Expert Answers to Thermal Mass Flow Questions

The Magnetrol® flow portal, flow.magnetrol.com, provides information about thermal mass flow meters and how they can improve the efficiency and safety of many processes. Periodically, MAGNETROL product manager Tom Kemme answers questions about flow meters in the portal’s Ask the Expert column. This week’s blog shares some recent Q&As.

thermal mass flow meters

Magnetrol® expert Tom Kemme answers your questions.

Will thermal mass flow meters be affected by changes in the composition of gas (i.e. will they require recalibration every time the composition changes)?

Thermal mass flow meters measure a flow rate based on convective heat transfer. Fluid properties are some of the many factors that influence convection. Each gas has unique properties, which is why these flow meters are calibrated for a specific application. You would not want a meter calibrated for an air application placed into a natural gas application without recalibration or some type of field adjustment if applicable.

All gas mixes are not created equal. If you had a gas mix with high hydrogen content, a variation in hydrogen would have a much greater effect than typical variation in natural gas content. Hydrogen has a tendency to create more heat transfer than most gases. For natural gas, it is common to have some slight variation in composition between the calibration of the device and the application itself. However, the effect is minimal for slight changes in methane or ethane at different times of the year. Natural gas fuel flow is one of the most prevalent applications for thermal mass.

Based on our experience, the biggest cause of malfunction in flow meters is improper installation. If you do not install a flow meter per the manufacturer’s recommendation this will greatly influence the performance of the meter. For thermal mass, this includes proper straight run, depth into the pipe (insertion probes) and flow arrow alignment.

Each application presents unique difficulties for every flow meter technology, and each end user has unique needs. There is no exact answer as to when a recalibration would be needed for thermal mass flow, as it is application dependent. You do not always need recalibrations for variation in gas composition.

What role do thermal flow meters play in emissions monitoring applications?

Thermal flow meters are at the forefront in flow measurement for emissions reporting and energy management projects. The energy management arena spans many markets, including some of the largest in the oil & gas and power industries. Some popular applications include monitoring gas fuel flow to a combustion source to report SO2 (sulfur dioxide) emissions, stack (flue) gas flow in power plants as part of a continuous emissions monitoring (CEM) system of NOX (nitrous oxide) and SO2, and flares in a gas field that need to be reported to environmental authorities. These applications prove difficult for many flow meter technologies.

For example, in a flare application most of the time gas is not being flared off, but it needs to be measured in case of an event. The user will want to monitor the low flow of pilot gas keeping the flare lit. This requires a flow meter with a very high turndown with good low flow sensitivity, which is a limitation of some technologies, such as differential pressure flow meters.

Many operators are most concerned with measuring CO2 (carbon dioxide) emissions. However, with thermal flow meters we are increasingly finding applications with the need for methane measurement. Methane is a greenhouse gas that has more than 20 times the global warming potential as CO2. No longer can coalmines or landfills emit this directly to the atmosphere. If not flaring the gas off, the owners are beginning to capture it, treat it, and produce usable natural gas from it. Some facilities that emit landfill gas, or facilities that produce biogas, are involved in carbon credit programs or clean development mechanisms. Similar applications can be found in wastewater treatment plants where customers are reporting digester gas emissions and even capturing this gas to produce electricity and reduce energy costs. Thermal dispersion flow meter technology, such as the MAGNETROL Thermatel® TA2, has become well accepted in all of these markets.

For more information, or to ask Tom Kemme a question about thermal mass flow technology, visit flow.magnetrol.com.

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Level Measurement Solutions for Ammonia Storage

Vaporized ammonia is used in catalytic and noncatalytic reduction systems for emissions control in power plants. Ammonia is injected into the flue gas stream and acts as a reducing agent. The EPA mandates the reduction and control of these emissions, and ammonia is a key part of ensuring that a power plant is in compliance with EPA regulations. It is also used to enhance precipitator efficiency for particulate control. In order to keep the supply of ammonia readily available for usage and avoid spillage or accidents, a robust ammonia storage system with accurate level measurement must be in place.

ammonia storage

An ammonia storage tank at a power plant.

