Investigation of a demand control steam distribution system : Maximized electricity production at Stora Enso Skutskärs Mill

One of the global sub-goals states that rehabilitation and adaptation of industrial infrastructure is important for making industries more sustainable, with more efficient use of resources by year 2030. Increased energy prices, strict environmental requirements, new control instruments for efficient end use of energy have created an increased desire to reduce energy use and related energy costs. Sweden has a goal of increasing the renewable electricity production by 18 TWh by year 2030 using the control instrument electricity certificate. Energy efficiency can be achieved at: the different kinds of processes in the mill, assistant systems, and heat and electricity supply (power generation). In this study, the main focus will be on power generation. The paper and pulp industry uses large amounts of different energy types in all processes in the factory. In this study, the focus is on the energy type steam. One of the basic requirements that a cogeneration system needs to follow is the steam pressure requirements of all the steam-consuming processes in the mill. In this study, all the steam-consuming processes on the low-pressure network have been investigated. The study is limited to the month of September year 2018. The system boundaries start from the recovery boilers and the bark boiler, and then the steam path is followed through the grid and ends at the steam consuming processes. The method is divided into two main parts: In the first part, a calculation model of the zero system was constructed. The second part is a study of the pressure requirements of the steam consuming processes on the low-pressure side. It is possible to demand control the turbine. The evaporation processes control the demand system. The other processes that limiting the lowest pressure are considered to be: The feed water tank and the receiver (at drying machine 8). The low-pressure network can be reduced from 3.2 to 2.92 bar (over pressure) without any applications. The pressure may be further reduced if a technical investigation is carried out over the turbine. The minimum design pressure of the steam consuming processes is considered 2.5 bar (over pressure). The pressure limit: 2.92 bar (over pressure) gave a cost reduction of 2.64 million SEK per year. 2.5 bar (over pressure) gave a cost reduction of 4,69 million SEK per year. Optimized operation is considered an approval measure for the allocation of electricity certificates. 8982 electricity certificates will be given if it is 100 percent allocation of electricity certificates of the turbines generated electricity with a design reduction of the pressure to 2.5 bar (over pressure). The certificates then corresponds to an income increase of 2.25 million SEK per year