Optimization of Utility Energy System Operations at a Paper and Pulp Manufacturing Plant

Abstract

Optimization of utility energy system operations at a paper and pulp manufacturing plant isstudied. The system consists of three boilers and two turbine-generators. The plant discharges a large amount of black liquid which is used as a fuel in the system as well as heavy oil. Steam energy consumed at the plant is produced by this system, while electric energy consumed at the plant is not only generated from the system but also purchased from an electric power company. The goal of the optimization is to minimize the amounts of heavy oil consumed in the system subject to restrictions of black liquid consumption, steam and electric energy requirements and ranges of system operations. Actual operations of the system is analized using the data obtained on every 3 hours. It is found from this analysis that energy characteristic of every unit contained in the system can be represented by a linearized model. This leads to an application of the linear programming to the optimization of the system operations. The results of this study show that in order to optimize the system operations, in general, a unit with higher efficiency is operated with priority to other units, while some inefficient operations are found subject to restrictions of the system operations. Some proposals are thus given; one is to enlarge the capacity of storage tank of the black liquid and the other is to reduce the purchased electric energy under some special operating conditions. It is concluded that a large amount of heavy oil can be saved by these optimized operations of the utility energy system.