Measuring pH in liquids with many dissolved solids is a constant challenge for all types of industrial plants. For Kyokuto Petroleum Industries (KPI) Japan, continuous failure of their pH measurement in their desulfurization scrubber was costing significant time and money.

The KPI scrubber is a magnesium hydroxide system. The pH measurement is installed after neutralization and the wastewater includes many magnesium sulfate solids. The flow chamber was sometimes clogged with solids.

KPI had been using a pH sensor with a water jet cleaning system. The cleaning system, however, was ineffective against solids that coated and plugged the glass and liquid junction of the sensor. After a few days of operation KPI could no longer trust the pH values being received as the readings would fluctuate significantly. Even when the sensor was cleaned manually, a time-consuming and expensive process, the pH sensor had to be replaced every month.

As a result, KPI often had to control the dosing of magnesium hydroxide manually based upon the experience and intuition of the operators. In addition to the cost, personnel time and extreme inconvenience, the plant was faced with significant local regulations regarding emission of SOx. If the manual control led to low magnesium oxide dosing, a SOx emission could occur with subsequent fines. If the dosing was too high, the costs of the expensive magnesium hydroxide soared and increased costs.

On top of all this, the pH sensor KPI had been using was connected to an analog device which made it impossible to get sensor status from the instrument automatically. The company could not predict sensor failure or receive other data without manual intervention.

With good reason, KPI was looking for a method of applying automatic control to its set points based on reliable pH measurement.

KPI switched their pH analysis to the Rosemount Analytical Model 1056 using the PERpH-X 3300HT-10-30 with SMART pre-amp as a sensor. The PERpH-X sensors are designed with an enhanced double junction reference that is specific to extreme applications. Reference flow into the process stream is controlled using a porous Teflon® junction that can be replaced in the event of fouling or plugging. The specially designed junction is chemically resistant and has a large surface area to maintain a steady reference signal in dirty or oily applications. This reference also resists poisoning which can occur with other sensors as a result of the diluted hydrochloric acid used to manually clean the sensor during preventive maintenance.

The 3300 has been able to operate accurately for two to three weeks before manual cleaning and the sensors are able to be used more than nine months in the process as KPI also takes advantage of the rebuildable reference feature of the 3300. The 3300 has lasted nine times longer than the previously used sensor – a dramatic improvement saving time and money.

The HART-enabled pH measurement by the 3300 allows KPI to monitor other valuable information such as reference impedance, glass impedance, temperature, etc. By monitoring these sensor parameters, KPI could detect a sudden large deposit of the reference impedance. Figure 1 shows the increasing reference impedance trend as well as the result of a sudden deposit. This information is used by KPI to improve the timing of maintenance. They are also able to use temperature data to determine clogging of the flow chamber which saves both maintenance costs and prevents shutdowns. Using the Emerson 1056P-HT with a 3300HT sensor with the SMART pre-amp and jet sprayer, KPI has been able to control the dosing volume of magnesium hydroxide automatically saving time and improving efficiency. While savings in actual product costs measures in the thousands of dollars, the value of the accurate measurement is incalculable.

Monitoring pH is critical in virtually every manufacturing plant, regardless of industry or process, but maintaining effective pH measurement can be challenging and complex. Problems with pH sensors can range from difficulties with field calibration to cracked glass to reference clogging, and these issues can result in expensive maintenance requirements or even process downtime.

The current issue of Plant Engineering features an article by our own Linda Meyers, senior product manager, Emerson Process Management, Rosemount Analytical, on new smart technologies for pH sensors that can communicate the health and status of sensors to control systems, reducing costs and preventing downtime.

Below is an excerpt from the piece, and you can CLICK here to read the entire article.

Ask plant operators about their most time-consuming and burdensome tasks, and chances are they will mention the field calibration of pH sensors. In addition, pH sensors are often isolated from the central plant information systems, which makes them maintenance nightmares and creates potential risks of downtime.

Fortunately, while pH technology is classic, the continuous improvements to pH systems are helping to overcome some of these operational problems for plant engineers. One of these improvements is making pH sensors “smart” — smart enough to hold calibration and other data and to communicate that information to central control systems. The result is lower cost of operation, substantially reduced maintenance requirements, and reduced downtime in a wide range of applications.

