Case Study No. 1 – Ammonium Nitrate Manufacturing

Ammonium Nitrate Fertilizer Manufacturer - High Temperature Inline Environments

• Strong Acid/Fluoride Resistant pH Element & High Temperature and Acid/Fluoride Resistant Solid State Reference Junction.
• Chemically & Thermally Resistant ULTEM & PEEK plastic body housings
• Application Oriented Engineering and Custom Built to Order sensor increased the lifetime by Two to Five Fold

The Problem
An ammonium nitrate fertilizer manufacturer was lacking a pH sensor that offered accurate measurement in high-temperature inline acid and ammonia environments, resulting in under reacted chemicals with lower production yields. The extreme process conditions resulted in limited lifetime for the sensor; which rarely exceeded days or weeks in the reactor and only functioned for up to a month in a specially constructed heat-reducing bypass system. To circumvent this problem, the manufacturer had to cool the sample by diluting it 1:1 with water via the heat-reducing bypass system. This action solved the temperature problem, but decreased the accuracy of the measurement making it dependent on the 1:1 sample to water ratio measurement. The signal also was delayed because of the addition of the bypass line. If the reaction was running on the ammonia excess side, the ammonia gas entered the sensor and destroyed the secondary reference half cell, thus suddenly and significantly reducing the operational lifetime of the sensor. If the process was allowed to run on the nitric acid excess side, the result was under reacted ammonia gas and rapid aging of the pH element.

The Solution
The combination of a high temperature and acid resistant pH element (with a protective seal against the ammonia gas) in conjunction with a high temperature and acid resistant solid state junction was able to facilitate all the measurement needs of this application. This system was encased within an acid resistant ¾"–1" MNPT ULTEM or PEEK thermoplastic sensor body housing. This permitted the manufacturer to place the sensor into the wall of the reactor and obtain real time pH readings thereby increasing the yield of their production. The improved design increased the lifetime of the sensor by approximately four times over the previously used sensor, despite the increase in the temperature and chemical exposure. The appropriate electronic components were integrated into each pH sensor to retrofit directly with the available pH transmitters.

The Ultra-High Temperature rated pH Sensor Used:
Model: PNA 6241/6441-873-10 Inline pH Sensor (Rated to 150 ºC at 150 psi)
Description: ¾"- 1" MNPT Immersion PEEK Bodied Ultra High Temperature, Dissolved Gas and Acid/Fluoride Resistant pH Sensor; Integrated 100 Ohm Platinum Temperature Element, Stainless Steel Solution Ground & Foxboro compatible 873 preamplifier; 10 feet cable to connect directly to Foxboro 873 pH Analyzer/Transmitter

The High Temperature rated pH Sensor Used:
Model: PNA 6131/6431-1181-10 Inline pH Sensor (Rated to 135 ºC at 100 psi)
Description: ¾"- 1" MNPT Immersion ULTEM Bodied High Temperature, Dissolved Gas and Acid/Fluoride Resistant pH Sensor; Integrated 3000 Ohm Balco Temperature Compensator & Uniloc-Rosemount compatible 1181 preamplifier; 10 feet cable to connect directly to Uniloc-Rosemount 1181 pH Analyzer/Transmitter

Case Study No. 2 – High Sulfide, High pH Process Media

pH & ORP Measurement in High Sulfide, High Temperature and pH process solutions

• Specialized Sulfide Resistant Triple Junction Reference Junction
• Thick Wall Ruggedized, High pH sensitive measurement element
• Waterproofing Assembly for completely Submersible Installations

The Problem
A catalyst manufacturer had a process requiring the removal of sulfides. The selected method of elimination was by stripping the sodium sulfide in a sodium hydroxide solution. The sodium sulfide concentration is controlled via a redox potential (ORP) measurement. In order to prevent free hydrogen sulfide gas from forming, the pH was kept at the maximum possible level (12 to 14.5). The problem having such a high pH solution was that it attacked the pH glass while the sulfide content entered the reference junction and destroyed the reference element causing premature sensor failure.

Similar side effects occurred when the pH drifted below 12, when hydrogen sulfide gas was produced. The gas then diffused through the reference junction into the sensor, destroying both the reference and pH components. The previously used sensors experienced corrosion problems, whereby sulfides would end the cable from the back side of the sensors, causing a sudden electrical short. The process conditions described manifested themselves in rapid sensor drift, frequent calibration and shortened sensor lifetime. The inaccuracy of the pH readings (particularly at very high pH) resulted in exceeding the emission limits, occasional emergency evacuations and EPA penalties.

The Solution
The solution was the combination of a high pH resistant pH and ORP glass elements sealed against sulfides together with a sulfide resistant solid state triple junction reference system. An ULTEM thermoplastic sensor body housing was chosen for its excellent chemical and thermal resistance to sulfides at a variety of pH and temperatures values. Waterproofing option "A" was installed on the sensors to make the assemblies suitable for completely submersible installation.

The appropriate electronic components were integrated into these built to order (custom) pH and ORP sensors such that they could be installed on the existing pH and ORP transmitters. The result of using ASTI's custom engineered pH and ORP sensors was to reduce the potential drift to a minimum and eliminate the need for frequent calibrations. The increased accuracy reduced the consumption of large quantities of chemicals and almost tripled the lifetime of the sensor, all with requiring the installation of new pH and ORP instrumentation.

