Document N2bYDOMKdbLeZ9eX8aM7JD8xV

--f Monsanto Chem)cai,s-Plastics .... K4__ AN INDIRECT AROCLOR HEATER for UNIT CHEMICAL OPERATIONS Monsonto Technical Bulletin No. P-130 September, 1949 Monsanto Chemical Company St. Louis (4), Missouri Aroclor* 1248 (chlorinated biphenyl) is an ideal nonflammable liquid phase heat-transfer medium for temperatures up to 300C. This bulletin describes the physical properties of ArocJor 1248 and illustrates the design and operation of heaters that have been used successfully by Monsanto plants during the past seven years. The units described are gas fired and the capacities are in the range of 200,000 to 400,000 B.t.u, per hour. Other larger commercial installations using Aroclor 1248 have capac ities ranging up to 2,000,000 B.t.u. per hour. Also small electrically heated stationary and portable units with capac ities around 40,000 B.t.u. per hour,using Aroclor 1248 as the heattransfer medium,are in service. Several leading manufacturers of heating equipment are in position to build or offer Aroclor heating units to meet specific requirements. > z i1 TO o > 0> Jo r o r; "O o m x >m H> OH Z5 O TO I Monsanto Technical B u lle tin No. P-130 September, 1949 Reg. U. S. Pet. Office The information contained In thla bulletin la, to our beal knowledge, true and accurate, bul all recommendation* or auggeallona are mede without guarantee, alnce the condition* of u*e are beyond our control. The Mon.anlo Chemical Company dlerlalrri* any liability incurred in connection wilh the uee of theae data or suggestion*. Furthermore, nothing contained herein (hall be construed a* a recommendation to uee any product in conflict with aiellng patent* covering any materia! or ita uae, 0508730 TOWOLDMONOQ34293 Reprinted from INDUSTRIAL AND ENGINEERING CHEMISTRY, Vo). 41, Page 1341, July 1949 Copyright 1949 by the American Chemical Society and reprinted by permission of the copyright owner Aii Indirect Aroclor Heater for Unit Chemical Operations MEADE McARIJLE1, L. C. GARKETT, AND P. G. BENIGNUS* Monsanto Chemical Comjmny, Anniston, Ala. The characteristics of Aroclor 1248 indicate that it Sprat Flammabiutt. When a tube ruptures in a liquid heat- is an ideal liqnii' phase heat-exchange medium for transfer system under high pressure, a spray or mist forms. temperatures up to 300 C. This article discusses its The possible fire hazard under those conditions requires considera properties and illustrates the design and operation of tions not covered by the foregoing discussions relative to the ma heaters that have been used successfully l>y Monsanto terial in the liquid form. In their comprehensive study of plants during the past seven years. flammability of the higher boiling liquids and tboir mists, Sulli van, Wolfe, and Zisman (3) determined tho spray flammability N CERTAIN manufacturing processes of the Monsanto limit of numerous materials in accordance with the percentage of I Chemical Company, it was necessary to employ a noncom- oxygen required for combustion. This value was then correlated buslible boat-transfer medium at pressures of 80 pounds per with the results of incendiary firing teste of the fluids conducted square inch or loss and temperatures up to 300 C. The following at the Naval Proving Ground, Dahlgren, Va, The oxygen re general properties of a hcat-cxchangc medium were required: quirement for Aroclor 1248 combustion in the spray flammability Freedom from fire hazards. Viscosities to permit pumping at room temperatures. Roiling point sufficiently above 300 C. to assure a liquid con dition at el) times. Stability against heat, with enough safety factor to accommo date accidental overheating. Controllable vaporization losses. Freedom from corrosive action against valves, piping, lank jackets, etc., made of cast iron and steels, bronze, and stainless steel. Freedom from toxicity hazard. limit studies was found to be 04%. Fluids requiring over 45 to 50% oxygen in the spray test failed to cause a fire in the incendiury test. These results establish the nonflammable and noncombusliblc qualities of Aroclor 1248. VISCOSITY