US3803996A

US3803996A - Acid pickle tank covers

Info

Publication number: US3803996A
Application number: US00179143A
Authority: US
Inventors: R Marshall
Original assignee: Ceilcote Co Inc
Current assignee: Sandoz AG; Ceilcote Co Inc
Priority date: 1969-10-13
Filing date: 1971-09-09
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16

Abstract

A cover assembly for tanks forming a pickling line or the like includes a plurality of separate molded plastic cover sections; each section includes a longitudinally extending top deck which is generally rectangular in shape. One or more longitudinally extending plenum chambers form an integral part of each cover section and are substantially coextensive therewith. Each plenum chamber includes intake openings facing inwardly into said tank for exhausting vapors released from the pickling line. A single longitudinal plenum chamber preferably is formed along the longitudinal centerline of the tank. When a plurality of longitudinal plenum chambers is employed, preferably one is positioned adjacent each longitudinal edge of the cover section and the remaining plenum chambers are positioned at spaced intervals therebetween. Each cover section preferably also includes a lateral exhaust duct along one lateral edge thereof.

Description

llnited States Patent 191 Marshall [111 3,803,996 ]*Apr. 16, 1974 ACID PICKLE TANK COVERS [75] Inventor: Robert M. Marshall, Pittsburgh, Pa.

[73] Assignee: The Ceilcote Company, Berea, Ohio Notice: The portion of the term of this patent subsequent to Mar. 14, 1989, has been disclaimed.

[22] Filed: Sept. 9, 1971 [211 Appl. No.: 179,143

Related US. Application Data [63] Continuation-impart of Ser. No. 865,944, Oct. 13,

1969, Pat. No. 3,648,593.

[52] US. Cl. 98/115 R, 134/64, 266/3 R,

2,325,158 7/1943 Wood 134/64 X 1,896,951 2/1933 Hahn 98/115 R 1,553,569 9/1925 Stickle 98/115 R 2,121,139 6/1938 Clauss et al 134/64 X 10/1940 True et a1. 134/64 4/1949 Sidell 923/36 [5 7] ABSTRACT A cover assembly for tanks forming a pickling line or the like includes a plurality of separate molded plastic cover sections; each section includes a longitudinally extending top deck which is generally rectangular in shape. One or more longitudinally extending plenum chambers form an integral part of each cover section and are substantially coextensive therewith. Each plenum chamber includes intake openings facing inwardly into said tank for exhausting vapors released from the pickling line, A single longitudinal plenum chamber preferably is formed along the longitudinal centerline of the tank. When a plurality of longitudinal plenum chambers is employed, preferably one is positioned adjacent each longitudinal edge of the cover section and the remaining plenum chambers are positioned at spaced intervals therebetween. Each cover section preferably also includes a lateral exhaust duct along one lateral edge thereof.

14 Claims, 10 Drawing Figures Pmm'rzmm 1 6 mm SHEET 2 (IF 4 INVENTOR. ROBERT M. MARSHALL ATTORNEYS.

PATENTEU R 15 SHEH 3 [if Q INVENTOR. ROBERT M. MARSHALL JW ATTORNEYS.

PATENTEDAPR 16 I974 sum MM INVENTOR. ROBERT M. MARSHALL ATTORNEYS.

ACID PICKLE TANK COVERS This application is a continuation-in-part application to application Ser. No. 865,944, filed Oct. 13, 1969, now Pat. No. 3,648,593.

The present invention pertains to a cover assembly, and more particularly to a cover assembly which has as an integral part thereof means for collecting and exhausting fumes, particularly toxic and/or corrosive fumes, released from a liquid contained in a tank.

The invention is particularly applicable to a continuous strip acid pickling line, and will be described with particular reference thereto, although it will be appreciated that the invention has broader applications, such as the collection of fumes in general, and toxic or corrosive fumes in particular, as may be released in other types of process lines, treatment or storage tanks and the like.

A continuous strip pickling line uses a plurality of acid tanks in end-to-end relationship with means to pass steel strip material in a longitudinal direction through the tanks for acid pickling.

The lines are long, for instance'360 feet in length, comprising perhaps four tanks each 90 feet in length. Heretofore, it has been conventional practice to cover the successive tanks with metal (steel) neoprene-lined covers. Usually the tanks are provided with a plurality of draft boxes which extend the full length of the tanks and are seated on top of the sides of the tanks, the'covers resting upon or being seated on top of the draft boxes. As with the covers, the draft boxes also are made of steel and are lined with a material such as neoprene. Openings are provided in the draft boxes facing inwardly, in the direction of the acid pickling baths, and the boxes are connected at suitable points to a plurality of exhaust ducts so as to exhaust acid fumes from beneath the covers, and from above the acid baths.

