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Flow optimization of hot-air burner branch ducts on a mill of a lignite power plant.

Chapter 1: Task

Chapter 2: Modeling of flow conditions

Chapter 3: Determination of parameters for modeling

Chapter 4: Analysis and optimization of the flow
conditions in the hot-air burner branch ducts


Chapter 5: Description of the aerodynamic test stand

Chapter 6: Test of hot-air burner branch ducts
on an aerodynamic test stand


Chapter 1: Task

Hot air flows in the hot-air burner branch ducts with a
temperature of about 290 ° C from the Ljungstrom air
pre-heater to the burner pipes after the coal mills.

The location of the hot-air burner branch ducts in relation
to the combustion chamber or the other mills is shown in
Figure 1.

Due to the construction of the air pre-heater, the hot air
contains a certain concentration of ash particles. This is
the reason why the relatively high flow velocity of about
25 m/s of the air lead to excessive wear, so that these
ducts underlie high maintenance costs.

As a result of the optimization work a longer lifetime will
be achieved through a lower wear.

This objective should be achieved by optimal alignment
of the duct geometry. Due to the optimal shape, extreme
loads in the ducts will be eliminated. Thus, the wear
spread out over the entire duct length, which increases
the lifetime of the ducts considerably. Through the optimal
shape of the duct geometry slipstreams and stalls will be
liquidated, so that the pressure losses of the flow through
the ducts can be substantially reduced.

A positive side effect is that the better utilization of the
channel cross-section can achieve a lower flow velocity
by the same volume rate.

A reduction of the gas flow velocity causes also a reduc-
tion of the flow velocity of the entrained abrasive ash
particles. Since the ability to abrasion of ash particles
depends on its own velocity the wear can be reduced.

Other positive side effects are reduced energy consump-
tions and reduced noise and vibration levels.

As shown in Figure 1, there are different nomenclatures for the hot-air burner branch ducts.

The optimization of hot-air burner branch duct HHL 20/50
(Figure 2) was selected as an example for the web-site.

They are divided into the branch ducts:
- HHL 20/50 BR 005 (Fig. 3 and 4)
- HHL 20/50 BR 006 (Fig. 5 and 6)

Figure 5:
Hot-air burner branch duct
HHL 20/50 BR 006 – drawing

Figure 6:
Hot-air burner branch duct
HHL 20/50 BR 005 – 3-D-drawing

 2. chapter

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Figure 1: Overview plan with the
position of the hot-air burner
branch ducts

Figure 2: Hot-air burner branch duct HHL 20/50

Figure 3: Hot-air burner branch duct HHL 20/50 BR 005 – drawing

Figure 4: Hot-air burner branch duct HHL 20/50 BR 005 – 3-D-drawing