Aeration Examples

To better understand cottonseed aeration systems, the following typical systems are considered:

Depth of Cottonseed (ft)
Airflow Rate (cfm/ton)
Static Pressure (in H20)
Power Required (hp/100 tons)
10
5.0
1.0
0.1
 
7.5
1.1
0.2
 
10.0
1.6
0.4
12
5.0
1.0
0.1
 
7.5
1.6
0.4
 
10.0
2.3
0.7
14
5.0
1.3
0.2
 
7.5
2.1
0.6
 
10.0
3.1
1.2
16
5.0
1.7
0.2
 
7.5
2.8
0.6
 
10.0
4.0
1.2
18
5.0
2.2
0.3
 
7.5
3.5
0.8
 
10.0
5.0
1.5
20
5.0
2.7
0.4
 
7.5
4.5
0.9
 
10.0
6.3
1.7
22
5.0
3.3
0.5
 
7.5
5.3
1.1
 
10.0
7.7
1.9
24
5.0
4.1
0.6
 
7.5
6.4
1.4
 
10.0
9.5
2.5
26
5.0
4.7
0.6
 
7.5
7.6
1.6
 
10.0
11.6
2.9
28
5.0
5.5
0.8
 
7.5
9.0
1.7
 
10.0
13.5
3.4
Table 4. Airflow resistance and fan power requirements for cottonseed at different storage levels and airflow rates.

Example 1. Design a storage and aeration facility for 1,200 tons of cottonseed. The cottonseed will be carried into storage with an existing small-pipe seed-handling system and unloaded with a front-end loader:

I. Building
Volume required for 1,200 tons of cottonseed is 96,000 ft3. The storage structure could be 60 ft wide and 100 ft long with an eve clearance of 18 ft to accommodate the front-end loader. It will be filled to a depth of 16 ft. The building should be constructed 120 ft long to provide access for unloading without using a bulkhead door.

II. Aeration System
System capacity = 1,200 tons of cottonseed. Design airflow rate = 10 cfm/ton.

Total air volume needed: 1,200 tons x 10 cfm/ton = 12,000 cfm.

Duct layout as shown in Figure 1 with 5 rows spaced 20 ft apart, 50 ft long (Maximum duct spacing: 1.5 x 16 ft = 24 ft).

Duct Design: Each duct carries 1/5 of the total air or 2,400 cfm per duct. Total surface area needed for a 10 ft/min face velocity is 240 ft2 (2,400 cfm/ 10 ft/min = 240 ft2) or 240 ft2/ 50 ft = 4.8 ft2/linear ft. From Table 2 select a 36-inch diameter half-round or 18-inch diameter round duct.

Supply pipes: Each supply pipe carries 1/5 of the total volume of air or 2,400 cfm. From Table 3 select an 18-inch diameter supply pipe that will carry 2,651 cfm at a velocity of 1,500 ft/min.

Manifold pipes: The manifold pipe carries air for two supply pipes or 4,800 cfm. From Table 3 determine that a 21-inch diameter manifold will handle 4,800 cfm at 2,000 ft/min. Because larger velocities can be tolerated for short distances and odd sized pipe is not common, a 20-inch diameter manifold could be used.

Fan and motor: At a cottonseed depth of 16 ft and an airflow rate of 10 cfm/ton the static pressure to be overcome by the fan is 4.0 inches of water and 15 horsepower requirements (Table 4).

From a manufacturer's catalog, select a centrifugal fan with a 15 horsepower motor which would deliver 12,500 cfm at 4 inches static pressure. An alternative would be to use five small fans and motors capable of 2400 cfm per fan. This would require 3 hp motors which could be operated with 220 volt single phase power and eliminate the manifold pipe.

Example 2. Design a storage and aeration system for 2,000 tons of cottonseed. The cottonseed will be carried into storage with an existing small-pipe handling system and unloaded with a front-end loader.

I. Building
The storage structure would be 60 ft wide and 160 ft long with 18 ft eve clearance. It will be filled to an average cottonseed depth of 17 ft. The building should be constructed 180 ft long to allow access for unloading.

II. Aeration System
System capacity = 2,000 ton. Design airflow rate = 10 cfm/ton.

Total air volume required is 2,000 ton x 10 cfm/ton = 20,000 cfm.

Duct layout is shown in Figure 2 with 850 ft rows spaced 20 ft apart.

Duct Design: Each duct carries 1/8 of the total air or 2,500 cfm per duct. Total surface area needed for a 10 ft/min face velocity is 240 ft2 (2,500 cfm/ 10 ft/min = 250 ft2) or 250 ft2/ 50 ft = 5.0 ft2 linear ft. From Table 2 select a 38-inch diameter half-round or 20-inch diameter round duct is needed.

Supply pipes: Each supply pipe carries 1/8 of the total air volume (1/8 of 20,000 cfm = 2,500 cfm. From Table 3 select an 18-inch diameter supply pipe.

The manifold pipe carries air for two supply pipes or 5,000 cfm. From Table 3 determine that a 22-inch pipe will carry 5,280 cfm at 2,000 ft/min. Because larger velocities can be tolerated for a short distance, a 20-inch manifold would be acceptable.

Fans and motors: At a cottonseed depth of 17 ft and an airflow rate of 10 cfm/ton (Table 4), the static pressure requirement is 4.5 inches of water (interpolate between 16- and 18-ft depths).

From a manufacturer's catalog, select a centrifugal fan with a 10-horsepower motor that would deliver 10,000 cfm at 4.5 inches of water, static pressure. Two fans and motors would be required for this system.


Figure 1. Aeration duct layout for 1,200 tons of stored cottonseed.


Figure 2. Aeration duct layout for 2,000 tons of stored cottonseed.
 

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