liquid Propellant Handling, ransfer, a PAUL M. TERLlZZll AND HOWARD STREIM
U. S.
Naval Air Rocket Test Sfation, Dover, N. J .
This article summarizes some important phases of liquid propellant handling, transfer, and storage problems, and the need for increased effort b y the chemical industry in keeping informed o f developments applicable to more efficient propellant handling, Phases discussed include: quality control, transfer operations, personnel protection, disposal and decontamination, fire fighting, and materials of construction.
HE increasing interest, both military and civilian, in the field of liquid propellants, has catapulted many new or modified chemicals into promising futures. Propellants as discussed in this paper are not necessarily limited t o guided missiles, but are very important chemicals in the efficient utilization of the rocket propulsion principle for a variety of applications. These applications range from the widely discussed use of propelling vehicles to outer space t o the assisted take-off of a heavily loaded modern airplane. Whatever the application, the chemical industry with its manufacturing, handling, transfer, and storage experience will be called upon to include many nerv or modified chemicals for propellant use in its product testing. Liquid propellants are divided into three classes-fuels, oxidizers, and monopropellants, In the majority of propulsion systems a bipropellant combination, both a fuel and an oxidizer, is utilized, whereas in a majority of gas generator systems a monopropellant, a single liquid or mixture of substances containing all necessary elements for release of energy, is employed. I n a bipropellant system the fuel and oxidizer are permitted to come together under high pressures in a combustion chamber, where by means of a selected ignition system, a chemical reaction occurs. Energy developed in the reaction is released by expansion through a nozzle. A monopropellant system operates in the same manner except that only one propellant is required, thus simplifying component requirements. Theoretically, the most effective fuel component is hydrogen and the most effective oxidizer component is oxygen or fluorine. In view of the particular disadvantages of handling these components for selected applications (liquefied gas characteristics of hydrogen and fluorine and special liquid oxygen handling equipment), chemicals were needed and sought t h a t could carry these desirable components in large quantities in their structure, yet have more desirable logistic and storage characteristics. This need, therefore, opened a field for a variety of heretofore little kno.ivn potential uses for certain chemicals. I n the variety of uses are propellants in the class of fuels-liquid ammonia, ethyl alcohol, aniline mixtures, hydrazines, hydrogen, and various petroleum products and derivatives-in the class of oxidizers -liquid oxygen, fuming nitric acids, fluorine, chlorine trifluoride, ozone and ozone-oxygen mixtures, and concentrated hydrogen peroxide-and in t h e class of monopropellants-ethylene oxide, hydrazine, hydrogen peroxide, and nitromethane. As seen, hydrazine and hydrogen peroxide can be utilized as a fuel and oxidizer, respectively, as well as a monopropellant. 1
Present address, Stauffer Chemical Co., 380 Madison Ave., New York
17, N. Y .
174
Although the propellants appear to be familiar in name, the concentrations used in many cases negate the usefulness of available handling, transfer, storage, shipping, and hazard data nornially considered acceptable for lorver concentrations. Ammonia, alcohols, aniline, ethylene oxide, and petroleum derivable-type propellants are comparatively well known niaterials insofar as their chemical characteristics are concerned; however, the folloTving propellants are not yet listed as industrial chemicals, and a review of t.heir characteristics appears necessary.