The acid which has been conventionally used for pickling is sulfuric acid. There is only a slight or no fuming of sulfuric acid, and the rubber lined metal covers and draft boxes, although subject to corrosion, served reasonably well with acceptable replacement costs and downtime. The toxicity of whatever sulfuric acid is released to the atmosphere from the acid baths is so slight that it is not unknown for an operator to remove and even dispense with the line covers during operation of the line; 1

In recent years, sulfuric acid has become more expensive, because of a shortage of sulfur, so that more and more, the steel industry has turned to hydrochloric acid for the pickling operation. One advantage-of hydrochloric acid is that with the use of substantially higher temperatures, the speed of the pickling line can be substantially increased. The temperatures employed are as high as 190F to 200F at the inlet end of the pickling line, dropping to about 160F adjacent to the outlet end.

These highertemperatures result in substantial fuming of the hydrochloric acid, considerably more than that experienced with sulfuric acid. In addition, hydrochloric acid is substantially more corrosive than sulfuric acid. For both reasons, the greater quantity of acid fumes and higher degree of corrosiveness, it was quickly found that the conventionally employed neoprene lined steel covers and draft boxes were unacceptable. the neoprene debonding fromthe metal and the metal corroding in an unacceptably short time.

It has been proposed to overcome this problem by coating the steel covers and draft boxes with natural rubber instead of neoprene. Not only is this a more expensive operation, but natural rubber also deteriorates when subjected to the hydrochloric acid fumes.

If a cover is corroded, it simply is lifted from the line and replaced with another cover; but to replace or rel-ine a draft box, the line must be shut down. Because of the complexity of replacing or relining a draft box, particularly in a large, i.e., long, unit, a line often must be shut down for a substantial period of time to do so.

It has also been proposed to use various plastics instead of lined metalfor construction of the pickling line covers, and polypropylene and fiberglass resins in particular have received significant acceptance in the industry. Both plastics have a long life in the presence of hydrochloric acid fumes.

. However, polypropylene cannot be used for construction of the draft boxes..The reason for this is the acid tanks conventionally are constructed of steel lined internally with several courses of acid brick, and acid brick has an expansion and contraction per foot with changesintemperature close .to that of steel, but substantially less'than the expansion and contraction per foot of polypropylene with changes in temperature.

Of necessity the draft boxes must be securely fastened or anchored to the sides of the pickling line acid tanks, to seal the space between the draft boxes and top surfaces of the acid tank sides. In the absence of such sealing, an excessively large draft of air flow is required overall area through which leaks can occur; and thus the draft or air flow required. This is particularly important in connection with hydrochloric acid because of the fuming and toxicity of this acid.

The problem is more acute with differential contraction than expansion. When the draft boxes have been constructed of plastic materials and anchored to the acid tank sides, there seems to be enough relative give in the component parts to accommodate the difference in expansion. However, polypropylene has a relatively low tensile strength, and when used for draft box construction, the boxes have quickly been pulled apart during cooling of the acid baths and following use, be-

cause of the greater contraction of the draft boxes relative to the tank sides to which they are attached. The problem is aggravated by the higher temperatures employed with the use of hydrochloric acid, as well as by the substantial lengths of the pickling lines. Fiberglass reinforced resins have beensuccessfully employed in approximately forty foot sections for the construction of draft boxes. in this type of installation the draft boxes are not anchored to the tank sides.

Accordingly, it is an object of the present invention to overcome the above problems, and in particular to provide a novel cover including a fume collection system which is resistant to high temperature corrosive hydrochloric acid fumes.

It is further an object of the invention to provide a cover assembly and fume collection system particularly adapted for a pickling line in which the overall area of leakage is minimized, thereby reducing the size of the acid fume exhaust and disposal system required.

It is also an object of the invention to provide an acid resistant fume collection system which is not subject to destruction from differential expansion and contraction with the acid tanks.

