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Three basic forms of fixed bed reactor
Release time:
Jul 21,2022
The hydrodesulfurization fixed bed reactor adopts the design structure of parallel reaction tubes.The reaction gas is hydrogen, and the liquid phase is 1% organic sulfur decahydronaphthalene solution or refined oil.The three-way gas phase and the two-way liquid phase can be flexibly switched, and nitrogen leak detection is used under the pressure of the two reactors.Purify and replace the air before hydrogen filling.
Fixed bed reactors are mainly used to realize gas-solid catalytic reactions, such as ammonia converters, sulfur dioxide contact oxidants, hydrocarbon steam conversion furnaces, vinyl acetate reactors, etc.When used in gas-solid or liquid-solid non-catalytic reactions, the bed is filled with solid reactants.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.
There are three basic forms of fixed bed reactors：
① Axial adiabatic fixed bed reactor.The fluid of the reactor flows axially through the bed from top to bottom, and there is no heat exchange between the bed and the outside world.
②The radial adiabatic fixed bed reactor.The reactor fluid flows radially through the bed, centrifugal or centripetal flow can be used, and there is no heat exchange between the bed and the outside world.
③The tubular fixed bed reactor consists of multiple parallel reaction tubes.The catalyst is placed in or between the tubes, and the heat carrier flows through the tubes for heating or cooling.The diameter of the pipe is generally between 25 and 50mm, and the number of pipes can reach tens of thousands.The tubular fixed bed reactor is suitable for reactions with large thermal effects (such as vinyl acetate reactions).
Gas-solid phase reactors are widely used in the chemical industry, mainly fixed bed reactors and fluidized bed reactors, as well as mobile bed reactors and drip bed reactors.The characteristics and structure of the fixed bed reactor are as follows：
advantage：
(1) Fluid flow can be regarded as an ideal displacement flow, so the chemical reaction speed is fast, and the catalyst and reactor required to complete the same production capacity are small in size.
(2) The gas residence time and temperature can be strictly controlled
The distribution can be adjusted, which is conducive to improving the conversion rate and selectivity of chemical reactions.
(3) The catalyst is not easy to wear and can be used continuously for a long time.
(4) Suitable for working under high temperature and high pressure.
Disadvantages：
(1) Poor thermal conductivity and complex temperature distribution.
(2) The fine-particle catalyst cannot be used, and the active inner surface of the catalyst cannot be fully utilized.
(3) The regeneration and replacement of the catalyst is inconvenient.
Design method of fixed bed reactor：
Empirical method: Based on the data measured by the laboratory, intermediate test equipment, or existing equipment in the factory under good conditions, such as airspeed, catalyst spatiotemporal yield, catalyst load, etc. as the design basis, the amount of catalyst, bed height, bed diameter, etc. are calculated and determined according to the prescribed production capacity.The method is simple, but the accuracy is poor.
Mathematical model method: According to the reaction dynamics, it can be divided into heterogeneous and quasi-homogeneous; according to the temperature distribution in the catalytic bed, it can be divided into one-dimensional model and two-dimensional model; the flow model can be divided into ideal flow model and non-ideal flow model.
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