GENERAL DESCRIPTION OF OPERATION
This manual excerpted here was designed specifically for use by Indiana Ordnance Works. Layout diagrams of the nitrocellulose facilities at this location are presented in Fig. 1 (A, B and C lines) and Fig. 2 (D, E and F lines). In addition, a schematic flow sheet is presented in Fig. 3.
The manufacture of military nitrocellulose for smokeless powder consists essentially of three general operations, (1) nitration, (2) purification and (3) finishing. Throughout this manual, these operations are discussed systematically under the sub-headings listed below:
II. General Description of Operations
III. Cellulose Preparation
IV. Acid Supply
VI. Wringing and Drowning
VII. Spent Acid Filtration
VIII. Fume Acid Recovery
XIV Final Wringing
XV.Slurry Tank House
XVI Sample Drying
The chemical specifications for the various grades and types of military nitrocellulose which may be prepared by the above sequence of operations were listed in Section XVII, Page 406. However, at Indiana Ordnance Works, the finished product was usually blended nitrocellulose (Grade C – Type I) which was delivered to the powder areas for use in the manufacture of smokeless powder. It consisted of about 65% High Grade (13.35% min. nitrogen) and 35% Pyro (12.60% 10% nitrogen) with an average nitrogen content of about 13.15%.
A brief description of each process in the manufacture of nitrocellulose follows.
Manpower requirements listed varied according to production schedules.
An understanding of the nature of both cotton linters and wood cellulose is dependent upon a knowledge of carbohydrate chemistry. Cellulose, a polymer or long chain molecule of glucose, acquires its chemically useful properties from the hydroxyl groups which are a part of its molecular structure. These alcoholic groups react with acids to form products called esters, such as the nitric acid ester of cellulose, nitrocellulose.
The fundamental building unit within the cellulose molecule is glucose. The glucose units, not at the ends of long chain cellulose molecules, have three, free, hydroxyl groups which may react with nitric acid during nitration. The terminal glucose units have four, free, reactive, hydroxyl groups.
The degree of esterification, measured by the nitrogen content of the nitrocellulose after nitration, depends upon how many hydroxyl groups, per glucose unit, in the cellulose molecule, react. A degree of esterification of two, theoretically, corresponds to the reaction of two hydroxyl groups per glucose unit.
The theoretical determination of the nitrogen content of nitrocellulose, with a degree of esterification of 2, is 11.1%; with a degree of esterification of 3, it is 14.1%; and with a degree of esterification of 4, it is 15.6%. At the Indiana Ordnance Works, Pyro N/C has a nitrogen content of about 12.6% and High Grade, 13.45%. Thus, theoretically, the Pyro nitrocellulose made at I.O.W. may corresponded to nitrocellulose composed of equal amounts of the second and third degree esters, while the High Grade may correspond to nitrocellulose composed of thirds of the second, third and fourth degree esters.
This points up the essential random character of the nitration of cellulose (esterification) which cannot be controlled to yield a nitrocellulose that is completely and ideally homogeneous. Conditions can be governed to yield a product with a desired nitrogen content since the nitrogen content represents the average nitrogen, corresponding to a nitrocellulose which is a composite of nitric esters of two, three and four degrees of esterification.
Since specifications on the properties of the N/C used for granulation are less tolerant than those upon the Pyro and the High Grade, cellulose is first nitrated to Pyro and High Grade. Calculated proportions of the Pyro and High Grade, depending upon their physical and chemical properties, were then blended to yield an N/C with desired characteristics.
A. Cellulose Preparation
Cellulose preparation serves two purposes. First, the cellulose is placed in a suitable physical form for contact with mixed acid, and second, the moisture content of the cellulose is reduced to the lowest practical value.
