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What are the advantages and disadvantages of a small fixed bed reactor?

Release time:

Aug 22,2022

A small fixed bed reactor refers to filling the reactor with a granular solid catalyst or solid reactant to form a laminated bed of a certain height.When a gas or liquid material flows through a static fixed bed through a particle gap, a heterogeneous reaction process is realized.The characteristic of this kind of reactor is that the solid particles filled in the equipment are fixed, which is different from the moving bed and the fluidized bed in which the solid material moves in the equipment, also known as the filled bed reactor.Fixed bed reactors are widely used in gas-solid and liquid-solid reaction processes, such as fixed semi-water gas generators in the ammonia industry, fixed bed ion exchange columns in water treatment, etc.A drip bed reactor can also belong to a fixed bed reactor.The gas phase and the liquid phase flow down through the bed in the form of gas-liquid-solid contact.

Advantages of small fixed bed reactor：

1.When the reaction is accompanied by a series of side reactions, a small backmix, reasonable contact between the liquid and the metal catalyst, and high selectivity must be obtained.

2.The consumption of metal catalyst machinery and equipment is small.

3.The structure is simple.

Defects of small fixed bed reactor：

1.When the heat conduction is poor and the reaction exothermic is large, even the tubular heat exchanger reactor may have an out-of-control temperature (the reaction temperature is out of control and greatly exceeds the allowable range).

2.During operation, the metal catalyst cannot be disassembled and replaced.Reactions where metal catalysts must be recycled frequently are usually not suitable for applications.It is usually replaced by a circulating fluidized bed reactor or a mobile bed reactor.

Metal catalysts in fixed-bed reactors are not limited to particulate matter. Metal catalysts with network structures have long been used in industrial production.Honeycomb and fibrous metal catalysts have also been widely used.

Mathematical analysis model：

A fixed bed reactor is a multi-component reactor with sufficient scientific research.There are many mathematical analysis models describing fixed-bed reactors, which can be roughly divided into two categories: quasi-homogeneous solid models and multicomponent solid models.Backmix can be considered in each category, divided into non-backmix solid model and backmix solid model.According to whether the axial concentration gradient and temperature field of the reactor are considered, it is divided into a one-dimensional solid model and a two-dimensional solid model.

Process design principles of fixed bed reactor：

1.The process design is not only a simple calculation and optimization of catalyst consumption, but also determines the process operating parameters from an engineering perspective based on the process characteristics and the actual situation of the project.

2.The type and structure of the catalytic bed should be comprehensively selected according to the requirements of process operating parameters, equipment preparation and maintenance, catalyst loading and unloading, etc.

3.The cylinder of the high-pressure reactor should be equipped with a catalytic bed, an out-of-bed heat exchanger, a cold shock trachea and a thermocouple tube, and sometimes an electric heater for starting preheating.These components should be reasonably combined in the reactor, the load coefficient of the catalyst should be high, the air flow distribution should be uniform, and the pressure drop of the air flow through the reactor should be small.

4.Taking into account the mechanical strength and temperature difference stress of certain components in the reactor at high temperatures, the mechanical structure should be reliable.

5.For multi-stage catalytic beds, the distribution of inter-stage gas and cooling gas and the uniform mixing device should be appropriately designed.

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