Control Moisture For Profit...important criterion for selecting a moisture control system is to...
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24 . Specialty Wood Journal· January/February 2004 www.bauminternational.com Control Moisture For Profit By John Robinson, Drying Technology, Inc. Feed Inle~ T Hot Moisture Content % Current Vol improved moisture control using the temperature drofJ method. Temperature drop measurement across an OSB rotary dryer. Introduction Drying is costly; poor moisture control makes it more costly through lost pro- duction, lowered product quality, and increased energy consumption. A highly significant factor affecting moisture control is location of the moisture sensor; if not located inside the dryer, the control system has one chance in three of making the cor- rect control decision. Moisture Sensing Problem The panel industry commonly uses two sensing methods as the basis for moisture control: conventional moisture sensors (Infra-red, Near Infra-red, Radio Frequency, Capacitance, Resistance, etc.), and dryer exhaust temperature as a surrogate for mois- ture content. Both methods are generally ineffective because conventional sensors use relatively small sample sizes, must be fre- quently calibrated, are unable to operate sat- isfactorily inside or around the dryers, and the exhaust temperature method provides no automatic means for setpoint adjustment when water load to the dryer changes. Sensor Selection Criteria The moisture content of a product exiting a dryer is either wet, dry or on target. If the commonly used "after-the-fact" (feedback) control system is in auto mode, its control decisions will be based on the moisture content of the product at the downstream moisture sensor. For example, if the mois- ture content at the sensor is on target and water load changes enter the dryer, the control system must assume that no control action is necessary until the change reaches the sensor. In general, this type of control system has only one chance in three of mak- ing the right control decision; in fact, its chance for success varies inversely with the time required for an entering change to be detected (dead time). For this reason, a con- trol system with its moisture sensor located downstream is prone to cycle and produce poor moisture distribution; this can lead to a reduction in the production rate, an increase in unit energy consumption, and poorer product quality. Obviously, the most important criterion for selecting a moisture control system is to install the moisture sensor inside the dryer so that it will make the cor- rect control decision 100% of the time. Conventional sensors sample only a frac- tion of the total production rate, usually a small spot on the product surface, therefore, a second moisture control selection crite- rion should be to select a sensor that uses (lS large a samfJle-size as fJossible. Some conven- tional sensors require frequent calibration; therefore, the third selection criterion is to select a sensor that requires no calibration. The exhaust temperature moisture sens- ing method, although an "inside-the-dryer" sensor, is incapable of maintaining the target moisture when water load changes enter the dryer. The operator must continu- ally search for the correct setpoint value in an "after-the-fact" manner, therefore, the fourth criterion for selecting a control system is to select a control system cafJable of automatically and continuously re-adjusting the temperature setfJoint to maintain the target moisture content. The Control Solution A moisture sensor is available that meets the recommended criteria for selection of a moisture control system. It is based on a patented mathematical model relating the moisture of the product leaving the dryer to the temperature drop (delta t) of hot air after contact with the wet product, and the dryer production rate. This "inside-the- dryer" type moisture sensor does not need calibration, uses total production for the sample, is based on rugged temperature sensors, and applies to most products and dryer-types. It is superior to the exhaust temperature sensor because its setpoint can be automatically and continuously adjusted to maintain target moisture content. Improved Moisture Control In Panel Manufacture OSB Moisture Control Figure I shows distributions of strand mois- tures from a rotary dryer before and after installation of a Temperature Drop control system. The standard deviation of the mois- tures was reduced by 50'};). The minimum reduction achievable is normally 30% for either rotary or conveyor dryers. Figure 2 depicts the temperature drop measurement across a rotary dryer and figure 3 shows the temperature drop measurement for a conveyor dryer. The control system uses these temperature drops to calculate
Transcript of Control Moisture For Profit...important criterion for selecting a moisture control system is to...
24 . Specialty Wood Journal· January/February 2004 www.bauminternational.com
Control Moisture For ProfitBy John Robinson, Drying Technology, Inc.
