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Sviluppo di una turbina a gas per micro-cogenerazione distribuita ad alta efficienza

(In lingua inglese)

- Micro GT and distributed Micro cogeneration.
- Technology development.
- What a MGT is.
- Cycle analysis: Effect of TIT and Component Efficiency.
- CFD Model.
- Mechanical integrity.
- Centripetal Turbine Optimization.
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Atti di convegni o presentazioni contenenti case history
mcTER Cogenerazione - Milano giugno 2019 Cogenerazione: la via più immediata ed efficace per migliorare le prestazioni energetiche degli impianti industriali

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Estratto del testo
Gli atti dei convegni e più di 10.000 contenuti su www.verticale.net Cogenerazione Termotecnica Industriale Pompe di Calore 1001GEN.P1-00 Sviluppo di una turbina a gas per micro-cogenerazione
distribuita ad alta efficienza
Federico Cernuschi - RSE Ricerca Sistema Energetico, Pietro Zunino '' Università degli Studi di Genova The distributed generation of energy is becoming more and more interesting from the economical and environmental
point of view for the possibility of installing, nearby the site of use, small generation units that can provide at the same
time electric and thermal energy that can be used directly for civil heating, cooling or for industrial processes. This is
called microcogeneration. Three fundamental characteristics of distributed microcogeneration 1. Long, heavy, expensive, environmentally impacting high voltage electric grid are avoided 2. Efficient use of fuel with more than 30% (state of the art) electric energy plus more than 45% of thermal energy
from the 100% fuel chemical energy. Large global energy generated for 1 kg of CO2 produced 3. Location of the small generation units in proximity of the civil, rural or industrial settlements requires low
pollution combustion. Small GT units with gaseous fuel premixed combustion guarantee low emissions. Micro gas turbines main features: ' Large global efficiency ηG > 75 % ' Very low emissions NOx < 15 ppm , Co < 15 ppm ' Long useful life > 60.000 hours ' Simple installation
' Simple maintenance
' Simple operation
' Simple and remote control
' High reliability Micro GT and distributed Micro cogeneration Technology development Usual fuels Special fuels Natural gas Mixt CH4 and H2 Diesel Oil LNG and bio LNG Kerosene Biofuels Syngas Vegetable oil Usable fuels '' Conversion of biomass and wastes in liquid fuel by thermal and catalytic pyrolysis '' Conversion of biomass and wastes in gaseous fuel by anaerobic bacteria GT Heat in excess to be used for the fuel production and purification processes What a MGT is A microturbine is a small gas turbine system in the range 30kW '' 2000kW Micro gas turbines overview Turbec T100, II series Increase MGT Electric Efficiency Ceramic turbocharger impeller out of silicon nitride Fraunhofer-Institut für Keramische Technologien und Systeme, IKTS Dresden Current micro GTs efficiency is around 30%, mainly
due to uncooled radial turbine materials (e.g.
Nickel-based superalloy) that limit TIT to 950 °C. In order to considerably improve micro GT operating efficiency two steps can be implemented: - New materials (ceramics or monocristalline Nickel super alloys), to stand TIT from 950 °C up to 1100-1200 °C and
allow higher stresses. New thermodynamic cycle and, therefore, new machine layout.
- Increase of component efficiency Joule simple real cycle 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 40 Ef ficie ncy [- ] Compression ratio [-] Efficiency vs compression ration simple cycle "Efficiency_beta_950_40beta.dat" u 2:10 "Efficiency_beta_1100_40beta.dat" u 2:10
"Efficiency_beta_1200_40beta.dat" u 2:10 Present graph shows efficiency vs compression
ratio @950°C, @1100°C, @1200°C for the simple
cycle
Original:
Compr. Efficiency 0.80 Turbine Efficiency 0.86 Regenerated Joule cycle 15 20 25 30 35 40 2 4 6 8 10 12 Ef ficie ncy [- ] Compression ratio [-] Efficiency vs compression ratio regenerated cycle "Efficiency_beta_950.dat" u 2:12 "Efficiency_beta_1100.dat" u 2:12
"Efficiency_beta_1200.dat" u 2:12 Present graph shows efficiency vs compression ratio
@950°C, @1100°C, @1200°C for the regenerated cycle
Original:
Compr. Efficiency 0.80 Turbine Efficiency 0.86 HX pinch point 70 °C Considering the maximum inlet Turbine temperature of 950 C° (1223 K°) for uncooled Gas Turbine and
compression ratio of 4 the efficiency of regenerated Gas Turbine open cycle increases from 18% to 30% .