The calibration nightmare
Traditionally, the only way to calibrate a pH sensor was to carry all of the calibration equipment into the field. New technologies now embed memory in pH sensors, which allows them to hold calibration information. This means a sensor can be calibrated in a controlled environment such as a lab or maintenance shop. The information is then held in the sensor memory as the sensor is taken into the field and installed. Pre-calibrated sensors can even be stored on shelves and then taken into the field to replace a sensor requiring calibration or maintenance. No more bottles and beakers in the snow, plus no downtime.

Smart diagnostics
Because the new sensor technologies store data in the sensor, they also solve another important pH measurement problem — unpredictable failure.

The information stored in the sensor that can be used to predict accuracy and sensor life include:

• Slope trends, which normally decrease over time
• Glass impedance trends, which normally increase over time
• Reference offset trends, which normally shift slowly over time
• Reference impedance trends, which normally shift slowly over time.

Read the full article by CLICKING here.

For more information on Rosemount Analytical SMART pH technology, CLICK here.

And CLICK here for a video on SMART pH Sensors and Instruments for Plug and Play Use.

A recent article in Chemical Processing by Dave Joseph of Emerson Process Management highlights the costly leak detection problem experienced by the Fujifilm chemical plant in Dayton, Tenn which was solved through the use of pH analysis. (To read the complete article, Click HERE.)

The site, which makes photosensitive chemicals, feeds dry materials and flammable solvents, including thionyl chloride (SOCl₂), to a reactor used to precipitate crystals. The volatile solvent is pulled from the reactor and routed through a heat exchanger using a liquid ring vacuum pump. Unfortunately, SOCl₂ produces hydrochloric acid when it comes into contact with moisture. When acid from the process got past the pump’s seal, it damaged the pump. In the last three years, the $28,000 pump was replaced multiple times due to corrosion.

Three alternatives could prevent the problem: using exotic materials of construction; installing an intermediate tank to capture vapor (not possible in the available space); or analyzing the seal fluid to detect leaks before they caused damage. Opting for a simple analysis system was the proverbial “no-brainer.”

Leak detection can be performed using either pH or conductivity analysis. The choice depends on the process. For pH to be used, a small amount of contaminant must cause a measurable change in the pH of the process; for conductivity to be suitable, the contaminant must significantly alter the conductivity. Conductivity can detect leaks of acids, bases or even salts but requires stable process conductivity for best results.

The chemicals to be monitored by Fujifilm affected pH. So, the plant installed a pH analyzer in the vacuum pump seal loop (see image below). It chose a wireless unit to obviate power and output wiring. Because a wireless gateway was already in place for other process control applications, implementing the analyzer was easy. It was incorporated into a self-organizing network that allows each device to function as a data repeater. Thus, if any pathway becomes interrupted, data automatically travels via an alternative pathway, assuring uptime. The pH monitoring system cost less than $3,500 to implement and was up and running in two days.

Unit monitors seal fluid to safeguard against corrosion of vacuum pump.

Since the plant installed the pH analyzer in June 2011, it hasn’t suffered any corrosion-related pump failures.

In the Fujifilm application, the normal pH of the seal fluid (water) is approximately 7; at that point, corrosion is minimized. To protect the vacuum pump seal integrity, when the analyzer finds the pH has dropped below 3, the process is stopped and the system is flushed to clear out the acid and return the process pH to 7.

The Fujifilm application is an excellent example of appropriate use of pH-based leak detection because when the process pH is near neutral (7.0) the pH response is greater, resulting in increased sensitivity to detect leaks. In general, however, pH may respond differently to the presence of contaminant, depending upon the process pH and the chemistry involved. To learn more about the use of pH analysis in a range of applications, Click HERE.

What kind of leak detection problems has your plant encountered?

Hello everyone. I’m Stéphane Canadas, Analytical Specialist at Emerson Process Management. A customer of ours in Europe has an application that demonstrates the importance of having a wireless technology that can meet the need of demanding field networks. The company performs sugar processing. While your application may be different, if you have a demanding application, there are lessons to be learned from this example.

As part of this company’s production process, clean, sliced beet is pumped into one of three rotating drum diffusers and then mixed with water at approximately 85^o C to extract the sugar. pH levels of the solution must be monitored within the drums to optimize the soaking period and ensure it has the correct pH level before it passes through the next stages of purification. In the past, the company performed the pH measurements manually with solution samples taken every hour and analyzed in a laboratory. As you can imagine, this was very time consuming and did not provide immediate or continuous information as needed. Collection of the sample was difficult, requiring an operator to open a valve on the rotating drum, fill a bottle from the port and close it, all in a few seconds while the drum was on the lowest part of its rotation. At times, the port would be blocked by beet fibers preventing a sample from being taken for several hours forcing the process to run blind. Has your plant ever experienced anything similar? If so you know how unsatisfactory such a procedure can be.

