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Pneumatic Conveying Systems

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Pneumatic Conveying Systems, Dilute Phase, Dense Phase, Pressure Conveying Systems, Vacuum Conveying Systems, Positive / Negative Pressure Pneumatic Conveying Systems, Pneumatic Conveying System Lines, Turnkey Projects, Manufacturer, Exporter, Supplier, Pune, Maharashtra, India

Electromech Technical Services is a professionally engaged dynamic firm in the Design, Consulting, Manufacturing & Export of pneumatic conveying system The quality of our range is check on the parameters laid by Bureau of Indian Standards. To completely satisfy the customer's demands with quality, time bound commitments and best prices in industry.

The pneumatic conveying systems is a tailor made conveying system depends on the product characteristics, particle size, capacity, number of sources and number of destinations. Each pneumatic conveying system is designed & customized as per the application.

Prime mover can be Pneumatic Conveying systems: Roots blower, Centrifugal blower, Centrifugal fan, Radial blower, Compressor or compressed air.

Pneumatic conveying system is a process by which bulk materials of almost any type are transferred or injected using a gas flow as the conveying medium from one or more sources to one or more destinations The system requirements are a source of compressed gas, usually air, a feed device, a conveying pipeline and a receiver to disengage the conveyed material and carrier gas. The system is totally enclosed, and if it is required, the system can operate entirely without moving parts coming into contact with the conveyed material. High, low Pneumatic conveying system or negative Pneumatic conveying system pressures can be used to convey materials. For hygroscopic materials dry air can be used, and for potentially explosive materials an inert gas such as nitrogen can be employed. A particular advantage is that materials can be fed into reception vessels Maintained at a high pressure if required.



1. Pressure Conveying Systems

A. Dilute Phase pressure conveying systems:
Dilute phase pneumatic conveying system is a suspension flows wherein the material to be conveyed is introduced into a moving air stream inside a pipeline. For the material to remain in suspension there is a minimum conveying velocity which varies for different materials. The quantity of material that is fed into an air stream is also dependent on material characteristics like bulk density, particle size, sieve analysis, frequency distribution etc. Generally, the material to air ratio varies between 3 to 10 kg of material to kg. of air Conveying velocities are in the range of 18 to 28 m / sec depending on the product characteristics. The dilute phase conveying system uses low-pressure air at pressures less than one bar in case of pressure conveying and (-) 5000 mm in case of vacuum convening, which is generated by positive displacement type roots blowers or by centrifugal blowers.

B. Dense Phase Pressure Conveying Systems :
Dense phase pneumatic conveying is a widely known as plug flow systems which is non-suspension flow. The product is filled in a pressure vessel, which is then pressurized with the air or gas to be used for conveying. Once a pre-set pressure is reached inside the vessel, the bottom discharge valve opens and the material is conveyed to the destination. The material to air ratios is higher in dense phase conveying in the range of 20 to 100 kg / kg. of air Dense phase conveying uses compressed air and requires an air compressor. Dense phase conveying is used for high capacity and long distance conveying. Dense phase conveying employs the pressure vessel with valves and instrumentation which is controlled through PLC based control panel.


2. Vacuum conveying system

A. Dilute Phase Vacuum Conveying Systems :
These vacuum pneumatic conveying systems are installed primarily wherein multiple feed points are involved. The advantage of this system is any leakage is inward due to which these systems are popular for conveying of explosive or hazardous products. As the system is operating below the atmospheric pressure the conveying velocities are generally higher than the pressure conveying. These systems are also popular for short distance conveying in food and pharmaceutical industries.


B. Dense Phase Vacuum Conveying Systems : Dense phase vacuum conveying systems are used for very short distance of conveying typically below 15 mtrs with 1 or 2 bends. The components are specially designed suction nozzle, conveying piping, product separator and airlock valve.These systems are operating below (-) 5000 mm of WG using roots blowers and used for product conveying from bags / drums or hoppers.