Both cotton linters and woodpulp were used as the basic raw materials for the manufacture of nitrocellulose at Indiana Ordnance Works. Cotton linters were received in compressed bales about 22″ wide by 18″ high by 48″long, and weighing about 150 pounds. The bales of cotton were transported to the feed end of the linters dryer as needed, stripped of heavy wrapping paper and baling wire, broken into batts 2″ to 3″ in thickness, and placed on a conveyor which feeds a picker roll. The picker roll reduced the batts to a fluffy mass and discharged this material to the dryer feed conveyor. The dryer feed conveyor dropped a uniformly thick layer of cotton onto an endless metal screen conveyor which carried the cotton through the dryer tunnel. Circulating hot air, maintained at about 95º C. reduced the moisture content of the cotton to between 0.5 and 2.5%. At the discharge end of the dryer, the cotton was carefully weighed into tared containers, The containers were placed on a chain conveyor, and transported to the dipping floor of the nitrating house.
Wood pulp is received in rolls about 36″ in diameter, consisting of a continuous sheet about 30″ wide by 0.045″ thick, and weighing about 600 pounds. The rolls of wood pulp were transported to the feed end of the wood pulp dryer as needed, stripped of paper wrapping, end discs and plugs. A steel mandrel was fastened in the core of the hoist. Usually three sheets were dried simultaneously, each making three complete passes from one end of the dryer to the other. Circulating hot air, maintained at about 165º C. reduces the moisture content of the woodpulp sheet to less than 2.5%. On leaving the dryer, the three pulp sheets pass under a common idler roll and were fed as a unit to a Hercules shredder by means of a power driven feed roll. The shredder shredded the pulp sheet to a fluffy mass of particles about 3/4″ long by 45″ wide by 0.045″ thick. The shredded particles were blown through a discharge chute to a pneumatic conveying system which discharged to a cyclone collecting bin. Shredded wood-pulp was raked from the collecting bin and carefully weighed into tared containers, each holding one dipping pot charge of cellulose. H.G. containers on linters hold two charges., The containers were placed on a chain conveyor, and transported to the dipping floor of the nitrating house.
Sketch – Cellulose Warehouse
Sketch – Cotton Dry House
Sketch – Cellulose Conveyor House
B. Acid Supply
Acid Supply has two functions: first, nitrating acids of compositions corresponding to predetermined standards are prepared for the dipping operation, and secondly, the mixed acid is delivered to the dipping pots at the optimum physical condition for nitrating.
Nitrating acids for the manufacture of nitrocellulose at Indiana Ordnance Works were prepared from spent nitrating acids and fortifying acids. Fortifying acids include sulfuric acids, 66º Baume and/or Oleum, F-83, an acid high in nitric and low in sulfuric, and weak nitric acid (45-48%) from the fume recovery system. Sulfuric acid and F-83 acid were received from the Acid Manufacturing Area; spent nitrating acids and cyclone acid were recovered from the Nitration Operation as described in subsequent sections.
To make a mix, a desired amount of spent nitrating acid was pumped from the spent acid storage tanks into scale tanks. After this spent acid had been agitated, a sample was taken and sent to the laboratory for analysis. From this analysis, the amounts of fortifying acids to be added were determined by the laboratory. The exact amounts by weight of fortifying acids were then taken and sent to the laboratory for analysis. If the analysis of this acid is within specifications, it was approved by the laboratory for use in nitration. The “mix” was then pumped to a mixed acid lag storage tank. If the “mix” was not within specifications, further fortification was made, as outlined above, until an acid conforming to specification is obtained.
Mixed acid of the proper composition was pumped from the lag storage tanks to an agitator equipped acid warming tank, where the temperature was adjusted to prescribed specifications.
When the desired temperature has been reached and the acid was ready for use, it was pumped continuously through the header supplying the measuring tanks for the dipping operation. Excess acid flowed through a return header to the warming tanks.
Four types of mixed acid were produced for use at Indiana Ordnance Works: High Grade Linters Mix (used in the production of high grade nitrocotton), Pyro Linters Mix for pyro nitrocotton, High Grade Woodpulp Mix for high grade nitropulp, and Pyro Woodpulp Mix for pyro nitropulp. These mixes differed only in the relative amounts of nitric and sulfuric acids that are found in each. The procedures used for each type of mixed acid are identical except as to the amounts of acid used and circulation temperatures.
Dipping is the immersion of purified and dried cotton linters or woodpulp in mixed acid with agitation for a specified period of time. The purpose of dipping is the complete and uniform nitration of cellulose to two grades of nitrocellulose, “pyro” and “high grade.” The manner in which the dipping operation is conducted largely determines the working properties of the resulting nitrocellulose.
