Reliability is one of the most important properties of processing systems because of its high level direct effect on the investment and operational costs. Still there is no general method that is capable of simultaneously considering the reliability during the design procedure of processing systems. The main reason of the lack of general method is that the process systems design and the reliability engineering are based on different types of mathematical modeling tools. While process systems design is traditionally considered as mixed-integer optimization, reliability engineering is based on probability theory. The enumeration of the alternative feasible solutions of a redundant processing system is highly combinatorial, and, therefore, it is very difficult if possible to embed it into the widely used mixed-integer programming procedure.