The pH Sensor Used:
Model: PNXTJ 6631-1000JYC-15 pH Sensor with Waterproofing Option "A"
Description: ¾"- 1" MNPT Immersion ULTEM Bodied Sulfide Resistant pH Sensor with Triple Junction reference system; Accu-Temp Fast Response Integrated 1000 Ohm Platinum Temperature Element and Stainless Steel Solution Ground; 15 feet cable to connect directly to Johnson Yokogawa pH Analyzer/Transmitter – with Waterpoofing Option "A"

The ORP Sensor Used:
Model: PNXTJ 6831/6631-1000JYC-15 ORP Sensor with Waterproofing Option "A"
Description: ¾"- 1" MNPT Immersion ULTEM Bodied Sulfide Resistant ORP Sensor with Triple Junction reference system; Accu-Temp Fast Response Integrated 1000 Ohm Platinum Temperature Element and Stainless Steel Solution Ground; 15 feet cable to connect directly to Johnson Yokogawa pH Analyzer/Transmitter – with Waterpoofing Option "A"

Case Study No. 3 – pH Control in NOx Treatment Systems

NOx Treatment System and pH Sensors for High Nitric Low Process Media

• High Acid – Wide Range pH Sensor for aggressive acid media
• Deep Insertion Distance from Hardware Interface Point
• Retrofit to Existing pH Transmitter for cost savings

The Problem
A catalyst manufacturer, in order to prevent the pollution of the atmosphere through the byproduct of its process, had to eliminate nitrogen oxides (NOx). The process requires the monitoring of the pH value, because the process acid has to be neutralized. Depending upon the hold on the environmental system, the pH could range from value of 2.0 to -0.3 (well over two Molar nitric acid). The oscillation in pH values depending upon system load and the necessity for measurement at very low pH values caused problems for the previously used pH sensors both in terms of drift and accuracy. The tank configuration presented a logistical problem due to the small 1¼" MNPT process connection suitable for 1.0" O.D. sensors when used with 1.0" compression fitting. The process solution was more than sixty inches away from the hardware installation point.

One of the other major problems with this installation was the build up of precipitation on the reference element, necessitating frequent cleaning and recalibration. In addition, the tank would sometimes have reduced solution volumes that resulted in the sensor being left exposed to only air for extended periods of time. Due to the mounting configuration and thus required overall sensor length, removal and insertion of the previously used sensor was quite time consuming and cumbersome. The maintenance and short lifetime of the sensor reduced the plant's process efficiency and profitability.

The Solution
Many specialized options from our sensor line were required to solve the various application problems. A high acid resistant, wide range pH glass element was employed in combination with a solid state conductive polymer reference junction. This improved measurement accuracy greatly. The use of a solid state reference system made pH sensor much more resistant to dehydration, minimizing the effect of prolonged exposures to only air at various times during its service life. The long insertion distance was accomplished by utilizing a 1.0" compression fitting together with a 1.0" O.D. sixty inch long 316 stainless steel insertion tube.

The solid state reference system enabled both aggressive mechanical and chemical cleaning methods to be employed when required, and reduce the overall necessity for maintenance time due to reduced cleaning requirements. Due to the sensor's stability and reproducible slope, only one point grab sample performed remotely using a grab sample from process. The use of grab sample calibration resulted in greatly reduced calibration time, and better process efficiency. The pH sensor interfaced readily to the existing Great Lakes pH transmitter resulting in excellent cost savings.

The pH Sensor Used:
Model: PN 6432-GLI5-25 pH Sensor
Description: ¾"- ¾" MNPT Immersion ULTEM Bodied High Acid/Fluoride Resistant pH Sensor with integrated 301 Ohm GLI TC Assembly, Stainless Steel Solution Ground and GLI Compatible 5-Wire Differential preamplifier; 25 feet cable to connect directly to GLI pH Analyzer/Transmitter

Case Study No. 4 – pH in Organic Solvent Recovery Systems

pH measurement in almost pure (99%) Organic Solvents & Solvent Recovery Systems

• Specialized Organic Solvent Resistant Solid State Reference System
• Wide Range pH element to handle wild pH fluctuations in small water phase of process (1% water total)
• Extremely high chemical resistance offered by PEEK sensor body housing
• Integrated high temperature rated temperature compensation elements, stainless steel solution ground, and high impedance CMOS operational amplifiers (preamplifiers) that allow retrofitting to almost any existing pH transmitter
• Proven Solution for pH measurement in Class I, Division I (Zone 0) Areas

The Problem
A manufacturer of organic chemicals required process control equipment for its solvent recovery system. This process consisted of the collection of the used solvents and the storage of a mixture consisting of fractional distillations. The solvents accumulated some water during the process, this water extracted acids or alkali from the product and was carried into the storage tank. Since there was only a small amount of water, the concentration of the resulting acids and alkali was very high. In some cases, the small percentage of water was so corrosive that the stainless steel tank was attacked and the solvents leaked into the atmosphere. Repeated attempts to measure the pH value failed because the solvent mixture either dissolved the sensor or attacked the reference junction making it inoperable. The rapid and sometimes unpredictable fluctuations in pH made accurate readings difficult. Due to electrical consideration and area classification rules, an integrated preamplifier was required to get stable usable potentials from the pH sensor.

The Solution
What was required was a sensor that was constructed of components that are impervious to the wide variety of process chemicals employed. This was accomplished by use of a wide range thick wall pH glass element, a solvent media resistant solid state reference junction and an immersion PEEK sensor body housing. The necessary temperature compensator, solution ground and preamplifier where embedded into the sensor as required for the area classification. This custom engineered pH sensor provided a reliable, fast responding and accurate measurement in the extreme acid and alkali environment found in the organic solvent recovery system.

The pH Sensor Used:
Model: PNLTS 6041/6441-870IT-10 pH Sensor
Description: ¾"- 1" MNPT Immersion PEEK Bodied Organic & Solvent Media Resistant Wide Range Acid/Fluoride Resistant pH Sensor; Integrated 1000 Ohm Platinum Temperature Element, Stainless Steel Solution Ground and Foxboro Compatible 870IT preamplifier; 10 feet cable to connect directly to Foxboro 870IT pH Analyzer/Transmitter

Case Study No. 12 – pH Control in Chlor-Alkali Manufacturing

Saturated Sodium & Dissolved Gas Resistant pH Sensors

• Saturated Sodium Resistant pH glass element and Dissolved Gas Resistant Solid State Polymer Reference System are specifically engineered for Chlor-Alkali and functionally similar Process Applications
• High Quality PEEK plastic is not damaged by presence of dissolved oxidizing gases such as chlorine and chlorine dioxide
• Vastly superior lifetime due to custom engineering and component selection
• Offered at very competitive prices as compared with other more generic sensors
• Ability to integrate requires electronic components means that these sensors can be retrofitted into almost any existing installation and mate with most process pH instrumentation

The Problem
A chlorine dioxide (bleach) manufacturing company wanted to improve their pH control, reduce sensor replacement and minimize maintenance time. Corrosive ClO2 dissolved gas was causing frequent sensor failure at the reference half cell, resulting in constant drift and eventually sensor removal. The saturated brine solution caused problems for many pH glass formulations, resulting in large offset errors from standard calibrations.

