Document 15me429vjOV6d8vmdy6Egjqom

TOWOLDMONOQ30438 TOWOLDMONOQ30439 FIRE-RESISTANT INDIRECT HEATING Aroclor 1248 is fire-resistant. It does not support combustion up to its boiling range, 652-725 F., and has a high flash point 380 F. Thus indirect heating with Aroclor greatly reduces plant fire hazard, thereby increasing worker safety and possibly preventing costly fire damage to plant and equipment. Aroclor is used in the liquid phase at atmospheric pressure or at low pressures, and does not require costly high pressure equipment. Explosion hazard is eliminated. Forced circulation indirect heating with Aroclor is efficient and uniform. It gives accurate control of heat put into the process. This often leads to increased production, lower costs, and better quality of the finished product. The general purpose of this booklet is to assist you in evaluating the benefits of using Aroclor for indirect heating in your plant or processes. 0358635 I TOWOLDMONOQ30440 HISTORY OF INDIRECT HEATING WITH In 1941, certain new manufacturing processes of the Mon santo Chemical Company required using a noncombustible heat transfer medium at pressures of 30 pounds per square inch or less and temperatures in the range of 500 to 600 F. Monsanto's Aroclor 1248 was the only commercial and economical material which met these requirements. Complete success in operating these early heaters using Aroclor created more general interest in the benefits of a high temperature, fire-resistant, heat transfer agent for a variety of industrial applications. Also about this time, heating design engineers had begun to advocate in this country the benefits of liquid phase high temperature heating. Subsequently, leading manufacturers of heating equip ment began to build heaters constructed specifically to accomplish maximum efficiency and maximum operating temperature using Aroclor liquid. TOWOLDMON0030441 A PARTIAL LIST OF PRESENT COMMERCIAL AROCLOR HEATING APPLICATIONS INCLUDES: 1. Heating chemical process equipment, especially where flamma ble materials are handled. 2. Processing varnishes and resins. 3. Molding plastics and rubber materials. 4. Heating bituminous materials. 5. Heating vegetable oils for deep-frying potato chips and other food processing operations. 6. Processing titanium and other metals. 7. Indirect heating in the manufacture of dyestuffs. 8. Heating corrugating rolls. 9. Indirect heating of distillation equipment. 10. Heating panels for continuous vacuum belt drivers. To assist industry with installation of indirect heating systems using Aroclor, a handbook entitled, "Aroclor 1248 Heat Transfer Data", giving engineering data is available from Monsanto. In addition, the names of leading heating design engineers and manufacturers who build heaters for Aroclor will be supplied when desired. Monsanto does not manufacture or supply equipment for heating with Aroclor. TOWOLDMONOQ30442 TOWOLDMONOQ30443 SIMPLICITY The heaters art* characterized by simplicity of construction and operation. There is no vapor formation and consequently no traps, feed pumps, etc. to maintain. An open vented tank permits free expansion of the fluid and avoids all problems of feed regulation, vacuum systems, or condensers. ACCURACY OF CONTROL Accurate temperature control for heating and cooling is provided. CONVENIENCE Aroclor heating units are compact, space saving and may be fired with gas or oil or heated electrically. Convenient controls for safety and tem perature regulation are provided. The viscosity of the fluid permits pump ing at room temperatures. 0358639 5 TOWOLDMONOQ30444 TOWOLDMONOQ30445 PERFORMANCE QUALITIES OF 1 1218 LIQUID PHASE LOW PRESSURE 600 F. MAXIMUM Aroclor 1248 is used in the liquid phase at atmospheric pressure or not over 20 to 30 PSI gauge and up to a maximum continuous operating temperature of 600 F. HIGH BOILING FLUID The maximum operating temperature is sufficiently below the 652-725 F. boiling range of Aroclor 1248 to assure a liquid condition at all times. EXCELLENT HEAT STABILITY Although Aroclor is very stable to heat, adequate forced circulation, (about 20 to 80 gpm depending on the size of the system) should be provided to protect the liquid against localized overheating. Fluid velocity should be about 5 to 8 feet per second. FORCED CIRCULATION AVOIDS LOCALIZED OVERHEATING Brief overheating may not be harmful but extended heat injury above 600 F. will result in an increase of viscosity and measurable dehydrohalogenation. TIGHTLY CLOSED SYSTEM ELIMINATES VAPOR LEAKS AND ODOR With the exception of an open vented expansion tank, the system must be completely closed and sealed tightly to prevent vapors and odor from entering workroom areas. DRY AND FULL SYSTEM ELIMINATES POSSIBLE CORROSION The system should be kept dry and free from moisture. It is desirable to keep the heater and piping full of Aroclor liquid at all points. This eliminates spaces where moist air might collect during shutdown periods. By following these simple precautions, possible corrosion is minimized or eliminated. 