What are the particle spectra at the spigot and overflow for each product that you classify? You are getting more in the overflow than at the spigot which sort of contradicts the idea of cycloning in the first place. How consistent is the airflow?

You produce 99.71% of sulphate but only 87% of sodium carbonate. What happened to the rest of the short supply?

How wet is the spigot product? Soda Ash is hygroscopic and you are mixing it with moist air as far as the diagram shows.

In the .pdf the baghouse inlets are the classical 'too low' type. You have to have the ID fans outside the product line. Wear and contamination spring to mind. How does the filter bag behave in arragement 1 seeing how there is no more suction downstream?

Why would someone build a plant before addressing these sort of questions? ■

Your Arrangement 2 is the correct way. But, why two blowers? If you are handling hygroscopic materials, then moisture will be a big problem for your bagfilter.

You should get help from a competent, well-known bagfilter supplier.

Michael Reid. ■

Dear uditha, Michael

In a vacuum system, there will normally be no condensation as the temperature does not drop and due to the lower absolute pressure in the system, the RH drops and the air gets drier.

Applying cyclones for materials in the 75 micron range seems rather optimistic to me.

BR

Teus ■

Uditha,

You are getting a bit less than 60% collecting efficiency from your cyclones. This is not good enough for product recovery. To get anywhere near a reasonable recovery (say 90%) with cyclones alone you will have to accept a very high pressure loss, say 2 to 3 kPa, depending.

The inlet load of 600 mg/cu.m is easily handled by a bagfilter so dispense with the cyclones.

I repeat, get the advice of a competent bagfilter supplier. This is not a difficult exercise for an experienced contractor.

Good luck,

Michael. ■

Originally Posted by Teus Tuinenburg

Dear uditha, Michael

In a vacuum system, there will normally be no condensation as the temperature does not drop and due to the lower absolute pressure in the system, the RH drops and the air gets drier.

Applying cyclones for materials in the 75 micron range seems rather optimistic to me.

BR

Teus

Hi TT,

With soda ash the problem is not condensation. This stuff will suck water out of any air.

There are no mass balances in the thread start. I think this thread has been partly translated & resubmitted down the Homepage not too far from here. What say? ■

Hi Louis,

I understand your remark that water vapor reacts also with the soda ash.

This problem is additional to the cyclone/filter issue.

Water vapor content of conveying air is more troublesome at low (or very low) solid loading ratios as the amount of air (water vapor) is high in relation to the soda ash amount and a higher soda ash percentage will bond.

This requires dried (de-watered) air, a closed air system or abandon pneumatic conveying.

The pneumatic conveying is not difficult, it is the chemistry of the product.

Take care

Teus ■

Uditha,

Keep in mind that the bagfilter will always contain some residual dust. The hygroscipic nature of the dust will cause you problems even when the system is not working.

You may need to insulate the bagfilter and heat it to avoid blockages and blinding of the filter bags.

Get the advice of an experienced bagfilter contractor!!

Michael. ■

Dear Michael,

As Louis pointed out, that even the water vapor bonds with the soda ash, isolation and or heating will not prevent the accumulation of bonded water and soda ash in the filter over time.

The only way left is dry (de-water) the conveying air, if necessary in combination with a closed air system or abandon pneumatic conveying.

I think.

Take care

Teus ■

Dear uditha,

Your conclusion that the bag house geometry will not change, because of the CFM, is correct.

The filter area has to be designed for the same CFM.

In case of a cyclone before the filter, mainly the dust will enter the filter.

By applying a filter hopper, which takes over the function of the cyclone, the cyclone is not necessary anymore. (Although in some (rare) occasions, a cyclone is built in, in a filter receiver hopper).

From your description, it is not clear, whether you are referring to a filter cartridge or a pulsed dry air cleaned filter.

Each with its own characteristics.

Your concern about additional pressure drop is also justified.

Probably, your vacuum conveying system will be negatively influenced by an extra filter, as you are using a centrifugal fan as air mover.

Consulting a reputable and experienced manufacturer is the safest way, as they have the learning curve behind them.

Best regards

Teus ■

Uditha,

The dust load is very low and you don't need a cyclone. Cfm stays the same without the cyclone, system pressure loss is less. Cyclones add an additional maintenance problem because of abrasion.

Here is a layout of a bagfilter (coloured green) in a mineral sands processing plant. The dust is very abrasive. The bagfilter has a "pre-separation" chamber with a hardened steel target plate opposite the inlet, bolted in place for easy maintenance. The velocity at the inlet is less than 15 m/s.

Get advice separately from filter bag manufacturers about the correct material. They have a very large data base of successful applications. They will advise you about surface treatments, hydrophobic coatings, foam coatings etc. Cartridge filters are not suitable for hygroscopic dusts.

It is normal for bagfilters to be insulated where high moisture is present in the conveying air, e.g., fluid bed dryers, galvanising plants. In galvanising plants, the hopper is heated to maintain the internal temp. above acid dew point. Without these features, the life of the equipment is very much reduced.

Regards,

Michael.

Attachments

ducting layout outside - iso1 (PDF)

img-z171208-0001 (PDF)

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