Synthesis of Work and Heat Exchange Networks Considering Practical Operating Constraints

Abstract

The synthesis of work and heat exchange networks (WHEN) has drawn much attention from process synthesis researchers in the present decade, arising as a promising field of study. The current literature has shown that simultaneously integrating heat and work may lead to substantial savings in utilities usage in highly energy-demanding processes. The problem, however, comprises highly nonlinear constraints and efficient solutions are difficult to obtain. Optimisation-based approaches have presented interesting solutions. However, in some cases, they may not be practical. When coupling several compressors and turbines via one single-shaft for work exchange, it may become technically difficult to maintain the same rotation speed. Moreover, discharge temperatures in compressors/turbines in some literature solutions may be considered impractically high/low. In order to address the first issue, the number of units that can be coupled via single-shaft was limited, and the use of multiple axes rotating at different speeds was considered. Such a new constraint is handled with a new stage coupled to a previous meta-heuristic method for solving the WHEN synthesis model. The method is able to identify optimal couplings respecting the constraints proposed for more mechanically practical designs. Regarding the discharge temperature issues, penalty functions were employed and the optimization approach was able to find solutions within practical operating range for compressors/turbines temperatures.