Cyclone Separators Information on GlobalSpec

8/13/2019 Cyclone Separators Information on GlobalSpec

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www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/cyclone_separators

Cyclone Separators Information

Image Credit: Koger Air Corporation, Aget Manufacturing Company, Ecologix Environmental Systems

Cyclone separators utiliz e gravity and a vortex to remove particulates from gaseous streams. Industrial cyclones are used in pollution control applications mostcommonly as a first st age, lower cost method for removing larger particulate matter (PM) from effluent gas st reams. Because cyclone separators do not incorporatefilter media or moving parts, the pressure drop (therefore, operating costs) and maintenance requirements tend to be low. They can also be constructed towithstand harsh operating conditions, and since separation in cyclones is a dry process, the equipment is less prone to moisture corrosion.

Advantages Disadvantages

Low capital cost. High operating costs (due to pressure drop).

Ability to operate at high temperatures. Low efficiencies (particularly for small particles).

Can handle liquid mists or dry materials. Unable to process "sticky" materials.

Low maintenance requirements (no moving parts).

Small footprint - requ ires relatively small space.

Cyclone Separator OperationCyclone separators operate by incorporating centrifugal, gravitational, and inertial forces to remove fine particles suspended in air or gas. These types of separatorsuse cyc lonic action to s eparate particulates from a gas stream. Typically, P M enters the cy clone separator at an angle (perpendicular to the flow stream,tangentially, or from the side), and is then spun rapidly. A centrifugal force is created by the circular airflow that throws the particulate towards the wall of thecyclone. Once the PM hits the wall, it falls into a hopper below. Clean exhaust is then either blown through or recirculated to be filtered again.

General la yout and function of a rev erse flow cyclone, indicating the flow paths of the gas and particulate matter (labeled powder in this diagram). Image Credit: GEA Niro

It is important to keep in mind that the c entrifugal force (Fc) a cyclone generates on a particle is related to the tangential air velocity (vt), particle mass (m), and theparticles radial distance from the cy clone wall (r) by the function:

Fc= m vt2/ r


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Typical data sheet for custom or manufacturer assisted cyclone selection, including a large range of design specifications. Image Credit: Fisher-Klosterman, Inc.

When selecting a cyclone separator, industrial buyers must consider various performance specifications, process conditions, construction, and applications. Thisguide is designed to help with this selection process by pointing out the key considerations and design aspects of cyc lones.

Cyclone PerformanceCyclones may be purchased from exis ting manufacturers stock or custom built t o certain customer design specifications. In either case, it is important to k nowthe required specifications and process conditions for operation.

SpecificationsThe primary means to selecting the right c yclone separator(s) is matching its performance specifications with the application requirements. These specificationsinclude process airflow and minimum filtered particle size.

Airflow or volumetric flow rate is the air flow generated or handled by a cyclone. This is usually given in cubic feet per minute (cfm). Some manufacturers

provide ranges in standard cubic feet per minute (scfm), as flow rates can vary greatly as environmental conditions stray for standard temperature and

pressure. To convert a given actual flow rate (QA)in actual cubic feet per minute (acfm) to standard flow (QS)in scfm, utilize the combined ideal gas

equation which includes volume (V), pressure (P), and temperature (T) at actual and standard conditions.


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(PSVS)/TS= (PAVA)/TA

If we know the temperature and pressure at actual conditions, we can substitute volume (V) with flow rate (Q, equivalent to volume per unit time) and rearrangeto solve for QS.

QS= QA (PA/PS) (TS/TA)

A cy clone with a higher airflow can accommodate larger gas streams for treatment. For effective operation, the airflow of the system at the point of installationshould fall within the rated airflow range of the cyclone.

Minimum filtered particle size is the smallest particle s ize a cy clone can filter to any measurable efficiency. It is generally measured in microns or

micrometers (m). If a cyclone is being used as the primary or only means of particle separation, the smallest particle size needed to be removed should be

above this minimum. Actual collection efficiencies of a cyclone vary greatly based on the design of the cyclone, operating flow rate, and various properties of

the gas and PM.

Collection efficiency, capture rate, or recovery rate is the overall removal efficiency of PM from an air stream. Manufacturers sometimes provide estimated

efficiencies upfront; however actual results will vary based on the properties of particles in the gas stream, and on certain environmental conditions.

