ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Unit-Type Batch Reaction JOHN F. MILLER Dow Chemical Co., Midland, Mich.
C
HEMICAL research in the high pressure range is both interesting and inherently dangerous. No amount of gadgeteering will eliminate all hazards. There are three types of hazards usually associated with high pressure chemical reactions-thermal and chemical burns, shrapnel and flying debris, and concussion or shock resulting from a pressure blast. The batch reaction cubicles described in this paper are intended for use when the following conditions are observed: Pressures are up to 5000 atmospheres Temperatures are up to 450” C. Reactors have a volume of not more than 200 ml. Reactors must not be filled to more than one half their volume with liquids or solids Calculations must show t h a t the potential energy released, in case of the reaction going t o completion, is nithin the range of protection provided by the cubicle construction Reactors must be provided with adequate rupture frangible protection This study of cubicles was first started in order to provide greater safety to laboratory personnel. We talked to all our men, always asking the same question, “What type of a cubicle can we build that will incorporate the greatest amount of safety, simplest construction, easy operation and maintenance, and flexibility of reaction change-over?”
large Conventional-Type Cubicles
tivity for opening and closing the valves. Many valve stems and seats were damaged because of this arrangement. 3. Access t o the inside of the cubicle was very easy, and the operators had a tendency to enter the cubicle to make adjustments to the equipment while it was in operation. This was a hazard that had to be eliminated. 4. The construction of the cubicle required that elaborate piping systems be prepared for each type reaction investigated. The down time for mechanical changes soon became more than the operating time. 5. The cubicles were very dark and required an elaborate lighting and ventilating system for the mechanics and operating personnel to do an efficient job.
S tn all Conventiona I-Type Cu b ic les The second type cubicle designed and constructed was much smaller in size-7 feet long, 4 feet wide, and 8 feet high, The backs of these cubicles were covered with a sheet of clear ethylcellulose plastic which admitted natural light into the cubicle area. The fronts of the cubicles were constructed BO that entrance to the equipment area was made through a 24-inch door. One half of the door n-as mounted on each side of the frame with an overlap on the edge. The two parts of the door turned into the cubicle for opening. The remaining 2 feet of the front Tvas uqed for gage openings, valves, and electrical switches. The side n-alls and ceilings of the cubicles w i e con+uctcvl of
The first cubicles designed and constructed a t Dow, Midland, were of the conventional type-two layers of interlocking steel piling, a/g inch thick, spaced 12 inches apart on the sides and 30 inches apart on the front. The spaces between the sides and the front were filled with sand. The steel roof mas attached to the sides and front by welding. The outside of the roof was sandcovered. The back of the cubicles was enclosed with a thin sheet of ethylcellulose plastic mounted on a n-ood frame which served as a safety blowout panel. Eight feet from the blowout panel, an 18-foot-high steel barricade, backed up with sand fill, was erected t o serve as a safety wall and to stop all flying objects that result from an explosion. The reflected shock wave resulting from this barricade was far more dangerous than the advantages gained in an attempt to control flying particles. The steel barricade and sand hill were removed, allowing free movement in one direction. It should be stated that there is an unoccupied area approximately 1 mile wide by 2 miles long in back of the high pressure laboratory ( 2 ) . The inside dimensions of the cubicles were 12 feet wide, 12 feet long, and 12 feet high. The floor was made of 12 inches of concrete reinforced with steel. Access to the cubicle was from the rear through a door in the safety blowout panel. The operating control room and instrument panel were in a separate building 3 feet from the front of the cubicle area. This type of cubicle has been discontinued for small scale research for the following reasons: 1. The sand fill between the piling wa3 always damp. The corrosion on the piling became an unknown factor which caused much concern for the safety of operating personnel. 2. Long extensions on all valve stems were necessary to reach from the inside of the cubicle to the inside of the operating control room. The long valve handle extensions removed all sensi-
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Figure 1. Crash mat a t top of cubicle of all-welded construction; entire back of cubicle is a plastic blowout panel on a frame
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48, No. 5
EXTREME CONDITION PROCESSING l/c-inch thick steel plates; 2-inch pipe was used as spacers between the plates. The steel plates were raised off the floor inch, and openings were provided a t the top for free circulation of air between the sides and top plates. These cubicles were in use approximately 2 l / 2 years. We found that this type cubicle was a great improvement over the first ones built, but i t was still a long way from offering all the advantages we desired. The cubicles still required a great amount of down time for mechanical change-over from one type reaction to another. The temptation for the operating personnel to enter the cubicle while a reaction was in progress was still a problem.
Unit-Type Batch Reaction Cubicles T h e third series of cubicles designed and constructed at the high pressure laboratory has been named “unit-type batch reaction cubicles.” I n our approach to high pressure cubicle design we have taken advantage of the ballistic pendulum theory developed by Robins in 1740 ( 1 ) . The fronts of the cubicles use this principle. The tops of the cubicles are equipped with a crash m a t of steel (Figure 1). We have tried t o eliminate the possibility of flying projectiles entering the operating area by the use of all-welded construction. The apace inside each pair of cubicles is 68 inches wide, 78 inches deep, and 106 inches high. A panel 79 inches above the floor and across the top has been welded in place t o form a closed portion of the front. On each side of this panel are two 12 X 12 inch doors t h a t open into the cubicle. The purpose of these doors is t o make the final high pressure connections t o the gas lines and final connections t o the electrical circuits. The front open space is 68 inches wide and 79 inches high. Each pair of cubicles can be divided into two separate cubicles by inserting a I/4-inch steel safety panel. The side walls are constructed of */,-inch steel plates, with spacers and free air space between the walls (Figure 2 ) . Each cubicle space is equipped with the usual high pressure gas lines, such as nitrogen, hydrogen, and oxygen. Service
Figure 3.
