Mgt Turbec t100 Cc

GT2011‐46090 ANALYSIS OF A MICROGASTURBINE FED BY NATURAL GAS AND SYNTHESIS GAS: MGT TEST BENCH AND COMBUSTOR CFD ANALYSISM. Cadorin,M. Pinelli, A. Vaccari, R. Calabria, F. Chiariello, P. Massoli, E. Bianchi

GT 2011‐46090

ANALYSIS OF A MICROGASTURBINE FED BY NATURAL GAS AND SYNTHESIS GAS:

MGT TEST BENCH AND COMBUSTOR CFD ANALYSIS

ASME Turbo Expo 2011June 6‐10, 2011

Vancouver, Canada

M. Cadorin1,M. Pinelli1, A. Vaccari1, R. Calabria2, F. Chiariello2, P. Massoli2,

E. Bianchi3

1 Engeneering Department of University of Ferrara, via Saragat 1, Ferrara, (Italy)2 Istituto Motori ‐ CNR, piazza Barsanti e Matteucci, Napoli (Italy)

3 Turbec S.p.A., via Statale, Corporeno di Cento (Italy)


SUMMARY

MGT Turbec T100 main features

Test bench description

CFD numerical simulation set-up

combustion chamber geometry

computational domain

numerical models

Comparison between experimental and numerical results (full

load and part-load conditions)

Natural gas feeding case

Synthesis gas feeding case

GT2011‐46090 ANALYSIS OF A MICROGASTURBINE FED BY NATURAL GAS AND SYNTHESIS GAS: MGT TEST BENCH AND COMBUSTOR CFD ANALYSISM. Cadorin,M. Pinelli, A. Vaccari, R. Calabria, F. Chiariello, P. Massoli, E. BianchiGT2011‐46090 ANALYSIS OF A MICROGASTURBINE FED BY NATURAL GAS AND SYNTHESIS GAS: MGT TEST BENCH AND COMBUSTOR CFD ANALYSISM. Cadorin,M. Pinelli, A. Vaccari, R. Calabria, F. Chiariello, P. Massoli, E. Bianchi

Electrical output 100 kW

Electrical efficiency 30 %

Pressure in combustion chamber 4.5 bar

Turbine Inlet Temperature 1200 K

Turbine Outlet Temperature 620-650 °C

Nominal speed 70000 rpm

NOx @ 15 % O2 15 ppm

CO @ 15 % O2 15 ppm

Turbec T100 Nominal Characteristics

TURBEC T100 MICRO GAS TURBINE


TURBEC T100 MICRO GAS TURBINE

Reverse flow tubular combustor

Single stage radial compressor and turbine


EXPERIMENTAL TEST‐BENCH

Decompression plant based on a pressure reduction system from 200 bar to 10 bar.Distribution plant designed for a rated capacity of fuel gas equal to 100 Nm3/h.Environmental monitoring system able to detect leaks of flammable gases.

To allow the use of low calorific value fuel of variable composition (with a chosen percentage of hydrogen)

Combustion chamber

Turbine

Compressor

Turbec T100 MGT

Air inlet

Flue gas outlet


MGT CONTROL AND MONITORING SYSTEM

PC CALCULATION STATION

ASYNCHRONOUS CONVERTER RS485/USB MICRO GAS TURBINE

TURBEC T100

• line for data transfer, from the machine programmable logic controller (PLC) to the control room

• system for data acquisition• PC calculation station, located in the control

room• asynchronous serial converter, that directly

connects the MGT PLC signal with the PC.

INTERNAL CONTROL MODE

EXTERNAL CONTROL MODE

• The user is enabled to set only the requiredelectrical power;

• All the operating parameters are calculated bythe machine software.

• It allows the exercise of the machine in user-defined working points;

• Possibility to define set-point referred to therotational speed, the opening level of the fuelsupply system valves.

MGT outlet temperature in external control mode

Time


CAD 3D software: SolidWorks 2010

Grid generation software: ANSYS ICEM

NUMERICAL TOOLS

Numerical simulation code: ANSYS CFX 12.0


COMBUSTOR 3D GEOMETRY – SOLID DOMAIN

Air inlet

Air inlet

INNER FLAME TUBE

OUTERFLAME TUBE

Main fuel line

Pilot fuel line

o Tubular combustor

o Reverse flow

o Two fuel supply lines: pilot line (diffusive combustion), main line (premixed combustion)


1. locating pins have been removed;

2. ridges on inner flame tube have been removed;

3. extension of air inlet duct;

4. extension of the inner flame tube.

