Document RBZDnjVLjpyQm8L83axNp3dE

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 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 cz z o n TO m Xn m 3: n > > TO o r~ n o TJ r- o m TO TO > X m -H > O Z H m (/> x o TO ? 3M | o rHn n o_ CP Reg. U. S. Pal. Office T*>. uilnnt i. to our baat knold,. truo and arrurata, but all rtrornmaralaliona or r. Ihr londiiiona ol u. art b*>viul our control. Tin Monaanro Chamlcal omirc'icn tonl. iho uao ol the,* data or auc,tiori. t>* coriatrurd a a racomn.rrvlatlun to war an* product lt conflict with 0222177 y g v 'O i ouo. TOWOLDMONOQ26797 Reprinted from INDUSTRIAL AND ENGINEERING 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 MCARDLE", L. C. GAItRETT, AND I*. G. BENIGNUS' Monsanto Chemical Company, Anniston, Ala. The characteriaticH of Aroclor 1213 indicate that it Sprat Flammabiutt. When a tube ruptures in a liquid heat- It an ideal liquir' phase heat-exchunge medium for transfer system under high pressure, a spray or mist forms. temperature* up to 300* C. Thia article discusses ila The possible fire hazard under these conditions requires considera properties and illustrates the design and operulion of tions not covered by the foregoing discussions relative to the ma healers that liuve Iseen 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 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 12-18 combustion in the spray flammability Freedom from fire hazards. Viscosities to permit pumping at room temperatures. Iioiling 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 cost 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 healing 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 FREEDOM FROM FIRE HAZARDS Flash Point. Limitations of this test for (he 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 Sortman, Realty, and Heron (S). 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 lire propagation. An operator's failure to start tho circulation of the heat-transfer medium when the gas heater was ou resulted in excessive coil temperatures ami caused the lower coil to soften and sag into the fire chamber. A weld ruptured and Aroclor 1248 poured into the red-hot tire chamber in contact with the flame. Dense amoko arose from the beater but there was no external fire. After the gas flame was cut off, the smoking topjH-d. 1 Pre*enl address, Monsanto Chemical Company, Organic Chemicals Division, Bt. Louis, Mo. * Prevent address, Monunto Chemical Company, Pboaphato Division, 8l. Louis, Mo. Appearance Absolute density, g./ml. Practically colorless mobile liquid C. ( r.) 1.44 1.41 1.37 1.27 1.17 30 (80) 60 (140) 100 (212) 200 (392) 300 (572) Absolute viscosity, centipoises 112 17.5 4.2 0.99 0.47 30 (60) 60 (140) 100 212) 200 (392) 300 (672) Thermal conductivity, B.t.u./hour/sq. loot/ * F./foot Distillation range, A.S.T.M. D-20, * C. Flash point. Cleveland open cup. A.B.T.M. D 92-45, * 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. 0.0513 0.0698 0.0800 340-375 30 (66) 60 (140) 100 (212) 193-190 None -7 0 000702 0.696 0.709 0.728 0.787 0.860 30 (86) 60 (140) 100 (212) 200 (392) 300 (572) Specific heat, eal./g./* C. 0.333 0.391 0.339 0.355 50 II32 100 1112) 200 0921 300 <512l Vapor pressure, mm. Hg O.OOU37 0.16 3.9 18.0 300.0 37.8 100 150 200 300 (100) (21-) (302) (3U2) (572) 02*Zl78 TOWOLDMONOQ26798 1342 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Table 11. Stability or Aroclor 1248 Heated for 30 Hours Temperature, Mf. of Ha per Cram of Aroclor 380 9.079 800 0.1M 310 0.199 320 0 223 330 0.248 Table III. Stability of Aroclor 1248 Continuously Heated AT 280 AND 330 C. Hour* Xlg. of HCl per Grarn of Aroclor 280* C 330* C. 30 0.079 0.248 SO 0.116 0.610 90 0.169 0.923 120 0.194 1.141 160 0.261 1.362 Table IV. Gab Analysis or Aroclor 1248 Heated 4 Hours at 260 C. and 210 Pounds per Square Inch Pressure Gu % Cxrbon dioxide Carbon monoxide Oxygen (derived from air) Melnane Hydrogen chloride Cnlorine Acidity (% by weight HCl) Prior to exposure After exposure None None 20.2 None None the healer 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 tbe 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 `rmperatures. The decom position is very low at temperatures up to 300 C. The stability of Aroclor 1248 in contact with L irou continuously heated at 280 and 330 C. is indicated by Table III. Those test results indi cate that Aroclor 1248 in con tact with iron can be used satisfactorily at temperatures up to 300* 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 becamo increas ingly apparent at higher tem peratures." at 310 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 inonoxiue, 0.17% oxygen (derived from the air). 