Key O&M Cost Point
Emphasizes information that will result in reduced purchase, operating, or maintenance costs.
Section Page Key O&M Cost Point
3.2.7 3-6 The fewest number of fans usually results in the lowest initial cost.
3.11.8 3-38 The best practice is to follow the fan manufacturer’s recommendation. If a change in damper operation is desired, data on startup times and motor current should be collected and discussed with the suppliers of the fan and motor.
6.2 6-10 Oil analysis tests are often offered free or for a nominal charge by the lubricant supplier as part of the overall service provided.
7.1 7-2 Recommendations from the manufacturer and operational experience can provide valuable insight in determining not only what checks should be done, but also how often they should be done.
7.1 7-2 A balance must be attained by performing PM but avoiding opening and inspecting equipment if no problems (such as high temperature or pressure) are present.
7.4.5.2 7-19 Blasting with frozen CO2 pellets has been used for cleaning, with the benefit of eliminating the need to remove the blast medium from the fan.
7.4.9.3 7-27 A simple adjustment of the fan-wheel-to-inlet-cone clearance can affect fan performance by 5% or more.
9.1 9-1 If additional fan capacity is needed, there are fan upgrades that can be
implemented that require only a fraction of the cost and outage time of complete new fans.
Key Technical Point
Targets information that will lead to improved equipment reliability.
Section Page Key Technical Point
3.2.1 3-3 Temperature affects fan performance, and thus, a margin on temperature is included to allow for variations in operation.
3.2.2 3-4 When specifying FD fans, pressure loss through the silencers (if they are provided) must be taken into consideration.
3.6.3 3-24 The design speed of the turning gear is critical. Most centrifugal fans have sleeve bearings that have a minimum speed. Below the minimum speed, the oil film between the journal and the sleeve is not adequate to prevent metal-to-metal contact, and the bearing will be damaged.
3.7 3-25 In many coal-fired plants, the ID fans are the limiting factor on plant electrical output. Although the ID fans may be the apparent cause of a load limit, in many cases the root cause is high air heater leakage, air heater pluggage, high gas temperatures, precipitator infiltration, or something similar.
3.7 3-25 Note that most curves are labeled as cfm, where it is understood that cfm is acfm.
Because fan performance depends on inlet density, the fan curve should specify the density.
3.7 3-26 Fan manufacturers usually present their curves in terms of vane angle, with 90 degrees being the full open position. Many boiler controls identify inlet vane position in terms of percent open, with 100% being full open.
3.7 3-27 The inlet vanes are designed for flow control and not to isolate the fan, and—with the vanes fully closed—the performance will be approximately the same as with the vanes 15 degrees open. Thus, controllability at this low vane opening may be a problem.
3.7.2 3-30 Note that fan static pressure is not the same as static pressure rise.
3.7.2 3-31 The pressure rise across the fan must be converted to the density on the fan curve.
3.8 3-33 Fan performance is based on conditions at the inlet.
6 6-1 The goal of condition monitoring is to identify changes in the condition of the fan, motor, or auxiliary that could indicate some potential failure.
6.1.2.1 6-3 The vibration amplitude-versus-frequency analysis method is considered to be the most useful. Over 85% of mechanical problems occurring on rotating equipment can be identified using this method.
7 7-1 The major maintenance areas for centrifugal fans are the blade liners, main shaft bearings, and inlet vane or inlet damper linkages.
7 7-1 Axial fans require considerably more maintenance than centrifugal fans.
Section Page Key Technical Point
7.4.1 7-6 Do not mix oils in the lubrication system or bearing housing. Chemical additives in different oils can cause a breakdown in the viscosity, cooling, or bearing
lubrication.
7.4.3.2 7-13 Verify that components used to restrict motor shaft movement are installed.
7.4.5.2 7-20 Coatings can affect the physical properties of the base materials of the fan. Cracks in coatings can propagate into the fan members. Tests using proposed coatings and fan structural material should be performed and evaluated before the coatings are actually used.
7.5.2 7-38 Improper welding of balance weights can cause cracks in the attachment weld that can propagate into the base metal of the fan.
Key Human Performance Point
Denotes information that requires personnel action or consideration in order to prevent injury or damage or ease completion of the task.
Section Page Key Human Performance Point
3.11.2 3-35 The startup procedures, in addition to the controls and interlocks, should follow the requirements of the current version of NFPA 85.
3.11.9 3-39 The fan control system should monitor the head and flow and give the operator a stall warning so that the operator can take action before a stall occurs.
4.1 4-6 Erosion is a significant failure mechanism for both centrifugal and axial fans. While erosion of ID fans is the major problem, erosion has also been reported on FD fans.
7.4.3.2 7-14 The locking feature of these fasteners becomes compromised when they are removed and reinstalled a certain number of times.
7.4.3.3 7-14 It is important to verify that the thrust load of the fan is not imposed on the motor thrust bearing. This requires knowledge of the magnetic center of the motor.
7.4.5 7-17 Damage (manifested in the form of cracking or corrosive wear) can be partial or total. Unchecked damage may result in an increase in vibration levels with additional wheel damage, which subsequently may increase in severity to catastrophic failure with a serious potential for injury to personnel.
7.4.5.1 7-18 Large centrifugal fan wheels are highly stressed rotating equipment. The design stress may be as high as 80% of yield, and the material may be a quenched and tempered high-strength material such as ASTM A514 or A517, with a yield strength of 100,000 psi. Many large centrifugal fans have had cracks, and there have been a few mechanical failures.
10.1 10-1 All personnel that operate, inspect, or maintain fans should be trained in the plant safety procedures.
Section Page Key Human Performance Point
10.6 10-2 Fans can suck in loose material and discharge it as dangerous projectiles. Large fans can also be dangerous to personnel.
10.7 10-2 Even when a fan is locked out electrically, it may be subject to “windmilling.”