Thermodynamic analysis of a cogeneration system in pulp and paper industry under singular and hybrid operating modes

Abstract

In the present study, a thermodynamic analysis of a cogeneration system in a pulp and paper industry under different operating modes i.e., singular and hybrid with a variable ambient temperature is conducted according to actual operating data. For singular operating mode, the power boiler is only employed using natural gas while for hybrid operating mode, the power boiler with the recovery boiler is employed using natural gas and black liquor as main fuels, respectively. The results show that for hybrid operating mode in comparison with the singular one, the thermal efficiency of turbine and condenser is enhanced by 1.36 and 7.7%, respectively while it is reduced by 2.8% for the power boiler. In addition, the overall thermal efficiency under singular and hybrid operating modes is 87.4 and 53.7%, respectively. For hybrid operating mode, the exergy destruction of power boiler decreases by almost 10% compared with that for the singular operating mode. Also, at hybrid operating mode, the soda is recovered with a mass flow rate of 33 tons/hour that is required for the cooking process in the chemical pulp section and additionally the consumption of natural gas in the power boiler is reduced by 11.8%.