Fundamentals of pH Control in Industrial, Municipal, and Commercial Applications

Handheld pH Meter & Sensor
(courtesy of Yokogawa)

Analytical measurement and control of pH within a system is necessary for many processes. Common applications include food processing, wastewater treatment, pulp & paper production, HVAC, power generation, and chemical industries.

To maintain the desired pH level in a solution, a sensor is used to measure the pH value. If the pH is not at the desired set point, a reagent is applied to the solution. When a high alkaline level is detected in the solution, an acid is added to decrease the pH level. When a low alkaline level is detected in the solution, a base is added to increase the pH level. In both cases the corrective ingredients are called reagents.

Accurately applying the correct amount of reagent to an acid or base solution can be challenging due to the logarithmic characteristics a pH reaction in a solution. Implementing a closed-loop control system maintains the pH level within a certain range and minimizes the degree to which the solution becomes acidic or alkaline.

An example of an automatic pH level control system is a water treatment process where lime softened water is maintained at a pH of 9, using carbon dioxide as a reagent. As the untreated water (or influent) enters the tank, the pH is continuously monitored by the pH sensor. The sensor is the feedback device to the controller where the setpoint is compared to the control value. If the values are not equal, the controller sends a signal to the control valve that applies carbon dioxide to the tank. The reagent is applied to the tank at varying rates to precisely control the pH level. With the pH level at 11 detected by the sensor, the controller commands the control valve to open and introduce more carbon dioxide. As the increased carbon dioxide mixes with the influent, the pH is lowered in a controlled manner. Reaching the setpoint, the carbon dioxide flow is minimized and the process is continually monitored for variation. The effluent is the treated water that is discharged out of the tank. The process continues to provide the lime softened water at the desired pH level.

A Better Load Cell for Weighing Heated, Vibration Prone Process Vessels

Most load cells are designed to handle vertical force and cannot discern errors introduced from side loading and/or torque loading. In real world conditions, though, load cells see much more than vertical loading, and unfortunately, can output erroneous values. While they are excellent for static weighing situations, such as scales, load cells typically can’t handle the rigors of process vessel applications.

A case in point is a chemical manufacturer with an several, existing three cubic meter batching tanks. It was decided the tanks needed modifications to provide more accurate weighing of the individual ingredients. The existing load cells were experiencing errors due to thermal expansion of the vessel, and the resultant side loads from expansion. Additionally there was a problem with vibration in the plant. A better solution was needed, and whatever the solution would be, the customer made it clear the new weighing system must provide system accuracy in the range of ±0.1%.

Load cell performance problems causes.

BLH KIS sensor

An approach to deal mechanically with the thermal cycling while using the same type of load cell was discussed. It involved several mechanical modifications that required significant and costly structural changes.

Another suggestion was to evaluate a unique load cell design that was particularly tolerant against thermal expansion, vibration, and high lateral forces - the BLH Nobel KIS series.  The KIS load cell offered some obvious advantages over rebuilding the tanks supports and frame, namely time and expense. Beyond the short installation time and easy modification, the KIS also offers excellent reliability and accuracy.

BLH Instrument

The customer decided to “take the easy way out” and just replace the old, error-prone load cells with KIS load cells. Installation and start-up was very easy, taking very little time. After installation, the customer was pleasantly surprised by the high accuracy of the new KIS load cells, despite the thermal expansion of the vessel and the inherent vibration.

The video below gives an excellent view inside the KIS design and why its ideal for process vessels.

Basics of pH Measurement

pH of Common Items
(image courtesy of
Wikipedia)

pH is a numeric scale used to designate the acidity or alkalinity of an aqueous solution. Solutions with a pH below 7 are acidic and solutions with a pH higher than 7 are basic. Pure water is considered neutral and are neither an acid nor a base.

pH measurement is very important in many industries including medicine, chemistry, agriculture, food science, environmental science, chemical engineering, water & wastewater treatment, and many others.

pH electrodes and sensors are the sensing portions of a pH measurement. Various installation options including retractable, flow thru, immersion, and direct insertion. Proper pH electrode/sensor selection is critical for optimal measurement results.

2 wire transmitter (Yokogawa)

pH meters, analyzers and transmitters are used for continuous process monitoring of pH to ensure water/product quality, monitor effluent discharge, batch neutralization, pulp stock, scrubbers, cooling towers, chemical, water/wastewater treatment and many other applications.

Four Wire Analyzers: 4-wire analyzers separate the power supply from the measurement output. As a minimum we need two wires for the power supply and two wires for the current output of the analyzer.

Two Wire Analyzers: 2-wire analyzers combine the wires for current output, power supply, and digital communication.

