Pneumatic Conveying and Centralised Vacuum Systems
Lean, Dense Phase Conveying and Powder Handling Systems
We have designed and installed lean phase conveying systems (suspension flow) for various products and materials, for instance plastic granules, wood shavings and dusts, various food stuffs, agricultural grains.
Conveying systems are designed to minimise product degradation and attrition to pipework systems. Attrition is abrasion due to the impact of particles against the inside walls of the pipe.
Particle degradation is in most cases undesirable because it can result in:
- Increased dust content in the product, in turn leading to problems with dust emission in further handling and poorer “handleability” of the material, e.g. hang-ups in hoppers, pipeline blockages etc. An increased ATEX (dust explosion) risk can also result.
- Structural damage to the particles, e.g. cracking the shell of grains leading to processing problems
- Increased breadth of particle size distribution, making segregation more severe
- Problems with customer perception of the product
Transport velocities are calculated depending upon; feed rates, product density, particle shape, our extensive experience and where appropriate pilot / trial system design (via Wolfson Centre)
A 25% increase in particle (air) velocity will give rise to something between a 60% and 90% increase in rate of wear. Particle breakage is less easily quantified, but is usually recognised to follow a similar trend, i.e. increased velocity leads to is proportionately increased particle damage. It is therefore essential to optimise transport velocity to the minimum required for specific, particle characteristics. Even small reductions in velocity will always bring big reductions in these problems.
However, with some materials it is possible to convey them at lower velocities than those needed for suspension flow. The mechanism by which such materials can be conveyed through a pipeline depends on the physical characteristics of the product in question, but typically is in the form of a moving bed or a slugging flow at high concentrations in the.
Typical air velocities are only 2-6 m/s at the material feed point. This approach is commonly known as dense phase or non-suspension conveying.
The combination of lower velocities and the fact that the majority of the particles are mutually self supported by their immediate neighbours, thereby preventing contact with the pipeline walls, means that a well designed system operating on this basis can result in a major reduction in particle degradation and pipeline wear compared with that of a dilute/lean phase system operating at the same duty.
Specialist testing / advice is required to access whether products are suitable for dense phase conveying – please contact us for advice.
A lean phase conveying system consists basically of:
- (high pressure) air mover / vacuum pump, ie roots blower
- Well designed pipe-work system minimising bends, possibly with stepped pipe diameters, attrition
- bend materials will be chosen for least wear resistance ie consideration given to polymers, metals and ceramics Note: a wear test may need to be carried out before making a decision on appropriate material or type of bend.
- Receiver vessel; for instance cyclone type dust collector with filtration
- A rotary valve, ‘double dump’, or gravity feed valve will generally be fitted to receiver to discharge the product into a storage vessel.
- Secondary filter prior to vacuum pump.
- ATEX considerations, such as earth bonding, ATEX valves, explosion relief / suppression on receiver vessels etc. Shut-off and explosion break valves.
System design should minimise the number of bends, as each bend will:
- increase system resistance and hence motor power
- increase particle breakage
- most attrition / wear will occur at pipework bends
Systems will generally be controlled with inverter driven motor / fans via from system pressure. This can provide benefits such as:
Improved control and hence Product Quality
Increase Production Thruput
Reduction in Raw Material usage
Hoppers and steerage vessels are designed for appropriate feed rates, storage and product characteristics; dry-fine symmetrical geometry provides free-flowing characteristics, whereas readily agglomerating, hydroscopic, fibrous materials can present Core Flow characteristics.
See also, dust extraction and collectors / powder injection systems
Centralised Vacuum Systems
In the same way as lean phase conveying, our centralised vacuumation systems are designed to minimise product degradation and attrition (abrasion) to pipework systems; in this way the system is designed for minimum flow resistance, reducing motor/ fan sizing and energy costs. Transport velocities are calculated depending upon; estimated transport velocities / feed rates, product density and characteristics etc.
Systems will generally be controlled with inverter driven motor / fans via from system pressure. See Motor Starters, Control panels, automation and monitoring systems
A complete range of industrial vacuum tools, shut-off and ball valves, antistatic flexible ducting, Sleeves Gaiters, etc are available for our vacuum systems.
Upgrading an existing LEV system with Vacuum Extract Points
It may be possible to upgrade an existing LEV extraction system with Vacuum points. This allows the extract system airflow to be diverted and re-directed through a connector/ball valve, attached to vacuum hose and fittings.
The existing LEV system will require a survey prior to installation of vacuum points
A Compressed air amplifier / venturi boosts the airflow for long or small diameter flex hose, connected to a range of industrial vacuum tools. The venture amplifier overcomes the very high resistance created by the flex duct.
The flex duct can be connected into tool extraction hoods via reducers (ie to 44 / 38 / 35mm etc), or to bench mortisers, brick jointers etc. etc.
In this way house keeping/cleaning tasks can be vastly improved, eliminating or reducing industrial vacuum cleaner use or sweeping up.
The system can consist of:
- A 450 ‘saddle’ connecting into the existing ductwork. A ‘blast gate’ shut-off damper/valve enables the airflow down stream of the ‘vacuum point’ to be diverted for use in the vacuum system. A connector/ball valve enables the connection of the (antistatic) vacuum hose, venturi unit* and floor, crevice tools etc.
- The ‘compressed air venturi’, boosts the power of the vacuum point and overcomes the resistance of ‘long’ lengths of narrow diameter flex hose.
There can be many advantages over individual or centralised vacuum systems:
- Far lower costs.
- Enables the LEV1 to ‘double-up’ as an effective vacuumation system
- Enables upgrade of existing systems or longer lengths of hose to be used for smaller systems.
Note: The compressed air is only used whilst the vacuum point is in operation