4 - Fan Systems and Audit

FAN SYSTEMS & FAN AUDIT

20/01/2009 - 1

Fan Systems & Fan Audit

LEARNING OBJECTIVES



At the end of the day the trainee shall be able to : - Meas Measure ure and and quali qualify fy fan fan perform performanc ance e • Revise fan curves • Determine system curves • Estimate power savings potential

20/01/2009 - 2


LEARNING OBJECTIVES



At the end of the day the trainee shall be able to : - Meas Measure ure and and quali qualify fy fan fan perform performanc ance e • Revise fan curves • Determine system curves • Estimate power savings potential

20/01/2009 - 2


FAN BASICS & FAN SYSTEMS

20/01/2009 - 3


FAN SYSTEMS - CONCEPTS OF PRESSURE pt TP

pSP s

p VP d

Air flow pt = ps + pd

• Static pressure (ps): • pressure exerted in all directions by a fluid at rest

• Dynamic pressure (pd): • pressure exerted by the velocity of a fluid : pd = ½ρv2

• Total pressure (pt): • the sum of static and velocity pressures 20/01/2009 - 4


FAN SYSTEMS – SYSTEM RESISTANCE ∆p = k ρ Q 2 k = Constant characteristic ρ = Gas density Q = Volume flow

Q

Q

p1

∆p

p2 20/01/2009 - 5


FAN SYSTEMS – SYSTEM RESISTANCE

• Each component in a system offers resistance to the gas flow.

• System resistance : The sum of all resistances to the flow The system resistance varies with air flow rate

• System curve : The relation between system resistance and flow rate

20/01/2009 - 6


FAN SYSTEMS – SYSTEM CURVES P

∆ ∆

• Constant static head • Airflow through a liquid pool • Fluidized bed

e c n a t s i s e r

∆ p = k

m e t s y S

Airflow rate Q

P

∆ ∆

• Complete turbulent flow • Standard fan systems

e c n a t s i s e r m e t s y S

∆ p = kQ 2

Airflow rate Q

20/01/2009 - 7


FAN SYSTEMS – SYSTEM CURVES

• Limit discussion to the completely turbulent system curve 12 10 8

∆ p = k ρ Q

2

p

∆ ∆

6 4 2 0 0

20

40

60

80

100

Q (m³/s)

20/01/2009 - 8


FAN SYSTEMS – PERFORMANCE CURVES Pressure vs Volumetric flow rate given by the fan • Defined for fixed specific operating conditions : • gas density (T, p, composition) • fan speed • Usually, power curve is given • Sometimes, efficiency curve

y c n e i c i f f E / r e w o P

e r u s s e r P

Flow rate blue = pressure red = power green = efficiency

20/01/2009 - 9


FAN SYSTEMS – FTP / FSP CONCEPT

• Fan Total Pressure (FTP) The European way FTP

= TP2 - TP1 = (SP2 + VP2)–(SP1 - VP1)

2

• Fan Static Pressure (FSP) The American way FSP

= TP2 - TP1 - VP2

1

= (SP2 - SP1)- VP1

• Static Pressure Rise(Good way!) =

SP2 - SP1 20/01/2009 - 10


FAN SYSTEMS – FTP / FSP EFFICIENCY

• •

Total efficiency (ηt)

: η t =

Q × FTP 3600 × P

Static efficiency (ηs)

: η s = η t

where

FSP FTP

=

Q × FSP 3600 × P

Q

:

fan flow (m³/h)

FTP FSP P

: : :

fan total pressure (Pa) fan static pressure (Pa) fan power (W)

Fan Total Efficiency Fan Static Efficiency Fan “Static Rise” Efficiency

83% 80% 85% 20/01/2009 - 11


FAN SYSTEMS – FTP vs FSP Performance Curve for IE 250 Fan 25

140 120

BHP

20

100 15

80

Total Efficiency

FTP

10 FSP Static Efficiency

5

60 40 20

0

0 0

5000

10000

15000

20000

25000

30000

35000

Flow Rate (cfm)

