Operability Considerations for Retrofit Design of Industrial Process Energy Systems

Abstract: Energy efficiency is crucial to reduce fuel usage and related emissions in industry.  In energy-intensive process industry, the use of heat accounts for a large share of the total energy use and a reduction of the heating and cooling demand is thus important for decreasing energy use. Reductions in heating and cooling demand can be achieved by increased heat integration through heat exchange within the industrial process. However, this often increases the number of process interconnections, which can lead to operability issues, which could potentially be a barrier for implementing the heat integration measures. To better estimate the potential for energy efficiency through heat integration and to enable the implementation of more heat integration measures, an open inventory mapping is needed to clarify which operability considerations are important to include in such analyses. This thesis presents an investigation of operability considerations for heat integrations retrofit proposals. The study is based on a theoretical framework, a qualitative evaluation and a model-based analysis of the consequences for operation of the process utility steam system. The theoretical framework was developed through a literature review and an analysis of possible operability effects through process implications resulting from increased heat integration. This framework was used to design heat exchanger network retrofit proposals that included selected operability issues at a case study oil refinery. The retrofit proposals were evaluated in an interview study with engineers at the oil refinery. The effect of the retrofit proposals on the steam system was analysed using a steam system model. The results indicate that it is valuable to take process aspects into consideration at an earlier design stage when designing heat exchanger network retrofits for increased heat integration. If operability, non-energy benefits, practical implementation issues and utility systems are considered in an early design stage, several issues can be avoided and large benefits could be achieved for the process.