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Posts Tagged ‘hopper’

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VTEC Vacuum Conveyor

Designed as a complete stand alone vacuum transfer system the VTEC Vacuum Conveyor is ideally suited to hopper loading and other small systems.

It is suitable for conveying various powders and granules at rates up to 9,000kg/hr.

Electric or compressed air operated units are available with booster kits if conveying difficult to handle materials. With integral controls the Vtec is a plug and play unit that can be easily dismantled for cleaning.

Features include:

  • Minimal maintenance
  • Low noise
  • Automatic filter cleaning
  • Low energy consumption
  • Simple to install
  • Compact Size
  • Easy to clean
  • Light weight
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Metering Screw Feeder

Metering screw feeders are used to accurately meter powdered, granular or flaky products in a process system.

Fresco offer both Volumetric (product flow rate by volume and set over a given time) and Gravimetric (product flow rate by weight and controlled using loadcells) types of metering screw feeders, with throughputs ranging from 1.76 l/ hr up to 13650 l/hr. Where very fluid powders are handled Fresco installs a pneumatically actuated flow control valve on the discharge of the screw tube to prevent flushing.

The crucial factor in achieving accuracy is consistent product bulk density by proper design and selection of an agitator in the conditioning zone above the screw auger. The agitator de-aerates and densifies the product to a uniform density and breaks any bridges, preventing hold-up in the hopper. This combination with a vast selection of screw sizes and types allows a wide cross-section of products to be fed very accurately.

Volumetric accuracy of ± 1% to ±2% and gravimetric accuracy of ±0.25% to ±1%, depending on the product, can be easily achieved. Weigh platforms fitted under the standard feeder linked to a batch controller provide accurate loss-in-weight feeding. Two-way RS 232 serial ports can be used to send and receive signals from other plant control systems. An easily removable front section provides access for cleaning and screw changes.

Fresco provides multiple weigh batching solutions, gain-in-weight and loss-in-weight systems that can be easily integrated with your equipment. Working with our electrical control and automation engineers we can provide high accuracy batching solutions that will ensure reliability and precision whatever your requirements.

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Blender

Ribbon Blenders are the most commonly used blenders.

The products to be mixed constantly circulate from end to end, making the Ribbon Blender particularly good for blending minor additives in the mix.

The agitator consists of an outer ribbon which moves the product from the ends to the centre while the inner ribbon moves the product away from the centre. The agitator design lends itself to mixing low-density free flowing products with a high degree of efficiency and accuracy. 

Fresco Ribbon Blenders are available in single, double or triple ribbons with either central or end discharge. The close tolerance of the ribbon to the body ensures nearly 100% product discharge.

Ribbon Blenders are also available in both direct drive and chain and sprocket drive depending on the application. 

All blenders should be connected to a dust collection system to prevent dust escaping into the environment. Various tip hatches and grills can be supplied to suit specific plant or product requirements. All Fresco Ribbon Blenders are supplied standard with a Dust Collection spigot. Access for cleaning and maintenance is gained through a fully opening hinged access lid, supported by gas stays and secure clamps. A smaller access hatch, complete with a hinged lid, gas stay and safety grill allow the operator to load manually while the blender is operating. CIP sanitisation and wash down units are also available.

Read About Blending Systems

Fresco recently responded to a customer’s requirements by providing a full turn-key blending system with ingredient traceability.

The scope was to provide a food grade blending facility capable of blending and tracking various ingredients including sugar, milk powder, flour, flavors and colorings to a better than 99% homogeneity at a rate of 6,000kg/hr. The system also required two blending lines to be run simultaneously.

Additional restraints also include the raw materials coming in various packaging types including bulk bags, 50kg sacks and 25kg bags.

After consultation with the customer, Fresco Systems offered a solution that meet all of the current requirements and allowed for future increases in plant capacity and the option to receive materials in bulk tanker delivery.

The solution consisted of a CITEC recipe based electrical automation system where the recipe for each blender is entered by the production manager for the day. Operators follow the schedule by manually weighing macro ingredients and tip these into the bag dump station following the prompts on the HMI operator interface panel. As each ingredient is entered the operator acknowledges it on the screen.

Minor ingredients are then tipped into the bag dump to flush the macros through the system. The bag dump stations are fitted with integral dust collectors so that any collected dust is returned to the product stream avoiding waste and cross contamination. All ingredients tipped through the bag dump station are passed over a vibratory separator sifter to ensure the ingredients are free of lumps or foreign objects. Major ingredients are received in 1000kg and 1200kg bulk bags which pass through an inline rotary sifter while conveyed on a gain-n-weigh basis to the receival hopper. A common dense phase vacuum system then conveys the ingredients to either of the two mixer receival hoppers. To allow for continuous operation, the macros, minors and major products are assembled in the receival hopper while the previous batch is being blended in the ribbon blender below.

