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Flow metering as a quality tool: Anheuser-Busch's Jacksonville plant uses modern metering practices to assure accuracy and sanitary flow measurements.

As it has grown to be the world's largest producer of beer, Anheuser-Busch has always kept quality as the number-one concern through every step of the brewing process. This starts with the acceptance of raw materials--such as barley malt, hops, grain adjuncts, yeast and water--and continues through every intermediate step of the brewing process, to filling bottles, cans or kegs with the finished product.

More and more, modern instrumentation plays a key role in quality control throughout the brewery. Critical among these modern instruments is the flowmeter--the focus of this article.

Plant metering practices at the Jacksonville brewery are somewhat typical of those at all 12 of Anheuser-Busch's breweries, scattered at key locations across the U.S. Corporate engineering in St. Louis, however, encourages each brewery to try out new instrumentation, where feasible.

The Jacksonville brewery had its first year of production in 1969 and now has an annual shipping capacity of 7.1 million barrels. This amount is just about the average for the 12 breweries whose total yearly production is running at nearly 87 million barrels.

Like the other regional A-B breweries, Jacksonville produces a variety of Anheuser-Busch brands--including Budweiser, Bud Light, Michelob, Michelob Light, Michelob Dry, Busch and Natural Light.

Even restricting this article to covering flowmeter systems and related instrumentation is a large order, so it has been further narrowed down to coverage of several key uses of magmeter systems. For over 20 years, such systems--continually enhanced with newer developments--have been the almost universal method for metering and controlling flows throughout the brewery. They offer the major advantages of high calibratable accuracy and easy adaptation to clean-in-place (CIP) methods, which are used extensively in the brewery.

As examples of metering practices, the following subjects are covered in the subsequent sections of this article:

* Accurate metering to fillers * Checking and maintaining metering accuracy * Quality control at K-filters * Magmeters simplify CIP * Accurate part-to-part ratioing

Accurate metering to fillers

Each of the seven filling lines--three for cans, three for bottles, one for kegs--has an F&P magmeter system. Fig. 1 shows a typical system, using an early design of magmeter (F&P Model 10D1418A). These meters have Teflon liners and Type 316 stainless steel electrodes--a combination which has proven very satisfactory in our Jacksonville plant over a period of some 20 years. We clean the meters with caustic solution via the clean-in-place (CIP) method.

In this final manufacturing step, highest accuracy of measurement and antibacterial growth are both paramount considerations. If anyone wants to change even a gasket on one of these lines, it must have the approval of the brewmaster, who will be sure that it has been tested and food-grade approved for such service.

For totalizing beer flows to each filler, we utilize the magmeter's calibrated accuracy of +/- 0.25% of scale and get high resolution of measurement by setting up the signal converters to deliver 10,000 pulses per barrel; each pulse represents 0.0031 gallons. The pulse output drives a digital totalizer that adds up the total beer flow to a given filling machine over a prescribed period.

The converter outputs also connect to Allen Bradley PLCs which count the pulses via a fast response card. As a backup, the PLCs also operate various alarms should the flow go below a certain setpoint. Totals for all seven filling lines are input to a central location and form an essential part of our records of brewery output.

Checking and maintaining metering accuracy

To check the accuracy of our magmeters, we use Fischer & Porter turbine meters, which are factory-calibrated and come complete with a certified calibration curve. This test meter is mounted in a pipe section some five feet long and of the same diameter as the filling line. The meter is equipped with a spoolpiece to establish straightline flow--essential to sustain its high calibrated accuracy. Between uses, we store this assembly, capped at either pipe end, in an air-conditioned room, suitably graded as a calibration standard.

Once a quarter--or more often, if there is a question about the meter's accuracy--we install the turbine meter assembly in the beer line downstream from the magmeter to verify accuracy. Both meters connect to separate digital totalizers and must agree in their readings within +/- 0.5% for a given test run.

As soon as the check is completed, the turbine meter assembly is immediately removed, thoroughly cleaned and then sanitized before being sent to storage. If ever it were left in the line during CIP, the caustic would ruin the bearings and it would have to be returned to Fischer & Porter for repair and re-certification. The same turbine meter assembly can be used to check magmeters on different lines, so long as the pipe diameter is the same--such as the three-inch pipe shown in Fig. 1. We have separate assemblies for other pipe sizes.

