PR PYR P06-17 v1 How to Improve Fan Efficiency

How to improve fan efficiency by internal inspection Pyroprocessing

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Introduction 

D ifferent factors im pactsthe efficiency of a fan:     

Build-up inside the im peller or betw een the im peller and the inlet cone W ears betw een the im peller and the inlet cone Inappropriate gap betw een im peller and inlet cone False air …

Objectives  

Low er the pow er consum ption of the plant C oncerning the ID fan (w hen in lim it), m aintain the kiln feed at the highest level. Effecti vely, in that case, a fan inefficiency w ill w aste kW , low er the gas flow available for the kiln and consequently reduce the kiln feed to m aintain the level of O 2 kiln inlet

Saf et y aspects 

Before enterin g the fan, com ply to all safety rules:  

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Lock out : fan, upstream /dow nstream flaps For big fans,block m echanically the im peller before enterin g the fan

Special caution in case of ID fansure there are no build-ups in the upstream duct. Build: m ake up can occur w hen w ater is injected in the duct.

W here applicable respect confined space rules and procedures

A sk the m aintenance departm ent to create a vi sit door in the outlet preheater duct. Before you enter the fan, ask M aintenance to open the door and to check that there is no bu ild-up.

Prerequisites

Before on-stop inspection, evaluate the level of fan efficiency: 

How to measure fan eff iciency

Evaluate the level of the fan false air:  

How to measure the f alse air

Y ou can evaluate false air by: 

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O 2 m easures inlet/outlet of the fan (w hen the gas isn’ t air). Be careful to be airtight at the hole you m ake the sam ple. The depression is som etim es very high (ex: -100 m b). A ny entrance w ill false the m easure. hearing any noise around the fan (ex: at flanges,around the shaft…) checking w ith “w ooden string technique”any aspiratio n. C heck especially the flanges of the casing, expansions joints…)

In this proce dure you m ay find referenc es to other inf ormation (tools , ot her “How to” procedure s, know ledge docum ents, etc) w hich are a vailable from th eir respective domain of th e Web Cement Port al (e.g. Grinding , Pyrop rocessing ...) or f rom t he BRS dat abase (indicat ors).

How to improve fan efficiency by internal inspection Pyroprocessing

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Act ion St eps 0.

General considerations

Figure :1assum ing

all else w ith the fan is in good shape, the alignm ent and critical gaps are generally found w here the stationary inlet cone interfaces w ith the rotation w heel. Show n below : Key area of c oncern

Inlet box Fan wheel

Inlet Bell

Fan casing

Figure :2in

high efficiency fans,the shape and positioning of the inlet to the fan w heel is aerodynam ically cri tical. Illustrated below .

Close-up of inlet to wheel If the gap is incorrect, either the inlet is too turbulent and/or too much air is allowed to recirculate inside the casing. POSITIVE PRESSURE wheel Inlet bell

Small amounts helps to reduce turbulence here.

Engineered gap, specified by OEM

Larger gaps = less efficiency Small gaps = more efficiency Inlet is shaped to guide air smoothly into the fan wheel – note that the curve of the inlet exit is close to the taper of the rotating wheel.

Old wheels have large gaps (>20 mm) Modern high efficiency wheels have small gaps (< 5 mm)

NEGATIVE PRESSURE

In any centrifugal fan the gaps betw een the rotating part and inlet;the overl ap of the inlet to the w heel is crucial. O therw ise the internal recirculation of air/gas increases f (rom positive si d e outside the w heel to negative inside the w heel) and thus increases the w asted energy as w ell the fan’ s capacity to m ove gas.

How to improve fan efficiency by internal inspection Pyroprocessing

PR PYR P06-17

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Comply w ith all s afet y rules

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Open the door and enter t

3.

Check a ll bui ld-ups

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he fan

Between impeller and inlet cone 

This build up has a strong influence on fan efficiency. It is com m on to be able to increase fan efficiency from 3 to 5 po ints w ith a thorough cleaning. 

C lean m anually w ith a sm allscraper around the inlet cone until you can see again the iron casin g.

C lean also the anti-rotatin g plate fixed on the inlet cone. They avoid turbulences and are very mi portant.

PLN ID fan Im peller

A nti rotating plates on inlet cone has to be clean

Rotatin g buildup on the inlet cone

Im peller

Inside the impeller 

A high pressure w ater jet can be used to rem ove build-up

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Check f or w ear Im portant w ear of the im peller due to recirculationg gas

Im peller

5.

Check for false air 

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6.

Based on the observations you m ade w hen the fan is running (see prerequisites), try to locate and rem ediate to false air. A nother way to check for false air is to close the fan door and check if you can see any outside light w hen in the dark.

Measure the gaps with maintenance department 

Penetratio n gap of inlet cone inside the im peller.For high efficiency w heels the overl ap is engineered. 

