Document 2q4Zv9zxNJ0KXea3jYa5O7n06

Reprinted from INDUSTRIAL AND ENGINEERING CHEMISTRY, Vol. 41, Page 1341, July 1949 Copyright 1949 by the American Chemical Society and reprinted by permission of the copyright owner An Indirect Aroclor Heater for Unit Chemical Operations MEADE McARDLE1, L. C. GARRETT, AND P. G. BENIGNUS' Monsanto Chemical Company, Anniston, Ala. The characteristics of Aroclor 1248 indicate that it Sprat Flammability. When a tube ruptures in a liquid heat- is an ideal liquid 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 these 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 by Monsanto terial in the liquid form. In their comprehensive study of plants during the past seven years. flammability of the higher boiling liquids and their mists, Sulli van, Wolfe, and Zisman (9) determined the spray flammability IN CERTAIN manufacturing processes of the Monsanto limit of numerous materials in accordance with the percentage of Chemical Company, it was necessary to employ a noncom oxygen required for combustion. This value was then correlated bustible heat-transfer medium at pressures of 30 pounds per with the results of incendiary firing tests of the fluids conducted square inch or less and temperatures up to 300 C. The following at the Naval Proving Ground, Dahlgren, Va. The oxygen re general properties of a heat-exchange medium were required: quirement for Aroclor 1248 combustion in the spray flammability Freedom from fire hazards. Viscosities to permit pumping at room temperatures. Boiling point sufficiently above 300 C. to assure a liquid con dition at all times. Stability against heat, with enough safety factor to accommo date accidental overheating. Controllable vaporization losses. Freedom from corrosive action against valves, piping, tank jackets, etc., made of cast iron and steels, bronze, and stainless steel. Freedom from toxicity hazard. limit studies was found to be 64%. Fluids requiring over 45 to 50% oxygen in the spray test failed to cause a fire in the incendi ary test. These results establish the nonflammable and noncom bustible 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 U. 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 as a heat-transfer medium are given in Table I. Table I. Physical Properties of Aroclor 1248 FREEDOM FROM FIRE HAZARDS Flash 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 (S, 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 Ignition 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 Sortman, 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 enclosed space, and the ventilation. 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 neat-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. Dense smoke arose from the heater but there was no external fire. After the gas flame was cut off, the smoking stopped. 1 Present address, Monsanto Chemical Company, Organic Chemicals Division, St. Louis, Mo. 2 Present address, Monsanto Chemical Company, Phosphate Division, St. Louis, Mo. . Appearance ' . Absolute density, g./mj. Practically colorless mobile liquid C. ( F.) 1.44 1.41 1.37 1.27 1.17 30 (86) 60 (HO) 100 (212) 200 (392) 300 (572) Absolute viscosity, centipoisea 112 17.5 4.2 0.99 0.47 30 (86) 60 (HO) 100 (212) 200 (392) 300 (572) Thermal conductivity, B.t.u./hour/sq. foot/ 0 F./foot Distillation range, A.S.T.M. D-20, C. Flash point, Cleveland open cup, A.S.T.M. D 92-45, 0 C. Fire point, Cleveland open cup, A.S.T.M. D 92-45 Pour point, A.S.T.M. D-7, C. Coefficient of expansion, ml./ml./ C. (25-- 65 C.) Specific volume, ml./g. - 0.0613 0.0698 0.0800 340-375 193-196 None -7 0.000702 0.696 0.709 0.728 0.787 0.860 30 (86) 60 (HO) 100 (212) 30 (86) 60 (HO) 100 (212) 200 (392) 300 (572) Specific heat, cal./g./ C. Vapor pressure, mm. Hg ' 0.29 0.335 0.405 0.44 0.00037 0.16 2.9 18.0 360.0 30 60 100 120 37.8 100 150 200 300 (86) (140) (212) (248) (100) (212) (302) (392) (572) DSW 260892 STLCOPCB4061809 1342 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Table II. Stability of Aroclor 1248 Heated for 30 Hours Temperature, C. Mg. of HC1 per Gram of Aroclor 280 0.079 300 0.186 310 0.199 320 0.222 330 0.248 Table III. Stability of Aroclor 1248 Continuously Heated at 280 and 330 C. Hours Mg. of HC1 per Gram of Aroclor 280 C. 330 C. 30 0.079 0.248 60 0.116 0.510 90 0.169 0.923 120 0.194 1.141 150 0.261 1.362 Table IV. Gas Analysis of Aroclor 1248 Heated 4 Hours at 260 C. and 210 Pounds per Square Inch Pressure Gas Carbon dioxide Carbon monoxide Oxygen (derived from air) Methane Hydrogen chloride Chlorine Acidity (% by weight HC1) Prior to exposure After exposure % None None 20.2 0.2 None None 0.0075 0.0075 the heater 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 temperatures. The decom 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 ohloride, 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 square inch, resulting from the introduction of compressed air. Following this treatment and cooling, the gases removed from the system were analyzed. 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 the 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 red 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. J DSW 260893 STLCOPCB4061810 uly 1949 INDUSTRIAL AND ENGINEERING CHEMISTRY 1343 Table V. Metals Aluminum Copper Magnesium Nickel Silver Tin Resistance of Structural Materials to Aroclor 1248 At 25 C. At 125 C. Metals At 25 C. At 125 C. R R Zinc RR R D Mild steel RR R RR R Phosphor bronze R D RR R Red brass DD R R Stainless steel RR RR R R Yellow brass R Re RR. Excellent resistance, less than 1.0 X 10 cm. 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 inch per year. D. Doubtful resistance, penetration between 10 X 10"* cm. per day and 100 X 10~* cm. per day or between 0.0014 and 0.014 inch per year. e. Following letter indicating resistance, signifies material may be better than indicated if totally immersed, as weight loss is believed to come from oxidation of part of test strip exposed to air. 