Cleaning and liquid contact with solids – Apparatus – Sequential work treating receptacles or stations with means...
Reexamination Certificate
1999-02-22
2001-01-30
Stinson, Frankie L. (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
Sequential work treating receptacles or stations with means...
C134S12200P, C134S201000, C134S182000, C454S067000
Reexamination Certificate
active
06178976
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a cover assembly for metal pickling tanks and more specifically to a cover assembly which has as a part thereof a means for collecting and exhausting toxic and corrosive fumes released from a picking line.
BACKGROUND OF THE INVENTION
Pickling is the process of chemically removing oxides and scale from the surface of a metal by the action of water solutions of inorganic acids. The reaction occurring when steel or iron materials are immersed in dilute inorganic acid solutions includes the solution of metal as a salt of the acid and the evolution of hydrogen. Steel pickled in dilute hydrochloric acid and sulfuric-acid solutions is an example of this reaction, with the end products of reaction being, respectively, ferrous chloride and hydrogen and ferrous sulfate and hydrogen. Adherent films of oxides are removed by the acid attack upon the scale on the base metal.
The pickling zone for pickling metal usually consists of several individual acid-proof tanks, typically about two to three feet in depth, located in series, comprising an effective immersion length of about 250 to 300 feet. While many lines have from three to five tanks, each about 40 to 80 feet long, some lines have only one long tank, divided by weirs into four or five sections. The strip is completely submerged under several inches of liquid acid bath as it travels through the tank or series of tanks forming the pickling zone.
The rate of pickling metal in the pickling zone is affected by numerous variables, including the metal-based constituents and the type and adherence of oxide to be removed. Solution temperature and concentration, ferrous chloride or ferrous sulfate concentration, agitation, time of immersion and presence of inhibitors all influence the rate of acid attack. Rate of acid attack and tank efficiency are important considerations when choosing operational parameters such as the choice of acid, hydrochloric acid or sulfuric acid for example, and the temperature of the acid bath. One of the most common efficiency problems in today's pickling systems is heat loss from the acid baths. The loss of heat lowers the efficiency of the overall system and will be more costly to operate.
Much of the heat supplied to the acid baths in pickling operations is lost at the surface of the acid bath by liquid evaporation. The heated acid bath solution evaporates into the air space between the acid bath and a cover enclosing the tank from the outside. In conventional pickling systems, the space above the acid bath and below the tank cover is used for transporting exhaust gases, evaporated acid bath fumes and air, to exhaust exits connected to the tank cover. Thus, the exhaust gasses in this space are not static, but form a fluid stream that typically flows in one direction, discharging through the exhaust exits. The contact of this fluid stream, traveling just above the acid bath surface, with the bath increases the evaporation rate at the air-liquid interface of the bath.
Increased evaporation leads to increased heat loss which means that more heat must be supplied to the acid baths in order to maintain the acid baths at a constant temperature. Maintaining the acid baths at a constant temperature is important in achieving even pickling of a length of metal product. By maintaining a specific acid temperature, the pickling process can either be sped up or slowed down to achieve the proper pickling of a product. But heat loss from the acid bath can complicate the pickling process by creating temperature gradients in the acid baths which can cause uneven pickling of the metal product.
In many present designs, the surface of the acid bath is open to the circulation exhaust gases from the pickling system. This facilitates heat loss. Because most of the heat loss of the acid is from the surface of the liquid in the form of evaporation, it is important to control this loss.
OBJECTS OF THE INVENTION
It is an object of the present invention to overcome the above disadvantages, and in particular to provide a pickle tank cover which minimizes heat loss and improves the efficiency of the pickling operation.
It is another object of the present invention to provide a cover assembly and fume collection system which is resistant to high temperature corrosive acid fumes.
It is yet another object of the present invention to provide fume removal at specific locations along the pickling tank for minimal heat loss of pickling acid bath.
It is still another object of the present invention to provide a tank cover that transports air and fumes so the moving air does not substantially contact the liquid surface of the acid bath of the pickling tank.
It is again another object of the present invention to capture escaping fumes at the inlet and exit openings of the pickling tanks where the metal strip enters and exits the pickle tanks and where the covers join.
It is a further object of the present invention to provide a fume exhaust system that is balanced.
It is still a further object of the present invention to provide an improved method for pickling a length of metal strip.
Finally, it is an object of the present invention to provide tank covers such that air is pulled from outside of the pickle tanks to form an air curtain around the entry and exit points to prevent fumes from escaping from the pickle tanks.
Other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a tank cover for a pickling operation which can improve the efficiency of the metal pickling operation and can overcome the disadvantages of prior art tank covers. It can also reduce the costs of the pickling operation. Specifically, the tank cover of the present invention reduces the heat lost from the pickling system and minimizes escape gases from the system by improving the flow of air and exhaust gases through the pickling system.
To the end of minimizing heat loss and achieving efficiency, the tank cover of the present invention separates the surface of the acid baths in the pickle tanks from exhaust gas flow through the pickling system. This separation reduces the acid evaporation rate which reduces heat loss and provides for a more efficient control over the exhaust gases.
A typical tank cover of the present invention extends the length of the pickle tank from the metal strip inlet to metal strip outlet at the opposite end of the pickle tank. Preferably the tank cover is made of a plurality of sections, which when connected, form a continuous cover enclosing the pickle tank. Specifically, the tank cover is constructed of a plurality of exhaust sections each having an exhaust outlet which is stationary and a plurality of sections which are movable. The sections which are movable can be opened for access to the inside of the tank if required for maintenance. The plurality of sections which are movable have a plenum chamber, which adjoin each other and the exhaust sections. Furthermore, the tank cover of the present invention is preferably constructed so that the exhaust sections form the entrance and exit of the pickling system in addition to being spaced evenly along tank cover between the sections having the plenum chamber.
The sections of the tank cover having the plenum chamber have an internal plenum chamber for collecting evaporated acid fumes and transporting these fumes to exhaust outlets connected to the exhaust sections. The separate collection and transportation of exhaust gases in the plenum chamber does not disturb the air-liquid interface of the acid bath, thereby reducing the evaporation rate. Once exhaust fumes have entered the plenum chamber, the fumes are transported to the exhaust outlet sections along the pickle tank cover where they are sent to a scrubber. Air velocities may be increased in the plenum chamber without concern for heat loss of the fluid in the pickle tanks because the fumes are not in contact with the
Armstrong, Westerman Hattori, McLeland & Naughton
Danieli Technology Inc.
Stinson Frankie L.
LandOfFree
Pickle tank cover with plenum chamber does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pickle tank cover with plenum chamber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pickle tank cover with plenum chamber will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2491810