Study of biomass applied to a cogeneration system : a steelmaking industry case.

Abstract

In this paper, a theoretical technical study was carried out using Brazilian available biomass materials (rice husk, coffee husk and elephant grass) compared to natural gas applied to an electric arc furnace (EAF) steelmaking process. Rice and coffee husk are biomass residues from the agriculture while elephant grass (Pennisetum Purpureum Schum) is an abundant, fast growing plant, which is used for cattle breeding. The ultimate analysis of the biomass materials was carried out in the research department of a Brazilian Steelmaking Industry. The results of the ultimate analysis were used to determine the lower calorific value and the mass flow rate of the biomass materials used in the cogeneration system. The actual steelmaking process uses natural gas to both improve the “cold spots” inside the furnace and contribute to minimize the use of electrical energy in the heating process. The feasibility study considers a combined heat and power plant (CHP) to generate electricity and heat to the electric arc furnace (EAF) process. This study used the First Law of Thermodynamics to determine the operational parameters of the cogeneration plant considering three cases of different operational parameters in the Rankine cycle. The technical results show that the natural gas consumption and exhaust gas generation were the lowest among the fuels in the three cases analyzed. Regarding the exhaust gases generation, some aspects should be highlighted: the combustion of biomass is considered carbon neutral; the exhaust gases generated may be used to scrap preheat; also, biomass is a renewable fuel in contrast with natural gas, which is a fossil fuel. Thus, an economic analysis, considering only the operational cost of the plant, was conducted exhibiting that elephant grass had the lowest operational cost, accounting for a reduction of about 9% in the second case and 15% in the third case compared to natural gas. Although the biomasses have lower LCV than natural gas, they showed a great promise of their use in the EAF process indicating their feasibility as an excellent alternative for the process of producing iron.