Magnetrol® has produced an applications brochure for the power industry, detailing measurement challenges and solutions for each step of the power generation process. This blog post is part of an occasional series exploring each application in detail.

Level Measurement Challenges and Considerations

Pure ammonia is stored in a pressure vessel rated for 250 to 300 psig. Aqueous ammonia (70 to 80% water) is stored in a tank rated for 25 to 30 psig. Storage requirements for aqueous ammonia are three to four times that of pure ammonia. A level measurement device for ammonia storage tanks must be able to withstand pressure and still measure accurately. Accidental atmospheric release of pure ammonia vapor can be hazardous, so safety and environmental measures may be required which affect the level control selected.

Level Measurement Solutions

MAGNETROL has produced several level measurement solutions for ammonia storage tanks:

  • For point level
    Model A15 displacer-actuated switch
  • For continuous level
    Eclipse® Model 706 guided wave radar transmitter with 7XP coaxial probe
  • For visual indication
    Atlas™ or Aurora® magnetic level indicators can be supplied with switches or transmitters

More Information

 For more information on level instrumentation for ammonia storage tanks or other power industry applications, download the power industry brochure.

power generation

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Flow Instrumentation Solutions for Tank Blanketing

Tank blanketing, or tank padding, is the process of injecting a gas into the empty space in a storage container. Nitrogen—the most widely used commercial gas—is the ideal tank blanketing gas when injected into the vapor space of a storage tank. It prevents ignition of flammable liquids, inhibits vapor loss, and protects chemicals from oxygen and moisture degradation. Nitrogen is also used as a purging agent and in cryogenic applications. tank blanketing

Magnetrol® has produced a brochure detailing different level and flow applications in ethylene plants and exploring measurement challenges and solutions for each one. This blog post is part of an occasional series exploring each application in detail.

Tank Blanketing Challenges and Considerations

For proper measurement and control of the gas used for tank blanketing, any flow instrumentation device needs to be sensitive to extreme low flows and pressures. Otherwise, the instrument will not be able to detect minor changes in the amount of gas in the tank. Flow monitoring of feed lines can prevent unsafe conditions that may arise when gas supply is insufficient. High-quality flow measurement can also ensure economical mass flow totalization.

Flow Measurement Solutions

Mass flow measurement is generally a trusted solution to monitor the nitrogen blanketing gas. A mass flow meter can track usage as a cost control measure and determine the particulars of gas usage.

MAGNETROL produces the Thermatel® TA2 thermal mass flow meter for use in these applications.

More Information

For more information about measurement solutions for tank blanketing and other ethylene plant applications, download the ethylene industry brochure. And to learn more about the THERMATEL TA2, visit flow.magnetrol.com.

ethylene brochure

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The Elusive Search for Non-Contact Radar Nirvana

When it comes to measurement, the ultimate goal for operators in the process industries is to find a trouble-free, loop-powered level transmitter that can be mounted, wired and forgotten. As instrument shops’ staffing has been whittled back to a minimum, it has become the goal of many manufacturers to meet that challenging need for “plug and play” devices. So, how close have we gotten to applying two wires and walking away? This blog post explores the search for non-contact radar nirvana and how radar technology has evolved over the years.

A History of Radar Advancements

In the late 1990s and early 2000s, low-cost, loop-powered radar burst onto the scene. It was enthusiastically applied due to its ability to work even in the changing conditions that plagued the most popular technologies of the time. No longer would changing specific gravity ruin the accuracy of DP cells or displacers, or changing dielectric spoil the performance of RF capacitance devices, or vapor space changes affect the propagation consistency of ultrasonics. In short, a new age was upon us.

non-contact radar level transmitter

The Pulsar® Model R86 radar transmitter.

Radar had already evolved into two variations: Non-contact/through-air (antenna-based) and contact/guided wave (probe-based). In a perfect world all transmitters would be non-contact so they would not have to contend with contacting the dirty, coating-prone, turbulent liquids that can wreak havoc with performance and mechanical integrity. However, since guided wave radar (GWR) employs a metallic probe, a highly efficient electrical path is provided to propagate the signal. This allows for extremely strong radar reflections from the liquid surface, thus providing excellent performance in difficult conditions.

