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When Bulk Solids Equipment Runs for 45 Years: Lessons From a Water Treatment Installation

In bulk material handling, reliability is not measured in days or months. The real test is whether equipment can continue doing its job year after year—often under abrasive, dusty and difficult operating conditions.

For a municipal water treatment facility, dependable solids handling is more than a maintenance concern. Materials such as lime and soda ash have to move from storage into the process reliably. Bridging, ratholing, inconsistent discharge or unexpected equipment failures can interrupt treatment operations and create significant maintenance problems.

That is why one recent Vibra Screw replacement project stands out.

At Gainesville Regional Utilities, two Vibra Screw Bin Activators installed in approximately 1980 remained in service for roughly 45 years handling lime and soda ash.

After more than four decades of operation, the decision was finally made to replace the original equipment.

And the replacement equipment?

Vibra Screw again.

The Application: Keeping Difficult Materials Moving

Lime and soda ash are common materials in municipal water treatment, but that does not mean they are always easy to handle.

Fine powders can compact in storage, bridge across an outlet or create ratholes that allow material to flow only through a narrow channel. When this happens, a storage silo may contain plenty of material while providing an inconsistent supply to the equipment below it.

The purpose of a Bin Activator is to address the problem at the source: the transition between bulk storage and controlled discharge.

Rather than relying on manual intervention, air cannons or mechanical devices pushing through compacted material, the Bin Activator uses controlled vibration to encourage material movement across the bin cross-section and toward the discharge.

That consistent flow is particularly important when the next piece of equipment in the process is expected to meter material accurately. A feeder cannot provide consistent performance if its material supply is inconsistent.

Vibra Screw’s current Bin Activator designs continue to use vibration and an internal baffle arrangement to promote controlled bulk-solid discharge and mass-flow behavior. Learn more.

Replacing Equipment That Had Already Proven Itself

The Gainesville project called for new equipment sized for the existing water-treatment application, including an approximately 8-foot-diameter Bin Activator for lime and a 6-foot-diameter Bin Activator for soda ash.

The replacement project also incorporated updated features such as slide plates and sleeve diverter rings based on the requirements of the installation.

This is an important distinction.

Replacing a 45-year-old piece of process equipment should not simply mean manufacturing a copy of what was installed decades ago. Plants change. Operating procedures change. Maintenance expectations change. Controls and downstream equipment change.

A properly engineered replacement considers both the success of the original design and what can be improved for the next generation of the system.

Forty-Five Years Is Impressive. It Isn’t an Isolated Example.

Long equipment life has appeared repeatedly throughout Vibra Screw’s installed base.

One Vibra Screw customer contacted the company about replacement parts for Live Bins manufactured in 1958. According to Vibra Screw, the equipment had accumulated approximately 63 years of operation before replacement vibration isolators were requested—and the original-style gyrators were reportedly still operating without replacement parts. Read more.

Another application involved eight Inconel 600 Bin Activators built in 1978 for handling corrosive chlorinated dry bleach. Vibra Screw reported that those units operated for approximately 48 years before corrosion and time finally made replacement necessary. Read more.

Different customers. Different materials. Different industries.

The common theme is designing bulk material handling equipment around the actual application rather than treating the equipment as a commodity.

What Long Equipment Life Really Means

For process engineers and plant managers, longevity is about considerably more than avoiding the purchase price of replacement equipment.

A reliable solids-handling system can mean fewer emergency shutdowns, fewer maintenance interventions, less production disruption and greater confidence that material will be available when the process requires it.

It also highlights something that is sometimes overlooked during capital-equipment selection:

The lowest acquisition cost and the lowest lifetime cost are not necessarily the same thing.

An industrial feeder, conveyor or bin discharger becomes part of a process that may be expected to operate for decades. Engineering decisions made during the original project—equipment sizing, material of construction, suspension design, vibration characteristics, sealing, accessibility and compatibility with the material—can continue affecting that plant long after the original purchase order has been forgotten.

Built Around the Material, Not Just the Machine

There is no universal solution for dry bulk solids.