Original:
Compr. Efficiency 0.80 Turbine Efficiency 0.86 HX pinch point 70 °C Optimised:
Compr. Efficiency 0.84 Turbine Efficiency 0.90 HX pinch point 30 °C 11/146 Cycle analysis: Effect of TIT and Component Efficiency Concept Design ' Performance target
' Technology to be used
' Thermodynamic cycle
' Simplified component design (1D) Preliminary Design '2D and 3D aerodynamic and thermo-mechanical design
'Multi-disciplinary optimisation Detailed Design ' Final performance evaluation
' Hot to cold procedure
' Detailed drawings and manufacturing drawings and specifications Prototype manufaturing and testing Design flow chart Preliminary geometry CFD Analysis FEM Analysis Database generation Learning Prediction New geometry from GA optimization CFD Analysis FEM Analysis Performance Performance Aerodynamic and mechanical optimized geometry A
N
N Iterative
loop Multidisciplinary optimization process MGT optimization strategy Coupled procedure for Fluid dynamic and Thermo-mechanical & modal analysis by means of
CFD and FEM tools
Objective: increase efficiency
&
Constraints:
mass flow, pressure ratio, mechanical stresses, eigenfrequencies CFD analysis Thermo-mechanical & modal analysis CFD Model  Mesh  Structured Low Reynolds Mesh (y+1), with HOH blocks  Density based time marching solver with multigrid acceleration  Turbulence model  k- SST  Fluid  Real gas with cp and cv function of temperature  Boundary conditions:  Inlet total quantities  Outlet static pressure varied to obtain the desired mass flow rate  Calculation time:  30 minutes for single calculation 1001GEN.P1-00 Mechanical analysis ' CalculiX '' CGX ' Structured and unstructured grid generator and post-processor '' CCX ' FEM solver: the solver is able to do linear and non-linear calculations.
Static, dynamic and thermal
solutions are available. Couplings between CFD and FEM and mechanical analysis CFD mesh Creation of impeller geometry, error fixing by ADmesh and FEM mesh generation through GMSH FEM mesh Thermomechanical and modal analysis performed using CalculiX, an opensource FEM tool The procedure implemented to generate the FEM mesh and to perform mechanical simulations has been integrally developed by using opensource software, namely: ADmesh, GMSH, CalculiX Mechanical integrity 1001GEN.P1-00 Centrifugal compressor design: parameterization Meridional channel contours, control points and angles convention Hub and shroud curves
simple line+ 4 points Bezier curve + simple line Several control points can move only along one direction to
guarantee slope continuity between successive curves, and
in order to link some hub and shroud points each other. Rotor row
4 points Bezier line for camber law
4 points Bezier line for symmetric thickness addition
Stator row
Bezier line for camber law
Two parameter law for symmetric thickness addition 26 geometrical parameters 3D Model for CFD Simulation Mesh generation
2.0 million of nodes
(600.000 nodes for stator)
(1.400.000 nodes for rotor) Optimization procedure: aerodynamic objective function and
penalty terms
'''''' = '''''''' + '''''''''' '''''''''' = '''' ''''' + ''''' + ''''''' '''' ''''' = ' '''' ''''' 1 '' ''''''' 0.1 2 ''''''''''' < 1 Efficiency penalty ''' '' = ''' '' 4.5 '' ''' 1 2 ''''''' < 4.5 0 ''''''' ' 4.5 Absolute total pressure ratio
penalty '''''' 𝐶 = '''''' ' 1 '' ''''' 1 2 ''''''''' ' 1 0 ''''''''' < 1 Absolute Mach number at
impeller exit penalty Optimization procedure: mechanical objective function and penalty
terms
Thermo-mechanical analysis
penalty Modal analysis penalty Compressor design: aeromechanical optimization results Absolute mach number Relative Mach number Its average value at diffuser inlet has not been
strongly affected by the optimization process even
though the different blade shape enables a smoother
velocity reduction and consequently a more efficient
pressure recovery Preliminary Optimised Mar Ma Preliminary Optimised The strong shock wave structure that is present in the preliminary
geometry analysis, due to the transonic flow at the blade tip , is
attenuated in the optimized design with a positive impact on
impeller efficiency Compressor design: aeromechanical optimization results Von Mises adimensional stress: original configuration Von Mises adimensional stress: optimized configuration The maximum Von Mises stress did not represent a limiting factor in the optimization procedure,
since the use of titanium and a reasoned parameters choice, which led to not excessive lean
angles and blade heights, enabled to limit the overall stress distribution in the impeller. Original geometry Centrifugal compressor design: aeromechanic optimization results Original Optimised ' '' [''''/''] 0.74 0.74 ''''''' [''] 0.80 0.84 ''''''' 4.4 4.6 Inlet relative '''𝐡 '𝐭 𝐢𝐦𝐩'𝐥𝐥'𝐫 𝐭𝐢𝐩[''] 1.4 1.25 A '𝐬𝐨𝐥𝐮𝐭' '''𝐡 '𝐭 𝐝𝐢''𝐮𝐬'𝐫 𝐢𝐧𝐥'𝐭[''] 1.3 1.15 ''''''''''' '''''''''' ''''''''''' [''] 1.54 0.95 Resonance 4EO No No Resonance NPF Yes No Multidisciplinary optimization enabled to achieve the following characteristics:
' higher efficiency (84%); ' high ''''''' in centrifugal single stage; ' Transonic rotor and stator; ' Von Mises stress field below the allowable limits; ' free from resonance behaviour of the impeller, in the speed operating regime, for the sources of excitation
considered.