Parameter When parameter increases, cyclone efficiency...

Particle Size Increases

Particle density Increases

Dust loading Increases*

Inlet gas velocity Increases*

Cyclone body diameter Decreases

Ratio of cyclone body length to diameter Increases

Smoothness of cyclone inner wall Increases

Gas viscosity Decreases

Gas density Decreases

Gas inlet duct area Decreases

Gas exit pipe diameter Decreases

*Only increases to a point before efficiency drops off.

Relation of various parameters to cyclone design efficiency.

Pressure drop is the amount of flow resistance the cyc lone will create in the sys tem. Pressure drop is usually measured in units of inches of water column

(in WC) or Pascals (Pa). Pressure drop is a function of flow rate, gas density, and cyclone design.

Design Tip:Correctly designed cyclones should have a recommended pressure drop range of operation, which for most designs is between 2 and 6 in WC(About 500 to 1500 Pa) at ambient conditions. Above this range, costs for flow losses begin to outweigh increases in efficiencies. Below the limits, particlerecovery becomes ineffective.

Process ConditionsProcess c onditions are the characteristics surrounding a cyclones operation. These include the air conditions and the particulate/dust conditions that are essentialto finding or designing an appropriate cyclone for a given system. When having a cyclone custom built, these conditions are requested from the cyclonemanufacturer.

Air conditionsinclude the pressure (psig or psia), temperature (F or C), and moisture content (weight or volume percent) at the inlet of the cyclone. Solids

collection becomes more difficult as humidity rises because the moisture tends to cause PM to adhere to the cyclone walls.

Dust conditionsat the inlet of the cyclone can include material type, specific gravity, bulk density (lb/ft3), dust load (lb/hr or grains/ft3 air), and particle size

distribution. Sizing, densities, and loads are needed to determine the required capacity and design specifications for sufficient capture. It is also important tospecify any unique characteristics of the particulate matter that may lead to corrosion or degradation of certain construction materials.

ConstructionA cyclone must be constructed properly in order to meet the sizing and performance requirements of its operation. The biggest variables in cyc lone design are itsopenings (inlets and outlets) and its body size.

ClassificationsCyclones can be classified into two types based on the construction and orientation of the inlet and outlet. These types are reverse flow and uniflow. In reverseflow(seen in Figure 1 above), the gas enters through a tangential inlet at the top of the cyclone body, shaped to create a confined vortex gas flow. The clean gasexits through a central pipe also at the top of the body. In uniflowor straight through cyclones, the gas enters at one end of the body and leaves at the otherend; this type is less frequently used in industry because it is a much less practical design in most cases.Cyclones can also be classified into two types based on the body size. High efficiencydesigns are characterized by long bodies in addition to small openings.This construction allows for high recovery rates at higher pressure drops. High ratedesigns are characterized by shorter bodies in addition to larger openings,which allow for a larger volume with lower capture rates or pressure drops.

Sizing and ConfigurationSizing a cyclone involves many factors, but the most important dimensions to consider are those of the inlet and the main body chamber.The sizing of inlets affects the airflow capacity of a cyclone, and also influences its pressure drop at a given flow velocity. Larger openings will tend to acceptgreater volumes of air and also will have lower pressure drops, but at the cost of efficiency. Inlet configurations can also vary based on the type of cyclone. The fourtypes include tangential, axial, helical, or spiral.Body size is important because, as mentioned above, the length of the cyc lone body is an important factor in collect ion efficiency. Body siz e is also directly


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proportional to a cyclones overall capital cost , and determines the space it occupies and its height.

Application ConsiderationsSome cyclone models are predesigned for specific applications, while others are built for specialized environments. Among the most important applicationconsiderations is the dust and gas composition. Specific types of particulate may be corrosive, abrasive, st icky, explosive, or toxic, thus requiring specialconstruction materials or designs in order to function properly.Cyclones are used for filtration in a wide variety of applications: abrasives, c oolant mists, explosive media, fine powders, metalworking chips, toxic media, andvarious production plant exhausts.GEA Niro - Cyclone, Figure 1Fisher-Klosterman - How to select and maintain a cyclone for maximum efficiency, Figure 2

Dr. L. Svarovsky - Gas Cyclones

Youtube - Modeled Cyclone Sepa rator, Vide o

Read user Insights about Cyclone Separators

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Cyclone Separators Information on GlobalSpec