Mixed acid of the specified composition and temperature was continually circulated between the dipping floor and warming tanks. Fiber cans containing the dipping pot charges of cellulose were delivered continuously on a monorail conveyor. A full container was removed from the conveyor, and placed on a rack adjoining a dipping pot charging port. A volume of mixed acid corresponding to exactly one dipping pot charge was drawn into a measuring tank. The high hat cover on the charging port was removed and the flow by gravity of the mixed acid is started to the dipping pot. Meanwhile, high speed agitation was started and a full charge of cellulose was rapidly forked through the high hat opening into the dipping pot. The high hat cover was then replaced. The acid inlet valve to the dipping pot was subsequently closed. After a period of digestion on high speed, agitation was reduced to low speed. When the total period of digestion was completed, the contents of the dipping pot were discharged by gravity into a centrifuge where the nitrocellulose was separated from most of the spent nitrating acid. In the meantime, the empty container was placed on the conveyor for refilling.
The operating procedure ws the same for the manufacture of both grades of nitrocellulose. The difference in nitrogen content is effected by the differences in acid compositions, temperatures, cellulose charge weights and immersion times for the types of nitrocellulose.
The two grades of nitrocellulose are kept separate until the blending operation.
Schematic Diagram – Nitrating (Dipping) House
Schematic Diagram – Dipping Buildings and Equipment (Nitrating House)
Schematic Diagram – Dipping Pot
D. Wringing and Drowning
The purpose of wringing is the separation by centrifugal action of the spent nitrating acid from nitrocellulose. The primary purpose of drowning is the dilution with water of the spent acid retained in the wrung nitrocellulose. Dilution of the retained acid reduces and decelerates chemical reactions of the nitrocellulose and the acid, such as hydrolysis and oxidation. A secondary purpose of drowning is to put the wrung N/C in a convenient form for transfer to the stabilization operation.
The wringing and the drowning were carried out as follows: An empty wringer was allowed to accelerate on low speed until a speed of 180-300 rpm is reached. Charging was then started by opening the discharge valve between the dipping pot and wringer. As soon as the dipping pot was empty, the discharge valve was closed. The loaded wringer was then placed on high speed for the remainder of the wringing time. This speed allowed uniform basket loading and tended to force only a minimum of nitrocellulose into or through the perforations in the basket.
After the wringing time was completed, the control switch was turned off, the brake applied, and the wringer stopped. An operator donned a face mask and rubber gloves, picked up a fork, and steped on the treadle board to start the water flow through the immersion basin. The wringer lids were set aside, the valve plate was raised, and the flow of water to the immersion basin was checked by looking into the immersion basin and listening for the sound of running water. The charge was then forked out of the wringer basket into the immersion basin. The wringer was turned on low speed for approximately 5 seconds after which the wringer basket was scraped to remove small pieces of nitrocellulose. The valve plate was then lowered, the lids replaced, and the treadle board catch released.
The nitrocellulose which had been forked out of the wringer dropped into the immersion basin, where it was drowned and broken into small pieces by the action of a water sparger. The nitrocellulose – water slurry flowed by gravity through a stainless steel trough to a large wooden tub in the basement of the building. From this tub the nitrocellulose water slurry was pumped to the stabilization operation.
Sketch: Drowning Tub
E. Spent Acid Filtration
Acid recovered by wringing always contains entrained particles of nitrocellulose. This nitrocellulose, if allowed to remain during storage, would increase the nitrosyl content of the acid at the expense of using nitric and sulfuric acids. In addition, the probability of acid tank fires would be increased. Therefore, all spent nitrating acid was filtered as soon as it leaves the wringers.
The spent acid flowed by gravity from the nitration wringers and entered the filter through the top. The filter contained a perforated filter basket which retained the entrained N/C particles and allowed the acid to flow through it. This spent acid was pumped to spent acid storage tanks in the Acid Mix Tank Farm for reuse. The pressure forcing the acid through the accumulated cake of nitrocellulose came entirely from the pressure head of acid in the filter. When the resistance of the nitrocellulose cake became so great that a full pressure head of acid no longer produced an adequate flow of acid from the filter, the flow of acid from the wringer was diverted to another filter.
