The reliability of a pneumatic conveying calculation is depending on:

- The accuracy of the input parameters and the degree in which they reflect the reality.

- The accuracy of the performance data of the pneumatic installation components.

- The completeness of the theory on which the calculation algorithm is built.

- The degree of approximations in the calculation algorithm.

Ambient conditions:

- Intake conditions:

For a pressure pneumatic conveying system, the intake conditions are important as they determine the mass flow of gas.

• The intake conditions are:
  • Temperature

The intake temperature determines the intake density of the compressor. A positive displacement compressor will compress a less dense volume and  therefore delivers less mass flow.

A diffuser controlled turbo compressor delivers a constant mass flow.

The intake temperature varies with the weather conditions.

• pressure

In pneumatic conveying, the air molecules pass the material particles and when they touch, the combination of the 2 exchange electrons until electrostatic equilibration is reached.

When the air and material part from each other, the exchanged electrical charges remain also separated and leave the particles electro statically charged.

In the example of pvc-resin, the air becomes positively charged and the pvc-resin becomes negatively charged. (see tribo electric series)

This phenomenon is called the tribo-electro effect.

The electrostatic charge of a particle increases with the number of contacts between air molecules and the particles until the maximum possible charge exchange is reached.

The maximum possible charge exchange is limited by the ratio between product particles and air particles. (In fact this is the Solid Loading Ratio).

In the example of PVC-resin, the pvc particles collect electrons up to a maximum.

This maximum absorption of electrons depends on the availability of air molecules, supplying these electrons.

A low SLR implies that there are more air molecules available per product particle, resulting in a maximum charged voltage.

Electrostatic charging is therefore stronger at low SLR’s

In the bulk-blog articles:

Pneumatic Conveying, Performance and Calculations:

http://blog.bulk-online.com/?p=65

 

Dense phase- or dilute phase pneumatic conveying:

http://blog.bulk-online.com/?p=238

 

Pneumatic conveying, turbo- or positive displacement air mover :

http://blog.bulk-online.com/?p=309

 

Energy consumption per ton of a pneumatic conveying system:

http://blog.bulk-online.com/?p=331

 

I described a theory of pneumatic conveying and the development of a pneumatic conveying computing model, based on the same theory.

 

The easy use of the program enables the calculation of all kinds of relationships between the parameters, acting in pneumatic conveying.

 

The relation between capacity, Solid Loading Ratio (SLR) and conveying length for various pipe diameters is investigated, as this relationship is very useful for the preliminary design of installations.

 

 

Pneumatic conveying installations suffer from the image of being not energy efficient.

Usually, this bad image is explained by the statement that a pneumatic conveying system is based on high velocities. High velocities are usually synonymous for high energy demand.

 

The definition of the efficiency of a pneumatic conveying system is (in case of an electric drive):

 

Total efficiency = Electric energy / tons       (in kWh/ton)

 

This Total efficiency can be divided in 4 partial efficiencies.

 

1) Drive efficiency = Mechanical energy / Electric energy

 2) Compressor efficiency = Thermal compressing energy / Mechanical energy

 3) Thermo dynamic conveying efficiency = Thermal compressing energy / Thermal expansion energy

 4) Pneumatic conveying efficiency = Thermal expansion energy / tons

 

Do you remember the times when some customers actually thought that reverse auctions where the thing to do for just about anything?  It probably started out pretty well for items such as commodities.  I used to be in utter disbelieve when a few customers started to also include capital equipment.  It ended up as a lot of unpaid consulting on our part since part if not all of the system design information would almost always end up on the web. 

More confounding was trying to figure out the question what if anything the customer was supposed to get out of this deal.  Sure, the thought of a vendor having to compete with his own bid must have been appealing to buyers and accountants.  A paper towel is pretty much a paper towel, but a bulk conveying system is just too specialized to be able to obtain comparable quotes.  Almost every system – even including primary air movers – is the culmination of years worth of detail laden OEM manufacturer experience.  Without proper communication the chance of getting such an endeavor successfully up and running were slim to none.  I am glad that these auctions are mostly history.  How about you? 

 

The choice between a turbo compressor or a positive displacement pump (blower or screw compressor with internal compression) air mover for a pneumatic conveying system can be evaluated by the influence of the pump characteristics on the pneumatic conveying parameters.

A positive displacement pump displaces a constant volume of air, irrespective of the pressure at the inlet.

