General methodology and optimization for the analysis of bottoming cycle cogeneration

Abstract

This paper aimed to develop a general calculation methodology for bottoming cycle cogeneration. The methodology considered the simultaneous generation of heat, power and cold; the energy rate demands curves of the process; the storage of cold thermal energy; the local environmental conditions for the calculations of the electricity generated; the performance coefficients of chillers; and the commercialization of electricity and carbon credits. The methodology shows the main performance indexes for bottoming cycle cogeneration, as well as the results of the minimum requirements for the cogeneration unit qualification, besides environmental and economic gains. A case study done for a small steel mill with 5,500 tons of pig iron average monthly production shown that ambient temperature and altitude influence remarkably on the electricity generation and cold production. It is observed that at lower ambient temperature and altitude, higher values of electricity generation and cold are given. Average environmental gains with electricity and fuel can reach 1,862,212 kg(CO2-Eq)/TT and 562,728 kg(CO2-Eq)/TT, respectively. Average economic gains from electricity, fuel and carbon credits can reach 1,893,249 US$/TT, 88,578US$/TT and 124,933 US$/TT, respectively. Performance indexes shown 26.15 % of energy efficiency, 1,326.78 kW of primary energy consumption reduction, 4,395.60 kW of primary energy saving and 6.085 % of primary energy savings gain. The presented methodology could assist governmental and non-governmental agencies in the elaboration of standards and laws to verify the performance indexes, environmental gains, and economic viability study of bottoming cycle cogeneration projects.