Heat transfer jacket

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... 

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... 

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. 

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 ... 

Effect of Reactor Type, Jacket Heat Transfer Fluid, and Reactor Fluid Viscosity... 

A simplified schematic for a jacket heat transfer service is shown in Figure 11 [18]. Here, two separate heat transfer fluid headers are used, and the control valve is on the outlet stream to reduce the temperature shocks that might occur if a single... 

Calculate the jacket heat-transfer rate, Qj, from Equations 7.4.7 to 7.4.9 and... 

Zakrzewska and Jaworski [101] performed single phase CFD simulations of turbulent jacket heat transfer in a Rushton turbine stirred vessel using the eight turbulence models mentioned above as implemented in FLUENT. In all simulations the boundary flow at the vessel wall was described by the... 

We demonstrate in this section that the besf temperature from the standpoint of controllability is not the highest possible. This results from the reduction in cooling-jacket heat transfer area that occurs as the size of the reactor is reduced. The temperature difference between the reactor and the jacket becomes bigger, resulting in a reactor that is more difficult to control. 

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