IMPROVING WOOD KILN BOILER RELIABILITY VIA A NEW WATER TREATMENT CONTROL TECHNOLOGY

Authors: John D. Deines, David A. Grattan, PhD, Thomas S. Hughes, Brian V. Jenkins, John Ostberg, Benjamin D. Riley, Catherine J. Stetenfeld, Nalco Company

Contributors: Ernie Lundquist, Steve Fuhriman, Ryan Lawrence and Robin Schernitzki, Boise Building Solutions, Manufacturing

Here’s what we’ll be covering this morning

• Purpose of the boiler in a wood products plant• Challenges associated with operating a boiler in a

wood products mill– Operational– Resources– Personnel work load

• Boiler chemical treatment, its application and evolution

• New developments in boiler feedwater scale and corrosion control

• Wood products plant application of the new technologies

• Outcome and benefits of the application

The boiler is crucial for wood products manufacturing

• Controls the drying process– Kiln coil heating– Steam humidification

• Optimum Moisture Content is Crucial– Higher end-use product value– Better material usability– Increased product strength– Lower shipping costs– Better insulating and finished material properties

• Drying too fast / too slow - both are bad

As much as 80% of a mill’s energy requirement can be for the drying process

Figure 1 Boiler scale greatly impedes heat transfer and reduces efficiency

There are two major water related challenges encountered in operating a boiler – scale and

corrosion

• Mineral Scale– Forms as a result of

dissolved minerals in the feedwater exceeding solubility

– Forms insulating material

– Impedes heat transfer

– Can result in equipment damage / boiler shutdown / loss of production

Corrosion is nature’s way of reclaiming refined metals…

• Corrosion– Two primary types

in boilers systems• Carbonic acid

(condensate)• Oxygen

– Reduce asset life• Pitting corrosion• General corrosion

– Cause iron deposits on boiler tubes (energy losses)

– Shutdown, production loss and safety issues

Over time, chemical treatment of boiler feedwater to prevent or reduce the impact of

these challenges has changed

For scale control, many advancements have taken place in chemistry over the last century

P r o g r a mD e v e l o p e d / u s e d A d v a n t a g e s D i s a d v a n t a g e s

C o a g u l a n t / S o d a A s h 1 9 0 0 - 1 9 5 0 R e d u c e d a n d e a s i e r t o r e m o v e s c a l e

S t i l l f o r m s s c a l e , p r o g r a m a d d s s o l i d s , i n c r e a s e s b l o w d o w n r e q u i r e m e n t s . S o d a a s h c a n r e s u l t i n i n c r e a s e d c o n d e n s a t e c o r r o s i o n

P h o s p h a t e 1 9 3 0 ' sR e d u c e d C a C O 3 s c a l eR e d u c e d s o l i d s a d d i t i o n S t i l l p o t e n t i a l f o r P O 4 s c a l e

C h e l a n t s E a r l y 1 9 6 0 ' s C o m p a r a t i v e l y l o w e r s o l i d s c o n t r i b u t i o nC o r r o s i o n p o t e n t i a l i f o v e r f e dP o t e n t i a l f o r M g S i O 3 s c a l e

P h o s p h o n a t e s L a t e 1 9 7 0 ' sC o u l d r e s u l t i n s c a l e i f f e e d w a t e r h a r d n e s s n o t v e r y w e l l c o n t r o l l e d

P o l y m e r o v e r l a y f o r p h o s p h a t e s o r c h e l a n t s L a t e 1 9 7 0 ' s

C o n d i t i o n e d s p e c i f i c t y p e s o f s u s p e n d e d s o l i d s - F e 3 O 4 , F e 2 O 3 , C a 3 ( P O 4 ) 2 , M g S i O 3 t o m a k e t h e m l e s s a d h e r e n t t o b o i l e r s u r f a c e s

S t i l l p o t e n t i a l f o r P O 4 s c a l eC o r r o s i o n p o t e n t i a l i f o v e r f e dP o t e n t i a l f o r M g S i O 4 s c a l e

P o l y m e r o n l y ( 1 s t g e n - p o l y a c r y l i c a c i d ) E a r l y 1 9 8 0 ' s

M a i n t a i n s h a r d n e s s i n s o l u b l e s t a t eR e d u c e s s o l i d s c o n t r i b u t i o n t o b o i l e r w a t e rR e d u c e d c o r r o s i o n p o t e n t i a l c o m p a r e d t o c h e l a n t p r o g r a m sD i s p e r s e s i r o n

