INDUSTRIAL, A N D ENGINEERIh’G CHEMISTRY
May, 1931
pacity, but there is still a naive tendency on the part of seasoned engineers, studying by-product carbon dioxide in general and Dry-Ice in particular, to base conclusions on the unwarranted assumption that the product manufactured can be sold without difficulty a t some price necessary to yield a profit in their own mind’s eye, and that the market is in no danger of over-supply and its usual train of economic consequence. To cite an example of rapid construction, the ground was broken for the Peoria plant on April 10, 1930, and, on July 17, a unit of 50 tons capacity was placed in operation, producing a t once steady and dependable quantities of salable product. I n many instances it is now possible to forecast accurately the
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rate of market development a t least four months in advance by following closely the progress of the principal users and prospective users in modifying their equipment and methods. For example, a change in refrigerated truck transportation of any large hauler of meat or frozen products requires several months for its accomplishment. Improved speed of plant construction, better intelligence as to the rate of introduction of new equipment and methods, and the construction of large seasonal storages, now aggregating 7000 tons of solid carbon dioxide capacity, have eliminated all hazard of any shortage of supply of the product and made it possible to undertake further developments along sound conservative lines.
Machinery to Make Solid Carbon Dioxide’ Terry Mitchell PRICKCOMPANY, INC., WAYNESBORO, P.\
GREAT deal has been written in the last two or three years about solid carbon dioxide, marketed under various trade names as a refrigerant. The growing interest being shown in the uses of the new refrigerant has also focused attention on the methods of preparing carbon dioxide gas in a form pure enough to be made into a merchantable product. Comparatively little has appeared, however, outlining the actual equipment for producing the ice. The plant making solid carbon dioxide comprises, briefly, a three-stage compression system, carbon dioxide condensers, three-stage liquid coolers, snow chambers, and auxiliaries such as mixers, intercoolers, filters, etc. The several stages of liquid cooling are synchronized with the corresponding stages of compression to give better efficiency, reduce the size of the machinery, and save horsepower. The physical basis of the manufacture of solid carbon dioxide is the reduction in pressure and cooling of the carbon dioxide below its triple point, which is a t -70” F. I n practice the liquid carbon dioxide may be allowed to expand to a pressure between 5 and 15 pounds gage, corresponding to a temperature of about -100’ F. Under these conditions part of the liquid carbon dioxide turns into ice and the remainder into gas, the latter representing the amount required to cool the liquid to the ice temperature and to take out the heat of fusion. It is evident t h a t t h e yield of ice, per pound of c a r b o n d i o x i d e handled, will be much greater if the liquid is precooled to a low degree. In this system the liquid is chilled to as low a temperature as possible, corresponding to the lowest suction pressure in the threestage compression plant, before it enters the icemaking cylinders.
A
Removal of Impurities
fires, fermentation vats, lime kilns, and “oil” wells. Gas from any ordinary source known a t present is too impure for direct conversion into the solid for refrigeration purposes, but must be purified to an extraordinarily high degree by processes more ‘or less elaborate, depending on the nature and amount of impurities present. The removal of inert gas, moisture, and substances causing odors, is particularly important. The gas obtained from alcohol plants and from natural wells in Mexico and some other places is sufficiently pure to require only simple treatment. The purified gas is fed into the system under a few pounds pressure by a rotary blower. Removal of moisture is necessary to prevent freezing and clogging with water ice in the low-temperature parts of the cycle. I n commercial plants, water is removed from the gas before it enters the system by freezing, sulfuric acid driers, or in some cases by absorbers using activated charcoal. The apparatus in the gas circuit between the stages of compression is provided with valves from which any water, precipitated by the higher pressure existing between these stages, may be drained. Whatever water vapor is condensed with the liquid tends to accumulate and freeze in the liquid carbon dioxide coolers. In cases where the gas is not dried thoroughly, continuous operation may be insured by installing these coolers in multiple, with by-pass piping arranged SO that one cooler can be thawed out while the other is in service. Even a small amount of m a c h i n e oil in the gas causes a yellow discoloration in the blocks of ice, and they cannot then be sold. Other impurities, depending upon the source from which the gas is taken, must be guarded against by special means.
The principal presentday sources of c a r b o n dioxide gas are coke 1
1931.
