Abstract:
A method and apparatus for mixing a corrosive mixture is provided. The apparatus having a lid for sealing an opening to the mixing vessel. The lid easily and quickly operated in addition to providing a secure pressure tight seal. It is necessary for the lid to be easily and conveniently operated to assure use of the lid.

Description:
RELATED APPLICATIONS 
     This application claims benefit of priority from U.S. Provisional Application No. 60/272,499, filed Mar. 1, 2001 and entitled METHOD AND APPARATUS FOR SEALING A VESSEL FOR MIXING CORROSIVE MATERIAL, which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method and apparatus for mixing corrosive material, and more specifically to a method and apparatus for mixing a corrosive material in a sealed vessel. 
     BACKGROUND 
     Everyday in various locations corrosive materials are mixed in vessels for use in commercial and industrial processes. In the oil industry, it is common for chemical solutions to be mixed and injected into wells for purposes ranging from inhibiting corrosion to cleaning portions of the adjacent formation. One very common practice is to inject acid solutions into a well to clean the formation to increase production. After the acid is injected, it is common to inject a alkaline solution, such as caustic soda or sodium hydroxide, into the well to neutralize the acid and prevent damage to the well and/or the formation surrounding the well. 
     The alkaline solution is very often mixed at the well site when needed. All too often workers are injured during this mixing process by the solution contacting the skin or from inhaling the fumes. Heretofore, it was common practice to dump bags of a chemical, such as caustic soda, into a mixing vessel or pot and mix with water. These vessels on occasions have a lid that is utilized to partially cover the top opening, which limits but does not prevent splashing of the solution or inhaling fumes as the solution is mixed. 
     It would be a benefit therefor to provide a method and apparatus for mixing corrosive material that facilitates an efficient and accurate method of mixing a desired solution while limiting workers to a hazardous exposure. It would be a further benefit therefore to provide a corrosive mixing vessel having a sealable cover. It would be a still further benefit to have a corrosive mixing vessel including a sealing cover, wherein the cover may be operated quickly, efficiently, and effectively promoting sealing of the vessel and increasing worker safety. 
     SUMMARY 
     A system and method of mixing a caustic solution is provided. The method of mixing a caustic solution, of the present invention, including the steps of providing a mixing vessel having a tub connected to a hopper via a valve, the hopper having a top opening; introducing a caustic chemical through the opening into the hopper; sealingly closing said opening with a lid; opening the valve depositing the caustic chemical on a screen disposed within said tub; closing the valve connecting the hopper and the tub; flowing a fluid into the tub to mix with the caustic chemical forming a caustic solution; introducing a gas into the tub to mix the caustic solution; and discharging the caustic solution for utilization. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of a preferred embodiment of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a side view of the corrosive material mixing apparatus having a sealing cover of the present invention. 
     FIG. 2 is a top view of the hopper. 
     FIG. 3 is a partial cross-sectional view of deck ring and lid in the closed position. 
     FIG. 4 is a partial cross-sectional view of the lid in the closed position within the deck ring. 
    
    
     DETAILED DESCRIPTION 
     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by similar reference numerals through the several figures. 
     FIG. 1 is a side view of the corrosive material mixing vessel having a sealing cover of the present invention, generally denoted by the numeral  10 . Mixing vessel  10  includes a hopper  12 , a tub  14 , and a lid  16 . 
     Mixing vessel  10  is constructed of material suitable for mixing corrosive material such as caustic soda. The method and apparatus will be described for use with caustic soda for brevity and clarity, although the mixer may be used for mixing many different solutions. Hopper  12  includes an opening  18  for loading hopper  12  with material. A loading tray  20  may extend from hopper  12  adjacent to opening  18  to aid in loading material into hopper  12 . It is also desirable to have ears  22  attached to hopper  12  to facilitate lifting of vessel  10 . 
     Hopper  12  has a fill mark line  21  indicating the level to which to fill hopper  12  with chemical. Tub  14  and hopper  12  are interconnected via a valve  13 . Tub  14  further includes a bottom head or ring  26  adapted for connecting vessel  10  to a structure, such as a mud tank (not shown), by welding or bolting. A screen  19  is positioned within tub  14 . 
     Mixing vessel  10  further includes ports for venting, dumping material, introducing liquids and/or gases, and for connecting instruments. All of the ports may be connected to the appropriate equipment in a manner well known in the art. Some of the connections include a water wash out line  50  at hopper  12 . Tub  14  includes a water mixing line  52 , a lower water washout line  54 , a pressurized air connection  56 , and upper vent line  58 , a lower vent line  60 , and at least one gauge connector  62  for a temperature and/or pressure gauge. 
