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In the current study, the exergoeconomic analysis of a cogeneration pulp and paper plant under bi-operating modes at different environment temperatures of 290, 295, 305, 310, and 320 K was investigated. Two operating modes of the cogeneration system, i.e., a hybrid operating mode using a power boiler and a recovery boiler and a singular operating mode using a power boiler only, were considered. Natural gas was utilized as the main fuel in the power boiler, while black liquor with heavy fuel oil was employed in the recovery boiler. The total capital investment, total operating, exergy, unit exergy, and exergy destruction costs for each operating mode were evaluated. The results indicated that the total capital investment cost was 3420.27 $/h, and the total capital investment and the operation and maintenance costs in the hybrid and singular modes were 5853.27 and 6226.67 $/h, respectively. As well, the unit exergy cost and the exergy cost of steam introduced by the power boiler were 39.31 $/MWh and 2503.69 $/h, respectively. Where these values for the recovery boiler were 34.69 $/MWh and 554.30 $/h, respectively. Furthermore, the exergy destruction costs at an environment temperature of 320 K for the power and recovery boilers were 1436.6 and 213.63 $/h, respectively. In the hybrid mode, the soda at a 10% concentration was recovered, with a rate of 32 t per hour desired for the cooking process in the pulp mill. In addition, the use of black liquor as a bio-fuel in the recovery boiler saved 14% of the consumption of natural gas. • Exergoeconomic analysis was performed for the pulp and paper industry. • Hybrid and singular operating modes for different ambient temperatures were studied. • Unit exergy cost, exergy cost, and exergy destruction cost were evaluated. • Using black liquor as a bio-fuel in RB saved about 14% of natural gas consumption. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]