0.99% hydrogen chloride, 2.1% combustible gas calculated as methane, 0.002% chlorite', 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 souare inch, resulting from the introduction of compressed air. Following this treatment and r*oiing, the cases removed from the system were 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 flainc on the pipe caused the pipe to glow & dark red for a space of about 2 inches. This unit was operated almost 3 months before a circulation stoppage occurred. When the line waa 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 uot been found necessary after 7 years of continuous use. Accidental leaks or spills constitute tbe only observed losses. PLAN AND PART SECTION B`B' Their workers analysed the decomposition products of Aroclor 1248 heated in the pres ence of hot Iron at 459 C. and also heated in an iron cylinder O a TOWOLDMONOQ26799 uly 1949 INDUSTRIAL AND ENGINEERING CHEMISTRY Tablk V. Resistance or Structural Materials to Aroclor 1248 U*uli AluBklDUU Copper KlMDtWuru Nielel Bil ter Tib 125* C. R Melnla Zine Mild Heel Phosphor brcate Red br*u SuinleM eteel Yellow br** Re RR. Excellent mitUnre. lew tbnn 1.0 X 10 ** cm. per day penetration or 0.00014 inch per ye*r. _. ____ K, Good reeutance. 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 rewibtanre, penetration between 10 X 10** cm. per dey and 100 X 10'* mi. per day or between 0.0014 and 0.014 ineh per year. *. Following letter indicatinc reriatance, aienifie* material may be b*tter than indicated if totally immersed, as weight ioaa ie believed to come Iroa oijdation of part of lest atrip 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 oi various metals (7) at 25 and 125 C. is given in Table V. Similar studies made at 325 C. (tf) indicate that the penetra Figure 3. Control and Safety Circuit 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 Heater Design. The general requirements of the heater are as a heat-transfer medium have shown that the material is prac tically noncorrosive to valves, piping, tank jackets, etc., made compactness, ease of construction and service, and avoidance of direct fi&me impingement on the tubes. 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 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 bums. 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 nil (linseed oil) should 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 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 In? no opportunity for workers to come in con tact with vapors from the hot heat-transfer medium. <Ma JTCAM OR WATER Youtlet jacketed *hpc cooler 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 Xo. 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 00 feet of l-inrli 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 pijie arranged in the same fashion. Results of tests on the small-size heater covering tenqicraturcs 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 GO'To 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-exchange coellicients for Aroclor 1248 to water in a double pipe heat-exchanger made from 1.25-inch pipe with a 2-inch pipe jacket are m the 120 to 180 range. These figures arc calculated from test results on this installation. Cooler. A very useful adjunct to the system is a double pipe cooler on tho outlet of the heater shown in ^WATER inlet --^kiXD- Figure 2. By turning water into the jacket, the Aroclor can be cooled and drain --C^-rC^- the temperature of the system lowered. This is helpful when it is necessary to PUMA -o-txH 6 -A JO i-------- :--m------------- cool a batch before removing it or wheu 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, Tump, anil Expansion Tank designed for hot liquid service. 