CONSIDERATIONS Cold Flow'. For most inside installations centrifugal pumps will handle Aroclor at reduced rates without preheating. Experi ence confirms this. Outside installations have been started at Aroclor, chlorinated biphenyl (registered in l). S. Patent 0 C. by heating the pump and feed line until circulation through Office), was selected. The pertinent physical characteristics relative to its use ns a heat-transfer medium are given in Table I. Table I. Physical Properties of Aroclor 1248 FKKKl>OM FROM FIRK HAZARDS Fi.ash Point. Limitations of this test for the prediction of the fire hazard of relatively nonvolatile organic fluids have been recognized by the American Society for Testing Materials com mittee (3, 4). Fire Point is a more significant, measurement. The Under writers' Laboratories (10) state that fire tests more truly reflect the (lack of) fire hazard of Aroclor. Spontaneous Ionition Temperature. The combustionresisting qualities of Aroclor 1248 are indicated by its high spon taneous ignition temperature of 704 C. (1299 F.) determined by Sullivan, Wolfe, and Zisman (9), using the convenient apparatus described by Sorlman, Beatty, and Heron (8). Under conditions of industrial use the spontaneous ignition temperature will be determined by factors including the nature of the hot surface, the amount of liquid impinging on it, the volume of enclosod space, and the ventilation. Absolute density. Absolute viscosity, centij>oise Distillation range, A.8.T.M, D-20, 0 C. Practically colorless mobile liquid *C. <?.> 1.44 1.41 1.37 1.27 1.17 (30) (140) 212) 80 (86) 60 (140) 100 (212) 0.0613 0.0698 0.0800 (80) (140) (212) Fnire ppooint, Cleveland open cup, A.S.T.M. D 92- Pour point, A.S.T.M. D-7, 0 C. An accidental failure in a heating system demonstrated the nonflammability of Aroclor 1248 and its freedom from the hazard of fire propagation. An operator's failure to start the circulation of the heat-transfer medium when the gas heater was on resulted in excessive coil temperatures and caused the lower coil to soften and sag into the fire chamber. A weld ruptured and Aroclor 1248 poured into the red-hot fire chamber in contact with the flame. Denser smoke arose from the heater but there was no external fire. After the gas flame was cut off, the smoking stopped. Present address, Monsanto Chemical Company, Organic Chemicals Division, Bt. Louis, Mo. 1 Present address, Monsanto Chemical Company, Phosphate Division, (. Louis, Mo. Specific volume, ml./g. Specific heat, cal./g./ C. Vapor pressure, mm. Hg 0.690 0.709 0.728 0.787 0.860 0.383 0.3*7 0.338 0.366 0.00037 (86) 140) !212) 392) 672) (SIS' <3*31 1613) 87.8 (100) (212) (302) (892) (672) osoam TOWOLDMONOQ34294 1342 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Table II. Stability or Aboclor 1248 Heated fob 30 Hours Mt- of RCI per Gram of Aroelor 280 0.079 800 0 180 310 0.199 820 0.222 830 0.248 Table III. Stability or Aroclor 1248 Continuously Heated at 280 and 330 C. Hour* Mg. of HCI per Gram of Aroolor 2804 C 330* C. 0.079 0.116 0.169 0 194 0.261 0.248 0.610 0.923 1.141 1.862 Table IV. Gas Analysis or Aroclor 1248 Heated 4 Hours at 260 C. and 210 Pounds per Square Inch Pressure Gai Carbon dioxide Carbon monoxide Oxygen (derived from air) Methane Hydrogen e Cklorine Aeidtty (% by weight HCI) Prior to expoeure After expoeure % None None 20.2 0.2 None None the hosier had been effected so that the system could operate normally. BOILING POINT Operating experience has shown that the boiling point of Aro clor 1248 (340 C. at 760 mm.) is enough above the 300 C. operating limit to prevent trouble from this cause. At the maxi mum operating temperature the vapor pressure is less than 0.5 atmosphere. HEAT STABILITY In order to establish a maximum practical operating tempera ture, the stability of the material when heated to elevated tem peratures in the presence of iron was noted. A slow stream of nitrogen was passed over the hot Aroclor to sweep the decom position products into a caustic trap. The amount of acidic material was determined and calculated as hydrochloric acid. The results