What are Magnetic Flowmeters and How Do They Work?

Magnetic Flowmeter
(courtesy of Foxboro Schneider Electric)

Crucial aspects of process control include the ability to accurately determine qualities and quantities of materials. In terms of appraising and working with fluids (such as liquids, steam, and gases) the flowmeter is a staple tool, with the simple goal of expressing the delivery of a subject fluid in a quantified manner. Measurement of media flow velocity can be used, along with other conditions, to determine volumetric or mass flow. The magnetic flowmeter, also called a magmeter, is one of several technologies used to measure fluid flow.

In general, magnetic flowmeters are sturdy, reliable devices able to withstand hazardous environments while returning precise measurements to operators of a wide variety of processes. The magnetic flowmeter has no moving parts. The operational principle of the device is powered by Faraday's Law, a fundamental scientific understanding which states that a voltage will be induced across any conductor moving at a right angle through a magnetic field, with the voltage being proportional to the velocity of the conductor. The principle allows for an inherently hard-to-measure quality of a substance to be expressed via the magmeter. In a magmeter application, the meter produces the magnetic field referred to in Faraday's Law. The conductor is the fluid. The actual measurement of a magnetic flowmeter is the induced voltage corresponding to fluid velocity. This can be used to determine volumetric flow and mass flow when combined with other measurements.  

The magnetic flowmeter technology is not impacted by temperature, pressure, or density of the subject fluid. It is however, necessary to fill the entire cross section of the pipe in order to derive useful volumetric flow measurements. Faraday's Law relies on conductivity, so the fluid being measured has to be electrically conductive. Many hydrocarbons are not sufficiently conductive for a flow measurement using this method, nor are gases.

Magnetic Flowmeter and controller.
(courtesy of Foxboro Schneider Electric)

Magmeters apply Faraday's law by using two charged magnetic coils; fluid passes through the magnetic field produced by the coils. A precise measurement of the voltage generated in the fluid will be proportional to fluid velocity. The relationship between voltage and flow is theoretically a linear expression, yet some outside factors may present barriers and complications in the interaction of the instrument with the subject fluid. These complications include a higher amount of voltage in the liquid being processed, and coupling issues between the signal circuit, power source, and/or connective leads of both an inductive and capacitive nature.

In addition to salient factors such as price, accuracy, ease of use, and the size-scale of the flowmeter in relation to the fluid system, there are multiple reasons why magmeters are the unit of choice for certain applications. They are resistant to corrosion, and can provide accurate measurement of dirty fluids ñ making them suitable for wastewater measurement. As mentioned, there are no moving parts in a magmeter, keeping maintenance to a minimum. Power requirements are also low. Instruments are available in a wide range of configurations, sizes, and construction materials to accommodate various process installation requirements. 

As with all process measurement instruments, proper selection, configuration, and installation are the real keys to a successful project. Share your flow measurement challenges of all types with a process measurement specialist, combining your process knowledge with their product application expertise to develop an effective solution.

Vent Management on Large Cavity Steam Heat Exchange Equipment Commonly Found in the Brewing Industries: Thermostatic Air Vents (TAV) and Vacuum Breakers (VB)

The following represents a primer on vent management devices on steam heat exchange equipment: TAVs, VBs, and the combination device, model TAVB-3. In order to do that, we will review the purpose and proper application of the devices to establish clarity.

What are Vacuum Breakers and why do we need them?

Vacuum breakers are spring-loaded valve and seat devices that are mounted on or near the steam space of a heat exchanger allowing steam pressurization of the space, but during throttling down or shut off of steam supply also allow the valve to overcome the spring force and open when vacuum is present. The vacuum is formed when steam, with its much higher specific volume than water, condenses to water with heat exchange and is not replaced in the heat exchange space with an equivalent volume of steam, i.e. when the control valve is throttling down from its process design maximum flow, or when steam is being shut off after completion of the process step. By “breaking” the sub-atmospheric condition which occurs in those situations by allowing air into what was the steam space through the open vacuum breaker device; condensate drainage from the heat exchanger by gravity is enabled. This prevents water hammer, internal corrosion, gasket or joint leakage, and potential damage to the heat exchanger and other equipment. Without this device, a reverse pressure differential is formed in the steam space due to vacuum which will suck available condensate from the return system into the calandria, coil, or other large cavity heat exchanger.

Stainless Steel Thermostatic
Air Vent/Vacuum
Breaker (TAVB)

What are Thermostatic Air Vents and why do we need them?

