https://orcid.org/0000-0002-7959-5283
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ABSTRACT
Aiming at the problem of high investment and energy consumption in separating the azeotropes, the feasibility and economy of pressure swing distillation processes combined with heat integration and heat pump technology for separating methylcyclohexane and n-butanol alcohol mixture were analyzed and discussed. The CO2 emissions, total annual cost and energy consumption are used as the evaluation indicators to assess the three modified pressure swing distillation processes. To obtain the optimal operation parameters of processes, the sequential iterative program is designed, which aims at the minimum total annual cost. In this work, heat integration pressure swing distillation and heat pump pressure swing distillation processes are compared with conventional pressure swing distillation in economic, energy-saving and ecological performance. The results show that the modified processes, whether heat integration pressure swing distillation or heat pump pressure swing distillation, significantly improves the economy and energy efficiency. Compared to the conventional pressure swing distillation process, the heat integration pressure swing distillation process can reduce CO2 emissions by 32.99%, total energy consumption by 32.99% and total annual cost by 23.61%. The heat pump pressure swing distillation process has the optimal economy and the least energy consumption among the three separation processes, which can reduce the total annual cost by 44.03%, the total energy consumption by 54.27% and the CO2 emission by 89.98%.
Nomenclature
| AC (m2) | = | Heat exchange area of condenser |
| AH (m2) | = | Heat exchange area of heat exchanger |
| AR (m2) | = | Heat exchange area of reboiler |
| CI ($) | = | Capital investment |
| CompC ($) | = | Compressor cost |
| D (m) | = | Column diameter |
| ElectricityC ($/year) | = | Electricity cost |
| EnergyC ($/year) | = | Energy cost |
| h (kJ/kg) | = | Enthalpy of stream |
| HPC | = | High pressure column |
| HIPSD | = | Heat integration pressure swing distillation |
| HPPSD | = | Heat pump pressure swing distillation |
| HXC ($) | = | Heat exchanger cost |
| L (m) | = | Column height |
| LPC | = | Low pressure column |
| MCH | = | Methylcyclohexane |
| NBA | = | N-butyl alcohol |
| NF1 | = | Feed stages of HPC |
| NT1 | = | Total number of stages of the HPC |
| NHV (kJ/kg) | = | Net heating value of fuel |
| NR | = | Recycle stream feed stages |
| NT | = | Number of stages |
| NF2 | = | Feed stages of LPC |
| NT2 | = | Total number of stages of the LPC |
| OC ($/year) | = | Operating cost |
| PSD | = | Pressure swing distillation |
| QC (GJ/h) | = | Condenser heat duty |
| QR (GJ/h) | = | Reboiler heat duty |
| Qcomp (kW) | = | Compressor duty |
| QH (kW) | = | Duty of the heat exchanger |
| Qh (kW) | = | heat output duty at high temperature |
| QP (kW) | = | Compressor duty |
| Qreb (kW) | = | Heat duty of the reboiler |
| RR1 | = | Reflux ratio of HPC |
| RR2 | = | Reflux ratio of LPC |
| SC ($/GJ) | = | The cost of LP steam |
| ShellC ($) | = | Column shell cost |
| StageC ($) | = | Column stage cost |
| TAC ($/year) | = | Total annual cost |
| TEC (kW) | = | Total energy consumption |
| TFTB (°C) | = | Theoretical flame temperature |
| TC (K) | = | Temperature of condenser |
| TR (K) | = | Temperature of reboiler |
| Tstack (°C) | = | Temperature of heat source |
| T0 (°C) | = | Temperature of the environment |
| UC (kW/(K×m2)) | = | Condenser exchanger coefficient |
| UH (kW/(K×m2)) | = | Heat exchanger coefficient |
| UR (kW/(K×m2)) | = | Reboiler exchanger coefficient |
| α | = | Molar masses ratio of CO2 and C |
| λ (kJ/kg) | = | Latent heat of hot steam |
Acknowledgement
This work is financially supported by the Postgraduate Research &Practice Innovation Program of Jiangsu province.