3. Mode Of Pneumatic Conveying Systems

If the material is conveyed in suspension in the air through the pipeline it is referred to as dilute phase conveying. If the material is conveyed at low velocity in a non-suspension mode, through all or part of the pipeline, it is referred to as dense phase conveying

A. Dilute phase Almost any material can be conveyed in dilute phase, suspension flow through a pipeline,regardless of the particle size, shape or density. It is often referred to as suspension flow because the particles are held in suspension in the air as they are blown or sucked through the pipeline. A relatively high velocity is required and so power requirements can also be high but there is virtually no limit to the range of materials that can be conveyed. There will be contact between the conveyed material and the pipeline, and particularly the bends, and so due consideration must be given to the conveying of both friable and abrasive materials. With very small particles there will be few impacts but with large particles gravitational force plays a part and they will tend to 'skip' along horizontal pipelines.

Types of Pneumatic Conveying systems in a Dilute Phase
There are several methods of transporting materials using pneumatic conveying system. In general, they seem to fall into three main categories : dilute phase, dense phase, and air conveying.

1. Dilute-phase pneumatic conveying system is the process of pushing or pulling air-suspended materials from one location to another by maintaining a sufficient airstream velocity. Dilute phase conveying is essentially a continuous process, characterized by high velocity, low pressure and low product to air ratio.

2. Dense-phase conveying system relies on a pulse of air to force a slug of material from one location to another. Dense-phase system is essentially a batch process, characterized by low velocity, high pressure and high product to air ratio unlike dilute phase which is a low product to air ratio.



Dilute-Phase Pneumatic Conveying System
dilute

Dilute phase conveying is the most common used method of transporting materials. This process uses a relatively large amount of air to convey a relatively small amount of material and at lower pressures than dense phase systems. The material is transported at high velocities through the system while being suspended in air. It is often referred to as suspension flow because the particles are held in suspension in the air as they are blown or sucked through the pipeline. To keep the material in suspension, it is necessary to maintain a minimum conveying air velocity that, for most materials, is of the order of 2500 - 6000 fpm.

Dilute-Phase pneumatic conveying system - suspension flows are


  • High velocity conveying @ 3,200 to 8,000 feet per minute
  • Operating pressures in range of 5-12 PSIG (positive) or negative pressures of 4-12" Hg
  • High air to solids loading ratios ( > 2.0 )


There is virtually no limit to the range of materials that can be conveyed with dilute - phase system. Products commonly conveyed in dilute phase systems include flour, resins, specialty chemicals, ground feeds, and granular and palletized products. Of the various types of pneumatic systems, a dilute phase system will generally be lowest in capital cost.

Components Of Dilute - Phase System
Major pneumatic system components include:
1. Pressure blowers and vacuum pumps with integral sound enclosures
2. Rotary airlock valves
3. transfer line including piping, elbows; divert valves (flex-tube diverters, wye-diverters, plug diverters and other line diverter configurations).
4. Filter receivers
5. Cyclone separators
6. Gain-in-weight and loss of - weight batching systems
7. Dust collectors and bin vents
8. Controls


Types Of Dilute - Phase Systems


The dilute - phase system can be designed in three ways:
1. Positive pressure pneumatic conveying system
2. Negative pressure or vacuum pneumatic conveying system
3. Combination of positive – negative pneumatic conveying system

Dilute phase - Positive pressure pneumatic conveying system
Positive pressure systems operate above atmospheric pressure and are used to convey bulk materials from a single or multiple sources to one or multiple destinations, over medium distances and with greater capacity than possible using vacuum systems. A typical positive pressure dilute phase system will consist of a rotary valve; pipe-work which would include long radius reinforced bends; a filter receiver or cyclone/filter arrangement; and positive displacement (roots type) air blowers. The schematic below shows a typical arrangement of the components of positive pressure systems.



Dilute phase transport positive pressure system

The product enters the convey line, which is at a higher pressure, via a special feeding device, usually a rotary valve airlock, or a venturi. The product is frequently suspended in the airflow, moving at relatively high velocities depending on the particle sizes and densities. The suspended material-air stream is separated at terminal point by means of a filter receiver / cyclone separator, or fed directly into process vessels that are vented to downstream dust collection devices. In this type of system, the material does not go through the fan / blower. There are two advantages to this. First, the fan wheel does not damage the material. Second, the fan does not experience any wear and tear from the material. These systems generally operate on a continuous basis - product is constantly supplied at the starting point, and arriving at the destination without interruption. This allows this type of system to be easily adapted for dosing and continuous weighing applications.