Characteristics of Propellants Puniing Nitric Acids. This class of acids with nitrogen dioxide cont,ents up to 20% are highly corrosive oxidizing agents. They react with most organic materials, often violently enough t o cause fire. These acids also react, mith sea water and attack most metals, particularly iron, copper, and their alloys. Evcn stainless steel, aluminum, and some plastics are attacked s l o ~ l y . To reduce corrosivity, as well as to impart more desirable ignitioil and stability characteristics to the acids, inhibitors are used. Chlorine Trifluoride. Chlorine trifluoride is a colorlees, highly reactive gas a t room temperature (melting point, -83" C.; boiling point, 11' C.). I t is one of the most reactive substances known, second only in its behavior to elemental fluorinc. Possessing a pungent odor similar to chlorine or mustard, chlorine trifluoride is corrosive in nature. It reacts with atmospheric. nioisture and with most organic and all aqueous solvents. I t also attacks glass, asbestos, and occasionally ignites Tefion. Chlorine trifluoride is a highly toxic material. The liquid, greenish yellom. in color, is more active chemically than the ga.8. Because of formation of a passivating fluoride film, chlorinc trifluoride may be stored and handled in the common metals. Such metals as copper, brass, steel, magnesium, monel, or nickel are satisfactory, but 18-8 stainless steel, nickel, and monel arc preferred. Soft copper and Teflon impregnaCed with 40% calcium fluoride are acceptable gasket materials. Ethylene Oxide. Ethylene oxide, a colorless liquid, boils a t 10.7' C. It is a gas a t room temperature, freezes a t -111.3" C., and has a characteristic ethereal odor that is irritating in high concentrations. I n air it forms explosive mixtures a t all concentrations from 37, ethylene oxide and above. It is a highly reactive compound and reacts with water, alcohols, amines, and organic and mineral acids. Ethylene oxide may be shipped in cylinders as prescribed for any compressed gas except acetylene. At present ethylene oxide is shipped in tank cars and in special 55-gallon drums. Nitromethane. Nitromethane, a st,ram-colored liquid boiling a t 101.2" C. and freezing a t -20" C., has a density of 1.12 and
INDUSTRIAL AND ENGINEERING CHEMISTRY
VoI. 48,No. 4
ROCKET PROPELLANTS a n acetic odor. If unconfined, it burns with a quiet flame; however, if confined in a strong container and brought to temperatures of 260” C. and above, a detonation will occur. The compound may be stored in mild steel drums that are sprayed in the interior x i t h a plastic coating. Hydrazines. The hydrazine family of propellants include the compounds hydrazine (N2H4)and unsymmetrical dimethylhydrazine [( CH&NNH2] of concentration above 95%. These compounds are strong reducing agents. All are flammable, absorb carbon dioxide from air, and all undergo spontaneous oxidation with oxygen in air. Contact with metallic oxides such as iron, copper, lead, and molybdenum can cause hydrazine t o ignite. Hydrogen Peroxide. Highly concentrated hydrogen peroxide is a very reactive oxidizing agent and an energy rich material which decomposes exothermically. When concentrated it reacts vigorously on contact with many inorganic compounds, such as potassium, permanganate aiid ferrous sulfate, and with many organic compounds, such as hydrazines, carbonyls, and phenolics. I t s decomposition is catalyzed rapidly by many substances, such as oxides of manganese, cobalt, lead, and silver, and by metals, such as platinum, silver, lead, mercury, manganese, cobalt, and others. Freely miscible with water, 90% hydrogen peroxide has a boiling point of 286” F. and a freezing point of 12.6” F. I n suitable containers free of contaminants, hydrogen peroxide can be kept for long periods of time. The foregoing sentence means more in the case of hydrogen peroxide than it would mean in acid or fuel storage. For example, a container of 1-gallon capacity, made of stainless steel, with attendant tubing, valves, etc., requires the following operations t o render it suitable for hydrogen peroxide use (“passivation”): The unit must be disassembled completely, degreased by agitating in a 1% detergent solution, and scrubbed in all areas with a stiff brush. All parts must be flushed with fresh water, immersed in 75% nitric acid solution for 4 t o 5 hours a t room temperature] and rinsed with distilled water. Then all parts must be conditioned with 35% hydrogen peroxide for 3 t o 4 hours and the rate of decomposition, if any, noted. If excessive decomposition is observed-i.e., if bubbles or gas “streamers” are seen-or heating of the part or hydrogen peroxide occurs, the part should be removed and cleaned again. The parts that pass the conditioning tests are removed from t h e 35% hydrogen peroxide solution, rinsed with distilled water, and inspected. Finally, the parts must be air- or oven-dried (if no plastic inserts or parts are present) and the unit reassembled. The assembled unit is packed in polyethylene or vinyl bags and marked t o indicate that it has been passivated. The sealed package must not be broken until the unit is ready for installation Handling, Transfer, and Storage Fairly complete handling, storage, and shipping data are available for a variety of chemicals used daily in industry. This information was developed through experience in handling thousands of tons of a product. By contrast, in the propellant field there is no time t o wait for this experience to be developed as a result of daily use. If a new propellant is developed, the chances are that a quantity of less than 10,000 gallons would be required for complete testing prior t o rejection or acceptance of a system. It is imperative that data on new propellants be developed as soon as possible and relayed into the evaluation system so that the potential use of the propellant can best be judged. Data considered of primary importance in the handling, transfer, storage, and shipping of liquid propellants include quality April 1956