20/01/2009 - 12


FAN SYSTEMS – FAN PERFORMANCE Performance Curve for IE 250 Fan 62

103 r w e P o

50

] r a b m [ 37 e r u s s e r P 25 l a t o T n 12 a F

BHP

Operating Point

88 74 60

E f f i c ie n c y

F a n T o t a l P r e s s u r e

45 30

P o w e r [ k W ] / % e f f i c i e n c y

15

0 0

2,5

5

7,5

10

12,5

15

0 17,5

Flow Rate [m³/s] 20/01/2009 - 13


FAN SYSTEMS – FAN + SYSTEM CURVES Performance Curve for IE 250 Fan 50

103 r w e o P

45 ] r a b m [ e r u s s e r P n a F

88

40 74

35 30

60

25 45

E f f i c i e n c y

20

F T P

15

30

10

P o w e r [ k W ] / % e f f i c i e n c y

15

5 0 0

2,5

5

7,5

10

12,5

15

0 17,5

Flow Rate [m³/s] 20/01/2009 - 14


FAN SYSTEMS – REALITY

• Measured operating point may not fall on the fan curve • Due to measurement errors and fan system effects • In Fan Curves spreadsheet, the flow rate is assumed correct

Actual fan curve (XYZ-200)

35

442

30 ] r a b25 m [ e r 20 u s s e r 15 P l a t o10 T n a 5 F

Operating

368

point

P o 295 w e r [ k 221 W ] 147

Operating point : 6,12 m³/s 28,62 mbar 249,9 kW

74

0 0

2,5

5

7,5

10

12,5

0 15

Flow Rate [m³/s]

20/01/2009 - 15


FAN SYSTEMS – OPERATING RANGES Unstable

Stable

Peak

Flow Rate 20/01/2009 - 16


FAN SYSTEMS – FAN TYPES Two large classes • Centrifugal Fans • Extensively used in cement plants • Clinker cooler fans • ID fan • Mill ventilation fans • Dust collector fans • Axial Fans • Kiln shell cooling fans • Airplane’s propeller 20/01/2009 - 17


FAN SYSTEMS – FAN TYPES Exploded View of a Centrifugal Fan Inlet

Outlet Cutoff

Hub Flange Side Sheet

Scroll

Inlet Guide Vanes Backplate Inlet Bell Blades

Impeller

Stationary Inlet 20/01/2009 - 18


FAN SYSTEMS – FAN TYPES Cutaway of a Vane-Axial Fan Inlet

Discharge Vanes

Inner Cylinder

Outlet

Belt Fairing Tailpiece (sometimes omitted)

Blades

Impeller Hub

Inlet Bell

Outer Cylinder Diffuser 20/01/2009 - 19


FAN SYSTEMS – FAN PRINCIPLES Centrifugal Fan Principles

vr : radial velocity

v

vr vt

vt : tangential velocity v : fluid velocity

20/01/2009 - 20


FAN SYSTEMS – FAN BLADES

• Different types of fans characterized by their blade type: • Straight radial • Forward curve • Radial tip • Backward inclined - flat blade • Airfoil • Different applications require different blade type • Each type has different fan performance curves 20/01/2009 - 21


FAN SYSTEMS – FAN BLADES Airfoil (AF) : 85 - 90 % Backward-curved (BC) : 85 % Backward-inclined (BI) : 75 - 80 % Radial-tip (RT) : < 71 % Forward-curved (FC) : 65 % Radial blade (RB) : 60 - 63 % 20/01/2009 - 22


FAN FA N SYS SYSTE TEMS MS – FA FAN N LAW LAWS S

• Fan performance curve made for specific conditions: • fan speed • air density (temperature, pressure) • Always AT INLET CONDITIONS

• What happens in other conditions? • What if I change the speed of the fan? (N) • What if the gas density changes? (ρ) • What if I change the size of the fan? (D) 20/01/2009 - 23


FAN FA N SYS SYSTE TEMS MS – FA FAN N LAW LAWS S

• Geometrically similar (impeller) fans • Volume is directly proportional to fan speed Q2 Q1

=

N 2 N 1

• Pressure is proportional to the square of the speed 2

 N  =  2  TP1  N 1 

TP2

• Power is proportional to the speed cubed  N 2  P2 =    N 1  P1

3

20/01/2009 - 24


Exerc Ex ercis ise e 5.1 5.1 – FA FAN N LAW LAWS S Question :

• Fan Details : n = 1305 [min-1] v (1) = 7,1 [m³/s]

Increased flow (2) v (2) = 8,5 [m³/s] n, dp , P =?

dpT = 7,6 [kPa] P = 66,5 [kW]