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. (d) 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 Heater Design. The general requirements of the heater are compactness, ease of construction and service, and avoidance of tically noncorrosive to valves, piping, tank jackets, etc., made direct flame impingement on the tubes. of cast iron and steels, bronze, and stainless steel. FREEDOM 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 burned 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 not 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.. EXPANSION TANK STEAM OR WATER outlet ry 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 by 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-inch 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 tests 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 B.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 (U) 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 coefficients 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 test results on this installation. Cooler. A very useful adjunct to &AROCLOR FROM HEATER JACKETED PIPE COOLER ^WATER INLET <D" HEATER 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 aroclor TO HEATER DRAIN "HXK-CXJ AROCLOR PUMP -0-cx} s. $AS i--1^hlXD- 036 i--------- xi- PILOT LIGHT Jo 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 HEATER PIPING the Aroclor 1248 may be any one of a number of standard centrifugal units Figure 2. Cooler, Pump, and Expansion Tank designed for hot liquid service. DSW 260894 STLCOPCB4061811 1344 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Pipe Construction Ells, tees, and reducers Flanges Bolts Unions Dope Gaskets Shut-off valves Control valves Check valves Safety valves Relief valves Valve stem packing Gage and glass Strainers Table VI. Piping Detail (Dimensions in inches) V through y 1 through 6 V through */4 1 through 6 Vi through V* 1 through 6 1 through 6 V through */4 through 3/< 1 through 2 21/: through 6 / through */4 1 through 2 2l/j through 6 y4 through 1 through 2 2 through 6 viy. 2 through 3 y gage y2-3/4 1 through 3 Schedule 80, A.S.T.M. A53 or A106 Schedule 40, A.S.T.M. A53 or A106 Screwed Flanged Bend in shop and field where pos sible. Must be cleaned to remove scale Forged steel screwed. Crane 300d series Welded fittings. Crane 300c Series 30 (to match valves) Machine bolts A.S.A. B-18.2 with hex agonal nuts for service below 500 F. Above use alloy steel. Crane tri plex A.S.T.M. A96 Crane 252h forged stee Crane 425 high tem perature thread compound Soft iron ring flat or corrugated Crane 3606W, screwed, gate Crane 3615W, flange, gate Crane 33XR, flange, gate Crane 3640 XR, screwed, globe Crane 3656 XR, flange, globe Crane 151 XR, flange, globe Crane 3674 X, screwed Crane 3686 X, flanged Crane 159 X, flanged Consolidated 1670 BW, screwed Consolidated 1612 W, flanged Goetze 340D or Durametallic D- 110 Type 100 PCPR Marsh 0-100 Ib./sq. inch gage siphon with Crane 222H bar stock valve. Jerguson Series 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 east steel and have a watercooled stuffing box and water-cooled bearings. The stuffing boxshould 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 system 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 system for Aroclor 1248 used up to temperatures of 300 C. (572 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 valves, 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 start-up. 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 the 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. VII.Table Safety and Control Equipment 1. High pressure alarm Mercoid DA-31, open circuit on high pressure. (detects stoppage Actual settings depend on individual layout of pipe) 2. Low pressure alarm Mercoid DA-31-3, open circuit on low pressure. (detects stoppage Actual settings depend on individual layout of pump) 3. Thermostat (detects Fenwal 18002. Contacts open on temperature excessive heating increase hence obstruction of flow) 4. Float switch (detects Mercoid Figure 40. S.P. switch. Open at low leakage from sys level tem) 5. Flame failure system Combustion Control Corp. Fireye FF6. Flame (cuts off gas if failure control for manual ignition gas burner pilot flame goes systems out) 6. Gas valve (cuts off General Control Corp. K-10-2. Closes with in case preceding current off ' devices act) 7. Red light (alarm) Ivillark VA-1 60 W, or Benjamin 7013-V 8. Horn (sounds alarm) Edwards 312 Alarm relay Type C-1104 1-NO, 1-NC wratertight (f) Stop horn relay Type C-1104 1-NO, 1-NC, watertight (/) Stop horn button l-HA-4 (S) 9. Thermometer well 0-360 C. mercury bulb thermometer (visual check of heater perform ance) 10. Thermometer well 0- 360 C. mercury bulb thermometer (visual check of heater perform ance) 11.' Thermometer well 0-360 C. mercury bulb thermometer (visual check of cooler 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 arrangement with a manually operated needle valve. The needle valve is adjusted to give almost enough heat to meet the requirements and the actual control is carried on by the solenoid valve, which opens and closes as directed by a tem perature-control instrument connected to the equipment being heated. 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 of 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. Soo. Testing Materials, Proc. Am. Soc. Testing Materials, 34, 53(1934). (4) Am. Soc. Testing Materials, "Standards on Petroleum Prod ucts and Lubricants," 1945. (5) Drinker, C. K., J. Ind. Hyg. Toxicol., 21,155 (1939). (6) Monsanto Chemical Co., Anniston, Ala., private communica tion, April 13, 1944. (7) Monsanto Chemical Co., St. Louis, Mo., Monsanto Tech. Bull. P-115 (August 1947), (8) Sortman, C., Beatty, H., and Heron, S., Ind. Eng. Chem., 33, 357 (1941). (9) Sullivan, M. V., Wolfe, J. K., and Zisman, W. A., Ibid., 39, 1607 (1947). . (10) Underwriters' Laboratories, Chicago, 111., "Miscellaneous Hazards," No. 2498,1934. Received August 27, 1948. Presented before the Meeting-in-Miniature, Alabama Section. American Chemical Society, December 8. 1945. DSW 260895 Printed in U. S. A. STLCOPCB4061812