Batch reactors are perhaps the simplest reactors used in chemical processes. The batch reactor shown below has a stirrer on the top.
When using batch reactors, reactants are first placed inside the reactor and then allowed to react over time. Batch reactors are closed systems that operate under unsteady-state conditions. The reactors shown below are used in the dairy industry.
The movie below shows the basic operation of a batch reactor. The reactants are placed into the reactor and then allowed to react, and products form inside the reactor. The products and unreacted reactants are then removed and the process is repeated.
While batch reactors are used in a variety of situations, they have some common design features.
Batch reactors contain ports for injecting reactants and removing products, and can be outfitted with a heat exchanger or a stirring system. While batch reactors are generally of constant volume, some are designed to maintain a constant pressure by varying the reactor volume.
The picture below shows the top of a batch reactor. Note the stirring device.
An autoclave can also be made into a batch reactor so that the reactions can run at higher pressures. These are mainly used for reactions that need pressures above 5,000 psi. Instead of having a mechanical agitator, the reaction is stirred by a magnetic stirrer. Sensors and valves are also necessary to ensure the safety of the system since it is being run at such high pressures.
Quick response to heating and cooling loads and proper wall temperature control are critical for the successful operation of a batch reactor.
A typical batch reactor body, like the one in the figure below, is surrounded by an outer jacket which circulates heat transfer fluid. Larger vessels have multiple injection points to better distribute the heat transfer fluid within the jacket.
The picture below shows two common designs of batch reactor jackets. The one on the left is the one-piece jacket, which forms an outer chamber around the vessel. Heat transfer fluid is injected tangentially into the jacket at high speed to support the mixing and dispersion of heat transfer fluid within the jacket. The one on the right is the “half coil” jacket. This one consists of a series of pipes cut along their longitude and welded outside the vessel. Heat transfer fluid travels in a plug flow manner through the channels.
Pictured below is a batch reacting vessel with a one-piece jacket used for temperatures up to 400°F.
The picture below shows a batch reactor with a constant heat flux control system. This system is a good solution to many temperature control problems in batch reactors.
This constant flux jacket is composed of multiple small heat-transfer channels. Each one of these channels is a pipe clamped or welded around the external surface of the vessel and connected to a multi-port piston valve. Heat transfer area is effectively controlled by varying the number of coils in service. Therefore, the system can change heating or cooling power at constant jacket heat flux. Constant flux jackets have essentially constant jacket temperatures.
Batch reactors are used in a wide variety of applications. Typically, they are used for liquid phase reactions that require a fairly long reaction time. The reactors below are used for beverage processes.
Batch reactors are also used when only a small amount of product is desired. For this reason batch reactors are favored when a process is still in the testing phase, or when the desired product is expensive. Batch reactors, like the one below, are used in the pharmaceutical industry, which requires consistent, high quality results. One batch reactor may also be used to make a variety of products at different times.
- High conversions can be obtained by leaving reactants in reactor for extended periods of time.
- Batch reactor jackets allow the system to change heating or cooling power at constant jacket heat flux.
- Versatile, can be used to make many products consecutively.
- Good for producing small amounts of products while still in testing phase.
- Easy to clean.
- High cost of labor per unit of production.
- Difficult to maintain large scale production.
- Long downtime for cleaning leads to periods of no production.
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