The stray current, something that can occur frequently in many chlor-alkali processes, caused problems for the silver/silver chloride half cell inside the pH and reference elements, resulting in early expiration of the sensor. Since instrumentation was widely standardized throughout the plant, changing out the pH instrumentation would be very cost prohibitive. Most pH sensor manufacturers require customers to use their make of transmitters and do not retrofit existing pH instrumentation.

The Solution
The solution to these manifold problems was complicated. The thermoplastic PEEK was employed due to its excellent resistance to dissolved oxidizing gases and strong electrolyte solutions. A truly saturated sodium resistant glass was selected to improve measurement accuracy. The pH element was fabricated so as to be hysteresis resistant to minimize the effect of stray electrical current. A triple junction reference system was employed in addition to a dissolved gas resistant solid state polymer reference junction.

The suitable electronic components were selected to directly retrofit with the existing transmitters, saving the customer the cost replacing their existing pH instruments. All of these improvements were provided at a price that was quite competitive to the previous pH sensors used. The sensor lifetime was more than doubled from previous pH sensors.

The pH Sensor Used:
Model: PNCTJHR 6141/6941-3000-20 pH Sensor
Description: ¾"-1" MNPT Immersion PEEK Bodied High Temperature, Saturated Sodium and Hysteresis Resistant pH Sensor with Triple Junction Reference System; integrated with Balco 3K Temperature Element; 20 feet cable to connect directly to TBI Analyzer/Transmitter

Choosing the Correct pH/ORP Sensor
1. Choose a sensor body type that suits the physical parameters of the installation (refer to the Configurations Portion of pH/ORP and Ion Selective webpages).
2. Choose a sensor that suits the process application, temperature, chemistry, and physical parameters of the installation (refer to Sensor Selection Guides and call factory or local sales agent for support)
3. Choose a sensor housing material that is compatible with the process chemistry, temperature & pressure (refer to Chemical Resistance Charts as posted under the Technical Documents portion of the website).
4. Select suitable temperature compensation element, solution ground & integrated preamplifier based upon the mating pH/ORP Instrument (refer to Electrochemical Instrumentation Page & ask for factory support).
5. Specify the required cable length based upon installation location (refer to Part Numbering Guide).

* Subject to application qualification and review by an approved ASTI sales agent and/or factory. Performance guarantee is posted on the ASTI online application questionnaire page.
** See list of supported pH/ORP/ISE Instruments webpages as posted on the ASTI website.
*** Completion of Application Questionnaire form is required. Other restrictions may apply.

Case Study No. 6 – pH & Fluoride Measurement in Acid Etching A system to determine and control the acid etching strength of a given process solution

• High HF and High Acid (Low pH) resistant pH and Fluoride Element
• Custom Engineered reference system for acid etching media
• Menu driven Ion Selective Industrial transmitter and controller for ion sensor calibration and process control outputs and alarms (all values controlled in ppm)

The Problem
A metal etching company needed to control the power of its fluoride etching bath. The quality of the etching solution depends on the activity of the fluoride and pH. The throughput depends on the total fluoride concentration of the bath and the speed of the line. Fluctuations in the fluoride activity will result in the incomplete etching of the parts, preventing further processing and the partial or complete dissolution of the aluminum parts. Since free fluoride ion concentration is a function of pH, they needed to monitor both the pH and fluoride ion concentration in order to properly control their bath.

Most commercially available pH sensors will be dissolved by fluorides. While the process is progressing, a crust is deposited on the surface of the pH and junction element reducing the sensitivity and elongating response time. The elimination of this phenomenon requires frequent cleaning and calibration that will eventually destroy the pH element. The large quantity of etching solution passing by the sensor will exhaust the reference element of its internal salts and cause constant drifting, thus requiring recalibration. The fluoride element used in these types of measurements also will be attacked by the acid/fluoride mixture. The acid is needed to activate the fluoride for the etching process. The acid also influences the available free fluorides and changes the readings in the control system. The fluoride ion selective sensors employed suffered many of the same difficulty as the pH sensors result in poor and sporadic process control.

The Solution
The pH sensor employed a specially constructed high acid/fluoride resistant pH element with acid/fluoride resistant solid state reference junction. The sensor was embedded with the appropriate temperature compensator and Rosemount compatible preamplifier such that it connected directly into the existing pH transmitter. The fluoride ion activity was measured with a fluoride ion selective sensor with a special engineering against the attack of the etching mixture. The protection against the process etching solution was accomplished via a special gasket for the fluoride crystal designed for this customer's application and a customized acid/fluoride resistant reference junction which did not undergo the shifting common to high ionic strength solutions.

This fluoride sensor also contained the appropriate temperature compensator and preamplifier for the existing fluoride transmitter. The accuracy and control of the measurement increased leading to product quality and production rate increases. The need for cleaning and frequent calibrations was nearly completely eliminated. Calibrations were perform for offset only (one-point), done via grab sample. The sensor lifetimes were vastly extended resulting in excellent cost saving.

