Pulp & Paper 23 Perspectives in Liquid Process Analytics News

INGOLD Leading Process Analytics

Durable and Intelligent Dependable pH Sensor for Sulfite Pulping

Regulating bisulfite feeding in sulfite pulping is a very demanding application for pH sensors. For a European paper mill, a METTLER TOLEDO solution not only tolerates the process, it has reduced maintenance by 50 %.

Global producer of paper products In sulfite pulping, regulating the bisulfite Our customer is a Sweden-based producer being fed to the liquor after the bleaching of paper, packaging and wood products. It tower is very important. Process pressure operates activities in in over 30 countries. is very high (5 – 6 bar) at this stage and the pulp is very thick (8 – 9 % solids), mak- At one of its European mills it produces ing successful in-line pH measurement newsprint, improved newsprint and un- extremely difficult, indeed all previously coated magazine paper. The focus within used sensors failed within weeks. However, each product area is to supply high- bisulfite regulation via pH control would quality products tailored to meet the be very useful during the procedure, if a specific requirements of individual cus- reliable system could be found. tomers. Production capacity is approxi- mately 1 million tons a year on four paper Rugged and dependable solution machines. METTLER TOLEDO was convinced that we could supply pH instrumentation that Well-proven process would tolerate the pressure and the highly The sulfite pulping method of producing caustic solution, and would measure reli- cellulose fibers was developed in Sweden ably in the thick pulp. After discussions in the 1870s, and it is this technique which with the chief mill engineer, we installed is still used at the facility. a system comprising the InPro 4801 i SG pH sensor, InTrac 785 housing and M400 Rapid start up Dramatic reduction in transmitter. InTrac 785 is a retractable housing, allow- maintenance ing sensor maintenance or replacement Many months after installation, the chief The InPro 4801 i SG is ideal for this ap- without any interruption to the process. mill engineer reports that the system is plication for four main reasons: The M400 transmitter offers full ISM working extremely well, and that the 1. It is designed to operate in pressures up functionality including the Dynamic original sensor is still operating reliably. to 13 bar. Lifetime Indicator and Adaptive Calibra- He is delighted not just with the perfor- 2. The pH membrane is flat, making it tion Timer sensor diagnostic tools, and mance of the system, but also with a drop suitable for measuring in thick pulp Plug and Measure for fast and easy mea- in sensor maintenance of 50 %, and the applications. surement point start up. advance servicing notifications ISM 3. The very long diffusion path provides an supplies. excellent barrier against poisoning of the reference electrode. c www.mt.com/InPro4800 4. Intelligent Sensor Management (ISM®) technology alerts engineers as to when maintenance or calibration will be re- quired and predicts the remaining sensor lifetime.

InTrac 785 retractable housing

M400 transmitter

Publisher / Production Mettler-Toledo AG Process Analytics Im Hackacker 15 CH-8902 Urdorf Switzerland InPro 4850 i pH sensor Illustrations Mettler-Toledo AG

Subject to technical changes. © Mettler-Toledo AG 01 / 15 Printed in Switzerland.

2 METTLER TOLEDO Pulp & Paper News 23 Can You Be Sure That Your pH Measurements Are Reliable?

The vast majority of installed pH measurement systems in the process industries still use analog glass sensors. And although such sensors are highly dependable, issues with cables and the environment around the process mean that your pH measurements could be out by several units! The answer? Digital technology. pH Measurement

The problem with cables For example, moisture ingress at the cable equipment will manifest as continuously The issue of unreliable pH measurements connector can severely disturb a signal. As fluctuating pH values. does not lie in the use of glass sensors a glass sensor has a high electrical imped- themselves. They have proven themselves ance of several hundred megaohms, liquid 100 % signal integrity to be reliable since they were first intro- in the connection will cause a short-cir- All these effects are eliminated completely duced 100 years ago. The cause of unreli- cuit, creating an equivalent impedance with the use of digital Intelligent Sensor able measurements lies elsewhere – with within the system. This can change the mV Management (ISM®) technology. Using the cable, or more precisely, the signal that output of the sensor to such an extent that an on-board microprocessor, pH is calcu- travels along it. your transmitter will calculate pH values lated inside the sensor itself (which means that are several units off it is more accurate) and forwarded to the the true level, or cause transmitter in a digital format. Being polarization effects that digital, the signal is immune to the foreign might be interpreted as influences that affect analog signals. Even drift. in the presence of moisture and over long cables, ISMʼs digital transmission gives In a chemical environ- you 100 % signal integrity – all of the time. ment, corrosive vapors can attack metallic con- Voltage drop shown at pH 4 (176 mV) due nectors, generating un- to sensor polarization caused by moisture predictable amounts of ingress millivolts and resulting in pH measurements so c www.mt.com/ISM-chem wrong that you will no longer be able to properly control your process.

