Bag filter capacity rating is about 70m3/m2/hr seems to be OK.

Only point that needs to be checked is whether the temperature of air filtered is above dew point. It it is not you may have to insulate the pipe line and dust collector casing.

You must be using dry air for positive pressure puffs. That is also necessary. ■

Amit,

What is the pressure of the cleaning air? It needs to be 600 - 650 kPa.

How often does the pulse of cleaning air occur? For new filters it should be approx. every 40 to 30 sec. or so, increasing in frequency as the filters age.

What is the duration of the pulse (the solenoid opening time)? Should be about 300 ms.

Is the compressed air clean and dry? Moisture will lead to blinding.

How often if frequent? What does the filter gauge read when you replace the filters?

The filter material is appropriate for this duty. The filtration velocity seems O.K for D50 8 microns.

Over-cleaning is a possibility. New filters should be allowed to build up a filter cake (dust layer) before the cleaning system is turned on. Premature cleaning can cause fine dust to blind the inner layers of the filters.

Have you talked to the bag filter supplier about this?

Michael Reid. ■

Dear Amit,

The particle size of 8 microns is very small for a filter material.

Check with the filter material supplier, whether the porosity of the filter medium is adequate for 8 microns or less.

The suspension velocity of an 8-micron particle of hydrated lime (material density 2211 kg/m3) is approx. 0.6 m/sec.

The upward air velocity between the filter bottoms must be below that velocity, otherwise the particles will be kept in suspension between the filters.

This upward air velocity (can velocity) can be calculated from your installation drawings.

You can check this phenomenon, by starting with a clean filter and monitor the filterdrop in time.

If the filter drop has increased to a certain level, switch off the pneumatic conveying airflow and let the filter clean itself for a short period.

Then start the monitoring again.

In case the procedure is reproducible, then there is a filter problem in keeping material trapped between the filters.

The solution is then to increase the size of the filter housing and increasing the distance between the filter elements.

In addition, the filter load of 1.13 m/min seems to be rather high for an average particle suspension velocity of 0.6 m/sec.

Increasing the filter area might also be necessary to consider.

Not having information about the pneumatic conveying system itself, it is advisable to check whether the system is not operating with too high air velocities.

If that is the case, it is possible to lower the air volume, improving the filter function.

As Michael said, over cleaning is a real issue to address (controlled by cleaning pressure, cleaning frequency and cleaning pulse time)

Have a nice day

Teus ■

Originally Posted by Amit Segev

...The problem is with the bag filter on the top of the silo which gets blocked frequently. .....

The cleaning device of the bags is positive pressure puffs and it working perfectly.

The bags do not look blocked. No layer of material is seen to accumulate on them.

What should I do solve the problem of the frequent blockage of the bags ?

Amit Segev

The evidence is contradictory. There must be something you are not telling us. Please try again.■

Dear Amit,

The filter bags are rather long, which may cause the particles to be sucked against the filter again before they are fallen down underneath the bag.

I calculated thecan velocity between the filter bags as follows.

Bag house area = 1 m2

Cross area of filter bags: 25 * pi/4 * 0.142^2 = 0.396 m2

Free area between bags = 1 – 0.396 = 0.604 m2

Can velocity = 1200/3600 / 0.604 = 0.55 m/sec (instead of your 0.8 m/sec)

As Mr vinayak stated, the temperature in the filter house must be above dew point temperature.

The intake conditions of the compressor + the water content in the hydrated lime determine the amount of water, present in the baghouse.

Suppose the bag house conditions are the intake air conditions of 25 degrC at 100% RH + 5000/100 * 0.85 kg water from the hydrated lime.

Then the baghouse temperature has to be maintained above 41 degrC, to avoid condensation.

However, when the injected pulse air is not properly dried and because of rapid expansion cools down below the dew point temperature, the possibility of water condensation in the filter material becomes suddenly real. This process may well develop over a longer period.

Microscopic research on the failed filters is now advised.

Success

Teus ■

Hello Amit,

Maybe, polyester felt(ptfe coating treatment),or with ptfe membrane can workable for this. Have you tried this material?

We are factory of needle felt and filter bag.

Sophie

Shanghai BG(www.bgfiltech.com)

sophie@bgfiltech.com ■

There is now an improved design, low profile, low cost Bin Vent Filters using a new technology called "POWER-CORE" are available in the market. Please contact hsi@wcoil.com or visit www.hawthornesystems.com or cal 419-643-5861 for more information . We will be glad to further advise and provide solutions to your present and/or future dust control problems.

Sincerely,

Unsal Yonak

Vice President

Projects Manager

HAWTHORNE SYSTEMS INC.

312 W.Main Str.

Beaverdam, OH

419-643-5861

hsi@wcoil.com

www.hawthornesystems.com ■

For temperatures which exceed the range of available cloth bag filters, consider metal filters which go as fine as HEPA range and are pulsed-jet cleanable. Systems are available that pulse when a programmed differential pressure is reached, eliminating much of the guesswork about timing between cleaning cycles. Information is available at www.porvairfiltration.com . ■