In accordance with the invention, there is provided a cover assembly for one or more tanks containing a fume releasing liquid, such as the tanks of an acid pickling line, which includes a plurality of separate molded plastic cover sections; each section comprising a top deck which is generally rectangular or square in shape; one or more longitudinally extending plenum chambers substantially coextensive with said cover, said one or more plenum chambers being an integral part of each section and containing inwardly facing intake openings longitudinally along the length thereof to exhaust vapors released from said tank.

Preferably, each of the cover sections comprises at the ends thereof a tongue-and-groove type of construction for mating one section with another, the plenum chambers of successive sections being aligned and open at the ends thereof so that the chambers are substantially continuous along the length of the line of pickling or other tanks.

Also, in accordance with a preferred aspect of the invention, each cover section includes adjacent at least one end thereof laterally extending duct means in communication with the plenum chambers, said duct means being an integral part of the said cover section and including means defining laterally disposed intake openings to exhaust vapors released from the pickling line in the area of connection or joining of successive cover sections.

The edges of the top deck of the cover sections which extend along the length of the line of tanks contemplated in certain aspects of the invention, i.e., which extend longitudinally, will be referred to as the side edges in this specification and in the claims. The edges of the cover sections which extend transversely or laterally of the line of tanks will similarly be referred to as the end(s) edges. These edges may have a substantially vertical wall" portion extending downwardly from the top deck. These portions shall be referred to as, respectively, cover side walls and cover end walls. The foregoing nomenclature is employed for the sake of clarity and should not be construed as excluding substantially square (as opposed to rectangular) cover sections, such square cover sections being contemplated by the invention.

By tanks" as used in this specification and claims, is meant one or more tanks arranged in sequence, or a single tank subdivided into sections.

Further, in accordance with the invention the plenum chambers are in communication with a plurality of collector ducts positioned at spaced intervals along both sides of the pickling line, the acid fumes in the plenum chambers being transmitted via the collector ducts to suitable disposal means.

Preferably the cover assembly comprises a'plurality of short collector duct sections similar to the cover sections in shape and configuration, but of substantially shorter length. The collector duct sections are interspersed at spaced intervals between the cover sections,

and each supports, as an integral part thereof, opposed laterally extending collector ducts which are in communication with the plenum chambers of the cover sections.

As a further preferred aspect, the intake openings in the plenum chambers are progressively increased in size the further they are spaced from the collector ducts to obtain a uniform removal of fumes lengthwise of the cover assembly. In areas where the cover assembly is penetrated by accessories for the pickle line, the intake openings are also enlarged.

It will become apparent that by replacing the conventional draft boxes with plenum chambers which are an integral part of the cover sections, and constructing the plenum chambers of the same acid resistant plastic materials used in the cover sections the problem of downtime for replacement and relining of draft boxes is eliminated. It also will become apparent that by using plenum chambers which are an integral part of the cover sections, the overall area for leakage is minimized permitting optimum minimum sizing of the plenum chambers, as well as the acid disposal system with which the plenum chambers are connected. Further eliminated is the problem of destruction of plastic draft boxes because of differential expansion and contraction of component parts. The plenum chambers being an integral part of the cover sections simply expand with the latter, the cover sections seating on the top edges of the upstanding, i.e., substantially vertical, walls of the acid tanks is sliding engagement therewith. By sliding engagement as that term is used in the specification and claims, is meant that the cover sections are not fastened to or interlocked with the tank walls, but merely rest upon them so that the cover and the tank walls are free to expand and contract at respectively different rates, without imposing such expansion and contraction forces (except possibly to an inconsequential extent by frictional resistance) one upon the other.

As an additional advantage, the fume collection system in accordance with the invention is part of a plurality of relatively small (as compared to the overall length of the line of tanks) self-contained sections which, if one is damaged, can be removed and replaced with ease and without significant downtime.

As a further advantage, the plenum chambers, being an integral part of the cover sections, constitute a means for cover reinforcement, as well as a means for fume removal.

The invention, and other advantages thereof, will become apparent upon consideration of the following specification, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic section elevation view of a continuous strip pickling line in accordance with the present invention;

FIG. 2 is an enlarged section view taken through line 2-2 of FIG. 1;

FIG. 3 is an enlarged partial section view of one embodiment of a pickle tank cover assembly in accordance with the present invention;

FIG. 4 is a section view taken through line 44 of FIG. 3;

FIG. 5 is an enlarged detail section view showing details of the connection means between successive cover sections of a cover assembly in accordance with the invention;

FIG. 6 is a section view through line 6--6 of FIG. 3;

FIG. 7 is a top plan view of the cover assembly of FIG. 3 in accordance with the invention;

FIG. 8 is a perspective end view of one cover section of a pickle tank cover assembly in accordance with the invention;

FIG. 9 illustrates an embodiment in accordance with the invention; and

FIG. 10 illustrates in cross section view, a detail of a centrally-positioned plenum chamber.

