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o o Portable Heater Using Chlorinated Biphenyl R. E. Howard Monsanto Chemical Co., Si. Louis, Mo. * Beprinled from Industrial and Engineering Chemistry Vol. 43, Page 782, March 1951 PCB-ARCH-EXT0375903 Reprinted from INDUSTRI/rfS AND ENGINEERING CHEMISTRY, Yol. 4$?~.r&ge 782, March 1951 Copyright 1951 by the American Chemical Society and reprinted by permission of the copyright owner LANTS Portable Heater Using Chlorinated Biphenyl R. E. HOWARD Monsanto Chemical Co., St. Louis, Mo. OR many pilot plant Foperations there is need for a source of beat capable' of reaching temperatures in excess of that obtainable with ordinary steam pres sures. It is frequently un desirable or unsafe to make use of direct gas-firing or inconvenient to use direct electrical strip beating. In answer to this problem a portable electrically heated unit using Aroclor (Mon santo Chemical Co. chlori nated biphenyl and poly phenyls), a nonflammable, To fill the need for a heat transfer system providing high temperatures for pilot plant use, a portable heating unit, using chlorinated biphenyl as a heat transfer medium, was designed and built. The unit involved the following elements: A reservoir for the chlorinated biphenyl heat transfer medium; a circulating pump; an electric oil immersion heater; a water-jacketed cooler; instrumentation to provide con trol of the circulating fluid temperature; and pipelines from the heating unit to and from the equipment to be heated. _ The unit has been used in carrying out reactions on a pilot plant scale at temperature levels up to 300 C. for both heating and cooling. The use of electrical.heating permits the use of the apparatus in hazardous atmos pheres. Portability was a desired feature of the unit and as a result it was mounted en tirely on a four-wheeled truck with power received via an extension cord; watre 'for cooling, when required, was supplied by hoses. Aroclor piping was arranged so that short lines might be run to and from the jacket of any desired reactor. In the particular pilot plant building for which this unit was designed it was necessary that the installa tion conform to Class 1, noncorrosive liquid heat Group D requirements, and transfer medium, was constructed. In such a system an inert therefore the motor, heating elements, thermostat, and all wiring liquid is heated in a suitable device and circulated with a pump are explosioDproof. For control and ease of operation the unit through the coil or jacket of the vessel to be heated. Since the was provided with aD on-off thermostat which controlled the liquid does not boil, condenser and traps axe unnecessary and the Aroclor temperature within =*2 C. of the desired setting. A system may be vented to atmospheric pressure. water-cooled coil was provided for quickly lowering the tempera- The unit to be described was built to service any one of several tine of the circulating Aroclor stream if desired. To provide pilot plant reactors in the Organic Division research pilot plant of for the considerable expansion of the Aroclor on heating, a buffer Monsanto Chemical Co., St. Louis, Mo. It was mounted on a tank was mounted on the unit. This tank served as a reservoir, portable frame so that it could be moved from one location to a buffer, and a vent for the system. another as required and connected to a given vessel with short The deared capacity of 40,000 B.t.u./hour equal to 11.7 kw. lengths of iron piping. The heated vessels were about 50 gallons resulted in selection of a 15-kw. Chromalox electric oil immersion working capacity. . heater, Mode) DCH612-3XX. McArdle et al. (2) have described design methods for indirect, gas-fired Aroclor heaters and present data on the stability and physical properties of Aroclor 1248. Additional data on the properties of other Aroclors are given elsewhere (5). EQUIPMENT DESIGN Premises of the design of the unit were: 1. Aroclor operating temperature: 300 C. maximum. 2. Capacity: approximately 40,000 B.t.u. per hour based on vaporizing about 200 pounds per hour of organic material having a heat of vaporization of 150 B.t.u. per pound and allowing for around 30% neat loss. In order to meet the above requirements Aroclor 1248 was chosen as a beat transfer medium srace it is the highest boiling The pump provided to circulate Aroclor through the heater, cooler, and jacket of the pilot plant reactors was sized to give a veiocit}' in the heater high enough to prevent surface boiling at an operating temperature of 300* C. A 2 X 1.5 iDch T4MD-7Vj Durco pump having a rated capacity of 60 gallons per minute at 20-foot bead was selected. The unit was driven by a LouieAllis, 5-hp., 1140 r.p.m., Class 1, Group D motor. Since the Dow required in the heater exceeded that needed in the reactor jackets, a