Most of chemical reactions encountered in inorganic or organic chemistry involve either release of heat or supply of heat to the reactor where the chemical reaction is in progress. One does not normally come across a chemical reaction which has zero heat effect. Chemical reactions carried out in continuous flow reactors, be it a CSTR or a plug flow reactor, most often require isothermal conditions to be maintained at any given cross-section or at any given point in the reactor under steady state operating conditions in the reactor. For reactions that are exothermic, the heat released from the reaction requires to be extracted in a manner that the temperature of the reaction mass in the reactor remains constant. For endothermic reactions, heat requires to be supplied to the reactor to hold the temperature constant.
Thermal effects are also relevant during dissolution of any chemical in a liquid. Dissolution of sodium hydroxide flakes or concentrated sulphuric acid in water are two of the most common examples where considerable heat is evolved.
The first task towards quantification of thermal energy involved during a chemical reaction or dissolution is achieved on the basis of published data available with respect to standard heats of formation, bond energies, or heats of dissolution. For those reactions where data is not readily available, thermal data requires to be generated through controlled experiments on laboratory scale.
Adiabatic reactor design is one of the core competencies of Chemical Process Engineers. The expertise available with Chemical Process Engineers starts with quantitative estimation of the thermal energy (Kcals) that is expected to be released during an exothermic reaction. The rate of heat transfer required to be maintained across the reactor wall is then computed through computations involving quantification of heat transfer coefficients, temperature difference which is the driving force between the reaction mass temperature and temperature of the cooling medium, and area available for the heat transfer to take place. Chemical Process Engineers develops the algorithm required to solve and compute the iterative relations involved in the computations to optimize the design.
For the design of a new reactor, the most optimum design for the reactor is arrived involving the reactor dimensions, agitation parameters, viz. impeller diameter & impeller speed, dimensions of the jacket or a coil, etc. are determined and produced in the form of a General Arrangement Drawing which then becomes a basis for the equipment manufacturer.
In the case of an existing reactor, Chemical Process Engineers help the end user in determining the set of operating parameters which can then help them in improving the performance of the reactor in terms of reaction time reduction and hence increased productivity from the existing reactor, if possible.Read More