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.
