In preliminary design, the space of design alternatives can be large. Automated synthesis tools may be used interactively to explore the design space, starting with a broad but coarse search and gradually progressing to more focussed and detailed searches. Recent developments in the search procedure used by the CHIPS process synthesis package enable the generation of partial solutions, solutions which although not feasible can be useful in the analysis of the synthesis problem. This enables one to use the tool as a device for exploration and experimentation. Furthermore, it provides a framework upon which the synthesis procedure can be expanded to provide automatic techniques for identifying suitable recycle structures. This paper briefly describes the approach for generating partial solutions. It demonstrates the use of the resulting tool in preliminary design through the presentation of a case study for the design of a Hydrofluoric acid plant, showing how the synthesis tool can be applied iteratively. The result is a process flowsheet suitable for more rigorous study.