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Simulation of Low-Btu Syngas Combustion in Trapped Vortex Combustor

K. Zbeeb and C. Ghenai Ocean and Mechanical Engineering Department College of Engineering and Computer Science Florida Atlantic University, Boca Raton, Florida

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• Project Goal and Objectives • Introduction • Governing Equations • Geometry, Mesh and Boundary Conditions• Syngas Fuel Compositions and TVC Operating Conditions • Validation of the CFD model • Results • Contours of Static Temperature • Pressure Drop • Combustor efficiency • Emissions: CO and NOx

• Conclusions

Outline

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Develop Next Generation Gas Turbine Engines: • Higher Efficiency • Higher Operating Conditions (High Pressure and Temperatures)• Lower Emissions – meet the new emissions requirements • Use flexible and alternative fuels such as High Hydrogen Content Fuels

Goal

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• CFD Analysis – Predict the combustion performance (temperature, combustor efficiency and pressure drop) of two-fore body trapped vortex combustor (TVC) using alternative fuels (High Hydrogen Content Fuels) • CFD Analysis - Predict the NOx, CO and other emissions from the vortex trapped combustor when natural gas fuel (methane) is replaced with alternative fuels such as hydrogen and synthetic gas produced from coal and biomass gasification• Develop new correlations for the temperatures, NOX, CO…

Objectives

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• Trapped Vortex Combustor or TVC: Burn a wide variety of gas fuels with different compositions and heating values (low, medium and high Btu fuels). The syngas fuel are obtained from coal and biomass gasification. • TVC - Accommodate pure hydrogen or high hydrogen gas fuel with high flame speeds• TVC combustor using lean premixed combustion technologies provides low NOX emissions – no need of exhaust gas after treatment or post combustion NOX emissions control using steam, nitrogen or CO2• TVC - Improve Combustion efficiency, flame stability and pressure drop through the combustor

Introduction

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• Syngas fuels – different compositions (H2, CH4, CO, CO2, N2, H2O) and heating values (low to medium lower heating values). This will affect the combustion performance and emissions. Need to determine these changes for different compositions, heating values and operating conditions. • Syngas gas fuels – lower heating value or low-btu. To keep the same power – need to increase the flow rate of the syngas fuels (4 -6 times the flow rate of natural gas)

Challenges – Transition from Natural Gas to Syngas Fuels

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• Lean premixed combustion technology has been used successfully to control the NOx emissions with natural gas fuel. Risk of using this technology with syngas fuel with high hydrogen content – potential of flash back of the flame into the fuel injector • Diffusion or non premixed flame are used with syngas fuels to control the NOX – The presence of inert gas (CO2, N2, H2O) in the syngas fuel are used to reduce the flame temperature and NOx emissions.

Challenges – Transition from Natural Gas to Syngas Fuels

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TVC Combustion Strategy

Create a stable vortex system in a cavity, where fuel and oxidant are injected, mixed and burn

with minimum pressure drop

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FAU Trapped Vortex Combustor Fuel and Air Injection System

Fuel

Air

TVC Combustor

After body

8 fuel injectors 24 air injectors

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• Conservation of Mass • Momentum Equations • Turbulence – K-ε model • Combustion – Pdf/Mixture fraction model for non premixed combustion • Energy Equation • Radiation – P1 radiation model

CFD Analysis - Governing Equations

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Geometry, Mesh and Boundary Conditions

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Syngas Fuel Compositions TVC Operating Conditions

Syngas Fuel Compositions

TVC operating conditions

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Validation of the CFD results

Experimental Study

Fuel: Propane Power: 35 kW X = 10 mm

X = 33 mm

X = 45 mm

Losurdo, M.A., Bruno, C., Calchetti, G., Giacomazzi, E., Rufoloni, M.; XXV Event of the Italian Section of the Combustion Institute. 3-5 June 2002 - Rome, Italy.

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Results – Contours of Static Temperature

Fuel: Propane Power: 35 kW

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Results – OH Contours

P = 50 kW

Schwarze Pumpe

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Results – NOX Contours

P = 50 kW

Schwarze Pumpe

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Results – Contours of Pressure Drop

P = 350 kW

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Results – Contours of Combustor Efficiency

P = 350 kW

In

Out

FractionMassFuel

FractionMassFuelEfficiencyCombustor −=1

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Results – Contours of Carbon Monoxide CO

P = 350 kW

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Conclusions • A computational fluid dynamics analysis of the combustion of propane, methane, pure hydrogen and three syngas fuels in Trapped Vortex Combustor were performed in this study• The CFD results for the combustion of propane fuel inside the trapped vortex combustor compare well with the experimental data• The fraction of hydrogen in the fuel affects the flame temperature and NOX emissions at the exit of the combustor. Higher the hydrogen fraction in the fuel, higher is the temperature inside the combustor and the NOx emissions at the exit of the combustor. The presence of small fractions of inert gas in the syngas fuel compositions such as CO2, N2, H2O will help to reduce the flame temperature and NOx emissions.

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Conclusions • The results of the combustor efficiency show that the hydrogen fuel is the most efficient fuel among all the tested fuels, however the high NOX emissions and the cost and the storage of the hydrogen can be very challenging for real applications. • Low NOx emissions were obtained for syngas fuels. Syngas fuel is an environmentally clean fuel and cost generally lower than other fuels. It can be used for a clean combustion with sensible reduction in pollutants emissions.

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EFFECTS OF H2/CO FRACTION OF VARIOUS SYNGAS FUELS ON THE NOX DISTRIBUTION AT THE OUTLET OF THE TVC COMBUSTOR

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EFFECTS OF H2/CO FRACTION OF VARIOUS SYNGAS FUELS ON THE CO DISTRIBUTION AT THE OUTLET OF THE TVC COMBUSTOR

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EFFECTS OF H2/CO FRACTION OF VARIOUS SYNGAS FUELS ON THE TOTAL PRESSURE DROP OF THE TVC COMBUSTOR

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EFFECTS OF H2/CO FRACTION OF VARIOUS SYNGAS FUELS ON THE EFFICIENCY OF THE TVC COMBUSTOR