As each ingredient is weighed, the actual weight is logged in the SCADA system for track and trace purposes as well as recording production details. Loadcells on the receival hopper also provide confirmation that the weighed product is completely discharged to the blenders. A magnet is also installed prior to the blenders to ensure that all metal contaminants are captured.

Flavours and colorings which would otherwise contaminate the vacuum conveying system are tipped directly to the blenders via a mini bag dump station. This removes the need to clean the system between recipe changes increasing process capacity. The mini bag dump stations are fitted with vibratory security screens and dust collection systems. The dust collection system also doubles as the balance for the displaced air as ingredients are discharged for the receival hopper in to the blenders.

The blenders are fitted with variable frequency drives ensuring that the product is handled with care reducing the risk of degradation during the mixing cycle. Once the blend time is reached the batch is discharged into bulk bags for storage and transferring to the various packing lines.

Fresco Systems tailors their standard range of bulk materials handling systems to suit each customer’s unique needs providing a tailored solution suitable to the operation and budget of each customer. As Fresco Systems designs, manufactures, installs and commissions their own systems, they are in complete control of the entire process offering customers cost competitive solutions of the highest quality.

Read More About Ribbon Blenders

The Fresco blender’s double ribbon configuration moves products through, constantly circulating them from end to end, making it particularly good for blending minor additives in a mix.

The agitator consists of an outer ribbon that moves the product from the ends to the center while the inner ribbon moves the product from the center to the ends.

The agitator design lends itself to mixing low-density free flowing products with a high degree of efficiency and accuracy. Various, standard sizes are available to suit the batch size and bulk density of the material being mixed. Shaft mounted and chain drive geared motors are available as required. The range of ribbon configurations include paddle, single, double or triple ribbons with either end or central discharge.

When filling the blender the operator can tip 25kg bags of various powders through the minors loading hatch or they can load via various lid configurations from bulk bags, mechanical conveyors or pneumatic conveyors. Loss in weight or gain in weight from bulk bags or pneumatic hoppers is also common methodology for major ingredients. The lid is fitted with safety switches and is hinged supported by gas stays providing the operator with full and easy access for cleaning between batches. Fresco blender can be fitted with a flush fit valve on the discharge feeding directly into a dust tight bulk bag fill head or a conveyor to processes downstream. Rotary sifters and magnets can also be incorporated into the system.

Fresco’s standard range of ribbon blender sizes range from 150 litres up to 4,000 litres and can be constructed in mild steel, 304 or 316 stainless steel with finishes ranging from industrial to pharmaceutical. With standard features such as integral mounting feet, air purge lip seals, double ribbon and easy access, the Fresco ribbon blender can also be tailored to meet a specific requirement.

For more information and to discuss potential systems, please contact sales@frescosystems.com or visit our contact page to find our nearest office.

Case Study:

Cone Blender
June 27, 2014/0 Comments
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Crumb Handling System

When a food manufacturing firm in Sydney had a requirement to feed bulk crumbs mixed with oils out of pallecons and into a process line, they knew they had a challenge on their hands.

The product compacts under its own weight causing it to bridge and rat hole, making it hard to deliver into conveyors.

Fresco Systems was able to prove through a series of product trials they had ability to work with the product. Fresco then designed and quoted a system that would allow the client to reduce the physical handling of the product while maintaining a continuous throughput, thus both reducing costs and improving productivity. The system provided is completely unmanned except for the loading and unloading of the bulk materials.

Fresco Systems design philosophy makes it a natural choice for this type of application – where ergonomics, safety and productivity go hand in hand. For this application it was imperative that all contact materials were manufactured to the highest standard from 316 S/S and incorporating full safety guarding and interlocks to a category 3 level.

The custom designed solution incorporates a hydraulic bin tipper, with a graduated tipping angle to allow an even flow of product through a mesh into the charging hopper. The hopper was specifically designed with an agitator and fluidisers to negate any chance of bridging or flow issues. This then feeds a charging adaptor for the flexible conveyor, which is tuned via a VSD to match the downstream flow requirements.

This complete system had to fit within tight space requirements meeting site specific protocols around operator access to controls and forklift loading of bulk materials.

Fresco systems is the obvious choice when the requirements are for anything that requires thinking outside of the square, with a team of specialist engineers they are able to customise the solutions to cost effectively meet or exceed the clients expectations.

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Pneumatic Hopper Discharge Flow Aid Devices

Pneumatic Hopper Discharge Flow Aid Devices

Vessels of many shapes and sizes have since been built through a process of trial and error, to store a huge range of bulk materials in virtually all spheres of industry. Particle technology has evolved considerably over the last 50 years, to produce a coherent set of theories and design guidelines.