control, transfer operations, personnel protection, disposal and decontamination, fire fighting] and materials of construction. Quality Control. I n liquid propellant work, quality control ends only when the propellant is loaded in the rocket, or other system, and is ready for use. This is necessary because the maximum efficiency of the reaction principle of chosen propellants for a selected application depends upon the reproducibility of its experimental characteristics in the field. This requires that field analysis methods be developed which enable handling crews, normally without the benefit of scientific training or facilities for detailed testing, to run quality control checks on propellants. Therefore, the use of simple techniques performed by instruments which can be carried about by one man are most desirable. Chemical control of propellants in the field is not always limited t o analysis. I n some cases ignition tests must be made in order t o ensure that no ignition delay results once the propellant system is ready for use. Transfer Operations. Transfer operations in principle are no different in the field of liquid propellant than in handling bulk chemicals in processing operations. Notable differences are that some liquid propellants possess high corrosivity, are extremely toxic, and sometimes react vigorously with water and air. Further, contamination by metallic or other impurities must be avoided, because in many cases they affect the propellant system performance. Effort is being applied to the development of a red fuming nitric acid tank trailer unit capable of storing, transferring, and metering acid deliveries in the field. Considerable effort is required in the development of flexible, compatible leakproof transfer hose, satisfactory pump gland packings, and automatic shutoff controls; in the installation of safety showers and personnel protective devices in the trailer-heating equipment for transfer operation in cold climates, preselected filling and metering devices, and safety controls; and in the inclusion of quality control equipment, special pumps, screens or filters, and equipment that is corrosionproof in the interior and on the exterior. An important problem is the remote control of transfer operations which will avoid personnel injury; however, effort is being put into this trailer development both by industrial and by government activities. Underground storage plays a n important part in propellant transfer operations. As test activity in the guided missile field increases, larger quantities of propellants will be used and will require ready storage near point of utilization. The most logical place, and that which will avoid hazards t o nearby personnel and equipment, is underground storage with each tank having its own special pumping, transfer, and related equipment. However, before such systems can be utilized efficiently, the development of proper pumping equipment and piping and transfer techniques is needed. This provides a n interesting challenge to materials handling personnel. Disposal and Decontamination. One very important advantage of locating liquid propellant testing facilities in desert areas is that the disposal problem is almost nil. However, not all testing can be handled a t such remote locations. Therefore, the disposal of highly reactive, corrosive, and toxic propellants becomes a problem in most areas. At the present, disposal of waste liquid propellants can be handled by burning in special furnaces (such as disposal of aniline fuels by burning with Diesel oil in a special furnace) ; neutralizing the acids and disposing of the solutions in the sea or distributing them to farmers for fertilizer; subjecting containers of materials to gunfire in order t o explode the contents or initiate rapid decomposition; and deposil ing waste propellants a t sea. Little effort has been directed to the decontamination and disposal of liquid propellants as the interest in propellant selection changes often. However, as several propellants are now actively being considered as “work horse” propellants a less haphazard approach t o the disposal problem must be made. Personnel Protection. The introduction of specialized fuels
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
175