After a spent acid filter had become filled with nitrocellulose, it was drained to remove as much acid as possible, but enough acid remained with the nitrocellulose to make its recovery by displacement economical. Water was floated on the nitrocellulose – acid heel in a filter. Under the influence of this head, the entrained acid was forced from the filter. As very little intermixing of acid and water occurs, recovery at high acid concentration was possible. As the acid reached the bottom of the filter, it was pumped from there into the pyro filter that was receiving spent acid from the nitrating process.
As the water – acid interface moved through the nitrocellulose, denitration of the nitrocellulose occurs. However, the amount of nitrocellulose retained by a filter was too small for the change in nitrogen content to be noticed elsewhere.
The nitrocellulose contained in the filter was transformed into a slurry by the addition of water through a high pressure sparger. It was then pumped to the drowning tubs in the nitration house from which it was subsequently sent to the boiling tub house.
There were six spent acid filter houses, one on each line. These were designated as Buildings 106-1 through 106-6.
F. Acid Fume Recovery
An exhaust system was installed on dipping pots, wringers, and spent acid filters to protect operating personnel and equipment from acid fumes. Once acid fumes had been picked up by the air entering the exhaust system, the concentration must be substantially reduced prior to releasing the contaminated air to the atmosphere. This is the primary purpose of fume acid recovery. A secondary purpose was to remove the acid from the air at such a concentration that it may be economically reused.
The current operating practice at Indiana Ordnance Works, of a two cyclone fume recovery system (connected in series) was to spray a portion of the strong first cyclone acid into the main fume duct and the weak second cyclone acid to the exhaust duct fan and duct feeding the second cyclone. As additional liquid volume was needed, steam condensate from the cellulose dryers was added to the second cyclone weak acid. Steam condensate was used to prevent chlorides from entering the system. About 95% of the total acid recovered was collected prior to and at the first cyclone. The remaining 5% was collected at the second cyclone. Of the 95% recovered at the first cyclone, about 45% was removed in the main fume duct.
Nitric acid from various points along the main fume duct and from the first cyclone was collected in a hold-up tank at a concentration of 45% – 48% HNO3. The acid which was not used as spray in the main duct was pumped to the Mixed Acid Tank Farm for use in fortification.
There is one fume recovery system located on each line. It was not enclosed in a building but located on a concrete apron adjacent to the nitration house.
The purpose of this operation was to eliminate the impurities and unstable particles that had been formed during the nitrating process. This was accomplished in large wooden tubs known as Boiling Tubs.
Nitrocellulose boiling tubs at Indiana Ordnance Works were filled by one of two procedures: the hot water process or the cold water process. In both processes, the filling procedure is identical with the exception that water used in the hot water process was preheated to 850 C in an external wooden tank elevated 40′ above the ground. The actual filling process was as follows: The nitrocellulose slurry was pumped from the drowning tank in the nitration house to the tub being filled in the boiling tub house. The water in the nitrocellulose slurry was continually drained as the tub was filled. When the nitrocellulose reached a predetermined level, the nitrocellulose slurry was diverted to another boiling tub. Water, hot or cold, depending on the process being used, was then added to completely cover the drained nitrocellulose. The entire contents of the tub were heated by steam to 850 C, and the water was then drained from the tub. This lowered the level of the nitrocellulose in the tub and more nitrocellulose slurry was pumped to the tub to refill it.
The tub was then filled with water. Steam was subsequently admitted to the tub. When the contents of the tub reached a temperature of 850 C, a Thermo-Compressor System was brought into use. This system enabled the nitrocellulose slurry to be more economically heated with steam by effecting a greater circulation of the steam in the tub. This increased circulation thus requiring a smaller quantity of steam to maintain the required boiling temperature.
The time of boiling was started as soon as the recording thermometer on the tub reached 950 C. provided the temperature of the tub surpasses 980 C within an hour. As soon as the temperature reached 980 C, the steam flow to the tub was regulated to maintain a temperature of 98-100º C.