given in Table II indicate the stability of Aroclor 1248 when individual samples were heated for 30 hours at the given **mperatures. The decom position is very low at temperatures up to 300 C. The stability of Aroclor 1248 in contact with L iron continuously heated at 280 and 330 C. is indicated by Table III. These test results indi cate that Aroclor 1248 in con tact with iron can be used satisfactorily at temperatures up to 800 C. The National Board of Fire Underwriters (10) reported that "decomposition of the product [Aroclor 1248} was not appreci able at temperatures below 400 C., but beoame increas ingly apparent at higher tem peratures." Their workers analysed the decomposition products of Aroolor 1248 heated in the pres ence of hot iron at 459 C. and also heated in an iron cylinder at 340 C. fitted with an internal gas burner so that the gas flame impinged directly on the surface of the Aroclor. Analysis of the gases produced under these conditions included 0.6% carbon monoxide, 0.17% oxygen (derived from the air). 0.99% hydrogen ohloridc, 2.1% combustible gas calculated as methane, 0.002% chlorine, and no phosgene. The same workers studied the stability of Aroclor when heated for 4 hours in an iron pipe at 260 C. under an internal pressure of 210 pounds per sauare inch', resulting from the introduction of compressed air. Following this treatment and cooling, the cases removed from the system wore analysed. The acidity of the Aroclor was determined prior to and after exposure to these con ditions. The results given in Table IV reflect an extremely small amount of decomposition under conditions similar to those selected for tbs practical use of Aroclor 1248 as a heat-transfer medium. In actual practice using the type of heating unit described below there has been no evidence of hydrochloric acid effect and no car bon deposits have been noted in the heater, pipes, or valves. The heaters have been operated successfully with combustion gases at approximately 600 C. in contact with the coils. At one time, a spiral coil type of heater was built and through faulty design a burner tunnel was located 1.5 inches from the 2inch steel pipe coil. The radiation from the white-hot refractory tunnel and the direct impingement of the flame on the pipe caused the pipe to glow a dark rea for a space of about 2 inches. This unit was operated almost 3 months before a circulation stoppage occurred. When the line was opened lumps of carbon were found to have come loose and moved forward to lodge in the globe valves. The lumps measured about 1 X 2.5 cm. and one face was formed to fit the pipe curvature. No hydrochloric acid effect was noted and the system was put back into operation after the burner location was changed, CONTROLLABLE VAPORIZATION LOSSES The heating systems in which Aroclor 1248 is used are sealed except for the expansion tank, which has a loose cover or a vent pipe. Because this tank is separated from the stream by a sub stantial length of pipe, the temperature in the tank remains low. In the light of the relatively low vapor pressure values for Aroclor 1248 (7), and as it is unlikely that the expansion tank will ever reach even the 1-mm. state (130 C.), there should not be a measurable loss of Aroclor from the system. Actual experience bears out this contention. Other Losses. Although Aroclor darkens on use, its charac teristics remain the same and replacement has not been found necessary after 7 years of continuous use. Accidental leaks or spills constitute the only observed losses. PLAN AND PART SECTION B f J Figure 1. Heater 0S08711 TOWOLDMONOQ34295 uly 1949 INDUSTRIAL AMD ENGINEERING CHEMISTRY 1343 Table V. Resistance or Structural Materials to Aroclor 1248 AlumlDum Copper MkBDesluru Nickel Silver Tio K Metals Zinc Mild eleel Pliosplior bronte Red braes Stainless steel Yellow brass R 125 C. R Re RR. Excellent resistance, lees tbau 1.0 X 10-4 i. per day penetration or 0.00014 Inch per year. R. Good resistance, penetration between 1.0 X 10** and 10 X 10"* cm, per day or between 0.00014 and 0.0014 inoh per year. D. Doubtful resistance, penetration