Modeling and Simulation of Borregaard's Steam System - Construction, Validation and Utilization of the Model

Abstract

The steam-system at Borregaard Sarpsborg big process plant consists of several kilometers of pipelines and different pressure-systems. The steam-system is the most important secondary aid system to Borregaard's main production. The objective of the steam-system is at all time to supply enough steam with correct quality to all factories.

To investigate and understand the complex dynamics of steam-system, a dynamical model is developed and established during this master project. The model is constructed with the simulation platform K-Spice. The developed model allows advanced dynamical simulation of the steam-system, and consists of all steam producers and most important steam consumers as input. The model will be used to investigate how the steam-system can be governed more effective than it is today. The main objective is to increase the overall pressure stability and investigate solutions that aims to reduce wasted steam.

The model is constructed and based on two P\&ID flowsheets, in addition to information gathered from physical inspection of the steam-system and external consultants. The validation of the model entails several simulations of reconstructed cases in K-Spice based on historical data from Borregaard's DCS (Distributed Control System). In these simulations the response of the steam accumulator and different pressure-systems was studied in detail. The final validation of the model involves comparison of historic measured data from the DCS against simulated predicted data from K-Spice. Where the inputs to the model is based on the same historic data.

Later in this thesis the model is used to understand and map the complicated steam-system by investigating control strategies and dynamical behavior of the steam-system. In order to find feasible solutions to the main objective it was performed several simulations based on real time periods, like in the validation process. The simulation results show that the pressure controllers in the steam-system highly interact with each other, and that only one poor setpoint may cause bad performance for a large part of the system. The results also reveals that the control loops of the accumulator has an important role in the overall steam-system. The amount of wasted steam is reduced considerably by tuning the accumulator's controller setpoints.

The developed model is also used to investigate pipe segment D-1033-300 at the 12-bar system, which is considered to be overloaded as of today. Simulation results show that the steam velocity through the pipe is frequently higher than the recommended velocity of 25m/s. On the basis of the simulation results it is suggested three solution to this particular issue.