Energy integration in sponge iron plant using heat of waste gas

Abstract

Direct-reduced iron (DRI), also called sponge iron, is produced from direct reduction of iron ore (in the form of lumps, pellets or fines) by a reducing gas produced from natural gas or coal. Unlike the conventional process, the process does not require coking coal; the coke ovens in a steel plant are expensive and polluting units. Direct reduction, has been developed to overcome these difficulties of conventional blast furnaces.

In the present work a system is designed to integrate the heat of waste gas in the sponge iron process. For this purpose a case study of typical sponge iron production process is considered. Waste gas from the rotary kiln of the sponge iron plant exits at a temperature around 900 °C. This gas has a lot of sensible heat and can be used for energy integration. This heat is used for heating water in a boiler. Superheated steam which is produced in the boiler is used to rotate a prime mover like a steam turbine. The objective in the project is to design a system that will utilize waste heat from the process.

For this design total power generation of 10.77 MW was found using steam turbine. The annual profit upon incorporating the design was found to be Rs 411 lakhs when the power generated is exported for use. The payback period for this system is 1.22 years.

Keywords: Waste heat, Energy integration, Steam turbine