Feed
Inle~
T Hot
Moisture Content %
Current Vol improved moisture control using the temperature drofJ method. Temperature drop measurement across an OSB rotary dryer.
IntroductionDrying is costly; poor moisture controlmakes it more costly through lost production, lowered product quality, andincreased energy consumption. A highlysignificant factor affecting moisture controlis location of the moisture sensor; if not
located inside the dryer, the control systemhas one chance in three of making the correct control decision.
Moisture Sensing ProblemThe panel industry commonly uses twosensing methods as the basis for moisturecontrol: conventional moisture sensors
(Infra-red, Near Infra-red, Radio Frequency,Capacitance, Resistance, etc.), and dryerexhaust temperature as a surrogate for moisture content. Both methods are generallyineffective because conventional sensors use
relatively small sample sizes, must be frequently calibrated, are unable to operate satisfactorily inside or around the dryers, andthe exhaust temperature method providesno automatic means for setpoint adjustmentwhen water load to the dryer changes.
Sensor Selection CriteriaThe moisture content of a product exiting
a dryer is either wet, dry or on target. If thecommonly used "after-the-fact" (feedback)control system is in auto mode, its controldecisions will be based on the moisture
content of the product at the downstreammoisture sensor. For example, if the moisture content at the sensor is on target andwater load changes enter the dryer, the
control system must assume that no controlaction is necessary until the change reachesthe sensor. In general, this type of controlsystem has only one chance in three of making the right control decision; in fact, itschance for success varies inversely with thetime required for an entering change to bedetected (dead time). For this reason, a con
trol system with its moisture sensor locateddownstream is prone to cycle and producepoor moisture distribution; this can leadto a reduction in the production rate, anincrease in unit energy consumption, andpoorer product quality. Obviously, the mostimportant criterion for selecting a moisturecontrol system is to install the moisture sensor
inside the dryer so that it will make the correct control decision 100% of the time.
Conventional sensors sample only a fraction of the total production rate, usually asmall spot on the product surface, therefore,a second moisture control selection criterion should be to select a sensor that uses (lS
large a samfJle-size as fJossible. Some conventional sensors require frequent calibration;therefore, the third selection criterion is toselect a sensor that requires no calibration.
The exhaust temperature moisture sensing method, although an "inside-the-dryer"sensor, is incapable of maintaining thetarget moisture when water load changesenter the dryer. The operator must continually search for the correct setpoint valuein an "after-the-fact" manner, therefore,the fourth criterion for selecting a control
system is to select a control system cafJable
of automatically and continuously re-adjusting
the temperature setfJoint to maintain the targetmoisture content.
The Control SolutionA moisture sensor is available that meetsthe recommended criteria for selection of
a moisture control system. It is based on apatented mathematical model relating themoisture of the product leaving the dryerto the temperature drop (delta t) of hotair after contact with the wet product, andthe dryer production rate. This "inside-thedryer" type moisture sensor does not needcalibration, uses total production for thesample, is based on rugged temperaturesensors, and applies to most products anddryer-types. It is superior to the exhausttemperature sensor because its setpoint canbe automatically and continuously adjustedto maintain target moisture content.
Improved MoistureControl In PanelManufactureOSB Moisture ControlFigure I shows distributions of strand moistures from a rotary dryer before and afterinstallation of a Temperature Drop controlsystem. The standard deviation of the moistures was reduced by 50'};). The minimumreduction achievable is normally 30% foreither rotary or conveyor dryers.
Figure 2 depicts the temperature dropmeasurement across a rotary dryer and figure3 shows the temperature drop measurementfor a conveyor dryer. The control systemuses these temperature drops to calculate
Specialty Wood Journal· January/February 2004 . 25
058, MDF, VENEER, etc.THE DELTA T
Moisture Com.nt %
Temperature drop measurement across an
MDF fhsh dryer.
Current vs improved moisture control of an
MDF dryer using temperature drofJ method.
sensor that operates inside a dryer, usesthe largest sample-size possible, requires
\eed
TCOId
~-. ~r- T••••T~:rc. -- -; - - ~ -
-+Inlet Hot AirTcoldf.-
Temperature drop measurement across an
aSB conveyor dryer.
