Sanitary stainless steel reactorIt is the key equipment for chemical reaction, mixing, dissolving, emulsifying and other processes in chemical, pharmaceutical, food and other industries. It is mainly composed of tank, mixing system, heat transfer system, sealing device, instrumentation control system and other parts.
I. Equipment structure and function principle
The tank is made of 304 or 316L stainless steel, and single-layer structure or jacketed structure can be selected according to the process requirements. The working pressure range of single-layer reactor is generally 0.1-0.6MPa, while jacketed reactor can withstand higher operating pressure. The ratio of tank diameter and height is usually controlled between 1:1 and 1:1.5 to ensure the stirring effect and heat transfer efficiency.
Mixing system design includes agitator type selection, speed determination, and power calculation. Common agitator types include paddle type, propulsion type, turbine type, anchor type and so on. Stirring speed is determined according to material viscosity, reaction requirements and other factors, generally ranging from 60-300rpm. The stirring power calculation formula is P=KρN³D⁵, where ρ is the density of the material, N is the rotational speed, D is the diameter of the stirrer, and K is the power coefficient.
The heat transfer system selects jacket heating, coil heating or external circulation heating according to the process requirements. Jacket heating is suitable for small and medium-sized reaction kettles with large heat transfer area and uniform temperature control. Coil heating is suitable for occasions requiring precise temperature control, with fast response speed and high adjustment precision. External circulation heating is suitable for large-scale production process, which can realize efficient heat transfer and energy recovery.
II. Technical points of the manufacturing process
Material selection in the manufacturing process of reaction kettle need to consider corrosion resistance, mechanical strength, thermal conductivity and other factors.316L stainless steel material molybdenum content control in the range of 2.0-3.0%, the carbon content does not exceed 0.03%. material thickness according to the design pressure and corrosion margin calculation to determine the general formula for the t = (P × D)/(2S × E - 0.2P) +C, where C is the corrosion margin.
Cylinder molding is rolled by three-roller plate rolling machine, and the end pre-bending treatment is carried out before rolling. Pre-bending radius is determined according to the plate thickness and equipment capacity calculations, the general empirical formula is R = (8-10)t. Rolling process control each roll angle does not exceed 45 °, to avoid excessive internal stress. The roundness tolerance of the cylinder after molding is controlled within 0.5% of the diameter.
The head adopts hot press molding process, the blank is heated to 950-1050℃ temperature range before stamping. The stamping die is made of high-strength alloy steel, and the surface of the die is specially treated to improve its service life. The stamping pressure is calculated according to the specification of the head and the thickness of the material, and the general pressure range is between 100-500 tons. After molding, the head is heat-treated to eliminate internal stress, and the temperature of heat-treatment is controlled at 600-650℃.
III. Welding process quality control
The welding process of reaction kettle requires strict requirements, and the main welding parts include the longitudinal seam of the cylinder, ring seam, receiver weld, stirrer bracket weld, etc. The automatic argon arc welding process is adopted for the longitudinal seam of the cylinder. The longitudinal seam of the cylinder adopts automatic argon arc welding process, and the welding current is adjusted according to the thickness of the plate, the corresponding current of 2mm plate is about 80-100A, and the corresponding current of 3mm plate is about 100-120A. The protective gas is selected to be high purity argon, with the purity of not less than 99.99%.
The welding of the jacket and the cylinder adopts gas shielded welding process. Before welding, it is necessary to carry out group checking to ensure that the gap is uniformly controlled in the range of 2-4mm. Control the heat input during the welding process to avoid overheating and affecting the performance of the cylinder. Appearance inspection after welding is completed, the weld surface is required to be smooth, without biting edge, cracks, pores and other defects.
The connection between the stirring shaft and the stirrer is made by welding plus keyway. The preheating process is carried out before welding, and the preheating temperature is controlled at 150-200℃. The welding process adopts low-current multi-layer welding process, and the thickness of each layer of weld is not more than 3mm. after welding, the weld is inspected by flaw detection to ensure that the strength of the connection meets the design requirements.