Referring now to the drawings wherein the showings are for the purpose of illustrating the preferred embodiment of the invention only and not for the purposes of limiting the same, the FIGURES show a continuous strip pickling line A which is covered with a pick tank cover assembly B. Part of the pickling line is a fume exhaust system C including collector ducts D to exhaust fumes from the space beneath the cover assembly B and above the baths E of pickling acid.

Referring to the FIGURES in detail, particularly FIGS. 1 and 2, the continuous strip pickling line comprises a plurality of acid pickle tanks 10, in this instance two, each tank being constructed of steel lined with acid brick, for example, three courses of brick. The tanks are provided with a floor 12, side walls 14 (FIG. 2) and end walls 16, the walls being substantially vertical. In each of the tanks is a bath of acid 18 at temperatures ranging from about 190F to about 200F at the inlet end 20 dropping to about l60F at the outlet end 22. Although there are only two tanks shown in the drawing of FIG. 1, obviously a greater number of tanks can be used, for instance four tanks, each having. a length of about 90 feet. It is to be appreciated that the subject invention is suitable for use with any fume emitting liquid, including a variety of pickling acids such as hydrochloric, sulfuric, nitric and hydrofluoric acids.

A strip of material to be pickled is fed from inlet rollers 24 over the leading lip 26 of the first tank, dipping through the first bath 28, over a pair of intermediate rollers 30 at the junction of the first and second tanks, dipping into the second bath 32, and then passing over lip 34 at the outlet end of the second tank for passage through a rinse area 36.

The cover assembly B for the acid tanks extends longitudinally over the two baths 28 and 32, the assembly comprising a plurality of successive cover sections 38 which are joined together at points 40 in a manner to be described.

' Also illustrated in FIG. 1 are conduits 42 for acid feed, or steam injection, and strip liftermeans 44, a plurality of each of these items being disposed at intervals along the length of the pickling line as required. Openings in the cover assembly are provided to accommodate the items. The fume exhaust system C for the pickling line, in addition to the collector ducts D which lead from the space between the surface of the acid bath and cover assembly, includes a plurality of downcomers 46 at spaced intervals on each side of the pickling line connected to each collector duct, and an exhaust manifold 48 leading to a fume disposal means schematically shown as item 50. It is to be appreciated that the collector ducts D could be connected above the cover assembly B, in which case downcomers 46 would be required only on one side of the pickling line even for connection of multiple plenum chambers to the exhaust manifold 48.

In FIG. 2, the concepts of the invention are illustrated in slightly more detail. Each cover section 38 of the cover assembly B is provided with a generally rectangular upwardly bowed roof or top deck 52 and downwardly and longitudinally extending cover side walls 54 which are integral and coextensive with the top deck. These cover side walls may obviously be of any convenient height, or may be eliminated, i.e., reduced to the thickness of the top deck, in which case the cover side wall would simply comprise the side edges of the top deck of the cover section. In any case, the lower portion of the cover side walls 54 terminate in a flange 58 which seats on the upwardly facing shoulders 56 of the side walls 14 of the acid pickle tanks 10. Integral with the top deck and forming an integral part of each cover section, is a single longitudinally extending plenum chamber 60 which is centered longitudinally in cover section 38, is coextensive therewith and integral with the top deck 52. Obviously, plenum chamber 60 may be located above or below the deck, may be off set from the longitudinal center line of cover 38, or there may be a plurality of such plenum chambers.

More details of the cover assembly can be seen with reference to FIGS. 3, 4, 5, and 6. Each of the successive sections 38 has an inverted box or shell-like configuration; the top deck 52 being bowed upwardly relativeto the downwardly extending side walls for the runoff of moisture which collects on the roof. The horizontally facing flanges 58 for the cover side walls 54 of the cover assembly are provided with longitudinally extending strips 62 of sealing means along the lower surfaces thereof, of any composition which is slightly resilient, to seal the space between the cover assembly flanges 58 and the shoulders 56 of the tank walls. The sealing strips 62 also are are of a material which is resistant to acid fumes. At spaced intervals along the top deck, the cover sections are provided with lifting lugs 64 for crane removal and replacement of the sections. It is to be appreciated however, that the cover sections can also be removed by means of air or hydraulic cylinders. To complete the inverted shell or box-like configuration each cover section has opposed downwardly extending cover end walls or ribs 66 which extend between the cover side walls 54.

