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Reactor Structure and Heating device | Reactor design

By WHGCM September 28th, 2023 89 views
Preamble
The reactor function has been introduced in previous articles, summarized, roughly as follows five points:
(1) Reactor can fully stir the medium to participate in the reaction so that the material is mixed uniformly;
(2) It can strengthen the heat transfer effect and interphase mass transfer;
(3) Make the gas uniformly dispersed in the liquid phase;
(4) make the solid particles in the liquid phase uniform suspension; 
(5) Make the immiscible another liquid phase evenly suspended or fully emulsified.
Design of reactor
Reactor design can be divided into Process Design and Mechanical Design.
The main contents of the process design are.
1, reactor's working volume; heat transfer area and composition form;
2, stirrer form and power, speed;
3, Nozzles' orientation arrangement.

The process requirements and basic parameters determined by the Process Design is the basis for Mechanical Design.
The Mechanical Design generally includes.
1, to determine the structural form and size of the reactor.
2, for the cylinder, jacket, head, stirring shaft, and other components of the strength calculation; 3, Selection of the stirring device according to the process requirements.
4, Select the shaft sealing device according to the process conditions. 
5, Choose transmission devices according to the process conditions.
Due to the wide variety of chemical products, materials of different phases, and reaction conditions vary greatly, the industrial use after the reactor also has a variety of forms. As per the reactor structure, reactors can be sorted as stirred kettle reactor, tube reactor, fixed bed reactor, and fluidized bed reactor.
The overview of a reactor structure
1. The structure of stirred reactor mainly consists of a cylinder, heat transfer device, transmission device, shaft sealing device, and a variety of receivers.

As shown in Figure 1-1 jacketed stirred reactor
structure picture of stirred reactor
Structure of stirred reactor
1 Motor;
2 Reducer;
3 Frame;
4 Manway/manhole
5 Sealing device:
6 Feed inlet:
7 Upper head;
8 Cylinder;
9 Coupling
10 Stirring shaft:
11 Jacket
12 Outlet of heat-carrying medium
13 Baffle,
14 Spiral deflector;
15 Axial flow stirrer;
16 Radial flow stirrer:
17 Gas distributor
18 Lower head;
19 Feed inlet.
20 Inlet of heat-carrying medium
21 Gas inlet
Figure 1-1
The inner cylinder of the kettle is usually a cylindrical shell that provides the space required for the reaction.
The role of the heat transfer device is to meet the temperature conditions required for the reaction.
The stirring device includes a stirrer, stirring shaft, etc., to realize the stirring of the working parts.
The transmission device includes a motor, reducer, coupling and frame, and other accessories, it provides the power of stirring.
The shaft sealing device is to ensure the formation of sealing conditions at work, to prevent the medium from leaking out of the components.
2. Cylinder and heat transfer device
The inner cylinder of the vessel is generally a steel cylinder. Most of the container head is the standard oval head, in order to meet the process requirements, the kettle body is installed with a variety of receivers, such as material import and export pipe, monitoring device receivers, and so on.
Commonly used heat-transfer devices are jacketed structures of the wall heat transfer and kettle-installed heat transfer tube heat transfer in two forms. The most widely used is the jacket heat transfer, see Figure 1-2a.  When the kettle lining structure or jacket heat transfer can not meet the temperature requirements, the commonly used snake tube heat transfer mode, see Figure 1-2b.

jaket and coil postions
Figure 1-2 Heat transfer device
(1) cylinder
In order to meet the medium reaction space required, process calculations have determined the required volume of reactor V0. In practice, the reaction medium may produce foam or a boiling state, so the actual volume of the cylinder V should be greater than the required volume V0 This difference is expressed in terms of the loading coefficient. The size of the volume depends on the size of the simplified body diameter Di and height H (see Figure 1-3 
Geometric relationship of the cylinder ).
Height dia ratio scheme
What is the best way to determine the appropriate height and diameter ratio for a cylinder on a reactor vessel? 
If the working volume is confirmed then the cylinder's height and diameter ratio should be at a proper range.
When the stirrer speed is confirmed, the stirrer's power consumption is proportional to the 
5th power of the stirring paddle's diameter.
If the cylinder diameter increases, in order to ensure the stirring effect, the stirring paddle diameter needs to be enlarged accordingly, so it increases the power consumption. Therefore, the vessel cylinder diameter should not be too large.

On the other hand, if the height increases, it can make the heat transfer area of
the jacketed container increase, which is good to heat transfer. So the fermenters and other reactors, that need good heat transfer, in order to ensure adequate contact time, the cylinder's height shall be big.

And if the height of the kettle is big, the length of the stirring shaft should be increased accordingly, then the strength of the stirring shaft and the rigidity requirements is high. In order to ensure the stirring effect, multi-layer paddles need to be set up, which makes the powder consumption increase. Therefore, we shall consider the impact of a variety of factors when choosing cylinder height and diameter ratio.

Guidelines for reactor pressure vessel design 
How to determine the appropriate reactor pressure in the vessel and jacket?
The vessel thickness of the cylinder and jacket should be determined according to the strength conditions or stability requirements.
(a)When the jacket is subjected to internal pressure, it is designed as an internal pressure vessel. If the vessel cylinders are subjected to internal pressure and external pressure, the thickness should be designed according to the most dangerous state that may occur when the reactor start, operation, and shutdown.
(b)When the vessel cylinder is a vacuum and has a jacket, the reactor shall be designed as an external pressure reactor. The design pressure equals the vacuum container design pressure plus the jacket design pressure.
(c)When the reactor vessel is operated under atmospheric pressure, the vessel's design pressure is the same as the design pressure in the jacket.
(d ) When the kettle is for the positive pressure operation, then the cylinder should be at the same time according to the design of the internal pressure and the external pressure, and its thickness to take the greater of the two.
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