-+ Sensor is located inside the dryer
-+ Requires no calibration
-+ Reduces MC variation 30 - 50%
-+ Uses cruise-control type startup
-+ Handles changes entering the dryer
-+ Requires minimal operator input
Cross Section
Summary And ConclusionsYou can expect a 30% to 50% reductionin product moisture variation by includingin your moisture control system a moisture
commercially installed in 1986 at BoiseCascade's mill in Florien, Louisiana, wherethree systems are presently in operation. Figure 7 shows the production rateincrease (15%) resulting from progressively installing Temperature Drop controlsystems on eight veneer dryers at KirbyForest Industries' three Texas mills, fromJanuary 1983 through July 1986.
VeneerThe Temperature Drop method for controlling veneer dryers was first installed ona veneer jet dryer at the Bon Wier, Texas,plywood mill of Kirby Forest Industriesin the early 1980's. The existing controlsystem was the usual brush-type moisturesensor at the end of the dryer that detectedand marked wet sheets for re-drying. Thedryer speed tended to cycle because it operated on "after-the-fact" moisture informa
tion. It was, at best, an automated re-dryinventory control system.
The Temperature Drop control methodinfers average veneer moisture contentinside the dryer by taking a temperaturedrop across a dryer section (Figure 6), andprocessing it through the model to generate an output signal proportional to theveneer moisture at the control section. In
this way, the entire veneer production issampled for moisture determination.
The Temperature Drop control systemconverts about one-third to one-half of
the normally produced redry sheets directlyinto acceptable veneer by minimizing thecycling effect of the "after-the-fact" typecontrol. The veneer lies flatter, has bettercolor, and glues better; fewer blows occur,and less over and under-dried veneer is
produced. The average production rateis increased by about 7.5%. It was first
an output signal that is proportional to themoisture of the strands. This output signal isused to manipulate the feedrate and/or theheat input to the dryer. In addition, the control system has the unique capability of constantly adjusting the temperature setpoint tomaintain target moisture content when thewater load is constantly changing.
MDF Moisture ControlThe Temperature Drop method was recentlyinstalled on three MDF flash dryers; figure4 shows the measurement of the temperature drop. Figure 5 describes the narrowingof the moisture distribution as a result of
using a moisture sensor inst;Jlled inside thedryer. The control system is also capableof continuously adjusting the temperaturesetpoint to maintain the target moisturecontent. Results indicate a minimum 3o(X,
and a maximum of 50% reduction in mois
ture variation can be achieved in this typeapplication.
Reader Service Card No. 1119
26 . Specialty Wood Journal· January/February 2004 www.bauminternational.com
For more information on a product, write the number at the end of the product information item on one
of the Reader Service Cards in this issue, complete the card and mail to Specialty Wood Journal at
2323 Boundary Road, Suite 203, Vancouver, BC, V5M 4V8, or fax it to 604-298-3966.
THat J Ig~II!IITII] I T Cold
---
t"'"
t---
t"'"
t
Cross Section
Cross section of a veneer jet dryer
temperature drop measurement.
••_ ••.•••,., ••. n _ •..••••.••••.•.. _ ••.•••••••.• _-M ••••.••
11m.
Effect of temperature drop control method on
cor/Jorate veneer production.
Moisture Content %
Shifting average moisture content.
no calibration, is essentially universally
applicable, and can be automatically and
continuously re-adjusting to maintain the
target moisture content. The overall results
are an improvement in quality, a reduction
in unit energy costs, and corporate stan
dardization of moisture control systems
for all dryers. Additionally, if production is
dryer-limited, it can be increased by shift
ing the average moisture content upward
as shown by Figure 8 .•
The new BMS3000 from L1MAB uses long
range, ultra-precise laser sensors to measure
board thickness without touching the surface.
