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2014-11-26 - Travail avec promoteur/Doctorat - Anglais - 316 page(s)

De Paepe Ward , "Flexible Heat Production from a micro Gas Turbine: Design and experimental analysis of humidified air cycles", 2010-09-01, soutenue le 2014-11-26

  • Edition : VUBPRESS
  • Codes CREF : Thermodynamique appliquée (DI2210)
  • Unités de recherche UMONS : Thermique et Combustion (F704)
  • Instituts UMONS : Institut de Recherche en Energétique (Energie)
Texte intégral :

Abstract(s) :

(Anglais) Micro Gas Turbines (mGTs) offer several advantages for small-scale Combined Heat and Power (CHP) production compared to Internal Combustion Engines (ICEs): low vibration level, cleaner exhaust and lower maintenance. The major drawback is their heat-driven use. In periods with no or low heat demand, part of the heat should be discarded to keep the mGT operated at high electric load. Compared to ICEs, the lower electric efficiency of mGTs makes them less attractive in this case and economic constraints could even lead to complete shutdown. In addition, the specific capital cost of the mGT is still high. This high capital cost makes that any shutdown has a severe negative effect on the economic performance of the mGT. In order to increase the flexibility of the mGT and to shift its use towards various heat and power demand profiles, the waste heat in the exhaust gases can be used to generate auto-raised steam or hot liquid water, which is then re-injected in the cycle. Humidifying the mGT working fluid will increase the electric performance, resulting in better economic performance of the mGT as CHP during periods with low heat demand. For the development of a humidified mGT, the dry and wet operation of the available Turbec T100 mGT needed to be fully characterized. For accurate wet simulations of the mGT, correct compressor maps are essential. The compressor map was reconstructed by performing dry and wet (with steam injection) mGT tests. Additional steam injection experiments were performed to characterize the behavior of the mGT in wet conditions. Steam injection experiments resulted in stable mGT operation at reduced rotation speed and pressure ratio and increased electric efficiency. Finally, the effect of water on the combustion of natural gas (lean blow-out limit) is experimentally studied in an atmospheric, premixed, variable-swirl burner. In a next step towards the humidified mGT, the optimal cycle for water introduction in the mGT could be determined by using black box analysis in combination with composite curves. Direct injection of heated water was identified as the most optimal cycle, resulting in an absolute efficiency increase of 4.4%. Transforming the existing T100 mGT into a micro Humid Air Turbine (mHAT) results in a lower electric efficiency increase of 2% absolute, but requires less changes to the T100 mGT. Therefore, the mHAT was selected as final humidified mGT layout. Transforming the T100 mGT into a mHAT requires the development of a saturation tower. To reduce the pressure drop, a new type of saturation tower, a spray saturation tower, was developed, using two-phase flow theory. Cross-current injection was identified as the optimal injection method for a spray saturation tower for mHAT applications. Based on these simulations, a cross-current spray saturation tower was developed and integrated in the T100 mGT cycle. Experiments on the modified Turbec T100 mGT were performed to evaluate the new test rig and identify its shortcomings. Two successful test runs of more than 1 hour with water injection at 60 kWe were performed, resulting in stable mGT operation at constant rotation speed and pressure ratio. Electric efficiency was only slightly increased due to the limited amount of injected water. The major shortcomings of the test rig were compressor surge margin reduction and the limited energy transfer in the saturation tower. Bleeding air to increase surge margin was the solution to prevent compressor surge, while increasing the water temperature and mass flow rate will enhance the energy transfer in the saturation tower. The first experiments on the mHAT test rig indicated its shortcomings but also its potential. Stable mGT operation was obtained and electric efficiency slightly increased. By increasing the amount of injected water, the electric efficiency can be increased more significantly. In conclusion, the proposed route for waste heat recovery by water injection in a mGT cycle offers high potential for electric efficiency increase without major changes to the mGT cycle. A stable mGT operation regime was obtained during water injection test, indicating the potential of the mHAT cycle.

Identifiants :
  • ISBN : 978 90 5718 183 2