Lime behaves differently from soda ash. Carbon black behaves differently from plastic pellets. Pharmaceutical powders create different requirements from foundry sand, wood chips or metallurgical coke.

That is why successful bulk solids handling starts with understanding the material and the process.

Bulk density, particle size, moisture, flow characteristics, required feed rate, storage geometry, construction material, temperature, sanitary requirements and downstream equipment all influence equipment selection.

For more than six decades, that application-driven approach has been at the center of Vibra Screw’s work in feeding, conveying, weighing and discharging dry bulk materials.

Sometimes the best evidence that an approach works isn’t found on a specification sheet.

Sometimes it is a piece of equipment that was installed in 1980—and was still doing its job 45 years later.

Have a silo that bridges, a feeder that won’t stay consistent, or an aging bulk solids system that needs to be upgraded? Vibra Screw can review the material, process requirements and existing equipment to develop a solution built around the application.

Vibra Screw Inc.
755 Union Boulevard
Totowa, NJ 07512
973-256-7410
info@vibrascrew.com
www.vibrascrew.com

Design Considerations for an Efficient Volumetric Screw Feeder

A volumetric screw feeder is a crucial component in many industries where precise and consistent feeding of dry bulk materials is required. Achieving an optimal design for a (volumetric screw) feeder is essential to ensure accurate and reliable material flow into process. This article will delve into various design considerations and guidelines for developing an efficient volumetric screw feeder that meets specific application requirements. From screw geometry to hopper design and control systems, each aspect plays a vital role in achieving precise volumetric feeding.

Read FULL Article on PowderBulkSolids.com website

Vibra Screw Featured in Waste Water Digest

Forth Worth upgrades feed, mix systems for hydrated lime

New feed and mix systems ensure consistent flow of hydrated lime at Fort Worth water treatment plants.

In less than 150 years, Fort Worth has grown from a population of approximately 500 to nearly 1 million. To serve people in its North Central Texas metropolitan area, the city of Fort Worth has a total treatment capacity of 497 million gallons per day for drinking water and 166 million gallons per day for wastewater.

The city of Fort Worth carries the designation of Superior Public Water System by meeting the requirements of the Texas Commission on Environmental Quality. This designation recognizes not only the quality of Fort Worth’s drinking water, which meets U.S. EPA requirements, but the city’s exceedance of minimum standards related to treatment, pumping and storage capacity. This helps enable the area’s quality of life and protects human health and the environment.

The challenge

Maintaining such a large and high-quality water system in Fort Worth requires constant monitoring and upkeep of its physical facilities, appearance, and operation, which are regularly inspected and evaluated by the Texas Commission on Environmental Quality.

With more than 3,336 miles of pipe in the water distribution system and 3,266 miles in the collection system, plus tons of machinery to enable the systems’ around the clock operations, maintenance is a never-ending challenge. But it is a challenge that Forth Worth meets successfully and continually.

Among the requirements at Fort Worth’s Rolling Hills water treatment plant, one of three operated by the city of Fort Worth, is the feeding of a steady and regulated quantity of lime into the water supply.

With the potential to affect downstream aspects of the water treatment system, lime feeding is the kind of operation that gets noticed if it goes awry. It is important, therefore, that volumetric feeders used in the Rolling Hills plant function smoothly and dependably, without interrupting the mixing of lime and its downstream flow required for consistent pH control.

The solution

In 2020, Fort Worth’s Rolling Hillswater treatment plant installed new equipment for its lime feeding system to replace an existing feeder.

The newly-installed equipment was a Vibra Screw system that consisted of a VersiFeeder volumetric screw feeder with a mix tank, mixer and plumbing connections to replace another brand of feeder.

The skid-mounted Vibra Screw system provided the performance and dependability needed to ensure a consistent flow of hydrated lime downstream. So, in 2022, the Rolling Hills plant installed a second Vibra Screw system to replace another existing feeder. This system featured a VersiFeeder volumetric screw feeder, mix tank, mixer, and plumbing connections. Later that same year, the plant purchased a third feed and mix system from Vibra Screw.