The system measures on 055, MDF, HDF,
particleboard, plywood, hardboard and any
other hard or soft panel surface.The BMS3000 includes I to 10 measure
ment tracks with sensors, PC, cabinet and
software. The software provides real time
graphics, trend graphs, numerical data display,
data logging, two levels of alarms with outputsand network communications.
The system employs our newly developed
PreciCura sensor that uses the latest digital
Continued on page 28 ...
I.. - •....• --
for COE, MOORE, PRENTICE,RAUTE, & BABCOCK Drvers
Replacement Dryer pans are stocked in bolb our USA& Canadian facilities.and include:
• Gudgeons, Star Gears, Sprockets, & Bearing Hangers• Bushings in Teflon, Graphite, Copper Impregnated, & Oak• 81X Chain & Chain Hold Oowns
• Dryer Rolls & Roll Baffles• Door Hardware & Door Seal
• Plug Up Detection Springs, Wires, & Insulators• Jet Tubes in standard & high volume configurations• Westmill's Patented "Sure Seal" Articulating Dryer Door Hardware
We also provide:
• Moisture Marking Ink in Regular & Disappearing• Moisture Detector Brushes, Spray Valves, Filters
• Floating Skin Dryer Doors & Replacement Panel Systems• Retrofit Fan/Motor/Housing "Production Modules"• Electro-Pneumatic Stack Dampers• Dryer Humidity Control & Spray Systems• Replacement Parts for Patchers, Sanders, Panel Saws, Strap Choppers, Glue
Spreaders, Veneer Lathes, Plywood Press & Pre-Press, and other Machines
FA. ~~~~~~~~Offices in USA and Canada
Toll Free 877-607-7010Email: [email protected]
Visit our web site at: www.westmillindustries.com
Westmill is a family owned business serving thepanel board industry since 19761
Reader Service Card No. 1131
I... - ...•.. - .. - .. - •.....
NEW AND REBUILT
Westmill specializes in new and rebuilt COE, MOORE, PRENTICE,and RAUTEVeneer Dryers. For new and rebuilt Dryers, our pre-built "Modular" Dryercomponents require minimal installation time and drastically reduce field labor.
Westmill's new and rebuilt Dryers provide many unique features, including:• Jet, Single & Two Zone Longitudinal Dryers in 4-5-6 & 8 Decks• Long Lasting, Seal Welded Insulated Stainless Dryer Floors• Dryer Jacking & Leveling System (patent pending) - no more shimming• "Automated Floor Cleaning" Option• Westmill's Patented "Sure Seal" Articulating Door Hardware
• Leak Proof Internal Dryer Housing System• ZERO Heat Transfer Outer Dryer Cladding• Steam, Gas, and Hot Oil Heating Systems Available• "State of the Art" PLC Based Dryer Control
With your choice of any conveyor components (CaE, MOORE,PRENTICE,RAUTE)tomatch your existing Dryer parts inventory.
Westmill also provides Dryer Infeeds, Outfeeds, Vacuum Feeders, Dryer Drives,Lappers, Scissor Lifts, One Piece - Fan/Motor/Housing "Production Modules", MaterialHandling Conveyors, Sheet Re-Entry Systems, and Special Application Dryers.
jl'- ~~~~~ ~~~Offices in USA and Canada
Toll Free 877-607-7010Email: [email protected]
Visit our web site at: www.westmillindustries.com
The Veneer Dryer Specialists
Reader Service Card No. 1132
26 . Specialty Wood Journal· January/February 2004 www.bauminternational.com
For more information on a product, write the number at the end of the product information item on one
of the Reader Service Cards in this issue, complete the card and mail to Specialty Wood Journal at
2323 Boundary Road, Suite 203, Vancouver, BC, V5M 4V8, or fax it to 604-298-3966.
THat J Ig~II!IITII] I T Cold
---
t"'"
t---
t"'"
t
Cross Section
Cross section of a veneer jet dryer
temperature drop measurement.
••_ ••.•••,., ••. n _ •..••••.••••.•.. _ ••.•••••••.• _-M ••••.••
11m.