COMBUSTOR 3D GEOMETRY – GEOMETRY SEMPLIFICATION

1 2 3

Solid domain

Fluid domain

4


COMBUSTOR 3D GEOMETRY ‐MESH

TETRAHEDRAL GRIDFor meshing the more complex combustor zone• fuel supply lines•swirler•air and fuel mixing zone•primary combustion zone

HYBRID VOLUME MESH

HEXAHEDRAL GRIDFor meshing the wider and more regular-sized zone• secondary combustion zone• liner•air inlet zone

Tetrahedral and hexahedral meshes have been separately generated and then merged in a single unstructured grid of 1500000 cells


CFD ANALYSIS – NUMERICAL MODELS

COMBUSTION MODEL

Combined Eddy Dissipation Model (EDM) / Finite Rate Chemistry (FRC)

Based on the comparison of the characteristic time time of the two models: FRC in which chemical reaction rate is determined through the Arrhenius law and EDM in which the rate of reaction is depends on the time needed to mix the reagents at molecular level.

Reaction scheme

Methane Hydrogen NO

2 Step - Westbrook-Dryer (1981) 1 Step - Westbrook-Dryer (1981) Zeldovich mechanism

OHOH 222 21

⇔+22

224

21

223

COOCO

OHCOOCH

⇔+

+⇔+

Reynolds Stress Models (RSM):

• all Reynolds stress transport equations are solved, without any simplifications• high accuracy and robustness• low flexibility and high complexity in the resolution of mathematical models

Solution of Reynolds stress transport equations for each of the 6 tensor components

Solution of the ω transport equation

BSL Omega Based RSM (Omega Based Reynolds Stress Model)

TURBULENCE MODEL


PRELIMINARY CFD ANALYSIS

o Sensitivity grid analysis

• Tetrahedral grid of about 1’100’000

• Hexahedral grid of about 2’000’000

• Hybrid (tetrahedral-hexahedral) grid of about 1’500’000

o Sensitivity analysis of turbulence models

• Standard Two-equation models (k-ε, k-ω, SST k-ω)

• Reynolds stress models (BSL-RSM, SSG-RSM)

o Sensitivity analysis of combustion models

• Eddy Dissipation (EDM)

• Finite Rate Chemistry (FRC)

• Combined EDM-FRC


OUTLET• Averaged

static pressure

AIR INLET•Mass flow rate•Temperature•Composition

WALL OUTER FLAME TUBE•Fixed temperature

Pilot fuel line

FUEL INLET•Mass flow rate•Temperature•Composition

WALL PRIMARY COMBUSTION ZONE•Adiabatic

WALL INNER FLAME TUBE•Fixed temperature

CFD ANALYSIS – BOUNDARY CONDITIONS

Main fuel line


CFD RESULTS: NATURAL GAS FEEDING

Corner vortexes located in the corner regions between the

secondary swirler and the liner

o Natural gas feeding

o Full load working condition (100 kWel)

o Reference fuel distribution: 15 % pilot line, 85 % main line

Counter-rotating vortexes located in correspondence

of the secondary combustion zone

(before the dilution holes)


CFD RESULTS: NATURAL GAS FEEDING

Temperature


o Full load working condition (100 kWel)


Temperature

Higher temperature in the primary combustion zone (diffusive zone).

Flame bifurcation in the central zone of the combustion chamber.

Strong temperature reduction due to the dilution air.


Electrical power [kWel] 80.3 90.1

Fuel volume flow rate [Nm3/h] 27.4 30.7

Turbine Outlet Temperature [°C] 641.9 642.2

Air Inlet Temperature [°C] 28.5 28.3

Rotational speed [rpm] 66780 69300

Turbine Inlet Temperature* [°C] 1180 1193

NOx [ppm@15%O2] 11 9

CO [ppm@15%O2] 2 2

* TIT is inferred through the TOT by means of a Cycle Deck calculation

• The experimental tests are conducted on the test rig installed in the laboratory of IstitutoMotori - CNR of Naples

• The experimental tests have been carried on in “internal control” mode, just setting electricalpower reference;

• The maximum electrical power output obtained is lower than the nominal value(100 kWel) due to the higher air inlet temperature.

CFD RESULTS AND PRELIMINARY EXPERIMENTAL RESULTS



• Natural gas feeding case;• the simulation has been performed using the same numerical models and boundary

conditions of the full operational load;• the fuel mass flow rate has been varied for a fixed air mass flow coming from the

compressor, in order to obtain the power output of the operating point chosen;• the air mass flow rate is the design one, m = 0.7658 kg/s

NUMERICAL 3D SIMULATION: BASELINE CASE

90.1 kWel

100 kWel

Temperature

Similar temperature distribution;temperature levels are lower because ofthe reduced thermal power input and themore diluted mixture.