Lime from a silo in the Rolling Hills water treatment plant is fed into the 1.5 cubic feet feed hopper of the Vibra Screw VersiFeeder. The integrated trough vibrator in the VersiFeeder system conditions the lime to a constant bulk density and assures a highly accurate flow — plus/minus 2% — into the system’s 150-gallon polyethylene mix tank. Mixing inside the tank is accomplished with a 3.3-inch impeller driven by a 1/2-horsepower motor. An AC controller supplied by Vibra Screw with a variable frequency motor assures smooth operation of the system.

These feed and mix systems provide Fort Worth the convenience of an engineered, preassembled, skid-mounted package — but the systems are also providing additional advantages at Rolling Hills. Because of the consistency of their day-in-day-out operation, the lime feed rate of the system was lowered with ease.

In fact, the plant reduced the augur size of the third VersiFeeder screw feeder from 4 inches to 3 inches in diameter because of their performance levels. The corrosion resistant paint of the units also withstands washing with muriatic acid several times per week.

“The Vibra Screw units are built well and have many excellent features,” said Plant Manager Joseph Tolson. “I would recommend the VersiFeeder units for use in lime mixing systems as well as other applications.”

Posted on April 3, 2023

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Teddies Peanut Butter (The Leavitt Corp) asked if we could provide parts for an existing Vibra Screw Live Bin used to handle whole peanuts. They sent photos of the bin and it turned out it was one of several Live Bins that were manufactured in Vibra Screw’s original Clifton, NJ building in 1958. The bins have been used for 63 years and we were able to provide necessary replacement parts (special vibration isolators). These bins are still using the old style gyrator (single shaft motor driving eccentric weights) without replacing parts. Built to Last, nice return on their investment.

Curbs segregation of bulk-stored mixes

Recent field experience indicates that segregation of dry mixtures in bulk storage can be eliminated by proper application of vibration to the material in storage. As a result, food processors are adding vibrating bin activators to the bottom of hoppers and bins not only to induce flow, but also to eliminate segregation.

An Indiana miller, for example, cut deviations in composition of a bakery premix by one half. Included in the premix are flour, salt. sugar, soda and cornstarch.

Although these ingredients differ widely in density, particle size and flow characteristics, vibration helps keep composition at discharge very close to that at the inlet.

Less segregation, better quality
Eliminating segregation in dry mixes brings three principal benefits. First, better product quality can be maintained on a consistent basis. Second, downtime and lost production due to rejected batches or remixes, can be reduced. And finally, engineering management gains more flexibility in plant design and operation. Larger quantities can be bulk-stored because the risk of segregation no longer limits storage capacity. It is also possible to mix first and store later in instances where the risk of segregation might previously have ruled out this option. Such added flexibility can lead to improved production and important cost savings.

In the static bin (left sequence) loaded with material of non-uniform particle size. A pipe forms down the center of the outlet. The vibration-assisted bin (right sequence) has a baffle over the outlets.
Vibration keeps all material mobile. and the baffle prevents the pipe from forming.

How vibration cuts segregation
Picture what happens when you pour a mixture of stone and sand on the ground. A rough cone forms, with stones mainly around the outside and sand mainly in the center. The stones tend to roll down the surface of the cone as it is formed, while the sand sifts down closer to the center. Segregation has taken place.

If, as usually happens in a conventional storage bin,
material discharges from the center of the bin first, finer material would emerge first and coarse material last.

The same basic thing happens in mixtures of dry ingredients having differing physical characteristics. Differences in particle size are the principle contributors to segregation. Differing flow characteristics and density may also influence the situation; however, the combination of a vibrating bin bottom with a built-in baffle over the final outlet substantially reduces the segregation problem.

Vibration keeps the material mobile and free-flowing, particularly at points of potential bridging, and the baffle directly over the outlet prevents material from emptying down a pipe in the middle first, and then off the walls as often occurs in static bins.
Because of the baffle. the pipe never gets a chance to form. Instead, the material draws evenly across the cross section. Moreover, the final discharge is a combination of materials from the center and those from nearer the walls. So even if there were segregation from the center out, there is re-mixing just before discharge. This flow pattern is called mass flow, or first-in, first-out flow.