Effect of temperature drop control method on
cor/Jorate veneer production.
Moisture Content %
Shifting average moisture content.
no calibration, is essentially universally
applicable, and can be automatically and
continuously re-adjusting to maintain the
target moisture content. The overall results
are an improvement in quality, a reduction
in unit energy costs, and corporate stan
dardization of moisture control systems
for all dryers. Additionally, if production is
dryer-limited, it can be increased by shift
ing the average moisture content upward
as shown by Figure 8 .•
The new BMS3000 from L1MAB uses long
range, ultra-precise laser sensors to measure
board thickness without touching the surface.
The system measures on 055, MDF, HDF,
particleboard, plywood, hardboard and any
other hard or soft panel surface.The BMS3000 includes I to 10 measure
ment tracks with sensors, PC, cabinet and
software. The software provides real time
graphics, trend graphs, numerical data display,
data logging, two levels of alarms with outputsand network communications.
The system employs our newly developed
PreciCura sensor that uses the latest digital
Continued on page 28 ...
I.. - •....• --
for COE, MOORE, PRENTICE,RAUTE, & BABCOCK Drvers
Replacement Dryer pans are stocked in bolb our USA& Canadian facilities.and include:
• Gudgeons, Star Gears, Sprockets, & Bearing Hangers• Bushings in Teflon, Graphite, Copper Impregnated, & Oak• 81X Chain & Chain Hold Oowns
• Dryer Rolls & Roll Baffles• Door Hardware & Door Seal
• Plug Up Detection Springs, Wires, & Insulators• Jet Tubes in standard & high volume configurations• Westmill's Patented "Sure Seal" Articulating Dryer Door Hardware
We also provide:
• Moisture Marking Ink in Regular & Disappearing• Moisture Detector Brushes, Spray Valves, Filters
• Floating Skin Dryer Doors & Replacement Panel Systems• Retrofit Fan/Motor/Housing "Production Modules"• Electro-Pneumatic Stack Dampers• Dryer Humidity Control & Spray Systems• Replacement Parts for Patchers, Sanders, Panel Saws, Strap Choppers, Glue
Spreaders, Veneer Lathes, Plywood Press & Pre-Press, and other Machines
FA. ~~~~~~~~Offices in USA and Canada
Toll Free 877-607-7010Email: [email protected]
Visit our web site at: www.westmillindustries.com
Westmill is a family owned business serving thepanel board industry since 19761
Reader Service Card No. 1131
I... - ...•.. - .. - .. - •.....
NEW AND REBUILT
Westmill specializes in new and rebuilt COE, MOORE, PRENTICE,and RAUTEVeneer Dryers. For new and rebuilt Dryers, our pre-built "Modular" Dryercomponents require minimal installation time and drastically reduce field labor.
Westmill's new and rebuilt Dryers provide many unique features, including:• Jet, Single & Two Zone Longitudinal Dryers in 4-5-6 & 8 Decks• Long Lasting, Seal Welded Insulated Stainless Dryer Floors• Dryer Jacking & Leveling System (patent pending) - no more shimming• "Automated Floor Cleaning" Option• Westmill's Patented "Sure Seal" Articulating Door Hardware
• Leak Proof Internal Dryer Housing System• ZERO Heat Transfer Outer Dryer Cladding• Steam, Gas, and Hot Oil Heating Systems Available• "State of the Art" PLC Based Dryer Control
With your choice of any conveyor components (CaE, MOORE,PRENTICE,RAUTE)tomatch your existing Dryer parts inventory.
Westmill also provides Dryer Infeeds, Outfeeds, Vacuum Feeders, Dryer Drives,Lappers, Scissor Lifts, One Piece - Fan/Motor/Housing "Production Modules", MaterialHandling Conveyors, Sheet Re-Entry Systems, and Special Application Dryers.
jl'- ~~~~~ ~~~Offices in USA and Canada
Toll Free 877-607-7010Email: [email protected]
Visit our web site at: www.westmillindustries.com
The Veneer Dryer Specialists
Reader Service Card No. 1132