The Fluoride Sensor Used:
Model: AB 6100-54-10 Fluoride Sensor
Description: 1"-1¼" MNPT Immersion ULTEM Bodied Acid/Etching Media Resistant Fluoride Ion Selective Sensor with integrated 100 Ohm Platinum Temperature Element & Rosemount Compatible 54 preamplifier; 10 feet cable

The pH Sensor Used:
Model: PNHF 6431-3081-10 pH Sensor
Description: ¾"-1" MNPT Immersion ULTEM Bodied High Acid/Fluoride Resistant pH Sensor with integrated 100 Ohm Platinum Temperature Element & Rosemount Compatible 3081 preamplifier; 10 feet cable

Case Study No. 11 – pH Control in HF Treatment Systems

High HF Resistant pH Sensors for HF neutralization

• Improved HF treatment system efficiency through more accurate pH measurement and control
• Reduced Sensor Usage through less breakage during cleaning
• Reduced maintenance and increased service time from sensors using solid state polymer reference system & specialized high HF resistant pH glass

The Problem
An aluminum can etching and a silicone wafer etching company wanted to effectively treat their wastewater using a traditional CaF2 removal system. This was achieved by using a pH sensor to control the amount of calcium hydroxide or calcium chloride added. Typical operating conditions result in a coating of the sensor that can adversely affect its performance. Such conditions are exacerbated by the intermittent excursions into the low pH and high fluoride conditions. Previously used sensors accelerated their own demise because the sensors became insensitive to pH change after coating, even with repeated cleanings, thus causing a process excursion due to a lack of caustic addition. This lack of caustic addition, then caused the system to flood, over time, with the process etching solution containing hydrofluoric acid, primed with either sulfuric acid (aluminum etching) or hydrochloric and nitric acid (wafer etching).

The Solution
A sensor that was less susceptible to fouling from the addition of calcium hydroxide was required. This was accomplished by selecting a solid state polymer reference system. The sensor would also need to survive the brief, but aggressive excursions into the low pH and high fluoride conditions that may occur due to etch solution dumping, intermittent process control problems or the use of strong acid cleaning solutions.

The use of a high HF resistant pH glass was able to survive these excursions to the low pH and high fluoride conditions, without giving up the accuracy and stability that only a glass pH element can provide. Alternative pH sensing element technologies used in high HF media by other companies such as antimony or ISFET survived the process conditions but did not offer adequate accuracy for process control. Lastly, the sensor required cleaning with concentrated hydrochloric or half dilute hydrochloric acid to effectively remove the calcium deposits without the use of abrasive cleaning. Both the solid state reference system and high acid/fluoride resistant pH glass element are well suited for such cleaning. The use of aggressive chemical cleaning supplemented by minimal mechanical cleaning greatly elongated the sensor lifetime due to reduced glass breakage and reduced overall damage to sensors during the cleaning process.

The pH Sensors Used In:

Aluminum Can Acid Etching Treatment Systems:
Model: PNHF 8431-1181-10 pH Sensor
Description: 1" MNPT Twist Lock (Quick Disconnect) ULTEM Bodied High Acid/Fluoride Resistant pH Sensor with integrated Balco 3K Temperature Element & Rosemount Compatible 1181 preamplifier; 10 feet cable

Silicone Wafer Acid Etching Treatment Systems:
Model: PNHF 6431-3081-25 pH Sensor
Description: ¾"-1" MNPT Immersion ULTEM Bodied High Acid/Fluoride Resistant pH Sensor with integrated 100 Ohm Platinum Temperature Element & Rosemount Compatible 3081 preamplifier; 25 feet cable

Choosing the Correct pH/ORP Sensor
1. Choose a sensor body type that suits the physical parameters of the installation (refer to the Configurations Portion of pH/ORP and Ion Selective webpages).
2. Choose a sensor that suits the process application, temperature, chemistry, and physical parameters of the installation (refer to Sensor Selection Guides and call factory or local sales agent for support)
3. Choose a sensor housing material that is compatible with the process chemistry, temperature & pressure (refer to Chemical Resistance Charts as posted under the Technical Documents portion of the website).
4. Select suitable temperature compensation element, solution ground & integrated preamplifier based upon the mating pH/ORP Instrument (refer to Electrochemical Instrumentation Page & ask for factory support).
5. Specify the required cable length based upon installation location (refer to Part Numbering Guide).

* Subject to application qualification and review by an approved ASTI sales agent and/or factory. Performance guarantee is posted on the ASTI online application questionnaire page.
** See list of supported pH/ORP/ISE Instruments webpages as posted on the ASTI website.
*** Completion of Application Questionnaire form is required. Other restrictions may apply.

Case Study No. 5 – pH Control in Copper Mining

High Temperature Agitated Slurry Copper Ore Mixtures

• Agitated heavy slurry mixtures are endured by the sensor by use of a strong break resistant thick-wall pH glass element (nearly unbreakable under ordinary mining slurries use)
• Build up on reference element is minimized by solid state reference system, which also allows for aggressive chemical and mechanical cleaning
• Retrofit sensor can connect to almost any existing pH Transmitter
• Advanced waterproofing assembly allows for continuous submersible installation with little or no solution intrusion onto cable from back of probe
• Unique sealing technology that is custom built and engineered for mining applications allows for continuous and aggressive dissolved ammonia gas exposure

The Problem
A mining company needed a pH sensor to monitor the extraction of the desired metals from a sulfide containing ore. The extraction involved the oxidation of the sulfides at high temperature and pressure by means of injected ammonia gas in a strong acid solution. Previously used sensors had lasted such a short period of time that the installation point of the measurement was changed so as to be farther away from the ammonia injection point. This lengthened the previous sensor's lifetime but reduced the accuracy and quality of the process control measurement resulting in lower product yields and efficiency.

The sensor required by the mining company needed to withstand (and be once again installed at) the high temperature process conditions at the ammonia injection point to provide good process control values. Initially the sensor would need to resist the dissolved sulfides in solution and later in the process the resulting mixtures of diluted strong acids. The sensor had to resist the temporarily liberated hydrogen sulfides at excess dissolved ammonia gas at high temperature and pressure. The heavy slurry solution was agitated, which can result in the breakage of the pH element. The constant build-up of the slurry on the reference and pH element caused inaccurate pH readings and required frequent cleaning and calibration. These cleanings slowed or stopped the extraction process. Previous sensors rarely lasted long enough to have cable corrosion appear to diminish sensor performance.