C o u l d c o m p l e x w i t h b o i l e r m e t a l i f o v e r f e dH i g h h a r d n e s s c o u l d c a u s e p o l y m e r / h a r d n e s s c o m p l e x t o d e p o s i t

P o l y m e r o n l y ( 2 n d g e n - s u l f o n a t e d p o l y m e r ) 2 0 0 1

M a i n t a i n s h a r d n e s s i n a s o l u b l e s t a t e . L e s s c o r r o s i v e t h a n c h e l a n t . I n c r e a s e d t h e r m a l a n d o x y g e n s t a b i l i t yK e e p s s u s p e n d e d s o l i d s d i s p e r s e dD o e s n o t p r e c i p i t a t e o r f o r m p r e c i p i t a t e s R e d u c e s i r o n d e p o s i t i o n r a t e . C o u l d b e c o r r o s i v e i f g r e a t l y o v e r f e d

For control of oxygen corrosion in preboiler equipment, we have developed effective chemical oxygen scavengers …

Indirect Direct

Measuring ChemicalResiduals

► Dearator Inspections

► Monitoring DissolvedOxygen

► IronTesting

► ?

… but we have still lacked technology that could reliably monitor and control changes in that environment!

…however, the basic approach to controlling boiler water chemistry has always revolved around a “test and adjust” approach…

• Gather sample• Test• Adjust chemical feed• “Repeat as necessary”

Equipment damage / efficiency loss / production loss

(wasted chemical)USL

LSL

…and is still largely centered around testing the water after it is in the boiler

D E A E R A T O R

An event taking place

here….

…could take hours or days to

show up here!

By then, its far too late to detect or remedy

We’ll be talking about two new technologies:

• 3D TRASAR Technology for Boilers™– Measures and controls scale inhibitor

chemistry• Nalco Corrosion Stress Monitor™

– Measures and controls pre-boiler corrosion environment

• Real time, on-line control 24/7• Process visibility for these areas• Assurance of asset protection• Optimized chemical usage• Improved energy savings

opportunities

New Boiler Automation Technology

Automat ically responds

Maintain opt imum treatment levels

Direct ly measures

ppm

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T R A S A R A u to m a tio n

Direct control of scaleInhibitor chemistry

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T R A S A R A u to m a tio n

ppm

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D a te

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ppm

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ppm

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T R A S A R A u to m a tio n

Direct control of scaleInhibitor chemistry

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Phase 2: LP #3 AT-T ORP Controlled Feed Of Eliminox

Phase 1: AEPCO Controlled Feed Of Eliminox Baseline Monitoring LP #3 AT-T ORP

LP #3 AT-T ORP Set Point = -350 mV

Figure 1: LP #3 AT-T ORP Results During Phase 1 and 2 of AEPCO Trial

Direct control of preboiler corrosion

NCSM Automation- 0 . 8

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Phase 1: AEPCO Controlled Feed Of Eliminox Baseline Monitoring LP #3 AT-T ORP

LP #3 AT-T ORP Set Point = -350 mV

Figure 1: LP #3 AT-T ORP Results During Phase 1 and 2 of AEPCO Trial

Direct control of preboiler corrosion

NCSM Automation

We implemented and evaluated these technologies at Boise Building Solutions,

Manufacturing in Kettle Falls, WAResults from on-site work

The boilerhouse at Kettle Falls is similar to many others

• 150 psi boilers• Average 30,000 lbs

steam / hour• Sodium zeolite,

dealkalized make-up water

• Steam used primarily for controlling the drying process

• Chemistry is adjusted by daily testing

C o n d e n s a t e R e t u r n f r o m K i l n s

1 8 0 2

3 D T O u t l e t

C i t y W a t e r

W A L C H E M B D C O N T R O L L E R

S O F T E N E R S

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C o n d e n s a t e R e t u r n f r o m

S a w m i l l

3 D T f o r B o i l e rG R A T E

C W

T o A t m o s p h e r e

F W R E C I R C

D E A L K A L I Z E R S

6 X D B L T R A C K K I L N S

3 5 C y c l e s

C l o s e d t a n k C l o s e d t a n k

G R A T E S

D E A R E A T O R

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C l o s e d t a n kC l o s e d t a n k C l o s e d t a n kC l o s e d t a n k

G R A T E S

D E A R E A T O R

W

E

Figure 2 – The boiler system at Boise Building Solutions, Manufacturing is similar

to many in the wood products industry

Background

There were several objectives for the evaluation

• Improved chemistry control• Optimized operating costs

– Reduced water costs– Reduced energy costs– Improved efficiency – avoiding iron deposits in the boiler

