Secret Losses in Dedusting SystemsSecret Losses in Dedusting Systems

Optimisation of Ducts & routing pays off!Optimisation of Ducts & routing pays off!

SEAISI Seminar Session KUALA LUMPURSEAISI Seminar Session KUALA LUMPUR

NOVEMBER 21 – 22, 2011NOVEMBER 21 – 22, 2011

Volker Knoth

Carsten Pfundstein

Introduction Pressure drop Dampers Mixing Benchmark figures Examples

Agenda

The following tasks are to be fulfilled by a duct system

Transport

Cooling

Mixing

Distribution

Change of diameter

Change of shape (e.g. oval ↔ rectangular ↔ round)

Easy operation and maintenance

INTRODUCTION

Introduction Pressure drop Dampers Mixing Benchmark figures Examples

Agenda

Ducts and chambers are the main “consumer” of static pressure…PRESSURE DROP – CONSUMPTION DEC*

* Consumption of booster fan capacity

Sum=65 %

Ducts and chambers are the main “consumer” of static pressure…PRESSURE DROP – FURNACE DIRECT EXHAUST

Sum=77%

h = 2000 mm

b = 1000 mm

p = 120 Pa

A dedusting system consists of the combination of different geometries… DUCT GEOMETRIES – ELBOWS & BENDS

p = 5 Pa/m

lequ. = 22 – 9 m

lequ. = 46 – 24 m

= 90°

h = 1000 mm

b = 2000 mm

R = 1333 mm

p = 45 Pa

Examples:

= 90°

d = 1500 mm

R = 1500 mm

p = 110 Pa

R = 1000 mm

p = 230 Pa

For reference:

Piece of straight duct

with same gas speed

lequ.

NOTE: Straight ducting with proper dimensions is usually not the major issue!

p – Factor:

2,1 – 2,7

= 90°

Va = Vd

pa = 170 Pa

= 45°Va = Vd

pa = 75 Pa

= 90° Va = Vd

p = 65 Pa

Ratio of flow rates and angle between ducts are the keys to success… DUCT GEOMETRIES – MERGING & DIVIDING OFF GAS STREAMS

Examples: = 45°Va = Vd

p = 25 Pa

p – Factor:

2,3 – 2,6

Vd

Va

V

Vd

Va

V

Even small deposits can have big impacts… DUCT GEOMETRIES – DUST DEPOSITS ACTING AS AN ORIFICE

Examples:

D = 2.000 mm

d = 1.900 mm

T = 50 mm

h = 135 mm

s = 1.000 mm

v = 22,1 m/s

p = 12,5 Pa

(165 000 Nm³/h @ 100 °C = 225 400 Am³/h; initial gas speed for D = 2000 mm is 20 m/s)

p – Factor:

5,2 – 20

dust deposit layer

0,5 · (D – d) = T = thickness of dust layer

Calculation model(based on orifice situation)

D d

D = 2.000 mm

d = 1.750 mm

T = 125 mm

h = 435 mm

s = 1.650 mm

v = 24,6 m/s

p = 65 Pa

D = 2.000 mm

d = 1.600 mm

T = 200 mm

h = 705 mm

s = 1.910 mm

v = 31,1 m/s

p = 250 Pa

h

s

Realsituation

D

In a dedusting system known or secret deficits exist in almost every caseDEDUSTING SYSTEM KEY COMPONENTS

EAFDOB

Canop

yhood

WCD

Coole

r

Bag

House #1Fan

Sta

ck

Damper

Damper

Mixing

DCD

SWD

DOB = Drop-out box

DCD = Down comer duct

SWD = Single walled duct

WCD = Water-cooled duct

Bag

House #2Fan

Distributing

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 5 000 Pa

Design of duct system not optimum, e.g. 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) 28 %*net capacity = without bag house

What is your guess on the sum of the above examples?DUCT GEOMETRIES – QUICK & DIRTY ESTIMATION

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) 7 680 h

Annual energy consumption 2 430 000 kWh

Cost impact (0,05 €/kWh) > 120 000 €/a

NOTE: the amount of wasted money on the operational cost side is more than you think!

Simple systems could help to save a lot of moneyCOMPARISON BETWEEN BSE HIGH TEMPERATURE QUENCHING (HTQ) SYSTEM AND CONVENTIONAL COOLERS LIKE TUBULAR COOLER

2x 90° turn2x diameter change20 m „duct“ length with low speed

2x 90° turn (minimum)2 – 6x diameter change1x distribution of flow80 m duct with medium speed3x 180° turn 1x unification of flow

=Booster Fanrequired for TC

Pressure Drop Ratio

HTQ : TC

1 : 5 – 6

No Booster Fan required for HTQ

Introduction Pressure drop Dampers Mixing Benchmark figures Examples

Agenda

Dampers are the regulating installation and need attention…DAMPERS – TYPES

Rotation direction for closing damper

Multi-blade Type(counter rotation)

Butterfly Type

Multi-blade Type(twin rotation)

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

Multi-blade damper characteristic more linear than butterfly damper

No precise control at low flow rates possible with butterfly damper

Dampers are the regulating installation and need attention…

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

BENEFITS OF A SMART DAMPER CONTROL SYSTEM

Introduction Pressure drop Dampers Mixing Benchmark figures Examples

Agenda

Some problems derive from hidden processes…MIXING – A KEY ELEMENT FOR LIFE TIME AND PERFORMANCE

Example: Optimisation of mixing

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.

Canopy Duct

DECDuct

Duct to Bag House

Canopy Duct

DEC Duct

Duct to BagHouse

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

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.

Right bag house inletTaverage = 84,5 °C

Left bag house inletTaverage = 157,0 °C

Canopy duct

DEC duct

DEC Duct

Canopy Duct

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.

- 23 -

Introduction Pressure drop Dampers Mixing Benchmark figures Examples

Agenda

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] =energy consumption [kW]

productivity [t/h]

Dedusting system efficiency [Am³/kWh] =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

Am³/kWh

200 650

20

60

!?

? ?

??

??

?

?

?

?

Depending on the system and level of revamping the sky is the limit…BENCHMARK FIGURES – WHAT IS POSSIBLE?

* kWh = electrical power consumption at main fans

CUSTOMER EXAMPLES

-13 %15 %

-20 %25 %

-52 %109 %

-49 %100 %

-33 %44 %

-45 %75 %

-20 %25 %

Upgrade

Upgrade

new

total

Upgrade

new

Upgrade

Plant A

Plant B

Plant C

Plant D

Plant E

Change of specific flow rate (Am³/kWh*)(Dedusting system efficiency)

Change of specific cost (Cost/Am³)(Operational cost)

Average-33 % 56 %

Introduction Pressure drop Dampers Mixing Benchmark figures Examples

Agenda

High pressure losses due to convoluted duct routingEXAMPLE OF HIGH PRESSURE LOSSES

High pressure losses due to sharp edges and elbowsEXAMPLE OF HIGH PRESSURE LOSSES

before after

CUSTOMER EXAMPLE – ASIA

Not only reduction of operational costs …

Simplifying of arrangement by applying the KISS (Keep It Simple and Stupid) principle

Thank you for your attentionThank you for your attention

Questions?Questions?

Please ask?Please ask?

Volker Knoth

Carsten Pfundstein