Our experience with these magmeters--especially the primary element mounted in the line--has been that they are very low maintenance items--once they are set up properly. In one case, however, the meter was installed near frequency inverters that created an RF (radio frequency) signal which caused serious drifting from the true flow reading. Once we found the signal's frequency range, working with F&P personnel, we added a suitable damping device (an RC circuit) that filtered out the interference and reestablished the accuracy.

Another important factor in sustaining accuracy is good electrical grounding, which is emphasized in the meter's instruction book. When the book says "use a good earth ground," it means not just "pipe to pipe." On these meters, we had to drive down 80-ft. rods to get a good earth ground. Without such a ground, connected directly to the meter body, we would get aberrant readings. In these cases, the turbine meter would sometimes drift high, showing excessive beer loss. At other times, it acted as if the filler was making beer!

Quality control at K-filters

Our last major process step in producing finished beer is the highly critical filtering of each type of beer via "K-filters." As the beer passes through, the filter is designed to remove any particles of yeast or other fine solid residues that may be left over from previous processing. Proper operation of the filter produces absolutely clear beer, which then passes on to finished beer storage tanks. There it is checked carefully to meet all product specifications, before being made available for the filling operation.

The K-filter comprises a vessel with a number of screens or "leaves," which are coated with just the right amount of diatomaceous earth (DE), so that yeast and other particles are held back while the beer continues to flow through, completely clear. DE in the form of slurry, called "body feed," is fed into the beer line just ahead of the filter, and its flow rate (about 300 gph) is measured by a unique type of F&P magmeter--appropriately, but by pure coincidence, called the K-MAG magnetic flowmeter.

Condition of the screens is continuously checked by a differential pressure measuring device, which is arranged to check for any clogging from filtered deposits. An increase in differential pressure means that more DE slurry is needed to bridge the other filtered solids so that beer can continue to flow through the filter.

Control of the body feed flow comes from a tie-in of the magmeter output, via an F&P microprocessor-based signal converter (50XM series), which outputs flow rate signals to an Allen Bradley PLC. The PLC includes a control loop which receives a signal from the differential pressure device; any increase in the pressure causes the PLC to operate a positive displacement pump on the body feed line to increase DE slurry flow into the filter.

DE slurry is very abrasive, so we selected the K-MAG meter which has a meter tube made of cast ceramic (99.7% Alumina) with fused platinum electrodes. Not only does this combination provide excellent resistance to abrasion, but it also has USDA approval and meets the stringent demands imposed for 3A sanitary applications. Thus, when a filter is down for maintenance, its magmeter can be cleaned in place.

The K-MAG meter is barely visible in Fig. 2 among the cable connections. It is mounted between pipe flanges on a vertical part of the one-inch slurry line. Its signal converter, which is directly above it, is shown in Fig. 3. Microprocessor-based, this type of "smart" converter provides a measuring accuracy of +/- 0.1% of scale and permits transmission of flow information to a remote control room via a PLC. Further, for possible future use, it has an optional feature, HART protocol, which can pass data over the 4 to 20 mA dc output signal of the converter.

Exit flows of beer from the filters are also measured by magmeter systems, with this flow data also being sent to the control room. As shown in Figs. 4 and 5, work stations in the control room provide operator interfaces to the PLCs, with CRT displays that can include all the K-filters, their piping and instrumentation. The PCs utilize an industrial-based software package (Factory-Link supplied by U.S. Data Corp. and implemented by Anheuser-Busch Corporate Engineering).

Some data from the K-Filter control room is passed on via our Local Area Network (LAN) to a report station, which also employs Factory-Link. It compiles a report that is important to several departments, including Brewing and the Quality Assurance Lab.

Magmeters Simplify CIP

Beside its sustained, high measuring accuracy and history of low maintenance, probably the most attractive feature of the magmeter is that the meter body can be selected to have wetted parts that permit CIP methods. Once installed, the magmeter body stays on whatever line it was installed in, until it is replaced--usually after years of service. The CIP liquids flow right through the meter and return via their piping systems.

