Thermal Mass Flow Meter Applications

As we discussed in last week’s blog article, thermal dispersion mass flow technology is rapidly becoming a preferred method to measure the flow rate of gas for industrial process operations. Thermal mass flow meters offer an attractive alternative to older measurement technologies, because they provide a direct, accurate measurement of mass flow rate, without having to correct for temperature and pressure conditions. Additionally, because of its properties of low flow sensitivity, wide turndown and low pressure drop, thermal dispersion mass flow measurement can improve process control in a wide variety of typical and more challenging applications.

Thermal Mass Flow Meter ApplicationsTypical Applications

  • Compressed air/gas. Measurement and totalization of compressed air or gas flow is utilized for internal plant allocation and measurement of overall consumption. Can be used for detecting and identifying general location of leaks. Government estimates show that leakage can account for 20-30% of compressed air generation. Eliminating a small ¼” leak can result in cost savings up to $4000 in a year.
  • Combustion air flow. Measurement of the mass flow rate of combustion air is desirable when determining fuel-to-air mixtures for proper combustion control. Thermal mass measurement is very appropriate due to its combination of direct mass measurement, excellent low flow sensitivity, wide turndown and low pressure drops.
  • Natural gas. In-plant measurement of natural gas flows to boiler, furnaces, dryers and heaters is an ideal application for thermal mass flow measurement. Knowing the natural gas usage of individual combustion sources can help identify efficiency, leading to reduced fuel usage. The composition of natural gas may vary slightly during the year. These changes in heat transfer characteristics of the gas are minor and will not have any noticeable effect on a thermal mass flow meter’s performance.
  • Greenhouse gas emissions. The EPA requires many facilities to annually report their greenhouse gas emissions from each combustion source. A thermal mass flow meter is an ideal method of determining the natural gas usage, in order to follow the EPA guidelines to calculate greenhouse gas emissions.

Difficult Applications

  • Flare lines. Thermal dispersion mass flow offers many benefits for flare lines – wide turndown, low flow detection and low pressure drop. Thermal flow measurement has successfully been used in this application. However, consideration must be given to changes in gas composition.Different gases have different thermal properties that affect convective heat transfer. Changes in gas composition will change heat transfer rates, resulting in inaccuracies in flow measurement.If used in a flare line with a consistent gas composition such as natural gas, there is no difficulty. However, if used in an application with wide variations in gas composition, especially major changes in concentration of hydrogen, the user must be aware of the considerable potential for inaccurate flow measurement. Hydrogen cools the sensor much greater than other gases; a small flow of hydrogen will appear like a much larger flow of hydrocarbon gases. In those applications with varying gas compositions, a thermal mass flow meter, such as the Thermatel® Model TA2, will provide a relative flow measurement. It can be used to provide an indication of changes and magnitude in flow rate, as well as duration of a release to the flare. Often a Model TA2 mass flow meter will be used to monitor the flow to the flare from individual production units, with a different technology flow meter measuring the main flare flow for environmental reporting or obtaining a mass balance. Provided that the flow meter is used for flow monitoring rather than flow measurement, consideration should be given to a simple calibration rather than trying to calibrate for an exact gas mixture.
  • Stacks. While thermal mass flow measurement has successfully been used for measurement of stack flow, generally multiple point array systems are utilized for large diameter stacks. Another option is to use four or more single point probes inserted from opposite sides of the stack. An external device is needed to average the flow rate.

For a complete overview of thermal mass flow technology, methodology and applications, Magnetrol® invites you to download our THERMATEL Thermal Dispersion Mass Flow Measurement Handbook.

Mass Flow Rate Handbook

Direct Mass Flow Rate Measurement for Industrial Process Applications

There are many well-established technologies used to measure the flow rate of gas within industrial process operations. While mass flow rate is the ideal measurement for typical process applications, common measurement methods, including differential pressure, vortex shedding, and ultrasonic, among others, measure actual volumetric flow rate and not mass flow rate. Therefore, flow meters based on these technologies must correct for temperature and pressure conditions in order to provide an accurate measurement of mass flow rate.

