The feasibility of using waste heat boilers to recover energy from the exhaust gases of electric arc furnaces

Abstract

Energy can be rejected in the waste gases of an UHP electric arc furnace at rates of up to about 15 MW, accounting for 200 kWh per tonne of liquid steel. The possibility of recovering a significant proportion of this energy as steam using a wast heat boiler has been investigated. The options of using the steam to satify the in-works demand and generating electricity are being considered. Extensive measurements of the conditions existing in the waste gas stream have been made throughout the steelmaking cycle for furnace practices involving oxygen blowing, continuous charging and supplementary firing with oxy-fuel burners. Various practical implications of the use of a waste heat boiler have been studied. These include the location of the boiler, the accretion of solid matter on tubes, the effect of the presence of the boiler on gas cleaning and the control of furnace extraction to achieve optimum performance. A case study involving a 180 tonne furnace used to produce special steels has shown that the payback of the capital involved in installing a boiler to generate sufficient steam to satisfy the works' base load would be less than two years, under the conditions prevailing during the project. The economic appraisal of electricity generation is being evaluated, but the initial indications are that the return of capital is not attractive if generation facilities do not already exist.