0222180 TOWOLDMON0026800 1344 INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 41, No. 7 Pipe Construction Table VI. Piping Detail (Dimensions in inches) '/through / '/through 'A 1 throug 6 Schedule 60. A.S.T.M. A53 or A1G6 Schedule 40. A.8.T.M. A53 or AIM Screwed Flanged Bend in ehop and field where pos sible. Must be cleaned to remove Ells. tee*, and reducers Flange* Bolt* A through / I through 0 Unions Dope A through */ Casket* Phut-ofl valves Control valves Cheek valve* '/ through / 1 through 2 2'/i through 6 *A through *A 1 through 2 2*/ through 6 / through 'A 1 through 2 Safety valves Relief valve* Valve stem packing I'/i through 3 Gage and glass A gnge Strainer* Vi*/. 1 through 3 Forged steel screwed. Crane SOOd senes Welded fittings. Crane 300e Series 3U (to match valves) Machine bolts A.?.A. B-18.2 with^hesagonal nuts for service below ft00 F. Above use alloy steel. Crane tri ples A.S.T.M. AM Crane 252h forged alee Crane 425 high tem perature thread compound Soft iron ring flat or corrugated Crane 300GW, screwed, gate Crane 3GI5W, flange, gate Crime 33XU, flange, gate Crane 3040 XR, screwed, globe Crane 3050 XR, flange, globe Crane 151 XU. flange, globr Crane 3074 X, screwed Crane 3080 X, flanged Crane 159 X. flanged Consolidated 100 lttt. screwed Consolidated 1C12 t\, flanged Goetze 340D or Durauiotallir Dno Tyt-o 100 PCPR Marsh 0-100 ll./sq. inch gogo siphon with Crane 22211 bar stock valve, .lerguson Scries 1120 Keflex type liquid level gage 62) tarway threaded 822 Yarway flanged The Dayton Dowd Type C pump is an example of the type required. It should he 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 Xo. D-110 or Garlock 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 svstem better than will a closed impeller. Enough horsepower for the most viscous conditions is required. PiriNQ 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 giveu 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 arc used throughout. Tito system requires an expansion lank 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 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 Derating conditions and to check the operation of the heater itself, it is often desirable to measure the temperature of the Aroclor in and out of the heater and cooler. Items \), 10, and 11 (l-'igurc 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 Mereoid DA-31, open circuit on high pressure. (detect* stoppage Actual nettings depend on individual layout of pipe) 2. Lot pressure alarm Mereoid DA-31-3, open circuit on low pressure. (delect* -toppage Actual setting* depend on individual layout of pump) 3. Thermostat (detect* Fenwal 18002. Contact* open on temperature esceaive heating increase hence obstruction of flow) 4. Float sw itch (detect* Mereoid Figure 40. S.P. switch. Open at low leakage from sys level tem) ft. Flame failure tvstem Combustion Control Corp. Fireye FF6. Flame (cut* off gas i( failure control for manual ignition gas burner pilot flame goes systems out) 6. Ca* valve (cut* off General Control Corp. K-10-2. Closes witb in case preceding current off devices set) 7. Red light (alarm) Kitlsrk VA-1 CO W, or Benjamin 70l3-V 8. Horn (sound* alarm) Edward* 312 Alarm rainy Tvj.e C-IHI4 1-NO. I-NC watertight (/) Stop horn relay Tyne C-l 104 1-NO. 1-NC, watertight (I) Stop horn button I-1IA.4 (#) 0. Thermometer well 0-300 O. mercury bulb thermometer (visual check of heater perform ance) JO. Thermometer wcJI 0-3GD C\ mercury bulb thermometer (visual check of heater perform ance) 11. Thermometer well 0-3G0 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 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. Sakf.ty 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. ACKNOW LF.DGM ENTS The authors arc 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., Bui/. 700. (2) Jbid., Bull. 800. (3) Am. Soc. 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. Jnd. Hyo- Torieol., 21, 165 (1939). (0) Monsanto Chemical Co., Anniston, Ala,, private communica tion, April 13, 1944. (7) Monsanto Chemical Co., St. Louis, Mo., Monsanto Tech. Bull. P-115 (August 1047). (8) Sortman, C., Beatty, H., and Heron, 8., Ind. Eno. Cokm., 33, 357 (1941). (0) Sullivan. M. V.. Wolfe, J. K., and Ziaraan, W. A..Ibid., 39, 1007 (1047). (10) Underwriters' Laboratories, Chioago, 111., "Miscellaneous Haiards," No. 2498,1934. Rkceivid August 27, 1048. Prnsonted before the Meetiog-in-Miniature. Alabama Section, Akbsicah CaawiCAt Bocim, Deoember 8. 1040. Puntan in U. 8. A. 02 22 it) l c o 0 TOWOLDMONOQ26801 o Monsanto Chbucals---Plastics ___^/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*MDM9*49 0222182 Printed In U.S.A. TOWOLDMONOQ26802