Friday, May 31, 2019

Electromagnetic Flowmeters and Dual Frequency Excitation

Magnetic flowmeter
(Yokogawa)
The electromagnetic flowmeter, commonly known as the "magmeter", gets its name from the magnetic field generated within the float tube that produces a signal proportional to flow. This principle employs Faraday's Law of Electromagnetic Induction. Magnetic flowmeters are built so the direction of the magnetic field is perpendicular to the flow and the line between the electrodes is also perpendicular to the flow. As a conductive liquid flows through the flowtube, an electro-motive force is generated. The electrodes detect the electro-motive force. The electro-motive force is proportional to the flow velocity, flux density, and the meter inner diameter. The flux density of the magnetic field and the meters inner diameter are constant values, therefore the magnetic flow meter can calculate the flow velocity and volumetric flow from the electro-motive force.

The basic components of the magnetic flow meter body are:
  • A lined flowtube (typically Teflon)
  • Excitation coils
  • Two electrodes mounted opposite of each other within the flowtube.
Current is applied to the coils in the magmeter to generate a magnetic field within the flow tube. As a conductive fluid flows through the meter, an electro-motiveforce is generated. This force is detected by the electrodes and the resulting value is converted to flowrate.

When magnetic flow meters were originally designed over 50 years ago, they utilized AC type excitation. AC powered magnetic flow meters use line frequency to generate the magnetic field. The frequency of AC excitation is typically 50 to 60 Hertz. This type of excitation has a very fast response time, making it suitable for slurry applications. The weakness of AC type excitation is that it has an unstable zero, and the accuracy is a percent of span, as opposed to a more accurate percent of reading. Because this type of excitation uses line frequency, the power consumption is also very high, making this an expensive meter to operate.

AC and DC excitation
Dual AC and DC excitation
In an effort to improve accuracy and reduce energy cost, pulsed DC type excitation was introduced several years later. The average excitation frequency is between three to eight Hertz, but can go as high as thirty Hertz. The major benefits of pulsed DC excitation over AC excitation is the improved accuracy and zero stability. The accuracy of a DC type meter is a percent of reading. This gives you a more accurate measurement throughout the entire measuring range. Unfortunately, because of the low frequency, the response time is very slow, making it a poor choice for noisy applications.

To overcome the disadvantages of the standard AC and DC excitation methods, and keep the advantage of a high signal-to-noise ratio, Yokogawa's patented dual frequency excitation is the ideal combination. Dual frequency excitation combines the positive benefits of both AC and DC excitation, using both a high 75 Hertz frequency, and a low frequency excitation of approximately six Hertz to drive the coils. Dual frequency excitation is an innovative method that superimposes high frequencies on low frequencies, and utilizes the advantages of each, while eliminating the previously discussed disadvantages. The combination of these methods results in the flow noise immunity and fast response of the high frequency excitation method, and the high zero stability of the low frequency excitation method simultaneously.

For more information on Fike products and capabilities, contact Flow-Tech, Inc. by calling 410-666-3200 in Maryland or 804-752-3450 in Virginia. Or, stop by the website at https://flowtechonline.com.

Saturday, May 18, 2019

Demonstration of Techniques Used to Mitigate Industrial Explosions and Overpressure Situations


There’s a number of different things that happen with an overpressure event or explosion at an industrial facility. Some are minor. Some are catastrophic. Improved industrial safety can start with something as small as paying careful attention to a speck of dust. Fike’s Combustion Test Lab offers comprehensive explosibility dust testing, providing invaluable data that ultimately helps protect lives and assets.

In August of 2018 an international audience of students, professors and other experts came together at the International Symposium on Hazards, Prevention and Mitigation of Industrial Explosions (ISHPMIE).  Fike Corporation, recognized globally as the most trusted producer of risk mitigation products, presented innovations and solutions at the Combustion Test Lab. This video highlights the demonstrations where a wide variety of overpressure and explosive situations were neutralized using specialized Fike equipment.

The kinds of events that were demonstrated were:
  • Open Air Deflagration
  • Explosion Venting (far right side of screen)
  • Flameless Venting (Fike's Flamquench product)
  • High Rate Discharge (Fike's HRD explosion suppression product)
  • Explosion Suppression (yellow cube with clear panes)
  • Active Isolation (Chemical and Mechanical)
  • Passive Isolation
  • Pressure Relief (featuring Fike's RD500 Atlas rupture disc)
  • Dust Collector Strength-of-Enclosure Test
  • Active Conveyance
  • Metal Dust Deflagration
For more information on Fike products and capabilities, contact Flow-Tech, Inc. by calling 410-666-3200 in Maryland or 804-752-3450 in Virginia. Or, stop by the website at https://flowtechonline.com.