Thermal mass flow technology, a more recent approach to gas flow measurement, does not require correction for changes in process temperature. As a result, the adoption rate for this technology is rapidly increasing. As a newer mass flow rate solution, however, many process control professionals aren’t familiar with how thermal dispersion mass flow meters work – and their advantages.

Principle of Operation

Thermal mass flow meters use temperature sensors (RTDs) located at the bottom of the probe to measure mass flow rate.

Thermal mass flow meters use temperature sensors (RTDs) located at the bottom of the probe to measure mass flow rate.

Thermal dispersion mass flow meters are primarily used in air and gas flow measurement applications. The meters consist of a transmitter and probe with temperature sensors (RTDs) located in the pins at the bottom of the probe. One sensor measures the process temperature and the other sensor is heated to a specific temperature above this. As the flow rate increases heat gets taken away from the heated sensor. Some manufacturers use a variable power operation to keep the temperature difference constant, while others keep the power constant and measure the temperature difference. The Magnetrol® Model TA2 thermal mass flow meter measures the power it takes to maintain a constant temperature difference between the sensors. This relationship between power and mass flow rate is established during calibration.

Technology Advantages
Thermal Mass Flow offers many advantages over other, more traditional, methods of measuring gas flow.

Excellent Low Flow Sensitivity. Thermal technology can measure velocities down to 10 standard feet per minute – much lower than any other flow device. The heat transfer rate is greatest at low flow rates and decreases as the flow rate increases. This makes this technology especially sensitive for low velocity measurement and high turndown requirements.

Excellent Turndown. The Model TA2 thermal mass flow transmitter offers the ability to measure low velocities as well as high flow rates. This can provide a turndown rate of 100:1 or more, depending upon the application requirements and calibration of the instrument.

Low Pressure Drop. The insertion probe has little blockage of the pipe, thereby creating very low pressure drops.

Ease of Installation. Using an insertion probe, the instrument can easily be installed in a pipe or duct. Many installations use a compression fitting or a retractable probe assembly for inserting the probe into the pipe.

Factory Calibration. Instruments are calibrated by leading manufacturers for application-specific requirements and user specifications. This allows the instrument to be installed and placed directly into service without the need for field setup, calibration or adjustment. MAGNETROL calibrates all Model TA2 thermal mass flow meters.

Low Installed Cost. No additional instrumentation is required to obtain a mass flow measurement using a thermal dispersion mass flow meter.

Mass Flow Rate Handbook

Webinar: Optimizing Level Control to Meet New Power Generation Demands

Register Now For This Informative Webinar

The addition of non-conventional, renewable power generation to the energy mix and the ongoing development of climate change protocols are having a significant impact on the operation of conventional fossil plants. Addressing limitations in flexible operation (such as cycling, ramp rates, load following and others) attributed to critical level controls with enhanced technologies can help ensure rapid response to market demands while mitigating system stress, unit trips and the negative consequences on heat rate.

Coal Fueled Power PlanOn November 12, 2014, at 11 am ET, Magnetrol® and Orion® Instruments will be sponsoring a free webinar on “Optimizing Level Control to Meet New Generation Demands.” The webinar will be led by Donald Hite, business development manager for the Power Industry division of MAGNETROL, and will address the following topics:

  • Level control concerns (including steam drums and feed water heaters)
  • Effects on ramp rates and cycling
  • Cost of heat rate deviation
  • Eliminating instrument induced errors
  • Optimizing performance
  • Case studies

MAGNETROL is committed to using its extensive expertise in level and flow technologies to explore challenges and new opportunities in the various industries that use its products. Join us for this webinar!

Optimizing Level Control Webinar

Magnetrol® Celebrates Facility Expansion in Zele

Magnetrol® International, Incorporated recently completed its new expanded facility in Zele, Belgium, and held the facility grand opening on Saturday, October 25. The grand opening event celebrated the growth that led to the expansion of the facility and included employees, distributers, and local leaders and dignitaries.

