Optimal integration of an Organic Rankine Cycle to a process using a heuristic approach
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ORIGINAL PAPER
Optimal integration of an Organic Rankine Cycle to a process using a heuristic approach Maria Nayara Pontes Santos1 · Mauro Antonio da Silva Sá Ravagnani1 · Caliane Bastos Borba Costa1 Received: 2 April 2020 / Revised: 28 September 2020 / Accepted: 15 October 2020 © Associação Brasileira de Engenharia Química 2020
Abstract Energy integration among processes has been one of the most relevant approaches in the field of process synthesis, allowing for better energy use and leading to positive environmental and economic impacts in industrial terms. Since the Organic Rankine Cycle (ORC) is a power cycle indicated for using low quality heat as the heat source, this study aims at integrating an ORC with process streams to use the recovered waste heat as the heat source for the cycle. A thermoeconomic optimization in terms of net power produced was proposed and, by means of a case study, an improvement of 6% in specific net energy was achieved over the best value reported in the literature using n-hexane as the working fluid. For working fluids pentane and benzene, improvements of 4.7% and 8.5% were obtained relative to the best specific net energy value presented so far. Keywords Organic rankine cycle · Energy integration · Optimization List of symbols Variables Ĥ Specific enthalpy (kJ/kg) ṁ ble Bleeding mass flowrate in Organic Rankine Cycle (kg/s) ṁ tot Total mass flowrate in Organic Rankine Cycle (kg/s) P Pressure (Pa) q Heat duty of a sub-stream (kW) QCS Heat load of cold streams (kW) QHS Heat load of hot streams (kW) QCU Cold utility demand (kW) T Temperature (K) in Sub-stream inlet temperature (K) Tsub out Sub-stream outlet temperature (K) Tsub Ẇ pump1 Required power in pump 1 (kW) Ẇ pump2 Required power in pump 2 (kW)
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s43153-020-00077-z) contains supplementary material, which is available to authorized users. * Caliane Bastos Borba Costa [email protected] 1
Chemical Engineering Graduate Program, State University of Maringá, Av. Colombo, 5790, Bloco D90, Maringá, PR CEP 87020900, Brazil
Ẇ t,ble Shaft work rate produced in the turbine up to the point of bleeding (kW) Ẇ t,out Shaft work rate produced in the turbine from the point of bleeding up to its outlet (kW) Ẇ net Net power produced by the Organic Rankine Cycle (kW) Y Heat deficit (kW) ΔĤ cond Enthalpy of condensation (kJ/kg) ΔĤ evap Enthalpy of vaporization (kJ/kg) 𝜌 Organic fluid density (kg/m3) 𝜓 Difference between the amount of heat of the integrated streams (kW) Parameters Cp Heat capacity (kJ/kg K) FCp Heat capacity flowrate (kW/K) QHU Hot utility demand of the standalone integrated process (kW) in Process stream supply temperature (K) Tproc out Process stream target temperature (K) Tproc ΔTmin Minimal approach temperature (K) 𝜂pump1 Pump 1 efficiency 𝜂pump2 Pump 2 efficiency 𝜂t Turbine efficiency Indexes i Hot stream j Cold stream
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Brazilian Journal of Chemical Engineeri
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