03586*1 7 TOWOLDMONOQ30446 1 CHARACTERISTICS OF A TYPICAL HEATER TAILORED TO FIT THE JOB Heating equipment using Aroclor is selected or designed to meet the requirements of the process, whether it is large or small. The heating equipment ranges in size from small portable units which are usually electrically heated to large gas or oil fired units with capacities ranging from 250,000 to more than 10,000,000 B.t.u.'s per hour. ADVANTAGES OF FORCED RECIRCULATION HEATERS Especially in the case of large size heaters where the maximum operating temperature of 600 F. is required, the forced recirculation heater is superior to any heater dependent on natural circulation. The forced circula tion system is engineered to give a positive, uniform fluid flow through all tubes fed from a header, whereas natural circulation units have no special design to equalize the flow in the heater tubes. Where natural circulation units are operated with thermal liquids, it is impossible to distribute the flow equally through all tubes. The thermal liquid seeks the shortest route to the discharge outlet. Consequently, the longer tubes, because of their greater resistance to flow, are subject to overheating. This becomes an important consideration when such units are operated at the high temperature range prescribed for a given fluid and may result in decomposition of fractions of the thermal liquid. Also, since the discharge temperature from the circuit through a natural circulation unit is the average temperature of the short-circuited fluid and the overheated fluid from the longer tubes, this causes variable temperatures which are produced at the heater outlet. 8 TOWOLDMONOQ30447 WWW UNIFORM TEMPERATURE Forced recirculation thermal liquid heaters, which consist of groups of small diameter tubes of equal length and orificed for uniform flow, provide even temperature distribution through all tubes in the circuit. Small diameter tubes, which are not practical in natural circulation heaters because they limit capacity, have a distinct advantage in forced recirculation units, In the smaller tubes the volume of fluid from the surface film to the center of the tubes is less and therefore heating is more uniform than in larger diameter tubes. The forced recirculation heater is designed to move the fluid at velocities of 5 to 8 feet per second. This high velocity and resulting turbulence, coupled with the small fluid content of the tubes assures high rates of heat transfer and extremely close control of the outlet temperature. Tolerances of plus or minus 2 F. or closer are possible. ELIMINATES SLUGGISH FLOW Forced circulation eliminates dead spots or sluggish flow areas where localized overheating of the Aroclor may occur. TOWOLDMONOQ30448 HEATER SYSTEM COMPONENTS I The next four pages describe the main features of the typical piping diagram shown on pages 14 and 15. A summation of primary advantages of heating with Arodor 1248 then follows. THE HEATER FLOW CIRCUIT The flow circuit consists of a thermal liquid heater and a recirculation pump which discharges the fluid returned from the system into the upper header of the heater as shown in Figure 1. THE PUMP All Aroclor heaters are designed to avoid direct flame impingement on the tubes. The recirculation pump may be any one of a number of standard centrifugal units designed for hot liquid service. The pump should be made of cast steel and have a water-cooled stuffing box and water-cooled bearings. The stuffing box should have room for at least eight rings of packing and a lantern ring. Durametalic No. D-110 or Garlock No. 234 may be used for packing the pump. Mechanical seals have also proved to be successful at elevated temperatures. An open non-overloading impeller is desirable, as it will handle the cool, more viscous liquid on starting the system better than a positive displacement type pump. THE BURNERS Gas and light-oil burners are usually used. Heavy oil burners using bunker "C" oil usually require furnishing steam to preheat the oil. INDUCED DRAFT FAN As an economy feature to eliminate the expense of building and main taining a high chimney, the heater is usually fitted with an induced draft fan. The products of combustion are discharged from the fan into an exhaust vent higher than surrounding buildings. 