Magnetrol_Zele_ExpansionAround 340 people were invited to the evening, which highlighted some of the countries where MAGNETROL has physical offices. Dance performances and a buffet dinner took attendees on a journey through these countries, including the United Kingdom, Germany, Italy, India, the United Arab Emirates, Russia, the United States, and, of course, Belgium. The evening also featured a ribbon cutting, as well as interviews with local dignitaries—including the Governor of East Flanders, the Mayor of Zele, and the Deputy Chief of Mission from the U.S. Embassy—and MAGNETROL leaders. On Sunday, October 26, friends and family of MAGNETROL employees had a chance to walk through the building and tour the new facilities.

Look for Robust Liquid Level Switch Design in Mechanical Buoyancy Level Controls

Mechanical buoyancy type liquid level switches were one of the first technologies used to measure fluid levels in process industries, and the devices remain a workhorse for reliable level detection in a wide range of applications, including those in the most challenging or hazardous environments.

When considering the specification of mechanical buoyancy level control instrumentation, it’s important to recognize that the design and construction of the magnetic switch mechanism – the driving component within mechanical buoyancy liquid level switches – has significant bearing on the performance characteristics of the unit.

Liquid Level Switch Mechanism

Magnetrol®, the manufacturer of the first magnetic switch designed for liquid level detection, has spent more than 80 years perfecting mechanical buoyancy switches. The following MAGNETROL switch design features demonstrate how intelligent design impacts the quality and reliability of mechanical buoyancy liquid level control solutions:

Switch Mechanism

  • Completely isolated from the process environment to prevent magnetic interference and protect integrity of switch activation.

Magnet Design

  • Magnet placed on non-wetted side of pressure boundary to prevent magnetic particles from adhering to magnet and affecting switch action.
  • Alnico magnet material ensures stability.
  • All magnets are stable to over +1000°F (+540°C).
  • Magnets “saturated” and “knocked-down” to ensure stable charge over the lifetime of the switch.

Return Spring Design

  • Return springs heat-treated to ensure consistent properties and performance over a vast temperature range.
  • All return springs used only within their elastic range to prevent damage and distortion.
  • Each return spring designed for required reset force of micro switch.

Pivot Design

  • Pivot pins machined for precision fit and smooth rotation.
  • Designed with “play” at pivots and magnet to prevent binding.
  • Adjusting screw factory-set for optimal micro switch actuation point and over-travel on both pull-in and fall-out, to ensure reliability over changing conditions.

Switch Design

  • Mercury-free, high-temperature switches for process temperatures greater than +1000°F (+540°C).
  • Silver or gold contacts that work for standard or low current applications.
  • Standard or hermetically sealed micro switches.
  • Ceramic terminal blocks provided on highest temperature applications.
  • Lead wire insulation for all application temperatures

The design integrity of MAGNETROL switch mechanisms has allowed our level controls to provide years of safe, accurate, reliable level control – with many clocking in more than a half-century of trouble-free service. For more information about MAGNETROL liquid level switch solutions, download the Mechanical Buoyancy Switch Mechanism Design Guide.

CTA Liquid Level Switch Design

Float Chamber Construction of an External Cage Level Switch an Indicator of Quality and Reliability

External cage level switches remain one of the most reliable level detection technologies available to process industries. These liquid level switches must perform in a wide range of level control applications, from basic to challenging or even hazardous. In fact, many external cage level switches must comply with the standards set out by industry authorities, such as NACE and ASME, to fulfill safety requirements pertaining to oil and gas processors, power generation plants and other sectors.

When specifying level measurement instrumentation, it’s important to recognize that its design and manufacture should fully support the needs of your critical applications. The float chamber in external cage level switch devices is built to meet specific industry ratings, making its construction an excellent indicator of the quality and reliability of the overall unit. Here are several hallmarks of design integrity of the float chamber.

