- Blowers for Combustion Systems

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 difcult. 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 uid 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 so on. 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 blower design are not discussed. To gain more knowledge 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 the following:

• Forced and induced draft fans for red heaters, burners, boilers, and thermal oxidizers

• Introduction of air for smoke suppression of are systems

John Bellovich and Jim Warren

CONTENTS

13.1 Introduction ................................................................................................................................................................... 335 13.2 Applications ................................................................................................................................................................... 335 13.3 Types of Blowers for Combustion Systems ............................................................................................................... 336 13.4 Fan Arrangements ........................................................................................................................................................ 336 13.5 Design Considerations ................................................................................................................................................. 337

13.5.1 Fan Control ........................................................................................................................................................ 346 13.5.2 Materials of Construction ................................................................................................................................ 347 13.5.3 Motors and Drives ............................................................................................................................................ 348 13.5.4 Couplings and Belts .......................................................................................................................................... 348 13.5.5 Bearings and Lubrication................................................................................................................................. 349 13.5.6 Vibration and Installation ................................................................................................................................ 350 13.5.7 Shaft Seals .......................................................................................................................................................... 350 13.5.8 Noise Considerations ....................................................................................................................................... 352 13.5.9 Filtration ............................................................................................................................................................. 352

13.6 Operational Costs ......................................................................................................................................................... 352 13.7 Inspection and Testing ................................................................................................................................................. 353 13.8 Maintenance and Troubleshooting ............................................................................................................................ 355 References ................................................................................................................................................................................ 357

• Cooling or purging of are systems • Movement of waste gases into the burner or

are system • Reoxygenation and quenching of thermal oxi-

dizer ue gases

There are primarily two types of blowers used in the combustion industry, centrifugal and axial. Centrifugal fans (see Figure 13.1), 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 of 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 13.2 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 13.3) have a set of internal guide vanes, while tube axial fans have none. Which type of 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 high volume low pressure fans, are usually lower in cost, and are typically a little more efcient. 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.