Document ev6KkZ1zb5XYO3q1KR9J4ae0e

I Monsanto I Chemicals I u__ AN INDIRECT AROCLOR HEATER for UNIT CHEMICAL OPERATIONS Monsanto 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 Aroclor 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 C Z z o TO 0m 1O m E o > > TO o o or *o 0 m TO to > 1 m > o zm to TO o TO Monsanto Technical B u lle tin No. P-130 September, 1949 Reg. V. S. Pat. Office The information contained in thia bulletin ia, to our beat knowledge, true end accurate, but all re commendation# or auggeationa are made without guarantee, eince the conditiona of ute are beyond our control. The Monaanto Chemical Company diaclaimt any liability incurred In connection with the uee of theae data or auggeationa. Furthermore, nothing contained herein ehell be conatrued aa a recommendation to uae any product in conflict with exletlng patent# covering any material or ite uee. __<C!S!33*7K TOWOLDMONOQ22868 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 McAHDLE1, L. C. GAItRETT, AND P. G. BENIGNUS* Monsanto Chemical Company, Anniston, Ala. I he chaructcriftticK of Aroclor 1248 indicate that it Spray Flammability. When a tube ruptures in a liquid heat- is an ideal liquid phase lieat-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 3000 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. 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 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 firo 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 ns a bent-transfer medium are given in Table 1. Table I. Physical Properties of Aroclor 1248 FHKFI>OM FKOM FIKK 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). Fjkb Point is a more significant measurement. The Under writers' Laboratories (JO) 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 Zismnn (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 heat-transfer medium when the gas heater was on resulted in excessive coil temperatures and caused the lower coil (_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 fromthe 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, Bt. Louis. Mo. 1 Present address, Monsanto Chemical Company, Phosphate Division, Bt. Louis, Mo. Appearance Absolute density, g./ml. Absolute viscosity, ccntipoises Distillation range, A.6.T.M. D-20, C. Flash point, Cleveland open cup, A.8.T.M. D 92-45, 0 C. Fire point, Cleveland open cup, A.8.T.M. D 92-45 Pour point, A.S.T.M. D-7, 0 C. Coefficient of expansion, ml./ml./ C. (25(55 C.) Specific volume, ml./g. . Specific heat, cal./g./ C. 0.0613 0.0698 0 0800 0.606 0.709 0.728 0.787 0.860 0.29 0.335 0.406 0.44 (140) (212) (302) (572) (86) (140) 212) (392) (672) (86) (140 (212) 30 (86> 60 (140) 00 212) 00 392) 100 (572) 30 (86) 60 (140) 00 (212) 20 (248) .8 (100) 00 (212) 60 (302) 100 (302) 100 (572) OM,2<t50 TOWOLDMONOQ22869 1342 INDUSTRIAL AND ENGINEERING CHEMISTRY Voi. 41, No. 7 Tabu: II. Stability ok Aroclor 1248 Heated kor 30 Hours ni|Hiraturc Mg. of IICl per Gram of Aroclor 0.079 0.180 0.190 0.222 0.248 Table III. Stability ok Arociair 1248 Continuously Heated at 280 and 330 C. Hours Mg. of 11Cl per Gram of Aroclor 280 C. 330 C. 30 0.070 0.248 00 O.lKi 0.510 90 0.100 0.923 120 0.194 1.141 150 0.201 1.302 Table IV, Gas Analysis ok Aroclor 1248 Heated 4 Hours at 260 C. and 210 Pounds per Square Inch Pressure Carbon dioxide Carbon monoxide Oxygen (derived from air) Methane Hydrogen chloride Chlorine Acidity (% by weight HCl) Prior to exposure After exposure 0 0075 0.0075 the healer had been effected so that the system could operate normally. . BOILING POINT Operating experience has shown that the boiling point of Aroclor 1248 (340 G. 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 t han 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 position is very low at temperatures up to 300 C. The stability of Aroclor 1248 in contact with 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 300 G. - The National Hoard of Fire Underwriters {10) reported that "decomposition of the product (Aroclor 1248] was not appreci able at temperatures below 400 C., but became increas ingly apparent at higher tem peratures." Their workers analyzed the decomposition products of Aroclor 1248 heated In the pres ence of hot iron at 469 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 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 G. 