and unconventional propellants for use in aeronautical, ordnance, and shipboard applications has created a need for new materials and designs in clothing which will protect personnel handling such propellants. Protective clothing includes such items as outer body coverings, foot and face shields, gloves, boots, shoes, and undergarments where required. The evaluation of protective clothing is made in laboratory and field tests. The laboratory tests determine compatibility, permeability, electrostatic characteristics, flammability, etc., on various materials, whereas field tests determine comfort (freedom of movement, design, closures, etc.), life (useful period), adaptability t o particular operation (propellant transfers, engine adjustments, flight controls, temperature, humidity conditions, etc.), easy removal in the event of emergencies, and such other special tests as may be required. For the majority of liquid propellant work the protective clothing consists of one of two types. One type is a glass fabric treated with vinyl plastic and used by some military installations in guided missile propellant programs. Changes in the design of the fabric are under way to improve the comfort of this type of clothing. Another type is a commercial design used often in test area work where short term exposure, less than 15 minutes, is involved. Recently the Bureau of Aeronautics required the use of specialized protective clothing for flight and field testing of a new aeronautical device. The propellant to be utilized was 90% hydrogen peroxide. I n view of the many manipulations required in its use and the fact that hydrogen peroxide is generally noncompatible with many known fabrics and coatings, 100% Dacron, a material which showed sufficient compatibility with 90% hvdrogen peroxide, was employed. During the use of this protective clothing in propellant operations heavy electrostatic discharges were experienced, suggesting that such discharges might prove hazardous in the presence of aviation fuels. A detailed search of the literature and discussions with manufacturers in the field indicated that the testile industry has long been aware of electrostatic charge built up on synthetic fibers, These data indicated that Dacron retains its electrostatic charge indefinitely (under certain humidity conditions), whereas other synthetic fibers, such as Orlon and nylon, dissipate their charge gradually. However, Orlon and nylon were not suitable for work with hydrogen peroxide. Steps have been taken in the textile industry to reduce charge accumulation by using ionization techniques, controlled humidity conditions, etc., but these steps cannot be utilized in liquid propellant applications. The most effective method of reducing electrostatic charge buildup in protective clothing applications is the employment of antistatic compounds. These provide a conducting surface to the fabric, thereby permitting redistribution and decreased intensity of the accumulated charge. I n addition t o the antistatic property, the antistatic compound must be compatible with 90% hydrogen peroxide and must not impart any undesirable characteristics t o the basic fabric, such as making it stiff, adding to its flammability, and affecting the skin of the wearer. The requirements for protective clothing are divided in three categories-hand and foot protection, head, face, and body protection, and respiratory protection. The hands and feet are always subject to liquid contamination during handling of propellants or propellant equipment, Therefore, impermeable gloves and boots should always be worn. The selection of a protective glove should depend on protection against the acid or other propellant and ease of finger manipulation. Boots of any of the preferable protective materials are not manufactured commercially; therefore, a n overboot, designed to be worn over regular safety footwear and high enough to fit comfortably under the cuff of the protective trousers, should be selected. Katural, reclaimed, or GR-S rubber boots may be used with reasonable safety provided contaminating agents are removed promptly and frequent inspections of the boots are made. For the head, face, and body protective clothing covered by
776
Specification MIL-S-4553 ( USA4F)(suit protective, acid resistant, vinyl-coated glass fiber) and Specification MIL-S-12527 (QMC) (suit protective, acid and fuel resistant) can be used. Polyethylene clothing is superior t o rubberized clothing items because rubberized clothing in some instances burns on contact with nitric acid. Glass fiber clothing impregnated with acidresisting plastics, such as Teflon and Kel-F, is excellent for acid handling. Vinyl-coated dyne1 or Dacron is acceptable also. I n all cases, the clothing selected must cover all exposed parts of the operator's body and be adjusted so as t o eliminate any possibility of drainage into the gloves or boots. Goggles and face shields only are not adequate. .4 hood t h a t covers the head and shoulders is required. For respiratory protection against acid vapors under controlled outdoor operating conditions the E1R3 or M9 combat gas mask, the M4Al-10A1-6 service gas mask, or the (Mine Safety Appliance Co.) industrial gas mask with a General Motors Corp. canister (for organic vapors and acid gases) may be used. However, no gas mask should be relied upon for protection against vapors of fuming nitric acid under emergency conditions or in confined areas. Under such conditions the Scott Air Pak or similar apparatus, or supplied air respirators should be used. Use of respiratory equipment for both fuel and oxidizer operations should be prohibited. Fire Fighting. Because some liquid propellants react with air, organic materials, and water, the techniques for fighting fires involving liquid propellants must be examined critically. Water and carbon dioxide are two of the primary fire-fighting agents; however, the use of nater in a fire involving chlorine trifluoride or fluorine would be disastrous. 