Case History No. 4

Industry & Location:

An iron foundry in the southeast

Problem:

Continuous bearing failures and reduced exhaust gas flow rate from the cupola.

Source of Detection:

Frequent bearing replacement and the inability to attain adequate draft from the cupola.

Cause of Problem:

The absence of turning vanes in the fan inlet duct causes unbalanced flow to each inlet box and prespinning of the gas to the impeller.

Solution:

The installation of turning vanes in the 90 degree elbow upstream of the fan inlet straightens the streamlines to the fan inlet and balances the flow between the two inlet boxes.

Inlet Duct Configuration

A double inlet fan normally uses sleeve bearings that have not been designed to accommodate excessive thrusting. Any unbalanced flow between the inlet boxes results in thrusting of the impeller and transmits thrust loads to the fixed bearing.

The 90 degree elbow upstream of the fan as shown in Figure 4.2 is also oriented to promote an angular inlet direction to the inlet box which results in prespinning and subsequent reduced pressure capability.

Pre-Spinning Induced by the Duct

Any inability of the fan to develop design static pressure will result in reduced volumetric flow from the system. The straightening of gas flow to the fan inlet eliminates this problem. Sometimes it is desirable to intentionally prespin the gas which the fan manufacturer achieves with prespin vanes This is done to improve efficiency while reducing pressure capability.

Pre-Spinning Vanes in Fan Inlet

Benefit:

Increased iron production because of higher volumetric flow and reduced maintenance costs.