Safe Practice i n t h e Viscose Rayon Industry' William Ή . Chesniat;, I > e p a r t m e n t o f Labor a n d I n d u s t r y , C o m m o n w e a l t h o f P e n n s y l v a n i a , Harriehurg, P e n n a .
Figuz»® 1.
A i r p l a n e V i e w o£ A m e r i c a n Viscose Lewistown, Penna.
JOINT survey has been conducted by the Federal Government and several of the states where viscose plants are located to determine the hazards from toxic gases involved in the manufacturing processes. The results o f this survev have been reported in the literature and are now well known to the industry. The toxic gases involved are carbon di sulfide and hydrogen sulfide, which earlier in the history of the plants were allowed to escape into the churn and spinning rooms. This discussion has to d o with ventilation and control of these gases and reports the results of a broad program to correct conditions, initiated by plants located in Pennsylvania. In manufacturing, wood cellulose is first treated with caustic soda, producing sodium cellulose, called "white crumbs". Thi3 process is known a s mercerizing. Xanthation, the next s t e p , has been car ried out in the churn room. The white crumbs are fed into a churn which is also charged with carbon disulfide. At the completion of the reaction the finished product is golden yellow, "orange crumbs". This material is dissolved in sodium hy droxide and is ejected into the acid co agulating bath in the spinning room where it emerges as a fiber. Small quantities of
Fi&ure 3.
carbon disulfide escape into the work room, but the quantities are sufficient t o produce toxic effects over an extended period of time. Τ η the spinning room hydrogen sulfide and carbon disulfide escape into the atmos phere, the former as a result of reaction in the spinning bath. At the plant of the American Viscose Corp.. Lewistown, Penna. (Figure 1), where there are 5000 employees, there are two 350-foot stacks buut to remove gases escaping from the spinning baths. Carbon disulfide is de livered in tank cars and piped to reser voirs submerged under water. The old stvie churn has an inlet pipe for carbon disulfide and beneath the churn is a truck into which the orange crumbs are dumped at the completion of the churn's cycle. These are hand trucks, which are then hauled to various locations in the churn room and the contents are shoveled through trap doors in the floor directly into the mixing machines on the floor below. After discharging the contents of the churn the film of xanthate which adheres to its
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A Presented before National Safety Congress, Afeîantio City, N . J., Ootober 19, 1939.
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Newly invented machine combines churn and mixer operation inner walls must be removed with the aid of hand tools. If this is not properly removed, the next batch will be contaminated. It is evident that the four hand operations—namely, dumping the churn, trucking, shoveling, and hand-scraping—involve hazards. This led the American Viscose Corp. to undertake research which has developed a new type churn (Figure 2). This churn combines xanthating and mixing so that the entire process is a closed mechanical one. Briefly described, this equipment is a water-jacketed vessel heavy enough to withstand moderate pressure. By the newly invented process the white crumbs are charged at the top, the equipment is closed, carbon disulfide is added, and xanthation takes place with the help of a rotating stirrer within the vessel. This operation of xanthation is performed under a vacuum which prevents the escape of carbon disulfide during the reaction. The material remains within the vessel and the next process, known as mixing or forming the viscose solution, is performed by the introduction of sodium sulfite and caustic soda solutions, which enter through a metered orifice. At the completion of this reaction the orange-
NEWS EDITION
OCTOBER 20, 1939 colored viscose solution is pumped t o aging tanks preparatory to spinning. The "churn-mixer" is cleaned with a slightly alkaline solution, thus eliminating hand-scraping, the agitating paddles or stirrer being useful in washing o r rinsing all surfaces free from viscose film. The enclosed valve room contains the system for measuring carbon disulfide, which resembles other measuring devices. The solvent action of carbon disulfide on the packing of the valves makes possible an occasional leak, so that the valve room is now enclosed and under negative pres sure. Ventilation is ensured by the two stacks to which reference has been made. These stacks are each approximately 350 feet high and the ducts leading into each stack are 17 by 20 feet. These ducts come directly from the spinning machines, and the system has for its purpose removal of the fumes arising during the reaction in the acid-coagulating baths. In addition t o natural draft there are motor-driven fans. each with a capacity between 300,000 and 500,000 cubic feet of air per minute, the diameter of each fan being approximately 18 feet. A unit of the spinning bath is shown in Figure 3. Each spinning bath is now en closed in glass to prevent the escape of fumes into the room. When work must be done periodically inside the glass en closure an automatic mechanism triples the ventilation of that section as each section of glass is lifted, thus removing any gases at their source. Philip Drinker, Harvard School of Public Health and consultant for the American Viscose Corp., has devised two types of automatic recording equipment—
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Figure 4 Through the installation of these two recording devices in the churn room and the spinning room, an invaluable aid will be provided for the control of all processes ana thus aid directly in the program of safe practice.
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Figure S one for hydrogen sulfide (Figure 4) and the other for carbon disulfide (Figure 5). In the hydrogen sulfide recorder, air con taining hydrogen sulfide impinges upon a moving strip of lead acetate-impregnated paper, thus producing the well-known dis coloration, the intensity of which may be used as a direct reading of the amount of hydrogen sulfide present. The quantita tive determination is possible by means of the photronic cells shown in Figure 4. T h e first cell records the reading on plain paper before discoloration and the second reading after formation of lead sulfide. In the carbon disulfide recorder, the contaminated air is led to a furnace where sulfur trioxide is formed from the carbon disulfide. The sulfur trioxide passes through a water bath where it is converted into a fog which is led to a fog chamber and the intensity of the fog recorded auto matically by the conventional process, using a photronic cell.
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Chemical Engineering Facilities at Cooper Union
M
ODERNIZATION of
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gineering facilities of Cooper Union, which nas extended over 3 years and will be completed during this semester, in cludes new appliances and working ar rangements for the qualitative, organic, and metallurgical laboratories, the in stallation of small-scale unit operation equipment for the new chemical engineer ing laboratories, three dark rooms for photographic and physical chemical re search, and the allocation of one labora tory t o undergraduate thesis and faculty research work. In the qualitative and organic labora tories new fume hoods have been installed, many of them equipped with explosionproof glass. Side panels are removable to allow for the erection of apparatus which would exceed the width of a single hood.
The fume-exhaust duct is made of leadlined sheet steel, and each hood has movable back and top partitions, explo sion-proof lights, and exterior controls for gas, air, vacuum, and water. All water baths are recessed, flush with the working surface, and are electrically heated. Hood tops, sides, and back are constructed of Transite e and working surfaces are of Shellstone. The chemical engineering laboratory now covers more than 3500 square feet. A portion of the floor at one end has been removed in order to create a two-story working space, where it is planned to install tne present nine-plate fraction ating column and add at least six plates. A double effect evaporator and a 20-foot stoneware absorption column are to be added. The gas-fired boiler, formerly used for steam generation in the engineer ing laboratory, has been converted to an experimental unit. Next year it is planned to enlarge facilities for the study of the unit proc esses, including sulfonation, nitration, chlorination, and absorption, and of the unit operations of sedimentation, extrac tion, and humidification. Chemical engineering students have participated in the building and assembly of a double pipe heat exchanger, a coil condenser, a pipe system for the study of friction drop of fiuids in conduits, and a packed column, 12 feet high and 8 inches in diameter.
