Two Types of Chemical reactors - 1 views
started by kbojezhang44 on 08 Apr 20
started by kbojezhang44 on 08 Apr 20
started by kbojezhang44 on 08 Apr 20
started by kbojezhang44 on 08 Apr 20
The reactors, in which chemicals are made in industry, vary in size from a few cm3 to the vast structures that are often depicted in photographs of industrial plants. For example, kilns that produce lime from limestone may be over 25 metres high and hold, at any one time, well over 400 tonnes of materials.The design of the chemical reactor is determined by many factors but of particular importance are the thermodynamics and kinetics of the chemical reactions being carried out.The two main types of reactor are termed batch and continuous.
Batch reactors
Batch reactors are used for most of the reactions carried out in a laboratory. The reactants are placed in a test-tube, flask or beaker. They are mixed together, often heated for the reaction to take place and are then cooled. The products are poured out and, if necessary, purified.
Following reaction, the reactor is cleaned ready for another batch of reactants to be added.
Batch reactors are usually used when a company wants to produce a range of products involving different reactants and reactor conditions. They can then use the same equipment for these reactions.
Examples of processes that use batch reactors include the manufacture of colorants and margarine.
Continuous reactors
An alternative to a batch process is to feed the reactants continuously into the reactor at one point, allow the reaction to take place and withdraw the products at another point. There must be an equal flow rate of reactants and products. While continuous reactors are rarely used in the laboratory, a water-softener can beregarded as an example of a continuous process. Hard water from the mains is passed through a tube containing an ion-exchange resin. Reaction occurs down the tube and soft water pours out at the exit.
Continuous reactors are normally installed when large quantities of a chemical are being produced. It is important that the reactor can operate for several months without a shutdown.
The residence time in the reactor is controlled by the feed rate of reactants to the reactor. For example, if a reactor has a volume of 20 m3 and the feed rate of reactants is 40 m3 h-1 the residence time is 20 m3 /40 m3 h-1 = 0.5 h. It is simple to control accurately the flow rate of reactants. The volume is fixed and therefore the residence time in the reactor is also well controlled.
The product tends to be of a more consistent quality from a continuous reactor because the reaction parameters (e.g. residence time, temperature and pressure) are better controlled than in batch operations.
They also produce less waste and require much lower storage of both raw materials and products resulting in a more efficient operation. Capital costs per tonne of product produced are consequently lower. The main disadvantage is their lack of flexibility as once the reactor has been built it is only in rare cases that it can be used to perform a different chemical reaction.