Distillation is one of the most important and common operations in chemical and petrochemical industries. Despite all of its advantages, distillation units are responsible for a significant part of the total heat consumption in the world’s process industries. Limitations and price of energy make scientists try to find solutions to reduce energy-consumption of distillation. Heat integration of thermally coupled distillation column is one of the best methods. Two columns with different pressures are used in this construction; columns are integrated such that the condensing duty of high pressure column is used to boil the low pressure column. This work provides a comparison between two simple columns with direct configuration and thermally coupled distillation column with direct sequence backward integration arrangement for separation of a water, methanol and dimethyl-ether mixture based on energy-consumption and cost. The influence of changing numbers of first and second column trays on heating and cooling rate of each column are investigated based on a developed mathematical model using conservation law of mass and energy and bubble-point method. The average relative error between calculated and industrial temperatures in some trays is about 0.996%. According to simulation the thermally coupled construction saves energy about 50% more than two simple columns, but increase about 6% capital cost. Since steam is not used in high pressure columns in thermally coupled distillation operating cost decrease about 20%, too. Keywords: Distillation, Energy consumption, Heat integration, Thermally-Coupled distillation
