SIMULATION OF MULTIPLE EFFECT EVAPORATOR

Abstract

Evaporation is one of the important unit operations used in the chemical industry for the concentration of aqueous solution i.e. removal of water from a solution by boiling the liquor in suitable vessel called evaporator and withdrawing the vapour. The various liquors to be evaporated can be classified in the following ways:- (a) Those that can be heated to high temperature without decomposition, and those that can only be heated to a low temperature. (b) Those which at any given pressure boil at about the same temperature as water, and those which have a much higher boiling point. Evaporation is carried out by adding heat to the solution to vaporise the solvent. The heat is supplied largely to provide the latent heat of vaporisation. Normal heating medium is generally low pressure steam or dowtherm or flue gases. Feed depending upon its physio-thermal properties can be introduced in a number of ways forward, backward, mixed or parallel over the years research efforts have been devoted to make the multiple effect evaporator more & more economical and energy efficient through changes in some geometrical design operating parameters and the like . In the multiple effect evaporators, steam economy can be increased by various means much as increasing the number of effects, splitting of feed condensate flashing & vapour recompression. Keeping the above in view, the present investigation has been planned to carry out simulation of four effect sugar evaporator and tripple effect caustic-soda evaporator for sugar and caustic-soda industry with following objectives:- 1. To develop a mathematical model for the simulation of multiple effect evaporators for aqeous solution of sugar and caustic-soda with and without flashing for all the three feed arrangements i.e. forward, backward and mixed. 2. To determine the steam economy of a multiple effect evaporator for sugar solution and caustic-soda with and without flashing with changes in the operating variables: feed temperature, feed concentration, feed rate, pressure in the last effect, and steam pressure.