Industrial fans
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Industrial fans and blowers are valuable tools for moving air and materials required in a wide variety of manufacturing processes and industries, including cement, power, mining, coal treatment, pollution control, oil and gas, ethanol and steel. Ranging in size from just a couple of feet to 12 feet in diameter, fans are categorized into one of four types: centrifugal, axial, high temperature, or mixed flow. They are used for a myriad of applications, including to supply combustion air for burners, to move dirty air streams, remove particulates from exhaust streams, ventilate mine shafts, blow coal dust into power plant furnaces, recirculate process gases, or induce drafts in kilns used to manufacture cement and other materials. Due to the extreme environments in which they are often used, these fans are frequently subject to corrosive chemicals, high temperatures and abrasive air streams. Therefore, for reliable service they must be carefully engineered. The latest computer modeling technologies, such as finite element analysis and computational fluid dynamics, are often employed in the design process, in addition to laboratory model testing.
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[edit] Types of Fans
Fan types and their sub-categories are industry standard, recognized by all major fan producers. [1]
Centrifugal Fans are versatile air-moving workhorses (with many blade shapes available).
Axial Fans are high-volume fans designed to operate against low flow resistance.
High-Temperature Fans run at extreme temperatures ranging from 300°F to as high as 1,800°F.
Gas-Tight High-Pressure are mixed flow combination Fans and Blowers.
[edit] Centrifugal Fans
Airfoil (Air Foil) – Used for a wide range of applications in many industries, hollow-bladed airfoil fans are designed, engineered and tested for use in airstreams where high efficiency and quiet operation are required. They are used extensively for continuous service at ambient and elevated temperatures in forced and induced draft applications in the metals, chemical, power generation, paper, rock products, glass, resource recovery, incineration and other industries throughout the world.
Backward Curve – Efficiencies nearly as high as the airfoil design. However, single-thickness metal blades prevent the possibility of dust particle buildup inside the blade. These fans can be built with long-lasting erosion-resistant liners. The robust design allows high tip-speed operation, and therefore this fan is often used in high-pressure applications. This design frequently offers the best compromise for long life and high efficiency.
Backward Inclined – Simple flat blades, but backwardly inclined to match the velocity pattern of the air passing through the fan wheel, which results in high-efficiency operation. These fans are typically used in high-volume, relatively low-pressure, clean air applications.
Radial Blade – Flat blades oriented in a radial pattern. These rugged fans offer high pressure capability with average efficiency. They are often fitted with erosion-resistant liners to extend the rotor life. The housing design is compact to minimize the floor space requirement.
Forward-Curved Radial Tip – This rugged design is used in high-volume flow rate applications when the pressure requirement is rather high and erosion resistance is necessary. It offers medium range efficiencies. A common application is the dirty side of a baghouse or precipitator. The design is more compact than airfoil, backward curved or backward inclined fans.
Paddle-Wheel – This is an open impeller design without shrouds. Although the efficiency is not high, this fan is well suited for applications with extremely high dust loading. It can even be offered with field-replaceable blade liners from ceramic tiles or tungsten-carbide. This fan may also be used in high-temperature applications.
Forward-Curve – This “squirrel cage” impeller generates the highest volume flow rate (for a given tip speed) of all the centrifugal fans. Therefore, it is often the smallest physical package available. It is commonly used in high-temperature furnaces.
Industrial Exhausters – Relatively inexpensive, medium-duty, steeply inclined flat-bladed fan for exhausting gases, conveying chips, etc.
Pre-engineered Fans (PE) – A series of fans of varying blade shapes that are usually available in only standard sizes. Because they are pre-engineered these fans may be available with relatively short delivery times. Often, pre-engineered rotors with various blade shapes may be installed into a common housing. These are often available in a wide range of volume and pressure requirements to meet the needs of many applications.
Pressure Blowers – High-pressure, low-volume blowers used in combustion air applications in furnaces or to provide “blow-off” air for clearing and/or drying applications.
Surgeless Blowers – High-pressure, low-volume blowers with a reduced tendency for “surging” even at severely reduced flowrates. This allows extreme turndown (low-flow) without significant pulsation.
[edit] Axial Fans
High-Temperature Axial Fans – High-volume fans designed to operate against low flow resistance in industrial convection furnaces. These are found in either single-direction or bi-directional designs. Extremely rugged, they are most often used in high-temperature furnace (up to 1800 degF) applications.
Tube Axial Fans – Cataloged high-volume low-pressure fan line with a wide range of available sizes. Suitable for temperatures up to 250 degF.
Vaneaxial Fans – Axial flow fans with higher pressure capability due to the presence of static vanes.
Variable Pitch Axial fans – Axial fans with manually adjustable blade angles. This allows operation over a much wider range of volume/pressure relationships. The blades are adjusted periodically to optimize efficiency by matching the blade pitch to the varying conditions for the application. (Often used in mining applications).
Variable Pitch on-the-fly Axial Fans – These are similar to “Variable Pitch Axial Fans” except these include an internal mechanism that allows the blade pitch to be adjusted while the fan rotor is in motion. These versatile fans offer high-efficiency operation at many different points of operation.
Variable Speed Fans – All of the fans described above can be used in conjunction with a variable speed driver. This might be an adjustable frequency AC controller, a DC motor and drive, a steam turbine driver, etc. Flow control by means of variable speed is typically smoother and more efficient than by means of damper control. Significant power savings (with reduced cost of operation) are possible if variable speed fan drives are used for applications that require reduced flow operation for a significant portion of the system operating life.
Industrial Dampers – for fan volumetric flow control during operation.
Louvered Inlet Box Dampers
Radial Inlet Dampers
Variable Inlet Vane (VIV) Dampers
Vortex Dampers
Discharge Dampers
[edit] High-Temperature Fans
– Single-direction flow for low-pressure, higher mass-flow applications.
– High-volume forward and reverse flow just by changing motor rotation.
Paddle Wheel – Higher pressure capability in furnace applications. Can handle dust-laden gas streams. High tip-speed capability.
Forward Curve – High-pressure and high-volume in a small package. Often used in high-velocity jet-impingement furnace applications.
Airfoil – This design offers high-efficiency operation in furnace applications. This reduces the overall power required for furnace operation. High-pressure capability is available for high-velocity jet-impingement heating.
[edit] Gas-Tight High-Pressure Fans and Blowers
Mechanical Vapor Recovery Blowers – Specially designed centrifugal fans designed to increase the temperature and pressure of saturated steam in a closed loop system. These high-efficiency units operate at a tip speed of approximately Mach 0.8. They are fabricated from special high-strength corrosion-resistant alloys with multistage carbon ring shaft seals.
Acid Gas Blowers – Very heavy construction blowers suitable for inlet pressures from full vacuum to +100 psig. These blowers are designed with machined ASME inlet and outlet flanges. In-shop pressure testing ensures gas-tight operation even at elevated temperatures. These blowers are equipped with custom-designed purged shaft seals. The materials of construction match the corrosion-resistant requirements for the gases and particulate being handled.
Specialty Process Gas Blowers - Used by the Petrochemical Industry – These blowers are designed, manufactured and tested to meet the customer-specified requirements of API 673 / API 560.
[edit] References
- ^ Air Movement and Control Association. AMCA. Retrieved on 2008-05-05.
