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AN INDIRECT AROCLOR HEATER for UNIT CHEMICAL OPERATIONS Monsanto Technical Bulletin No. PO30 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 Aroclor 1248 and illustrates the design and operation of heaters chat 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 c Z2 o TO Om X m o 3: n > r > TO O n o T> m r~ o TO TO > X m > O z m (/> TO O TO f 3M s n r S' o_ co c ri. u. s. p. oriic. bulltdn l>. to our brat knoldt, trga and arrurata, bat all rtrontmaralaliona or ITi3f r vO O 0222177 TOWOLDMON0026797 WATER_PCB-00011266 Reprint'd from INDUSTRIAL AND ENG IN DURING CHEMISTRY, Vol 41, Page 1341, July 1949 Copyright 1949 hy 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. BENIGNUS1 Monsanto Chemical Company, Anniston, Ala. The cliaracteriaticH of Aroclor 1214 indicate that it Sprat Flamuabiutt. When a tube ruptures in a liquid heat- ! an ideal liquit' phnpc heat-fxchunge medium for transfer system under high pressure, a spray or mist forms. temperature* up to 300 C. This arliele discusses its The possible fire hazard under these conditions requires considera properties and illuvtrnlcB the design and operution of tions not covered by the foregoing discussions relative to the ma heaters that have lucn used successfully hy 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 apray flammability JN CERTAIN manufacturing processes of the Monsanto Chemical Company, it was necessary to employ a noncom- limit of numerous materials in accordance with the percentage of oxygen required for combustion. This value was then correlated bustil.le heat-transfer medium at pressures of 30 pounds per with the results of incendiary firing teste of the fluids conducted equare inch or less and temperatures up to 300 C. The following at the Naval Proving Ground, Daldgren, Va. The oxygen re general properties of a hoat-cxchange medium were required: quirement for Aroclor 1218 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 all times. Stability against- heat, with enough safety factor to accommo date Accidental overheating. Controllable vaporization Josses. _ 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 04%. 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 heal-transfer medium are given in Table I. Table I. Physical Properties or Arocloii 1248 FRKKItOM FROM FIRE HAZARDS Flash Point. Limitations of this test for (he prediction of the Ere 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' Gullivftu, Wolfe, and Zisman (9), using the convenient apparatus described by Sortman, Beatty, and Heron (5). 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 ou it, the volume of enclosed space, and tho ventilation. An Accidental failure in a heating system demonstrated the nonflammability of Aroclor 124S and its freedom from the hazard of fire propagation. An operator's failure to start tho circulation of the heut-lramder medium when the gas beater was ou resulted in excessive cil temperatures And caused the lower coil to soften ami sag into the fire chamber. A weld ruptured and Aroclor 1248 poured into the red-hot tire chamber in contact with the flame. Dens'* amoke arose from the heater but there was no external fire. After the gas flame was cut off, the smoking lopjied. 1 Present address, MonunUj Chemical Cnrnpany, Organic Chemicals Divinoo, Be. Louis, Mo. ' Present address, Monsanto Chemical Company, Phosphate Division. 