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 typo 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 ami through faulty design a burner tunnel was located 1.5 indies from the 2inch steel pipe coil. The radiation from the white-hot refractory tunnel ana the direct impingement of the flame on the pipe caused the pipe to glow & dark red for a space of about 2 indies. This unit was operated almost 3 months before a circulation stoppage occurred. When the line was opened lumps of eat bon 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 /it the pipe curvature. No hydrochloric add effect was noted and the system was put back into operation after the burner location was changed. CONTROLLAIILK VAPORIZATION LOSSES The heating systems in which Aroclor 1218 is used are sealed except for the expansion tipik, 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'B' Figure 1. Hcuter TOWOLDMONOQ22870 uly 1949 INDUSTRIAL AND ENGINEERING CHEMISTRY 1343 RESISTANCE OK STRUCTURAL MATERIALS TO AROCLOR 1248 Metals Copper Magnus! mi Nlckol Silver Tin H Mtlii steel Phosphor bn Red brass Stainless stei H Yellow brass R Ke HR. Kxoellont resistance, les n 1.0 X 10-*c t. per day penetration o 0.000)4 ineb per year, K. Good resistance, penetration between 1.0 X 10" and 10 X 10"* cm. per day or between 0.00034 and 0.0014 inch per year. 1). Doubtful reiiinlanec, 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. Followinjit letter indicating resistance, aicnifies material may be belter than indicated if totally immersed, as weight loss iB believed to come I row oxidation ol part of lest strip exposed to air. DESIGN AND CONSTRUCTION Heating System. The healing system required to utilize Aroclor 1248 as the exchange medium includes a heater (Figure 1), cooler, pump, and expansion lank (Figure 2), and control and safety circuits (Figure 3). l-'RF.KDOM HiOM 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, Figure 3. Control and Safety Circuit 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 noncoiTosive to valves, piping, tank jackets, etc., made direct flame impingement on the tubes. of cast iron and steels, bronze, and stainless steel. Direct flame impingement is prevented by directing the gas FREEDOM FROM TOXICITY HAZARD flame through an enclosed channel with half-thickness fire brick protecting the tubes above until the high temperature of the 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 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. 60 insulation on the cooler spots.. should he 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 repealed washings with a vegetable oil (linseed Two sizes of units are used; One lias a maximum capacity of 200,000 R.t.u. per hour, as shown in Figure 1. The larger has a range of 200,000 to 400(000 H.t.u. The small size consists of 00 feet, of ]-inch standard weight steel pipe made into three coils of six pipes each and connected in oil) should be used. The vupors emitted V>y Aroclor 1248 heated to elevated tem peratures are injurious to the liver on prolonged exposure and should not be breathed. Drinker (d) indicated that 0.5 mg. of 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 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 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 H.t.u. per hour when a natural gas of 1000 B.t.u. per cubic foot is burned. A Surface ingly, there should lie no opportunity for workers to come in con tact with vapors from the hot heat-transfer medium.. 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 a- STEAM OR YWATER OUTLET 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 the system is a double pipe cooler on 4 JACKETEO PIPE COOLER -- - ^WATER INLET ""I the outlet of the heater shown in Figure 2. Hy turning water into the --^DKD- jacket, the Aroclor can be cooled and DRAIN --CXJ-KXO- the temperature of the system lowered. This is helpful when it is necessary to till , I AROCLOR PUMP -0 _Yo -{XI- 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. 