An Update on Consistency Transmitter Measurement Technology & Process Considerations Mike Hendricks Applications Manager BTG Americas Inc.

Agenda Consistency Overview Rules for Good Control Dilution The Control Loop Consistency Transmitters Calibration

Consistency Overview

The weight of suspended solids per litre of liquid Units used: 1 % Cs = 10 g/l 1 g/l=1000 mg/l Definition of pulp consistency

Consist of Fiber, Fines, Fillers Fiber comes from different processes: Chemical  Sulphate/Sulphite Mechanical  Ground wood  CTMP/TMP Recycled Suspended Solids

Most critical papermaking parameter –Controls basis weight of paper –Optimum performance of process equipment –Mass flow calculations –Maintain ratio between fiber types –Dosing of additives Why measure pulp consistency?

Or put another way… Improve the bottom line – Reduce fiber usage – Optimize fiber blending ratio – Reduce energy usage – Reduce chemical usage – Improved process stability There are no “Silver Bullets” in process control It all starts with consistency and flow control Everything else builds off of and further improves control

Advanced Process Control Chemicals are added as percent applied (flow of chemical x concentration) / (flow of stock x consistency) If you start with bad production rate (flow of stock x consistency) information there is no amount of APC that will make up for it In bleach plants (and other areas) it is human nature to over apply chemicals due to the importance of maintaining pulp quality requirements A well designed & implemented APC project can easily return over $1MM in annualized savings

Fiber Blending

Adjust to optimum consistency: Process plant efficiency ($ & Tonnage) Final product specifications Basis weight Formation Physical strengths Remove process variations: Optimum equipment performance Runnability MD & CD variations Benefits of consistency control

Process equipment examples Stock prep refining 3-5% Screening & cleaning<1% ClO 2 Bleaching10-16% Flotation cells<1% Machine chest3-4% RF Pulping3-6% Headbox<1% Whitewater<0.4% HD storage10-16%

Pulp Consistency Ranges

Illustration of Consistency

Rules for Good Consistency Control

Dilution steps should be small: – The consistency should be reduced by no more than % in one step Ensure good mixing: – Correct mixing of the suspended solids and the water is essential – Design the system around the pump to take advantage of the pump’s mixing ability Rules for Good Consistency Control

Ensure good dilution: – The time required for the dilution to reach the pump should be short – The dilution water flow must not interfere with the free flow of stock to the pump – Dilution header pressure must be constant – Use a dilution control valve with a high resolution and suitable range Rules for Good Consistency Control

Minimize Dead Time (transmitter type and position): – 2-3 secShort – 6 secNormal – 15 secToo long Ensure good chest agitation: – The pump will mix stock and water when they arrive at the impeller together. The pump can’t smooth out stock variations which are strung out along the suction line, which is why chest consistency variations travel Rules for Good Consistency Control

Locate consistency transmitter correctly: – Follow the manufactures instructions for the piping run for the transmitter Distances, velocities, pipe angles Install consistency transmitter correctly: – Check if turbulent or plug flow is essential for the transmitter function – Mount the transmitter according to the manufactures recommendations e.g., Mounting is critical for blade transmitters which must be parallel to the stock in both planes Rules for Good Consistency Control

Max % dilution in one stage Cs = 5% Cs = 4% Single Dilution

Multiple Dilution Steps

Coarse Dilution (75-80%) (8-12%  5-6%) Fine Dilution (20-25%) (5-6%  4%) Double Dilution

The Control Loop

Glossary Cs – consistency CT – consistency transmitter FT – flow transmitter PV – process variable SP – setpoint DCS – distributed control system CE – control element Repeatability – how well multiple measurements of the same thing are repeated Accuracy – the sum of CT and lab repeatability

Consistency of the stock in the pipe is measured (process variable or PV) PV is compared to a set point (SP) in the DCS (control system) The output from the controller affects an actuator on a dilution water valve (control element or CE) The amount of dilution water is varied to alter the consistency to the set point Set point How consistency control works SP

1.Stock chest with agitator 2.Stock pump 3.Dilution water supply 4.Dilution control valve 5.Dilution nozzle 6.Consistency transmitter 7.Controller/DCS 8.Sample valve 9.Lab work Consistency Control Loop Everything is important The weakest link will decide the result!

