Design and simulation of a multiple-effect evaporator using vapor bleeding

Abstract

The objective of this report is to develop a model for a five-effect evaporator system. Vapor bleeding is incorporated in the model as a means to reduce the amount of steam consumed in the evaporator. Since evaporation is the most energy-intensive stage in any industrial operation, measures to reduce energy consumption in the evaporator-house are greatly beneficial towards making an operation cost-effective. Other energy reduction schemes like condensate, feed and product flashing, vapor compression etc. are also available. Vapor bleeding brings about an increase in the steam economy of the process, but at the added cost of the required heat exchangers.
A model for an evaporator used for the concentration of sugar solution is developed using a set of non-linear equations derived from the mass and energy balance relations. These equations are then solved using the Newton-Raphson method by developing a matlab code for the same. For the present system steam requirement without vapor bleeding is computed first. Other variables like effect temperatures and liquor flow rates are also a result of the modeling procedure. The same system is then modeled by incorporating vapor bleeding for which steam requirement is also found. Additionally, the purchase and installation cost of the heat exchangers required are computed.
Vapor bleeding brings an improvement in the steam economy of a process by 26% but at the added cost 43,200 in the cost of steam is achieved. The payback period of the modified design of five effect evaporator system is found as 2 years 5 months and 12 days.