Series3 External Cage Level SwitchLook for Best-In-Class Float Chamber Design and Benefits

  • Magnetic Attraction Sleeve: no magnet in process to attract ferrous particles
  • Spiral Wound Head Flange and E-Tube Gaskets: Suitable for high pressures, high temperatures and steam service
  • All Stainless Steel Trim Parts: Corrosion resistant
  • Overall Designed for High Pressure: Suitable for the toughest conditions
  • Bolting Per ANSI B16.5
  • ASME Section IX Welding: Performed by qualified welders to qualified procedures, documented and traceable
  • Weld Examination Per ASME B31.1/B31.3: Visually inspected, radiography and liquid penetrant testing as required, documented and traceable
  • Welded Float and Stem Assembly: Provides durability
  • Hydrostatic Tested at 1.5 Times Rated Pressure, Including Float: Verify pressure boundary with safety margin
  • Full Penetration Chamber and Branch Welds: High strength weld
  • Integrally Reinforced Forged Branch Outlet (Bonney-Forge style) Couplings: Allows full penetration welds
  • Low SG Floats and Displacers: Suitable for most applications
  • ASTM Listed Pressure Boundary Parts Procured with Certificate of Conformance: ASME compliance
  • Designed With Allowable Stresses Per ASME B31.1/B31.3
  • Flanges ANSI B16.5 Compliant
  • Welds and HAZ Hardness Tested: Ensures hardness levels compliant with NACE standards
  • Post Weld Heat Treatment of All Welded Carbon Steel Components: Ensures hardness levels meet NACE requirements
  • Solution Annealing of Stainless Steel Parts as Required: Ensures hardness levels meet NACE requirements

Magnetrol® manufactures an extensive offering of vertical and horizontal float and displacer switch and transmitter devices that represent the industry standards for highly reliable, highly repeatable performance. Unlike some competitive float chambers constructed “to the intent” of ASME standards, MAGNETROL chambers are designed to ASME B31.1, ASME B31.3, NACE MR0175 and MR0103 standards, meeting the toughest industry specifications. Quality engineering benchmarks have resulted in decades of maintenance-free performance from MAGNETROL liquid level switches – some of which have been in the field for as long as 50 years.

For more information about NACE and ASME specifications and float chamber construction, download the MAGNETROL Float Chamber Design Guide.

External Cage Level Switch Design

Magnetrol Elected as Regional Voka Ambassador

Zele, Belgium, September 18, 2014- Magnetrol International NV, in Zele, Belgium, was recently elected as a Regional Voka Ambassador for the Dendermonde region. The Voka Ambassadors program recognizes excellence in entrepreneurship throughout the East of Flanders.

Magnetrol employees accept the Voka Ambassador election. From left to right: Katrien Geerinckx, Johan Vanderyse, Marc Baert, Geert de Ruysscher, Maddy de Loose, Ann Robberecht, Paul D'Hoey and Steven Decrock.

Magnetrol employees accept the Voka Ambassador award. From left to right: Katrien Geerinckx, Johan Vanderyse, Marc Baert, Geert de Ruysscher, Maddy de Loose, Ann Robberecht, Paul D’Hoey and Steven Decrock.

Each year, Voka selects the regional Ambassadors based on a financial analysis and other information about the company’s business model. Voka then assigns a score to each company. The highest-scoring companies are given a chance to make a brief presentation to the Voka jury. This jury (and the audience) then elects the Ambassador based on the high scores and the strength of the presentation. Magnetrol was the elected Ambassador for the Dendermonde region and will compete against other regional Ambassadors in a further competition for the East of Flanders Ambassador on November 24.

Ultrasonic Level Transmitter Instrumentation Revives Transformer Sumps

A Magnetrol® Applications Study:

A key regional energy company owns a large coal-fired electric generating facility in the Midwest, with seven coal-fired units creating a total of 2,220 megawatts. The facility was part of the company’s massive environmental retrofit projects, an undertaking that included new selective catalytic reduction (SCR) and wet flue gas desulfurization (FGD) equipment, all of which will greatly reduce nitrogen oxide and sulfur dioxide emissions.

