Tillvaratagande av spillvärme

Abstract

This diploma work was performed at Ovako Steel’s plant in Hofors, Sweden. At the tube mill, hot rolled seamless tubes are produced. Large amounts of energy are needed for the rolling and the heat treatment of the tubes. The purpose of this thesis was to investigate possibilities to reduce the consumption of energy in the tube mill. The heating of steel at the tube mill is mainly done by combustion of propan95, a fossil fuel. An inventory of the energy flow in the tube mill, made by heat balances over the process stages showed that the furnaces (a rotary furnace and heat treatment furnaces) are in poor condition. Significant improvements can be achieved with economical and environmental revenues as a result. The tubes are placed on a cooling bed after the rolling. A lot of heat is released from the tubes on the cooling bed and should be recovered, but today technology is not available that is applicable to the conditions of the cooling bed in the tube mill. Since propan95 is a fossil fuel, combustion will increase the content of carbon dioxide in the atmosphere. By exporting waste heat to a nearby heat and power plant, biofuel will be released that can replace fossil fuel in another heat plant and global carbon dioxide emissions will be reduced. An improvement of the rotary furnace will decrease the consumption of propan95 from 2388 tons per year to 1600 tons, which also leads to a decrease of the emissions of carbon dioxide by 33 %. Recovery of the heat in the flue gas by export of waste heat would decrease the emissions by another 633 tons per year. The heat treatment furnaces can reduce the use of propan95 by 25 %, but recovering heat in the flue gas stream is not recommended.