Using cable that is not properly shielded can also have undesired ef- fects. Due to the high impedance nature of the measurement the cable acts like an antenna, and vibration and fields gen- Subassembly of a digital pH sensor erated by surrounding

METTLER TOLEDO Pulp & Paper News 23 3 Developments in Process Analytics for the Pulp and Paper Industry

Stefan van der Wal at METTLER TOLEDO is an expert in the deployment and use of process Interview analytical measuring systems in pulp and paper production. He travels around the globe advising mills on how to improve their processes and increase profitability. Pulp and Paper News spoke to him about the growing role of process analytics.

Mr. van der Wal, process analyt- of a real-time continuous measurement at important. Not only for pulp quality but ics is playing an increasingly process conditions is so much higher than also in the recovery of byproducts like tall larger role in the pulp and paper periodic analyses of samples that may oil. industry. How do you explain have been taken hours beforehand and this? therefore no longer represent anything At the paper mill, analytics are less impor- I think there are several reasons. First of thatʼs going on at the process side. tant but there are still measurements that all, competition is pressurizing mills to do should be done in stock preparation and more with less. In-line analytics keep an Pulp mills and paper mills are at the wet end to ensure fibers have the eye on processes so personnel can concen- very different places. Is process desired strength and retention. trate on other tasks. Secondly, there is ever analytics equally valid in both? stronger environmental legislation that Because of the strong liquors produced pH sensors haven’t changed much requires monitoring and control of waste and chemicals used in pulp manufacture, in many decades. Why is that? effluent. process analytics can play a major role in That is and isnʼt true. There are now dif- the control of reagent dosing, monitoring ferent ways of measuring pH, but glass- Thirdly, though being very conservative, effluent, and so on. Also, as the quality of membrane electrodes still offer the best the industry understands that in-line the pulp influences the quality of the technology and I canʼt see that changing. analysis has enormous benefits over labo- finished product, tight control of pH, ORP Also, the reference system in pH sensors ratory analysis of grab samples. The value and conductivity at the pulp mill is very has improved a lot. Long diffusion paths and better electrolyte fluids to protect electrodes from poisoning means sensor lifetime is much longer than itʼs been in the past.

And digital technology is making a huge change to sensors for pH and other param- eters. Having a microprocessor inside a sensor opens up a host of advantages that normal analog sensors canʼt compete with.

Where does digital technology have the greatest impact? Thereʼs a lot of moisture in pulp and paper mills, and moisture is not good for process analytical systems because it corrodes connections and interferes with measure- ments. Digital sensors simply donʼt have

4 METTLER TOLEDO Pulp & Paper News 23 those problems, so the measurement at the And that's what matters most transmitter is more reliable. these days, isn’t it? Improved Process Efficiency That and avoiding standstills. Nobody in Tall Oil Production – Also, with our ISM technology we offer wants unscheduled shutdowns due to some Greater Yield with Less Chemicals predictive diagnostics. In-depth on-line unreliable measurement or failing process sensor diagnostics provide a wealth of equipment. Thatʼs why sensor diagnostics information with regard to the measure- are so valuable. ment and the condition of the probe. Now the maintenance technician knows when each sensor will need calibrated or main- tained, so heʼs not servicing sensors when they donʼt need it, or worse, when itʼs too late. This white paper explains how Do you think digital sensors will robust pH sensor design combined become the accepted standard in with recent developments in analyti- the pulp and paper industry? cal technology can lead to increased tall oil yield, and reduced chemicals Without doubt. The advantages are just too use. great. Itʼs not only about the diagnostics and the digitized signal. Another major Download your copy today. benefit of ISM is the possibility to do bench c www.mt.com/pro-tall-oil calibrations. No longer do you need to carry buffer solutions around the plant. ISM allows you to take a sensor out of the process and calibrate it at your desk under controlled conditions. Bench calibration and sensor diagnostics reduce cost of ownership.

