Heat Integration opportunities in an Average Scandinavian Integrated Pulp &Paper Mill using Pinch Analysis
Examensarbete för masterexamen
Mehmood Iqbal, Asif
Pulp and paper production has a high turn over of energy. Previous energy analyses of this industry have revealed that there are great steam saving opportunities. However, most of the research is focused on pulp mills and thus less can be found about integrated mills in the literature. The aim of this master thesis was to investigate the heat integration opportunities in a model mill resembling an average Scandinavian fine paper mill. However, the paper machine of the model mill was not modelled on a detail level; therefore data from an existing paper machine (PM2 at Stora Enso Nymölla) has been used. With this data, heat integration opportunities within the paper machine and the whole mill were investigated. The paper machine was connected to two different model pulp mills with different water consumption. The energy saving potential was assessed using pinch analysis. The analysis of PM2 at Stora Enso Nymölla showed that the minimum hot utility demand according to the pinch analysis was very close to the present utility demand. This shows that further heat integration within the paper machine is hard to obtain. From the analysis of the integrated mill, no reasonable heat integration opportunities between the pulp mill and paper machine were found. However, integration opportunities within the two parts of the mill separately was found and the total steam savings amounted to 40.5 MW (16%) and 43.8 MW (17%) for the high water usage (HWU) and the low water usage (LWU) mills respectively. The steam surplus achieved in the retrofit can either be turned into electricity, by investment in new turbines, or less steam can be produced by decreasing the fuel consumption. The investment costs in the case of increased electricity production were about 28 M€, including investments for steam saving measures. In the case of saving bark, the investment costs were about 12 M€. The overall result was found to be dependent on the electricity and bark prices. At electricity prices ranging from 60 to 70 €/MWh, a payback period of 3.5-4 years is obtained. At these electricity prices, bark prices of 14-20 €/MWh results in a payback period between 2 and 3.3 years. One conclusion of this study is that there is less excess heat available in the average integrated mill than in the average pulp mill, due to a higher warm water demand in the integrated mill. However, there are still considerable savings to be achieved, both in the pulp mill and in the paper machine even though no integration opportunities worth considering were found between the two parts of the mill.
Kemiteknik , Chemical Engineering