| Reference : Energy Efficiency Optimization of Low Grade Waste Heat Recovery via a Carbon Dioxide ... |
| Dissertations and theses : Doctoral thesis | |||
| Engineering, computing & technology : Energy | |||
| Entrepreneurship and Innovation / Audit | |||
| http://hdl.handle.net/10993/54036 | |||
| Energy Efficiency Optimization of Low Grade Waste Heat Recovery via a Carbon Dioxide Rankine Cycle | |
| English | |
Wolf, Veronika  [University of Luxembourg > Faculty of Science, Technology and Medecine (FSTM) > > ; University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Life Sciences and Medicine (DLSM) > Applied Thermodynamics] | |
| 2022 | |
| University of Luxembourg, Luxembourg | |
| Docteur en Sciences de l'Ingénieur | |
| 180 | |
| Leyer, Stephan | |
| Scholzen, Frank | |
| Hansen, Joachim | |
| Bertrand, Alexandre | |
| Ullrich, Peter | |
| [en] Energy Efficiency ; ORC Cycle ; Carbon Dioxide ; Thermal Compression ; Isochoric Heat Addition ; Waste Heat Recovery | |
| [en] Global energy consumption is continually increasing, and intelligent energy supply is
a critical concern for our generation. Rising concerns about climate change, as well as rising greenhouse gas emissions from the usage of fossil fuels, highlight the need of clean energy generation. Waste heat recovery might be one solution to this problem. Waste heat is generated as a byproduct of various processes and is discharged into the environment and the majority being generated at temperatures below 250°C. This lost energy has the potential to be absorbed and turned into useable energy, notably electricity. A Rankine cycle is capable of converting heat energy into electricity. Organic Rankine cycles employ working fluids with low evaporation temperatures (41-78°C), but are harmful to the environment due to their high global warming potential and greenhouse gas factor. CO2, on the other hand, has become a popular refrigerant in recent years due to its environmental friendliness and strong heat transfer capabilities. For medium to high temperatures about 250°C, converting waste heat to power works effectively. However, the efficiency is quite poor at temperatures below 100°C. This work seeks to improve the energy efficiency of waste heat recovery at low temperatures. Different techniques from the literature on how to increase the thermal cycle efficiency were studied in order to evaluate the optimization potential. Cycle adjustments such as reheated expansion, intercooled compression, and recovery were reported. However, the majority of the existing work is limited to medium to high temperatures. They were examined under equal operational settings to see if these cycle adjustments can also be used at low temperatures. A thermodynamic simulation using Matlab and EBSILON Professional was created for this purpose. For waste heat temperatures ranging from 60 to 100°C and a heat sink temperature of 20°C, the evaluated power cycles produced cycle efficiencies ranging from 2.35 to 8.16 percent. The aforementioned cycle adjustments only had a minor impact on efficiency at low temperatures. As a result, the basic cycle arrangement with no layout changes was determined to be the optimum for the examined temperature range. Another significant discovery was that fluid compression is the primary cause of poor efficiency. Because the compression of the fluid consumes a considerable portion of the energy provided by the turbine, the net power output is poor. Consequently, lowering the compression energy increases the net power production and thus the cycle efficiency. A thorough examination of how to compress a fluid with less (electric) energy input was carried out. Based on this, a thermal compression device (TCD) was designed, which uses heat rather than electricity to increase the pressure of a fluid. FLOWNEX and Matlab were used to simulate the TCD. A fluid flow due to gravity and pressure differential was developed in this model. The isochoric heat addition (IHA), a batch process, was modelled along with two buffer vessels upstream and downstream. For the thermodynamic cycle, the buffer vessels should allow for a steady mass flow. The results demonstrated that the pressure difference between the vessels has a significant influence on system performance and must not be neglected. Furthermore, the simulation revealed that the mass flow is declining during operation, indicating that the containers have not been completely emptied. As a result, the TCD’s throughput is reduced. This issue may be solved by adding a piston in the vessel, which allows for exact adjustment of the vessel volume and fluid flow control. The enhanced TCD, which incorporates the changes was also simulated in FLOWNEX. The main advantage of the TCD is that it uses less electrical energy to pressurize a fluid by using waste heat, which is abundant. Another key advantage is that the constraint of a conventional pump or compressor to a distinct fluid phase - liquid or gaseous - is removed. The TCD can manage both of these fluid phases, as well as a phase shift during the pressurization process. The economic analysis contrasts the traditional ORC with the ORC using the TCD, revealing that the cost of electricity production is cut in half and the investment payback time is cut by 11 years. | |
| Researchers ; Professionals | |
| http://hdl.handle.net/10993/54036 | |
| FnR ; FNR12541056 > Veronika Wolf > LOWTORC > Energy Efficiency Optimization Of Low-grade Waste Heat Recovery Via A Numerical Investigation Of An Organic Rankine Cycle Using Supercritical Co2 > 01/12/2018 > 30/11/2022 > 2018 |
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