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BURNER MODELING FOR THE DESIGN ENGINEER 

In some cases, a good deal of useful information about air and fuel flow in a burner can be learned from a simple flow

solution without resorting to complex combustion modeling. For example, complete combustion with minimal generation

of CO and unburned hydrocarbons usually requires proper premixing of fuel and air. Also, appropriately preheating air

upstream of the burner can provide energy savings of 30 to 50%. Additional savings can be achieved by minimizing

pressure drop within the burner. Simulation can assist in optimizing all of these aspects of the burner by including only

flow and basic heat transfer in the model.

In one example, Astec Inc. used computer simulation to reduce the time

needed to develop a new aggregate drying burner, designed for use in

asphalt plants, from the normal 6 to 12 months to only 32 days. Under

unusually tight time constraints, the burner needed to meet stringent

requirements for highly efficient combustion and low emissions of NOx,

CO, and noise. Astec engineers developed an initial premix burner

design, and then confirmed through simulation that gas injection resulted

in near-ideal mixing, avoiding uneven concentrations of air and fuel that

would increase emissions levels and reduce combustion efficien-

cy. As seen in Figure 3, the fuel is brought into the mixing

chamber through holes in pipes arranged in a radial pat-

tern. Visualization such as this allowed the engineers not

only to evaluate the mixing performance, but also to gain

a clear physical understanding of the flow in the burner.

In a second example, Coen Company used flow modeling to evaluate

the design of a windbox for a 250MW utility boiler project in Buenos Aires, Argentina. The purpose of the study was to

ensure uniform distribution of flow to the burners with the lowest pressure drop possible. Initial results showed that veloc-

ity distributions at the outlet were uneven, which would have impacted performance. New simulation models including flow

vanes were built, and the new results showed less than a 4% variation in mass flow (Figure 2). These changes in the

design improved the burner performance and stability, reduced emissions, provided proper flame shaping, and mini-

mized overall fan power requirements. As a result, major modifications to the windbox were not necessary, and eventual

field test measurements confirmed the predicted performance.

Tools that make virtual modeling more accessible to the design engineer

have been under development for several years and are available

in the marketplace today. Flow simulation no longer requires an

advanced degree or a constant string of projects to maintain the

required skill set. Figure 3 shows the user interface for one such tool.

It displays pathlines colored by velocity magnitude for a windbox

similar to the one in Figure 2. A CAD drawing of the equipment

geometry is required as input. Clear guidance is given at each stage

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in the analysis, with “next” and “back” buttons available

for navigation between steps. Alternatively, movement

between set-up stages can be accomplished through

the navigator in the upper left of the screen. Green

checkmarks indicate which steps have been finished.This user friendly analysis capability allows small burn-

er manufacturers to benefit from in-house flow analysis

without requiring expertise in computational methods or

combustion models.

SUMMARY 

Fluid flow modeling technology has been used for more than 20 years to analyze burners and combustors. In recent

years, the usability of the tools has improved such that design engineers can now take advantage of engineering

simulation, saving time and money for industrial burner manufacturers.

1 Improving Industrial Burner Design with Computational Fluid Dynamics Tools: Progress,

Needs, and R&D Priorities, Department of Energy Office of Industrial Technologies &

Sandia National Laboratory, 2002.

http://www.eere.energy.gov/industry/combustion/pdfs/cfd_wkshp_report.pdf