between 10 X 10** cm. per day and 100 X 10cm. per day or between 0.0014 end 0.014 inch per year. e. Following letter indicating resistance, signides material may be baiter than Indicated if totally immersed, as weight loss is believed to come from oxjdatlon of part of test strip exposed to eir. DESIGN AND CONSTRUCTION Heating System. The heating system required to utilize Aroclor 1248 as the exchange medium includes a heater (Figure 1), cooler, pump, and expansion tank (Figure 2), and control and safety circuits (Figure 3). - FREEDOM FROM CORROSIVE ACTION The resistance of various metals (7) at 25 and 125 C. is given in Table V. Similar studies made at 325 C. (6) indicate that the penetra tion, in inches per year, for mild steel is 0.0028; for yellow brass, 0.00047; for copper, 0.00145. Many years of practical operating experience with Aroclor 1248 as a heat-transfer medium have shown that the material is prac tically noncorrosive to valves, piping, tank jackets, etc., made of cast iron and steels, bronze, and stainless steel. FKKEIKIM FROM TOXICITY HAZARD Aroclor 1248 is a very stable, unreactive liquid. If the material is spilled on the skin, there are no noticeable ill effects; however, it is well to wash the skin with soap and water after contact. A skin burn resulting from accidental contact with hot Aroclor should be treated in the normal procedure used for hot oil burns. Aroclor adhering to the burnod area need not be removed im mediately unless treatment of the burn demands it; in this case soap and water or repeated washings with a vegetable oil (linseed oil) should be used. The vapors emitted by Aroclor 1248 heated to elevated tem peratures are injurious to the liver on prolonged exposure and should uol be breathed. Drinker (5) indicated that 0.5 mg. of Aroclor 1248 per cubic meter of air is the maximum safe amount permissible in workrooms. In commercial heat-transfer installations, the presumption is that the Aroclor is in a closed system free from leaks. Accord ingly, there should be no opportunity for workers to come in con tact with vapors from the hot heat-transfer medium. Heater Design. The general requirements of the heater are compactness, ease of construction and service, and avoidance of direct flame impingement on the tubes. Direct flame impingement is prevented by directing the gas flame through an enclosed channel with half-thickness fire brick protecting the tubes above until the high temperature of the flame is reduced bv heat conducted through these bricks and radiated to the two bottom coils. The size of the heater is reduced to a minimum by using only 4.5 inches of insulating fire brick in the hottest areas and 2 inches of Eagle No. 66 insulation on the cooler spots. Two sizes of units are used: One has a maximum capacity of 200,000 B.t.u. per hour, as shown in Figure 1. The larger has a range of 200,000 to 400,000 B.t.u- The small size consists of 90 feet of 1-incli standard weight steel pipe made into three coils of six pipes each and connected in series. The larger size consists of 144 feet of 1.5-inch standard weight steel pipe arranged in the same fashion. Results of tesla on the small-size heater covering temperatures from 150 to 300 C. show temperature rises to 10 to 20 C. in the Aroclor while circulating at a rate of 15 to 20 gallons per minute. The outlet gas temperature is consistently within 75 C. of the outlet Aroclor temperature. It is observed that the bottom two coils ab sorb the major part of the heat. The small unit indicates 50 to 60% efficiencies for capacities up to 200,000 Ii.t.u. per hour when a natural gas of 1000 B.t.u. per cubic foot is burned. A Surface Combustion Company high pressure inspirator and tunnel burner set is used in this installation. Over-all heat-exchange coefficients (O for the furnace are in the range of 7 to 10 B.t.u. per hour per square foot per degree Fahrenheit. Over-all heat-exchange coeflicients for Aroclor 1248 to water in a double pipe heat-exchanger made from 1.25-inch pipe with a 2-inch pipe jacket are in the 120 to 180 range. These figures are calculated from lest results on this installation. HEATER PIPING Figure 2. Cooler, Pump, and Expansion Tank Cooler. A very useful adjunct to the system is a double pipe cooler on the outlet of the heater shown in Figure 2. By turning water into the jacket, the Aroclor can be cooled and the temperature of the system lowered. This is helpful when it is necessary to cool a batch before removing it or when an exothermic reaction starts to get out of control. Pump. The pump for circulating the Aroclor 1248 may be any one of a number of standard centrifugal units designed for hot liquid service. 