IV. Technical requirements for surface treatment
The internal surface treatment of the reactor consists of two steps: grinding and polishing and passivation. Weld area grinding requirements to remove the residual height, and smooth transition with the base material. Grinding tool selection angle grinder with fiber grinding wheel, grinding wheel size from 80 mesh gradual transition to 320 mesh. After grinding surface roughness control in Ra ≤ 0.4μm.
Mechanical polishing adopts special polishing equipment, and the polishing process is divided into three stages: rough polishing, medium polishing and fine polishing. Rough polishing uses 120 mesh polishing wheel to remove obvious scratches; middle polishing uses 240 mesh polishing wheel to improve surface finish; fine polishing uses more than 400 mesh polishing wheel to achieve mirror effect. The roughness of the polished surface is controlled according to the customer's requirements, and the general range is Ra≤0.2-0.4μm.
Passivation treatment adopts nitric acid solution for chemical passivation. The concentration of the passivation solution is 20-25%, the temperature is controlled at 50-60℃, and the treatment time is 30-45 minutes. After passivation, a chromium oxide film with a thickness of about 2-3nm was formed on the surface, which significantly improved the corrosion resistance. The passivation effect is verified by the blue dot test, which requires no blue spots to appear.
V. Technical requirements for mixing systems
The agitator design needs to be optimized according to the material characteristics and process requirements. Paddle agitator is suitable for the mixing of medium and low viscosity materials, the ratio of diameter to tank diameter is generally 0.4-0.6. Propeller agitator is suitable for fluid transportation and homogeneous mixing, which requires a higher speed, generally not less than 200rpm.
Turbine agitator is suitable for shearing and dispersion of high viscosity materials, the ratio of diameter to tank diameter is generally 0.3-0.4. Anchor agitator is suitable for heat transfer and mixing of high-viscosity materials, and the gap with the wall of the tank is controlled in the range of 5-10mm. Stirring speed is determined according to the material viscosity and reaction requirements, the general empirical formula is N = K / √μ, where μ is the material viscosity.
Stirring power calculation needs to consider the nature of the material, stirrer type, operating conditions and other factors. The power calculation formula is P=Np×ρ×N³×D⁵, where Np is the power number, which is determined by checking the table according to the type of agitator and flow state. For the turbulent flow state, the paddle agitator power number is about 1.5, the propulsion type is about 0.3, and the turbine type is about 4.0.
VI. Key points of heat transfer system design
Jacket heat transfer design needs to consider the heat transfer area, heat transfer coefficient, flow resistance and other factors. Heat transfer area is calculated as A=Q/(K×ΔT), where Q is the heat load, K is the heat transfer coefficient, and ΔT is the temperature difference. The jacket thickness is calculated according to the design pressure and material strength, and the general empirical formula is t=(P×D)/(2S×E)+2.
Coil heat transfer design needs to consider the selection of pipe diameter, pipe spacing, flow rate control and other factors. Pipe diameter according to the heat transfer requirements and pressure loss to determine the general selection of 10-50mm range. Pipe spacing control in the pipe diameter of 1.5-2 times to ensure adequate heat transfer area and flow space. Flow rate control in the range of 1-2m / s to ensure heat transfer and avoid excessive pressure drop.
External circulation heat exchange system includes heat exchanger, circulation pump, control system and other parts. Heat exchanger plate heat exchanger or shell and tube heat exchanger, according to the process requirements for selection and calculation. Circulation pump flow according to the heat transfer requirements and system resistance to determine the head to meet the requirements of the system pressure loss. The control system realizes the function of automatic temperature adjustment and flow control.
VII. Technical requirements for sealing devices
Mechanical sealing device selects double end face mechanical seal which meets the hygiene requirements. The sealing surface is made of hard alloy or silicon carbide, and the friction coefficient is controlled in the range of 0.05-0.1. The sealing spring is made of stainless steel, and the spring force is calculated according to the sealing pressure and structural requirements. The seal cooling system adopts clean water circulation cooling to ensure the long-term stable operation of the seal.
