| Boiler technology Above: Induced draft (ID) fan wheel with shaft, prepared for shipment
wear and premature failure, fans should be constructed with robust, wear-resistant materials such as heavy-duty carbon steel. The surfaces that are most susceptible to wear – like the fan’s blades – should also be covered in a blade liner or other overlay material to protect the underlying material from damage. A liner or overlay can be more easily replaced when it erodes and at a much lower cost, compared to replacing an entire wheel that has eroded beyond repair.
Boiler fans must also be able to withstand extremely high levels of heat — from normal operating temperatures to potential short spikes of very high heat in the event of boiler malfunction. In some power generation applications, operating temperatures can reach up to 1800°F (982.2°C), as already noted. The design temperature should include an ample safety factor to ensure that the major fan components can survive even if there is an unexpected failure in the system. With the limitations on availability and increased pricing for stainless steel options due to COVID, it is best to work with the fan manufacturer to determine exactly what is needed in terms of construction materials and liner options. Steel and special alloy prices are largely inflated right now due to increased demand, which can lead to even higher initial costs for building an over-designed robust fan.
● Limit particulate buildup and uneven wear
The impact of debris buildup on fan components is another key consideration for boiler fans. Buildup of particulates on the blades can reduce the fan’s performance, efficiency, and reliability. In addition, debris often is not uniformly distributed, accumulating on the blades in uneven patterns that can cause rotor imbalance, uneven wear patterns, and increased vibration.
If these conditions are not resolved promptly, the fan may sustain significant damage requiring expensive and unplanned repairs that can take the fan offline unexpectedly. A reputable fan manufacturer will specify the ideal blade geometry that will help reduce particulate buildup on the blades. However, debris buildup
is unavoidable even for the best-designed fan rotors. A solution may be to install remote monitoring devices enabling predictive and preventative maintenance, which can assist in preventing unplanned downtime and extending the life of the fan.
● Integrate remote monitoring capabilities
One recent significant technological advance is the integration of remote monitoring devices for forced draft (FD) and induced draft (ID) fans. A manifestation of the Industrial Internet of Things (IIoT), remote condition monitoring helps to ensure reliable, energy-efficient operation while reducing both power and maintenance costs. The enhanced insights into the performance of operating equipment can help to identify problems before they escalate and/or trigger alerts if there are spikes in vibration or temperatures beyond what is expected. Being proactive in monitoring can increase operational life of equipment, avoid downtime and costly repairs, and allow for changes in real-time based on analytics and data.
Remotely monitoring airflow and pressure readings from air moving equipment gives end users real-time visibility as to a fan’s performance and energy consumption. If a fan is running inefficiently and drawing more power than necessary, users can proactively make adjustments. For example, if pressure exceeds a set threshold, the change can trigger an alert to personnel to investigate, analyse and diagnose the inefficiency causing the excessive power consumption.
● Reduce maintenance costs and downtime with predictive maintenance Integrating remote monitoring equipment with boiler fan packages also enables adoption of a predictive maintenance regime. Compared to preventative maintenance plans that rely on scheduled maintenance at regular intervals, predictive maintenance uses real-time data from the equipment itself to reliably diagnose problems and resolve them before a breakdown. Predictive maintenance eliminates human error in capturing or interpreting the data to ensure
maintenance is both timely and accurate. Using remote monitoring for the fan shaft and bearings can provide real-time notifications if there is a problem. The process is simple: vibration and temperature sensors are installed onsite, and alarm thresholds are set to trigger an automatic alert if temperature or vibration is outside the baseline level for normal operation, runup, and rundown processes. Personnel can then quickly resolve any issues that arise – like repairing a faulty bearing or removing debris that may be causing excess vibrations – before it becomes a bigger problem. By integrating predictive maintenance technologies, boiler fan packages can be maintained in a more proactive rather than reactive manner. This can actually reduce overall maintenance requirements and costs while increasing the lifespan and operation of equipment.
Special circumstances In addition to the above considerations, it is important to keep in mind that special circumstances may affect fan options. Therefore, clear communication and understanding of the primary mode of boiler operation is necessary to ensure the best fan designs are selected.
In one example, a large natural gas fired package boiler was specified in the 100 000 lb/h steam flow range. The boiler air flow was to be provided by an FD fan equipped for flue gas recirculation using a pair of louvered dampers and a mixing box.
However, in reading the specification, a 5:1 turndown ratio was noted. This seemed unusual, but the project proceeded in normal fashion, and the equipment was manufactured and installed.
Once in operation problems began to be experienced almost immediately. Burner flame conditions were unstable at turn-down. Investigation into the problem revealed that a relatively small pressure pulse due to blade stall at the (normal) low flow rate was being amplified by the burner to the point that burner air flow was reversing. The average pressure wave associated with blade stall is 10% of peak fan pressure and it occurs at a frequency of
Above: Motor vibration sensors
www.modernpowersystems.com | October 2021 | 47
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59
