Energy Saving in Polysilicon Manufacturing Process by using Pinch Technology and Divided Wall Column

Abstract

Spot market price of polysilicon is in decline; therefore, in order to be competitive, polysilicon manufacturing industry must reduce the manufacturing cost of polysilicon. This can be done by saving energy in the existing plant or developing alternative cost-effective process design. In this work, two techniques have been used to reduce operating and capital costs of the polysilicon manufacturing process: heat integration and complex column structure such as divided wall column. First, process simulation model for polysilicon manufacturing process has been developed. For heat integration, pinch technology has been used to identify pinch rules violations in the current process. An alternative heat-integrated heat exchangers network has been developed which satisfies the pinch rules. Economic analysis results demonstrate that heat-integrated polysilicon manufacturing process can save 255.91 million US$ per year operating cost and 491.97 US$ capital cost. Moreover, a new methodology for process design and optimization of divided wall column has been proposed. This methodology has been applied to design and optimize a divided wall column (DWC) for silicon tetrachloride (STC) purification. According to results, the DWC for STC purification saves 8 stages, 10.91% reboiler duty and 10.86% condenser duty as compared to the base case of conventional two columns in-series structure for STC purification.