| Feasibility and flexibility are important attributes in chemical processes. They are conventionally defined as the process ability to satisfy design parameter deviations or to handle variations in operational conditions. However, these definitions are often confusing and make them difficult to be included into the design objective. In this work, new definitions on these attributes are proposed. Corresponding evaluation methods are developed. These provide valuable information for debottlenecking or improving the existing processes' operability and better designs. Chemical process designs based on economic, feasibility and flexibility considerations are discussed focusing on three types of processes with different kinds of parameter deviations. They are: trigeneration systems with periodical utility demands, low temperature heat exchanger network (LTHEN) under deviating stream conditions and batch process with varying product demands. In trigeneration design, the influences of demand variations at different time periods on the overall system performance have been demonstrated. Feasibility and flexibility evaluations of different design options allow the achievement of proper design decisions so as to meet the changing demand needs economically. Due to the existing difficulties in LTHEN computation, a systematic approach for design optimization is developed. This approach combines the Pinch analysis and mathematical programming to synthesis the heat exchanger network. This eases feasible LTHEN construction at different flexibility levels. In batch process design, a novel mathematical formulation is proposed to demonstrate how discrete operations can be modeled with a continuous operation zone. This guarantees fulfillment of basic feasibility requirement. Moreover, flexibility measurement is incorporated to generate feasible design combinations at different degree of flexibility attractiveness. These proposed methodologies can generally be applied to all chemical process and provide important techniques for chemical process development. These ensure smooth operation and maintain process economics under the volatile process and market conditions nowadays. |