Our CIP procedures are essentially those of the industry--involving (1) a pre-rinse with water to remove any foam as well as beer in the lines; (2) cleaning with caustic solutions; and (3) a post-rinse with sterile hot water. The caustic solution is normally a 3% to 4% solution, at around 140 to 160 degrees F; the post-rinse of sterile hot water is at about 190 degrees F.

Because both the caustic and post-rinse flows must exceed a certain minimum flowrate for proper cleaning and rinsing, another advantage of the magmeter is that it can be used to check these flow rates and sound an alarm if the proper rate is not maintained. The measurement of CIP flowrates does not have to be as accurate as, for example, the beer meters, and usually, the system calibrated for beer is sufficiently accurate to be used.

In some cases, we have a rather elaborate arrangement of magmeter systems installed just for CIP. Shown in Fig. 6 is such a setup, using four 4-inch magmeters of the wafer (flangeless) type (the F&P Mini-Mag flowmeter). Two of the metered lines serve for CIP of new vertical fermenters; the other two are for the K-Filters and associated equipment on the fifth floor.

As shown, the meters mount between standard flanges with bolts through flange holes spanning the meter body. Three such meters are visible near the bottom of the view (arrow points to middle one), mounted on vertical portions of the pipelines.

The four signal converters for these magmeters are also shown in Fig. 6, across the top of the view. These are of the newer 50XM type, microprocessor-based and equipped with the HART Protocol option (not currently used). They output to Allen Bradley PLCs which have set points at prescribed flow rates to assure proper cleaning.

How the Magmeter Measures Flow

The magnetic flowmeter (commonly called "magmeter") is a volumetric, liquid flowrate measuring instrument. It utilizes the property of a conductive liquid to generate an induced voltage as the liquid flows through a magnetic field. The amplitude of the voltage thus produced is directly proportional to the flowrate of the liquid.

The mathematical relationships involved are based on Faraday's Law of Electromagnetic Induction, as illustrated in Fig. A. The magnetic field, with a flux density B, is generated by a pair of magnet coils.

The coils are arranged so that the magnetic field crosses the flowing liquid at right angles, as shown. V represents the velocity of liquid flowing through a pipe section (metering tube) of inside diameter D. The pipe is part of the meter body and must be insulated by a "liner," to prevent the electrical flow signal from shorting out to the metal body or pipeline in which the meter is installed.

The voltage E, induced by the flowing liquid, is sensed by a pair of electrodes which are located on opposite sides of the pipe. For this arrangement, Faraday's Law may be stated: E = K x B x D x V, where K is the equation constant. With B and D being constant, voltage E is then directly proportional to V, the liquid velocity. E is actually a rather small milli-voltage that requires a "signal converter" to amplify, condition, and present the signal in a more usable form--usually a 4 to 20 milliamp dc output, which is the industry standard.

Since the output signal from a magmeter is linear with respect to flow velocity, a current output of 4 mA dc corresponds to zero flow and 20 mA dc, to 100% flow of the range setting, and there is a straight-line relationship for all values in between. These values can be expressed in suitable engineering units--such as gallons per min (gpm). With the current output, an optional scaled frequency output is available for flow totalization--such as gallons over a 24-hour period, or whatever.

Instead of generating a current output as a measure of flow, the signal converter can generate a frequency output (also called an unscaled "pulse" output)--such as 0 to 1,000 Hz or 0 to 10,000 Hz. The same linear relationship prevails and a certain frequency can represent a flowrate of so many gpm.

The signal converter can be mounted remote from the magmeter or integral with it, as shown in Figs. B-1 and B-2. Together the magmeter and the converter form a system, with each device being individually calibrated during manufacturing. Thus, the accuracy statement, such as +/-1% (or +1/-0.5%) of flow rate includes both pieces of equipment.

Signal converters, which started out basically as precise voltmeters, today include models that are sophisticated, microprocessor-based instruments. They can perform a wide-range of measurement and control functions, as well as diagnostics and remote communications, with the capability of "uploading" and "downloading" of the database. Hence, they can be called "smart" transmitters.
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Title Annotation:includes related article; Anheuser-Busch Inc.
Author:Lively, Bud; Westberry, Carey M.; Zaun, Todd M.
Publication:Modern Brewery Age
Date:May 10, 1993
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