Ultrasonic Level Transmitter Use in Power GenerationFor the project’s transformer sump level monitoring, competitive non-contact ultrasonic level transmitter units were installed. But it wasn’t long before Magnetrol® received a call from the energy company saying that several applications with the competitor’s ultrasonic transmitters were not working consistently. Our customer informed us that they wanted replacement units that were both 120 VAC-powered and loop-powered. The Echotel® Models 335 and 355 ultrasonic level transmitter units were put to the test.

After demonstrating key features of the two ECHOTEL units, we toured the plant for a closer look at the applications. Each of our competitor’s transmitters showed loss-of-echo on their display. There was nothing particularly unusual about the application other than the presence of a slight surface agitation. The level range was less than ten feet (3m).

The ECHOTEL 335 was trialed so that the customer could gauge performance in the most demanding applications. The no-obligation trial lasted two weeks. After that period of time, the customer confirmed the ECHOTEL transmitter worked without a single loss of echo during the entire trial. The customer immediately ordered three Model 335s and two Model 355s. The units have been installed and are working fine.

The success at this large coal-fired plant has carried over to other plants owned by the energy company. Currently, dozens of ECHOTEL ultrasonic transmitters are helping this customer generate over 20,000 MW. The power industry is second only to the municipal industry for sales of ECHOTEL non-contact loop- and line-powered transmitters.

Level Measurement Techniques: Minimizing Guided Wave Radar Probe Buildup

Level measurement applications in natural gas, condensate and crude processing have some special requirements that are not always evident from instrument data sheets. The potential of solids or other materials building up on a guided wave radar probe is one example. The experience of Magnetrol® field engineers has led to the development of some simple but effective level measurement techniques to address field issues related to buildup that may not be evident in data sheets.

Level Measurement Techniques Radar Probe Buildup

A sampling of probes for the Eclipse® GWR Transmitter

Natural gas, condensate and crude processing applications can experience paraffin, asphaltenes, grit and grime. The degree to which any of these can accumulate on guided wave radar (GWR) probe buildup varies by application. Even in applications where buildup isn’t typically prevalent, it can happen over time, during cold weather periods, or when bringing units up or down due to temperature, pressure and process material fluctuations. Like distillation columns, chambers/cages/bridles may require cleaning from time to time. Below are some good practices that can minimize buildup and reduce maintenance time.

  • The use of enlarged coaxial GWR probes with more clearance reduces the chance for buildup to occur.
  • Consider using a chamber probe whenever possible. Magnetrol® offers a unique family of chamber probes, which combines the sensitivity and performance associated with coaxial probes with the viscosity immunity of a single rod.
  • Insulate the probe necks of overfill probes to reduce any cooling at the top of the probe inside the vessel, chamber, cage or bridle.
  • Chambers should be insulated even in warm weather locations. The temperature differential between a warm/hot vessel (like a separator) and uninsulated chamber/cages can be significant, resulting in paraffin deposition and/or viscosity increases.
  • Insulate chamber flanges to reduce any cooling at the top of the probe.
  • Use probes with integral flushing connection to simplify flushing/dissolving paraffin or grit. Flushing connections are an option available on all MAGNETROL coaxial GWR probes.

Eclipse Microsite


The global power generation industry is rapidly changing. Increases in power consumption, economic growth and environmental pressures are creating significant opportunities for safe and reliable plant operation.

Power Plant Efficiency Opportunities
Level control applications in power plants lend themselves to performance improvements that can enhance a plant’s overall safety, efficiency or profitability. Technologies offering more precise level indication that are not affected by process variables provide operators with the ability to better manage overall power plant performance. For example, feedwater heaters in coal-fired plants historically suffer from inefficiencies due to poor level controls, which increase heat rate, thus reducing efficiency. The illustration below indicates some of the most common level control applications in the power generation industry.