Control Parameters PID Constants – Proportional – Integer – Derivative Dead Time Filter Sample Time Update Rate Dilution Valve "PID en updated feedback" by TravTigerEE - Own work. Licensed under CC BY-SA 3.0 via Commons - dback.svg#/media/File:PID_en_updated_feedback.svg

Constants Proportional – current error Integer – accumulation of past error Derivative – predicted error – normally not used in Cs control

Should be minimized as much as possible Make A  B as short as possible A B  Variations with frequency < to the dead time are not possible to control at all  Variations with frequency < 12 times the dead time are hard to control effectively Dead Time

TdTd 44 Deadtime ~ 20 sec Open loop Time Constant (  ) ~ 30 sec B Dilution valve closing Output signal blade type transmitter (not in control) 63% Dead Time

Time constant is 63% of full change Filter will cause a slower response and increase dead time High frequency noise disturbs good control Rule of thumb is to have a time constant on the filter less than 0.5 times process time constant Process time constant = 30 sec Filter time < 15 sec Filter

Today’s transmitters are digital They update the output signal after each measurement The update rate has to be at least the same or faster than the controllers sample time 5-10 times faster than the time constant of the controlled process Process time constant = 30 sec Update rate every < 3 sec Update Rate

Dilution

Dilution water – Pressure controlled – Adequate pressure (+0.5bar) – Isolated Control valves – Properly sized – Maintained properly – Stiction – Actuators – Located close to line

Dilution point V1 = 3-5 m/s V2 = m/s G = Min mm Delta P = min. 0.5 bar L = 3 x D / min 1 m

Dilution nozzle The unfortunate fact of the matter is that we are stuck with what we got There is a right way

Consistency Transmitters

All transmitters are “inferential” in that they measure something other then consistency and infer consistency based on calibration (correlation) with laboratory analyze of a representative sample or samples The laboratory is the only “real” measurement, and while there is a TAPPI standard, not everyone follows it, lab repeatability There is no “consistency transmitter”

Repeatability vs Accuracy Repeatability – how well something measures the same thing over and over, i.e. lab and transmitter results are repeatable Accuracy – what you get when you put lab and transmitter repeatability together

Comparing technologies Shear force active blade Shear force rotating Shear force static blade Optical - transmitted Optical - reflective Microwave

Velocity and consistency profiles What does the process provide? What does the transmitter need

Shear force Most widely used Measures only the fiber part of the suspension Needs fiber network (+1.5% Cs) Insensitive to color and chemicals Shear force

Low cost Inexpensive installation Flow dependent Require plug flow - dead time issues Lowest repeatability % cons Static blade

Static Blade – Flow Changes 43 Green: Stock Flow (gpm) White: % Consistency 4000 gpm 8000 gpm 3.0% Consist 1.5% Consist Long Fiber from Fractionator Increased Flow increases “consistency” reading Decreased Flow lowers “consistency” reading Adds variability into refiners

B A A > B Measuring principle

Low cost Inexpensive installation Less flow dependent Require plug flow - dead time Lowest repeatability 1.5-8% cons Moving blade

Virtually flow insensitive High repeatability – 0.003% Large range of applications More expensive Expensive installation Rotating shear force

Measurement principle

Rotating shear force % consistency Used at high accuracy demand/’difficult’ applications Can be used most anywhere in the process – many variants / proven safe choice Little effect from flow, fiber composition and type, freeness etc. Not affected by air, pressure, conductivity, color, etc. Weak points: More moving parts, some influence by fiber type, does not measure total consistency, installed cost

True total consistency Low consistency, 0.01 – 3% Measures fine particle and fiber separately Large range of low consistency applications Limited consistency range up to ~3.0% Transmitted optical

No fiber passes the light gap Transmits a large amount of light The Peak Information on the filler content of the stock The Peak Both small and large particles pass the light gap A fluctuating signal (DC signal) Information on both small and large particles in the stock DC signal The signals combined provide the basis for evaluating the consistency of the pulp suspension Transmitted optical

0.01-3/3.5% Consistency Virtually insensitive to fiber type and composition, fillers, flow, color, etc. Simple design - no moving parts - low maintenance Low installation cost Suitable for low-consistency applications: screens, cyclones, de-inking cell, effluents, etc Weak points: High consistency, +25% filler content, minimum of 1.3m/s flow velocity Transmitted Optical

True total consistency Wide range, 1.0 – 16% Measures total consistency Large number of application possibilities Installed in turbulent flow – minimum process deadtime Inexpensive CT Inexpensive installation No moving parts Conductivity & pressure non-issues Small measuring volume, demands good mix of the suspension (turbidity) TiO 2 & changes vivid colors Reflected optical

