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Impact of Ethane, Propane, and Diluent Content in Natural Gas on the NOx emissions of a Commercial Microturbine Generator. Andr é s Colorado Vince McDonell Paper # 070IC-0200. 8 th U. S. National Combustion Meeting May 19-22, 2013. Outline. Introduction Motivation Methodology

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Impact of Ethane, Propane, and Diluent Content in Natural Gas on the NOx emissions of a CommercialMicroturbine Generator

Andrés Colorado

Vince McDonell

Paper # 070IC-0200

8th U. S. National Combustion Meeting

May 19-22, 2013

  • Introduction
    • Motivation
  • Methodology
    • Experiments
    • CFD
    • Chemical Reactor Network
  • Results
  • Conclusions
motivation nox emissions
Motivation (NOx emissions)
  • NOx Problems
  • NOx forms nitric acid - Acid rain
  • NO2 is a traveler (lifetime)
  • Photochemical smog (NO2 reacts with ozone+ sunlight)
  • Health
motivation nox regulations
Motivation (NOx regulations)

NOx Emission Trends for All Acid Rain Program Units, 1990–2009.

Source: EPA, 2010

  • In the near future, regulations will be even more stringent.
  • Manufacturers and scientist must find solutions to reduce even more NOx emission.
  • The Clean Air Act requires states to reduce ground-level ozone
  • From 1990 to 2009 the SO2 rate has dropped 71 % and the NOx rate has dropped 77 %.
motivation problem solving
Motivation (problem solving)

How can combustion scientists reduce NOx emissions?

By understanding

How the NOx is formed in the combustion process

Depends on

Fluid dynamics

Chemistry (kinetics)

The composition of the reactants

The way we mix the reactants-mixing patterns-recirculation

The addition of other compounds impacts the kinetics-NOx

Complex systems such as turbine-combustion chambers

predicting nox emissions mtg case
Predicting NOx emissions (MTG case)

Experiments MTG

Chemical kinetics software tools for solving complex chemical kinetics problems.

  • Complete set of chemical kinetics
  • GRI-Mech contains 325 reactions and 53 species
  • Short calculation time
  • What about the fluid dynamics in the chamber?
  • We can measure actual NOx
  • What about the chemical kinetics?
  • What about the fluid dynamics in the chamber?
predicting nox emissions mtg case1
Predicting NOx emissions (MTG case)

Computational fluid dynamics

  • Full access to the combustion chamber.
  • Nice colors that make everything understandable
  • chemistry 
  • A 3D geometry requires a lot of meshes. We need to solve the fundamental equations for every mesh.
  • What about the chemical kinetics?
  • Coupling fluid dynamics with full chemistry. High computer cost (simulations can take months)


Chemical kinetics


Chemical reactor network (CRN)

  • Step 1: Gain Details about Reaction Structure

Mesh of the combustion chamber, C65 engine

  • CFD models
  • Turbulence: k-ε
  • Combustion: Finite rate/Eddy dissipation
  • Methane air- 2 steps
  • Boundary conditions=experimental

CFD contours

  • Outputs from the CFD are inputs to the CRN
  • Residence time
  • Volume of each reactor
  • Temperatures
  • Flow distribution.
  • Flame shape.
  • Step 2: Develop CRN

. Air dilution zone


1. Premixing and distribution


Post-dilution & exhaust .


4. & 5. Planeof 4 injectors

7. secondary air

8. Post dilution zone

2. Plane of 2 injectors

6. Post flame

  • CRN performance
    • Very good agreement

Comparison NOx emissions, experimental vs CRN

  • Effect of higher hydrocarbons
  • Effect of diluents

100% CH4



80%CH4-20% CO2

results effect of heavier alkanes
Results- Effect of heavier alkanes

Comparison of NOx emissions (CRN and experimental) at constant adiabatic flame temperature and preheated combustion air temperature (AFT= 1850K, preheated air temperature=835K)

Experimental and CRN

NOx pathways

Hack and McDonell 2008 found that at full load the addition of higher hydrocarbons leads to higher NOx emission levels when compared to 100% methane.

Influence of the different NOx pathways .

results effect of diluting gases
Results- Effect of diluting gases

Experimental and CRN

Higher levels of diluent produce less NOX

Influence of the different NOx pathways.

  • The reactor network analysis (RNA) indicated that the addition of heavier hydrocarbons increases the production NOx. On the other hand the addition of diluents reduces the production of NOx. The same trend was observed experimentally.
  • The CRN methodology indicated that under the conditions of the MTG the N2O pathway is responsible for over 50% of the NOx emitted by the turbine.
  • Dr. Vince McDonell
  • Professor S. Samuelsen
  • Zhixuan Duan
  • Howard Lee
  • Brendan Shaffer
  • APEP mates.