A fan upgrade can be a win-win. Understand the basics of fan operation to achieve better fan performance and reduce energy consumption.
Fans are mechanical devices that use a rotating impeller to move gases. They fall under the broad classification of turbomachinery (a group that also includes pumps, turbines, and compressors.) They are commonly used throughout the chemical process industries (CPI) for cooling, combustion, gas cleaning, dust collection, and process gas transport.
▲Figure 1. This hot-gas centrifugal fan (left) is installed at a steel plant. This axial fan (right) provides ventilation in a mine.
Fans are classified into two design categories according to the direction of the gas flow through the impeller: centrifugal and axial (Figure 1). In both cases, gas enters the impeller parallel to the axis of rotation. Centrifugal fans force gas radially outward, perpendicular to the axis of rotation. The centrifuged gas is typically contained in a volute-shaped housing that has inlet and outlet connections. Axial fans discharge gas from the impeller parallel to the axis of rotation, i.e., the gas exits in the same direction that it entered. (Fans may also be classified as mixed flow, which have characteristics of both the centrifugal and axial designs.)
Fans may be plagued by five operational problems: noise, vibration, capacity, control, and mechanical failure. Often, several problems occur simultaneously. Solving an operational problem often goes hand-in-hand with the optimization of fan energy requirements. It is important to first understand root causes of problems before considering energy reduction measures. An upgrade project to improve performance is easier to drive forward than projects done only to reduce energy use. Systems experiencing problems are ideal candidates for upgrades because multiple parties have a vested interest in implementation.
This article discusses the basics of fans and fan operation, as well as the five operational problems that impact fan systems and how these relate to system energy requirements. Examples illustrate how it is possible to realize multiple objectives by making upgrades that also require less energy.
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