Systems and Methods for Ballasting Covers for Gas-Holding Sludge Digestors
A method of ballasting a cover of a sludge digester that is comprised of a storage tank and the cover. The method includes placing a ballast into the storage tank in a first predetermined position, placing the cover onto the storage tank, lowering a lifting member of a lifting device through an access port in the cover and into the storage tank, securing the lifting member to the ballast, using the lifting device to lift the lifting member and the ballast until the ballast is in a second predetermined position that is substantially above the first predetermined position, engaging a support bracket attached to the cover with a support member; and securing the ballast to the cover with the support member while the ballast is in a third predetermined position that is substantially below the second predetermined position.
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This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 60/974,758 entitled “Ballast Support System,” filed Sep. 24, 2007, the complete disclosure of which is herein incorporated by reference for all purposes.
BACKGROUNDSludge digesters typically include a storage tank for holding decomposing sludge, and a cover that contains, and floats on, an envelope of gas that is above, and generated by, the decomposing sludge. It is common to attach ballast to the cover to increase the weight of the cover, and the pressure of the gas within the digester. The pressure of the gas within the sludge digester is proportional to the effective weight of the ballasted cover. Examples of gas-holding storage tanks, such as sludge digesters, are found in U.S. Pat. Nos. 251,245; 1,989,589; 2,050,686; 2,050,915; 2,373,797; 3,187,897; 3,288,295; 3,535,236; 4,060,175; 4,378,437; 4,391,705; 4,648,968; 4,710,292; 5,092,482; 5,238,844; 5,384,033; 5,423,895; 6,247,278; 7,069,655; and U.S. Patent Application No. 2004/0232148, the disclosures of which are hereby incorporated by reference in their entirety for all purposes.
Most sludge digesters that include a ballasting system for the cover include horizontal support shelves that are attached and orthogonal to the lower end of the cover's side skirt, and that extend inwardly from the side skit toward the center of the storage tank. These support shelves are generally welded into place after the cover has been constructed and placed on top of the storage tank. In order to attach the ballasts to the support shelves, the ballasts must be lifted vertically from the base of the tank to a height that is greater than the support shelves, moved horizontally to a position above the support shelves, and then lowered onto the support shelves. The ballast is then secured to the support shelves where they are supported during operation of the digester.
This process presents a number of problems. First, because the support shelves are welded to the lower end of the side skirt after the cover is placed onto the storage tank, the support shelves and portions of the side skirt must be painted, while the cover is on the storage tank, so as to inhibit corrosion of the otherwise unpainted portions of the cover in the highly corrosive environment within an operating sludge digester. This is often very difficult, and costly, because some of the portions of the cover that need to be painted are not readily accessible, due to the tight fit between the side skirt and the outer wall of the storage tank. Some portions of the cover may not be painted effectively, thus increasing the risk of corrosion.
Second, because the ballasts must be lifted vertically, moved horizontally and lowered vertically in order to be secured to the support shelves, the ballasts must be moved in such a manner using either (a) a make-shift pulley system within the storage tank, which is difficult to use and construct due to the extreme weight of the ballasts, or (b) a crane or other lifting device that can only move the ballast onto the support shelves if the roof includes a elongated radial opening in its roof that permits the crane to lower and raise its cable or other lifting member vertically, and to move the ballast horizontally relative to the support shelf. If a lifting device is used through an elongate opening in the roof of the cover, then after the ballast is secured to the support shelf, and prior to operation of the digester, the opening must be sealed, such as by welding cover plates over the openings, to ensure that the cover is gas-tight.
Third, moving the ballast horizontally and vertically relative to the support shelves during installation of the ballasts creates a risk that the ballast will scrape paint off of the support shelves or the side skirt, which increases the risk that the support shelf will corrode and eventually fail. These problems are alleviated by the invention disclosed herein.
The present invention relates to systems and methods for ballasting covers for gas-holding sludge digesters having a storage tank and a cover.
The storage tank 12 may include a bottom wall 24 with a cylindrical vertical side wall 26 extending upwardly from the bottom wall. In the embodiment shown in
The cover 14 is dimensioned to fit onto the storage tank 12, and as such, the cover is designed and manufactured when the dimensions of the storage tank are known. These dimensions include the diameter of the storage tank, the height of the side walls 26, the height of the corbels 28 above the bottom wall 24, the volume and pressure of gas that must be accommodated by the digester, and the high and low liquid levels in the storage tank. The cover may include a substantially dome-shaped roof 30 and an annular or cylindrical side skirt 32 extending downwardly from the top wall.
The roof 30 of the cover 14 may be constructed of a plurality of pie shaped panels 34 separated and connected by radial beams 36, or ribs, that reinforce the structure of the roof, where the number and size of the panels and radial beams depends on the size of the storage tank and cover. The roof panels and radial beams may be connected using any suitable fastening means, such as nuts and bolts, and/or welding.