Mass flow of bulk materials from a bin has been demonstrated in experiments in which layers of different-colored materials are loaded into a bin equipped with a bin activator, developed by Vibra Screw Inc.

Achievement of true mass flow from a bin eliminates risk of dead areas, spoilage and contamination among products processed on the same equipment.

Case in point
The Indiana miller’s experience underscores most of these points. The plant produces dough for dinner rolls and sweet rolls. The basic operation is to blend the dry ingredients into a dry premix. It is stored in a pre-mix bin, and discharged at a controlled rate to a scale hopper, then to a mixer where wet ingredients are added and the dough is developed. The bin is 7-feet- diameter by 15-feet-high and holds more than 10,000
pounds.

Originally, all feeding and dispensing of dry ingredients were by gravity. But a disparity in physical properties of the dry ingredients led to segregation within the storage bin. Densities ranged from 38 to 75 pounds-per-cubic-foot. and particle sizes from 30 to 400 mesh. As a whole. the mixture has a density of 55 pounds-per-cubic-foot and a moisture content of 5 percent.
To minimize segregation, a 7-foot-diameter bin activator was installed on the premix bin.

Closer control also was maintained over the quantity of material stored in the bin. This kept retention time of material in the bin close to 50 minutes. The bin activator mounts to the bottom of the bin in place of the standard bin bottom. Special hangers isolate it vibrationally from the bin. A patented gyrator on the bin activator generates vibratory forces up to 6,000 pounds to vibrate the entire bin bottom and its contents, but not the bin itself. In addition, an integral dished baffle mounted horizontally in the bin activator above the outlet vibrates to induce mass flow from the bin. It also prevents packing at the outlet due to static head loads.

Result of the installation was immediate reduction in segregation. This company measures composition of the premix by monitoring pH of the dough after blending.

Too high a pH means excess alkaline ingredients such as soda. A low pH indicates that level of acidic ingredients, such as salt, is running too high.

With the activator generating controlled vibration into the premix and inducing true mass flow in the bin. the number of samples falling within specifications rose from 68 percent to 78 percent. Moreover, deviations one percent below specifications dropped from 22 percent to 10 percent, deviations two percent below stayed constant at five percent, and deviations on the high side increased from three percent to only five percent.

In addition to improved quality control, the company reports that eliminating segregation improved line machinability of the product as it moves through the process. Based on this experience, it has installed another activator on a second process line.

Industrial Hemp, cousin to Marijuana but without the effect, has been a usable fiber for over 50,000 years. Used to make commercial items ranging from paper, textiles, clothing, plastics, paint, food, animal feed and biofuel, it is seeing a resurgence over other natural fibers such as wood because: it yields four times the crop per acre without need for herbicides and with fewer pesticides, takes only 3-4 months from planting to harvest, in paper production does not require environmentally harmful bleaching agents and can be recycled 3 times more, and as a composite substitute for wood in construction reduces the depletion of old growth forests. Hemp seeds are a rich nutrient in human and animal diets and produce hemp oil for biofuels and CBD medicinals.

Hemp plants produce a range of dry bulk materials. They each present a unique challenge in handling during processing. The plant inner “hurd” and outer “blast” fibers are light [10-12 lbs/cuft] and will not move freely from a storage bin or IBC or feed readily into process. Hemp seeds are free flowing however their natural oil can cause them to set up in storage. The flour and meal made from ground seeds is not dissimilar to wheat and corn varieties and readily hoppered and fed with well proven equipment designs.

Vibra Screw has over 65 years of dry material processing equipment experience. Our Bin Activators are proven on fibers, powders and seeds. Our Bulk Bag Unloaders and Fillers provide complete IBC handing with hoists and vibration or massage paddle discharge. Feeding is accomplished with a wide range of precise volumetric and gravimetric equipment including vibrating tube and pan feeders for fibers and screw and belt feeders for powders and seeds. We complete the line up with Flexible screw conveyors, blenders and full system controls.

We have a full scale test lab where your material can be pilot run and an active R&D program where the latest techniques for improving the processing of materials like Hemp are pioneered every day.

If your business is Hemp processing, contact us with your challenges for a no obligation solution.

