Dear Calvin.wck,

I assume that you are referring to a pressure pneumatic conveying installation for fly ash.

A compressor of 250 m3/min is a VERY big one. (approx 800 kW at 2 bar)

Either the conveying capacity is very high or the conveying distance is very long.

A third possibility is that your design pressure is very low, requiring a high airflow.

Nevertheless, a rule of thumb for an ample sized silo filter installation is:

Filter area 2 times the airflow, resulting in 2*250 = 500 m2

Filter fan 2 times the filter area, resulting in 2*500 = 1000 m3/min at approx. 400 mmWC

Additionally, install an over- and under pressure safety valve on top of the silo.

With this installation, certain under pressure is maintained in the silo, in order to prevent dust emissions through possible silo leaks.

If you can design the pneumatic conveying installation for a lower airflow, the pipeline diameter and the filter installation can be smaller

Success

Teus ■

Dear Calvin,

I'm from Dantherm Filtration, Dust collector manufacturer.

Normally, the volume of air goes through filter as same as the feeding air. In your case, you need to have the filter for 250m3/mn, and maybe you need support fan to suct the air out because of low pressure preumatic conveyor.

Depends on the size of silo, 1 or 2 filter could be use and the cartridge filter or bag filter could be use with filter load, 80-100 m3/h.m2.

If you need more info, please contact me doth@danthermfiltration.com.

www.danthermfiltration.com

Best regards,

Doan Thang. ■

Dear Calvin.wck,

For a compressor of 80 m3/min, the calculation of the filter installation is as follows:

Filter area = 2 * 80 = 160 m2

Fan volume = 2 * 160 = 320 m3/min

The filterload is then 2 m/min

The filter fan volume must be higher than the compressor volume, to be sure that there is always an under pressure in the silo. Even when the filter is in use after a while.

have a nice day ■

Dear Calvin.wck,

To avoid misunderstanding.

The figure of 80 m3/min corresponds with the compressor displacement.

This displacement is ( apart from internal leakage) constant, regardless the pressure.

Thus:

80 m3/min at 3 bar does NOT result in 240 m3/min at atm pressure, but is 80 m3/min.

A compressor displacement of 80 m3/min results at 3 bar in 80/(3+1) = 20 m3/min. (Temperature neglected)

In the filter sizing, the compressor displacement figure must be used.

all for now

Teus ■

Dear Calvin.wck,

Yes, the factor 2 (Filter load in m/min) has to be considered as a rule of thumb.

best regards

Teus ■

Dear Calvin.wck,

Your perception of the installation is right.

The fan will not suck more air from the silo than there is air supply to the silo.

However, the airflow to the silo is not only the compressor airflow, but also the leak air, which is depending of the under-pressure in the silo.

This under-pressure is required to prevent dust escaping through the silo leaks.

In addition, the airflow from the pneumatic conveying system is not constant in time.

There may be surges from expanding (empty) kettles.

An air surge would increase the pressure in the silo above the atmospheric and create dust clouds through the silo leaks.

The fan will set itself on its own volume/pressure curve to an under-pressure corresponding with the balance of incoming air and out flowing air.

In case of a surge, this working point is shifting, but trying to keep an under-pressure in the silo.

In case of malfunctioning of this system, an under- and over pressure safety valve keeps the pressures in the silo between safe limits

Best Regards

Teus ■

dear Calvin,

A centrifugal fan has a stable operation between maximum pressure / no flow and minimum pressure / maximum flow.

According to the formulas, your conclusion is correct.

However, if your system is using 2*80 m3/min at 3 bar pressure for only 67 tons/hr of fly ash, resulting in abt 10 kWh/ton, I suggest that the design of the intended installation is thoroughly reviewed. ( Or it is indeed a special installation)

success

Teus ■