Discussion on the design of agitator in chemical equipment
Abstract: The stirring device is installed on the center line of the vertical equipment cylinder. Can prevent liquid from being produced near the agitator? Cylindrical gyration zone? . According to the requirements of SH/T3 150-2007 Technical Regulations for Agitator Engineering in Petrochemical Industry, the service life of agitator should be at least 20 years.
Keywords: agitator, equipment, chemical industry
I. Classification, Composition and Function of Mixing Device
(1) classification
1. Center stirring of vertical container. The stirring device is installed on the center line of the vertical equipment cylinder, and the driving mode is generally belt transmission and gear transmission, which is directly connected with the ordinary motor or reducer.
2. Eccentric mixing. The stirring device is eccentrically installed on the vertical container, which can prevent liquid from being produced near the stirrer? Cylindrical gyration zone? It can produce a stirring effect similar to that when adding baffles.
3. Inclined mixing. In order to prevent eddy current, for simple cylindrical or square open vertical containers, the stirring device can be installed on the upper edge of the equipment cylinder with a splint, and the stirring shaft can be directly inserted into the cylinder. , equipment.
4. Stir in a horizontal container. The mixing device is installed on the horizontal container, which can reduce the installation height, improve the impact resistance of the mixing equipment and improve the suspension state.
5. Horizontal biaxial stirring. This stirring device is mainly used for highly viscous liquids. The purpose of using horizontal double-shaft stirring equipment is to obtain self-cleaning effect.
6. Stir at the bottom. The mixing device is at the bottom of the equipment, which is called bottom mixing equipment.
7. Combine and stir. Sometimes, in order to improve the mixing efficiency, it is necessary to combine two or more kinds of mixing equipment with different forms and speeds. This kind of mixing equipment is called combined mixing equipment.
8. Stir sideways. Side-entry stirring device is to install the stirring device on the side wall of the equipment cylinder. For side-by-side mixing, the highest mixing effect can be obtained with the same power consumption.
(2) Composition
The agitator device is generally composed of transmission device, coupling, frame, agitator shaft, shaft seal, agitator and other parts.
(C) Function and its influencing factors
The function of the agitator is only to provide energy and appropriate flow for the stirring process, so as to achieve the purpose of the stirring process. , equipment. This effect is produced by the moving impeller, so the shape, size, quantity and speed of the impeller have a direct impact on the function of the agitator. At the same time, the function of the agitator is also related to the physical properties of the stirring medium and the working environment. In addition, the shape and size of the stirring tank, the setting of the baffle and the way of materials entering and leaving the tank all belong to the working environment. The installation position of the agitator in the tank and various factors can affect the function of the agitator to varying degrees.
Stirring power is the power needed in the stirring process, including stirrer power and stirring operation power, which have different connotations but are related. The power required for continuous operation of the agitator is the agitator power. The power required to make the liquid in the stirring tank complete the stirring process in the best way is the stirring operation power. Ideally, the power of the stirrer is equal to the power of the stirring operation.
Second, the design of agitator in chemical equipment
(1) design process
The design and modeling of mixer should be closely combined with the purpose of mixing operation. Various mixing processes need to be realized by different mixers. When designing and modeling, we should first determine the type of mixer, motor power and mixing speed according to the purpose and requirements of mixing operation, and then select reducer, frame, mixing shaft, shaft seal and other components. Generally speaking, the design process of agitator in chemical equipment is: setting and determining stirring conditions? Choose the type and internal components of the mixing impeller? Determine the size and speed of impeller? Calculate the stirring power? Mechanical design of mixing device. The specific design process is as follows:
1. According to the process conditions, mixing requirements and purposes, choose the agitator style, fully grasp the dynamic characteristics of the agitator, the flow state generated by the agitator during the mixing process, as well as various influencing factors and their relationship with the mixing purpose.
2. According to the determined agitator type, the flow state generated by the agitator in the process of stirring, and the control requirements of the process on mixing time, dispersion and settling speed, the motor power, stirring speed and agitator diameter are determined through experimental means and computer simulation design.
3. According to the motor power, stirring speed and process conditions, select and determine the reducer model from the reducer selection table. If the reducer is selected according to the actual working torque, the actual working torque must be less than the allowable torque of the reducer.
4. According to the output shaft head D of the reducer and the support mode of the mixing shafting, select the frame and coupling with the same model and specification as D. ..
5. Select the shaft seal type according to the size, installation space, working pressure and working temperature of the frame mixing shaft head.
6. According to the installation form and structural requirements, design and select the structural type of the mixing shaft, and check its strength and stiffness; If it is designed according to the rigid axis, n/nk? 0.7; If the flexible shaft is designed, N/NK >: = 1.3.
7. Choose to install the bottom cover, flange base or flange according to the size of the frame, the type of agitator shaft and the pressure grade.
According to the requirements of SH/T3 150-2007 Technical Specification for Agitator Engineering in Petrochemical Industry, the design and manufacturing life of agitator should be at least 20 years, and it is expected to run continuously for more than 2 years. , equipment.
(2) Design of agitator irrigation structure
1. Length-diameter ratio of storage tank. , equipment. , equipment. The influence of the length-diameter ratio of the tank on the stirring power, if the stirring power needs to be larger, the length-diameter ratio can be selected to be smaller; The influence of length-diameter ratio of tank on heat transfer, when the product is fixed, the greater the length-diameter ratio, the greater the surface area and the better the heat transfer; At this time, the closer the heat transfer surface is to the center of the tank, the greater the temperature gradient of the material, which is beneficial to the heat transfer effect. Therefore, simply from the perspective of jacket heat transfer, it is generally hoped that the length-diameter ratio will be larger. The requirement of material characteristics on the length-diameter ratio of tank requires sufficient liquid material height, and it is hoped that the length-diameter ratio will be larger.
2. Mixing tank loading. Given the length-diameter ratio H/Di,
Weighing volume Vg: the volume of materials in operation.
1) loading factor?
Vg=V
Generally take 0.6 ~ 0.85. In the process of reaction, the material should be foamed or boiled, and the charging coefficient should be low, about 0.6 ~ 0.7; The reaction of the material is stable, with the numerical value ranging from 0.8 to 0.85, and the viscosity of the material is high and the numerical value is high.
3. The structure of the top cover. The transmission device comprises a motor, a reducer, a coupling and a stirring shaft. The calculation of shaft strength refers to: bearing torsion and bending, mainly torsion, only considering torque in engineering, and then increasing the safety factor to reduce the allowable stress of materials to make up for the errors caused by ignoring bending. , equipment. Under static load, [? ]=(0.5~0.6)[? ]。 However, the calculation of shaft stiffness is often to prevent excessive torsional deformation of the shaft, so as to avoid vibration during operation and cause shaft seal failure. The torsional deformation of the shaft should be limited within the allowable range. Torsion angle per unit length in engineering? O Do not exceed the allowable twist angle [? O] as a condition of torsional stiffness.
References:
1 Wang Kai edition, mixing equipment [M]. Chemical Industry Press, 2003
2 Gu Fangzhen, Chen, ed., Fundamentals of Chemical Equipment Design [M]. Tianjin University Press, 1994
3 Wang Hongqun, Yu Peiqing, Research on Mixed Design [M]. Mechanical Engineer, 2009(9)
4. Pingliang, selection and design of agitator [J]. Petrochemical equipment technology, 1996( 1)
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