The document below (courtesy of Yokogawa) provides a comprehensive understanding of pH/ORP measurement and how to achieve reliable results. Basic information on the principles of measuring pH/ORP, the construction of the sensing elements and their basic use in process applications are provided.

The Basics of pH Measurement from Power Specialties, Inc.

For more information, contact:

Power Specialties, Inc.

9118 E. 72nd Terrace
Raytown, MO 64133
Toll Free: (800) 432-6550
Phone: (816) 353-6550
Fax: (816) 353-1740

www.powerspecialties.com

Failure Prevention: Detecting Hot Spots in Air Cooled Generators

General Condition Monitor
(courtesy of E ONE Utility Systems)

Because of advancements in air-cooled generator designs and their increasingly higher power ratings, significantly greater stresses on materials and structures is increasing the probability of overheating. An early warning system for generator hotspots can mean the difference between a brief shut down for minor repairs versus a major and costly overhaul. The solution is to incorporate Generator Condition Monitors for Air Cooled Apparatus (GCM-A).

High concentrations of sub-micrometer particles (pyrolysis products) are released whenever any material is heated sufficiently to create thermal decomposition. The GCM-A detects the pyrolysis particles emitted into the cooling air (or ambient air) as a result of overheating or arcing.

The GCM-A monitors multiple air sample lines (locations) using a highly sensitive particle detector. The detector used to make these invisible particles large enough to monitor for concentration is a Wilson Cloud Chamber. The Wilson Cloud Chamber has been used and proven effective as an early warning, air sampling type, fire detector for several decades.

One sample line monitors ambient air, which serves as a reference since the particle level in the ambient air can change significantly and influence the particle level of the generator cooling air. One or more additional sample lines (or probes) are used to monitor the generator cooling air, which is compared against the particle level of the ambient air. High particle levels in the generator cooling air, without a corresponding increase in the ambient air, confirms the source of the pyrolysis particles is from within the generator. Conversely, if the particle level in the ambient air increases the source of the overheating must be outside the generator.

A more in-depth review detecting hot spots in air cooled generators can be found here.

To discuss your interest in this application, please contact:

Power Specialties, Inc.
9118 E. 72nd Terrace
Raytown, MO 64133
Toll Free: (800) 432-6550
Phone: (816) 353-6550
Fax: (816) 353-1740

www.powerspecialties.com

Operating Principles, Applications, and Advantages of Coriolis Mass Flowmeters

Image courtesy of
Wikipedia

Oscillation without flow
(courtesy of Wikipedia)

The Coriolis effect acts on a medium that is accelerated through a rotating system, like a ball on a rotating disk its movement is straight, however, if the observer turns with the disk the ball is apparently deflected.

The same effect occurs with a water hose that rotates around its own axis, like a skipping rope. As soon as water flows through the host also twists. The twisting is stronger or weaker, depending on the amount of water flowing through the hose.

Oscillation with flow
(courtesy of Wikipedia)

The Coriolis effect also appears with an oscillating movement, and in a Coriolis flowmeter, two symmetric metal tubes are set vibrating by an internal driver coil. The tubes oscillate with a resonance frequency similarly to that of a tuning fork.

The oscillation is measured precisely by two pick-ups at the inlet and outlet sections. If liquids or gases flow through the tubes, a phase shift occurs the pickups measure the spatial and temporal displacement (twist). The amount of twist is proportional to the mass flow rate of fluid passing through the tubes. The greater the amount, the stronger the tubes oscillate outwards.

Finally, sensors and transmitters are used to measure the twist and create a linear flow signal as an output for monitoring and control.

Coriolis mass flowmeters are widely used throughout the process measurement and control field. Their basic operating principle, combined with modern sensor and signal processing technology,

Yokogawa ROTAMASS
Coriolis Flowmeter

provide a list of positive aspects.

• Directly measure mass flow rate based on the principle of measurement.
• Measure the mass flow rate with high accuracy of ±0.1%.
• Provide a wide usable measurement range.
• Deliver density measurement based on oscillating frequency.
• Not materially impacted by fluid viscosity or density.

Coriolis flowmeters also do not need straight pipe sections upstream or downstream of the flowmeter. They also have the ability to measure non-conductive fluids.

The video below is produced by Yokogawa, a world class manufacturer of industrial process measurement and control instrumentation. It provides a clear and insightful illustration of the Coriolis principle and how it is used to provide accurate mass flow measurement.

Use High Visibility Dials on Pressure and Temperature Instruments

Reotemp HiVis Dials

Here is a real-life case study of how high visibility (HiVis) dials on pressure and temperature gauges improved safety and efficiency at a US power plant.

