Limestone Silo - Bag Filtration 3

[sdlee2008]

Hello guys,

I've been given the task of checking whether the filtration system (filter sock/bag) on our Limestone silo is undersized or not.

Ideally, any information that people can provide in regards to reference texts would be enormously appreciated.

The following is the basic information I have gathered. I'll present it here to help myself brainstorm for a solution.

Tanker pumps at 100 kPa through a 100 mm hose to the Silo. An estimated limestone flow rate was calculated using the load capacity (38 tonne) and the time to unload (2 hrs). This results in 5.27 L/s or 11.17 cfm using an SG of 1 or 1 t/m^3. Average particle size is 35 microns.

Sorry for being so vague with the explanation, but I really don't have much to go on and haven't really been exposed to the design side of Silos before.

I'm assuming that the silo dimensions are 12-ft diameter, a 16 ft straight sidewall height, and a 60 deg conical bottom.

No fan is present on the top of the silo. The only pressure exerted on the limestone is from the truck's blower. An overpressure relief mechanism must also exist then if this is the case.

The bags use a reverse jet system to dump the filtered particles.

The dust collector is a pulse cleaning type that cleans the filter cloth while the exhaust.

Our supplier recommends a unit with a minimum filtration area of 20 m^2. My initial recommendation would be to replace the filter bags (20 m^2) and if there is no noticeable reduction in the filtration effectiveness, then further research into alternate possible filtration methods.

Does 20 m^2 seem undersized based on the figures given?

 

[shahyar]

Bin filters are sized based on "air to filter area" number which specific to eachpowder. Air here means air flow rate at the end of offloading.

 

[cub3bead]

Check with your chemical supplier and get the flow rating off the blower's nameplate.

The rule of thumb for sizing these things is 3-5 cfm/ft^2 of filter bag surface. ZMI/Portec standard bag house provides 295 ft^2 of bag surface and spec's a max air flow rate of 1175 cfm. This is a bitless than 4 cfm/ft^2.

Mke sure you spec a bag shaker to clean the bags when the transfer is finished.

 

[chief]

Check out a cyclone separator dust collector system . No more bags.

Offshore Engineering&Design

 

[nbog]

As cub3bead said, air-to-cloth ratio 3-5 should be OK for this case although, if you have a bin-vent type of baghouse (i.e. air flows upwards from the baghouse base, calculate min. settling velocity of your powder and make sure it is higher than the air velocity in the baghouse. Otherwise, you will have "back-flow" of pulsed-off powder to the filters.
Make sure you have correct air flow data. If you have pneumatic transport, your air flow should be = Air flow from the hose + Air flow generated by displacing air by powder in the silo;
To check if it undersized or not, I would first:
- look up the variables like filter pressure drop and frequency of pulsing
- if your DeltaP is in 1-5 "WG and bag cleaning frequency is >10 min then you should be fine.
- calculate the required filter area as mentioned above and in cube3bead's post