The acid boil for High Grade Nitrocellulose was sixty hours. During this time acidity tests are taken at the end of 2, 10, 20, 30, 40, 50 and 60 hours of boiling. If during these acidity checks the acidity was higher than 0.40% (calculated as sulfuric acid), the tub was allowed to drain sufficiently to reduce the acidity within a range of 0.28 to 0.40%. The tub was then refilled with hot water to the predetermined level and boiling was continued. If the acidity was below .28%, a proportionate amount of mixed acid was pumped from the nitration house.
At the end of the sixty hour boil the steam was shut off and the tub drained. It was then filled with hot water and put on boil for five hours. The above procedure was repeated for a second five hour boil. After the second five hour boil, the tub was drained and filled with cold water and allowed to stand until it was sent to slurry tube* The stabilized nitrocellulose was subsequently pumped to the Pulping House.
The same filling and boiling procedure as outlined above were followed for pyro nitrocellulose with the exception of the initial boil, which was thirty hours with acidity tests taken after the 2, 10, 20 and 30 hour boils. Pyro nitrocellulose also required two five hour boils with a change of water between each boil.
The purpose of pulping is to reduce the size of the nitrocellulose particles. This enhances the leaching of the undesirable nitric esters from the nitrocellulose in the poaching operation. Pulping also facilitates the blending of pyro and high-grade nitrocellulose in the blending process. Further, pulping increases the ether alcohol colloiding properties of the nitrocellulose. Thus the colloiding process in First Stage Powder is benefited.
Pulping is the subdividing of the nitrocellulose in a number of Jordan engines (machines for beating and refining pulp). In general, this required that a charge of high-grade nitrocotton pass through three Jordans (3 passes) while pyro nitrocotton received two Jordan passes. Both grades of nitropulp normally received two Jordan passes.
A slurry of stabilized nitrocellulose was pumped from the boiling tub house to the pulping house, where it was discharged on a Memphis Dewaterer for removal of excess water. The dewatered slurry passed into an initial slurry tank where it was agitated with sufficient sodium carbonate to give a slightly alkaline reaction to phenolphthalein. The slurry was then pumped to an overhead stuff tank above the first Jordan and flowed by gravity through the first Jordan to a dewaterer from which it was pumped to the overhead stuff tank above the second Jordan. This operation was repeated until the nitrocellulose had passed through the necessary number of Jordans. The nitrocellulose flowed from the last Jordan into a catch tank where it was diluted with “white water” from the savealls and then pumped to the Poaching House.
All water leaving the pulping operation and subsequent operations passes to large concrete circular basins (savealls) where particles of entrained nitrocellulose are settled out. Periodically, a saveall is drained, and the nitrocellulose was slurried with high pressure water and pumped to poaching for a complete poaching treatment and reuse.
The purpose of the poaching treatment is to neutralize any acid liberated from nitrocellulose by pulping and to remove any soluble impurities from the nitrocellulose.
Nitrocellulose water slurry from the pulping house was pumped to a cypress tub which had been prepared for filling by proper adjustment of all valves and lines. Water was continuously decanted and pumped to a saveall as the tub was filling. When about 70% of the volume was filled with settled nitrocellulose, the tub was completely charged. The decanter line was lifted, flow of slurry into the tub stopped, and agitation started.
After sufficient soda ash solution to give an alkaline reaction to phenolphthalein had been added the tub was filled with hot water, and heated to above 95½º C by the injection of steam through a Venturi sparger. The temperature is maintained at 95½0 C for 4 hours. The steam was then shut off, the agitator stopped, and the tub contents allowed to settle one half hour. Water was then decanted from the tub to the 30%mark and the tub refilled with hot water and put back on boil. This boiling procedure was repeated for one two-hour and two-one-hour boils.
When the last one hour boil was completed, the tub was decanted to the 30%mark, filled with cold water, and agitated for thirty minutes. The agitator was stopped and the and the slurry allowed to settle for one hour. The tub was again decanted to the 30% mark and refilled with cold water. This washing procedure was repeated until the specified number of cold water washes had been given the tub charge. The tub was filled to the 115″ mark with cold water the seventh time. Agitation was resumed and after thorough mixing, samples for stability tests and final weight determination are taken. From every tenth charge an additional sample was also taken for solubility in ether, alcohol, and acetone.