20/01/2009 - 25


Exercise 5.1 – FAN LAWS Solution : N2 =

Q 2 N1 Q1

=

8.5 ×1305 7.1

= 1562 min −1

2

 N 2   1562    TP2 = TP1  = 7,6 ×   = 10.89 kPa   1305   N1  3

2

3

 N 2   1562   = 66.5 ×  P2 = P1   = 114.0 kW  1305   N1  20/01/2009 - 26


20/01/2009 - 27


FAN SYSTEMS – FAN LAWS - SPEED Performance Curve for IE 250 Fan 75

185

1 8 2 2 m i n - 1 1 6 7 0 m i n - 1 1 5 1 8 m i n

62,5 ] r a b 50 m [ e r u37,5 s s e r P n 25 a F

150

110

- 1

75

P o w e r [k W ]

40

12,5 0

0 0

2,5

5

7,5

10

12,5

15

17,5

20

Flow Rate [m³/s]

20/01/2009 - 28


FAN SYSTEMS – FAN LAWS - DENSITY

• Fans are constant volume machines • Affects the pressure generated and power consumed

• A change in density affects the system curve

20/01/2009 - 29


FAN SYSTEMS – FAN LAWS - DENSITY Performance Curve for IE 250 Fan 50

120

45

105

40 90

1.13 kg/m³

35 ] r a b 30 m [ e r 25 u s s 20 e r P n 15 a F 10

75 60 45

0.56 kg/m³

P o w e r [k W ]

30 15

5

0

0 0

2,5

5

7,5

10

12,5

15

17,5

Flow Rate [m³/s]

20/01/2009 - 30


FAN SYSTEMS – FAN LAWS - DENSITY Dust collector on inlet side of fan • total pressure drop: 20 mbar • inlet of fan - 20 mbar

Clinker cooler fan • total pressure drop: 20 mbar • inlet of fan: atmosphere

For same air flow, fan selection would be different due to density change at fan inlet 20/01/2009 - 31


FAN SYSTEMS – FAN LAWS (SIZE)

• Used mostly to compare two similar fans of same type

• Some examples of “tipping out” fans • Casing often has to be redesigned

20/01/2009 - 32


FAN SYSTEMS – FAN LAWS (SIZE) Performance Curve for IE 250 Fan

] r a b m [ e r u s s e r P n a F

40

75

35

67,5 60

30

52,5 25

45

20

37,5

+10% D

30

15

22,5

D

10

P o w e r [k W ]

15

5

7,5 0

0 0

2,5

5

7,5

10

Flow Rate [m³/s]

12,5

15

17,5

D = Diameter 20/01/2009 - 33


FAN SYSTEMS – FAN CONTROL

• •

Requirement to control the air flow from a fan The system resistance curve governs the fan output • Air flow can be changed by changing : • The fan curve • The system resistance curve • Available methods: • Discharge dampers • Variable inlet vanes • Box-vane control • Variable speed drives 20/01/2009 - 34


FAN SYSTEMS – FAN CONTROL Discharge Dampers

Opposed Blades

Parallel Blades

• More flow on one side of duct • Not very linear response 



 

Yields more uniform profile More linear response

The discharge dampers change the system resistance curve Power wasting devices 20/01/2009 - 35


FAN SYSTEMS – FAN CONTROL Discharge Dampers 90

20% open 40% open

75

] r a b m [ 60 e r u s s e r 45 P n a F

60% open 80% open

30

Wide open 15

0 0

5

10

15

20

25

30

35

40

Flow rate [m³/s]

20/01/2009 - 36


FAN SYSTEMS – FAN CONTROL Variable Inlet Vanes

• Installed at the inlet of the fan • Controls volume and direction of air flow • Designed to give a spin to the air in the direction of the impeller • Pre-spin unload the impeller reducing the pressure • Less pressure implies less power

Closed Position

Open Position

20/01/2009 - 37


FAN SYSTEMS – FAN CONTROL Variable Inlet Vanes 100

75

90

67,5

80

60

70

52,5

40

P o 45 w e r 37,5 [ k W ] 30

30

22,5

20

15

e r 60 u s s 50 e r P

10

25% open

50%

7,5

75% 100%

0

0 0

5

10

15

20

25

30

35

40

Flow rate [m³/s]

20/01/2009 - 38


FAN SYSTEMS – FAN CONTROL Box Vane Control

• Similar to inlet vanes: pre-spin effect

• Blades always parallel • Must be used with an inlet box • Power efficiency: a little less than inlet vanes.