Applications

Dilute phase pressure conveying is particularly suitable for systems which convey materials at low to moderate capacities over medium distances, from single or multiple sources to single or multiple destinations. These systems are versatile and adaptable for different materials and the low operating pressures allow lower cost pipelines and fittings. Cement, fly ash, food items, resins and dry chemicals are examples of products that can be conveyed successfully using this method.


Typical Specifications Convey Rates

:

Low to High, typically from <1 to 50 tons / hr

Convey Velocities

:

Typically 3200 - 8000 fpm

Convey Distances

:

Up to 600 ft or longer

Air Mover

:

Positive displacement (roots Type) blower, or fan

Operating Pressure

:

Up to 14.7 psig

Air/Material Ratios

:

> 2.0



Dilute Phase Negativepressure ( Vaccum ) Pneumatic conveying Systems

Negative pressure system are commonly used for drawing material from multiple sources to a single point. There is little or no pressure difference across the feeding device and so multiple point feeding into a common line presents few problems. As a consequence, the feeding feeding device can be a very much cheaper and simple item in a negative pressure system than in a positive pressure system Negative pressure ( vacuum ) is generally used to convey material from multiple sources such as storage vessels, process equipment, trucks and rail cars, to individual or multiple destinations. Vacuum systems are excellent for multiple product inlets through the use of simple diverter valves; however, it becomes costly to have multiple destinations because each must have its own filter receiver with partial vacuum capability.

Negative pressure systems generally use positive displacement ( roots type ) exhausters providing up to 50% vacuum to convey materials through a pipeline to the destination where the air and product are separated at a receiving vessel with a filter, or a cyclone.

The product enters the convey line directly, or if metering is required, via a special feeding device such as a rotary valve or screw feeder. The conveyed product is discharged from the receiving vessel either on a continuous basis by a rotary airlock or intermittently by valves to surge hoppers, storage vessels or other discharge points.

In vacuum conveying, no moving parts contact the materials and no dust can escape into the atmosphere. Because of this superior leak containment, they are often specified on the basis of cleanliness, particularly when handling hazardous materials.

The drawback of this system is that if the loading is high or the length of the system is large, the components must be designed for high vacuum. This adds cost to the components and must be considered when comparing methods of transport.



Applications

Vacuum conveying systems are particularly suitable for systems which convey materials at low to moderate capacities over medium distances, from multiple points to a single destination. These systems are versatile and adaptable for different materials and the low operating pressures allow lower cost pipelines and fittings. This method is frequently used for central vacuum cleaning systems and other applications, which require a reticulated network of vacuum pipes to convey product to a single collection point.



Typical Specifications Convey Rates

:

Low to Medium, typically <10 tons/hr

Convey Velocities

:

Typically 3000 - 8000 fpm

Convey Distances

:

Up to 300 ft or longer

Air Mover

:

Positive displacement (roots type) exhauster, or fan

Operating Pressure

:

Up to 50% Vacuum

Air/Material Ratios

:

> 2.0


Dilute phase -Combination Negative - Positive pressure pneumatic conveying systems:

This pull-push system incorporates the advantages and benefits of both negative and positive pressure arrangements in a single system. These systems are used where there are multiple material entry points, and multiple delivery points. A very common application is the unloading of a standard railcar. Since the cars cannot be pressurized, air is pulled from the outside, through the car (carrying solids with it) to a filter. Then after the filter, a blower can be used to forward the solids to the final receiver. If the final receiver is next to where the rail car is being unloaded it may be practical to use a complete vacuum system.

