Energy, exergy, economic, and environmental compromising performance of dual-stage evaporation-ammonia hybrid compression–absorption refrigeration system for the cooling supply of keto-benzene dewaxing process

Abstract

Absorption refrigeration systems driven by low-temperature waste heat is one way to achieve “carbon neutrality.” Meanwhile, the keto-benzene dewaxing equipment needs a cooling capacity of 5 MW, with refrigeration temperature of −10 °C and −25 °C. This paper researches the feasibility of Dual-stage Evaporation-Ammonia Hybrid Compression–Absorption Refrigeration System (DSE-AHCARS) replacing the vapor compression refrigeration system for keto-benzene dewaxing process based on Energy, Exergy, Economic, and Environmental (4E) analysis. At the primary- and secondary-stage evaporation temperature of 0 and –23 °C, respectively, the coefficient of performance (COP) reaches the maximum value of 0.85; however, COP-electricity reaches the minimum value of 8.1. When the secondary-stage refrigeration temperature is −23 °C, CO₂ emission increases from 1150 t·a⁻¹ to 3600 t·a⁻¹, and Life Cycle Climate Performance increases from 3.29 × 10⁴ to 7.7 × 10⁴ t, with the primary-stage refrigeration temperature being −15 °C–0 °C, as well as matching three parameters to ensure the 4E compromising performance by the multi-objective optimization. To guarantee that the Life Cycle Climate Performance is less than 5.5 × 10⁴ t, the payback period is <2 a, and COP is >0.6 at the optimal operation ranges, such that the refrigeration temperature difference between primary stage and secondary stage is within 20 °C. The power of DSE-AHCARS was reduced by 77% compared with the vapor-compression refrigeration system. Therefore, the DSE-AHCARS can reduce CO₂ emissions by about 6250 t·a⁻¹ and save 1.2 × 10⁵ t of CO₂ in the Life Cycle Climate Performance term. This result shows that the DSE-AHCARS can completely replace the vapor-compression refrigeration system.