Tuesday, May 7, 2019

Steam Use Measurement Presents Unique Challenges for Colleges and Universities

Steam poses a unique challenge for colleges and universities.

Many schools want to accurately track, and then internally bill, for steam usage in each of their buildings as part of a wider effort to improve resource management. However, traditional steam metering technologies tend to be a less than optimal choice.

Most times, it’s necessary to place campus steam meters in the basements of buildings where there isn’t a lot of room for piping. That causes issues because flow meters typically require significant runs of straight pipe upstream and downstream of the meter to work correctly.

School administrators also encounter issues by trying to measure steam usage during the low-demand summer months. Common vortex meters, which contain a shedder bar mounted across the diameter of a pipe to measure flow, work well at higher flows. When it comes to low flows, however, they can stop working completely (i.e., low flow cutoff problems). Differential pressure (DP) flow meters coupled with the proper electronics, by comparison, can push the low flow cutoff value downward. However, most DP meters can’t get around the straight-run requirements.
ExactSteam™ V-Cone® Flowmeter
The ExactSteam™ Solution

McCrometer’s ExactSteam solution is designed to overcome those hurdles.

The ExactSteam V-Cone Flowmeter works well with short straight-pipe runs, so it addresses the lack of space issues faced by colleges and universities. It also measures steam across the entire range, performing better at lower flows.

The High Cost Of Low Flow Cutoff

Steam system operators can pay a steep price for generating product that passes through a meter but fails to get measured. Also known as low flow cutoff, those losses are a function of the turndown ratio of flow meters. The ratio — defined as the maximum measurement capability of a device compared to its minimum — dictates how wide a flow spectrum can be measured. On campuses, this creates a major issue because demand for steam in the colder weather can be extremely high compared to off-peak times.

McCrometer’s ExactSteam
ExactSteam™ V-Cone® Flowmeter
ExactSteam is a DP-style flow meter that can be adjusted for colleges during winter months. It contains McCrometer’s established V-cone flow meter combined with a newer electronics package to aid in the downward adjustment of the turndown ratio. A growing number of college campuses, especially larger schools, are seeing the benefits of ExactSteam and adopting the technology.

Some examples include:

Case Study #1 - An East Coast University Steam Operation

This school designed its system to measure from 84,000 lbs/hr to 8,400 lbs/hr, which accounted for a 10:1 turndown ratio and velocities of 420’/second to 42’/second. After the meter was installed, system operators determined their actual flow range was 20,000 lbs/hr to 1,000 lbs/hr (a 20:1 turndown ratio) and velocities were 100’/second to 5’/second.

Because flow rates were overstated, the university dropped below the low flow cutoff and wasn’t measuring at all during the off-season.

The solution: Purchase another meter with a larger cone that would produce more differential pressure at the correct flows. The school has since installed an ExactSteam V-Cone Flowmeter.

Case Study #2 – A University Hospital Using Both Condensate And Steam Meters

During the winter, the steam meters were always measuring more steam than the condensate meters.  The difference was justified because the condensate meters were not capturing steam usage of the autoclaves.  However, during the summer, the condensate meters were measuring more than the steam meters, which was impossible.

The steam meter was designed for flows from 14,000 lbs/hr to 1,400 lbs/hr.  During the summer months the hospital flows frequently dropped below 1,400 lbs/hr, which was below the low flow cutoff.  It was also determined that their highest flow during the summer was 5,000 lbs/hr.  The hospital needed more turndown and a lower flow range.

The solution: The ExactSteam V-Cone Flowmeter was installed.  It was designed for flows from 6,000 lbs/hr to 300 lbs/hr and was able to fit in the basement between two elbows.

Well Positioned For Campus Use

Key aspects of McCrometer’s ExactSteam solution include: a complete flow meter for steam metering, factory-configured for energy metering or mass flow; the ability to measure saturated (dry), superheated, and unsaturated (wet) steam; the V-Cone acts as its own flow conditioner by disrupting all centralized flow disturbances; signal stability allows it to measure a wider range of flow than other meters, minimizing pressure loss; and minimum installation requirements, so retrofitting and new installations are easier.

Because of the inherent conflicts, traditional steam metering technologies are not a good fit for many colleges and universities. However, there are solutions available to campus steam system operators to capture readings from most — if not all — of their steam production, even in less than ideal conditions.

For more information on all aspects of flow measurement and campus metering, contact Flow-Tech, Inc. by calling 410-666-3200 in Maryland or 804-752-3450 in Virginia. Or, stop by their website at https://flowtechonline.com.

Reprinted with permission from McCrometer.