Stress usage factor = '''''''' '''''''' '''''''''''''''''' Mass flow: 0.74 [kg/s] Press.Ratio: 4.6 [-] Rot.speed: 75000 RPM Blade n:
10+10 impeller
19 diffuser Radial turbine design: parameterization Meridional channel contours, control points and angles convention Hub and shroud curves
simple line+ 4 points Bezier curve + simple line Several control points can move only along one
direction to guarantee slope continuity
between successive curves, and in order to link
some hub and shroud points each other. Stator row
Simple Bezier line for camber law
Two parameter law for symmetric thickness
addition
Rotor row
4 points Bezier line for camber law
4 points Bezier line for symmetric thickness
addition 22 geometrical parameters Parametric 3D rotor model 3D Model for CFD Simulation Mesh generation
1.5 million of nodes
(500.000 nodes for stator)
(1.000.000 nodes for rotor) Optimization procedure: aerodynamics objective function and
penalty terms
Mass flow penalty function Efficiency penalty function Outlet flow angle penalty Optimization procedure: mechanical objective function and
penalty terms
Thermo-mechanical analysis
penalty Modal analysis penalty Turbine design: aeromechanical optimization results Entropy: original configuration Entropy: optimized configuration In the optimised case the optimisation tool increases the
tangential component of the absolute velocity at the
rotor, thus minimizing the incidence angle at the impeller
leading edge. This re-establish a right incidence
condition to the impeller as well as by the absence of
recirculating flow region. Reduction of relative velocity
within the runner Turbine design: aeromechanical optimization results Von Mises adimensional stress: original configuration Von Mises adimensional stress: optimized configuration In the original configuration there is a high bending stress mainly due to the lean angle of the
blade. Optimised configuration shows lower level of stress and stress peak is concentrated in the
fillet radius, where local plastic strains are allowed. Original geometry Stress and Temperature distribution on the turbine rotor with TIT=950C and n=75000 rpm High temperature alloys creep testing TIT=1050 °C , Tblade ̴ 850 °C Creep analysis: Larson Miller parameter '' Andamento del carico di rottura e a 1% di deformazione a creep in funzione del parametro LM per la lega MAR-M-247 𝐿'''' '' = '' '' [log ' + 20] Turbine design: aeromechanical optimization results Original Optimised 0.907 0.769 0.872 0.927 250.24 246.17 Blades- Vanes 14-20 13-20 2.54 0.98 Resonance 4EO Yes No Resonance NPF Yes No Multidisciplinary optimization enabled to achieve the following goals:
' high efficiency (92.7%); no separated flow regions;
' Von Mises stress field below the allowable limits, defined as a function of temperature;
' free from resonance behaviour of the impeller, in the speed operating regime, for the sources of excitation considered. Stress usage factor = '''''''' '''''''' '''''''''''''''''' '' Allowable stresses have been calculated according to metal temperature in each runner location Conclusioni 1 Centripetal Turbine Optimization
Through this integrated design approach , starting from a preliminary 1D design, the following goals have
been achieved: - high efficiency (84%);
- Von Mises stress field below the allowable limits, defined as a function of temperature;
- free from resonance behaviour of the impeller, in the speed operating regime, for the sources of excitation considered. .Centrifugal Compressor Optimization
Through this integrated design approach , starting from a preliminary 1D design, the following goals have
been achieved: - high efficiency (92%);
- Von Mises stress field below the allowable limits, defined as a function of temperature;
- free from resonance behaviour of the impeller, in the speed operating regime, for the sources of excitation considered.
This approach has demonstrated to be reliable; the versatility of the tool developed enables to introduce
further extensions. Conclusioni 2 ' l''Università di Genova, utilizzando un modello di microturbina sviluppato al proprio interno, ha ottenuto
e fornito ad RSE mappe descrittive della distribuzione della temperatura e delle sollecitazioni
meccaniche che si instaurano nel rotore di turbina quando la TIT sia pari a 950°C, 1000°C e 1050°C. ' Sono state localizzate le zone più sollecitate del componente e, sulla base degli esiti di prove di creep e
di fatica oligociclica effettuate da RSE è stato possibile valutare con quali vantaggi e quali limiti le leghe
monocristalline prese in considerazione potrebbero effettivamente essere applicate per la realizzazione
di un rotore di microturbina. ' Il principale risultato di questa attività è che utilizzando superleghe monocristalline si potrebbe pensare
di incrementare la TIT fino a 1050°C ed oltre (si stima che forse si potrebbe arrivare fino a poco oltre i
1100°C), ottenendo così nel caso più favorevole un incremento di rendimento di circa 5-6 punti
percentuali.


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