Packing seal is suitable for low pressure, non-critical sealing occasions. The packing is made of food-grade graphite or PTFE material, and the thickness of packing is determined according to the shaft diameter, which is generally 0.2-0.3 times of the shaft diameter. The packing gland pressure is uniform, and the compression force is controlled within the design range to avoid excessive compression affecting the sealing life.
The sealing performance test includes two steps: hydrostatic test and running test. Hydrostatic test pressure for the design pressure of 1.1 times, holding time of not less than 30 minutes, no visible leakage requirements. Running test in normal operating conditions, continuous operation time of not less than 4 hours, check the sealing surface temperature, leakage rate and other parameters.
VIII. Quality control and inspection standards
Strict quality control is implemented in the whole manufacturing process of reaction kettle. Material control includes verification of material certificates, chemical composition analysis, mechanical property testing and so on. Manufacturing process control includes process parameter monitoring, process inspection, process discipline inspection and other links. Finished product inspection includes appearance inspection, size measurement, performance test and other items.
Welding quality control implementation of NB/T 47014 "pressure equipment welding process evaluation" standard. Welding process evaluation includes the determination of welding process parameters, welding specimen preparation, mechanical properties testing and so on. Welder qualification management requires welders to hold the appropriate qualification certification, and welding operators are qualified by professional training.
Non-destructive testing includes ray detection, ultrasonic testing, magnetic particle testing, penetration testing and other methods. Radiographic testing is suitable for detecting internal defects in the weld, and the detection ratio is determined according to the design requirements and standards. Ultrasonic testing is suitable for detecting internal and surface defects of the weld, and the sensitivity requirements are in line with the relevant standards.
The pressure test is carried out in accordance with TSG 21 "Safety Technical Supervision Regulations for Fixed Pressure Vessels". Hydraulic test pressure for the design pressure of 1.5 times, holding time of not less than 30 minutes. Pneumatic test pressure for the design pressure of 1.15 times, holding time of not less than 10 minutes. Check the pressure change, shell deformation, weld status and other parameters during the test.
IX. Technical standards and normative basis
Reaction kettle design and manufacturing followRelevant national technical standards and norms. Design criteria basisGB 150 Pressure VesselsManufacturing standards are based on NB/T 47003 "Steel Welded Pressure Vessels". Welding standards are based on NB/T 47014 "Pressure Equipment Welding Process Evaluation", and inspection standards are based on TSG 21 "Safety Technology Supervision Regulations for Fixed Pressure Vessels".
Hygienic design requirements comply with GB 16798 "Food Machinery Safety and Hygiene". The design of mixing system implements HG/T 20569 "Mechanical Mixing Equipment" standard. Seal device requirements in line with GB/T 24797 "Mechanical Seal Technical Conditions". The design of heat transfer system is based on GB/T 151 "Heat Exchanger" standard.
Technical documents include design calculations, construction drawings, process documents, inspection procedures and so on. Design calculations should include strength calculation, stability calculation, fatigue analysis and so on. Construction drawings need to be complete and accurate, including general drawings, component drawings, parts drawings and so on. Process documents need to be detailed and specific, including process parameters, operation points and so on.
X. Application scope and selection guidance
Sanitary stainless steel reactors are suitable for production processes in a variety of industries. In the pharmaceutical industry for synthetic reaction, crystallization, extraction and other processes, the equipment is required to meet GMP standards. Used in the food industry for ingredient mixing, emulsification, fermentation and other processes, requiring materials to meet food safety standards. Used in chemical industry for polymerization reaction, condensation reaction and other processes, the equipment is required to have good corrosion resistance.
Equipment selection needs to consider process conditions, production scale, investment costs and other factors. For intermittent production process, choose batch reactor, the volume is determined according to the production batch. For continuous production process, choose continuous reactor, the design parameters are calculated according to the production capacity requirements. For high viscosity materials, choose the strong stirring reactor to ensure the mixing effect.
Operation and maintenance require detailed operating procedures and maintenance programs. The operating procedures include start-up procedures, operation control, shutdown procedures and other content. Maintenance plan includes regular inspection, preventive maintenance, troubleshooting and other items. Personnel training requires operators to familiarize themselves with equipment performance and operation methods.
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