Components Of Dilute - Phase System
Major pneumatic system components include:
1. Pressure blowers and vacuum pumps with integral sound enclosures
2. Rotary airlock valves
3. transfer line including piping, elbows; divert valves (flex-tube diverters, wye - diverters, plug diverters and other line diverter configurations).
4. Filter receivers
5. Cyclone separators
6. Gain-in-weight and loss of - weight batching systems
7. Dust collectors and bin vents
8. Controls and electrical equipment
9. Silos, day bins and other storage vessels



Electromech Technical Services Ways to Increase the pneumatic conveying Capacity :

1. Optimize solids / air ratio
2. Minimize the number of bends
3. Shorten the total conveying distance
4. Reduce conveying velocities to just above saltation

5. Step up the line diameter near the end of the system
    • Doing so decreases the total system pressure drop
6. Minimize flex hose length and eliminate where possible



Electromech Technical Services Ways to Minimize Wear in Pneumatic Conveying system Lines

1. Reduce conveying velocities
2. Use wear resistant materials for more prevalent abrasive materials - Sand, carbon black, etc.
3. Minimize line length and number of bends
4. Enter the vessel radially, not tangentially
5. Hang a flapper in the middle of the bin to allow the material to contact it instead of the vessel wall
6. Step up the line diameter before the vessel entrance



Essential Points to be required Dilute Phase Pneumatic Conveying systems

1. Do not use sloping pipe runs. The refluxation, (run-back and re-conveying of the same material), will require the pipe to re-transfer the product slipping back on top of its normal load, and the effect is accumulative. At best it will significantly increase the conveying burden, but is more than likely tend to block the lower bend.

2. Allow a 'reasonable' horizontal conveying length before the first bend to allow the bulk material to accelerate to a stable conveying speed and reduce the sectional loading of the conveying pipe. Material slowed by the bend occupies a greater proportion of the pipe's cross sectional area and thereby offers more obstruction to the air flow, which increases the pressure drop along the system.

3. Do not fit bends close together on the pipe run for reasons similar to the above.

4. Consider stepping the pipeline on long runs. Air expands with pressure drop, so velocities inevitably increase along a constant pipe run. Higher material velocities increase wear on bends and product degradation.

5. 'More air' can be 'less transfer capacity in dilute phase systems. Larger solids and gas frictional losses caused by higher gas velocities can absorb more energy than the extra input of energy. There is an optimum gas flow rate for a given lean phase flow system. Check with a specialist for the correct solids / gas ratio balance and top performance.

6. Product damage and wear at bends is very material dependent. Blind Tee does usually have much merit, but cause a higher pressure drop than long radius bends.

7. Rotary valves do leak and also pass air differentials through the returning empty pockets. They also tend to fill with product on one side of the valve as the empty pockets are rotated to present a space for material to flow in. Back flow of gas and biases intake causes many feed problems. Make sure that the valve is properly vented and that the feed channel is of good form for flow across the whole cross section. A short inlet standpipe is useful for such duties as a cyclone outlet or a feed into a high pressure line.

8. Check that cyclones have an unobstructed outlet. If there is intermittent or periodic discharge, allow clear buffer capacity to avoid interfering with the cyclone operation.

9. Allow for the pressure drop on the supply line to the blower. Include an allowance for any filter, silencer, acoustic box or compressor enclosure and extended supply run, as may be appropriate. Be sure to compensate for the temperature increase due to gas compression.

10. Provide adequate instrumentation; this is essential to know what is going on and to facilitate a proper investigation of any problems that may arise.



Electromech Technical Services Dense phase pneumatic conveying systems:

dense

In dense phase conveying two modes of flow are recognized. One is moving bed flow, in which the material is conveyed in dunes on the bottom of the pipeline, or as a pulsatile moving bed, when viewed through a sight glass in a horizontal pipeline. The other mode is slug or plug type flow, in which the material is conveyed as the full bore plugs separated by air gaps. Dense phase conveying is often referred to as non-suspension flow. Moving bed flow is only possible in a conventional conveying system if the material to be conveyed has good air retention characteristics. This type of flow is typically limited to very fine powdered materials having a mean particle size in the range of approximately 40-70_m, depending upon particle size distribution and particle shape. Plug type flow is only possible in a conventional conveying system if the material has good permeability. This type of flow is typically limited to materials that are essentially mono-sized, since these allow the air to pass readily through the interstices between the particles. Pelletized materials and seeds are ideal materials for this type of flow