10 03586<< TOWOLDMONOQ30449 EXPANSION TANK . FIG. 1 THE PIPING AND CONTROL CIRCUITS AFt 0Cl OR FROM HLATER AROCLOR TO HI ATIR STEAM OR WATER OUTLET JACKETED PIPE COOLER WATER INLET DRAIN FILL PUMP GAS TEMP. GAUGES AIR HURNER PILOT HI AllR PIPING A typical heater piping and control circuit is shown in Figure 1. All piping larger than 2i-inch is flanged or welded; experience has shown that hot Aroclor penetrates screwed joints of larger sizes. Steel and cast steel are used throughout. Spiral wound stainless steel and asbestos gaskets are recommended for all connections. For operation in areas where the Aroclor temperature may drop so low as to make the fluid unusually viscous, it may be desirable to steam-jacket the Aroclor circulating lines to facilitate rapid start-up in cold weather (or "when needed"). 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 system during subsequent high temperature operation. 03586*i5 11 L TOWOLDMON0030450 DIFFERENTIAL PRESSURE CONTROL SAFETY AND TEMPERATURE CONTROLS Connected to the suction and discharge sides of the pump, this device shuts off the burner in case of pump failure or a broken pipe line. Any factor causing a decrease from the desired operating pressure will activate this device to shut down the burner. TEMPERATURE CONTROL This unit modulates the burner in response to temperature variation of the liquid. FLAME FAILURE CONTROL An electronic flame control apparatus pilots the flame and stops the burner in case of unsatisfactory combustion. TEMPERATURE LIMIT CONTROL This contains thermocouples attached to discharge ends of the tubes at critical points. Excessive temperature rise induces the control to shut down the burner. PUMP MOTOR STARTER The motor starter should be furnished with an auxiliary switch. The auxiliary switch is on the burner circuit so that any motor failure or short-circuit will stop the burner. 12 03566*6 TOWOLDMONOQ30451 f LIQUID LEVEL CONTROL This should be located at the highest point in the system, usually in the expansion tank. Its purpose is to shut off the burner in case of a liquid level drop in the system such as would result from a pipe break or excessive leakage at the pump. AIR SAFETY SWITCH This control is applied to the suction side of the induced draft fan. Its purpose is to stop the burner in case of fan motor burn-out or over heated bearings. VENT TANK The vent tank or expansion vessel is located at the highest point in the system and "floats" on the line. It is best connected to the intake side of the pump as this tends to give a positive head on the pump. The Aroclor in the vent tank should be relatively cool. It acts as a seal. However, the tank should be closed and fitted with a vent pipe and elbow with a moisture trap to keep out moist air. The capacity of this tank is normally 25% of the volume of Aroclor in the system. COOLER A very useful adjunct to the system is a double pipe cooler on the outlet of the heater. By circulating water through the jacket, the Aroclor may be cooled and 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 requires control. 03596*7 13 TOWOLDMONOQ30452 FIG, 2. THE COMPLETE HEATING CIRCUIT WITH USER NO. 1 JACKETED KETTLE VENT TEMPERATURE CONTROL USER NO. 2 JACKETED KETTLE R 3 VENT LIQUID RETURN VENT RELIEF VALVE FILL CAP MANHOLE FOR REMOVAL OF SLUDGE STORAGE TANK VENT CIRCULATION PUMP MAKEUP AND DRAIN PUMP EXPANSION JOIN I EXPANSION JOINT INDUCED DRAFT EAN HOT LIQUID TEMPERATURE CONTROL BURNER CLEANOUT DOOR PUMP DIFFERENTIAL CONTROL TOWOLDMONOQ30453 TOWOLDMONOQ30454 SUMMARY OF BENEFITS FROM INDIRECT HEATING WITH 16 0350650 TOWOLDMONOQ30455 1. Safety from fire and explosion. 0. Product uniformity results from 2. Operating temperatures up to 600 more accurate temperature control. F. in properly designed recircula tion heaters. 7. Reduced product cost results from better control of quality. 3. Accurate and uniform temperature A control. 0. Heating and cooling in the same equipment. 4. Economy of heating, low cost non- pressurized equipment, low main tenance, space savings, low fluid make-up. 0. Different individually controlled temperatures at various user sta tions in the circuit gives flexibility. 5. Increased production. In some processes, production rates were lO. Simplicity of installation and oper increased as much as 50%. ation. For engineering data or further information on the uta of Aroctor 1248 for heat trantfer, contact Momanto Chemical Company, Organic Chemicali Divition, Pott Office Box 478, St. louit, Mittouri. 0356651 TOWOLDMONOQ30456 TOWOLDMONOQ30457