LININGSFOR CHEMICAL
CERAMIC
EQUIPMENT PERCY C. KINGSBURY General Ceramics Company, New York, N. Y.
c
I
ORROSION of chemical plant equipment is one of the culty to the potter accustomed to the manufacture of the complicated shapes demanded by the chemical industry. major moblems incident to large-scale txoduction. It The success of this method of construction, therefore, is not encointered in production on a smkl or moderate depends entirely on the jointing material and its application. scale where glass and stoneware equipment are used, since Of the many materials available, a selection must be made these materials duplicate, for practical purposes, the ware used with particular reference to the nature, concentration, temin the laboratory and thus no extrinsic difficulties are introduced in translating a process from the laboratory to the perature, pressure, and physical condition of the products to be handled. Attempts to produce a universal acid-proof plant. Consequently, the chemical manufacturer of a few decades ago, with his comparatively small production units, cement resemble the quest for the philosopher’s stone and have somewhat less prospect of success. For most chemical was seldom troubled with the corrosion problems that beset purposes, however, there is a t least one cement that will give the large-scale producers of today. adequate service although none of them has the resistance of Although remarkable advances have been made in recent the acid-proof brick or tile used for the lining. years in the manufacture of stoneware equipment, there is a definite limit to the size in which it can be made, and increased production requires a multiplicity of units of moderate caSilicate Cements pacity which ultimately becomes impracticable. This situaAn extensive bibliography is available covering acid-proof tion has led to the introduction of so-called corrosion-resisting cements for special purposes ( I ) , but reference here will be materials which, while not possessing the universal resistance of ceramic products to corrosion, are satisfactory for service made only to those in common use for bonding acid-proof masonry. The base of most proprietary acid-proof cements is under certain specific conditions. There is abundant evidence sodium silicate mixed with an aggregate of some inert material, in the voluminous literature and frequent symposia on the such as ground silica, stoneware. or asbestos. Other materials subject of corrosion that the problem of large-scale equipment are s o m e t i m e s added for resistant to attack by active w h i c h s p e c i a l merits are chemical products is still far claimed, but usually they from solution. contribute nothing of value A protective lining of ceto t h e p r o p e r t i e s of the ramic tile or brick cemented cement. When properly proto a base of metal, concrete, portioned and set, a sodium or masonry has been found silicate cement will withstand satisfactory in many industhe action of all chemicals extries, notably for sulfite pulp cept hydrofluoric acid and digesters, sulfuric acid towers, caustic alkalies, and is not afand metal pickling tanks; fected by high temperatures. this type of construction for It is hard and strong but someother purposes in the chemical what porous. These properindustry offers a t t r a c t i v e ties are relative since they depossibilities. The manufacpend on the nature and parture of such linings, made of ticle size of the aggregate and the same high-grade ceramic the form of the silicate. A material as is used for chemim i x t u r e of approximately cal stoneware equipment and Courtesy, Qeneral Ceramics Company equal parts of coarse and fine with the same resistance to TILES,(Above) WITH DOVETAILED BACK FIGURE 1. CERAMIC aggregate (20 and 100 mesh) corrosion, presents no diffiAND (Below) WITH CLINCHER BACK 402
I
seems to give the most satisfactory result. A variable and heterogeneous "run of mill" mixture of ground silica or stoneware usually makes a poor cement. I n some proprietary cements the silicate is added in the proper proportion to the aggregate in the form of a powder to which it is merely necessary to add the requisite amount of water. About 37 pounds of this cement are required per cubic foot of joint or backfill. I n other cases only the aggregate is sold, the purchaser being instructed to mix it with a specified grade of silicate of soda in specified proportions. This type of cement requires about 45 pounds of aggregate and 27 pounds of silicate of soda 41" BB. per cubic foot. In either type of cement a preliminary set takes place in an hour or less due to the drying of the silicate. This makes a perfect joint due to the adhesive properties of the silicate but it is unfortunately water soluble. The final set occurs when the joint is brought into contact with an acid which neutralizes
takes place as fast as I the mason can handle I the work, and the I joint as well as the backfill is set all the way through. For a lining of this type the shell should be liquid-tight and the inside surface protected from corrosion by coating with a bituminous, rubber, or other suitable compound. The ideal construction, where the working conditions permit, is to line the shell with sheet rubber against which the brick or tile lining is built. This construction has found particular favor in the large tanks used for pickling steel sheets. The brick lining helps to insulate the rubber from the high temperature of the bath and also protects it from mechanical damage. If these were the only functions of the ceramic lining almost any kind of brick would serve the purpose, and on this assumption the short-sighted policy of using a cheap common brick is occasionally adopted. It costs as much and sometimes more to lay inferior brick as acid-proof brick of good quality and the small initial saving in comparison with the cost of the finished job is far outweighed by the short life of the cheaper product and the consequent heavy expense for shut-down and replacement.
