The diagram below shows a typical fan characteristic which is a function of pressure and volume flow. Also shows a typical system characteristic, the operating point of the system is at the intersection of those two curves. If the required volume of air is deviating from this point, the fan or system characteristic needs to be changed.
Fig.1 Fans in the sugar factory
Traditionally, the most common way of changing the operating point is to use a damper which alters the system characteristic (operating point moves from position 1 to 2, see Fig. 11) and increase the system losses. However, no matter increasing or decreasing the fan speed, with a variable speed drive, the fan characteristic will change itself (point of operation moves from position 1 to 3, see Fig. 11) without adding additional losses. The energy consumption can be reduced significantly.
Fig.2 Typical fan characteristic operating point
Fig.3 Power consumption for various fan control methods
The advantage of INVT VFDs driving:
1.Significant energy savings
Since fans typically run at partial load, huge energy savings can be achieved by controlling their speed with VFDs. A small reduction in speed can make a big reduction in energy consumption. A fan running at half speed may consume as little as one-eighth of the energy compared to one running at full speed.
By employing VFDs on centrifugal fans, instead of throttling or damping, the energy bill can be reduced by as much as 50%.
2.Reduce motor and fan system maintenance costs
The control method employed has a major effect on running costs. High control accuracy, excellent energy economy and reduced maintenance costs are achieved with VFDs for all fans in the sugar and power plant process.
Be able to soft start, no excessive thermal or mechanical stress on the motor, resulting in a longer lifetime.
4.High availability and superior control characteristics
VFD driving can realize fast and precise process control under all conditions. It also has high availability.
Fig.4 INVT VFDs for fans in the site