(90c) Energy Targeting under Varying Driving Force Distribution Conditions in Heat Recovery Systems

Oil and gas supplies are very tight and its markets are suffering high level of uncertainty. The demand for more fossil fuel is increasing and there is no sign it will decline in the foreseen future. Almost all production facilities are doing their best to save as much as possible in their energy bill to keep its competitive edge. Energy conservation and energy efficiency optimization practices have become a normal operation mode for industrial facilities. Optimal driving force distribution in energy systems comes from the combined effect of system's process conditions and hot and cold streams minimum approach temperatures. Optimal driving force distribution in energy systems can have huge effect on energy consumption, utility selection and utility systems as well as energy recovery systems capital investment.

Process changes can result in reduction in energy utility but also may bring reduction in the global DTmin. Thus in the current state-of-the-art pinch technology applications the capital/energy trade-off in energy system synthesis should be readjusted after each process change. This process of readjusting after each change is a real challenge due to the combinatorial nature of the whole process-utility system. In addition the change in the driving force distribution due to stream-specific DTmin and all possible combinations of process changes would have an affect on the utility level selection and quantities. Simply the problem of finding optimal utility system and heat recovery system driving force distribution is interlinked and multi-dimensional in which process changes and stream-specific DTmin selection are competing for optimal selection of utilities, optimal process conditions and optimal energy recovery system synthesis as well as optimal utility system synthesis. Pinch technology most widely used in process industry falls short in solving, systematically and without iteration, the first part of the problem which is the finding of the energy targets ahead of the process and utility systems synthesis due to all possible combinations of process conditions changes and different practical stream-specific DTmin.

In this paper we introduce a systematic method and software for energy targeting under varying driving force distribution conditions in heat recovery systems.