METTLER TOLEDO Pulp & Paper News 23 5 Inductive Conductivity Sensors Reduce Brown Stock Washer Costs

Achieving cost savings in brown stock washers requires careful control of the dilution factor. This lowers loss of chemicals and overuse of water. Measurements from inductive conductivity are an excellent indicator of washing efficiency and leads to improved brown stock washer control and reduced running costs.

Efficient brown stock washing liness of the stock, and the concentration Conductivity measurement at the brown Brown stock, the “dirty” pulp coming out of chemicals in the solution going to the stock washers requires a sensor that is of the digester, is washed in a concurrent recovery boiler. There is a fine balance immune to clogging from pulp fibers system with cleanliness increasing with between effective washing and conserva- and that can tolerate the white liquor each wash. The goal is to achieve clean tion of the liquor concentration for down- chemicals. stock using a minimum amount of fresh stream processing. water and to avoid unnecessary dilution of Process tolerant InPro 7250 the white liquor chemicals fed at the di- Even though it is called the dilution factor, conductivity sensor gester. These chemicals are concentrated concentration of the brown stock is fairly The best solution for this application is an in the recovery boiler, and a high concen- high and can be successfully determined inductive conductivity sensor. With this InPro 7250 Conductivity Sensor tration of water makes this process inef- by conductivity measurement. At this stage type of probe, no electrodes are directly in ficient or even impossible. in the process, conductivity is in the range contact with the process, they are therefore of 50 to 100 mS / cm, depending on the not directly affected by contamination. The concentration of chemicals in the individual plant, process and stock. That The InPro 7250 is constructed of PEEK, solution coming out of the last stage corresponds to concentrations in the low which is highly resistant to the white li- washer determines the cleanliness of the one digit percent range. Dilution in that quor chemicals. For best performance, the stock as well as the dilution factor. At this sense is relative to the two digit concentra- InPro 7250 should be installed where it stage, fresh water is added to the system. tions present in the digester. will be in contact with a representative The amount added determines the clean- sample of the washing solution, e.g. in the washer itself or in the drain line.

M400 transmitter with Hot wash water diagnostics Brown stock washers As to the transmitter, the M400 is the best Brown stock choice. Simple operation, precise and reli- 1 2 3 able measurements as well as low cost of ownership reduce effort and expense. The M400 accepts both analog probes and digital Intelligent Sensor Management sensors. InPro 7250 M400

High c www.mt.com/InPro7250 density Bleach plant storage tank

Brown stock washers process

6 METTLER TOLEDO Pulp & Paper News 23 M400 multi-parameter InPro 7250 inductive conductivity transmitter sensor • Wide range of chemical concen- • Inductive design is ideal for tration curves dirty applications • User-defined concentration • PEEK body is highly resistant curves to aggressive chemicals • IP 65 waterproof rated enclo- • Robust design for maintenance- sure free operation • Advanced PID controller for • Highly temperature and pressure process safety tolerant • Integrated temperature sensor

METTLER TOLEDO Pulp & Paper News 23 7 Magnesium Oxide Slurry Control with a Diaphragm-less pH Sensor

The InPro 4260 i pH sensor has been developed for difficult applications such as slurry control. Its solid polymer electrolyte, resistance to poisoning, and advanced diagnostics ensure exceptional performance and reduce maintenance. i pH Sensor

One goal, two results ration occur together in a wet scrubber. Overcoming a challenging The recovery of cooking liquor chemicals Absorbent preparation begins with the situation in pulp manufacture results both in a suspension of the separated ash. The In order to obtain a reliable in-line pH reduction of environmental loads and magnesium oxide reacts with water to signal for use as a control parameter for