9 fire involving nitromethane, a monopropellant, would not be extinguished by either water or carbon dioxide alone. Studies are now under way t o determine the best fire-fighting techniques as well as extinguishing agents for each propellant or combination of propellants. Storage. There are tn.0 types of storage areas in storage facilities for liquid propellants-the main storage area where large quantities of propellants not in immediate use are stored, and the ready storage area TT-here smaller quantities of propellants and materials for scheduled test operations and immediate use are stored. Structural framework of all storage buildings should be steel or masonry and should not contain any mood. Sidings of brick, plaster, tile, corrugated sheet asbestos, aluminum, or steel, with proper protective coatings, are recommended. Roofs of such materials as slate, shingles, corrugated sheet asbestos, aluminum, or asbestos shingles should be used. Conventional petroleumbase roofing materials are prohibited. Wooden or rubberized floors are also prohibited. Floors should be made of concrete, and all electric wires should be installed in rigid conduits. Materials of Construction. Stainless steel and aluminum are predominately employed in liquid propellant handling, transfer, and storage operations, because of their excellent corrosion resistance. However, in some applications considered these metals are undesirable, because of the possible contamination of propellants with metallic ions of aluminum, iron, molybdenum, etc., during long term storage periods. The use of additives in various propellants for freezing point depression or corrosion inhibition may sometimes affect the container material by imparting undesirable characteristics to the propellant, such as delayed ignition, clogging of filters by particles, burning out of chambers by solids in propellants caking out on chamber walls during regenerative cooling process, and other special conditions. i lstudy conducted a t the Kava1 Air Rocket Test Station showed that for short term storage of highly corrosive nitric acid oxidizers (up t o 6 months), plastics (Kcl-F, Teflon, Fluorothene, etc.) can he used in a variety of forms as a barrier between the corrosive propellant and a metal backing which is not necessarily stainlcss stecl or aluminum. Sprayed plastic coatings are inferior to plastic sheet bonded t o metal, but the limitations of design
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48 No. 4
ROCKET PROPELLANTS prevent use of this construction in other than simple fabrications. Deep drawing or the use of drum-manufacturing techniques is completely unsatisfactory for plastic t o metal-bonded fabrications. Advances in the field of reinforced plastic show promise of the availability of lightweight, corrosion-resistant plastic constructions useful for tank trailers, underground storage tanks, and pressurized propellant tanks. Ceramic-coated metals are resistant t o a variety of liquid propellants, but their fabrication into intricate shapes, such as propellant tanks, liners, valves, etc., are impractical. However, ceramic coatings (enamel) on metals used extensively in industrial chemical process work is generally satisfactory for long term storage if imperfections, such as pin holes, can be eliminated. Ceramic coatings cannot be applied t o containers that have small openings, as propellant tanks in aeronautical applications. There are many other probleme connected with liquid propellant handling, transfer, and storage that cannot be discussed
in a general paper of this nature, but they should be mentioned. These include shipping, packing, and marking requirements, procedures t o be employed in the event of shipping and transfer accidents, and classification of new propellants as explosives, flammable liquids, compressed gases, etc. I n order to provide up-to-date information on liquid propellant handling, transfer, and storage, a working group consisting of representatives of Armed Services agencies has been formed. This group, Liquid Propellant Safety Regulations Working Group under the direction of the Naval Air Rocket Test Station, is assembling information on liquid propellants employed in aeronautical, ordnance, and shipboard application. The information includes general properties, hazards (health, fire, explosion), safe handling, transfer techniques (containers), material and equipment, test area, decontamination, storage, shipping, and safety bills. RECEIVED for review September 23, 1955.
ACCEPTEDJanuary 31, 1856.
I
4.
6
Configurations of fluid jets used in liquid propellant injector heads: (1) Unlike impinging (2) Like-on-like impinging (3) Nonimpinging (showerhead) (4) Splash plate (5) Mix plate (Enzian) (6) Converging-diverging cones (7) Intersecting cones and jets (V-2 Rosette) with 0 2 in center (8) Premix (9)Coaxial
(The drawings of jets used in liquid propellant injector heads and a number of photographs included in the symposium on rocket propellants are reprinted from the 25th Anniversary issue (November 1955) of Jet Propulsion, the journal of the American Rocket Society.)
END OF SYMPOSIUM April 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
-
77