At Indiana Ordnance Works, in order to increase the production capacity the poacher houses were equipped with a number of Internal Screen Tubs for cold water washing. Whenever possible, charges were transferred at the end of the poaching boils to an Internal Screen Tub. After the transfer to the Internal Screen Tubs, the charge was drained to about half the tub volume. The tub was then refilled with cold water, and the agitator was started. The charge was agitated for 15 minutes and immediately drained to about one half its volume. The above process is repeated for the specified number of cold water washes. Specified samples were taken after second and fourth tub refills.
After the poaching treatment has been completed, the charge is agitated in the tub until it is to be used in the screening operation.
The purpose of the screening operation is to separate from the nitrocellulose, any foreign material or portions of the product that have not been properly pulped in the Pulping House.
After final treatment in the poacher tub, nitrocellulose, in slurry form, is discharged to either one or both vibrating Packer Screens. Nitrocellulose of the desired size passes through slots in the screen. This nitrocellulose flows as a slurry into the top of a settling tank. Any foreign matter that is heavier than nitrocellulose sinks to the bottom of the tank. The nitrocellulose slurry flows into a dewaterer where its consistency is reduced. The slurry from the dewaterer is continuously pumped to the Blending House. Any nitrocellulose that fails to pass through the Packer Screen is recovered and returned to the Pulping House to be repulped.
The purpose of the blending operation is the mechanical mixing of slurries of high grade and pyro nitrocellulose to obtain the desired ether-alcohol solubility and nitrogen content required for the manufacture of smokeless powder. The time of agitation is controlled to obtain uniform mixing whereas the consistency is controlled for uniform operation during subsequent wringing.
Nitrocellulose is pumped directly from the packer screen to a blender. The relative amounts of high grade and pyro nitrocellulose pumped to a blender are calculated in order that the final nitrogen content of the blend is 13.15± .05%. A blender is continuously decanted as it is being filled. When a blender has been filled, the consistency of the charge is adjusted to a predetermined level.
After the consistency has been adjusted, the blend is agitated for a predetermined period of time and sampled. The sample is sent to the laboratory for analysis. If the analysis shows that the blend has the desired chemical specifications, the nitrocellulose is ready for the final wringing operation. However, the failure of the blend to meet the desired nitrogen content requires that the blend be recalculated. This is necessary so that additional high grade and/or pyro nitrocellulose can be added to the blend to bring the nitrogen level within specifications. After the addition of the recalculated amounts of nitrocellulose, the blend is agitated once more and again sampled. The above procedure is followed until the desired nitrogen content has been achieved. The approved blend is continually agitated as it is pumped to the final wringers through a recirculation line.
C. Final Wringing
The purpose of final wringing is to reduce the moisture content of the nitrocellulose to within specified limits. Moisture limits are necessary (a) to re- duce the danger of nitrocellulose fires and (b) to prepare the nitrocellulose for complete dehydration.
The general principles of acid wringing may be applied to final wringing. During the wringing of a nitrocellulose blend, nitrocellulose slurry is continuously being circulated between the given blending tank and the final wringers through a recirculating line. The slurry is discharged to individual wringers from this line. A wringer is first placed on low speed for a short period of time. The slurry valve is then opened and the wringer charged. When the wringer has been charged, the flow of slurry to the wringer is stopped and the wringer is placed on high speed. Upon completion of the total wringing time, the wringer is stopped and nitrocellulose is discharged from the wringer directly into a nitrocellulose car below. When a car is filled, it is sampled for moisture content and pushed into lag storage where it remains awaiting dehydration. The water removed during wringing is pumped to an empty blender where entrained nitrocellulose is settled out and used as a heel for another blend. The excess water that is decanted off flows to a high grade saveall tank.
The samples that are taken from the nitrocellulose cars after final wringing are sent to the Sample Dryer in the Nitrocellulose Area. The Sample Dryer also receives the following samples from various locations in the Nitrocellulose Area:
1. All solubility samples
2. Final weight samples
3. Nitrogen samples
4. All stability samples
The desired tests on the above samples are either made on the nitrocellulose at the Sample Dryer or these samples are sent to the laboratories of the Technical Department for analysis.