A Love-Hate Relationship

Non-contact radar (NCR) slowly became the technology many people love to hate. Theoretically, NCR can be so effective it should be everyone’s first choice. It is small and easy to install. This means that measurement in tall tanks does not necessitate a long, expensive and unwieldy probe like GWR, and the device sits up high in the tank, away from the tank contents. However, the vagary of launching an electromagnetic signal into space and waiting for its return is fraught with potential complications: false reflections from objects in the vessel, severe turbulence that can scatter the signal and foam that can absorb it are just some of the issues that exist to render NCR ineffective. Users reported challenges getting these devices ideally configured, which discouraged others from using them.

The Goldilocks Dilemma

Two of the keys to the effective use of NCR are correct installation and proper configuration. Installation includes avoiding sidewall and false target reflections. Configuration is getting the gain (amplification) settings just right. This is the “Goldilocks dilemma”— it can’t be too hot or too cold—too hot (excessive gain) and the echo saturates (distorts), deteriorating accuracy; too cold (insufficient gain) and the weak signal is lost. Optimal configuration is not an impossible task, but it is one that has eluded many good instrument personnel.

How Circular Polarization Helps

Electromagnetic energy can be launched using linear or circular polarization. Linear polarization has a constant E-field and needs adjusting to avoid sidewall reflections. To remove these launcher adjustments, the new Pulsar® Model R86 non-contact radar transmitter from Magnetrol® employs circular polarization which has a rotating E-field. In this way, no antenna adjustment is necessary during commissioning, getting the user closer to the “plug and play” goal.

When configured properly, the Model R86 can be everyone’s go-to transmitter. Having said that, no transmitter ever made is totally trouble-free. But if problems occur, MAGNETROL should have the ability to diagnose them quickly and bring the device back on line as fast as possible.

That means no more waiting for the trouble-free, loop-powered level transmitter that can be mounted, wired and forgotten. Non-contact radar nirvana is finally here.

For more information about this new innovation in non-contact radar, visit r86.magnetrol.com.

R86 transmitter

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Level Measurement Solutions for Fuel Oil Storage

In coal-fired power plants, fuel-fed igniters initiate the boiler flame and start the combustion process. Most power plants use natural gas or atomized fuel oils such as light grade #2 or heavy grade #6. Natural gas and propane can also be used. In combined-cycle plants, gas turbines often use natural gas and liquid fuel oils as ignition fuel. Large gas turbines are designed to operate alternately or simultaneously with both gas and liquid fuels. In dual-fuel plants, a False Start Tank will temporarily hold diesel fuel after an unsuccessful attempt to fire the turbine. Plants may have several fuel oil storage tanks for different purposes such as these.

Magnetrol® has produced an applications brochure for the power industry, detailing measurement challenges and solutions for each step of the power generation process. This blog post is part of an occasional series exploring each application in detail.

fuel oil storage

Fuel oil storage tanks.

Level Measurement Challenges and Considerations

At any plant where fuel is stored, the risk of fire and accidents has to be carefully managed. The level of fuel must be kept stable to prevent overflow and spillage. All possible fire safety precautions must be taken. In particular, crude oils with lower flash points represent a greater fire hazard and require more extensive fire protection systems. Switches and transmitters should be safety certified to ensure they provide the strongest possible protection. They should also be reliable at detecting both low and high levels.