Side skirt 32 may be constructed of a plurality of arc-shaped panels 38 reinforced by a plurality of stiffeners 40, where the number and size of the panels and stiffeners depends on the size of the storage tank and the length of the side skirt. The length of the side skirt is dependant on the height of the corbels 28 above the bottom wall 24, and the volume and pressure of gas that must be accommodate by the digester 10, and must be sufficient to maintain the liquid seal with the liquid within storage tank 12. When the cover 14 is placed onto the storage tank, as shown
The cover 14, including the roof 30, the side skirt 32, and any additional structures associated with the cover, may be made of any suitable material, including stainless steel, steel, fiberglass, carbon fiber, etc., although any suitable material can be used.
As discussed above, the system for ballasting the cover may include a ballast 16, one or more support brackets 18 attached to the cover, a support member 20 for selectively engaging one or more support brackets, and a selectively sealable access port 22 in the cover. Generally, the ballast will be made of concrete, although other materials may be used. The ballast may be any suitable size, shape and weight. In one embodiment, the ballast may be cylindrical concrete ballast, which is pre-formed and commercially available, thus preventing the need to create a mold and pour the concrete ballast during assembly of the digester 10.
The support brackets 18 may include any structure attached to the cover 14 that can be securely engaged by the support member 20 and has sufficient strength to bear some or all of the weight of the ballast 16 when the ballasting system is in a ballasting configuration (i.e. when the support member is engaged with the support bracket and is bearing the weight of the ballast in a manner that secures the ballast to the cover). As shown in
The support member 20 may include any high-strength structure for selectively engaging and disengaging one or more of the support brackets 18 attached to the cover 14, and further for supporting the weight of the ballast 16 in a manner that secures the ballast to the cover 14 when the ballasting system is in a ballasting configuration. For example, as shown in
The support member 20 may include one or more engagement members 42 for engaging the one or more support brackets 18 attached to the cover 14. For example, as shown in
Although the discussion above only refers to a single support member 20 for use in securing a particular ballast 16 to the cover 14, it should be appreciated that a plurality of support members may be used to secure a particular ballast to the cover. Each support member may engage support brackets attached to the cover in accordance with the above disclosure. For example, if two support members are used to secure a ballast to the cover, and each support member includes a pair of engagement members 42, then up to four support brackets 18 (two upper and two lower support brackets) may be necessary to secure the ballast to the cover. Moreover, a plurality of ballasts may be secured to a particular cover, where each ballast is secured to the cover with one or more support members, and each support member requires one or more support brackets.
Because the ballasting system of the present invention does not include a support shelf, a ballast 16 may be secured to the cover 14 by vertically raising the ballast, such as with a crane or other lifting device, from a first position to a second position directly or substantially above the first position, where the support member 20 can be wrapped around the ballast and secured to one or more support brackets 18. The lifting device can then be used to lower the ballast slightly until the weight of the ballast settles into the support member, and gravity pulls the support member and each engagement member 42 tightly against each support bracket 18. After the weight of the ballast has settled into the support member, the ballast may be in a third position directly or substantially, (albeit slightly) below the second position.
In order to enable the aforementioned movement of the ballast 16 without the need (a) for make-shift pulley systems, and (b) to cut a hole in or disassemble the cover, or (c) to attempt to remove the cover with the ballast attached, the ballast support system includes access ports 22 in the roof 30 of the cover 14. These access ports provide access to the ballast 16 with a lifting device. Each access port may be substantially or directly above the position where the ballast 16 is secured to the cover when the ballasting system is in a ballasting configuration (see
The system for ballasting the cover described above eliminates the need for welding a support shelf to the bottom of the side skirt 32, and for painting the support shelf and/or side skirt after such a welding process. The system also reduces the risk that the ballast 16 will scrape paint off portions of the cover, thereby decreasing the risk of corrosion and failure. Finally, the system provides a substantially more efficient means for performing a method of attaching and detaching ballast to the cover.
For example, as shown in
If the digester 10 is ever in need of maintenance or repair, and/or if the cover 14 ever needs to be removed from the storage tank 12, then the ballast system described herein readily allows for removal of the ballast 16 from the cover. First, the removable sealing member may be removed from the access port 22, thereby unsealing the access port. A lifting member 50 may then be lowered through the access port and into the storage tank and secured to the ballast. The lifting device may be used to lift the lifting member and the ballast slightly to remove the gravitational force applied by the ballast on the support member 20. The support member then may be unsecured from the cover, such as by disengaging the one or more engaging mechanisms 42 from the one or more support brackets 18. The lifting device may then be used to lower the lifting member and the ballast to the ground (such as onto a base or platform 48 on bottom wall 24), where the lifting member is disengaged from the ballast. Once the ballast has been removed from the cover, the lifting member can be removed from the storage tank through the access port. In some cases, once the ballast has been removed, the cover may be form the storage tank removed in its fully constructed.