Resinous Cement
surface of the -joint, which is relatively small compared with its v o l u m e , it often takes weeks or months for a complete final set to take place. This has led to the investigation of additions to the cement that will induce setting without the application of acid, and several such cements are now available. The use of sodium silicofluoride for this purpose has recently been patented (2). Although joints made with cements of this type appear to be somewhat more porous than those set by drying and subsequent treatment with acid, these new c e m e n t s h a v e simplified to a great extent the technic of laying brick and tile linings in chemical equipment. It is no longer necessary to build a few courses and then allow time for the cement to dry before proceeding. The setting
A specialized use of ceramic lining is in the protection of Haveg equipment from abrasion, particularly where a liquid to be agitated contains sharp particles in suspension. Since Haveg is a molded phenol-formaldehyde condensation product on an asbestos base, it is possible to mold the tile lining into the Haveg equipment a t the time of manufacture. This is the preferred method, but the tile may also be cemented in place with the special cement Havegit. This cement consists of a liquid resin made into a paste with an inert filler and hardened by admixture with about 10 per cent of alcoholic sulfuric acid (about 30 per cent HzS04). It begins to harden in 30 to 40 minutes and sets in 2 to 3 hours. It can be used in about 6 to 10 hours although it is better to allow 2 or 3 days; the maximum strength is reached in 4 to 6 weeks a t room temperature. The setting can be accelerated by the application of heat. Havegit can be used a t temperatures up to 130"C. (266' F.) and has the remarkable chemical resistance common to phenolic resins but should not be used with oxidizing acids, strong sulfuric acid, organic bases such as pyridine and aniline, caustic alkalies, sodium hypochlorite, and acetone.
Courtesy, Atla8 Mineral Product8 Company
STEELNEUTRALIZING TANK FIQURE 3. BRICK-LINED 403
INDUSTRIAL AND ESCISEERIXG CHEMISTRY
404
-
GCRE
4. C E R ~ M M I C
VOL. 29, NO. 4
impairs the fluidity of the c e m e n t , a n d t h e aggregate may separate out mhile the cement is in the molten statc.
claimed for this cement over other sulfur cements are a greater bondmgstrength tometal and ceramic
F I Q U R E5. CERAMIC-LINED PLUUCOCK Courtesy. Generd enarnica company
A special grade IS available that is resistant to hydrofluor~c acid. If it is used on a base material such as cement or iron that is subject to attack by the sulfuric acid used in the catalyst, it is necessary first to protect the surface by meaiis of a coating of compounded ruhber and graphite or a qpecially prepared resinous lacquer
Litharge and Glycerol Cements The well-known litharge and glycerol cement used by the plumber and pipe fitter finds many useful applicat~onsfor miscellaneous jobs in a chemical plant. It withstands the action of most corrosive solutions and dilute acids and of temperatures up to about 200' C. (392' F.). About 23 pounds of litharge and 5.25 pounds of 90 per cent glyceml make 1 cubic foot of cement which sets in an hour or so and increases in hardness for several days thereafter. Its most important Use is for laying the brick lining of sulfite pulp digesters.
Sulfur Cements Sulfur is inert to many of the corrosive material~used in industry and finds a wide application in the chemical and allied fields aa a bond fur acid-proof masonry. Although the adhesive strength of sulfur alone compares favorably with other bonding materials, it is substantialIy increased by the admixture of a properly proportioned and graded aggegate. This, however,
CERUIC-LINED CENTRIFUGAL ROURE 7 (Above) Cowfew.
Genaol
Ceramm
C0mpR"Y
FIGURE 8 (Left). CERMICLINEDEXHAUST FAN cour1eay.
opnerol
C"mpS",,
Cwomlc.
and containing flanged outlets, plug s e a t s , s h e l v e s for filter dates. co&xs. and dther d e ~ a i ~ s ~ makes this type of construction v e r y flexible.
surfaces, greater elasticity, greater resistance to mechanical and thermal shock, and a lower coefficient of expansion. Other materials used with sulfur for bonding brick or tile are rosin, asphalt, and pitch with fillers of sand, clay, infusorial earth, ground glass, silica, or stoneware. I n using sulfur-base cements, the brick or tile is set up with quarter-inch joints, the horizontal joints being formed either by small integral projections or by chips used as spacers. The joints are first sealed to retain the molten cement by means of paper held in position by wooden forms or sand, or by pasting the paper temporarily to the brickwork by sodium silicate. The cement is heated in an iron kettle and poured by means of a bucket at a temperature of 130' to 150' C. (266' to 302" F.). The equipment is ready for service as soon as the joints have solidified. Structures so bonded can be used at temperatures up to 90' C. (194' F.). The joint is practically nonabsorbent and will withstand the action of most mineral and organic acids and their salts. It will not withstand caustic alkalies or oxidizing agents such as strong nitric and chromic acids. Many other acid-proof cements are used in the chemical industry, but most of those for setting brick and tile are of the types just described. . Their composition and method of application are simple, but, where any considerable amount of work is involved, it is usually more satisfactory and sometimes more economical to use the proprietary cements of reputable manufacturers and have the work done by experienced operatives.