8t. LouU, Mo. Appearance Absolute density, g./ml. Practically eoloiieaa mobile liquid *C. CT.) 144 1.41 1.37 1.27 1.17 30 (80) 60 (140) 100 (212) 200 (392) 300 (672) Absolute viscosity, eentipoise* 112 17.S 4.2 0.99 0.47 Thermal conductivity, B.t u./hour/sq. foot/ * F./foot Distillation range, A.B.T.M. D-20, * C. Flash point. Cleveland open cup. A.B.T.M. D 92-45, * C. Fire point, Cleveland open cup. A.B.T.M. D02-45 Pour point, A.B.T.M. D-7, * C. Coefficient o( expansion, ml./ml./* C. (25 65* C.) Specific volume, ml./g. 0.0613 0.0608 0.0800 310-875 103-100 N... -7 O 000702 o.eee 0.700 0.728 0.787 0. BOO 30 (80) 60 (140) 100 (212) 200 (392) 300 1572) 30 (86) 60 (140) 100 (2J2) 30 (86) 60 (140) 100 212) 200 (392) 300 (572) Specific heat, eal./g./* C. Vapor preaaure. nun. Hg MU 0.370 0.346 O.OOU37 0.16 8.9 18.0 800.0 c IOC 300 300 37.8 100 160 200 300 i tll> illli 0#3i (4121 (100) (212) (80J) (302) (572) OZ2217 6 TOWOLDMON0026798 WATER_PCB-00011267 1342 INDUSTRIAL AND ENGINEERING CHEMISTRY Yol. 41, No. 7 Table 11. Stability or Aroclor 1246 Heated for 30 Hours Temperature, 380 00 9 078 0 1M 810 0.100 820 930 0 0 2222 Table III. Stability or Aroclor 1248 Continuously Heated at 280* and 330 C. Hour* Mj. of HCI pr Gram of Aroclor ' 280* C 380* C. 80 0.078 0.246 80 0.116 0.S10 BO 0.169 0.923 120 0.194 I.141 160 0.261 1.363 Table IV. Gab Analysis or Aroclor 1248 Heated 4 Hours at 260 C. and 210 Pounds per Square Inch Pressure Gee % Cerbon dioxide Cerbon monoxide Oxygen (derived from air) MelUne HydrosTM chloride Chlorine Acidity (% by weight HCI) Prior to exposure After expoeure None None 20.2 0.2 None None 0.0075 0.0076 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 1218 (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 Id 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 `emperatures. The decom position is very low at temperatures up to 300 C. The stability of Aroclor 1218 in contact with L irou continuously heated at 280 and 330 C. is indicated by Table HI. These test results indi cate that Aroclor 1248 in con tact with iron can be used satisfactorily at temperatures upto300*C. The National Board of Fire Undenrriters(/0)reportod that "decomposition of the product (Aroclor 124S) was not appreci able at temperatures below 400* C., hut became incrcaa- ingly apparent at higher tem perature's." at 310 C. fitted with an internal gas burner eo that the bas flame impinged dircrily 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 chloride, 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 200 C. under an internal pressure of 210 pounds per souare inch, resulting from the introduction of compressed air. Following this treatment and r<*oling, the cases 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 email 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 Las 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 healer 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 carl>on 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 a3 it is unlikely that the expansion tank will ever reach even the 1-min. state (130 C.), there should not be a measurable loss of Aroclor from the system. Actual experience beam out this contention. Other Losses. Although Aroclor darkens on use, its charac teristics remain the same and replacement has not been found ncccss&ry after 7 years of continuous use. Accidental leaks or spills constitute the only observed losses. PLAN AND PART SCCTlON 1 J Their workers analysed the decomposition products of Aroclor 1248 heated in the pres ence of hot iron at 459 C. and *Im healed in an iron cylinder G 0 0) J TOWOLDMON0026799 WATER_PCB-00011268 uly 1949 INDUSTRIAL AND ENGINEERING CHEMISTRY 1343 Table V. Resistance or Structural Materials to Aroclor 1248 M*uli Aluminum Copper Nielel &l'tt Tio 125* C. R Meiali Zine MilJ kteel Pliospltor bronco Red brtu SuinleM oteel Yellow brn 25* C. 125* C. Re RR. Emllent remUnre. Icm ibtn 1.0 X 10 * cm. per day penetration or 0.00014 inch per year. _ ____ H. Good reeietanee. penetration between 1.0 X 10 "* and 10 X 10'** cm. per day or between 0.000)4 end 0.0014 inch per year. D. Doubtful rewibtaiire. penetration between 10 X 10** cm. per day and >00 X 10* cm. per day or between 0.0014 end 0 014 ineb per year. t. Followinc letter indicalinc reriaunte, elznifiet tuatenal may be b*t(er then iodietied if totally mmiereed. as weight low ie believed to come |tow oi^detion of part of lest strip reposed to sir. 