Thermostatic air vents (TAV) are also valve and seat devices that are actuated by temperature, typically a “balanced” bellows. The bellows has an alcohol and water charge inside that evaporates and expands on temperature increase approaching the steam saturation curve for the particular steam pressure. The expanding bellows drives the valve into the seat and closes the device. On steam start-up of the heat exchanger, cool air is expelled quickly by using this device until steam reaches it which quickly closes the valve. Similarly, on decreasing temperature, at some point a few degrees lower than the steam saturation curve, the mixture in the bellows condenses and contracts the bellows which pulls the valve plug away from the seat and thus opens the vent. This signifies that non-condensable gases have accumulated and the temperature has depressed enough to allow the valve to open and expel them from the steam space. Pressure is inconsequential up to the TAV design pressure since the alcohol charge is designed to follow the steam saturation curve, offset but parallel, always activating a few degrees below saturation temperature for any given pressure (including vacuum).

Doesn’t the Steam Trap do this as one of its functions?

It is true that one of the three primary functions of the steam trap is to remove non-condensable gases. By virtue of the modularization of steam supply and condensate removal equipment at some distance away from the internal heat exchangers of kettles and cookers for example due to floor space restrictions in the brew house, size, configuration, and internal area of heat transfer equipment in modern breweries and the demands of production, it is imperative that these supplemental devices be used to remove these gases as close and as quickly as possible to the area where they would be entrapped: opposite the steam supply connection of the exchanger.

Why is it so important that air be removed?

There are several reasons, but most importantly, air is an excellent insulator and, without removal, serves to insulate internal heat transfer surfaces from the steam trying to transfer its latent heat. Surface temperature drops of 20-30% are not uncommon with systems unable to effectively remove non-condensable gases. From a secondary standpoint, air and other gases create internal oxidation and corrosion that corrode the system from the inside out. As we already know, a major source of air in the system comes from the vacuum breakers which contribute to piping oxidation if the air is not removed. CO2 entrained in steam turn condensate into carbonic acid (H2CO3) when turned into solution if not removed.

These two devices, TAVs and VBs, are frequently confused as to their function. Remember that TAVs primarily expel non-condensable gases and air on startup; and VBs primarily allow air in on shutdown. Their mounting is critical to their successful operation. Observe the following rules for mounting:

• As close to the exchanger as possible on a line with a vertical accumulator, if not on the exchanger itself, opposite the steam supply. 
• Condensate line must be large enough to allow disengagement if horizontal or a vertical accumulator will be needed. If not, the TAV will discharge condensate which means it is not discharging air. The vacuum breaker will spit and leak over time as well. 
• The vertical accumulator is used to provide an accumulation area for non-condensables. It is typically 2” or larger pipe, approximately 2 ft. high if space allows. An isolation valve should be used between the accumulator and the TAV to isolate for maintenance or system air testing. Note that these devices should be excluded from any air test boundaries since the bellows is “balanced,” meaning that steam pressure has a corresponding saturation temperature to “balance” internal pressure of the bellows against external pressure caused by the steam pressure. Air would not allow this balance to take place and would either not close the valve on the air test, or would rupture the bellows if the isolation valve were downstream. 

Since mounting preferences are similar for both vacuum breakers and air vents, a new device has been developed which accomplishes both functions in one device. This is the TAVB-3 which has become standard at a large brewing company.

Article written by Steve Huffman, Mead O'Brien, Inc.

A Look Inside the Neles NDX Intelligent Valve Controller

Neles intelligent valve controller 

Metso’s Neles NDX is the next generation intelligent valve controller working on all single acting control valves and in all industry areas. It guarantees end product quality in all operating conditions with incomparable performance, unique diagnostics, and years of reliable service.

Operating Principle:

The NDX is a 4–20 mA powered micro-controller based intelligent valve controller. The device contains a local user interface enabling configuration and operation without opening the device cover. Configuration and operation can also be made remotely by PC with asset management software connected to the control loop.

After connections of electric signal and pneumatic supply, the micro-controller (μC) continuously reads measurements:

Click for larger view

• Input signal 
• Valve position with contactless sensor (α), 
• Actuator pressure (I) 
• Supply pressure (S) 
• Device temperature

Advanced self­-diagnostics guarantee that all measurements operate correctly.