The Solution
The solution to this very tough measurement application was the combination of a high temperature, sulfide, acid and slurry/viscous material resistant pH element with a high temperature, dissolved ammonia gas, acid and sulfide resistant solid state triple junction reference system. A chemically and thermally resistant immersion ULTEM sensor body housing was employed. The high performance waterproofing style "C" assembly was implemented to offer maximum resistance against cable corrosion even during deep and continuous submersion installation (shown below) under aggressive conditions. The lifetime in this application was increased over five-fold and the required pH calibrations were nearly reduced to one-third of the previous frequency.

The pH Sensor Used:
Model: PNCTJHR 6031/6131/6631-3000JYC-25 pH Sensor - with Waterproofing Option "C"
Description: ¾"- 1" MNPT Immersion ULTEM Bodied Low Impedance, High Temperature, Sulfide, Dissolved Gas and Hysteresis Resistant pH Sensor with Triple Junction reference system; Integrated 3000 Balco Temperature Element and Stainless Steel Solution Ground; 25 feet cable to connect directly to Johnson Yokogawa pH Analyzer/Transmitter – with Waterproofing Option "C" (Shown Below)

Case Study No. 9 – pH Control in Nickel Mining

High Temperature Agitated Slurry Nickel Ore Mixtures & Solvent Extractions (SX)

• Agitated heavy slurry mixtures are endured by the sensor by use of a strong break resistant thick-wall
• pH glass element (nearly unbreakable in most mining slurries)
• Build up on reference element is minimized by solid state reference system, which also allows for aggressive chemical and mechanical cleaning
• Retrofit sensor can connect to almost any existing pH Transmitter
• Advanced waterproofing assembly allows for continuous submersible installation with little or no solution intrusion onto cable from back of probe
• Unique sealing technology that is custom built and engineered for mining applications allows for continuous and aggressive dissolved ammonia gas exposure
• Unique organic solvent & hydrocarbon resistant reference systems and sealing technology allow for continuous submersed sensor use with little degradation

The Problems
A nickel mining company wanted to perform pH measurement for sulfide removal by ammonia injection (leaching) and solvent extraction (SX) portions of their nickel extraction operations. The high temperature, heavy agitated slurry mixtures with the presence of dissolved hydrogen sulfide and ammonia gas is quite similar to that which is described in far greater detail in ASTI's case study # 5 problem section. The solvent extraction process utilizes significant amounts of kerosene, other hydrocarbons and solvents. These extraction agents in combination with the complex slurry ore mixture present a corrosive and aggressive process media for measurement. Previously used sensors required frequent cleaning and recalibration due to organic coating on the sensors. The need for frequent maintenance accelerated the previously used sensor's demise because the frequent removal from the process resulted in performance degradation due to repeated temperature cycling.

The Solutions
The solution to the leaching application is similar to that described in ASTI's case study # 5 solution section, except that the higher process temperatures and heavier slurry mixture necessitated the use of a thicker walled twist-lock style body from a PEEK material of construction (see further details in pH sensor used for leaching on next page of case study). In addition, a more elaborate cable isolation was required of the waterproofing assembly (Style "B" shown below) due to the deeper submersion installation. The solution to measuring pH in solvent extraction mining processes was the combination of an organic solvent, acid, sulfide and dissolved gas resistant solid state reference system and thick wall, acid, organic and dissolved gas resistant engineered pH element. The proper temperature compensation and preamplifier electronics were integrated into the sensor to allow the retrofit pH sensor to install directly onto the existing explosion proof Rosemount pH transmitter. The maintenance requirements and lifetime of the sensor exceeded the previously used models over three fold, saving operator time and reducing sensor consumption. Hydrocarbon resistant waterproofing style "E" was required to ready the sensor for submersible service.

The pH Sensor Used in Leaching:
Model: PNCTJHRGR 8141/8441/8641-3081-30 pH Sensor - with Waterproofing Option "B"
Description: 1" MNPT Twist Lock (with Tines) PEEK Bodied High Temperature, Sulfide, Dissolved Gas and Hysteresis Resistant pH Sensor with Triple Junction reference system; Integrated 100 Ohm Platinum Temperature Element; 30 feet cable to connect directly to Rosemount 3081 pH Analyzer/Transmitter – with Waterproofing Option "B" (Shown Below)

The pH Sensor Used in Solvent Extraction (SX):
Model: PNCLTS 8431/8631-2081-25 pH Sensor - with Waterproofing Option "E"
Description: 1" MNPT Twist Lock (with Tines) PEEK Bodied High Temperature, Sulfide, Dissolved Gas, Solvent and Organic Media and Hysteresis Resistant pH Sensor with Triple Junction reference system; Integrated 100 Ohm Platinum Temperature Element; 30 feet cable to connect directly to Rosemount 3081 pH Analyzer/Transmitter – with Waterproofing Option "E" Waterproofing Engineering for Solvent Extraction SX Environments (Shown Below)

Choosing the Correct pH/ORP Sensor
1. Choose a sensor body type that suits the physical parameters of the installation (refer to the Configurations Portion of pH/ORP and Ion Selective webpages).
2. Choose a sensor that suits the process application, temperature, chemistry, and physical parameters of the installation (refer to Sensor Selection Guides and call factory or local sales agent for support)
3. Choose a sensor housing material that is compatible with the process chemistry, temperature & pressure (refer to Chemical Resistance Charts as posted under the Technical Documents portion of the website).
4. Select suitable temperature compensation element, solution ground & integrated preamplifier based upon the mating pH/ORP Instrument (refer to Electrochemical Instrumentation Page & ask for factory support).
5. Specify the required cable length based upon installation location (refer to Part Numbering Guide).

* Subject to application qualification and review by an approved ASTI sales agent and/or factory. Performance guarantee is posted on the ASTI online application questionnaire page.
** See list of supported pH/ORP/ISE Instruments webpages as posted on the ASTI website.
*** Completion of Application Questionnaire form is required. Other restrictions may apply.