FIG. 5 illustrates the manner in which the successive sections are joined or brought together into sealing engage'ment. The sections can be described generally as having a tongue-and-groove type construction, one section having exterior roof wall and

side wall flanges

68, 70 which extend beyond cover end wall 66 of the section, and which slide over and engage the exterior roof and cover side wall surfaces 72, 74 of the adjacent section. The

exterior flanges

68, 70 of the one section are dimensioned so as to accommodate a sealing material 76 against which the exterior surfaces 72, 74 of the other section are positioned. Preferably each cover section 38 would have

plain surfaces

72, 74 at one end and the flange surfaces 68, 70 at the other end. When the successive sections are brought together, the end walls 66 thereof are contiguous or in abutting relationship. Our purpose of cover end walls 66 is that they constitute strengthening ribs for the ends of the cover sections. A longitudinally extending rib 77 (FIG. 4) also is provided integral with the roof portion on the underside thereof and positioned between the opposed side wall portions 54.

FIGS. 4 and 6 show a plenum chamber 60 positioned adjacent the side edge of the cover section; other additional plenum chambers (not shown) may of course be employed.

The plenum chambers 60 are half-round in configuration and extend substantially the full length of the cover sections. The abutting cover end walls 66 of the cover sections are provided with cutouts or openings 80, clearly shown in FIG. 8 (which shows three plenum chambers, one centered and one adjacent each edge). Each opening 80 is aligned with each plenum chamber, so that when one section 38 is abutted against another section, the respective plenum chambers of the two sections are in alignment and in flow communication with each other. In this way, the plenum chambers together define continuous passages along both sides of the pickle line which extend substantially the entire length of the pickle line. Although the plenum chambers 60 are shown in the form of half-round cross sections, square or rectangular cross sections would work equally as well.

Each of the plenum chambers 60 is provided with an intake slot or opening 81 which runs substantially its entire length, the slots or openings 81 being downwardly directed and oriented slightly towards the cover side walls 54 of the cover sections, to pick up fumes which might otherwise escape between the flange 58 of the cover side walls 54 and shoulders 56 of the acid tank walls. The slots or openings 81 can be, for example, from one-sixteenth inch in width or larger, depending upon the width of the tanks and the amount of acid fumes to be removed.

Instead of continuous slots or openings, the plenum chambers can be provided with a plurality of holes, an important feature being that they are downwardly oriented and located at or near the lowermost portion of the plenum chamber to allow acid which may condense in the plenum chambers to drain back into the pickle tanks, thereby eliminating a hazard to personnel or operators of the pickling line.

In order to exhaust or remove acid fumes which might otherwise escape between the cover end walls of adjacent cover sections there are provided smaller transverse flue ducts 82 which are integral with and formed along the inside surfaces of at least one of the end walls of each section. These smaller flue ducts are provided with, for example, three-eighths or one-half inch intake openings 84 at spaced intervals in a transverse direction, the openings being oriented to exhaust fumes in the area of connection between the cover sections, and, like the openings in the plenum chambers, positioned to drain condensate back into the tank. Obviously, the transverse ducts could be slotted similarly to the plenum chambers or provided with larger or smaller openings, in accordance with design criteria.

Collector ducts D are located at spaced intervals along the cover assembly, and plenum chambers 60 are in flow communication therewith. In the specific embodiments shown in FIGS. 3-6, collector ducts D are integral with and part of short collector duct sections 86. Sections 86 may be, for example, about four feet in length, each such section being provided with tonguean'd-groove ends similar to the ends of cover sections 38, for interconnecting insertion of short collector duct sections between the cover sections 38. As an alternative, the collector ducts can be made an integral part of the cover sections 38.