Level Measurement Solutions

MAGNETROL has produced level measurement solutions for fuel oil storage tanks:

  • For point level
    Displacer level switches
  • For continuous level
    Eclipse® Model 706 guided wave radar transmitter; Pulsar® Model R86 pulse burst radar transmitter; or Echotel® Model 355 non-contact ultrasonic radar transmitter

More Information

For more information on level measurement solutions for fuel oil storage tanks and other power industry applications, download the power industry brochure.

power generation

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Level Solutions for Liquefied Gas Storage

Gases are frequently converted to a liquid in order to facilitate convenient storage. Many gases liquefy by cooling at normal atmospheric pressure, while others require pressurization as well. Industrial gases commonly stored in this fashion include liquid oxygen, liquid nitrogen, liquefied chlorine, liquefied natural gas and liquefied petroleum gas. Liquefied gas plays a role in the ethylene industry as well. Feedstock to an ethylene plant’s fractionation towers contains a liquid cryogenic hydrocarbon mixture as a result of going through compression and refrigeration trains after the quench tower.

liquified gas storage

A liquefied gas storage tank.

Magnetrol® has produced a brochure detailing different applications throughout the ethylene industry and exploring measurement challenges and solutions for each one. This blog post is part of an occasional series exploring each application in detail.

Liquefied Gas Level Measurement Challenges and Considerations

Above- or below-ground insulated storage tanks are built to specifically hold liquefied gases and minimize the amount of evaporation. Liquefied gas storage tank level monitoring typically contends with pressurization, extremely low temperatures and low dielectric media. Any instrument measuring liquefied gas must be able to produce an accurate, reliable reading in these challenging process conditions.

Level Measurement Solutions

MAGNETROL offers a range of level instruments for liquefied gas and cryogenic storage:

  • Eclipse® Model 706 guided wave radar transmitter
  • Pulsar® Model R86 pulse burst radar transmitter
  • Echotel® 961 and 962 single and dual point ultrasonic level switches
  • Aurora® or Atlas™ magnetic level indicator

More Information

For more information on level measurement solutions for liquefied gas storage and other ethylene industry applications, download the ethylene industry brochure.ethylene brochure

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Introducing the Model R86, A New Non-Contact Radar Level Transmitter From Magnetrol®

Non-contact radar transmitters are used in a variety of industries, from oil and gas to water and wastewater to chemical manufacturing. The reliability, safety and ease of use of a non-contact radar level transmitter makes it a natural choice for many difficult process conditions.

At Magnetrol®, we are taking these transmitters to the next level with our latest innovation.

MAGNETROL is introducing the Pulsar® Model R86, our first industrial, 26 GHz pulse burst non-contact radar transmitter. Based on a platform developed for the Eclipse® Model 706 guided wave radar transmitter, this new PULSAR transmitter is the product of over 13 years of MAGNETROL radar design and application experience. The design and performance improvements offered by the higher frequency signal makes this transmitter the first choice for many applications.

non-contact radar level transmitter

The Pulsar® Model R86 radar transmitter.

The Model R86 offers many features and benefits, including:

  • Improved performance. The 26 GHz radar signal has a smaller wavelength, allowing for smaller antennas and improved resolution.
  • Circular polarization. With circular polarization, there’s no need to adjust the antenna to avoid false targets. This simplifies installation and delivers proper alignment in virtually every application.
  • Nozzle extensions to 72” (1.8 meters). The R86 can be installed into nozzles longer than 12” (300mm). This means non-standard nozzle lengths and underground vessel standpipes are never a problem.
  • Improved diagnostics. The graphic LCD display clearly communicates performance issues and displays troubleshooting tips when necessary. This helps reduce downtime.
  • SIL 2 capability. SIL 2 hardware compliance is standard. The Safe Failure Fraction (SFF) of 93.2% reflects high reliability.
  • High temperature, high pressure antennas. The antenna range of up to 750 °F (400 °C)/ 2320psi (160bar) allows installation into demanding applications and punishing conditions.

If you’re interested in learning more about the new PULSAR Model R86, and the advanced features of this non-contact radar level transmitter, visit the R86 site.

