Today, many older power plants are operating under conditions that are different from when they were originally constructed. The plants have been modified over the years to meet evolving demands, but these changes have often been approached in a piecemeal fashion, introducing inefficiencies into the total system. In many of these plants, an area eligible for cost-effective course-correction is the air handling system, particularly the forced draft (FD) fans.
For example, ProcessBarron worked on a plant where the boiler was originally equipped with two 7,000 horsepower FD airfoil fans for pressurized service. When the system was later converted to a balanced draft operation, the FD fan pressure requirements were drastically reduced. This modification made it so FD fans had to be operated in a substantially dampered mode to minimize pressure development while still requiring the volumetric flow rate of the original design.
At its worst, this sort of mismatching can cause turbulence that will damage the air handling system. What is far more common, though, is simple excessive use of horsepower, which means excessive power consumption, which in turn translates to excessive spending. Too often, we find that a fan is mismatched to its surrounding system so that it operates below 50 percent efficiency, costing its operators thousands of dollars per day.
Because replacing these fans would simply replicate the problem, plant managers have two options if they wish to optimize an FD fan:
- Purchase new FD fans to match new system requirements
- Retrofit or modify existing FD fans to operate more efficiently at the new system requirements
Purchasing new fans is a cost-prohibitive option for most. Retrofitting, on the other hand, can be significantly less expensive. Often, just the impeller needs to be modified to produce substantial results, allowing owners and operators to preserve the existing fan housing. In some cases, it’s even possible to use existing shafts, bearings, and bearing pedestals.
The limited scope of FD fan retrofits leads to cost savings in three main areas:
When performing an FD fan retrofit, one does not alter the ductwork, dampers, or even the fan housing. The only major pieces of equipment being changed are the impeller and inlet cones or bells, which cost a fraction of an entirely new fan.
With a retrofit, only minor modifications are required to the fan housing. Because the surrounding system remains intact, the total installation cost is also relatively affordable.
FD fan retrofits can be accomplished during planned outages, when generating stations would be out of service for maintenance anyway. No unanticipated or lengthy downtimes are required to perform these sorts of operations.
ProcessBarron has been doing these sorts of FD fan retrofits for over 30 years — long enough to see the power plants that were state-of-the art when we started age to the point that they now need this sort of attention.
For a recent example of how we’ve applied this thinking in the field, download our case study documenting an FD fan retrofit we did for the Escalante Generating Station in New Mexico, saving the plant $459,133 per year. The job paid for itself in less than 12 months.