Case Study No. 10 – Bleaching in Pulp Mills pH and ORP sensors as used for process control in bleaching operations at Pulp Mills

• Specially Engineering Dissolved Chlorine Gas Resistant Solid State Reference
• Flat, yet rugged break resistant glass minimize cleaning requirements
• Application specific engineered thermoplastics and conductive polymer materials of construction lead to optimized sensor lifetime and accuracy

The Problem
A pulp and paper producer wanted to improve their control and reduce their maintenance time and costs for their ClO2 bleaching process lines. They wanted to better control the brightness of the resultant pulp and reduce down time due to pH and ORP sensor failure and cleaning requirements. This meant that they were replacing their sensor every 1-2 months and cleaning and calibrating bi-weekly.

Conventional pH/ORP sensors experienced fast intrusion into the reference element due to the high temperature (from 100 to 150 ºC, 212 to 302 ºF) and pressure (50 to 100 psi) in the presence of high concentrations of chlorine dioxide gas. Previously used pH and ORP sensors required frequent calibrations due the drift of the reference element. The strong bleaching agent attacked both the sensor's internal "O"-rings and other external "O"-rings that sealed it to the titanium sheath. Failure of these "O"-rings permitted the dangerous process gas to intermittently escape intermittently during removal and insertion of the multi-component valve retractable sensor assembly. The sealing agent for the junction and pH components were dissolved and eroded, allowing the gas to intrude all the way through the reference element and to the back of the sensor.

The Solution
The hardware solution was the use of a 316 stainless steel, complete isolation double ball valve sensor retraction and insertion assembly. The sensor solution incorporated dissolved gas (chlorine dioxide) and slurry/viscous material resistant pH and ORP components. These sensors were sealed from the front and back end with agents that were selected based upon the chemicals and process conditions present. The non-porous cross-linked high-density conductive polymer triple junction reference system did not allow for the chlorine dioxide to diffuse in the junction thus extending the lifetime of the sensor five-fold.

The frequency of calibration was significantly reduced as well as the drift of the reference signal. The single unit, completely sealed, "O"-ring free design sensor design allowed the high grade thermoplastic (ULTEM and PEEK) sensor body housed ¾"-¾" MNPT immersion sensors to be installed directly into the double ball valve retraction assembly. This significantly reduced maintenance time required, eliminating the need for disassembly and re-assembly of insertion sheaths (unlike other manufacturer's multi-component valve retractable designs). The safety of operating the double ball valves improved by removing the possibility of "O"-ring seal through ASTI's "O"-ring free design. The required temperature compensation element was embedded directly into the sensor, permitting the cable to be connected directly from the back of the sensor in the original equipment manufacturer's (OEM) transmitter. In this way, the company was able to leave the process control loop in place, yet greatly improve the quality of their process through superior pH & ORP sensor performance and lifetime.

The pH Sensor Used:
Model: PNCTJ 6342-3000-15 pH Sensor
Description: ¾"- ¾" MNPT Immersion PEEK Bodied Slurry/Viscous Material and Dissolved Chlorine Gas Resistant pH Sensor with Triple Junction reference system; Integrated 3000 Balco Temperature Element; 15 feet cable to connect directly to TBI-Bailey-ABB pH Transmitter

The ORP Sensor Used:
Model: PNCTJ 6842-0000-15 ORP Sensor
Description: ¾"- ¾" MNPT Immersion PEEK Bodied Slurry/Viscous material and Dissolved Chlorine Gas Resistant ORP Sensor with Triple Junction reference system; No Temperature Element; 15 feet cable to connect directly to TBI-Bailey-ABB ORP Analyzer/Transmitter

Choosing the Correct pH/ORP Sensor
1. Choose a sensor body type that suits the physical parameters of the installation (refer to the Configurations Portion of pH/ORP and Ion Selective webpages).
2. Choose a sensor that suits the process application, temperature, chemistry, and physical parameters of the installation (refer to Sensor Selection Guides and call factory or local sales agent for support)
3. Choose a sensor housing material that is compatible with the process chemistry, temperature & pressure (refer to Chemical Resistance Charts as posted under the Technical Documents portion of the website).
4. Select suitable temperature compensation element, solution ground & integrated preamplifier based upon the mating pH/ORP Instrument (refer to Electrochemical Instrumentation Page & ask for factory support).
5. Specify the required cable length based upon installation location (refer to Part Numbering Guide).

* Subject to application qualification and review by an approved ASTI sales agent and/or factory. Performance guarantee is posted on the ASTI online application questionnaire page.
** See list of supported pH/ORP/ISE Instruments webpages as posted on the ASTI website.
*** Completion of Application Questionnaire form is required. Other restrictions may apply.

M300 Transmitter - Conductivity/Resistivity, Dissolved Oxygen, Ozone, Flow, pH, ORP and Temperature

The M300 multiparameter transmitter measures from two channels of conductivity, resistivity, pH, ORP, dissolved oxygen and/or dissolved ozone. With four display lines and four analog outputs, the multiparameter M300 can provide full capability on both analytical measurements and temperatures. Versatility includes the choice of 1/4 DIN panel-mount or 1/2 DIN wall- and pipe-mount enclosures.

With its innovative USB port, the M300 is open to the future – for remote configuration, data logging or software upgrade.

Features and Benefits:

• Two Field-configurable channels for any pair of parameters:
• Conductivity, resistivity, pH, ORP, dissolved oxygen and/or dissolved ozone
• Reduces number of instruments and amount of panel space
• Includes all features of single parameter instruments

Specifications - THORNTON M300 Multiparameter

Measured units: pH, mV, S/cm, S/m, ohm-cm, %HCI, H2SO4 & NaOH, ppb & ppm O2, ppb & ppm Ozone

Power supply: 100...240 V AC, or 20...30 V DC

Protection: 1/4 DIN: IP65 / NEMA 4X(front); 1/2 DIN: IP65/NEMA 4X

Current output: 0/4 to 20 mA, 22 mA alarm

Relays: 2-SPDT and 2-SPST mechanical rated at 250 VAC or 30 VDC, 3 Amps; 2-Reed rated at 250 VAC or DC, 0.5 Amp switching, 10 watts

Temperature inputs: Pt1000 (Pt100 with adapter)

Communication: USB port, type B

Mounting options: 1/4 DIN: panel mounting; 1/2 DIN: wall & pipe mounting

Short description: The M300 Multiparameter Transmitter measures two channels of Conductivity, Resistivity, pH, ORP, Dissolved Oxygen, and Ozone, in any combination.

