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Coen uses Computational Fluid Dynamics (CFD) to evaluate aspects of duct
burner combustion. Computer modeling can often be helpful in estimating
the flame length relative to heat exchanger components downstream of the
duct burner.
This particular model involves two cases. In the first case, a simple
2D model of a single burner element was created to evaluate its combustion
properties. This technique is often used because much more detail can
be included in the burner’s geometry. A cyclic, or periodic, boundary
condition was used for the top and bottom edges of the model, so that
flow that crosses the top boundary has an identical effect at the bottom
boundary. Also, the finite reaction rate combustion model was used here.
The results are shown in the first pair of figures below.
The second model includes an array of 12 burners and 13 baffles. Due
to the increased size of the modeled domain, far less detail was given
to each burner element. The goal of this model was to determine the average
temperature of the combustion products entering the Heat Recovery Steam
Generator (HRSG), which is the area between the two vertical black lines
in the second pair of figures below. In this case, the mixture fraction
(PDF approach) combustion model was used because of its better convergence
characteristics.
Single-element methane distribution. |
Single-element temperature distribution. |
Full-array temperature distribution through the HRSG. |
Full-array CO distribution through the HRSG. |
CFD Features Used in This Model:
- A 2D structured grid (quad mesh).
- The standard k-e turbulence model.
- Variable properties (viscosity, thermal conductivity, and specific
heat are functions of temperature.
- The buoyancy model.
- Porous zones to simulate pressure drops.
- The DTRM radiation model.
- The finite reaction rate combustion model used for single-element
model.
- The mixture-fraction/PDF combustion model used for full-array model.
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