0S08733 TOWOLDMONOQ34296 1344 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Pipe Construction Table VI. Piping Detail (Dimensions in inches) >/ through / '/through /< ] throug 6 Schedule 80, A.8.T.M. A63 or A106 Schedule 40, A.8.T.M. A53 or A106 Screwed Flanged Bend in shop and field where pos sible. Must be cleaned to remove Ells, tees, and reducers Flanges Bolts >/< through 1/4 1 through C Unions Dope 1/4 through */s Gaskots Shut-off valves Control valves Clicck valves Siifcty valve* ' lie! valves ' > vo stem licking */ through */t 1 through 2 2l/i through 6 '/* through */ 1 through 2 2>/i through 0 V* through `A 1 through 2 2 through 6 li/, through 3 C: n *j<- and glass /4 gage 8trainer* /*-/ 1 through 3 Forged steel sorewed. Crane 300d series Welded fittings. Crane 300c Series 30 (to match valves) Machine bolte A.S.A. B-18.2 with hex agonal nuts for service below 500 F. Abovo use alloy steel. Crane tri plex A.8.T.M. A96 Crane 252h forged stee Crane 426 high tem perature thread compound Soft iron ring fiat or corrugated Crane 3000W, sorewed, gatf Crane 361SW, flange, gate Crane 3640 XR, screwed, globe Crane 3GS0 XR, flange, globe Crane 151 XR, flange, globe Crane 3074 X, screwed Crane 3086 X, flanged Crane 1S9 X, flanged Consolidated 1012 \V, flanged Goetse 340D or Durametallio D110 Type 100 PCPR Marsh 0-100 In./sq. inch gage siphon with Crane 222H bar stock valve, .lerguson Scries R20 Reflex type liquid level gage 821 Yarway threaded 822 Yarway flanged The Dayton Dowd Type C pump is an example of the type required. It should be made of cast steel and have a watercooled stuffing box and water-cooled bearings. The stuffing box should have room for at least six rings of packing and a lantern ring. Durametallic No. D-110 or Garlock No. 234 may be used for packing the pump. An open impeller is desirable, as it will handle the cool, more viscous liquid on starting the svstem better than will a closed impeller. Enough horsepower for the most viscous conditions is required. Piping System and Expansion Tank. The detail of the piping sy iem for Aroclor 1248 used up to temperatures of 300 C. (6<2 F.) and 100 pounds per square inch pressure is given in Table VI. The valves and specialties given indicate the type re quired. All piping larger than 0.75 inch is flanged or welded; ex perience has shown that hot Aroclor penetrates screwed joints of the larger sizes. Steel and cast steel are used throughout. The system requires an expansion tank located at the highest level of the installation. The size of this tank is normally about 25% of the capacity of the Aroclor system. Connections with valvos, made on either side of the pump, enable the operator to connect a flexible hose and to pump in or out as required. For operation in locations where the Aroclor temperature may drop to where the attendant viscosities may make pumping im practical in the system as designed, it may be desirable to steamjacket the Aroclor circulating lines to facilitate rapid startrup. Suitable safety provisions, such as safety pop-off valves, must be installed in the steam jacket system to prevent pressure ruptures which would develop if any condensate remained in a closed sys tem during high temperature operation. In order to establish operating conditions and to check the operation of tho heater itself, it is often desirable to measure the temperatures of the Aroclor in and out of the heater and cooler. Items 9,10, and 11 (Figure 2) provide for this. They may be dial thermometers or mercury bulb thermometers of any commercially available type recommended for the service. Table VII. Safety and Control Equipment 1. High pressure alarm Mercoid DA-31, open circuit on high pressure. (detect* stoppage Actual settings depend on individual layout of pipe) 2. Low preseure alarm Mercoid DA-31-3, open circuit on low pressure. (detect* 'toppage of pump) Aotual settings depend on individual layout 3. Thermostat (detect* Fenwal 18002. Contacts open on temperature excessive heating increase hence obstruction of flow) 4. Float switch (detects Mercoid Figure 40. 