Process weighing and gravimetric control technology … is it new or old?

Vibra Screw has been designing batch and continuous gravimetric control systems for decades. We were quick to adopt useful technology by incorporating digital and graphics displays, as well as an ever-growing number of I/O interfaces into our products. As expected, customer response to these improvements was overwhelmingly favorable.

However, all gravimetric control systems, no matter how fancy the user interface, measure weight using a transducer called a load cell. (See Figure 1) The load cell converts mechanical weight into an electrical signal. The most common type of load cell employs a strain gauge transducer (See Figure 2) in a Wheatstone bridge and can be found in devices ranging from deli scales to systems designed to process solid rocket fuel.

While computer technology has enabled high tech gravimetric control systems to evolve significantly over the last 30 years, a load cell is still the basic workhorse at their core. And, though it may be hard to believe, the strain gauge load cell technology got its start in the late 1800’s. In 1843 Sir Charles Wheatstone perfected and popularized his Wheatstone bridge. (See Figure 3) A resistance change in the bridge produces a proportional change in voltage across the bridge. Then almost 100 years later, in 1930’s, Edward E. Simmons and Arthur C. Ruge invented a device that could measure strain in an object.

It wasn’t long before the strain gauge and Wheatstone bridge technologies were combined and the “load cell” was born. This transducer changes mechanical energy into a proportional electrical signal. Even with the invention of the transistor following World War II, the load cell still found it’s primary application in laboratory test instrumentation. The small signal created by the load cell wasn’t ready for commercial/process gravimetric control systems. Lever scale and balance remained the preferred method of measuring weight.

Finally, in the computer age of the late 20th century, electronic technology had advanced enough to accurately measure small signal changes and the load cell started to replace the balance and mechanical lever scales used in processing industry. Even in today’s cutting edge technology, over 170 years later, the strain gauge load cell continues to be the preferred transducer used for process weighing and gravimetric control and the one used by Vibra Screw.

Figure 1

A load cell usually consists of four strain gauges in a Wheatstone bridge configuration.

Figure 2

The strain gauge load cell changes resistance proportional to the tension or compressive force acting on it.

Figure 3

A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of a Wheatstone bridge is its ability to provide extremely accurate measurements.

50 Years of Serving the U.S. Aerospace and Ordnance Industries

Rocket Launch — Vibra Screw is proud of the role it has played in our nation’s defense and exploration of space.

For over a half-century, Vibra Screw has been a major supplier of hoppering and feeding equipment used to make much of the United States solid rocket fuel and ordnance. Vibra Screw vibrating systems, without mechanical agitation or conveying, are ideal for safely discharging and moving solid rocket propellants and explosives. Vibra Screw’s Bin Activator’s and Feeders and over 60 years of bulk material handling experience provide proven solutions.

Hercules Aerospace, now Alliant Techsystems [ATK], constructed a solid rocket fuel manufacturing facility in Utah to process solid fuel for the Space Shuttle and nearly all the nation’s other launch vehicles and strategic missiles. It required precise weighing of the ingredients that make up the fuel. Design criteria included batch accuracies of 0.05%, safety factors that permit remote operation and do not require periodic recalibration and self-cleaning characteristics that permit total elimination of residue between cycles. Vibra Screw was awarded the contract to provide the turnkey system. Based entirely on scale mounted Bin Activated Bins and Vibrating Tube conveyors to deliver precise weighed batches of propellant ingredients, the design was the first time screw-less conveyors had been used for these materials, creating a much simpler and safer operation.

Thiokol Corporation, also now part of ATK, has used Vibra Screw equipment continuously since the 1970’s for similar propellant production. The unusually sticky nature of some of their materials led to Vibra Screw developing a cleaner profile Bin Activator, without internal cross bracing, that greatly enhanced flow from storage while reducing welds in the material contact areas.

The nation’s major ammunition depots have also used Vibra Screw equipment for decades. Again, the simplicity of vibration-only movement of dangerous material provided many safety benefits when handling explosive powders.

Can you afford to get caught without a critical part?

