Energy transfer diagram for improving integration of industrial systems

In industrial processes, heat is transferred from the heating utilities to the environment or converted to another form of energy. Process operations and heat exchanges decrease the energy quality, i.e. the heat is cascaded to lower temperatures. This paper focuses on the energy retrofit analysis by screening the transfer of energy across process operations and heat exchangers. A new conceptual diagram is proposed to capture the flow rate of heat transferred from the heating utilities to the environment through each heat exchanger and process operation as a function of temperature. The diagram considers heat savings by retrofit of the process units and the heat exchanger network (HEN), which was not fully addressed by previous methods. As an example of application, the diagram is used to identify heat saving modifications in a furfural process, alone or hosted in a kraft pulp mill. The heat consumption in the furfural process alone can be reduced by 40% by two modifications in the HEN; the net heat consumption in the furfural process hosted in a kraft pulp mill can be reduced by 60%–84% with a few simple modifications in the HEN and process operations.