by-pass was provided so that some of the flow could be circu lated back to the pump rather thaD passing through the reactor jacket, but it was arranged so that the full pump flow would al ways go through the heater. Since hot Aroclor vapors are somewhat toxic it is imperative that the piping and pump stuffing box be completely free of leaks unless local exhaust ventilation can be provided. Drinker (7) has indicated that 0.5 mg. of Aroclor per cubic meter of air is the maximum safe concentration. Aroclor that can readily be pumped at room temperature. The A photograph of the completed unit is shown in Figure I and a recommended maximum operating temperature for this material schematic flow diagram showing the pipiDg arrangement is given is 300 C. in Figure 2. PCB-ARCH-EXT0375904 Figure 1. Portable Electrically Heated Aroclor Unit EXPERIMENTAL RESULTS The unit as previously described was hydrostatically tested for leaks, then dried by flushing with acetone, followed by extended purging with air. Approximately 25 gallons of Aroclor 1248 were charged to the unit and preliminary tests were made to determine its capacity. The value of insulation was strikingly demonstrated by the fact that the maximum temperature attainable with the unin sulated unit at no load was only 257 C. After insulation, two methods were used to determine the useful heat output of the uni t. These in vol ved: 1. Measurement of the rate and temperature rise of cooling water when using the heater and cooler simultaneously. 2. Measurement of the electrical input (with a tong tester) to the heater correcting for the fraction of the time the heaters operated to maintain the set temperature. Results of the cooling water measurements are summarized in Table I. Table II gives the electrical input to the heaters while operating at various temperatures, and Table III gives the data on the heater operating cycle as controlled by the "on-off" ther mostat. In Table III, the per cent of the thermostat cycle dur ing which the heater<^as off is considered to represent the useful beat output of the unit)"and this percentage is multiplied by the kilowatt rating of the heater interpolated from Table II to give x HOT AROCLOR TO EQUIPMENT VENT AROCLOR RESERVOIR -H- Et PA IS COOLING COOLER ICATER AROCLOR FROM EQUIPMENT T OP _1 :: -M--------- X 1DRAIN RECIRCULATING LINE Figure 2. Flow Diagram for Aroclor Heater PCB-ARCH-EXT0375905 ' OUTPUT KW (Ol AND ENGINEERING CHEMIS INDUST Vol. 43. No. 1 OUTPUT BTU/HRXIO Table I. Capacity of Aroclor Heater bt Heating Water in Cooler c. .. 217 266 285 Water Temp., C. In Out 14 44 16.6 75 16 57 Lb./Hr. 697 266 293 Test Min. 60 30 10 Capacity B.t.u./Hr. Ew. 37,500 28,000 21,500 11.0 8.2 6.3 Table II. Capacity of Aroclor Heater by Tong Tester Aroclor Temp., Av. It, - c. Volts Amp. Amp. Kw. 100 450 17.5 7.9 13.6 200 450 17.2 7.7 13.4 250 450 17.0 7.6 13.2 Figure 3. Temperature-Capacity Curve for Portable Aroclor Heater the "useful load" figures. The results of both methods are plotted in Figure 3 which gives the capacity of the unit as a function of operating temperature. Table III. Capacity of Aroclor Heater by Thermostat Cycle Aroclor Temp., 0 C. Max. Min.. Heater Cycle, Seconds On os Useful Load % of full load Kw. B.t.u./hr. . 202 197 57 240 58 247 80.81 81.0/ 10.8 36,900 244 240 62 168 73.0) 63 166 72.-5/ 9.6 32,800 274 272 65 115 63.81 65 113 63.5/ 8.3 28.400 302 300 75 72 45 37.5) 45 38. S/ 4.e 16.700 Table IV. Heating and Cooling Rates with Aroclor Heater _______Heating Rate______ Time, Min. Temp., # C. 0 26 e 100 29 200 45 250 67 300 _______ Cooling Rate Time, Min. Temp., c C. 5 217 10 116 20 85 40 60 Figure 4. Typical Heating and Cooling Curves for Aroclor Heating Unit Of interest also is the heating and cooling rate of the unit at no load. This data is presented in Table IV and Figure 4. DISCUSSION v The unit as described previous)}' has been successfully used for over 2 years on a wide variety of pilot plant jobs requiring high temperature heating and has proved both versatile and effective. A unit haE been designed for a similar application where the heat requirements are greater. This design is the same as the unit de scribed here except for the addition of a second 15-kw. heater in series with the first. ^ Although piping details and selection of auxiliaries will neces sarily be modified for larger installations, units up to several mil lion B.t.u. per hour capacity have been designed by commercial fabricators and good operation has been achieved. LITERATURE CITED (1) Drinker, C. K., J. Ind. Bvo Toxicol., 21, 155 (1939). (2) McArdle, M.. Garrett, L. C., and Benignus, P. G.. Ind. Eng. Chem., 41, 1341 (1949). (3) Monsanto Ohemiral Co.. St. Louis, Mo.. Monsanto Tech. Bull. P-115 (August 1947). Received Jude 12. 1950 Prixted ix U. S. A PCB-ARCH-EXT0375906