Simulation and pinch Analysis of Värö Mill

Abstract

In this diploma work, a mass and energy model of Värö pulp mill has been developed and a pinch analysis has been performed. The aim of the pinch analysis is to find excess heat that can be used to produce more hot water for the bleach plant. It is also used to examine the district heating heat exchanger that is to be installed at the mill to produce district heating to Varberg. The modeling tool used is the simulation program Extend, and the model describes the energy and mass flows in the digester and surrounding equipment. Parallel to this work a model of the evaporation plant, the washing, screening, bleaching and drying have been constructed. Using data from the model and the mill, a pinch analysis has been performed, using the New Composite Curves. This analysis leads to four retrofitting alternatives that produce the water needed in the bleach plant. Three of these alternatives produce the hot water necessary without using live steam; in addition to this, two of them do not require steam for the district heating production. None of these alternatives imply large investment costs. The analysis also visualizes ways of eliminating pinch violations, hence reducing the live steam demand in the plant. One example of pinch violations that could be eliminated, leading to live steam reduction, is heating the fresh water to the feed water tank with excess heat found in the pinch analysis, such as the gases after the heavy stripper, instead of live steam.