InPro 4260 lower operating costs. Chemical recovery form magnesium hydroxide and serves as the recovery of chemicals in spent pulp

plants work on the basis of a wet process an SO2 absorbent. In the alkaline sulfite liquor, proper sensor selection is critical:

during which the sulfur dioxide (SO2) and stages, crystalline magnesium sulfite is Product characteristics, requirements for magnesium oxide (MgO) contained in the formed which is converted into magne- acid flushing, temperature range, and flue gas from the recovery boiler are con- sium bisulfite through further contact reliability of the measurement must all be

verted into magnesium bisulfite. with SO2. This results in raw acid which is considered. drawn off and passed on for acid prepara-

Reaction steps where Mg (HSO3)2 tion. After clarification, insoluble impuri- pH sensor with high process is produced ties can be discharged by means of sedi- tolerance There are several stages to achieve this, mentation. With further fortification, The InPro 4260 i sensor is designed for

one of which is SO2 absorption. In the wet cooking acid is produced for reuse in the high performance in this application. It process, ash separation and flue gas satu- process. features Xerolyt Extra solid polymer elec-

Glass InPro 4260 i pH sensor with Xerolyt® Extra Open solid polymer solid electrolyte junction electrolyte Measuring solution

8 METTLER TOLEDO Pulp & Paper News 23

Measuring Glass XEROLYT® solution trolyte for precise pH measurement and stress or degradation and transfers the longer sensor lifetime, even in the most information to the connected transmitter. difficult high particle concentration in- dustrial environments. The advanced diagnostics features of ISM interpret this data to inform the user when This diaphragm-less sensor features an sensor cleaning, calibration or replace- open junction, allowing direct contact ment is required. Thus, maintenance can between the process media and the sensorʼs take place when it is needed, rather than electrolyte. As there is no diaphragm, the waiting until measurement performance possibility of clogging is greatly reduced, from the sensor is reduced, or conducting and hence frequent cleaning is not neces- regular maintenance when it may not be sary. necessary.

Maintain sensors only when c www.mt.com/InPro4260 necessary The InPro 4260 i is part of the METTLER TOLEDO Intelligent Sensor Management (ISM®) range. Miniaturized circuitry in the sensorʼs head monitors for signs of

METTLER TOLEDO Pulp & Paper News 23 9 Keep Silica at Bay with a Low Maintenance Analyzer

Silica in boiler feedwater can very quickly lead to deposit formation in turbines. As it can only be removed during out-of-service cleaning, preventing silica from entering the water cycle is the best course of action. The 2800 Si Silica Analyzer quickly detects trace level contamination and calibrates itself automatically, saving valuable operator time. Si Silica Analyzer 2800

Although it has no significant corrosive effect on The 2800 Si is a highly reliable on-line instrument boilers, silica's presence in water / steam is none- designed for water / steam cycle monitoring. It theless very detrimental. It forms extremely hard provides early ppb detection of trace silica con- coatings in water / steam passageways and on tamination with minimal operator supervision. turbine blades, leading to reduction in heat transfer efficiency and unbalanced blades. If left unchecked, Automatic zeroing after every measurement cycle silica build-up can result in unplanned shutdowns ensures excellent stability. and extra maintenance. c www.mt.com/Thornton-silica

At-a-glance monitoring Low maintenance Robust design

Simultaneous display of silica and mea- Large reagent containers enable a long surement timing provides convenient service interval analyzer status, saving operator time

Rugged enclosure protects components and reagent containers from the mill environment

10 METTLER TOLEDO Pulp & Paper News 23 2800 Si Silica Analyzer

METTLER TOLEDO Pulp & Paper News 23 11 Get in-line with METTLER TOLEDO

Intelligent Sensor Management for the Pulp and Paper Industry

ISM® is METTLER TOLEDO’s digital technology platform for process analytical measurement systems. With ISM solutions, maintenance becomes predictable, sensor handling is simple, and process uptime is increased. Visit our website and discover how ISM delivers: Greater process reliability Easy sensor handling Reduced maintenance

c www.mt.com/ISM

Mettler-Toledo AG www.mt.com/pro Process Analytics Visit for more information Im Hackacker 15 CH-8902 Urdorf Switzerland