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. (tf) 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 1243 as a heat-transfer medium have shown that the material is prac tically noncorrosive to valves, piping, tank jackets, etc., made of east 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 uotice&ble ill effects; however, it is well to wash the skin with soap and water after contact. A skiu burn resulting from accidental contact with hot Aroclor should be treated in the normal procedure used for hot oil bums. Aroclor adhering to the burned area need not be removed im mediately unless treatment of the bum demands it; in this case soap and water or repeated washings with a vegetable oil (linseed oil)bould be used. The vapors emitted by Aroclor 1248 heated to elevated tem peratures arc injurious to the liver on prolonged exposure and should not be breathed. Drinker (5) indicated that 0.5 mg. of Aroclor 1248 per cubic mclcr 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 bhould be no opportunity for workers to come in con tact with vapors from the hot heat-transfer medium. Figure 3. Control and Safety Circuit Heater Desion. 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 name 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 Xo. 60 insulation on the cooler spots. Two sizes of units arc used: One has a maximum capacity of 200,000 B.t.u. per hour, as bIiowii in Figure 1. The larger has a range of 200,000 to 400,000 B.t.u. The small size consists of 00 feet of 1-ineli 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 sled pijie arranged in the same fashion. Results of tests on the small-size heater covering teni|>cratures from 150 to 300 C. 6huw 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 GOTc 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 tuunel 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-exchaiige coellicieiits for Aroclor 1248 to water in a double pipe heat-exchanger made from 1.25-iuch pipe with a 2-inch pipe jacket are m the 120 to 180 range. These figures are calculated front 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 w hen it is necessary to coo) a batch before removing it or wheu 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. 0222180 J TOWOLDMON0026800 WATER_PCB-00011269 1344 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Pip* Construction Ell*. ton, nod rvductr* Vnioni Dope CaikeU Phut-ofl valves Control valvra Cheek valve* Fhlcty valve* Keitel valve* Valve stem packing Ge*e and glau Strainer* Table VI. Piping Detail (Dimension* in inehea) >/i through V 1 through 6 1/4 through '/* /i through / bcbrauie so, a.h. .m. ao or aiuo Schedule 40, A.8.T.M. A53 or A100 Screwed Flanged Bend id ahop and field where poe- ible. Must be cleaned to remove rale _ _ Forced steel c rewed. Crane SOOd 1 through 6 I through 0 </* through */* */ through /4 1 through 2 j'/i through 6 V. tlirovirL V< I throrgh 2 2>/ through 8 /a through /< 1 through 2 2 through C V* l>/t through S A gftge Vl-'/r 1 through 3 Welded fitting*. Crane 300e Sene* 30 (to match valves) Machine bolt* A.S.A. H-18.2 with^beaagonal nut* (or service below 500* F. Above uae alloy ateel. Craoe tnplea A.S.T.M. A96 Crane 252li (orged alee Crane 425 high tem perature thread compound Soft iron ring flat or corrugated Crane 30OGW, aerewed. gate Crane 3lil5W, flange, gale Crunc 33XK, flange, gate Crane 3040 XR, screwed, globe Crane 3050 XR, flange, globe Crane 151 Jill, flange, globe Crnne 3074 X. acrcwed Crane 3080 X, flanged Crane 159 X. flanged Consolidated 1070 lt\V, eerewed Cottaoiidaled 1012 \V, flanged Cottar 340D or burauictillir D110 Tyi* 100 PCPK Marsh 0-100 Ib./sci. inch gogc aiphon with Crane 22211 bar stock vatve. lergufon Series 1120 Ilcfles type liouitl level gage 21 Yarway threaded 822 Yaru-ay flanged