Magna-dash mounted on portable base and front panel
facilities are also available, such as controlled electrical outlets, water, steam, and ventilating fans. The base and front panel is made of two pieces of 6-inch channel iron, covered with a plate of 1/2-inch steel, 32 inches wide, and 58 inches long. The front is made of 1/2-inch thick steel plate 32 inches wide and 72 inches long. The front is fastened t o the base by welding the bottom edges and is braced by welded tie rods from front to base. All equipment, such as mixing devices and heating units, is mounted on the base (Figure 3). Each unit is designed and equipped for a specific type of reaction. This eliminates a high degree of down time for piping and equipment change-over. Each unit (Figures 4 and 5), regardless of the type of reaction for which it is designed, can be placed in any cubicle space and the reaction conducted. The removable units are constructed in our own mechanical shop and special attention is given t o piping. The tubing lines are kept very short and, whenever possible, are placed on a slant toward the reactor t o eliminate the possibility of product holdup. Each unit that is not in use is repaired, if necessary, cleaned, and stored for future use. This permits us t o change from one type reaction t o another on a moments notice. The size was chosen so t h a t the completed unit could be transported from the shop area t o the laboratory area for loading and unloading the reactors. The unit is then transported to the cubicle area for completing the reactions; it can be taken through any door when mounted on our low hydraulic transport. Our instrument panel is of the portable type, and consists of the following units: 1. One eight-point SR-4 strip chart pressure indicator 2. One eight-point strip chart temperature recorder 3. One single-point SR-4 Dynalog 4. One single-point temperature recorder 5 . Six temperature controllers 6. A few miscellaneous instruments for very special uses
Figure 2.
May 1956
Empty cubicle with removable safety panel separator in place
T h e instruments are connected to the units by flexible twist lock receptacles.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Figure 4.
Portable panel in place in one cubicle
Safety and Operational Features The unit-type batch reaction cubicles were designed with the following features of equal. importance. Safety. The danger of chemical and thermal burns has been minimized by the availability of extra spaces. There is no need to remove the reactor before the temperature and pressure have been reduced t’o normal. The gas and electrical connections must be removed before the front panel can be withdran-n for entrance into the cubicle area. Each cubicle space is equipped with a carbon dioxide extinguisher system. The operating group has always realized the hazard involved in entering a cubicle during the progress of a chemical reaction. At times the temptation to enter the cubicle and make a minor adjustment was too great. ‘We removed the possibility of entering the cubicle by eliminating the doors. No attempt t o confine the explosion resulting from an uncontrolled reaction has been made. An attempt has been made to direct the explosion shock waves toward a blowout mall. This wall is. in effect, the entire back of the cubicle space and is constructed of an angle-iron frame covered with a 5-mil thick transparent ethylcellulose plastic material. Experience with chemical explosions has indicated that the reactors usually will rupture but not break into fragments. The shrapnel more often comes from the u w of hardened or brittle hold-down rings and caps, To minimize this effect, the reactors are always placed close to the blow out wall in the cubicle. Tubing, valves, fittings, and like accessories are carefully selected t o m-ithstand much higher pressures than those specihed for the reactor. Liberal use is made of safety blowout units, and new disks are installed after a limited number of runs. A complete history is kept of each reactor. The reactor must pass a series of rigid inspection tests at regular intervals including a pressure test of one and one half times its rated working pressure. Controlled explosions of various sizes show that the front panel has a pendulum effect, The panel is fastened rigidly only a t the top; the base is held down by its own weight and the equipment installed on it.
am
Figure 5.
Portable panels in place in two cubicles
This pendulum is four times more effective in controlling an explosion than rigid-wall construction ( 1j. Each reaction includes the same routine: Job safety instruction to all personnel, equipment inspection, and a discussion of all hazards involved. Ease of Construction and Maintenance. The mechanical group has free access t o all sides of the equipment. Assembly and repair of the units take place in the shop area where all tools and machine shop facilities are available. Ease of Loading and Unloading Reactors. The units can be taken to the laboratory where proppr facilities are available for handling the products and residues. Portability of Batch Reaction Units. The relation of the reaction unit to the cubicle area is such that flexibility of operation is greatly increased. Any unit n-ill fit into any cubicle area, no changes of equipment are involved. ilt the time the unit is no longer in use it is removed to the storage area intact. Better Utilization of High Pressure Equipment and Xnstruments. The same instruments can be used for all types of reactions in all cubicles. JTe have eliminated the need for duplication of instruments in many cases. The instruments are disconnected after the reaction is completed and then connected to another unit that is in the cubicle and ready for use. We do not consider our cubicles as perfect; no doubt other types are possible that would provide great advantagcs. Continued use of the unit-type batch reaction cubicles has helped t o pinpoint the advantages and limitations of our approach to high pressure research ( 2 ) . ,
Literature Cited
(1) Anderson, 0. L., Newhall, D. H., “Safety Problems Associated with High Pressure Equipment,” unpublished. (2) Savage, R. L., “Laboratory Design,” chapt. o n High Pressure
Laboratories, Rational Research Council Washington, D. C.; Report on design, construction, and equipment of laboratories, Reinhold, New York, 1951.
RECBIVED for review October 13, 1955.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ACCEPTED M a r c h 21, 1956.
voi. 48, NO. 5
