Heating jacket

Heaters. The preferred methods for heating are a double-jacket heated tank, nonmetaUic heat exchangers, quartz heaters, or Teflon-coated low watt density stainless steel heaters. Localized overheating must be avoided. 

The maximum or minimum temperature attainable in a vessel can be limited by properly designed jacket heating systems. If steam heating is used, maximum temperatures can be limited by controlling steam pressure. A steam desuperheater may be needed to avoid excessive temperature of superheated steam from a pressure letdown station. 

Buildup can occur either rapidly during an unstable batch or slowly over many normal batches. Buildup drastically reduces jacket heat transfer, slowing heatup and cooldown and, if serious... 

There is a middle steady state, but it is metastable. The reaction will tend toward either the upper or lower steady states, and a control system is needed to maintain operation around the metastable point. For the styrene polymerization, a common industrial practice is to operate at the metastable point, with temperature control through autorefrigeration (cooling by boiling). A combination of feed preheating and jacket heating ensures that the uncontrolled reaction would tend toward the upper, runaway condition. However,... 

Seal vessel turn on jacket heat (140°C steam)... 

Reactor electrical heat input(l) Coil/jacket heat balance Condenser heat extract rate (1) Reactor heat loss... 

The first-order consecutive exothermic reaction sequence, A —> B —> C, is carried out in a thick-walled, jacketed batch reactor, provided with both jacketed heating and cooling, as shown below. 

J-acid, 9 402, 403 Jackets, heat-transfer, 16 111—718 Jacobsen s ligand, 20 305 Jacobson-Stockmayer theory, in siloxane polymer manufacture, 22 558 Jacquinot advantage, 14 228 J-aggregation, 9 508 Jahn-Teller distortion, 22 203 Jahn—Teller effect, 6 611 Jai Tire process, 21 476 Jameson cell, 16 653 Jamming phase diagram, 12 18 Jams... 

ShelI l..oadi ng with 80/20 Amatol, Part of the mixt maintained in the kettle at 90—95° (See above under Preparation) was transferred to the hopper of an extruder which was provided with a stirrer and jacket heated with steam at 3—5 lbs pressure. The extruding machine consisted of a steel tube in which a worm screw rotated slowly. This... 

Place a mixture of l.Og of the hydrocarbon, 10 ml of dry dichloromethane or 1,2-dichloroethane, 2.5 g of powdered anhydrous aluminium chloride and 1.2 g of pure phthalic anhydride in a 25-50 ml round-bottomed flask fitted with a reflux condenser (127 mm jacket). Heat on a water bath for 30 minutes (or until no more hydrogen chloride fumes are evolved). Cool in ice and add 10 ml of concentrated hydrochloric acid cautiously and with constant shaking. When the reaction has subsided, add 20 ml of water and shake vigorously. (All the solid... 

A, = jacket heat transfer area (m2) = 7rDL D = reactor diameter (m)... 

Before we leave this example, let us take a look at the issue of heat transfer. In setting up the simulation, we have specified the reactor temperature (430 K) and volume (100 m3) but have said nothing about how the heat of reaction is removed. The simulation calculates a heat removal rate of 12.46 x 106 W. If the aspect ratio of the vessel is 2, a 100-m3 vessel is 4 m in diameter and 8 m in length, giving a jacket heat transfer area of 100.5 m2. If we select a reasonable 30 K differential temperature between the reactor and the coolant in the jacket, the jacket temperature would be 400 K. Selecting a typical overall heat transfer coefficient of 851 W K-1 m-2 gives a required heat transfer area of 488 m2, which is almost 5 times the available jacket area. Aspen Plus does not consider the issue of area. It simply calculates the required heat transfer rate. 

In all the simulations up to now the jacket volume has been calculated by using the jacket heat transfer area and assuming a jacket thickness of 0.1 m. The jacket volume has no... 

The 1-CSTR process has a conversion of 98% in the single reactor with a reactant concentration of 0.16 kmol/m3. The reactor volume is high (262 m3), and the jacket heat transfer area is large (190 m2). The resulting jacket temperature is 339 K. Linear analysis gives an ultimate gain of 52.6 (dimensionless) and an ultimate period of 1419 s. 

The ethylbenzene CSTR considered in Chapter 2 (Section 2.8) is used in this section as an example to illustrate how dynamic controllability can be studied using Aspen Dynamics. In the numerical example the 100-m3 reactor operates at 430 K with two feedstreams 0.2 kmol/s of ethylene and 0.4 kmol/s of benzene. The vessel is jacket-cooled with a jacket heat transfer area of 100.5 m2 and a heat transfer rate of 13.46 x 106 W. As we will see in the discussion below, the steady-state simulator Aspen Plus does not consider heat transfer area or heat transfer coefficients, but simply calculates a required UA given the type of heat removal specified. 

All of reactant A is charged to the vessel at the beginning of the batch at a temperature T0 = 294 K. The amount of the initial charge fills the vessel. In the discussion below, different heat transfer areas are considered, starting with the jacket heat transfer area and increasing the area if necessary by using an external heat exchanger. 

To illustrate some of the design and control issues, a vessel size (DR = 2 m, VR = 12.57 m3, jacket heat transfer area Aj = 25.13 m2) and a maximum reactor temperature (7j) ax = 340 K) are selected. The vessel is initially heated with a hot fluid until the reaction begins to generate heat. Then a cold fluid is used. A split-range-heating/ cooling system is used that adds hot or cold water to a circulating-water system, which is assumed to be perfectly mixed at temperature Tj. The setpoint of a reactor temperature controller is ramped up from 300 K to the maximum temperature over some time period. 

The kinetics used are those given in Chapter 2 (Table 2.2). The desired operating temperature is 340 K. The diameter of the reactor is 2 m, giving a total volume of 12.57 m3 and jacket heat transfer area of 25.13 m2. The reactor is initially charged with 6.285 m3 of pure B with a composition CB = 8.01 kmol/m3. The initial reactor temperature is 300 K. 

The sulfonation reaction is exothermic, but not highly corrosive, so sulfonation can be conducted in steel, stainless-steel, or cast-iron sulfona-tors. A jacket heated with hot oil or steam can serve to heat the contents sufficiently to get the reaction started, then carry away the heat of reaction. A good agitator, a condenser, and a fume control system are usually also provided. 

Start up of a jacketed batch reactor requires control of the heat-up and cool-down rates. This involves determining and setting the jacket heat transfer fluid temperatures. An alternative is to make a trial heat-up and incorporate the results into a time-dependent heat transfer equation ... 

Tray dryers, the simplest type of dryer, are commonly used for batch drying of biological materials, where the wet solids are placed on trays which are then transferred into a chamber. The chamber may have a heating jacket, heated tray supports, or a hot air supply. Vacuum may be applied to reduce the temperature at which the liquid evaporates, preserving heat labile products. These are well suited to low-volume products or flexible plants where a number of different products with different characteristics must be dried. They are relatively inefficient to operate, difficult to clean, and labor intensive to operate. The product is exposed when being loaded and unloaded, so the dryer may need to be located in a clean room or area for pharmaceutical products. 

---