Analysis of an operating TMP mill using advanced composite curves and Heat Load Model for Pulp and Paper

In this study an operating thermo mechanical pulp and paper mill (TMP) is analyzed using advanced composite curves. Case mill utility consumptions are examined in a more detailed level, e.g. temperature levels to direct the utilities correct exploitation, the effect of temperature difference and potential to improve heat exchanger network by rearranging installed heat exchanger areas. 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). Case mill theoretical minimum consumptions of both hot and cold utilities are calculated, and these are compared against true utilities consumption figures. HLMPP is a generic tool for screening energy reduction potential in pulp and paper industry with reasonable effort and with sufficient data accuracy. The goal of the model is to convert the mill data into heating and cooling requirements of the process, and thus lot of process details have been left out. In the model, several sources for wood fibre and several paper machines for different paper products and drying section setups can be applied. The model parameters are adjusted to the mill in question. The tool has been proven to work on a suitable accuracy level in previous studies. The mill used as an example in this study is an 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.