May, 1931 INDUSTRIAL, A N D ENGINEERIh’G CHEMISTRY 523

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 unwar- ranted 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. In many instances it is now possible to forecast accurately the

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

PRICK COMPANY, INC., WAYNESBORO, P.\

GREAT deal has been written in the last two or three fires, fermentation vats, lime kilns, and “oil” wells. Gas from years about solid carbon dioxide, marketed under any ordinary source known a t present is too impure for direct A various trade names as a refrigerant. The growing conversion into the solid for refrigeration purposes, but

interest being shown in the uses of the new refrigerant has must be purified to an extraordinarily high degree by proc- also focused attention on the methods of preparing carbon esses more ‘or less elaborate, depending on the nature and dioxide gas in a form pure enough to be made into a merchant- amount of impurities present. The removal of inert gas, able product. Comparatively little has appeared, however, moisture, and substances causing odors, is particularly im- outlining the actual equipment for producing the ice. portant. The gas obtained from alcohol plants and from

The plant making solid carbon dioxide comprises, briefly, natural wells in Mexico and some other places is sufficiently a three-stage compression system, carbon dioxide condens- pure to require only simple treatment. The purified gas is ers, three-stage liquid coolers, snow chambers, and auxiliaries fed into the system under a few pounds pressure by a rotary such as mixers, intercoolers, filters, etc. The several stages blower. of liquid cooling are synchronized with the corresponding Removal of moisture is necessary to prevent freezing and stages of compression to give better efficiency, reduce the clogging with water ice in the low-temperature parts of the size of the machinery, and save horsepower. cycle. In commercial plants, water is removed from the

The physical basis of the manufacture of solid carbon gas before it enters the system by freezing, sulfuric acid dioxide is the reduction in pressure and cooling of the carbon driers, or in some cases by absorbers using activated char- dioxide below its triple point, which is a t -70” F. In prac- coal. The apparatus in the gas circuit between the stages tice the liquid carbon dioxide may be allowed to expand to a of compression is provided with valves from which any pressure between 5 and 15 pounds gage, corresponding to a water, precipitated by the higher pressure existing between temperature of about -100’ F. Under these conditions part these stages, may be drained. Whatever water vapor is of the liquid carbon dioxide turns into ice and the remainder condensed with the liquid tends to accumulate and freeze into gas, the latter representing the amount required to cool in the liquid carbon dioxide coolers. In cases where the gas the liquid to the ice temperature and to take out the heat of is not dried thoroughly, continuous operation may be in-

sured by installing these coolers in multiple, with

fusion. It is evident t h a t t h e yield of ice, per pound of carbon by-pass piping arranged d ioxide handled, will SO that one cooler can

be thawed out while the other is in service.

be much greater if the liquid is precooled to a

Even a small amount low degree. In this sys- tem the liquid is chilled of machine oil in the

gas causes a yellow dis- to as low a temperature as possible, correspond- coloration in the blocks ing to the lowest suction of ice, and they cannot

then be sold. Other im- pressure in the three- stage compression plant, purities, depending upon

the source from which before it enters the ice- making cylinders. the gas is taken, must

be guarded against by special means. Removal of Impurities

The principal present- day sources of carbon dioxide gas are coke

1 Received February 12,

Compressors

The compressors are of either the vertical single- acting enclosed type, 4

Diagram of Machinery for the Manufacture of Solid Carbon Dioxide 1931.

blocks will be 10 inches square in cross section, ano will there- fore fit into the storage and shipping boxes now in use, but the length of the blocks m:ty be increased to 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 keep 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 g parts to freeze fast, and the inclina- tion 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 sched- ule, 24 hours a day. The pressures and temperatures throughout the system will be different under various con- ditions 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 Phila- delphia

Quick-Setting Silicate of Soda Cements for Acid- Proof

S THE construc1,ion of solid masonry, acid tanks, I toxers, and chimneys, or

for lining metallic casings, a cement that will not tleterio- rate rapidly is essential. The cements most widely used for this purpose are prepared by mixing suitably blended inert materials, such as sili- ceous aggregate, with specified amounts of high-silica sodium silicate. The ma jo r i ty of such cements are sold as a carefully graded dry mixture, and the silicate solution of a

Tank and Tower Construction' Foster Dee Snell and Howard Farkas

133 CLISTOS Sr., BROOKLYS, S . l'

Silicate of soda cements for acid tank and tower con- struction may be considered as of three types. The first is a mixture of inert material with sodium silicate, and hardens by slow drying. The second is a mixture of inert and acid material with sodium silicate and hardens both by drying and by reaction to liberate silicic acid. The third is a mixture of inert and alkaline or neutral material with sodium silicate, which by reaction will produce an insoluble silicate to give a set prelimi- nary to drying. The neutral or alkaline self-harden- ing cements do not set so hard initially and are there- fore better able to take up the strains incidental to fur- ther building operations.

construction are given. Details of representative

specified grade is added just prior to use. At least one manu- facturer offers a ready-mixed product of this type in air-tight containers. h typical mesh analysis of a siliceous mix for this purpose is as follows:

Mesh Retained on 20

40 60 80

LOO 300

Through 200

c- /o

0.02 0 . 4 1 2 .69 2.37 6 . 6 3 17.38

70.50

The silicate solution almost always used is that having a ratio of 1:3.86, sold in the trade as water glass. This contains 6.4 per cent NazO and X.7 per cent silicon dioxide, and has a reading of approximately 34 O BB.

When applied as the acid-proof mortar between chemical bricks, such a cement dries out to form a strong bond, which, after treatment with acid, becomes highly resistarit to further attack by acids. The chief objection to the product is that the silicate requires a considerable length of time to dry out. About

'Received February 20, 1931. Presented before the Division of In- dustrial and Engineering Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 193 I .

a week m u s t be allowed for the cement to harden, during which time 110 stress can be placed on the masonry because of the softness of the mortar. The contraction in drying is often serious. Con- trol of this factor by grad- ing of the aggregate is limited by the viscosity of the sodium silicate solutions used and the resulting thickness of the film about tKe particles of cement. Only 4 to 12 courses of brick, according to size, can be laid per d a y with this type of

cement. More rapid construction causes some of the partly set cement to be squeezed out from the lower courses. In order to hasten the set, artificial heat is often used.

An acid treatment is given the cement joints after harden- ing has taken place to render them fully acid-tight. The bonding strength of the wet mortar is dependent on the ad- hesiveness of the colloidal silicate solution. During drying it becomes less readily soluble in water, and when fully dried it has a considerable water resistance. As soon as the mortar joints are painted or sprayed with sulfuric acid, the sodium silicate with which i t comes into contact is decom- posed to give silicic acid and sodium sulfate, along with the unaffected filler. During use acid gradually penetrates the joint or lining, so that the bond is more or less completely transformed from that of dried silicate of soda to that of silicic acid. Even though silicic acid is insoluble in water and of itself has no adhesive or bonding strength, the cement so transformed in place has a very definite and satisfactory bonding strength. The h a 1 result is therefore a cement lining or joint which is both acid- and water-proof. Such a cement carefully handled and properly air-dried gives a tensile strength up to 1700 pounds.

When food products with delicate flavors are to be handled,

types of acid-proof lining