     FIG. 2 is a top view of hopper  12 . Hooper  12  includes an L-shaped deck ring  28  defining opening  18 . Deck ring  28  includes a vertical wall  30  (FIG. 3) and a horizontal leg  31 . Lips  32  extend inwardly from leg  31  to create a portion of deck ring  28  having a smaller inside diameter than the majority of deck ring  28 . 
     FIG. 3 is a partial cross-sectional view the deck ring  28  and lid  16  in the closed position. Lid  16  includes a cover  17  and a locking bar  36  functionally connected to a lug  38 . Locking bar  36  has a length less than the inside diameter of the majority portion of leg  31  and greater than the diameter between lips  32 . Lid  16  is placed within deck ring  28  so that a portion of lid  16 , including sealing elements  34 , rest atop of leg  31  of deck ring  28 . In the closed position, a locking bar  36  connected to lid  16  is located under lip  32  of deck ring  28 . By tightening a lug  38 , locking bar  36  is pulled toward lid  16  compressing sealing element  34  against leg  31 , creating a sealed closure. 
     FIG. 4 is a partial cross-sectional view of lid  16  in the closed position within deck ring  28 . Lid  16  is placed within vertical wall  30  of ring  28 , with locking bar  36  offset from lip  32 . Stops  40  extend downwardly from an interior portion of lid  16  to maintain locking bar  36  in a set position. Lid  16  is then rotated utilizing handles  42  until locking bar  36  encounters stops  44  (FIG.  3 ). When stops  44  are encountered, locking arm  36  is positioned beneath lips  32 , and is in the locked position. Additionally, marks  46  and  48  may be utilized to confirm that lid  16  is in the closed position. A tool, such as a wrench, is utilized to turn lug  38  to secure and seal lid  16 . 
     A complete description of lid  16  is provided in U.S. Pat. No. 3,209,663 to Baier which is incorporated by reference herein. Although only a circular, unhinged lid  16  is shown in this embodiment it should be recognized that other configurations, either hinged or unhinged can be utilized. 
     A method of use of mixing vessel  10  and a sealing lid  16  is described with reference to FIGS. 1 through 5. Vessel  10  is lifted by ears  22  and placed over a tank (not shown) for installation. Bottom head  26  is secured to the tank, for example by bolting or welding. Various fluid lines, including gas and liquid lines, dump lines, and overflow lines are connected to vessel  10 . A line is connected to a tank, such as a mud tank, to dump valve  24 . A water line is connected to mixing line connection  52 , preferably with both a valve and a check valve within the line. A pressurized air source is connected vial a line to tub  14  at connection  56 . Do not use excessive air pressure in tub  14  Lower vent tube  60   a  should be connected to the tank above the standing fluid level, lower vent tube  60  is utilized to check fluid level in tub  14 . Upper vent tube  58   a  should be directed into the mud tank above the fluid level or to a well ventilated area avoiding contact with humans or animals. Check air by filling tub  14  to lower vent  60   a  with water and using a regulator to control fluid roll in tub  14 . Excessive air will force water out of lower vent tube  60   a . A fluid source via a line is connected to lower wash out  54  to clean tub  14 . Upper washout valve  50  in hopper  12  is for fume or vapor check and also for cleaning hopper  12  and valve  13  with fluid. Cover  16  should be closed during cleaning and fume check. 
     Once mixing vessel  10  is connected to a mud tank or other vessel established for transporting the caustic fluid for use, remove lid  16  on mixing unit  10 . Check flapper valve  13  and screen  19  for debris and water in mixing unit. If debris or fluid is present, clean and drain. Close flapper valve  13  on mixing unit  10 . Close valves  50 ,  52 ,  54 , and  56 . Pour caustic chemicals into hopper  12 . A mark  21  may be provided to aid in identifying level of chemical to be used per mix. Check seal  34  on lid  15  for damage and replace if necessary. Install lid  16  in opening  18  of hopper  12 , rotating lug  38  until lid  16  is sealingly secured to hopper  12 . Open flapper valve  2  dumping the chemical on screen  19 . Close valve  13 . Open lid  16  to assure all the chemical is out of mixing hopper  12  and on screen  19 . Reinstall lid  16  and seal opening  18  in hopper  12 . Open water mixing valve  52  filling mixing tub  14  until fluid escapes lower vent tube  60   a , then shut valve  52 . Open air valve  56  introducing air to roll fluid and mix the solution in tub  14 . Temperature gauge  62  is provided to monitor during the mixing process. With valves  50 ,  52 ,  54 ,  56  and valve  13  closed, open dump valve  24 , dumping fluid mixture into the tank. From the tank the caustic mixture can be pumped where desired. 
     Although the present invention and its advantages have been described in relation to the illustrated embodiments if should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, it should be realized that various elements as described in the various embodiments can be combined in varying combinations to satisfy the invention as claimed. As demonstrated above, elements of the invention that are the same or similar in various figures are numbered in a manner to reflect the similarity while numbering elements to correspond to the particular figure referenced.