The Dayton Dowd Type C pump is ait example of Ihc type required. It 6ht>uld 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- DurameUllic Xo. D-110 or Gnrlock Xo. 234 may lie 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. ririNQ System and Expansion Tank. The detail of the piping system for Aroclor 1248 used up to temperatures of 300 C. (672 F.) and 100 pounds per square inch pressure is given in Table VI. The valves and specialties giveu indicate the type re quired. All piping larger than 0.76 inch is flanged or welded; ex perience has shown that hot Aroclor penetrates screwed joints of the larger sizes. Steel und cast Gtccl arc used throughout. The system requires an expansion tank located at the highest level of the installation. The site 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 safely pop-off valves, must l>e 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 oprrating conditions and to check the operation of the heater itself, it is often desirable to huh.surc the temperatures of the Aroclor in and out of the heater and cooler, ltcmat), 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 High pressure alarm Mereoid DA-31, open circuit on high pressure. (detect* stoppage Actual nettings depend on individual layout of pipe) 3. Low pressure alarm Mereoid DA-31-3, open circuit on low pressure. (detect* -towage Actual settings depend on individual layout of pump) 3. Thernio-tat (detect* Fenwal 18002. Contacts open on temperalure e*ceaive heating increase hence obstruction of flowl . Float sw itch (detect* Mereoid Figure 40. 8.P. switch. Open at low leakage front sya- level ft. Flame failure *v*lem Combustion Control Corp. Fireye FF6. Flsme (tut* off gan tl failure control for manual ignition gas burner pilot flame goes systems out) 6. C vlve (cuts ofl General Control Corp. K-10-2. Close* with ' preceding current ofl drvir let) 7. 8. Alarm rainy Kitlark VA-1 80 W, or Benjamin 701j-V Edward* 312 To..e ('-1104 1-NO. l-SC watertight (/) Stop horn relay Stop horn button IW.e O..-.l 104 1-NO. 1-NC, watertight () Thermometer well 0-3 VO' C bulb thermometer (visual check of heater perform ance) Thermometer well 0 300' C. mercury bulb thermometer (visual check ol heater perforin- Thermometer well (visual check or eooler perform ance) Solenoid valve 0-300' C. mercury bulb thermometer General Control K-10-2. Control) Aroclor temperature to meet demands of system c For automatic temperature control a solenoid valve, item 12, is indicated in a by-pass arrangement wit ha 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 One unit was set up with temperature control using a Leeds & Northrop Models 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 conditiou9. Provision is made for shutting off the warning horn while tho 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. ACKNOW LF.DGMENTS The authors arc grateful to A. M, Ellcnburg 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. Testing Moitruiti, 34,53(1934). . (4) Am. Soc. Testing Materials, "Standard* on Petroleum Prod ucts and Lubricants," 1945. (5) Drinker, C.K., J.Jnd. Hyg. Toxicol., 21, 165 (1930). (0) Monsanto Chemical Co., Anniston, Ala., private communica tion, April 13, 1941. (7) Monsanto Chemical Co., St. Louis, Mo., Monaonlo Tech. Bull. P-1J5 (August 1947). (8) Sortm&n. C.. Beatty, H., and Heron. B., Ind. Eno. Cdem., 33, 357 0941). (9) Sullivan. M. V.. Wolfo, J. K., and Ziaroan, W. A., Ibid., 39.1C07 (1047). (10) Underwriters' Laboratories, Chioago, 111., "Miscellaneous Hasards," No. 2498,1934. flKnivm Augiiit 27, 1048. Presented before the Meetiog-in-Mimalure, Alabama Section, AwaaicsM CaauiCAt Sccirri, Deoember 8. 1045. 0 9 0222181 | TOWOLDMON0026801 WATER_PCB-00011270 o & Monsanto Chbucals-Pustics __ V/d__ 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-UDU'49 0222182 O Prlnttd in U.8.A. TOWOLDMON0026802 WATER_PCB-00011271