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.
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Abbreviations
- \(\hat{H}\) :
-
Specific enthalpy (kJ/kg)
- \(\dot{m}_{{ble}}\) :
-
Bleeding mass flowrate in Organic Rankine Cycle (kg/s)
- \(\dot{m}_{{tot}}\) :
-
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)
- \(Q_{{CU}}\) :
-
Cold utility demand (kW)
- \(T\) :
-
Temperature (K)
- \(T_{{sub}}^{{in}}\) :
-
Sub-stream inlet temperature (K)
- \(T_{{sub}}^{{out}}\) :
-
Sub-stream outlet temperature (K)
- \(\dot{W}_{{pump1}}\) :
-
Required power in pump 1 (kW)
- \(\dot{W}_{{pump2}}\) :
-
Required power in pump 2 (kW)
- \(\dot{W}_{{t,ble}}\) :
-
Shaft work rate produced in the turbine up to the point of bleeding (kW)
- \(\dot{W}_{{t,out}}\) :
-
Shaft work rate produced in the turbine from the point of bleeding up to its outlet (kW)
- \(\dot{W}_{{net}}\) :
-
Net power produced by the Organic Rankine Cycle (kW)
- \(Y\) :
-
Heat deficit (kW)
- \(\Delta \hat{H}_{{cond}}\) :
-
Enthalpy of condensation (kJ/kg)
- \(\Delta \hat{H}_{{evap}}\) :
-
Enthalpy of vaporization (kJ/kg)
- \(\rho\) :
-
Organic fluid density (kg/m3)
- \(\psi\) :
-
Difference between the amount of heat of the integrated streams (kW)
- \(Cp\) :
-
Heat capacity (kJ/kg K)
- \(FCp\) :
-
Heat capacity flowrate (kW/K)
- \(Q_{{HU}}\) :
-
Hot utility demand of the standalone integrated process (kW)
- \(T_{{proc}}^{{in}}\) :
-
Process stream supply temperature (K)
- \(T_{{proc}}^{{out}}\) :
-
Process stream target temperature (K)
- \(\Delta T_{{min}}\) :
-
Minimal approach temperature (K)
- \(~\eta _{{pump1}}\) :
-
Pump 1 efficiency
- \(~\eta _{{pump2}}\) :
-
Pump 2 efficiency
- \(\eta _{t}\) :
-
Turbine efficiency
- \(i\) :
-
Hot stream
- \(j\) :
-
Cold stream
- \(I\) :
-
Set of hot process streams
- \(J\) :
-
Set of cold process streams
- \(ORCI\) :
-
Set of hot sub-streams from Organic Rankine Cycle
- \(ORCJ\) :
-
Set of cold sub-streams from Organic Rankine Cycle
- \(PC\) :
-
Set of pinch candidates
- 1 to 11:
-
Label that identifies the organic fluid state in the Organic Rankine Cycle
- s :
-
Label that indicates state that would be achieved if isentropic compression/expansion took place
- p :
-
Pinch candidate
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Acknowledgments
The authors acknowledge the financial support from Coordination for the Improvement of Higher Education Personnel–CAPES, process 88881.171419/2018-01 and the National Council for Scientific and Technological Development—CNPq, processes 305055/2017-8, 311807/2018-6 and 162451/2018-0.
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Santos, M.N.P., da Silva Sá Ravagnani, M.A. & Costa, C.B.B. Optimal integration of an Organic Rankine Cycle to a process using a heuristic approach. Braz. J. Chem. Eng. 38, 653–667 (2021). https://doi.org/10.1007/s43153-020-00077-z
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DOI: https://doi.org/10.1007/s43153-020-00077-z