However, there are many challenging materials whose behaviour cannot be easily accommodated hopper design i.e., fibrous, spring-like, wet / moist, stick & tacky, visco-elastic, highly compressible, caking prone and very fine bulk materials. For these types of materials, applications where conventional design does not provide an acceptable solution and retrofit situations where operating difficulties are encountered, discharge aids or discharge systems are often used to secure discharge and empty the contents of silos.

These devices are almost invariably selected based on past industrial experience or by a process of trial & error. Selection must take into account constraints that are imposed by the process and the available space. There is usually a significant economic penalty for incorrect or sub-optimal choice of a discharge system in terms of extended commissioning costs, production delays and interruptions, loss of output, product wastage, loss of quality, increased maintenance and manual attention cost.

Due to the many industries these flow problems are found, and their specific requirements, a Fresco Systems engineer will visit site to discuss your particular requirements in detail. If the facility into which a system is being considered exists the engineer will carry out a detailed survey, if a new facility we would work from project drawings. We have 20 plus years of combined experience in the design of discharge aids or discharge systems, with installations across a whole spectrum of industries from pharmaceutical and production facilities to mineral processing and power generation.

The objective of this paper is to summarise information on pneumatic air flow aid discharger device that are currently prevalent in industry. An effort is also made to provide guidelines for their selection and specification as part of an integral design, or for retrofit to overcome operating problems.

Background

Discharge aids may be defined as devices that stimulate or improve bulk solids flow out of bulk storage container. Items may be installed downstream of discharge aids to provide a means to shut off or regulate the flow of bulk solids. Slide gate valves and feeders are examples of discharge controllers. A discharge system can either be integrated with the silo or installed as an add-on, depending on the design and reason for its inclusion.

It is important to distinguish between the basic objectives of discharger aids and those of feeders to avoid misapplications. The primary purpose of a discharger aid is to promote flow, not necessarily to regulate it, and without regard to the order of zone discharge. A feeder, on the other hand, depends on the material flowing reliably to its inlet. Feeders influence the flow regime developed in the storage container and will not function if flow in the bin is unreliable. A feeder and its supply hopper are therefore an integral system.

Types of Flow Problems

The more common forms of flow difficulty are concerned with the restriction of flow, either complete or erratic stoppages, or a delivery rate less than that required. Circumstances also arise where the discharge rate is in excess of requirements, uncontrollable, in an unsuitable condition for handling, process or use or is incomplete. These difficulties arise for a number of different reasons, such as:

  • Arching: where the product forms a blockage over the outlet and flow ceases. Two basic types of arch can create a stable obstruction over a hopper outlet. One is that created by the bulk strength of a cohesive material being able to span the dimension of the opening. The other is when lumps come together to make a continuous structural across the orifice by virtue of the contact points offering a static relationship that makes a continuous load path as in a bridge.
  • Rat Holing (Piping): where material empties from a central core above the outlet up to the surface level of the stored material but no further product collapses into the empty flow channel.
  • Irregular flow: where the discharge rate is erratic or subject to cyclic variations, that is not compatible with the specific process requirements of the operation.
  • Flushing: a form of uncontrollable flow, generally due to the presence of excess air or gas in the voids that dilates the bulk material to a weak condition with virtually zero shear strength.
  •  Static zones: where subsequently problems occur due to deterioration of flow property or product quality because of extended residence time or Residue material unable to discharge by gravity.
  • Segregation: that leads to flow or processing difficulties or loss of quality.

All discharge aids work using one or more of the following principles:

  1. Dilate the material to enhance flow. The flow function of dilated material exhibits significantly lower unconfined yield strength (see Figure 3) thereby making it flow better. (Air injection may be used to dilate the bulk or inhibit time consolidation due to settlement).
  2. Induce stresses that exceed the strength of the bulk material. (Vibration and mechanical agitators may be used to deform the bulk).
  3. Reduce the friction between particles and the wall of flow channel. (Change the surface finish to a contact friction of lower value)
  4. Modify the flow regime to one more favourable to flow.
  5. Alter the bulk material flow properties by additives or surface modifiers. (Inhibit particle to particle adhesion or ‘caking’).

Pneumatic Discharge Aids

A wide range of pneumatic discharge aids are available in the market, namely

  • Aeration or fluidising pads, fluidising hoppers
  • Directed air-jet type (continuous and pulsed)
  • Pneumatically inflated dischargers or air pillows
  • Air cannons

Aeration or fluidising pads and fluidising hoppers

These discharge aid rely on dilation of bulk material (increase in inter-particle separation) by injecting air in the interstitial space between the particles. Powders tend to behave like fluids when fully aerated, but total fluidisation is not essential to promote the flow of fine particulate material, in fact doing so can result in the powder being difficult to control or not be in a suitable state for packing. Bulk materials comprised of particles of size less than 75 microns (-200 mesh), or with at least a 25% fraction less than 75 microns, (-200 mesh), are suitable candidates for aeration. However, powders with particles mostly less than 10 microns are very slow to settle, but difficult to re-fluidise, since they then exhibit channelling behaviour. Good air dispersion may be re-achieved by pulsing large airflow rates that creates shock waves to cause massive agitation.