Liquid Level Applications

Power Plant Efficiency Opportunities

  1. Fuel Oil Storage: Crude oils with lower flash points represent a greater fire hazard and require safety-certified liquid level switches and transmitters.
  2. Open Atmosphere Sumps: Level control in collection and processing basins must often tolerate corrosive media, punishing weather conditions and liquids with high solids content.
  3. Condensate Storage: Accurate, reliable liquid level monitoring in the condensate storage tank ensures the proper supply of make-up water.
  4. Deaerator: Pressure fluctuations are extensive in the deaerator and result in flashing, thereby requiring level controls that can withstand varying temperatures and pressures.
  5. Condensate Drip Legs & Drains: Level instrumentation must contend with high temperatures and pressures associated with drip legs, to ensure proper functioning of the condensate collection system and prevent damage to the turbine.
  6. Steam Drums: Precise level in the steam drum is important to optimize steam/water separation and steam quality.
  7. Condenser Hotwell: Level control in the hotwell can prevent make-up water loss in the turbine cycle due to leakage, steam venting or other usage.
  8. Feedwater Heaters: Feedwater heater level is controlled to prevent damage to expensive hardware, while at the same time optimizing level control to improve efficiency (heat rate) during base load, as well as load following operations.
  9. Boiler Blowdown Tank: Good boiler blowdown practices reduce water treatment needs and operation costs, as well as the chance of catastrophic explosion.
  10. Lubrication Oil Tanks: Reliable level monitoring of lube oil reservoirs ensures proper functioning of turbines, electrical generators and other equipment with integral lubrication systems.
  11. Ammonia/Caustic/Acid Storage: Managing hazardous and non-hazardous chemical storage inventory and replenishment safely and reliably is critical to ensure availability during normal operation.
  12. Cooling Tower Basin: Proper level control in the cooling tower basin eliminates low-level damage to pumps, while preventing costly overflow conditions. Vulnerability to foam from chemical injection and modest buildup considerations are fundamental to selecting the correct level technology.

Liquid Level Control Solutions
Magnetrol offers the power generation industry one of the most complete lines of liquid level control technology solutions, as well as extensive power plant efficiency applications experience for challenging process control environments.

  • Series 75 Sealed External Cage Liquid Level Switch: Self-contained units designed for side mounting to a tank or vessel with threaded, socket weld or flanged pipe connections.
  • Series B40 High-Pressure/High-Temperature Liquid Level Switch: Specifically designed for HPHT service conditions such as boilers, available in rugged industrial or ASME B31.1 construction.
  • Tuffy® II Side-Mounted Float Switch: Compact-sized, float-actuated device for horizontal mounting in a tank or vessel through threaded or flanged pipe connections.
  • Digital E3 Modulevel® Displacer Transmitter: Advanced, intrinsically safe two-wire instrument utilized buoyancy principle to detect and convert liquid level changes into a stable output signal.
  • Displacer Type Liquid Level Switch: Offering a wide choice of alarm and control configurations, these units are well suited to simple or complex applications, including foaming or surging liquids and agitated fluids, and typically cost less than other level switch technologies.
  • Eclipse® Model 706 Guided Wave Radar Transmitter: Loop-powered, 24 VDC device utilizes diode-switching technology for outstanding signal strength, and offered with a comprehensive probe offering for a wide variety of applications.
  • Pulsar® Model RX5 Pulse Burst Radar Transmitter: The latest generation of non-contact radar transmitters offers lower power consumption, faster response time and ease of use, compared to most loop-powered radar transmitters.
  • Model R82 Pulse Burst Radar Transmitter: An economical, loop-powered, non-contact radar transmitter that brings radar performance to everyday applications.
  • Magnetic Level Indicators: AtlasTM and Aurora® magnetic level indicators offer reliable visual indicator solutions, with or without accompanying continuous level transmitters.
  • Jupiter® Magnetostrictive Transmitter: High accuracy and high linearity at a reasonable price.

Power Plant Efficiency