Function of Retrofitting in Centrifugal Fans

A centrifugal fan system loses its optimum quality after a certain period of time. So, it is necessary to perform retrofitting in centrifugal fans to boost the efficiency and performance. The main purpose of retrofitting the centrifugal fan is to increase the flow rate, regulate the variations of static pressure, reduce power consumption and improve the fan speed & efficiency. Retrofitting also has some indirect benefits such as it saves the additional cost, improves fuel efficiency (when run by petroleum liquids), increases productivity of plant and helps in balancing the environment.

1. Increases flow rate
Flow of gases is the main function of any fan and centrifugal fans produce high pressure to the air-flow. However, the flow rate can be reduced after a period of time due to many reasons, for instance fans at material handling can accumulate dust particles on them and restrict the flow. Similarly, gases that are being circulated may have high temperatures which can reduce the flow rate. Flow rate of centrifugal fans depend mainly on the impeller design. So, retrofitting impeller and its components will increase the flow rate of gases.

2. Variation of static pressure
Static pressure is the pressure exerted by the gases on the fan when it is at rest. Static pressure sometimes can be increased or decreased based on the industrial need. For example in case of raw mill fan used in cement industry, the static pressure needs to be reduced whereas in the kiln ESP fan, static pressure needs to be increased.

3. Reduce power consumption
For centrifugal fan the overall efficiency is determined as the ratio of output power to the input power supplied. To have an increased efficiency, the denominator which means the input power must be less. With retrofitting, the work-done can be increased for the same given input power. This can be possible by changing the casing and increasing the flow at the inlet, or by imparting high velocity to the inlet flow.

4. Increases fan speed
Retrofitting helps in regaining the original speed of the fan. Fan speed determines the pressure of the outlet gas. Fan speed can be increased by using a light weight material for impeller or having a high capacity motor or by changing the bearings of the fans. In most of the cases where a new impeller is installed, a light weight material is used to manufacture the impeller because it helps to improve the fan speed.

5. Increases fan efficiency
Efficiency is the most important aspect of any industrial fan. To increase the overall efficiency it is necessary to increase the total power output or reduce the power consumed. The rated power input cannot be varied but we can achieve more power output by various possibilities. The total work can be increased by retrofitting impeller either by trimming or tipping or by replacing the existing impeller with a new one. Trimming or tipping does not demand for a change in casing or inlet cones but when replacing a new impeller it may require a change in casing and a set of new inlet cones.

Retrofitting has other advantages as well, such as it reduces the overall halt time of a plant, and works as a better alternative than going for a complete new installation.