Process design and intensification for the production of solar grade silicon

Abstract

Solar grade silicon (SiSG) is typically used in photovoltaic applications, and it is commercially manufactured via the Siemens process. Despite the fact that current levels of demand are satisfied, there may be a shortage of SiSG in the near future. To improve the low yield of the Siemens process, two alternative types of SiSG production processes have been developed and analyzed using a stochastic optimization scheme within ASPEN PLUS. The first one is an intensified Fluidized Bed Reactor (FBR) process using a reactive distillation column. The second one is a hybrid process combining both the Siemens and the conventional FBR processes. In addition to supplying future demand, these processes are intended to reduce the use of raw materials. The results show the great value of optimizing the processes, since it achieves savings in the TAC of 53.28%, 67.65% and 62.58% (Siemens, Intensified FBR and Hybrid process), respectively. Siemens process shows the lowest TAC ($0.50 M/y), but this does not mean that it is the process with the highest potential, since it has the lowest silicon production rate, 0.47 kt/y. The Intensified FBR Union Carbide Process turns out to be the most expensive of the three ($2.57 M/y), with a large production of Si(SG), 1.49 kt/y. However, it is the hybrid process which shows the larger yield by far, with a production of 1.89 kt/y of Si(SG) and TAC of $1.95 M/y, showing the highest profit from sales, $40.47 M/y. However, from the environmental point of view, the Siemens process shows the lowest environmental impact based on the eco-indicator 99, while the Hybrid process is the second best.