Recently the following question came in for Dr. Vent Goode: “For round collectors, what are the provisions to control the gas to individual dust collectors? How will even, constant, flow be directed to each bag house?”
Dr. Vent Goode’s answer
Good flow distribution is important to maximize performance on any multiple module baghouse, with circular modules or not. I’m glad you bring this up, because this effort begins at the plant layout stage. There are also three more important considerations to optimize flow distribution, per the following:
We want to make sure that the inlet to the baghouse and the outlet to the fan are on opposite sides of a multiple module baghouse. An example is that if you have an east and west modules with the inlet coming from the west, then the outlet and the fan should be on the east side. If the inlet is from the south, then the outlet should be to the north, not the east or west.
An example of a poor layout on a baghouse would be when a two-module unit has an inlet from the south, with the outlet and fan to the east. The result is that the east module sees a lot more loading because the fan tends to ‘pull’ more on that side.
Sometimes, a perfect layout simply cannot be implemented. In those cases, the outlet of a given compartment(s) can be partially restricted with a flat plate to help apply similar fan suction to each module. CFD studies can be made for complex situations. Note that restricting the inlets (dusty flow) is not recommended because of abrasion.
Duct Branching and Sizes
The inlet flanges into the two modules are the same, both sized to handle the required flow. Both come from a main duct that splits into the two smaller diameters, keeping velocities constant. There are well established guidelines to design this split/reduction.
The same goes for the outlets. Both similarly sized outlet ducts join to a larger main duct going to the fan. Proper design of this connection is simple, but important. I also recommend avoiding extra elbows or detours that would make one module have more flow restriction than the other.
The baghouse should have a single controller that follows a defined cleaning sequence that pulses all rows before starting the sequence again. Having two controllers, each pulsing as necessary, is definitely not recommended because the compartment with more loading will end up pulsing more, accelerating wear on the loaded compartment and exacerbating the balance problem.
With the recommended setup, the loaded compartment will accumulate more material. Since it cleans the same frequency as the other compartments, the additional material will send more flow to the ‘cleaner’ compartment, helping the system self-balance.