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Case Study No. 13 – Fluoride Ion Monitoring in Drinking Water and Water Applications (or non Acid/Etching Wastewater)

Online Fluoride Ion Monitoring for Water Districts and other Water Authorities

• Simple to use inline fluoride ion monitoring system operates just as easily as any inline low flow pH system
• Reliable menu driven Industrial Ion Selective Analyzer calibrates, displays, outputs and controls all in fluoride ppm units
• Inline fluoride ion sensor is completely sealed from both sides and requires no chemical addition -- unlike many popular competing sampling fluoride analyzers

The Problem
A water district was required to monitor the levels of fluoride in the city drinking water supply. If the levels were too low, fluoride was required to be added. If fluoride levels were too high, fluoride must be removed. Because of the natural temperature variance at the measurement point, the existing sampling fluoride analyzer gave erratic results. The constant requirement of adding reagents to the sampling analyzer placed a high burden on the busy maintenance staff, and resulted in reduced plant efficiency. When the problems with the sampling fluoride analyzer could not be addressed, grab sample analysis was used. The use of constant grab sample during times of problems with the online equipment created an undue burden on the maintenance staff, and defeated the purpose of having an online fluoride monitoring system.

Since multiple measurement points were required, a complex system of piping was installed to deliver sample to the few sampling analyzer available. One a few sampling analyzer were installed due to their prohibitively high cost. This caused the two fold problem of a delay in the measurement due to the piping of the sample to the analyzer (not real time) and the centralization cause the entire system to go down at once when problems occurred with any of the few analyzers that were installed.

The Solution
An inline fluoride ion selective sensor, specially engineered to water and wastewater application was chosen, with a rugged fluoride mono-crystal ion sensing element, and a virtually maintenance solid state reference system. In order to optimize the stability of the inline fluoride sensor measurement, a low flow sample bypass system was employed. A menu driven, simple to use, industrial ion selective transmitter and analyzer that was capable of calibrating, displaying, outputting and controlling in ppm units was selected. A convenient bayonet style twist lock inline installation style was selected for its ease of removal, facilitating the required calibration and cleaning. Calibration solutions were formulated that were ten fold (one decade) apart in value and would bracket the target concentration range. The calibration solutions were designed to closely mimic the expected ionic background of the measured solution. The calibration system simplified the validation of the online fluoride analysis system and reduced the need for grab sample calibration all while replacing the cumbersome sampling fluoride analyzer.

The Fluoride Sensor Used:
Model: AB 8100-100-10 Fluoride Ion Selective Sensor
Description: 1" MNPT Twist Lock (Quick Disconnect) ULTEM Bodied Fluoride Ion Selective Sensor; Integrated 100 Ohm Platinum Temperature Element; 10 feet cable to connect directly to Rosemount 54e-ISE Analyzer/Transmitter/Controller

Case Study No. 7 – Total Ammonia Analysis in Wastewater

Total Ammonia Determination through online ammonium ion and pH monitoring

• Industrial grade ammonium ion selective membrane and application engineered solid state conductive polymer reference can withstand the rigors of industrial process lines
• Ammonium calibration system has been optimized to yield reproducible results in a variety of wastewater systems
• Ammonia gas resistant pH sensor delivers the accuracy needed for total ammonia computation via a PLC or DCS from the ammonium ion and pH input values

The Problem
A sweetener manufacturer wanted to control the total nitrogen content in their process. This was a difficult proposition since they had a mixture of dissolved ammonia gas and ionized ammonium ions in solution. Fluctuation of process pH did not allow for a simple mathematical correction or computation, and made real time control arduous. The complex process solution necessitated significant interaction between ASTI and the customer to develop the proper custom calibration solutions. The total nitrogen must be calculated based upon an equation whose variables are pH and ammonium activity. Creating an accurate calibration system is a challenge in a complex system, whose primary function is not to determine simple activity, but rather a computed or derived total concentration. Common TISAB (total ionic strength adjustment buffer) solutions are often inadequate ISE standards for industrial calibrations because they do not accurately reflect the ionic strength and pH of the process solution. This application then necessitated not only determining the proper multi-point calibration for both pH and ammonia/ammonium, but also developing an interactive curve and standard ion buffer background which accurately reflected the process. Getting agreement and consistency between laboratory titrations and on-line measurement or process values was accomplished by using custom calibration solutions as the common reference standard for both the laboratory and process measurements.

The Solution
The solution was a ammonia gas resistant pH sensor and an industrial grade organic polymer ammonium ion selective sensor. Both the pH and ammonia sensor were sealed against any dissolved ammonia gas which may attack the reference element at lower pH. The reference element was designed to be insensitive to the interferences experienced by the ammonium polymer membrane. The ammonium ion analyzer, in combination with the PLC, was capable of computing the total nitrogen concentration via a multi-parameter algorithm. The multi-point calibration developed for this application allowed the PLC to create an accurate curve at any point along the operating pH range. The total ammonium analysis system was able to deliver reproducible and accurate results, replacing slow and inaccurate grab sample laboratory analysis.

The Ammonium Ion Sensor Used:
Model: AB 6410-873DPX-25 Ammonium Ion Sensor
Description: ¾"- 1" MNPT Immersion ULTEM Bodied Ammonium Ion Selective Sensor with integrated 100 Ohm Platinum Temperature Element, Stainless Steel Solution Ground and Foxboro 873DPX compatible preamplifier; 25 feet cable to connect directly to Foxboro 873DPX (Dual Channel Auto pH Compensation) pH/ISE Analyzer/Transmitter

The pH Sensor Used:
Model: PNA 6031-873DPX-25 pH Sensor
Description:¾"- 1" MNPT Immersion ULTEM Bodied Dissolved Ammonia Gas Resistant General Purpose pH Sensor with integrated 100 Ohm Platinum Temperature Element, Stainless Steel Solution Ground and Foxboro 873DPX compatible preamplifier; 25 feet cable to connect directly to Foxboro 873DPX (Dual Channel) pH/ISE Analyzer/Transmitter

