Energioptimering av SSAB:s kraftverk i Oxelösund : Pinchanalys på det befintliga ångsystemet

Sammanfattning: In Oxelösunds there is a complete production facility, from metallurgy with the production of steel to rolling, formatting and hardening of sheet metal. SSAB Oxelösunds is producing world-famous trademarks such as Hardox, which is considered one of the world’s most advanced steel. SSAB has a goal to improve its energy efficiency by taking advantage of excess heat to reduce the demand of purchased energy, both in terms of fuel and electricity. Today SSAB Oxelösunds uses excess heat (blast furnace gas, coke gas and hot water) internally and also as additional fuel in the company’s power plant for electricity generation and district heating. The district heating and electricity are used internally and are also sent to Oxelösunds district heating network and the grid. One way to achieve SSAB’s energy efficiency goals is to perform an energy optimization of the factory’s existing power plant. The purpose of the thesis at SSAB’s power plant is to identify opportunities and for recovering excess heat from the existing steam system using Pinch analysis. This is done to increase electricity generation in the factory’s power plant. The aim is to produce flowchart for the existing plant based on an energy survey done on the power plant. The goal is also, by implementation of Pinch analysis over the existing heat exchanger network, to present changes to reduce energy consumption in the power plants that lead to increased power generation and how these changes can be made in practice. The thesis has been done at SSAB and the necessary data for the analysis has been developed using the IP21 database, which consists of logged data and as well as measured data with two different thermometers. Based on the generated data, a pinch analysis has been performed to investigate how heat exchange occurs in the plant which reveals how optimized the exchange of heat is. The pinch analysis has shown pinch violations consisting of heat exchange of streams over the pinch with streams under the pinch and vice versa by 1.5 MW. Possible measures to optimize and eliminate pinch violations have been investigated in the OK2 heat exchanger. OK2 consist of two boilers, 1 and 2, which is used for production of process steam and district heating. By using the high-grade 5 bar steam which is used in the current OK2 for district heating production to do a mechanical work in the high-pressure steam turbine in OK3 and then the condensed steam from the turbine can be reused for district heating production. OK3 consists of high and low-pressure steam turbine and district heat condenser. The suggested improvement means that the entire district heating production should be done by the condenses steam from turbine, both in the district heat condenser in OK3 and the heat exchanger in OK2.  The improvement suggestion lead to a decrease in entropy generation and an increase in exergy recovery, which means increased electricity production of 2.8 MW compared with the current operation. Assuming that district heating costs 0.22 kr/MWh and electricity costs 1 kr/MWh, the upgraded OK3.2 gives an extra income of 33 kr/MWh per fed fuel. The implementation of the improvement suggestion is expected to increase the overall energy efficiency of the plant, resulting in economic benefits. Based on discussions with operating technicians in the power plant, a possible change does not require major investment either.