Like most industrial plants, there were a number of recessed areas where light was blocked by equipment, piping, etc. This created low-light areas and shadows that can make it difficult to see and read instrumentation like pressure gauges. In some cases, gauges were mounted high above head and were difficult to read from the floor.

When gauges are hard to locate and read, it makes the operator’s job more difficult and increases the likelihood of human error.

Without Hi-Vis Dial

• Gauges can be misread.
• Gauges can be misidentified.
• Gauges can be overlooked. 

With Hi-Vis Dial

• Gauges are more easily seen in low light environments.
• Gauges are easier to read at a distance.
• Gauges are more noticeable and easier to locate.
• Safety is increased. Hi-Vis = Hi-Safety.

After walking around the plant and evaluating the gauge’s visibility in a few low-light areas, the plant supervisor was confident the Hi-Vis dials would increase gauge visibility and plant safety. The decision was made to transition every gauge in the facility to the Hi-Vis dials.

In the following months, over 100 Hi-Vis dial pressure gauges were installed. The operators were now able to easily locate and read all of the pressure gauges. The plant’s supervisor had successfully increased the safety in his facility and has continued to use the Hi-Vis as the standard for all new pressure gauge applications. Plans are underway to replace all existing gauges in the Cooling Towers and Chiller Plant

For more information, contact:
Power Specialties, Inc.
9118 E. 72nd Terrace
Raytown, MO 64133
Toll Free: (800) 432-6550
Phone: (816) 353-6550
Fax: (816) 353-1740

Magnetic Level Gauges for Visual Tank Level Monitoring and Control

Magnetic Level Gauges
(courtesy of Hawk Measurement)

Magnetic Level Gauges (MLG) are widely applied in the monitoring and process control of liquid level and interface for many industries; such as petroleum, chemical, power, paper, metallurgy, water treatment etc. They are suitable for real time, precise, safe and reliable continuous measurement of process level.

Based on the principle of magnetic coupling and buoyancy, the magnetic level gauge provides real-time measurement for level and interface. The Magnetic Level Gauge (MLG) is connected to a process vessel. Within the chamber is a float containing a 360° magnetic ring. Outside of the chamber is an indicator equipped with a vacuum glass tube, which contains a bi-colored two-face magnetic bargraph. In response to the level movement, the float moves accordingly, forcing the magnetic bargraph to turn and change color. True liquid level is indicated or “read” from the corresponding point on the measuring scale. The indicator uses hermetical sealed glass tube technology to clearly indicate the level, which eliminates the common problems of glass gauges, such as vapor, condensation and liquid leakage etc.

Typical Applications:

• Boiler: Steam drum liquid level
• Power generation: Auxiliary machinery liquid level (HP reheater, LP reheater, deaerator, condenser and heating network heater etc), chemical water
• Coal Chemical: Methanol, dimethyl ether, synthesis ammonia/urea, MTO, CTL, SNG
• Silicon industry: Organic silicon, polycrystalline silicon
• Petroleum and petrochemical: Oil and gas, ethylene, trimerization and etc.
• Fine Chemicals: Methane oxide, epoxy ethane, aniline, PTMEG, BDO, carbon fiber, POM,acetic acid, styrene, rubber, crude benzol refining
• Others: Metallurgy, paper-making, water treatment, biological, pharmaceutical, food and beverage etc.

Magnetic Level Gauges have a simple modular design, composed a main chamber, a float and an

Mag level gauge construction

indicator.

Typical main chamber features:

• ANSI standard design or special manufacture
• Multi-forms installation and process connection
• Chamber Material: 304/304LSS, 316/316LSS, 317SS, 321SS, 347SS, Ti2, Hastelloy C-276, Zr-702, Nickel-6, 304+PTFE, CPVC and PP.

Typical float features:

The float is the key component of the level gauge, which magnetically couples to the outside indicator, liquid level switch and transmitter.

• Hermetically sealed incompressible
• 360° magnetic ring
• 316LSS, Hastelloy C-276, Zr-702, Nickel 6, Ti2, 304SS+PFA, grade V aviation titanium alloy and other materials
• Special structure and precision manufacturing technology of pulse TIG and laser weld
• Range of temperature: -320 to 1000°F (-196 to 538°C)
• Range of pressure: vacuum to 600 psig (vacuum to 42MPa)
• Suitable for harsh working conditions, such as HTHP, cryogenics and strong corrosion.

Relationship of float, chamber and indicator.

Typical indicator features:

• 316SS or aluminium ruler
• Hermetically sealed glass tube with no contact with medium
• Magnetic bargraph is made from special high and low temperature - resistant materials
• Magnetic bargraph is mechanically interlocked to avoid random rotating
• Selectable engineering units
• Immune to oxidation, corrosion and the effects of dust