In this study an operating thermo mechanical pulp and paper mill (TMP) is analyzed using advanced composite curves. The use of advanced composite curves is a relatively novel method developed in Chalmers University by Nordman and Berntsson. It is a graphical pinch based approach that takes into account the existing heat exchanger network and the utilities used. With this information provided it is possible to predict order of magnitude of the cost associated to retrofit certain part of the heat exchanger network. The method also reveals the possibilities to integrate heat pumps into the system. The mill is modelled using the Heat Load Model for Pulp and Paper (HLMPP). The mill used as an example in this study is a European mill, producing paper on three paper machines. The mill has three pulp lines; two TMP lines and one DIP line. The study also covers debarking and waste water treatment plants. The analysis shows a potential for improvement. The technical economical possibilities of achieving this potential are discussed.