One single fiber passes the light beam Reflects a large amount of light The Peak Information on the fiber content of the stock The Peak Both small and large particles pass the light beam A fluctuating signal (DC signal) Information on both small and large particles in the stock DC signal The signals combined provide the basis for evaluating the consistency of the pulp suspension Reflected optical Spread Min. and Peak DC and Peak are used for the total consistency. Min. gives information on fines and fillers

+ Accurate Close to total consistency Measures both fiber, fines and filler Not sensitive to fiber shape and size – Air sensitive Conductivity, temperature and vibration sensitive Limited range of application Microwave Transmitter

0-8% consistency Good repeatability Application specific – typically blend or machine chest Virtually unaffected by flow, fiber composition and type, freeness, etc. With compensation can measure total consistency No moving parts - low maintenance Weak points: High sensitivity for entrained air/pressure, temperature and conductivity variation. Pulp must be screened

Selecting the right transmitter Consistency range Accuracy needs – Chemical application – Basis weight – Fiber blending – Specific energy Process area Pulp type – Recycle – Virgin – Synthetic – Mixed Line pressure Conductivity Chemicals used Metallurgy pH Flow/Velocity Available calming distance/process deadtime Remember………. no transmitter type is best for all applications

Measurement versus application ApplicationAccuracy NeededImpact of 0.5% inaccuracy Broke ConsistencyLow Can be high for blending control Refining consistencyHighEnergy overuse Blending controlMediumFurnish cost differential Machine ChestHighPoor Basis weight control TypeAccuracy (Std. Dev.)Flow sensitivityEntrained air sensitivity Static bladeLowPoorMedium Moving BladeMedium Good MicrowaveMedium-HighGoodPoor Active bladeMedium-HighMedium-GoodGood OpticalHighGood-MediumGood Rotary, MechanicalHighGood

Best Practice Good Stock mixing Sensor in right place Appropriate Sensor Correct Dilution Valve Correct Sample Valve Control loop Tuning Max 20% dilution in 1 step Correct Calibration

Installation guidelines Rotating 3x & 1.5x ( 8%) Blades 10x & 5x Opticalimmediately after pump

Calibration Or how to ruin a perfectly good day

Calibration Guess what – they aren’t all the same! – Shear force is non-linear – Optical is linear – Microwave is linear – Filler & Fines effect – Transmitter repeatability Also…………. – A good calibration requires samples from all grades – A good calibration requires samples at different consistencies Don’t short change it!!

Different calibrations - why Different calibrations – Single point – Multipoint – Recipe curves How to select – Application – Quality of lab – Process

Calibration ideas The process determines the calibration – You can’t force the calibration – Good single point calibration will work – Good multipoint calibration will work Questionable lab – Single point calibration – Recipe calibration

Calibration thoughts…….. Application – Machine chest – Pulper – Dump chest – Feed to refiner Grade structure Fiber mix Number of samples How much can operations move the dilution control valve

Single point calibration

Recipe calibration

Single Point Calibration Data

2 Point Calibration

Multipoint Calibration Data

Combined Calibration Data

Calibration Comparison

Accuracy of Sample Sampling method Sampling technique Lab equipment Lab repeatability Transmitter repeatability

Lab Procedures – TAPPI – A repeatable procedure – Does everyone uses same procedure Equipment – What is and isn't there – Condition of equipment – Scale – significant digits, 2? 4? Personnel – Trained – Does anyone care

Sample is taken at pipe Dewaters pulp unless fully opened Everyone opens it differently Gives large volume and splashes at high line pressure Low price Exception? Ball valves

Water film Important to have an accurate and repeatable sample Well-designed valve: – Takes the sample well inside the pipe wall – Always fully open or closed – Not dependent on operator – Safe Selecting a sample valve – Consistency – Pressure – Error on side of safety & reliability Pulp Sampling

Calibration See……………. It isn’t that bad

Success Management – Drives the level of importance – Provides the capital – Understand and support reliability program Operations – Understand the benefits of running in control – If the control loop isn’t working they investigate – Ownership of their process area

Success Maintenance – Reliability program – calibration verification – Transmitter inspection – Control loop Labs – Good sample valves – Standard procedures that everyone follows, – Good lab equipment – SPC or control chart documentation

Summary Consistency Overview Rules for Good Control The Control Loop Dilution Point Consistency Transmitters Calibration

Thank You Questions?? Mike Hendricks Application Manager BTG Americas Inc