Case Study No. 15 – Sodium & Calcium Ion Analysis for Water Softener Systems

Calcium (Ca++), Magnesium (Mg++) & Sodium (Na+) Ion Analysis

• Before and After Water Softener to determine Water Quality Feed to Boilers
• Industrial grade sodium ion selective membrane and application engineered solid state conductive polymer reference can withstand the rigors of industrial process lines
• Sodium calibration system has been optimized to yield reproducible results in a variety of boiler water systems

The Problem
A company wanted to automate the water quality testing on their water softener used to feed their boilers. When the softener ceased to function properly, the water softener needed to be regenerated. A delay in this service may cause damage to the boilers, eventually leading to a shutdown to clean and repair the boilers. The existing manual sampling routine or online sampling analyzers were slow and expensive, respectively. In addition, the delay caused by not having an accurate real-time online method to determine the effectiveness of the water softener could cause hard water to spread throughout the plant, leading to operational difficulties.

The Solution
ASTI's online ion selective sensors can be used to measure the effectiveness and state of the water softening system, although this measurement must be performed indirectly. The customer indicated a desire to measure the activity of calcium (Ca++) ion at a point after the water softening system. This measurement is not feasible due to the degree of excess of sodium present. The permissible ratio of excess of sodium (interfering) ion to calcium (analyte) ion for our calcium ion selective sensors is 100 fold (on a molar basis), whereas the lab analysis revealed an excess of 2600 fold (also computed on a molar basis). This then indicates that the concentration of sodium is 26 times too high to perform the calcium measurement after the water softener. ASTI found an excellent and feasible method to indirectly measure calcium after the softener and determine the effectiveness of the softening system as a whole. .

Typical Concentrations Before Softener
Sodium - Na+ = ~ 48 ppm
Calcium - Ca++ = ~ 160-250 ppm.

Typical Concentrations After Softener
Sodium - Na+ = ~ 300 ppm
Calcium - Ca++ = ~0.200-0.600 ppm.

The ion exchange system is clearly replacing calcium ions with sodium ions. If the ion exchange system fails or deteriorates, the sodium ion activity at the post softener location is changed from about 300 ppm to about 48 ppm. This is almost a step change in concentration. Measurement of such a change is an appropriate use of an inline ion selective sensor. At the post softener position, all concentrations of interfering ions for the sodium ion selective sensor are within the permissible range. The sodium ion activity as measured prior to the water softener can provide a valuable baseline sodium ion (Na+) level. The magnesium ion (Mg++) contribution to water hardness is ignored because it will be also be converted to sodium ion, which will be analyzed at the after softener measurement position. In addition, the concentration of magnesium is often five to ten (5-10) times less than calcium and usually occurs at a fixed ratio to calcium.

When the softener is functioning properly, the sodium ion (Na+) levels as measured after the softener will be quite high (~300 ppm), corresponding to a lack of calcium ion (Ca++) in the softened water (see abbreviated water analysis above). When the softener fails to work properly, the sodium ion levels at the post softener measurement point will return to the low levels as measured at the before softener measurement point (~30-50 ppm). This provides a very simple method to use the ion selective system as an alarm and indicator as to the state of the water softening system. In addition, the ion selective analyzer can automatically switch the water (via a relay) to a functioning secondary water softening system to avoid any downtime. A Rosemount 54e industrial sodium ion selective analyzer was employed to conveniently calibrate and operate in familiar ppm units. This ion selective analyzer had the necessary 4-20 mA outputs (scaled in ppm) and relays (also set in ppm) to enable the automation of this implicit water hardness (Ca++ & Mg++) determination for water quality analysis of the water softening system.

The Industrial Sodium Ion Selective Sensor Used:
Model: AB 8430-100-10 Industrial Sodium Ion Selective Sensor
Description: 1" MNPT Twist Lock Quick Disconnect ULTEM Bodied Industrial Sodium Ion Selective Sensor with integrated 100 Ohm Platinum Temperature Element; 10 feet cable to connect directly to Rosemount 54e Ion Selective (ISE) Analyzer and Transmitter

Choosing the Correct pH/ORP Sensor
1. Choose a sensor body type that suits the physical parameters of the installation (refer to the Configurations Portion of pH/ORP and Ion Selective webpages).
2. Choose a sensor that suits the process application, temperature, chemistry, and physical parameters of the installation (refer to Sensor Selection Guides and call factory or local sales agent for support)
3. Choose a sensor housing material that is compatible with the process chemistry, temperature & pressure (refer to Chemical Resistance Charts as posted under the Technical Documents portion of the website).
4. Select suitable temperature compensation element, solution ground & integrated preamplifier based upon the mating pH/ORP Instrument (refer to Electrochemical Instrumentation Page & ask for factory support).
5. Specify the required cable length based upon installation location (refer to Part Numbering Guide).

* Subject to application qualification and review by an approved ASTI sales agent and/or factory. Performance guarantee is posted on the ASTI online application questionnaire page.
** See list of supported pH/ORP/ISE Instruments webpages as posted on the ASTI website.
*** Completion of Application Questionnaire form is required. Other restrictions may apply.

Organic Membrane Ion Selective (ISE) Sensors

• Tetrafluoro Borate (BF4+)
• Hydronium (H3O+ - pH)
• Primary Amines (R-NH3+ Cl-)
• Ammonium (NH4+)
• Barium (Ba+2)
• Calcium (Ca+2)
• Carbonate (CO-3)
• Cesium (Cs+)
• Chloride (Cl-)
• Lithium (Li+)
• Magnesium (Mg+2)
• Nitrate (NO3-)
• Nitrite (NO2-)
• Potassium (K+)
• Perchlorate (ClO4-)
• Silver (Ag+)
• Sodium (Na+)

Solid State Ion Selective (ISE) Sensors

• Bromide (Br-)
• Chloride (Cl-)
• Cyanide (CN-)
• Fluoride (F-)
• Iodide (I-)
• Silver (Ag+)
• Sulfide (S-)
• Thiocyanate (SCN-)