There are two main techniques of employing product aeration:

  1. Air injection during discharge – This works by reducing the materials bulk strength and particle wall friction, particularly near the outlet region.
  2. Continuous air slide injection during storage – This works by inhibiting de-aeration and the gain of bulk strength of the whole mass due to time settlement.

It should be determined whether the bulk material has a tendency to flush/flood or flow uncontrollably in fluidised state. In such cases, option #2 is more suitable. The amount of air required to avoid high strength gain of fine powders due to time settlement is very small, but the technique is not appropriate for products that rapidly de-aerate (particle size greater than 200 microns).

Excessive fluidisation can result in bubbling and the elutriation of fines. It can also aggravate the segregation of coarse and fine fractions within the hopper.

Aeration or fluidisation pads are easily mounted on existing hoppers as retrofits, multi-layer metal mesh or woven media is typically used as air distributor. Uniform air distribution is achieved by maintaining a large pressure drop across the media. The air consumption is typically 8.5 m3/min per square metre of pad area. These inject air only when discharge is required. They generate a pressure differential between the injection points and the hopper outlet, providing both a driving force and a supply of air to satisfy the void demand of bulk expansion for flow.

Bulk control can be achieved by use of an aeration pad that covers the whole container base. Dilatation of the bulk improves the materials ‘flowability’ by reducing both wall friction and inter-particle cohesion. Activation of the entire hopper section allows a shallow hopper design to be employed. This may be supplied with a low, controlled-volume injection during storage, to stabilise the flow condition whilst the material is static, and increase the degree of aeration by injecting a higher rate of air for discharge. It is critical to supply oil free, clean and dry air for aeration to avoid product contamination. Appropriate arrangements must also be made to exhaust excess air and contain entrained dust at the top of the bin/silo.

case017_aDirected air jets

Directed jets can be effective in using the kinetic energy of air-jets to dislodge material from surrounding hopper wall and provide better gas dispersion through turbulence generation (Figure 1). The effective radius of these jets is limited to 1- 2 feet. Therefore, the jets must be placed in effective locations or multiple units need to be installed on the hopper wall to avoid dead zones. These jets can be timed and pulsed to minimise gas consumption. It is critical to supply oil free, clean and dry air to avoid contamination and prevent plugging of fine nozzles. The crucial flow region for discharge is that near the outlet, because the smaller span at this location is the most likely place for stoppages to form. Clearing this region, or part of the periphery of the orifice, is equivalent to having a larger opening that can be sufficient for the remaining contents to discharge.

Pneumatically Inflated Dischargers or Air Pillows

These are flexible bladders mounted on the cone or inclined walls of the bin/silo. Upon pressurisation (typically 1 to 3 bars), the flexible bladders expand and force the material towards the centre. They are helpful in breaking ratholes or “brittle arching”. These devices should not be used when the hopper outlet is closed or where the material is unable to flow, as local compaction will aggravate the flow difficulties, or with sharp or abrasive products that can puncture or wear through the flexible diaphragm.

case017_bAir Cannons

Air cannons (or blasters) are designed to inject blasts of high pressure gas, (up to 10 bars), in a short duration (typically fractions of a second). The shockwave traveling through the bulk solid provides a substantial force to break an arch or a rathole. Air cannons must be located where the stored material can be moved into an empty flow channel. Typical application includes use with sticky, wet, adhesive, fine, caking and fibrous materials. These devices are also used to knock sticky or adhesive materials and residual pockets of material from the walls of a bin/silo. The force created by discharging air cannons is directly proportional to the reservoir pressure. The duration of the pressure pulse depends on both the size of the reservoir and the initial air pressure. The blast from air cannons or blasters can be directed either tangentially, (along the wall), or into the bulk material at various angles. Various shapes of nozzles are available to create different dispersion patterns. When operating multiple air cannons, those at the bottom should be fired first, and the other moving progressively upwards at regular intervals. These devices should not be used for continuous operation. They are most useful for restarting flow after long downtime, after a process upset or for terminally clearing the bin after gravity flow has cleared what will discharge of its own accord. Every blast causes a reactionary force on the silo wall, so reinforcement of walls near the blasters fittings must be considered, especially for retrofit situations. Large chunks of caked or consolidated material may be dislodged from a wall, arch or rathole, to generate significant impact stresses within the silo. The silo and any associated equipment must accommodate such conditions.

Fresco Systems engineers are no strangers to devising ingenious and innovative solutions to assist you in creating a healthier and safer working environment.

Fresco Systems flexible approach means that whatever the application, no industry or production facility is precluded from a system installation.

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