• Easier to maintain than inlet vanes (hot and dusty applications) 20/01/2009 - 39



Box vane controls

20/01/2009 - 40



20/01/2009 - 41


FAN SYSTEMS – FAN CONTROL Variable Speed Fans

• Direct application of the fan laws: Q 2 N 2 = Q 1 N 1

 N  =  2  TP1  N 1 

TP2

2

P 2  N 2  =  P 1  N 1 

3

• Maintain same efficiency at different speeds • The most efficient method of controlling fans • Higher initial cost 20/01/2009 - 42


FAN SYSTEMS – FAN CONTROL Variable Speed Fans Efficiency :

η 1 =

Q1 × TP1 P1

Fan Laws :  N  Q2 = Q1 2   N 1 

η 2 =

Q 2 × TP2 P2

 N  TP2 = TP1  2   N 1 

=

2

 N   N  Q1  2  × TP1  2   N 1   N 1   N  P1  2   N 1 

3

 N  P2 = P1 2   N 1 

3

2

=

Q1 × TP1 P1

20/01/2009 - 43


FAN SYSTEMS – FAN CONTROL Power Savings 100 90 80 70

r e w o P %

l r o t n c o e a n v x e s B o

Discharge damper

60

n v a t l e n I

50 40 30

Variable speed

20 10 0 0

10

20

30

40

50

60

70

80

90

100

110

% Flow 20/01/2009 - 44


Exercise 5.2 – VARIABLE SPEED ID FAN Question : 100% open

Fan Inlet P = -70mbar T = 350C

Fan Outlet P = -2mbar T = 350C Flow = 144.4m3/s

• (a) Plot the operating point on the fan curve • (b) What is the speed of the fan? • (c) What is the shaft power of the fan? • (d) Is the fan selection good? Why? 20/01/2009 - 45


Exercise 5.2 – VARIABLE SPEED ID FAN

20/01/2009 - 46


Exercise 5.2 – VARIABLE SPEED ID FAN

20/01/2009 - 47


Exercise 5.2 – VARIABLE SPEED ID FAN Solution :

• REMEMBER – ALWAYS CONVERT TO INLET CONDITIONS ! • 144.4m3/s x 3600 = 519840m3/hr at the outlet • Remember ‘Ideal Gas Law’ • PV = nRT or P1V1/T1 = P2V2/T2 • So, Flow at inlet Conditions, • = 519840 x (1013-2)/(1013-70) = 557327m3/hr • From Performance curves, • Delta P = 68mbar => Speed is 990rpm • Shaft Power is 2025kW 20/01/2009 - 48


FAN SYSTEMS – FAN CONTROL Drive Arrangements Belt drive • Standard speed motors can be used • no need for slow speed motors (expensive ) • Exact fan speed for required air and volume can be obtained • Speed can be adjusted by simply changing pulley ratio

Direct drive • Reduces initial cost if standard speed motor could be used • no extra supports, pulleys, bearings, shafts • Elimination of power loss by belt drive (5 to 10%) • No maintenance required from stretching belts 20/01/2009 - 49


FAN SYSTEMS LAFARGE PREFERRED SPECIFICATIONS

•

•

Important points are : • Safety margin : 10% on volume & 10% on pressure • Recommended maximum fan speed • Far enough to be from critical speed • Variable inlet vane dampers(clean gas) or variable speed • V-belt drive Often required : • Piezometer • Silencer 20/01/2009 - 50


FAN AUDIT

20/01/2009 - 51


FAN AUDIT Objective : Reduce energy consumption

Indicators: • kWh absorbed by the motor • Fan efficiency • Fan reliability factor

20/01/2009 - 52


FAN AUDIT

20/01/2009 - 53


FAN AUDIT

Hardfacing was removed

Deformation

Crack

20/01/2009 - 54


FAN AUDIT PROGRAM

•

Many fans don’t operate at optimal point • Operating conditions has changed since installation • Bad initial selection at installation

 Energy is wasted

•

•

Audits every five years or more frequently • To check operating conditions of the fan • Identify improvements to bring it to optimal performance (efficiency) • Identify solutions if fan is a process bottleneck Coordination between Maintenance, Production and Process departments 20/01/2009 - 55


