DESIGN OF FABRIC FILTER
Pressure Drop: The pressure drop is the sum of the pressure drop across the filter housing and across the dust-laden fabric.
Where, v=the filtration velocity; K1=the flow resistance of the clean fabric; K2=the specific resistance of the dust deposit; w=the fabric dust areal density; K1 is related to Frazier permeability, which is the flow through a fabric in cfm/ft2 of fabric when the pressure drop across the fabric is 0.5 in w.g. as follows :
Evaluation of specific resistance K2 : The dust collected on a membrane filter and K2 should be calculated from the increase in pressure drop (ΔP2- ΔP1) with filter weight gain (M2- M1) as follows:
Where, A is the surface area of the membrane filter.
Problem 2.4.1. A fabric filter is to be constructed using bags that are 0.1 m in diameter and 5.0 m long. The bag house is to receive 5 m3/s of air. Filtering velocity is 2.0 m/min. Determine the number of bags required for a continuous removal of particulate matter.
Given that: Diameter of bag (d) = 0.1 m; Length of bag (L) = 5 m; Flow rate (Qg)= 5 m3/s; Filtering velocity (u)=2 m/min=0.0333 m/s.
T otal area of filter =
Area of single bag = Ab = 3.14 x 0.1 x 5.0 = 1.57 m2
Number of bags = N
The numbers of bags required for a continuous removal of particulate matter are 96.
Problem 2.4.2. A bag house is to design to handle 1000 m3/min of air. The filtration takes place at constant pressure so that the air velocity through each bag decreases during the time between clearing according to the relation
Where, u is in m3/m2 min of cloth and t is time in min. The bags are shaken in sequence row by row on a 30 min cycle. Each bag is 20 cm in diameter and 3 m height. The bag house is to be square in x-section with 30 cm spacing between bags and 30 cm clearance from the walls. Calculate the number of bags required.
Given: Ratio of flow rate air to cloth area
( m3/m2 min of cloth). Time (t)=30 min; d- Diameter of bag (d)=0.2 m; Length of bag (L)=3 m; Flow rate (Qg)=1000 m3/min.
Average velocity (Vavg)=? (m/min)
Total area of filter (At)=? (m2).
Area of single bag (Ab)=? (m2).
Number of bags (N)=?
Put the values in equation, we get the average velocity
The numbers of bags required for a continuous removal of particulate matter are 553.