01B2S52 TOWOLDMON0022871 1344 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Tabi-e VI. l'lpo Construction l/ through */ 1 through 6 '/ through */ 1 through 0 1:11s, tecs, an<l reducer* Flanges Itoitn V* through */i 1 through G 1 through G Gasket* Rlmt-ofT valves Control valves Check valves Safely valves Helie} valves / through */* 1 through 2 2'/t through 6 V* through / 1 through 2 2V through G >/ through */< 1 through 2 2 through G / l'/j through 3 imcking Cage and glass >/ gngc Piping Detail in inches) 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. Mu be cleaned t scale Forged steel screwed. Crane 300d Welded fittings. Crane 3005 Scries 30 (to match valves) Machine bolts A.S.A. D-18.2 with hex agonal nuts for service below 500 F. Above use alloy steel. Crane tri plex A.S.T.M. AOG Crane 2521) forged stce Crane 425 high tem perature thread Soft iron ring flat or Crane 3G0GW. screwed, gate Crane 3G15W, flange, gate Crane 33XR, flange, gate Crane 3040 XR, screwed, globe Crane 3650 XII, flange, globe Crane 151 XII, flange, globe Crane 3074 X, screwed Crane 3086 X, flanged Crane 159 X, flanged Consolidated 1070 I1W, screwed Consolidated 1012 W, flanged Cnetze 3401) or Duramctallic D110 i'yiie 100 PCl'R Marsh 0-100 lb./sc|. inch gage siphon with ' 22211 bar stock valve. Jerguson Series R20 Relic* ' 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 Btcel and have a watercooled stulling 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 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 capaoity 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 at tendant 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. Table VII. Safety and Control Equipment 1. High pressure Alarm Mercoiil DA-31, open circuit on high pressure. (detects stoppage Actual settings depend on individual layout of pipe) 2. I.ow pressure alarm Mercoid DA-31-3, open circuit on low pressure. (detects stoppage Actual settings depend on individual layout 3. Thermostat (detects Fenwat 18002. Contacts open on temperature excessive heating hence obstruction of flow) 4. Float switch (detects Mercoid Figure 40. 8.P. switch. Open at low leakage from sys tem) 5. Flame failure system Combustion Control Corp. Firoyo FF6. Flume (cuts off gas if failure control for manual ignition gas burner pilot flame goes out) 0. Gas valve (cuts off General Control Corp. K-10-2. Closes -ith in case preceding devices aet) current off 7. Red light (alarm) Killark VA-l 00 \V, or Henji .in 7013- V 8. Horn (sounds alarm) l.d wards Alarm relay Stop horn relay Typo C-1104 1-NO, 1-NC v tertight G Type C-1104 l-NO, 1-NC. w erlight (/) Stop horn button l-IiA-4 9. Thermometer well 0 300 O. mercury hull, the (visual check of heater perform- 30. Thermometer well 0 30,0 C. mercury hull, thermometer (visual check of heater perform ance) 11. Thermometer well 0 300 C. mercury hath thermometer (visual check of cooler perform- 12, Solenoid valve General Control K-10-2. Controls Aioelur 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 bv the solenoid valve, which opens and closes as directed hv 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 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. 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) Alton Bradley Co., Milwaukee, Wie., Bull. 700. (2) Ibid., Bull. 800. (3) Am. Soc. Testing Materials, Proc. Am. Soc. Testing Materials, 34,53(1934). (4) Am. Boo. Testing Materials, "Standards on Petroleum Prod ucts and Lubricants," 1946. (5) Drinker, C. K,, J. Ind. Hyg. Toxicol., 21, 165 (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. Enq. Chem., 33, 367 (1941). (9) Sullivan, M. V., Wolfe, J. K., and Ziam&n, W. A., Ibid., 39, 1007 (1947). (10) Underwriters' Laboratories, Chicago, III., "Miscellaneous Hazards," No. 2498,1934. Received August 27, 1948. Presonted before the Meeting-in-Miniature, Alabama Section. American Chemical Society, December 8. 1945. 01A2A53 Printed in U. S. A. TOWOLDMONOQ22872 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. Montreal* Toronto Vancouver MONSANTO (AUSTRALIA) PTY LTD. Melbourne MONSANTO CHEMICALS LTD. London Representatives in the F'rincipal Cities of the World POB:UAO'MM'9*49 Printed In U.S.A. TOWOLDMONOQ22873