Secret Losses in Dedusting Systems
Optimisation of Ducts & routing pays off!
SEAISI Seminar Session KUALA LUMPUR
NOVEMBER 21 – 22, 2011
Volker Knoth
Carsten Pfundstein
Agenda
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Introduction
Pressure drop
Dampers
Mixing
Benchmark figures
Examples
The following tasks are to be fulfilled by a duct
system
INTRODUCTION
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Transport
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Cooling
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Mixing
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Distribution
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Change of diameter
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Change of shape (e.g. oval ↔ rectangular ↔ round)
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Easy operation and maintenance
Agenda
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Introduction
Pressure drop
Dampers
Mixing
Benchmark figures
Examples
Ducts and chambers are the main “consumer” of
static pressure…
PRESSURE DROP – CONSUMPTION DEC*
Sum=65 %
* Consumption of booster fan capacity
Ducts and chambers are the main “consumer” of
static pressure…
PRESSURE DROP – FURNACE DIRECT EXHAUST
Sum=77%
A dedusting system consists of the combination
of different geometries…
DUCT GEOMETRIES – ELBOWS & BENDS
For reference:
Piece of straight duct
with same gas speed
Examples:
j = 90°
d = 1500 mm
R = 1500 mm
Dp = 110 Pa
R
= 1000 mm
Dp = 230 Pa
lequ.
j
h
b
R
Dp
= 90°
= 1000 mm
= 2000 mm
= 1333 mm
= 45 Pa
h = 2000 mm
b = 1000 mm
Dp = 120 Pa
Dp = 5 Pa/m
Dp – Factor:
lequ. = 22 – 9 m
2,1 – 2,7
lequ. = 46 – 24 m
NOTE: Straight ducting with proper dimensions is usually not the major issue!
Ratio of flow rates and angle between ducts are
the keys to success…
DUCT GEOMETRIES – MERGING & DIVIDING OFF GAS STREAMS
Vd
V
Vd
V
b
b
Va
Examples:
b = 45°
Va = Vd
Dp = 25 Pa
Va
b
b
= 90°
= 45°
Va = Vd
Va = Vd
Dp = 65 Pa
Dpa = 75 Pa
Dp – Factor:
2,3 – 2,6
b
= 90°
Va = Vd
Dpa = 170 Pa
Even small deposits can have big impacts…
DUCT GEOMETRIES – DUST DEPOSITS ACTING AS AN ORIFICE
Calculation model
D
(based on orifice situation)
d
D
Real
situation
h
s
Examples:
D = 2.000 mm
d = 1.900 mm
T = 50 mm
h = 135 mm
s = 1.000 mm
v = 22,1 m/s
Dp = 12,5 Pa
0,5 · (D – d) = T = thickness of dust layer
dust deposit layer
D
d
T
h
s
v
Dp
= 2.000 mm
= 1.750 mm
= 125 mm
= 435 mm
= 1.650 mm
= 24,6 m/s
= 65 Pa
D
d
T
h
s
v
Dp
= 2.000 mm
= 1.600 mm
= 200 mm
= 705 mm
= 1.910 mm
= 31,1 m/s
= 250 Pa
(165 000 Nm³/h @ 100 °C = 225 400 Am³/h; initial gas speed for D = 2000 mm is 20 m/s)
Dp – Factor:
5,2 – 20
In a dedusting system known or secret deficits
exist in almost every case
DEDUSTING SYSTEM KEY COMPONENTS
Bag
Fan
House #1
Damper
Mixing
Canopy
hood
Distributing
Stack
Damper
SWD
Cooler
DCD
EAF
DOB
DOB =
WCD
Bag
Drop-out box
DCD =
Down comer duct
SWD =
Single walled duct
WCD = Water-cooled duct
House #2
Fan
What is your guess on the sum of the above
examples?
DUCT GEOMETRIES – QUICK & DIRTY ESTIMATION
Assumptions
Typical dedusting system with primary and secondary exhaust system
Two bag houses installed after upgrade of overall capacity
Typical static pressure supply of main fan
Design of duct system not optimum, e.g.
5 000 Pa
90° elbows
4 pc
unification of flows
1 pc
dividing of flows
1 pc
dust deposits (100 – 150 mm)
3 pc
Additional pressure drop due to design
(4x120+1x40+1x100+3x75) Pa =
845 Pa
Percentage of available pressure level
based on full fan capacity (5 000 Pa)
17 %
based on net capacity* (~3 000 Pa)
*net capacity = without bag house
28 %
NOTE: even small items can sum up to remarkable levels of losses!
What is your guess on the operational cost
impact?
DUCT GEOMETRIES – QUICK & DIRTY ESTIMATION
Assumptions
Typical dedusting system with primary and secondary exhaust system
Two bag houses installed after upgrade of overall capacity
Pressure losses due to design problems
845 Pa
Total flow rate of the exemplary dedusting system at main fans
1 366 300 Am³/h
1 000 000 Nm³/h
Temperature at bag main fans
100 °C
Resulting power consumption wasted for the unnecessary pressure loss
315 kW
Yearly operation time
(320 d x 24 h)
Annual energy consumption
Cost impact
NOTE:
7 680 h
2 430 000 kWh
(0,05 €/kWh)
the amount of wasted money on the operational
cost side is more than you think!
> 120 000 €/a
Simple systems could help to save a lot of money
COMPARISON BETWEEN BSE HIGH TEMPERATURE QUENCHING (HTQ)
SYSTEM AND CONVENTIONAL COOLERS LIKE TUBULAR COOLER
Pressure Drop Ratio
HTQ
:
TC
1
:
5–6
2x 90° turn
2x diameter change
20 m „duct“ length with low speed
 No Booster Fan required for HTQ
2x 90° turn (minimum)
2 – 6x diameter change
1x distribution of flow
80 m duct with medium speed
3x 180° turn
1x unification of flow
Booster Fan
S = required for TC
Agenda