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See n° 7 o n ap pend ix 1 and illu st rati on s in Figu res 3 and 4

Radial gap betw een im peller and inlet cone. For high efficiency w heels the overlap is engineered. See n° 8 o n appen dix 1 and illu str atio n i n Figure 5

Before taking the m easures, block the im peller alw ays at the sam e position. The inlet cone is probably not circular.It w ill change the gaps m easured. Identify w ith a “m ark”on the coupling. C om pare w ith the design value (usually on a draw ing plan). If there is none, ask the supplier for the values and acceptable tolerances. 

See Fig ure 5

CAUTI ON, for high eff icienc y f ans in hot gas a pplications to leranc es are given f or “cold” conditions to allow for t herma l grow th w hen at running tempera ture. 

C heck that fan is aligned inside the casin g and not skew ed 

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See Fig ure 3

If there is an im portant unbalance, ask the M aintenance departm ent to correct the gap by adjustm ent (m oving the casing a little to reduce penetratio n gap for exam ple). It is mandatory to align t he fan to it mot or, not the oppo site.

s housing firs

t, then t o align the fan shaft and th

e

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O ther points to check: 

the cut-off near the fan casing outlet is im portant to the fan’ s perform ance. 

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See Figures 6, 7

at the inlet there is som etim es a vortex splitter or “blocking plate” . These need to be in good shape.

Figure 3 –The

w heel m ay be m isaligned inside the casing, creating excessive gaps.

Alignment Problems Wheel separated from inlet

Too much internal recirculation

Wheel pushed into inlet

Too much inlet turbulence

Wheel skewed to inlet

Too much recirculation and inlet turbulence (BTH Kiln ID fan 02)

Figure 4 –In

the past the inlet m ay have been cut to facilitate wheel rem oval, but not restored. N ote covering the gap w ith a rolled piece of steel w ill im prove the fan’ s efficiency but it w ill still be less than perfect, since it w ill still be aerodynam ically poor. It w ould be a good tem porary act ion.

Inlet bell cut to ease wheel replacement, but never restored. Huge gap left causing high internal recirculation. (WSK Kiln ID fan, 88)

Inlet bell replaced with scrolled flat steel. Loss of aerodynamic inlet. (ESW K5 ID fan, 04) Covering gap is better than leaving open but inlet turbulence is high.

How to improve fan efficiency by internal inspection Pyroprocessing

PR PYR P06-17

Figure 5 –The radial gap, all around

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the w heel m ust be correct.

Excessive gap

CAUTION – HOT FANS

Wheel Wheel inlet Inlet bell

When wheel is not centered to the inlet. Allows more internal recirculation. (BTH FM ID fan, 01)

Figure 6 –Fan

Except in case of hot fans – OEM spec.’s different gap clearances from top vs. bottom. Purpose is toallow for thermal growth of casing. When at temperature, gap clearances will be OK.

outlet « cut-off »

Cut-offs prevents air from spinning inside the casing. Sometimes this is asmall piece of plate welded inside. (BTH FB mill ID fan 97) – caution may not show on drawings. Often needed when installing a modern wheel inside an old casing.

Figure 7 –Inlet box

vortex splitter Fan Wheel will have a tendency to try and rotate the mass of air in the inlet box – which uses up power.

Inlet box

To fan wheel

VORTEX SPLITTER

The vortex splitter BLOCKS a portion of this spin – especially to the outside of the inlet. Shape is engineered. OEM sometimes forgets to install this. (May not be shown on drawings.) Not always used – depends on the design of the inlet box. BTH FB mill ID fan (86)

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How to improve fan efficiency by internal inspection Pyroprocessing

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Appendix

1.

ID f an, do uble ent 

rance ty pe

Schem atic show ing parts and criticalm easuring points

4

6

1 3

2

7 8 9

5 1 2 3 4 5 6 7 8 9

- Im peller –Inlet cone or in let bell or in let pavilion - A nti rotating plate - Inlet gas - O utlet gas of the im peller - In ternal recycling of the fan.TO BE AVOIDED - G ap: penetratio n pavilion in im peller - Radial gap im peller and pavilion - W ear of the im peller

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How to improve fan efficiency by internal inspection Pyroprocessing

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PR PYR P06-17

Gaps meas 

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ur em ent at Por t -La- Nou velle Plant (F rance)

D esign gaps :

C = 30m m + /-1 D = 13.5mm (top) a nd 7.5 mm (bottom )

1 Impeller

D (top) 2 Inlet cone

B

30

41 43 60 19

September 2005 35 29 60 25

30 13,5 7,5

17 20 10

31 20 10

Obje ctive Janua ry 2006

A (btm.)

A

C

(measure) top bottom

B C (C=B - A) D

top

(mm) (mm) (mm) (mm)

bottom Top Bottom

(mm) (mm) (mm)