Accordingly, while embodiments of methods and systems have been particularly shown and described with reference to the foregoing disclosure, many variations may be made therein. Various combinations and sub-combinations of features, functions, elements and/or properties may be used. Such variations, whether they are directed to different combinations or directed to the same combinations, whether different, broader, narrower or equal in scope, are also regarded as included within the subject matter of the present disclosure. The foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or later applications. The claims, accordingly, define selected inventions disclosed in the foregoing disclosure. Where the claims recite “a” or “a first” element or the equivalent thereof, such claims include one or more such elements, neither requiring nor excluding two or more such elements. Further, ordinal indicators, such as first, second or third, for identified elements are used to distinguish between the elements, and do not indicate a required or limited number of such elements, and do not indicate a particular position or order of such elements unless otherwise specifically stated.
Claims
1. A method of ballasting a cover of a sludge digester that is comprised of a storage tank and the cover, the method comprising:
- placing a ballast into the storage tank in a first predetermined position;
- placing the cover onto the storage tank;
- lowering a lifting member of a lifting device through an access port in the cover and into the storage tank;
- securing the lifting member to the ballast;
- using the lifting device to lift the lifting member and the ballast until the ballast is in a second predetermined position that is substantially above the first predetermined position;
- engaging a support bracket attached to the cover with a support member; and
- securing the ballast to the cover with the support member while the ballast is in a third predetermined position that is substantially below the second predetermined position.
2. The method of claim 1, wherein the access port is positioned substantially above the first, second and third predetermined positions.
3. The method of claim 1, wherein the support bracket is attached to a side skirt of the cover.
4. The method of claim 1, wherein the support member is substantially rigid, and includes a portion having a shape that is complimentary to the shape of the ballast.
5. The method of claim 1, wherein the support member is flexible.
6. The method of claim 1, wherein securing the ballast to the cover includes at least partially wrapping the support member around a bottom portion of the ballast.
7. The method of claim 1, wherein the support member includes an engaging member, and engaging the support bracket with the support member includes engaging the support bracket with the engaging member.
8. The method of claim 7, wherein the engaging member includes a hook adapted to hook onto the support bracket.
9. The method of claim 7, wherein the engaging mechanism includes a clip adapted to clip onto the support bracket.
10. The method of claim 7, wherein the cover includes a second support bracket, and the support member includes a second engaging member, and wherein securing the ballast to the cover with the support member includes engaging the second support bracket with the second engaging member.
11. The method of claim 10, wherein the second support bracket is attached to a side skirt of the cover.
12. The method of claim 1, wherein the support member includes two engaging members, and wherein engaging the support bracket with the support member includes engaging the support bracket with each of the two engaging members.
13. The method of claim 12, wherein the support bracket is attached to a side skirt of the cover.
14. The method of claim 1, further comprising:
- disengaging the lifting member from the ballast;
- using the lifting device to lift the lifting member through the access port and out of the storage tank; and
- sealing the access port with a removable sealing member.
15. The method of claim 14, wherein the access port includes a threaded hole, and the sealing member includes a threaded cover that can be selectively engaged and disengaged from the threaded hole of the access port.
16. The method of claim 14, further comprising:
- removing the sealing member from the access port, thereby unsealing the access port;
- lowering a lifting member of a lifting device through the access port and into the storage tank;
- securing the lifting member to the ballast while it is secured to the cover;
- unsecuring the ballast from the cover;
- lowering the ballast to a base; and
- disengaging the lifting device from the ballast.
17. The method of claim 16, further comprising removing the cover from the storage tank.
18. A method of ballasting a cover of a sludge digester that is comprised of a storage tank and the cover, the method comprising:
- moving a ballast from a first predetermined position to a second predetermined position that is substantially above the first predetermined position;
- attaching a portion of a support member to the cover, wherein another portion of the support member includes an engagement member that is not attached to the cover;
- selectively engaging a support bracket attached to the cover with the engagement member while the ballast is in the second predetermined position;
- allowing the weight of the ballast to settle into the support member whereby the ballast is secured to the cover by the support member.
19. The method of claim 18, further comprising:
- disengaging the engagement member from the support bracket;
- moving the ballast to a base; and
- removing the cover from the storage tank.
20. A method of ballasting a cover of a sludge digester that is comprised of a storage tank and the cover, the method comprising:
- lowering a lifting member through an access port in the cover and into the storage tank;
- securing the lifting member to the ballast;
- using the lifting device to lift the lifting member and the ballast until the ballast is in a predetermined position relative to the cover; and
- selectively engaging a support bracket attached to the cover with a support member while the ballast is in the predetermined position relative to the cover, whereby the support member secures the ballast to the cover;
- wherein the access port is positioned substantially above the predetermined position.
Type: Application
Filed: Sep 24, 2008
Publication Date: Apr 23, 2009
Applicant:
Inventors: Lynn W. Cook (Eugene, OR), Steven R. Hough (Junction City, OR), Jeffrey L. Wight (Eugene, OR)
Application Number: 12/237,348