Collector ducts D, as shown in FIGS. 3, 4 and 6, are L-shaped members disposed adjacent the sides of each collector duct section, each having a substantially vertically positioned leg 88 which is affixed to the top deck 52 of the section, adjacent to the edges thereof, and having substantially horizontal legs 90 and downwardly extending substantially vertical legs 92, the latter beng connected to the downcomers 46 of the fume collection system. Each collector duct section along the sides thereof is provided with short passageways or plenum chamber portions 94, similar to those of the longer cover sections, except that the top deck is cutout in areas for substantially the entire length of the section (notice FIG. 7) and the legs 88 are pyramidshaped (FIGS. 6 and 7) forming a sloped umbrella over the cutout areas. In this manner, collector ducts D have a substantial area in flow communication with the plenum chambers portions 94. Cover end walls 66 of the collector duct sections are also cutout, at areas in alignment with the plenum chambers thereof, as with the longer cover sections, so that the collector ducts on each side are in flow communication with all of the cover plenum chambers on that side of the cover assembly. Any suitable number of plenum chambers may be employed, at the edges or at an intermediate location in the cover section.

Reinforcement means in the form of a pair of angles 96 are provided bracing the collector ducts to the top decks of the collector duct sections.

On assembly, the collector duct sections, of which the collector ducts are an integral part, are positioned along the line of pickling tanks so that the downwardly extending legs of the collector ducts mate with the downcomers of the pickle line fume collection system. Preferably, the short or small sections of the cover assembly are secured to the acid tanks or fume collection system, and would seldom be moved.

In FIG. 3, there are shown cutout areas 98 for acid, water and steam jet conduits or pipes 42, FIG. 4, at spaced intervals in the cover side walls 54 of cover sections 38. The cutout areas are U-shaped openings, sufficiently large to accommodate the acid, water and steam jet conduits, but are dimensioned as small as possible to minimize the clearance in the cutout areas for the escape of acid fumes. The cutout areas are spaced slightly below the plenum chambers, and the intake openings or slots 81 in the plenum chambers in the proximity of the cutout areas are slightly enlarged to draw air inwardly through the clearance between the side walls of the cover sections and the conduits penetrating the side walls, to avoid dispersion of acid fumes outside of the acid tanks.

FIG. 3 also shows a larger cutout area 100 for the strip lifters 44. In this instance, the cutout area extends upwardly to the elevation of the plenum chambers, and inwardly into the top deck or roof portion of the cover sections. This is also shown in FIG. 7, the penetration into the top deck or roof portion being substantial. To accommodate this penetration, the plenum chambers are looped or bypassed inwardly, as shown in FIG. 7, at points 102, so that the plenum chambers define substantially continuous flue ducts along the entire length of the pickle tank line. Plenum chambers which are not adjacent the side edges of the cover sections are of course not interrupted by the cutout.

As with the cutouts for the acid, water and steam jets, the clearance at areas 100 is minimized and made only as large as necessary to accommodate the items (the strip lifters in this case) which are to pass therethrough. In addition, the intake openings or slots 81 in the plenum chambers are enlarged in the area of the strip lifter cutouts to increase the flow therethrough so as to help prevent leakage of fumes in the clearance spaces around the strip lifters.

An alternative in accordance with the present invention is illustrated in FIG. 9, wherein the plenum chambers 104 are integral with but on the upper surfaces of the top decks thereof. Openings from the plenum chamber in this embodiment are longitudinally extending slots 106 provided in'the top deck between the plenum chambers and areas above the acid baths. Openings 106 are enlarged at cutout areas in a manner similar to that described with reference to openings 81.

Not shown in FIG. 9 is an arrangement by which moisture collecting on the top deck is allowed to 'drain from the deck. Suitable enclosed channels can be provided penetrating the plenum chambers at spaced intervals.

Most large pickling lines will utilize about 16 collector ducts, so that each duct handles about 40 feet'of plenum chamber, although it is obvious that this can vary depending upon design considerations.

FIG. shows in detail in cross section a plenum chamber 60 positioned along the longitudinal center line of the cover section. Longitudinally extending ribs 77 may, in such case, be offset from the centerline. Transverse ducts 82 pass through suitable cutouts in ribs 77. In all other respects, the structure is the same as that described in the other embodiments, and corresponding parts are identically numbered.

While the embodiments described in detail above show, respectively, one and three plenum chambers per cover section, obviously fewer or more longitudinal plenum chambers may be employed. When a single longitudinal plenum chamber is used, the plenum chamber will normally, although notnecessarily, be positioned along the longitudinal center line of the cover section. More than two longitudinal plenum chambers may be employed in which case, normally though not necessarily, one plenum chamber will be positioned adjacent each side edge with the remaining chambers disposed therebetween. The choice of the number and location of longitudinal plenum chambers is obviously a design choicedepending upon the the amount of fume generation, tank size, number of tanks, design of the fume removal system, and other design criteria.