FAN AUDIT - PREPARATION

• List fans that make up for 80% of power consumption

• Operating conditions, new and future, adapted to Process requirements

• Maintenance history of the fans • Fan curves • Ducting arrangement / flowsheet • Adequate position of measuring points • Creation of a common (Maintenance, Process) file 20/01/2009 - 56


FAN AUDIT - MEASUREMENT

• Flow rate • For one operating point • More could be required for fans with wide ranges of operating point • Static pressure at fan inlet • after damper if any • before variable inlet vane if any • Static pressure at fan outlet • before damper if any • Static pressure on other side of damper • to determine pressure drop through damper • Damper opening 20/01/2009 - 57


FAN AUDIT - MEASUREMENT

• Gas temperature and composition • For density • Moisture content if significant • Correction for dust load if significant

• Fan speed • Absorbed power • Fan elevation • Atmospheric pressure • Ambient air temperature 20/01/2009 - 58


MEASUREMENT FOR FAN STATIC PRESSURE

20/01/2009 - 59


FAN AUDIT – MECHANICAL EVALUATION

•

External inspection (fan running): • Bearings temperature • Vibrations of bearings and housing • Noise level • Leakage (holes in housing, ducting,…) • Even air flow distribution at fan inlet • Pressure drop through dust collector (if any)

20/01/2009 - 60



•

Internal inspection (fan stopped) : • Fan impeller alignment • Impeller and housing: wear and material accumulation • Dampers: proper opening / closing, damages and material accumulation • Louvers: configuration of blades, functioning of individual blade • Turning vanes condition 20/01/2009 - 61



•

Internal inspection (fan stopped) : • Belt drive : tension and wear • Coupling alignment • Internal cone adjustment (too large a gap?) • Accumulation of material in the duct • Type of fan wheel – To confirm drawings / fan curve • Validation of existing drawings 20/01/2009 - 62


FAN AUDIT – ADDITIONAL INFORMATION

•

Fan system diagram showing : • fan • damper (position and type) • position in relation with its environment • elbows • duct expansions, contractions • turning vanes

20/01/2009 - 63


FAN AUDIT – ADDITIONAL INFORMATION

•

Statistics on flow, pressures and damper opening • Aspen / IP21

•

Fan curve • Correct to actual conditions (elevation, temperature, density, RPM)

•

Fan and motor name plate information

20/01/2009 - 64


FAN AUDIT – EVALUATION

• Position operating point on fan curve • Does it match? Why?

• Calculate efficiency • Is it good?

• How can we improve the efficiency? • How can we increase flow or pressure, if required? 20/01/2009 - 65


FAN AUDIT – EVALUATION Duty Cycle :

• For fans with highly variable flow demand such as: • Cooler exhaust • Kiln I.D. • Some cooler fans



Variable Frequency Drive (VFD) ? 20/01/2009 - 66


FAN AUDIT – EVALUATION Duty Cycle :

• For constant duty fans such as: • Mill draught • Primary air

 Find most cost effective solution to gain efficiency • Replace belt (and motor?) • Modify impeller? 20/01/2009 - 67


FAN AUDIT – EVALUATION What Is The Damper Saying?

• If fan damper never open > 75% then fan is oversized and wasteful



Downsizing?



Replace belts?



VFD? 20/01/2009 - 68


FAN AUDIT – EVALUATION Fan Design –

• •

Poor efficiency fan design costs all the time Many pre-1985 fans are straight radial : • 60-75% efficiency

•

Current technology : • Curve radial (dirty air) : to 82% efficiency • Airfoil (clean air)

: to 85% efficiency

20/01/2009 - 69


FAN AUDIT – EVALUATION Low Cost Solutions –

• Is Hermit Crab solution possible? • Can shaft & bearing be retained? • Can you take advantage of the need to replace an impeller for maintenance reason?

• Is there a retired fan that could do the job? • Inlet turning vanes can improve efficiency by 2% • Is there a way to modify ducting configuration to reduce system effect? 20/01/2009 - 70


FAN AUDIT – REPORT

• Summary • Measurements • Mechanical observations • Other information • Findings • Fan curve • Original • Corrected to actual conditions with operating point and duty cycle • Recommendations • Follow up of actions • Include action plan in PIP 20/01/2009 - 71

4 - Fan Systems and Audit

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