8.P. switch. Open at low leakage from sys tem) level 6. Flame failure system Combustion Control Corp. Fireye FF8. Flame (cuts off gas if failure control for manual ignition gas burner pilot flame goes systems out) 0. Gas valve (cute off Oeneral Control Corp. K-10-2. Closes dth in case preceding current off devices act) 7. Red light (alarm) Killark VA-I 60 W. or Benjamin 70li-V 8. Horn (sounds alarm) Edwards 312 Alarm relay Type C-1104 1-NO. 1-NC watertight (/) Stop horn relay Type C-1104 1-NO, 1-NC, watertight (J) Stop horn button l-IiA-4 () 9. Thermometer well 0-300 C. mercury bulb thermometer (visual check of heater perform- 10. Thermometer well 0 300 C. mercury bulb thermometer (visual check of heater perform ance) 11. Thermometer well 0-360 C. mercury bulb thermometer (visual check of coolor perform ance) 12. Solenoid valve General Control K-10-2. Controls Aroclor temperature to meet demands of system For automatic temperature control a solenoid valve, item 12, is indicated in a by-pass arrangementwith a manually operated needle valve. The needle valve is adjusted to give almost enough heat to meet the reauirements and the actual control is carried on by the solenoid valve, which opens and closes as directed by a tempcraturc-control instrument connected to the equipment being One unit was set up with temperature control using a Leeds & Northrop Model S all-electric control with droop corrector. Very close control over a wide range of heat demand resulted, when a throttling range adjustment ot 4 was used on this control device. Safety Circuit. Figure 3 shows a safety circuit which auto matically protects the system by closing off the gas supply in the event of faulty operating conditions. Provision is made for shutting off the warning horn while the system is being put back into operation after a safety shutdown. A detailed list of the safety and control equipment is given in Table VII. The equipment named indicates the type required. ACKNOWLEDGMENTS The authors are grateful to A. M. Ellenburg of Monsanto's Re search Laboratory at Anniston, Ala., for furnishing many of the technical data about Aroclor 1248 and for assistance in preparing the manuscript. LITERATURE CITED (1) Allen Bradley Co., Milwaukee, Wis., Bull. 700. (2) Ibid., Bull. 800. (3) Am. Soc. Testing Materials, Proc. Am. Soc. Titling MateriaU, 34,53(1034). . (4) Am. 8oc. Testing Materials, "Standards on Petroleum Prod ucts and Lubricants," 1945. (5) Drinker, C. K., J. lnd. Hyg. Toxicol, 21, 155 (1030). (6) Monsanto Chemical Co., Anniston, Ala., private communica tion, April 13, 1944. (7) Monsanto Chemical Co., 8t. Louis, Mo., Montanto Tech. Bull. P-115 (August 1947). (8) Sortman, C., Beatty, H., and Heron, 8., Ind. Eno, Chem.. 33, 357(1941). (9) Sullivan, M. V., Wolfe, J. K., and Zisraan, W. A., Ibid., 39, 1607 (1947). (10) Underwriters' Laboratories, Chioago, HI., "Miscellaneous Hasards," No. 2498,1934. Received August 27, 1948. Presented bfor the Meeting-in-Miniature, Alabama Section, American Cbbmical Socibtt, December 8. 1946. Pbixted in U. 8. A. 0508/34 TOWOLDMONOQ34297 Monsanto Chemicals-Plastics _________ 9 MONSANTO CHEMICAL COMPANY ST. LOUIS AKRON BIRMINGHAM BOSTON CHARLOTTE . CHICAGO CINCINNATI CLEVELAND DETROIT HOUSTON LOS ANGELES NEW YORK PHILADELPHIA SAN FRANCISCO SEATTLE MONSANTO (CANADA) LTD. MONSANTO (AUSTRALIA) PTY LTD. Montreal. Toronto Vancouver Melbourne MONSANTO CHEMICALS LTD. London Representatives in the Principal Cities of the World POB:UAO*Ul>U.-4 Print'd in U.8.A. 0308735 TOWOLDMONOQ34298