Introduction
Pressure drop
Dampers
Mixing
Benchmark figures
Examples
Dampers are the regulating installation and need
attention…
DAMPERS – TYPES
Multi-blade Type
(twin rotation)
Butterfly Type
Multi-blade Type
(counter rotation)
Rotation direction for closing damper
Dampers behave differently according to their design…
DAMPERS – FLOW PATTERN & TURBULENCE
Dampers are the regulating installation and need
attention…
DAMPERS – INFLUENCE ON FLOW RATE
Damper curve for 4 – blade single blade design
No precise control at low flow rates
possible with butterfly damper
Multi-blade damper characteristic
more linear than butterfly damper
Dampers are the regulating installation and need
attention…
BENEFITS OF A SMART DAMPER CONTROL SYSTEM
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Improved dedusting efficiency in
Am³/kWh
Reduction of specific dedusting
cost in cost/t
Control and visualisation of the
entire dedusting system
Protection of valuable equipment
Simplification of emission control
Optimised maintenance work
Data trending for better process
understanding and delay tracking
Attractive cost/performance ratio
for a quick return on investment
Agenda






Introduction
Pressure drop
Dampers
Mixing
Benchmark figures
Examples
Some problems derive from hidden processes…
MIXING – A KEY ELEMENT FOR LIFE TIME AND PERFORMANCE
Example: Optimisation of mixing
Canopy Duct
Canopy Duct
DEC
Duct
Duct to Bag
House
DEC Duct
Duct to Bag House
NOTE:
The duct to bag house is split vertically into two ducts feeding two lines.
Left design: left duct = left bag house side encounters much more heat and dust load.
Optimised right design distributes heat and dust well balanced to both sides.
Some problems derive from hidden processes…
MIXING – A KEY ELEMENT FOR LIFE TIME AND PERFORMANCE
Example: Unbalanced load to bag filter lines after mixing chamber
Canopy Duct
Canopy duct
Right bag house inlet
Taverage = 84,5 °C
DEC duct
DEC Duct
Left bag house inlet
Taverage = 157,0 °C
Green & red stream
lines show bad mixing
and unbalanced
distribution.
Improper mixing and unbalanced distribution leads to strong
differences in bag house line inlet temperature.
NOTE:
Theoretical computer simulation results
have been proven by real measurements.
Symmetrical design is a good choice in many
cases…
MIXING – A KEY ELEMENT FOR LIFE TIME AND PERFORMANCE
Mixing of DEC and SEC is done quick and
uniformly before arriving at first split.
Agenda
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- 23 -
Introduction
Pressure drop
Dampers
Mixing
Benchmark figures
Examples
Some easy to calculate figures show you the
potential…
BENCHMARK FIGURES – WHERE IS YOUR SYSTEM?
kW
= specific energy consumption of dedusting system
= sum of all energy consumers of system (fans, water pumps, compressors, etc.)
t/h
= productivity of steel production related to the investigated system
Am³/h
= total flow rate of system after main fans
Specific energy consumption [kWh/t]
=
Dedusting system efficiency [Am³/kWh] =
energy consumption [kW]
productivity [t/h]
total flow rate [Am³/h]
energy consumption [kW]
Some easy to calculate figures show you the
potential…
BENCHMARK FIGURES – WHERE IS YOUR SYSTEM?
ACTION DEMAND DIAGRAM
kWh/t
60
!
?
?
?
?
?
?
?
?
?
?
?

20
Am³/kWh
200
650
Depending on the system and level of revamping
the sky is the limit…
BENCHMARK FIGURES – WHAT IS POSSIBLE?
CUSTOMER EXAMPLES
Change of specific cost (Cost/Am³)
(Operational cost)
Plant A
-13 %
Upgrade
15 %
Plant B
-20 %
Upgrade
new
total
25 %
-52 %
109 %
-49 %
100 %
Plant C
-33 %
Upgrade
Plant D
new
Plant E
Upgrade
Change of specific flow rate (Am³/kWh*)
(Dedusting system efficiency)
44 %
-45 %
75 %
-20 %
25 %
-33 %
* kWh = electrical power consumption at main fans
Average
56 %
Agenda






Introduction
Pressure drop
Dampers
Mixing
Benchmark figures
Examples
High pressure losses due to convoluted duct
routing
EXAMPLE OF HIGH PRESSURE LOSSES
High pressure losses due to sharp edges and
elbows
EXAMPLE OF HIGH PRESSURE LOSSES
Not only reduction of operational costs …
CUSTOMER EXAMPLE – ASIA
before
after
Simplifying of arrangement by applying the KISS
(Keep It Simple and Stupid) principle
Thank you for your attention
Questions?
Please ask?
Volker Knoth
Carsten Pfundstein