R86 transmitter

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Verifying Thermal Mass Flow Meter Calibration in the Field

When Magnetrol® sends a Thermatel® TA2 to a customer, the instrument is already pre-configured and calibrated for the specific application where it will be used. Whether the TA2 is being used to measure natural gas at an upstream oil and gas facility, nitrogen tank blanketing in a chemical plant or digester gas in a wastewater treatment plant, it arrives to the customer ready to use. However, many customers utilize these meters for regulatory purposes or for energy management projects, and want to verify reliability and performance in the field, most often on an annual basis. If the instrument has to be sent back to the manufacturer, recalibrations can cost tens of thousands of dollars and cause process downtime or loss of measurement. To meet these needs, MAGNETROL has developed a procedure to verify thermal mass flow meter calibration at the customer site with no external equipment necessary to purchase.

Verifying TA2 Calibration

In order to verify calibration, low flow and high flow conditions are simulated. This establishes baseline values that can be used for comparison at a later date. These baseline values are stored in the TA2 and located in the calibration certificate. All verification procedures should be conducted at room temperature.

A Thermatel® TA2 thermal mass flow meter

Low Flow Validation

To test low flow validation, the heater power is set and a temperature difference between the resistance temperature detectors (RTDs) is measured. In order to do this, first wrap the sensor tips of the TA2 to prevent air flow. On the TA2 display, select the diagnostic section and enter the Low Cal validate option. Once you enter, the test begins to run. In a short time, the temperature difference will stabilize and two temperatures will show on the display. One of the two is the original temperature difference between the sensors when the TA2 left the factory. The other is the new temperature difference that has just been measured. If the values are within 1.5 °C, the device is still within calibration. Some variance in temperature difference is given for variation of ambient temperatures as well as test methods. The user can store the value obtained (if it is different from the original value) and use it as the new baseline value or keep the original value that is reflected on the calibration certificate.

High Flow Validation

In order to test high flow validation, the TA2 must be placed vertically in a water bath. An easy way to do this is to hold the TA2 in place with a test stand and let the water settle. Select High Cal validate from the diagnostics section, just as you did with Low Cal validate for the low flow test. The heater power is once again set and the temperature difference is measured. These steps can be completed exactly as they were with the low flow validation to verify thermal mass flow meter calibration.

Both the low flow and high flow tests verify if the RTDs still measure the same amount of heat transfer in low and high flow conditions covering the entire calibration curve. Since thermal mass flow measurement is based on heat transfer, this is a true calibration test. All the features needed to test your TA2 are included at no extra charge and require no special equipment.

More Information 

For more information on the TA2 or to watch a video that demonstrates thermal mass flow meter calibration, visit flow.magnetrol.com.

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Level Measurement Solutions for Natural Gas Separators

Natural gas separators remove solid particles and liquids from a continuous gas stream supply. Dust, dirt, sand and pipe scale as well as water, natural gas liquids and light hydrocarbons can be removed. Removing these substances from the natural gas supply creates a more refined product and protects downstream process equipment from malfunctioning.

Magnetrol® has produced an applications brochure for the power industry, detailing measurement challenges and solutions for each step of the power generation process. This blog post is part of an occasional series exploring each application in detail.

natural gas separators

Natural gas separators in the field.

Level Measurement Challenges and Considerations

In a typical system, an inlet separator allows particles and liquids to settle out and the gas to rise. The gas collects at the top of the separator where it is removed by means of a gas compressor. The collected particles and liquids are then dumped into a water tank. The amount of water that is drawn off needs to be precisely modulated. If the level rises too high, the liquid will enter the compressor inlet. Liquid level measurement instrumentation can monitor the water level and prevent it from entering the inlet.

Level Measurement Solutions

MAGNETROL has produced level instrumentation solutions for natural gas separators:

  • For point level measurement
    Model B35 external cage float-actuated switch, ASME B31.1 construction
  • For continuous level measurement
    Eclipse® Model 706 or Horizon® Model 704 guided wave radar transmitters; E3 Modulevel® displacer transmitter
  • For visual indication
    Atlas™ or Aurora® magnetic level indicators can be supplied with switches or transmitters

More Information
For more information on level measurement solutions for natural gas separators and other power industry applications, download the power industry brochure.

power generation

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WWTP Waste-to-Gas Initiative Enabled by Advanced Level and Flow Technology