Air mass flow rate[kg/s] Fuel distribution

Baseline 0.7658 15 % pilot- 85 % main

Case a 0.7658 13 % pilot- 87 % main

Case b 0.7012 15 % pilot- 85 % main

Case c 0.7012 13 % pilot- 87 % main

• Baseline: air mass flow and fuel distribution as in full load• Case a: air mass flow as in full load, the measured fuel distribution values have been used• Case b: lower air mass flow rate value and standard fuel distribution between the supply lines

In order to have a more reliable air mass flow, a Cycle Deck calculation has been performed• Case c: lower air mass flow rate and measured values of fuel distribution

Setting of different fuel distributions andair inlet mass flow rate values

To assess the effectiveness of the simulation in reproducing the variations of

the actual operating conditions

No air mass flow measurement



Case a: m=0.7658 kg/s; P13%-M87%

Case b: m=0.70 kg/s; P15%-M85%

Case c: m=0.70 kg/s; P13%-M87%

TIT[K]

CO[ppm@15%O2]

NO[ppm@15%O2]

Numerical

Baseline 1163 1 4

Case a 1162 1 1

Case b 1187 1 13

Case c 1187 1 7

Experimental 1193* 2 9

* TIT of the experimental case is inferred through the TOT by means of a Cycle Deck calculation

• Reducing the inlet air mass flow produces an increment in TIT values.

• Reducing the fuel mass flow rate to the pilot line contributes to the reduction of NOx values to the outlet section of the combustion chamber.


Temperature


90.1 kWel80.3 kWel

Temperature

Load Parameter Numerical results

Experimental results

80.3kWel

TIT [K] 1178 1180

CO [ppm@15%O2] 1 2

NO [ppm@15%O2] 10 11

Good agreement between the numerical and the experimental data, in particular in terms of TIT

and NOx concentration.


o According to the above considerations, air mass flow rate for 80.3 kW has beendetermined by means of the Cycle Deck calculation

o Fuel distribution was set as the measured values of fuel distribution



o Full load operation condition (100 kWel)

o Variation of the fuel distribution

Fuel distributionPilot line Main line

P15-M85 (Reference) 15 % 85 %

P20-M80 20 % 80 %

P30-M70 30 % 70 %

Fuel PILOT

Fuel MAINSimulation of different fuel distribution

between the two supply lines have been provided, in order to determine

the behavior of the combustor

CFD RESULTS: FUEL DISTRIBUTION


Velocity [m/s]

• the fluid dynamic behavior is not strongly affected by the increasing of fuel percentage to the pilot line;

• the morphology and position of the vortexes do not vary;

• in all the cases there are two symmetric vortexes in the central zone of the combustor.

REFERENCE CASE15 % PILOT - 85 % MAIN






With the increasing of fuel percentage to pilot line:• temperature reduction in the primary combustion

zone (diffusive zone);• flame displacement towards the combustor axial

position;• flame bifurcation due to the vortex located in the

central area. Temperature

REFERENCE CASE15 % PILOT - 85 % MAIN






Temperature

NO molar fraction


TIT[K]

NO[ppm@15%O2]

Numerical

Pilot 15 %Main 85 % 1202 15.2

Pilot 20 % Main 80% 1199 26.8

Pilot 30 %Main 70 % 1200 7.8

Nominal Pilot 15 %Main 85 % 1200 15

The overall energy balance does not present significant differences between the studied cases.

The thermal power output developed within the combustion chamber and the temperature of gases at the outlet of the combustor are not influenced by the fuel distribution.


Synthesis gas derived from the pyrolysis of forestry biomass.Lower heating value equal to 9400 kJ/kg.

% CH4 % CO2 % CO % H2 % H2O21 38 29 7 5 % vol

• Neither the combustor geometry nor the fuel system geometry have been modified;• the simulation has been performed using the same numerical models and boundary

conditions of the natural gas supply case;• the fuel mass flow has been varied for a fixed air mass flow coming from the

compressor, in order to obtain the same power output of natural gas supply case.

CFD RESULTS: SYNTHESIS GAS FEEDING

o Synthesis gas feeding




• Uniform temperature decrease in the primary combustion zone;

• similar configuration of the temperature field.

• Decrease of NO formation in relation to the temperature decrease;

• CO increase located in the fuel injection ducts due to the fuel composition.

These results are in accordance with the phenomena related to the combustion process of LHV fuel.

CFD RESULTS: SYNTHESIS GAS FEEDING


FINAL CONSIDERATIONS

From the CFD analyses:the fluid dynamic behavior is not strongly affected by fuel distribution, while the temperature field is strongly influenced by the fuel distribution and consequently the NOx concentration.The synthesis gas feeding allows to reduce the NOxconcentration.The comparison between CFD and the preliminary experimental results at different operating points suggests that the numerical simulation is able to reproduce the combustion chamber overall behavior.


Thanks for your attention.

Anna [email protected]

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Mgt Turbec t100 Cc