable for cleaning filtration membranes in the unconventional conditions associated with use at great or very great depths, as well as a method for cleaning the membrane of the underwater water treatment unit.

1 . An underwater water treatment unit suitable for injection into a hydrocarbon field, said unit including:
 means for supplying the underwater unit with power;   an underwater water treatment system which includes at least one filtration membrane, a water intake which is suitable to bring a flow of water drawn from the environment of the system into the underwater unit, a pipe connecting said water intake and said filtration membrane, a discharge pipe for treated water and at least one supply pump which is suitable for carrying out the water filtration;   a hydraulic cleaning circuit for cleaning said membrane, said circuit forming a loop between the inlet and the outlet of said membrane, and having a discharge pipe;   at least two water storage tanks, each water tank being connected to the cleaning circuit;   at least one tank for storing a cleaning product selected from among an acid and a base, the cleaning product tank being connected to the cleaning circuit;   at least one cleaning pump which is suitable for setting the liquids in the cleaning circuit into motion;   
       said filtration membrane being provided with at least one heating means, and at least one of the water tanks being provided with at least one means for heating the tank. 
     
     
         2 . The underwater unit as claimed in  claim 1 , wherein the filtration membrane is a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane or a reverse osmosis membrane. 
     
     
         3 . The underwater unit as claimed in  claim 2 , wherein the water treatment system includes a nanofiltration membrane and an ultrafiltration membrane which is situated upstream of said nanofiltration membrane, the hydraulic cleaning circuit forming:
 a loop between the inlet and the outlet of the nanofiltration membrane or   a loop between the inlet and the outlet of the ultrafiltration membrane, or   two loops between the inlet and the outlet of the nanofiltration membrane on the one hand and between the inlet and the outlet of the ultrafiltration membrane on the other hand, valves being situated in the loops in order to allow the membrane desired for cleaning to be selected.   
     
     
         4 . The underwater unit as claimed in  claim 1 , characterized in that said unit includes at least two storage tanks for the cleaning product, at least one of the tanks being a storage tank for an acid and at least one of the tanks being a storage tank for a base, the acid and base tanks being connected to the cleaning circuit. 
     
     
         5 . The underwater unit as claimed in  claim 1 , wherein said unit includes at least three water storage tanks, at least two of the water tanks being provided with at least one means for heating the tank. 
     
     
         6 . The underwater unit as claimed in  claim 1 , wherein the supply pump and the cleaning pump are mounted on the same shaft. 
     
     
         7 . The underwater unit as claimed in  claim 1 , wherein said unit further includes a discharge pipe which allows the contents of the hydraulic cleaning circuit to be discharged into the water storage tank or tanks. 
     
     
         8 . A method for cleaning the filtration membrane of an underwater unit including means for supplying the underwater unit with power:
 an underwater water treatment system which includes at least one filtration membrane, a water intake which is suitable to bring a flow of water drawn from the environment of the system into the underwater unit, a pipe connecting said water intake and said filtration membrane, a discharge pipe for treated water and at least one supply pump which is suitable for carrying out the water filtration;   a hydraulic cleaning circuit for cleaning said membrane, said circuit forming a loop between the inlet and the outlet of said membrane, and having a discharge pipe;   at least two water storage tanks, each water tank being connected to the cleaning circuit;   at least one tank for storing a cleaning product selected from among an acid and a base, the cleaning product tank being connected to the cleaning circuit;   at least one cleaning pump which is suitable for setting the liquids in the cleaning circuit into motion;   
       said filtration membrane being provided with at least one heating means, and at least one of the water tanks being provided with at least one means for heating the tank, said method including the steps consisting in:
 a) cutting off the inlet of water into said filtration membrane; 
 b) injecting water contained in one of the water storage tanks into the hydraulic cleaning circuit, and making said water circulate in a loop in the hydraulic cleaning circuit using the cleaning pump; 
 c) heating the filtration membrane up to a temperature of between 15° C. and 40° C. inclusive using the heating means; 
 d) injecting a cleaning product contained in at least one storage tank into the hydraulic cleaning circuit; 
 e) discharging the contents of the hydraulic cleaning circuit via the discharge pipe; 
 f) injecting water contained in one of the water storage tanks into the hydraulic cleaning circuit again, and making said water circulate in a loop in the hydraulic cleaning circuit; and 
 g) discharging the contents of the hydraulic cleaning circuit via the discharge pipe again. 
 
     
     
         9 . The method for cleaning as claimed in  claim 8 , wherein the cleaning product injected into the hydraulic cleaning circuit during step d) is an acid. 
     
     
         10 . The method for cleaning as claimed in  claim 8 , wherein said method includes, between step f) and step g), the steps:
 d′) injecting a cleaning product that is different from the product injected during step d) into the hydraulic cleaning circuit, said product being contained in at least one storage tank;   e′) discharging the contents of the hydraulic cleaning circuit via the discharge pipe; and   f′) injecting water contained in one of the water storage tanks into the hydraulic cleaning circuit again, and making said water circulate in a loop in the hydraulic cleaning circuit.   
     
     
         11 . The method for cleaning as claimed in  claim 10 , wherein the cleaning product injected into the hydraulic cleaning circuit during step d) is a base and the cleaning product injected into the hydraulic cleaning circuit during step d′) is an acid. 
     
     
         12 . The method for cleaning as claimed in  claim 8 , wherein said method subsequently includes the steps:
 h) resuming the water treatment in the water treatment system of the unit; and   i) replacing the water which has been used during steps b) and f), by injecting water obtained leaving the treatment system into the water storage tanks.   
     
     
         13 . The method for cleaning as claimed in  claim 8 , wherein the water injected into the hydraulic cleaning circuit during step f), is heated to a temperature of between 15° C. and 40° C. inclusive thanks to the means for heating the water storage tanks or tanks. 
     
     
         14 . The method for cleaning as claimed in  claim 8 , wherein the underwater water treatment unit is placed underwater, at a minimum depth of 500 meters. 
     
     
         15 . The method for cleaning as claimed in  claim 8 , wherein the contents of the hydraulic cleaning circuit is discharged into the water storage tanks or tanks which has or have been drained following step b). 
     
     
         16 . The method for cleaning as claimed in  claim 12 , wherein the method includes the step of replacing the water which has been used during step f′ injecting water obtained in leaving the treatment system in the water storage tanks. 
     
     
         17 . The method for cleaning as claimed in  claim 13 , wherein the water injected into the hydraulic cleaning circuit during step f′ is heated to a temperature of between 15° and 40° C. inclusive thanks to the means for heating the water storage tanks or tanks.