Evaluat ion goals

Like a lot of other mills and manufacturing plants, this plant has wide swings in steam load

Figure 4 shows the steam load variations common to wood plants

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am F

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rBackground

We began by establishing current control baseline – for both scale control and boiler feedwater corrosivity, there was extensive variability

Figure 5 – Steam load and scale inhibitor levels vary greatly during the monitoring phase of the

new control technology implementation

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Figure 6 – Boiler feedwater corrosivity also varies widely with steam load swings during the

monitoring phase

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Scale cont rol levels in the feedwater

Steam load

Boiler feedwater corrosivity

Baseline

Many useful discoveries occurred during the evaluation

A return condensate pump outage showed up as a large increase in feedwater corrosivity

Figure 7 – A condensate return pump outage is recorded as a change in

feedwater corrosivity by the NCSM

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A condensate pump failure, result ing in a

reduct ion in returned

condensate…

…which resulted in an increase in feedwater

corrosivity

Monitoring mode

In a control mode, this change in feedwater corrosivity would have automat ically been addressed

A short term boiler outage showed how this technology could avoid an overfeed

Monitoring mode

Figure 8 shows how a chemical overfeed can occur in the absence of real-time control capability

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3 - Boiler feedwater flow re-

established, chemical

concentration drops

1 - ID fan turned off,

boiler shutdown

2 - Chemical feed continues

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3 - Boiler feedwater flow re-

established, chemical

concentration drops

1 - ID fan turned off,

boiler shutdown

2 - Chemical feed continues

On Mid February, the technology was put into Phase 1 (on/off) control mode…

Figure 10 shows the before / after control improvement in scale control and oxygen

scavenger chemistry

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m)

N e x G u a r d S e t P o i n t = 8 . 0 p p m

N C S M A T O R P S e t P o i n t = - 4 0 0 m V S t a r t O n / O f f C o n t r o l

Figure 11 shows the comparatively wide swings in steam load this mill experiences for the same time frame as Figure 10– this is a normal scenario for

most manufacturing plants

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Ste

am F

low

lb/h

r

…and despite the wide variat ion in steam loads…

}Control started

Control implementat ion

One of the other advantages of this technology is the ability to view the data on the web in real

time to ensure control is maintained

Excellent improvement in control capability resulted

Feedwater Scale Inhibitor Desired control range: 8 ppm +/- 0.5 ppm

Pre-boiler Corrosivity Desired control range: -400mV +/- 10 mV

Before automation 1/9-2/12/09

After initial automation

2/14 – 3/3/09

Comments Before automation 1/9-2/12/09

After initial automation

2/14 – 3/3/09

Comments

Average dosage

17.01 ppm 6.7 ppm Operating above the control range wastes treatment chemicals; operating below the

control range increases the risk of scale (wasted fuel), damage to the boiler

and production losses

Average reading

-366 mV -401 mV Values approaching zero (more positive) indicate a more corrosive environment. Excessively negative numbers may mean excessive oxygen scavenger use, leading to higher blowdown levels

Standard deviation

+/- 23 ppm + /- 2.4 ppm An 89.6% reduction in standard deviation

Standard deviation

+/- 71mV +/- 13 mV An 82% reduction in standard deviation

Outcome

Wet Chemistry Results…

As expected, wet chemistry control has gotten tighter as well.

Standard deviation has decreased by 49.2%

Another achievement was the reduction in water per volume of production

Some of the improvement highlights included

• Improvement in pre-boiler corrosion stress control– Before - 44% in desired range– After – 87.1%

• Scale control overfeed reduced from 73% to 15%– More improvement anticipated as next control protocol steps are

taken• Summary of improvements and ROI

– From the initial work since implementing the overall program – cycles have increased from 10 to 30

• Blowdown reduced by 69%• Water saved – 2.4 Million gallons

– Reduced wet testing– Extended equipment life– Improved efficiency– Greatly increased knowledge of system behavior– Enhanced process visibility– Reduced total operating cost

Summary

Key Take Aways…

• Asset Reliability and Efficiency is the Key in Steam Plant Operations

• Controlling Scale and Corrosion is the Key to Asset Reliability

• New Methods of Measurement and Control have “Changed the Game”

• Indirect Control to Direct Control• Reactive to Proactive• Greater Visibility with less Operations Time Requirement• Equals Greater Asset Reliability with lower Total Costs of

Operations

Summary