What is the main purpose of fluidized bed, and what is the working principle of fluidized bed?

When the air passes through the material layer in the state of random filling of solid particles from bottom to top, and the air velocity reaches or exceeds the critical fluidization velocity of the particles, the particles in the material layer are churning up and down, and some particles are entrained by the air flow and the state of the material layer is called the fluidized bed.

The function is generally used in solid drying, boiler combustion materials, etc., such as fluidized bed boilers, fluidized bed dryers, fluidized bed conveyors.

Fluidized bed. The working principle is to evenly stack the solid particles in a container with an open bottom to form a bed, if the fluid passes through from top to bottom, the particles do not move, and it belongs to the fixed bed stage.

If the fluid passes through the bed from top to bottom, when the flow rate is low, the situation is no different from the solid bed, the flow rate increases, the particles will move to expand the bed, and when the flow rate is further increased, the particles will leave each other and the source width will move in the fluid, the greater the flow velocity, the more intense the activity, and move in various directions in the Bi crack rock bed. The last case is called the solid fluidized state, and the particle bed layer after the fluidized state is called the fluidized bed.

A kind of reactor that uses gas or liquid to pass through a granular solid layer to make solid particles in a suspended state of motion, and carries out a gas-solid phase reaction process or a liquid-solid phase reaction process. When used in gas-solid systems, it is also called an ebullating bed reactor.

The early application of fluidized bed reactors in modern industry was the Winkler furnace (see Coal Gasifier) for pulverized coal gasification that appeared in the 20s of the 20th century; However, the development of modern fluidization reaction technology is represented by petroleum catalytic cracking in the 40s. At present, fluidized bed reactors have been widely used in chemical, petroleum, metallurgy, nuclear industry and other sectors.

Classification According to the application of fluidized bed reactors, it can be divided into two categories: one type of processing object is mainly solid, such as ore roasting, which is called solid phase processing process; The other type of processing object is mainly fluid, such as petroleum catalytic cracking, enzymatic reaction process and other catalytic reaction processes, called fluid phase processing process.

The structure of the fluidized bed reactor is available in two forms: There is a continuous feeding and discharging device for solid materials, which is used for solid phase processing or liquid phase processing where the catalyst is rapidly deactivated. In the catalytic cracking process, for example, the catalyst is significantly deactivated within a few minutes and must be continuously separated and regenerated by the above-mentioned devices.

The continuous feeding and discharging device without solid materials is used for the reaction process where the properties of solid particles do not change significantly for a long time (such as half a year or one year).

Features Compared with fixed bed reactors, the advantages of fluidized bed reactors are: continuous input and output of solid materials can be realized; The movement of fluids and particles makes the bed have good heat transfer performance, and the internal temperature of the bed is uniform and easy to control, especially suitable for strong exothermic reactions. On the other hand, due to the severe backmixing, it can have a certain impact on the efficiency of the reactor and the selectivity of the reaction.

In addition, the presence of bubbles in the gas-solid fluidized bed makes the gas-solid contact worse, resulting in an incomplete gas reaction. Therefore, it is generally not suitable for reactions that require a high conversion rate in a single pass. In addition, the abrasion of solid particles and dust entrainment in the gas stream also limit the application of fluidized beds.

To limit backmixing, a multi-layer fluidized bed or internals can be set up in the bed. In this way, a certain concentration or temperature difference can be established in the bed. In addition, the contact between gases and solids can be improved due to the redistribution of gases.

In recent years, fine-grained and high-velocity turbulent fluidized beds and high-velocity fluidized beds have been used in industry. Under the condition that the gas velocity is higher than the particle entrainment velocity, the bed is maintained through the circulation of solids, which is especially conducive to the situation where the interphase mass transfer resistance is important because the contact between the gas and solid phases is strengthened. On the other hand, because a large number of solid particles are entrained by the gas, they need to be separated and recirculated back to the bed, so the requirements for gas-solid separation are also very high.

Summary. The basic working principle of the fluidized bed is to suspend the solid particle material in the reactor by gas fluidization to form a fluid-like state, so as to achieve efficient mass transfer, heat transfer and reaction process.

The basic working principle of the fluidized bed is to suspend the solid particle material in the reactor by gas fluidization to form a state similar to the chain core spring fluid, so as to achieve efficient mass transfer, heat transfer and reaction process.

Specifically, a fluidized bed reactor is usually composed of a reactor body, a gas distributor, a solid material feeding device, and a discharging device.

In the reactor, the gas is introduced into the gas distributor at the bottom of the reactor through the gas import and export, so that the gas is evenly distributed in the splitting source trapped cracker, and then the solid particle material is suspended in the gas through a gas fluidizing medium such as compressed air or nitrogen.

In this process, the velocity of the gas fluidized medium and the rolling flow rate control the suspension state of the solid granular material, and the mixing of rubber liquor, mass transfer, heat transfer and reaction between solid and liquid or solid gas are realized from the large difference. At the same time, by adjusting the parameters such as flow rate and temperature of the gas fluidization medium, the control and optimization of the reaction process can be realized.