Approximately three billion gallons of waste greases are produced by restaurants and institutions every year in the U.S., according to the EPA’s Office of Solid Waste. These massive amounts of fats, oils, and greases (FOGs) have traditionally ended up in landfills or have been poured down drains to coat and clog sewers and contaminate the environment. Disposing of grease has become increasingly more challenging, as many landfills no longer accept it. Those that do often levy a hefty dumping surcharge. In response to this problem, many wastewater treatment plants (WWTPs) are using a creative tactic: transforming waste to gas that can fuel heating, dehumidification and power generation units.

waste-to-gas

An Echotel® ultrasonic transmitter from Magnetrol® measures grease level through a fog of vapor at the WWTP grease receiving station. Grease is being fed from a tanker through the green hose.

In fact, a sanitary district in Northeastern Illinois, U.S. has undertaken just such a green initiative and is turning common forms of waste grease into a biofuel that boosts self-sufficiency for the plant’s heat and electricity needs. Methane gas captured for process heating and dehumidification has already saved the plant over $115,000 in natural gas costs annually. An upgrade to be completed this year will boost digester methane production and use the gas to generate electricity to further save the plant an estimated $100,000 per year.

Conversion to Biogas

Through a process called co-digestion, the sanitary district is increasing its methane gas production in five anaerobic digesters by using waste grease collected from regional waste haulers and offloaded at their facility’s grease receiving station. Fed into digester feed water, the grease is converted into biogas for fueling generators to make electricity. Anaerobic digestion naturally produces methane gas as it breaks down organic matter, but when waste grease is added it not only accelerates the digestion process but produces more methane of a higher quality. Adding grease wastewater to the anaerobic digestion process typically increases methane gas concentration and raises the average BTU value of the methane from 500 to approximately 625. Harvesting this high-grade methane for electric power is an innovative way to offset a facility’s power needs.

The waste-to-gas process reduces energy and maintenance costs and provides security from interruptions in the natural gas and electricity grids. Diverting FOGs into biofuel before they seep into sewers further conserves resources, since FOGs clogging municipal sewer pipes are responsible for 80 percent of the sanitary sewer overflow events in the U.S. Commercial haulers offloading grease can also create revenue for WWTPs from “tipping fees.”

Increased Efficiency

According to the Northwest Biosolids Management Association (NBMA), approximately 15,000 WWTPs operate anaerobic digesters across the United States, but only one-third put their biogas to work—and even fewer use it to produce electricity. That puts this sanitary district ahead of the curve. Although the plant’s original digesters were performing well and producing energy for process heating, management wanted still more efficiency from the treatment system. With the average WWTP consuming more electricity than any other municipal service—sometimes as much as 30 to 40 percent of overall energy consumption—it’s not surprising that this facility has moved steadily toward increasing self-sufficiency in energy generation.

Because of its long-standing relationship with the sanitary district, Magnetrol® was called in to address the level and flow needs for the new waste-to-gas system. The first application to be addressed was the grease receiving station at the project’s front end, a 12-ft. (3.6 m) deep in-ground cement repository where waste haulers offload their grease. The level measurement application was somewhat challenging, because warm grease dumped during colder months can create steam that the level device must cut through in order to make accurate measurements.

It was precisely for its ability to detect true level despite the compromised atmosphere that the non-contact Echotel® Model 355 ultrasonic level transmitter was selected for the grease receiving station. Each of the five floating roof digesters also utilizes a pair of Model 355 ultrasonic transmitters. At the back end of this multi-million dollar project, three Thermatel® TA2 thermal mass flow meters monitor methane gas flow from the digesters. Initially, plant personnel did not know how much methane would be produced with any degree of certainty. Knowing the exact amount of methane was necessary in order to select the generator with the right capacity for the job. The TA2 flow meters compiled the required data and the generator was specified. As a result of the waste-to-gas initiative, the sanitary district anticipates the ability to generate 50 percent of its electricity from biogas.

More Information
To learn more about how MAGNETROL products can help increase efficiency for a variety of operations in water and wastewater treatment plants, visit water.magnetrol.com.

wastewater treatment plants

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