You can’t drive your car forever with the same oil, brakes, muffler and tires. Periodically it will need to be serviced. Solids processing equipment is no different. It needs to be properly maintained in order to perform within its design parameters. And, eventually certain parts will need to be replaced. Maintaining a spare parts inventory is often considered a luxury you can’t afford. But stop to consider how much downtown you can afford if a critical part fails. There is no perfect answer but here are some insights into some different types of equipment and parts.

Spare parts for solids processing equipment might include sleeves (elastomer seals), hangers, flight screws, conditioning screws, isolators and wire screws.

In the best of conditions, solids processing equipment like vibrating bins, bin activators, vibrating conveyors and screw feeders, are subject to stresses that will, over time, cause critical part failure. Even if the part in question is a standard item and readily available, you need to gauge the consequence of the downtime resulting from ordering, shipping and installing that part. What if that part requires custom manufacturing? How much downtown is too much? At what point should you consider having a replacement in your spare parts inventory. It is a question you should be asking before a part fails.

Bin Activators have two critical parts that will need to be replaced and we recommend you have spares.

Elastomer seals between the bin and the bin activators
Isolators for your bin activator hangers

After two years of service these parts should be carefully inspected. This inspection should then be repeated every six months. Obvious signs of degradation are checking and cracking. Also examine your isolators for sag. If signs of fatigue or wear are detected, these parts should be replaced. If you have spare parts on hand, be sure to inspect them carefully before installing them. Elastomer parts in extended storage can be compromised. Nevertheless, the cost of the part vs. the cost of the downtime suggests having spares is a wise decision.

You might think that the Gyrators on vibratory equipment are subject to a high rate of failure due to what is perceived as their high-stress function. The fact is, in continuous use situations, they are subject to very little stress. Gyrators are oil lubricated and with proper maintenance they can last years. Simply conduct the recommended inspections every 1000 hours of operation and change the oil every 6000 hours. Like a well maintained car, you can get years of trouble-free service following a simple maintenance routine. When processing is not continuous and Gyrators are frequently started and stopped, stresses on the Gyrators are increased and these inspections become more important.

There are also parts that are custom engineered and built specifically for the equipment they help operate. For example, most feeder screws are unique to the feeder they are shipped with. If the equipment is operated according to manufacturer’s guidelines, the screw can last longer than the feeder. But in real world situations, screw failure is all too common and when they break, there is no quick fix. Again, you have to weigh the cost of having a spare on hand vs. the downtime you will experience having to order a custom-engineered part.

So…to borrow a tried and true motto, be prepared. Consider what equipment you are operating, how it is being used and your tolerance for downtime. Refer to your manufacturer’s recommended spare parts list. If you have questions consult your equipment manufacturers and get their recommendations to help find the balance between the investment you are able to make in spare parts and the risk you are willing to take. Our experience shows that you should have some spare parts on site. It will pay off some day.

Bin Activators Cure Material Segregation

Picture what happens when you pour a mixture of stone and sand on the ground. A rough cone forms, with stones mainly around the outside and sand mainly in the center. The stones tend to roll down the surface of the cone as it is formed, while the sand sifts down closer to the center. Segregation has taken place.

The same thing can happen in storage bins with a material mixture of differing particle sizes. In a conventional bin [Fig. 1], materials separate as it is loaded. On discharge, finer material emerges from the center of the bin first, down a pipe and coarse material last. In a production process requiring a uniform blend, product quality suffers and the downtime from rejected batches can be costly.

When storage bins are equipped with Bin Activators, the segregation problem can be eliminated. [Fig. 2]. Vibration keeps material mobile and free-flowing, particularly at points of potential bridging. An integral baffle directly over the outlet prevents material from emptying down a pipe in the middle first and then off the walls as in conventional bins. Because of the baffle, the pipe never gets a chance to form. Instead material draws evenly across the bin cross section. And the final discharge is a combination or remix of materials from the center and those from nearer the walls. This flow pattern is called mass flow.

With Bin Activators, larger quantities can be bulk stored because the risk of segregation no longer limits capacity. Management gains more flexibility in plant design for example with fewer bins and conveyors required. That can lead to improved production and important cost savings.