What are the basic structures of circulating fluidized bed.

Its basic structure consists of the following main components:

1. Burner: The burner is the core part of the circulating fluidized bed, which is used to burn solid fuel potato husks. It usually consists of a combustion chamber, a combustion bed, and a burner hand leakage air** system.

2. Circulator: The circulator is used to circulate solid particles from the bed back to the burner. It is usually composed of circulating pipes, circulating valves, and circulating fans.

3. Fuel supply system with virtual fuel: The fuel supply system is used to transfer solid fuel to the burner. It usually includes fuel storage equipment, fuel delivery devices, and fuel pre-treatment equipment, among others.

4. Guchun volume separator: The solid separator is used to separate the solid particles in the bed from the regret gas. It is usually composed of a solid separator body, a solid discharge device and a macro discharge device before exhaust gas exhaust.

5. Heat exchanger: The heat exchanger is used for the heat energy generated by combustion in the bed, and the common heat exchangers include grate, superheater and reheater.

6. Lead control monitoring system: The control system is used to monitor and control the operation of the circulating fluidized bed, including the monitoring and adjustment of temperature, pressure, flow and other parameters.

How is the bubbling of a bubbling fluidized bed formed.

The bubbling in the bubbling fluidized bed is sprayed from the bottom of the fluidized bed by the air residue imitation body, and interacts with the solid large ballast particles when it rises in the vertical blind layer of the bed, resulting in moist foam and increasing volume.

When the rising velocity of the gas and foam reaches a certain level, the foam is separated and bubbling is formed due to the action of the surface tension of the liquid.

The size and number of bubbling are related to factors such as the operating conditions of the fluidized bed, the characteristics of the material, and the height of the bed.

Advantages: It can realize the continuous input and output of solid materials; It is especially suitable for strong exothermic reactions; It facilitates the continuous regeneration and circulation of catalysts.

Limitations: Low yield of the target product; The reaction conversion rate is low; The catalyst accelerates pulverization and the loss is large; Empirical operation, casual silver reputation slippery.

Vibrating fluidized bed is a kind of equipment that uses vibration force and air flow to work together, which is used for the drying, cooling, screening, classification, coating and other processes of solid particles. Its main point is that a flow state is formed inside the bed, so that the solid particles show a flow state under the action of air flow, so as to realize the treatment of solid source contact particles. At the same time, the vibrating fluidized bed also has the advantages of low energy consumption, high processing efficiency and easy operation.

In view of the problem of vibrating fluidized bed, it is suggested that we can start from the following aspects:

1.Equipment selection: select the appropriate vibration fluidized hail bed equipment according to the actual needs, including the selection of bed size, vibration force, air flow and other parameters.

2.Operation specifications: When using the vibrating fluidized bed, it is necessary to operate in accordance with the operation specifications, including the start, stop, cleaning and other operations of the equipment, as well as regular maintenance and maintenance of the equipment.

3.Process optimization: The operating parameters of the vibratory fluidized bed can be optimized for specific process requirements to improve processing efficiency and product quality.

The fluidized bed drying method uses heated air to evaporate water through particles or pellets to achieve the purpose of drying.

When the air passes through the material layer in the state of random filling of solid particles from bottom to top, and the air velocity reaches or exceeds the critical fluidization velocity of the particles, the particles in the material layer are churning up and down, and some particles are carried out of the material layer by the air flow.

Key properties of fluidized beds.

Fully fluidized beds exhibit liquid-like properties. Fluids with a density less than the average density of the bed can be suspended on the bed; The bed surface is kept level; The bed obeys a hydrostatic relation, i.e. the pressure difference between two sections with a height difference of l.

p= gl particles have similar fluidity to liquids and can be ejected from small holes in the wall of the apparatus; The two connected fluidized beds can adjust the upper surface of the bed so that they are on the same level.

The above properties make the processing of granular materials in the fluidized bed can be continuously fed and discharged like fluids, and because the particles are fully mixed, the bed temperature and concentration are uniform, so that the bed has unique advantages and can be widely used. [

Main characteristics of fluidized bed.

Fully fluidized beds exhibit liquid-like properties.

The particles have a fluidity similar to that of a liquid and can be ejected from a small hole in the wall of the device;

A fluid that can be suspended on the bed is less dense than the average density of the bed;

The bed obeys the hydrostatic relation, that is, the pressure difference between the two sections with a height difference of l p= gl ;

The bed surface is kept level;

The two connected fluidized beds can adjust the upper surface of the bed so that they are on the same level.

Advantages: It can realize the continuous input and output of solid materials; It is especially suitable for strong exothermic reactions; It facilitates the continuous regeneration and circulation of catalysts.

Limitations: Low yield of the target product; The reaction conversion rate is low; The catalyst accelerates pulverization and the loss is large; Empirical operation, large arbitrariness.

The heat withdrawal effect is good, and the gas-solid mixing is uniform, similar to the full mixed flow.