ABSTRACT
Compared to industrial air handling or air conditioning blowers, blowers and fans used in the service of combustion systems have some unique requirements that make design, installation, and operation a little more dif“cult. An incorrect fan design or material selection can have a disastrous effect on the performance of an entire facility. It is very important to understand the service of the fan as well as its performance in order to properly run a combustion system. The terms “blower” and “fan” are used interchangeably in the context of this book. Blowers and pumps are very similar in the fact that they both push a ˆuid from one point to another by putting more energy into the system. Pumps push liquids and fans push gases. Fans for combustion systems can be used to introduce air into a combustion zone, prevent smoke formation, move exhaust gases, cool or reoxygenate a stream, purge a stack, and more. The purpose of this section is to introduce the basic concepts of blowers for combustion services and give awareness to the critical issues. The intricacies of
on the topic, consult the Fan Engineering Handbook by the Howden/Buffalo Fan Company.1 Other valuable resources include any of the Air Movement and Control Association International (AMCA) standards.2,3 Some good general references related to this topic are also available.4-8
Typical applications for fans in combustion systems include
•Forced and induced draft fans for “red heaters, burners, boilers, and thermal oxidizers
• Introduction of air for smoke suppression of ˆare systems
•Cooling or purging of ˆare systems •Movement of waste gases into the burner or
ˆare system •Reoxygenation and quenching of thermal oxi-
CONTENTS
3.1Introduction..................................................................................................................................................................... 73 3.2 Applications ..................................................................................................................................................................... 73 3.3 Types of Blowers for Combustion Systems ................................................................................................................. 74 3.4 Fan Arrangements .......................................................................................................................................................... 76 3.5Design Considerations................................................................................................................................................... 77
3.5.1Fan Control.......................................................................................................................................................... 83 3.5.2 Materials of Construction .................................................................................................................................. 84 3.5.3 Motors and Drives .............................................................................................................................................. 84 3.5.4 Couplings and Belts ............................................................................................................................................ 85 3.5.5Bearings and Lubrication................................................................................................................................... 86 3.5.6Vibration and Installation.................................................................................................................................. 87 3.5.7 Shaft Seals ............................................................................................................................................................ 89 3.5.8 Noise Considerations ......................................................................................................................................... 89 3.5.9 Filtration ............................................................................................................................................................... 89
3.6Operational Costs........................................................................................................................................................... 89 3.7Inspection and Testing................................................................................................................................................... 90 3.8 Maintenance and Troubleshooting .............................................................................................................................. 92 References .................................................................................................................................................................................. 93
There are primarily two types of blower used in the combustion industry, centrifugal and axial. Centrifugal fans (see Figure 3.1), also known as radial fans, are very similar to centrifugal pumps. The air enters the center of the impeller and is ejected radially outward and “pushed” by the impeller blades through the housing and out the exit. Centrifugal fans usually have the same basic con“guration with options concerning what type of impeller and drive system is used (see Figure 3.2 for different impeller designs). Other variations of the centrifugal fan will include high pressure fans and multistage turbo blowers. Axial fans are more like an airplane propeller that pushes the air along in the direction of the axis of rotation. Axial fans fall
into two categories, vane axial and tube axial. Vane axial fans (see Figure 3.3) have a set of internal guide vanes, while tube axial fans have none. Which fan is used will depend on the application. Centrifugal fans typically can generate higher pressures than vane axial fans, and the motor can be maintained outside of the fan. Vane axial fans are a high-volume low-pressure fan, are usually lower in cost, and are typically a little
more ef“cient. Unless the vane axial fan is belt driven, the motor is usually inside the fan housing and the unit would have to be disassembled for work on the motor. Some vane axial fans have an extended shaft to move the motor out of the housing, but these are generally for large ventilating applications.