In practice, the cover sections and fume collection system will be fabricated from a thermoplastic or thermoset material, possibly reinforced with fiberglass. A suitable plastic is polypropylene, which is resistant to corrosion by hydrochloric acid fumes.

In manufacture, the plenum chambers, collector ducts, and transverse end wall flue ducts can be fabricated or molded separately from the cover sections, and then simply welded to-the cover sections by the use of known filler rod welding processes. Obviously, any other suitable manufacturing process may be used.

An advantage of the invention is that the cover sections are suitable for newly constructed lines of tanks or for replacement of'existing covers and flue systems for existing lines of tanks. In the latter instance, the existing structures are simply removed, and the cover sections are positioned in place with the flanges 58 resting upon the upper shoulders of the tank sides. It is a simple matter to dimension the cover sections to locate the collector ducts at downcomer locations of theexisting fume removal system. This is made simpler by employing small sections for the collector ducts between larger cover sections for the rest of the tank line. Most important, no provision need be made for differences in expansion between the cover assembly, fume collection system, and acid tanks.

Whether the cover assembly is for an existing line or new line, it is apparent that the problem of downtime for replacement or relining of draft boxes is avoided.

Because the plenum chambers, collector ducts and other components are an integral part of the cover sections, the weight of the sectionsis sufficient to provide excellent sealing' between the cover sections and the tank sides notwithstanding the lack of a connection or interlocking between the cover and the tank walls.

This and the elimination of other potential leakage points by the provision of an integral assembly, increase the efficiency of acid fume removal, resulting in a reduction in the size or capacity of the acid fume handling system which is required.

In this respect, by enlarging the plenum chamber intake slots or openings 81, 106 in the proximity of penetrations made in the cover assembly for accessories and pulling an increased vacuum at these penetrations, the efficiency of acid fume removal is increased, thereby reducing air flow requirements for the exhaust system.

Particularly in new installations, the exhaust system can be reduced in size, reducing the capacity costs involved in a pickling or other line installation.

As a further advantage, in accordance with the invention, since the cover assembly is in the form of selfcontained small sections, it is a simple matter to remove a section which is damaged and replace it with a substitute section, avoiding substantial maintenance costs and downtime.

As an additional advantage, the plenum chambers being an integral part of the cover sections, act as reinforcement means for the cover sections.

Although the invention has been described with reference to specific embodiments, variations within the scope of the following claims will be apparent to those skilled in the art upon reading and understanding the foregoing.

What is claimed is:

1. A tank cover assembly including tanks containing a liquid which emits noxious fumes; said tank being subject to thermal expansion and contraction and having opposed, longitudinally extending upstanding tanks side walls, comprising a plurality of separate plastic cover sections;

each section comprising a roof portion with opposed longitudinally extending side edges seated in slidable engagement upon the upper portion of said tank side walls whereby said tank side walls and said side edges are free to longitudinally and laterally thermally expand and contract at respectively difierent rates;

each section further comprising first and second opposed end walls extending between said side edges;

one plenum chamber extending longitudinally along said section, and being an integral part thereof; and

1 1 inwardly facing intake openings in said plenum chamber disposed longitudinally along the length thereof in flow communication with fumes emitted from said liquid.

2. The cover assembly of claim 1 wherein said plenum chamber is positioned substantially along the longitudinal centerline of said section.

3. The cover assembly of claim 1 wherein said tank is an acid pickle tank for a continuous pickling line, and said cover sections are removable to permit removal of a metal strip being pickled.

4. The cover assembly of claim 1 wherein said cover sections are fabricated of polypropylene reinforced resin.

5.. The cover assembly of claim 1 wherein said plenum chambers are in flow communication with collector ducts and said intake openings in the plenum chambers are smaller in the vicinity of said collector ducts than elsewhere in order to obtain a substantially uniform air flow along the length of said tanks.

6. The tank cover assembly of claim 1 further includmg laterally extending exhaust ducts adjacent at least one end wall of each cover section and integral therewith to exhaust fumes from said liquid in the vicinity of the joint between successive sections.

