Design of heat integrated multiple effect evaporator system

Abstract

Evaporators can minimize the production of regulated waste residues, and increase the potential for recovering valuable materials from those wastes. Multiple-effect evaporators (MEEs) are common to industries that concentrate different products, regenerate solvents,or
separate solid-liquid mixtures. Process integration can help to choose the best configuration of MEE in order to achieve a more efficient process in the sense of energy use.
In present work a number of configurations and difficulties of MEE system such as condensate flashing, vapour bleeding, steam splitting, preheating of liquor using condensate,
variable physical properties and boiling point rise are taken into consideration to develop different models of evaporation system.In the present work seven effect evaporator system of typical Indian pulp and paper industry is considered for analysis based on above configurations. These systems is described by a set of nonlinear algebraic equations that include total and solute mass balances, energy balances, heat transfer rate equations and the composition and temperature dependence of relevant thermodynamic properties such as vapour pressures and enthalpies.The models are solved using ‘system of nonlinear equations’.Pinch analysis of the MEE network is also done. Economic evaluation to optimize the number of flash tanks is carried out for seven effect evaporator system. The two different types of configuration of vapor bleeding are considered and comparison of both configurations is done. Considering the optimum number of flash tanks and the best configuration of vapor bleeding, a system was designed.Considering the maximum possible number of flash tanks and preheating of liquor using condensate,a final system was designed. This modified design enhances the steam economy by 23.77% and reduces the steam
consumption by 36.76% in comparison to simple system.