Powerful micro-controller calculates a control signal for I/P converter (prestage). I/P converter controls the operating pressure to the pneumatic relay (output stage). Pneumatic relay moves and actuator pressure changes accordingly. The changing actuator pressure moves the control valve. The position sensor measures the valve movement. The control algorithm modulates the I/P converter control signal until the control valve position matches the input signal.

The video below demonstrates the NDX's operation. Below the video is the complete installation, maintenance and operation manual for your convenience.

Neles NDX Intelligent Valve Positioner from Mead O'Brien, Inc.

Dampening the Effects of Vibration on Industrial Pressure Gauges

Vibration must be considered
when applying pressure gauges.

Pressure gauges rely on precise and responsive mechanisms to display changes in system pressure as rotational needle movement. By their very nature, these mechanisms are responsive to pulsations within the pressurized system and vibrations that may be evident in the connected piping and structures. The effect of vibration and pulsation is seen as an indicating pointer oscillating rapidly, making a definitive or even useful reading impossible. One solution, applied traditionally, was to fill the gauge with a viscous liquid that would dampen the rapid oscillation of the indicating needle.

While a liquid filled gauge does solve the oscillation problem, it does have a drawback. The liquid in the gauge presents its own set of operational issues requiring consideration in any application.

Provision should be made to check and maintain the liquid level in the gauge
A liquid filled gauge is an additional source of potential leakage in a facility

Ashcroft, a globally recognized manufacturer of gauges for commercial, industrial, and laboratory use, offers a different solution that provides the deflection dampening of a liquid gauge without liquid fill. Available on many of their gauges, the "Plus" option enables stable gauge face display in a dry gauge.

The video below provides a side by side demonstration of a liquid filled and a Plus gauge, so you can see the performance of both types. Share your process gauge requirements and challenges with instrumentation experts, combining your process knowledge with their product application expertise to develop effective solutions.

Boiler Safety in Brewing: Mead O'Brien's Steve Huffman Podcast with Master Brewers Association

Boiler Safety in Brewing

From sanitization to pasteurization, steam heating is critical in the brewing process and steam boilers are one of the most important investments a brewery will ever make. Understanding boiler components and safe boiler operation is crucial to ensuring the protection of people and property, as well as for maximum operating efficiency and optimal energy savings.

This video contains The Master Brewers Association of the Americas (MBAA.com) recent podcast with Mead O'Brien's Steve Huffman about steam boiler safety, operation, and performance.

Mead O’Brien is recognized as leading experts the industrial and commercial use of steam including industrial and commercial boilers, traps, condensate pumps, temperature and pressure controls, heating coils, and heat exchangers.

For more information, visit Mead O'Brien at http://www.meadobrien.com or call (800) 892-2769.

Listen to the discussion below:

Season's Greetings from Mead O'Brien

Season’s Greetings! In warm appreciation of our association during the past year, we extend our very best wishes for a happy holiday season.

May your holidays glitter with unforgettable moments of happiness, laughter, and good cheer.

A Peek Inside an Industrial Centrifugal Separator

A centrifugal separator is a piece of equipment that uses centrifugal force, the force of gravity, and inertia to separate two or more materials. Centrifugal separators work by spinning the material in a chamber at high speed which causes the heavier materials to settle out separately from the lighter materials.

Upon entering the spinning chamber of a centrifugal separator, the spinning force affect materials differently. Heavier materials are more affected by gravity, while lighter materials are affected by inertia. As the materials separate, they are collected in various mechanical or physical ways, such as filtering and screening.

Gases can be purified through the spinning process to remove particulate matter and moisture. The pure gas gas is then be collected as it escapes through the top of the centrifugal separator. Similarly liquids of different weights and viscosities are divided into various chambers in the separator as it moves along.

The Anderson Hi-eF™ Centrifugal Separators operate on a patented two-stage principle of separation that employs carefully controlled flow guiding the entrainment laden vapor through a series of vanes and baffles.  Each component of the separating element is designed to obtain maximum separating efficiency.  Briefly, in the first stage of the separation, impingement against a baffle removes the larger droplets of entrainment. In the second stage of separation, the separator removes the fine mist entrainment by utilizing centrifugal scrubbing action through a uniquely designed contact element.  In each stage, the gas medium and the separated liquid are carefully and continuously guided for maximum efficiency.  The separators are designed to handle large volume flow of a broad range of fluids.  Self-cleaning and engineered without filters or moving parts, the separators are free from maintenance and repair.  For more information visit http://www.meadobrien.com or call  (800) 892-2769.

Watch this video to see an animation of what happens inside the centrifugal separator.