7. The cover assembly of claim 1 wherein said cover sections are fabricated of a polyester reinforced resin.

8. A cover assembly for a process tank containing a liquid which emits fumes, said tank having upstanding tank side walls comprising;

a cover including a roof portion and opposed side walls extending downwardly from the roof portion, said side walls being seated in slidable engagement upon the upper portion of said tank side walls whereby said side walls and said tank side walls are free to thermally expand and contract at respectively different rates;

one plenum chamber extending longitudinally along said cover, said plenum chamber being an integral part thereof; and

inwardly facing intake openings in said plenum chamber disposed longitudinally along the length thereof for exhausting vapors from said process tank.

9. A tank cover assembly for tanks containing a liquid which emits noxious fumes, said tank being subject to thermal expansion and contraction and having opposed, longitudinally extending upstanding tank side walls, comprising:

a plurality of separate plastic cover sections;

each section comprising a roof portion with opposed longitudinally extending side edges seated in slidable engagement upon the upper portion of said tank side walls whereby said tank side walls and said side edges are free to longitudinally and laterally thermally expand and contract at respectively different rates;

three or more plenum chambers extending parallel to and adjacent said side edge portions, the plenum chambers being an integral part of said sections; and

inwardly facing intake openings in said plenum chambers disposed longitudinally along the length thereof in flow communication with fumes emitted from said liquid.

10. The cover assembly of claim 9 wherein said tank is an acid pickle tank for a continuous pickling line, and said cover sections are removable to permit removal of a metal strip being pickled.

11. The cover assembly of claim 9 wherein said cover sections are fabricated of polypropylene reinforced resin.

12. The cover assembly of claim 9 wherein said plenum chambers are in flow communication with collector ducts and said intake openings in the plenum chambers are smaller in the vicinity of said collector ducts than elsewhere in order to obtain a substantially uniform air flow along the length of said tanks.

13. The tank cover assembly of claim 9 further including laterally extending exhaust ducts adjacent at least one end wall of each cover section and integral therewith to exhaust fumes from said liquid in the vicinity of the joint between successive sections.

14. The cover assembly of claim 9 wherein said cover sections are fabricated of polyester reinforced resin.

Claims

1. A tank cover assembly including tanks containing a liquid which emits noxious fumes; said tank being subject to thermal expansion and contraction and having opposed, longitudinally extending upstanding tanks side walls, comprising a plurality of separate plastic cover sections; each section comprising a roof portion with opposed longitudinally extending side edges seated in slidable engagement upon the upper portion of said tank side walls whereby said tank side walls and said side edges are free to longitudinally and laterally thermally expand and contract at respectively different rates; each section further comprising first and second opposed end walls extending between said side edges; one plenum chamber extending longitudinally along said section, and being an integral part thereof; and inwardly facing intake openings in said plenum chamber disposed longitudinally along the length thereof in flow communicatIon with fumes emitted from said liquid.

5. The cover assembly of claim 1 wherein said plenum chambers are in flow communication with collector ducts and said intake openings in the plenum chambers are smaller in the vicinity of said collector ducts than elsewhere in order to obtain a substantially uniform air flow along the length of said tanks.

6. The tank cover assembly of claim 1 further including laterally extending exhaust ducts adjacent at least one end wall of each cover section and integral therewith to exhaust fumes from said liquid in the vicinity of the joint between successive sections.

8. A cover assembly for a process tank containing a liquid which emits fumes, said tank having upstanding tank side walls comprising; a cover including a roof portion and opposed side walls extending downwardly from the roof portion, said side walls being seated in slidable engagement upon the upper portion of said tank side walls whereby said side walls and said tank side walls are free to thermally expand and contract at respectively different rates; one plenum chamber extending longitudinally along said cover, said plenum chamber being an integral part thereof; and inwardly facing intake openings in said plenum chamber disposed longitudinally along the length thereof for exhausting vapors from said process tank.

9. A tank cover assembly for tanks containing a liquid which emits noxious fumes, said tank being subject to thermal expansion and contraction and having opposed, longitudinally extending upstanding tank side walls, comprising: a plurality of separate plastic cover sections; each section comprising a roof portion with opposed longitudinally extending side edges seated in slidable engagement upon the upper portion of said tank side walls whereby said tank side walls and said side edges are free to longitudinally and laterally thermally expand and contract at respectively different rates; each section further comprising first and second opposed end walls extending between said side edges; three or more plenum chambers extending parallel to and adjacent said side edge portions, the plenum chambers being an integral part of said sections; and inwardly facing intake openings in said plenum chambers disposed longitudinally along the length thereof in flow communication with fumes emitted from said liquid.