Pekka Ruohonen

Determination of the Real Loss of Power for a Condensing and a Backpressure Turbine by Means of Second Law Analysis

All real processes generate entropy and the power/exergy loss is usually determined by means of the Gouy-Stodola law. If the system only exchanges heat at the environmental temperature, the Gouy-Stodola law gives the correct loss of power. However, most industrial processes exchange heat at higher or lower temperatures than the actual environmental temperature. When calculating the real loss of power in these cases, the Gouy-Stodola law does not give the correct loss if the actual environmental temperature is used. The first aim of this paper is to show through simple steam turbine examples that the previous statement is true. The second aim of the paper is to define the effective temperature to calculate the real power loss of the system with the Gouy-Stodola law, and to apply it to turbine examples. Example calculations also show that the correct power loss can be defined if the effective temperature is used instead of the real environmental temperature.

Increased thermal efficiency in Scandinavian integrated TMP and paper mills – analysing the potential for steam savings using the heat load model for pulp and paper

In this paper the potential for steam savings and excess heat levels is analysed for four Scandinavian TMP mills using the Heat Load Model for Pulp and Paper (HLMPP). The results are compared with similar results from previous studies for two other TMP mills. Further, an analysis is made regarding the linkage between the steam consumption and temperature level of excess heat and mill specific characteristics such as e.g. production rate and fresh warm water usage. Based on the results and the analysis the potential for implementation of different biorefinery concepts is discussed. The results indicate that steam savings of 2-20 % can be found in Scandinavian TMP mills. The pinch temperature is rather low, around 0-70 °C for most of the studied TMP mills, compared to the pinch temperature usually found at kraft pulp mills (100-140 °C) and thus the potential utilization options for the excess heat is rather limited. The results also show that the level of heated fresh water is affecting both the steam consumption and the pinch temperature and thus also the potential for efficient integration of different biorefinery processes.