Precautions A few obvious precautions must be observed in setting up ceramic-lined chemical equipment. The work including the brick, block, or tile for the lining should be dry and warm and carefully protected until properly set. I n large equipment that is subject to change in temperature, provision may have to be made for expansion and contraction. If the lining has a rubber backing, this may be all that is necessary. Otherwise a special expansion joint must be provided in the structure by substituting rubber or mastic for the hard-setting cement in one or more courses. Ceramic-lined equipment is usually heavy and requires a substantial foundation that should be free from deflection or vibration. Although this type of construction is best adapted to the construction of tanks, scrubbing towers, chimney stacks, sewers, and other large pipe lines, it may also be used for blow cases, autoclaves, exhauster and pump housings, rotary dryers, evaporating pans, kettles, ball mills, filters, and it has been suggested for lining tank cars. A floor laid in acidproof brick or tile has the advantage that, by means of special ceramic shapes which are easily procurable, gutters, drains, sumps, traps, and other details may be built into it to make a practically monolithic construction.
Specifications for Linings Brick and tile of excellent quality for lining chemical equipment can be secured from practically all the manufacturers specializing in ceramic equipment for the chemical industry, but the efforts of some manufacturers of clay products in other lines to adapt their ware to this service have not been entirely satisfactory. The ware must be dense, mechanically strong, nonabsorbent within practical limits, and highly resistant to chemical corrosion. This implies a well-vitrified product, but, if it is too vitreous, there may not be complete adhesion between the ceramic ware and the cement. Occasionally large stoneware tiles 12 square feet or more in area and 2.5 to 4 inches thick are used for the purpose of reducing the number of joints to the minimum. Such tiles are, however, rather expensive, very awkward to handle, and, in common with other clay products, liable to a certain amount of warpage. Consequently, it has been found convenient for the manufacturer, as well as the user, to limit the area of the tile to about 1square foot. A 2.5-inch-thick tile of this type weighs about 28 pounds which is not too heavy for one man to handle. Occasionally the weight is reduced by making it in the form of hollow building tile. Such tile is usually 12 inches wide and 3 inches thick and is available in lengths up to 5 feet. Hollow tile in larger dimensions is also available. Thin tile (1.5 inches or less) is usually furnished with a dovetailed or clincher back (Figure 1) to hold them in place. No univereal standards have been established for acidproof brick. The standard dimensions for firebrick of the American Refractories Institute, based on 9 X 4.5 X 2.5 inches straight, are preferred and have been adopted by some acid brick manufacturers. Others have established standards based on 8 X 4 X 2.25 inches straight. Special sizes have been adopted for certain specific purposes-for example, the blocks used for lining sulfite pulp digesters which have a 9 x 7 inch face and vary in thickness with the diameter of the shell to which they are fitted. The use of blocks shaped to bond in with the brickwork
Armored Stoneware Complete chemical stoneware equipment is encased in a metal shell when it has to withstand stresses beyond the safe limit for the unprotected ware. Equipment so armored is also used where it is subject to severe mechanical abuse. I n such cases the active materials to be handled do not come in contact with the joint, and a grout of Portland cement and sand is used for cementing the ware into the housing. Examples of such armored equipment are shown in Figures 4 to 8. Ceramic-lined chemical equipment presents no complete solution to the corrosion problem of the chemical engineer who demands production units much larger than the stoneware manufacturer can supply. It can obviously be applied only to certain types of constructional work but within this limited field it compares favorably with alternative methods, since it offers in a rugged, substantial form and a t a reasonable cost, the unique resistance to corrosion of a vitrified clay product.
Acknowledgment The particulars given above are taken from the files of the General Ceramics Company, supplemented by information furnished by Maurice A. Knight, J. M. W. Chamberlain of U. S. Stoneware Company, W. H. McAdams, Jr., of Haveg Corporation, C. R. Payne of Atlas Mineral Products Company, and others whose assistance is gratefully acknowledged.
Literature Cited (1)Anonymous, Trans. Inst. Chem. Engrs. (London), 12,248(1934). (2)Snell, F. D.,U. 5. Patent 1,973,732(Sept. 18, 1934). RECIUIVED February 18, 1937.
405