The customer wanted to install a continuous automated monitoring system. They first tried a wired installation using a slip ring but the connection points for both power and data proved to be very unreliable causing data signals to be lost. They next set upon a wireless solution to solve the problem but wanted any wireless system they purchased to perform a number of tasks across the plant. It was important, therefore, that they selected an open standard technology that would not lock them into a single vendor.

After reviewing a range of systems, the customer settled on the Rosemount Analytical Model 6081-P wireless pH transmitter. The transmitter, along with a 3500 SMART pH sensor, was installed on the rotating drum. Because of the inherent ease-of-installation of the Emerson field network system, the wireless devices began transmitting data the minute they were attached to the drum. Since the sensor is preconfigured in the lab by Emerson, it received its specific setup through the wireless network and began immediate operation. Measurement data from the device is transmitted every sixty seconds from the sensor to a Smart Wireless Gateway and then transmitted to the customer’s DCS providing the much-needed continuous measurement.

Initially, the wireless system just provided continuous pH measurements to be viewed by the operator who then made manual adjustments to control the pH levels. However, since the initial four-week trial period proved so seamlessly integrated and reliable, they are now using the wirelessly transmitted data to control the pH level in the diffusion drums automatically.

The bottom line is that with the selection of a field network wireless system with the configuration, security, reliability and simplicity required by demanding applications, this company was able to significantly improve productivity and process quality while reducing energy use, water and rework. These results were achieved in a highly demanding rotating drum application. The decision to move from monitoring to control is strong testimony in the company’s confidence in the Model 6081-P and Emerson Smart wireless field network solution. We might call that a sugar of a deal.

 In what demanding applications have you used or considered using wireless technology?

Hi — my name’s Dave Anderson. This week I’m blogging about pain points in pH and, from an analytical perspective, there are a number of them within a biopharmaceutical plant where effective analytical monitoring can improve operations. First and foremost, the Process Analytical Technology (PAT) Initiative has opened the door to take traditional off-line, laboratory measurements and put those methodologies in the process or at the process. The customers benefit through real time measurements of key parameters. By automating the process, customers can capture the data as well as document the calibration logs electronically.

One particular pain point is with pH control in bioreactors. Customers are asking for tighter pH control, some as tight as +/- .01 pH units. One customer mentioned if they can improve pH tolerances by 10%, they estimate savings of $250,000 per batch.  The problem with maintaining tight pH measurement is how the sensors are used in the process. Prior to a batch, the pH sensors are calibrated with pH buffers to ensure the sensors will accurately respond to real process changes. After the sensors are calibrated, those chemicals must be cleaned from the sensor. The typical cleaning process is to steam sterilize the vessel at a minimum of 121º C for 30 minutes.  Some processes require steam cleaning at 145º C for 60 minutes.  The pH-sensitive glass will become stressed from the exposure to high temperatures and subsequent cooling. This stress can result in significant offsets in the pH readings or critical failures in the form of cracked glass. Because of these concerns, redundant sensors are often utilized.

To optimize plant productivity, there are new pH sensors with Accuglass^® technology that can withstand the thermal stresses from the cleaning process. For example, comparison testing with competitive sensors proved the Model 3800 steam sterilizable pH sensor will withstand more steam-in-place cycles than any sensor on the market.

Additionally, today’s transmitters can deliver real-time diagnostics at the operator’s work station. Monitoring one pH loop locally at a transmitter is simple, but when operators have hundreds to thousands of I/O points with different measuring technologies to manage, it can be overwhelming. Diagnostic information such as “glass impedance” and “zero offset” will update the operators whether a sensor has a critical failure or is beginning to drift. For those operators with less experience, there can be Embedded Help Menus that explain in detail what the conditions mean and appropriate actions to take. This is easy to access in AMS^® Suite by clicking and dragging the question mark over the field in question.

These two technologies allow plants to confidently automate pH measurement, greatly minimizing operator interface. When an operator needs to get involved, these tools allow them to make informed decisions with the assurance of accuracy and stability in the process.