Simultaneous energy targeting, placement of utilities with flue gas, and design of heat recovery networks

Energy targeting and optimal utility placement are among the key steps in the cost-effective design of a process utility system. Composite Curves (CCs) and Grand Composite Curves (GCCs) are the popular Pinch Analysis tools for multiple utility targeting and placement. Although the CCs and GCCs can provide useful insights and yield acceptable utility targets, they could not be used to design a heat recovery network and to perform heat allocation involving the process and utility system. The Stream Temperature versus Enthalpy Plot (STEP) that was introduced in 2010 has the ability to overcome these limitations. Apart from giving the pinch points and energy targets, STEP can also graphically represent the maximum heat allocation (MHA) that can be converted into a maximum energy recovery (MER) network on a temperature versus enthalpy diagram. STEP has also been used for targeting closed-loop utilities having fixed supply and return temperatures that include steam, hot oil, refrigerants and cooling water circuits. However, the available STEP technique is unable to handle cases involving the “once-through” utility such as flue gas where the target temperature and flowrate needs to be simultaneously optimised in order to minimise fuel consumption. This paper presents a new approach to further extend STEP's capability for the simultaneous energy targeting, optimal placement of process utility systems that include flue gas streams with variable-temperatures and flowrates, and design of heat recovery networks featuring such targeted utilities.