Definition of Chemical reactors
A reactor is a device for carrying out chemical reactions. Materials with specific mole fraction and condition enter the reactor and materials with a new nature are discharged as product. Reactors are used in all industries including chemical reactions. Chemical reactors used on industrial scale require professional and specialized design. The design of these reactors is done in two stages: process design and mechanical design. In the process design, the requirements for production including temperature, pressure, and retention time and so on are examined. The mechanical design is then carried out to determine the dimensions, spare equipment, etc. and finally the reactor of the specified size and essential equipment are constructed for use in desired condition. Mechanical design of the reactor is often done by PV-ELITE software.
The main parts of a reactor include reaction chamber, shaft and stirrer, valves, inlet and outlet nozzles, heating and cooling system, instrument equipment (for temperature, pressure, concentration, etc.), baffle, sparger, sealing equipment, electromotor and gearbox and some optional components based on the operation. All of mentioned components need carefully design to allow proper function of the reactor.
Figure 1 : reactor shape
Body of reactor: As mentioned earlier, the reactor is used as a reaction space to produce specified products from the raw materials. The shape and properties of the reactor vary depending on the operating condition and reaction type. In other words, the reactor may have a variety of internal and external equipment based on the design, so the appearance of reactors can vary. On the other hand, determining the reactor material and dimensions (including the length, diameter and thickness of the sheet used in the construction of rector body) is very important; for example, if the operating pressure is higher, the body thickness should be grater. However, it should be mentioned that the thickness can be increased to a certain extent due to the limitations of the construction. Moreover, the reactor can be constructed from carbon-steel (iron) and stainless steel (e.g. steel 304, steel 316, steel 321) depending on the raw material. Generally, constructing a stainless steel is more complicated than a conventional iron reactor. The assembly, cutting and piping of stainless steel reactors are very important. It should be noted that special welding (argon welding) should be used for these reactors because they are stainless.
Inlet and outlet nozzles position, sampling location, material discharge paths, Manholes, safety and instrument equipment and so on should be considered in the design of reactor body. In addition, how a reactor is constructed is very important; for example, rolling, standard caps constructions, welding, heat treatment and so on are also important. It should be mentioned that mechanical design of body, shaft and other components is based on the ASME standard.
Flat bottom valve: Flat bottom valve is used to eliminate the dead zone between bottom of reactor and outlet valve. When the valve is closed, the bottom of reactor does not have any dead zone. Thus, all materials are stirred very well.
Flat Bottom Valve
Stirrer: most chemical reactions require stirring. Generally, a stirrer is used for proper stirring. The stirrer consists of electromotor, gearbox, shaft, shaft seal and blade. The electromotor provides the necessary rotational motion that is transferred through the shaft to the blades; the blades stirred materials by their rotational motion. The gearbox converts the electromotive speed to power; the output speed of the gearbox usually varies between 60 to 100 rpm. It should be mentioned that the required power (kW) of electromotor and torque of gearbox are calculated based on the ATEX standard. In stirred reactors, the shaft entrance should be sealed. Generally, three types of seals are used: packing seal, mechanical seal and magnetic seal; one of these seals is selected based on the project. The stirrer design with suitable blades is done concerning viscosity of reactants.
Cooling and heating system: two types of thermal systems are used in reactors: in an external thermal system, chute, half pipe or jacket containing fluid does not have direct contact with the reactor material and is outside the chamber; in an internal thermal jacket, pipes are inside that reactor and in contact with the materials. Steam (or hot water) or hot oil is used as a heating fluid, so the steam boiler or oil boiler is used to supply the required fluid depending on the operating condition. For cooling the reactor, water is usually used as cooling fluid, thus the cooling tower or chiller is used to supply the required fluid depending on the condition.
Baffle: in some operating condition, baffle is used for better stirring. For example, in gas-liquid reactions, stirring plays a significant role in reducing the use of gaseous reactant; thus the baffle is used for these reactors. The baffle design is done according to reactants, diameter and length of the reactor.
Sparger (gas dispenser): in gas-liquid reactions, a sparger should be designed for entering the gas into the reactor. The function of the Sparger is to distribute the gas particles well into the liquid solution. The sparger design is done according to the reaction stoichiometry, liquid reactant, stirrer, length and diameter of reactor.
Different kind of Spargers
Instrumentation equipment: Instrumentation equipment such as a thermometer, barometer, level gauge, pH meter, concentration meter, etc. are required to monitor and control the reactor operation online. A PLC program can also link the amount read by each of these equipment to another equipment such as an inlet or outlet valve.
Tanks are generally used to store chemicals. A tank looks similar to a reactor, except that it does not have auxiliary equipment (such as stirrer, thermal system, etc.), since no reaction is done in the tank. Depending on the materials used for storage, the tank can be constructed from carbon-steel and stainless steel with different grades.
Design, manufacture and after sales services
Vandad Chemical Industry Company is capable of designing and constructing various chemical reactions and storage tanks of various dimensions and capacities by acquiring knowledge, skills and valuable experiences over the years. Mechanical design of reactors is done by the engineering team of Vandad Company according to process data such as pressure, temperature, material type, viscosity, capacity and heat transfer based on the specified standards.
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