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

      Introduction Pressure drop Dampers Mixing Benchmark figures Examples

The following tasks are to be fulfilled by a duct system INTRODUCTION

       Transport Cooling Mixing Distribution Change of diameter Change of shape (e.g. oval ↔ rectangular ↔ round) Easy operation and maintenance

Agenda

      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 d = 90 = 1500 mm R = D R = ° 1500

p = 110 Pa

1000 mm mm D

p = 230 Pa

j h = 90 ° = 1000 mm b = 2000 mm R = 1333 mm D

p = 45 Pa

h b D = 2000 mm = 1000 mm

p = 120 Pa

D

p – Factor: 2,1 – 2,7

l

D l equ.

p = 5 Pa/m equ.

= 22 – 9 m l equ.

= 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

V d V a b V V b V a Examples: b = 45 ° V a = V d D

p = 25 Pa

b = 90 ° V a = V d D

p = 65 Pa

D

p – Factor: 2,3 – 2,6

b = 45 ° V a D

p

a = V d

= 75 Pa

b = 90 ° V a D

p

a = V d

= 170 Pa

V d

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

D Calculation model (based on orifice situation)

Real situation

h s Examples: D d T

h

= 2.000 mm = 1.900 mm = 50 mm

= 135 mm

s = 1.000 mm v = 22,1 m/s D

p = 12,5 Pa

0,5 · (D – d) = T = thickness of dust layer dust deposit layer D d = 2.000 mm = 1.750 mm T

h

= 125 mm

= 435 mm

s = 1.650 mm v = 24,6 m/s D

p = 65 Pa

D d T

h

s = 2.000 mm = 1.600 (165 000 Nm³/h @ 100 °C = 225 400 Am³/h; initial gas speed for D = 2000 mm is 20 m/s) mm = 200 mm

= 705 mm

= 1.910 mm v = 31,1 m/s D

p = 250 Pa

D

p – Factor: 5,2 – 20

In a dedusting system known or secret deficits exist in almost every case DEDUSTING SYSTEM KEY COMPONENTS Bag House #1 Fan Canopy hood Damper Mixing Damper

SWD DCD

EAF DOB

DOB = DCD = SWD = WCD = Drop-out box Down comer duct Single walled duct Water-cooled duct

WCD Distributing Bag 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.

Additional pressure drop due to design

Percentage of available pressure level 90 ° elbows unification of flows dividing of flows dust deposits (100 – 150 mm) (4x120+1x40+1x100+3x75) Pa = based on full fan capacity (5 000 Pa) based on net capacity* (~3 000 Pa) * net capacity = without bag house 5 000 Pa 4 pc 1 pc 1 pc 3 pc

845 Pa

17 % 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 Total flow rate of the exemplary dedusting system at main fans Temperature at bag main fans

Resulting power consumption wasted for the unnecessary pressure loss

Yearly operation time (320 d x 24 h) 845 Pa 1 366 300 Am³/h 1 000 000 Nm³/h 100 °C

315 kW

7 680 h Annual energy consumption

Cost impact (0,05 €/kWh)

2 430 000 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 money COMPARISON BETWEEN BSE HIGH TEMPERATURE QUENCHING (HTQ) SYSTEM AND CONVENTIONAL COOLERS LIKE TUBULAR COOLER Pressure Drop Ratio HTQ 1 : : TC 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 S = Booster Fan 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

        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 DEC Duct Duct to Bag House Duct to Bag House Canopy Duct DEC Duct 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 T average = 84,5 °C DEC duct DEC Duct Green & red stream lines show bad mixing and unbalanced distribution.

Left bag house inlet T average = 157,0 °C 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.

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Agenda

      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] = 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

20

kWh/t

60 200

?

?

!

?

?

?

?

?

?

?

?

?

 650

Am³/kWh

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

CUSTOMER EXAMPLES

Plant A Plant B Change of specific cost (Cost/Am³) (Operational cost)

Upgrade

-13 %

Upgrade

-20 %

new

-52 %

total

-49 % Plant C -33 %

Upgrade

Plant D

new

-45 % Plant E -20 %

Upgrade

Change of specific flow rate (Am³/kWh*) (Dedusting system efficiency) 15 % 25 % 44 % 75 % 109 % 100 % 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