A turbo compressor compresses the air adiabatically and is therefore best compared with a screw compressor with internal compression.

A turbo compressor transfers impulse to the air in its impeller.

The more mass flow of air, the more power is consumed.

Therefore, the turbo is kept at a constant mass flow of air by regulated throttle at the inlet, which keeps the pressure ratio constant.

The application of controllable diffusers at the exit of the impeller makes it regulate to control the airflow between approx. 50% to 100% without efficiency reduction.

A turbo compressor always operates at its design point and therefore always consumes a constant (full) power over the full pressure range of the system. 

The screw compressor with internal compression consumes less energy at partial pressure, but still requires energy for the internal compression.

The energy consumption of a blower is proportional to the system pressure drop. 

In pneumatic conveying systems there are pressure systems and vacuum systems to recognize.

In a pressure system, a positive displacement pump and a turbo compressor deliver a constant mass flow of air, as the inlet conditions of the air are constant (atmospheric).

In a pneumatic conveying system with fluctuating pressure, the turbo compressor has the disadvantage of consuming high energy per ton at lower pressures as the power demand of the turbo is constant.

Applying a turbo compressor for sewage aeration with a constant pressure (water height) is a good choice.

In pneumatic vacuum conveying, the influence of the pump characteristics is much more complex.

In the bulk-online forum are several pneumatic conveying questions posed, using the descriptions dense phase conveying and dilute phase conveying.
It seemed then that there was not a general understanding about the definition of the two conveying regimes.
After the discussion on the Forum it became clear that the definition was related to the so called Zenz-diagram.
The Zenz diagram is widely accepted as a description of pneumatic conveying with explanatory properties.
Since the calculation of a Zenz diagram is now possible by an extensive computer program, it is also possible to investigate how the diagram is formed. 

The calculation approach is described in the Bulkblog article “Pneumatic Conveying, Performance and Calculations!”. By varying the air flow at constant capacity, the resulting partial pressure drops were calculated and combined into a table.
The summation of the partial pressure drops results in the total pressure drop of the system under the chosen conditions.
Dividing the calculated pressure drops by the total length, the pressure drop per meter is derived.

 

Reading the article “Wood Pellet Combustible Dust Incidents” of John Astad, I remembered the following.

 

All biological products are subject to deterioration.

This deterioration is caused by micro organisms (bacteria and micro flora)

 To prevent bacterial deterioration, it is necessary to condition the circumstances in such a way that micro organisms cannot grow.

 

1)      By killing the micro organisms through sterilization, pasteurization or conservation. In transport also the gassing with methyl bromide is common but not without danger.

2)      Creating an environment that micro organisms cannot develop by f.i. adding acids, salt, sweet or drying and cooling.

 

In storing cereals, grains, seeds, and derivatives, drying is the mostly used method to prevent bacterial heating.

 To prevent bacterial deterioration those materials need to be DRY before storing.

 

Terminals and factories, receiving their (raw) materials by ship, operate unloaders.

One category of unloaders is the pneumatic unloader.

Although the unloading does not belong to the core business of the company, it can be considered as an umbilical cord to the company’s process or trade.

Without incoming materials there will be no end product nor sales.

A stevedoring company will even stop to perform immediately.

Owners of such installations should be aware of the possible impact on their day to day operations and possible risk in case of failures and therefore should evaluate the offers for their installations with great care.

Purchasing under quality- or under designed and built units will create unpleasant problems (and costs) later on.

In those cases where a pneumatic unloader does not fulfill the specified expectations, the following causes are possible:

1. Installation does not reach the design specifications

In many industrial processes and transport, materials have to be stored and moved from one location to another location. For long distances, e.g. from one country to another country (or continents), modalities are used e.g. ships, aircraft, trains, trucks, etc.

Where changes are made in the transport (or storage) modality, various technologies are used to move the material from one modality to the other modality.

The basic applied technologies are :

• mechanical systems
• grabs
• screws
• belt conveyers
• buckets
• etc.

• Carrying medium systems
• Hydraulic systems using liquids as carrying edium
• Pneumatic systems using gas as carrying medium

The bulk handling sector over the world is a key player in economics as it handles all kinds of commodities such as cereals, seeds, derivatives, cement, ore, coal, etc., which are processed in the industry to other commodities, which have to be transported and handled again.