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Heat Transfer Methods In Batch Reactor


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#1 Abdullah_28

Abdullah_28

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Posted 06 May 2019 - 03:53 PM

Background:

Heating and cooling are critical since temperature plays vital role in chemical reaction such as product quality and safety. From that standpoint, this article will spot light on the design aspects of heat transfer method in batch reactor.

Reactor is the heart of chemical process which is a pressure vessel used to contain chemical reactions. An industrial reactor is a complex device where heat transfer, mass transfer as well as diffusion may happen along the chemicals. Reactors are classified into two types based on mode of operation as following:

Continuous Reactor
Raw material and product flow continuously thought the duration the process.

Batch Reactor
Raw material is loaded into reactor at the start of process and product is removed sometimes later.

Batch reactors can be found in various industry areas such as chemical, pharmaceutical as well as food. The benefit of batch reactor is that can be used to carry out a sequence operations that would result in producing different products.

In general, batch reactor consists of vessel that is equipped with agitator and integral heating and cooling system. Batch reactors may well differs in size and materials. For instance, Class Lined Reactor is used when high corrosive materials are used in reaction such as acids.

Heat Transfer Methods:

Chemical reactions contained by batch reactors typically either liberate heat (exothermic) or absorb heat (endothermic). Hence, heat transfer plays major role in reactor performance.

Heating is needed for endothermic reactions, for vaporizing liquids during vacuum distillation, and for bringing a vessel up to the desired operating temperature. Cooling is required for exothermic reactions, condensing vapors, and to bring a vessel down to the desired operating temperature.

Heat can be transferred to reactor through jacket, internal coil or external heat exchanger. Both coil and jacket are limited by the physical dimension of reactor. Hence, where coil or jacket can’t provide the required surface area such as in case of highly exothermic reaction, recirculation loop with external heat exchanger can be used.

Jacket Types:

Jacket could be in three shapes either simple jacket, dimpled or half pipe (see below figures).

The simple jacket is an open jacket with an annular space holding the heat transfer media on the external surface of the reactor. It has several features such as simplicity in construction and full coverage for reactor.

Hint:

The simple jacket that has no internal welded baffles is usually inefficient for heat transfer due to the low velocity bring about low heat transfer coefficient for non- isothermal fluid such as hot oil and cooling water. However, heat transfer coefficient for isothermal fluid such as steam does not depend on velocity.

The dimple Jacket is a thin exterior shell is attached to the reactor shell with spot welds located in a regular pattern. The cost of dimple jacket is comparatively inexpensive. As a result of turbulence in dimple jacket, the pressure drop is around 10 to 12 times than the simple jacket. Hence, the velocity should be limited to 0.6 m/s (2 ft/s).

The half pipe jacket Comprises of a welded half pipe that furls around the external of the reactor, creating a circular path for the heat transfer fluid to pass through. The cost is generally higher than the dimple and simple jacket. Conversely, it may be cheaper for a high pressure on the service side. Furthermore, it has the advantage that more than one service can be supplied to different sections of the wall. However, a limited surface area can be applied to reactor as the enormous amount of weld can lead to mechanical concerns.

Jacket Type selection:

The jacket type can be based on some general guidelines as following (Reference 1):

For ≤ 500 gal (1.89 m3) Use the simple jacket

For ≥ 500 gal (1.89 m3) Use the dimple or half pipe jacket

Jacket Pressure ≤ 300 psi (20.7 bar) Use the dimple jacket

Jacket Pressure >300 psi (20.7 bar) Use the half pipe jacket

If reactor pressure is greater than twice the jacket pressure, use the simple jacket

Those guidelines are taken from “Chemical Process Engineering: Design and Economics Book “

Internal coil:

Internal coils are generally full helical coils to provide maximum surface area especially for extreme exothermic reaction. However, the coil cleaning can be an issue in industries that need extreme sanitation and / or food safety protocols.

Hint:

Internal coils do not provide the degree of safety from contamination by the heat transfer medium that jackets can offer.

The choice between jacket and coil is based on several factors such as:

The jacket is preferred when the process fluid is highly reactive or corrosive. Since it is not with direct contact with process fluid and jacket provides the degree of safety from contamination by the heat transfer medium. For instance, jacket is always used in glass lined reactor where high corrosive materials are used in reaction such as acids.
The coil has benefit that large surface area can be provided such as in case of highly exothermic reaction.
Jackets provide a more even heat transfer distribution.
Jackets have a lower utility velocity that can increase fouling rate.
Coils provide quicker and more aggressive heating and cooling.
References:

1-Chemical Process Engineering Design and Economics.

2- Advances in Reactor Measurement and Control.

#2 clarenceyue

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Posted 07 May 2019 - 09:27 PM

And what is your question?






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