Compressors
Received February 12, 4
Diagram of Machinery for t h e Manufacture of Solid Carbon Dioxide
The compressors are of either the vertical singleacting enclosed type,
blocks will be 10 inches square in cross section, ano will therefore fit into the storage and shipping boxes now in use, but the length of the blocks m:ty be increased t o 20 inches to save time in handling and to aid in preventing evaporation. The cast-iron snov chamber is heavily insulated, as can be seen in the photographs. Inside the chamber is fitted a square piston or ram, worked by a hydraulic cylinder below the floor level; a similar hydraulic cylinder controls the head or cover of the chamber. The operating levers and mater valves are clearly sliown in the foreground of one of the views. The hydraulic cylinders being of ample she, a simple centrifugal pump provides the necessary water pressure. 4 n open surge tank is part of the water system. A blowback valve and suction pipe are installed above the expansion connection, due precautions being taken to keep the flakes of snov from entering the blowback line and eventually clogging the heat exchanger. The vertical design of the machine k e e p the prwsure of the ram froni setting up
uneven strains on the frame or fuuiidation of the unit. The tendency of the m o ~ i n gparts to freeze fast, and the inclination of the top of each block of ice to be soft and porous, with broken corners, have also beeu overcome. The loose snow formed in the chamber can be given either one or two compressions, by manipulation of the controls, and by admitting an extra amount of liquid before opening the blowback valve a heavy, more solid block of ice can be tormed if desired. The machines are usually operated on a continuous schedule, 24 hours a day. The pressures and temperatures throughout the system will be different under various conditions but average pressures of 100, 350, and 900 pounds gage, respectively, for the three stages, are typical. Plants of the type described are in operation in this country and abroad. The largest installation, having a capacity of about 50 tons of solid carbon diovide per day, is in Philadelphia
Quick-Setting Silicate of Soda Cements for AcidProof Tank and Tower Construction' Foster Dee Snell and Howard Farkas 133 CLISTOSSr.,BROOKLYS,S . l '
Silicate of soda cements for acid tank and tower cona week m u s t be allowed struction may be considered as of three types. The for the cement to harden, solid masonry, acid tanks, first is a mixture of inert material with sodium silicate, during which time 110 stress toxers, and chimneys, or and hardens by slow drying. The second is a mixture of for lining metallic casings, a can be placed on the masonry inert and acid material with sodium silicate and cement that will not tleteriobecause of the softness of the hardens both by drying and by reaction to liberate silicic mortar. The contraction in rate rapidly is essential. The acid. The third is a mixture of inert and alkaline or drying is often serious. Conc e m e n t s most widely used neutral material with sodium silicate, which by reaction trol of this factor by gradfor this purpose are prepared will produce an insoluble silicate to give a set prelimiing of the aggregate is limited by mixing suitably blended nary to drying. The neutral or alkaline self-hardenby the viscosity of the sodium inert materials, such as siliing cements do not set so hard initially and are theresilicate solutions used and the ceous aggregate, with specified fore better able to take up the strains incidental to furresulting thickness of the film amounts of high-silica sodium ther building operations. about tKe particles of cement. silicate. The m a j o r i t y of Details of representative types of acid-proof lining such cements are sold as a Only 4 to 12 courses of brick, construction are given. carefully graded dry mixture, according to size, can be laid and the silicate solution of a per d a y with this type of specified grade is added just prior to use. At least one manu- cement. More rapid construction causes some of the partly facturer offers a ready-mixed product of this type in air-tight set cement to be squeezed out from the lower courses. In containers. h typical mesh analysis of a siliceous mix for this order to hasten the set, artificial heat is often used. An acid treatment is given the cement joints after hardenpurpose is as follows: ing has taken place to render them fully acid-tight. The c/o Mesh bonding strength of the wet mortar is dependent on the adRetained on 20 0.02 40 0.41 hesiveness of the colloidal silicate solution. During drying 2.69 60 it becomes less readily soluble in water, and when fully 80 2.37 LOO 6.63 dried it has a considerable water resistance. As soon as the 300 17.38 Through 200 mortar joints are painted or sprayed with sulfuric acid, the 70.50 sodium silicate with which i t comes into contact is decomThe silicate solution almost always used is that having a ratio posed to give silicic acid and sodium sulfate, along with of 1:3.86, sold in the trade as water glass. This contains 6.4 the unaffected filler. During use acid gradually penetrates per cent NazO and X . 7 per cent silicon dioxide, and has a the joint or lining, so that the bond is more or less completely reading of approximately 34 O BB. transformed from that of dried silicate of soda to that of When applied as the acid-proof mortar between chemical silicic acid. Even though silicic acid is insoluble in water bricks, such a cement dries out to form a strong bond, which, and of itself has no adhesive or bonding strength, the cement after treatment with acid, becomes highly resistarit to further so transformed in place has a very definite and satisfactory attack by acids. The chief objection to the product is that the bonding strength. The h a 1 result is therefore a cement silicate requires a considerable length of time to dry out. About lining or joint which is both acid- and water-proof. Such a cement carefully handled and properly air-dried gives a 'Received February 20, 1931. Presented before the Division of Intensile strength up to 1700 pounds. dustrial and Engineering Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 193 I . When food products with delicate flavors are to be handled,
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S T H E construc1,ion of