Dense Phase Conveying

In a dilute phase conveying system, the product is transported by lift, or suspension, of the individual particles in the air stream. As the velocity is subsequently reduced, the larger particles cannot sustain this lift and they begin to fall from suspension to the bottom of the pipe. The technical term used in the industry that describes the velocity at which particles fall from suspension from the air stream is "saltation velocity". Unlike dilute phase conveying systems that typically use larger amounts of air to move relatively small amounts of material at high velocities in suspension, dense phase offers he enormous advantage of efficiently "pushing" a much denser concentration of bulk solids at relatively low velocities through a conveying line. The best, single description for identifying if a system is dense phase is whether the product velocities in the pipe are designed to be operating below the saltation velocity.



Applications of Dense Phase Pneumatic Conveying Systems :
The number one reason to apply a dense phase design is when the product being handled is highly friable. Many products within the food industry fall into this category. As an example, if a consumer opens a bag of cheese puffs and finds them broken, he will quickly change loyalty to the brand. Broken pieces do not command the salable price and are usually discounted for wholesale use. The cost effect of material damage due to degradation can be huge and preventing degradation is thus a high priority especially in food processing and canning operations of meat lumps, softened grains and vegetables etc.

By virtue of the low velocity characteristics, the next best application for dense phase is transportation of highly abrasive materials. The higher velocities associated with dilute phase conveying can lead to rapid pipe wear. Many materials such as sand, alumina etc. are so abrasive that they can wear a hole in a pipe elbow in just a few weeks. The pipe wear can also result in a contamination of the product.

There is really only one other main reason for selecting dense phase. This is typically found within the plastics and petrochemical industry. Some of the softer plastics, such as polypropylene and polyethylene, will smear onto the pipe wall when the product slides along the outer wall of an elbow in a dilute phase transport system. The plastics will actually melt from the frictional contact with the pipe wall and will leave a long thin layer of material. The layers are peeled off into strips and re-entrained into the system. These strips are commonly referred to as a "streamers" and they will quickly build up in awkward places and stop product flow. Dense phase transportation will eliminate the streamers that are commonly associated with dilute phase conveying.



Dense Phase Theory

The main principle of a dense phase conveying system is to slow down the velocity of the product in the pipe to a point that is below the speed at which the product breaks or degrades. At low velocities, the product lies for periods of time in the bottom of a horizontal line and it is blown under pressure to the discharge point in slugs or plugs.

The dense phase pneumatic conveying systems uses low volume, medium pressure air stream and relies on a continuously expanding volume of air pushing cohesive slugs of material along the pipe. This system uses a transfer vessel / pump tank to feed the material into the conveying line. It is a batch system with plugs of material separated by cushions of air. The velocity range at the source can be as low as 200 fpm for the majority of products. The product velocity at the destination is always a function of the system differential pressure, but in most cases it rarely exceeds 2000 fpm.

Dense phase technology reduces the air consumption to the absolute minimum by allowing the system to convey at maximum density. This maximum density conveying technique has three main advantages.


Typical Specifications Convey Rates

:

High, up to 100 tons / hr or higher

Convey Velocities

:

Low, 200 to 2000 fpm

Convey Distances

:

High, up to 10000 ft or longer

Air Mover

:

Compressor (Screw, rotary, reciprocating)

Operating Pressure

:

Up to 125 psig

Air / Material Ratios

;

< 0.2



Types Of Dense Phase Systems
The following different modes of dense-phase conveying are in use.


1. Fluidized dense phase
2. Low velocity slug flow
3. Low velocity plug flow

4. Bypass conveying
5. Single slug conveying

6. Extrusion flow
7. Air assisted gravity conveying



Quality Control and Inspection

All the manufacturing, Fabrication and machining of the equipments is carried out as per relevant Indian / International standard. The quality control personal check every product as per relevant Quality Assurance plans procedures before dispatched. We provide excellent reliable sales and service.



Guarantee

Electromech pneumatic conveying system, are guaranteed for a period of 12 month from the date of shipment against any manufacturing defects, when properly installed, operated and service in accordance recommendations. System Wear And Tear Is Not Covered By The Guarantee.