History of Cyclones For many years it was felt that "any cyclone was just a cyclone" - that "all cyclones were created equal." The basics seemed simple enough. All that seemed necessary was to pass dust laden air through the inlet and the dust would magically fall out the bottom. The air (with the finer dust particles still entrained) would pass out the vortex finder.

The cyclone dust collector was patented in 1886, and has been used extensively in bulk handling process operations ever since. The device was never thought to have potential for ultra high efficiency collection processes until researchers such as Gerhard Miczek and Christian Doerschlag explored the potential of cyclones as ultra high efficiency devices. They demonstrated that the basis for choosing an ultra high efficiency design over the "run of the mill" textbook design is exacting and involves a different approach. It is unfortunate that hundreds of "run of the mill" or "created equal" cyclones still change hands yearly as used equipment without the depth of analysis required to determine its suitability for the specific application.

Modern Advances in Cyclone Performance The ability to remove and collect a high degree of particulate using a cyclone is possible. Cyclones may now be designed with efficiency levels in excess of 99.99%. Performance at that level of efficiency requires application review and cyclone design by engineers with a high degree of understanding of cyclone theory. Unfortunately, most cyclones are misapplied due to a lack of "proper understanding". Prior to the 1970's Clean Air Act, the objective of a cyclone was to capture the bulk of a product, allowing the finer dusts to escape to the atmosphere. During the 20 years following the first Clean Air Act, environmental awareness has been heightened to make it undesirable to allow even fine dusts to pollute the area around the emission source.

To avoid misapplication one has to analyze the input to a cyclone and the affects, variations of input, and causes that alter the end results. A number of pieces of data are required to make a proper assessment. The primary data considerations for a proper selection are as follows: Q = Actual Gas Volume (ACFM) entering the cyclone inlet ? = Gas Density based on temperature, pressure/vacuum, humidity and composition V = Viscosity of the transporting gas stream Grain Loading = The ratio of grains/actual cubic foot of conveying gas = pounds/minute of particulate x 7000 gr/pound

ACFM Specific Gravity = Particle density of the particulate particle size distribution of the particulate expressed aerodynamically in Stokes equivalent diameters. It is important that this be accomplished utilizing an acceptable test method. Efficiency = Expressed as the percentage of the total distribution of particulate entering the cyclone E% = Particulate (lbs) entering ? Particulate (lbs) leaving x 100

Particulate (lbs) entering Conditions = Since efficiencies are based on dry particulate free flow considerations it is important to assess the potential effect due to stickiness, abrasiveness, explosive, toxic, corrosiveness. Pressure Drop = The extent of pressure drop in a well designed cyclone can have a high impact on efficiency Space = The relationship of the inlet, body, cone, discharge and vortex finder are important considerations in seeking high efficiency Materials of Construction = Can be extremely important in determining the life of cyclone

Looking at the above items, one can start to visualize the effects caused by changes to any individual data item or a combination of data items. For example: An increase in volume (ACFM) will effect pressure drop, efficiency, and ultimately the life of the cyclone. In summary, a change to any one or more of the above functions can provide cause for a complete change in cyclone designs.

The System Effect on the Cyclone

A cyclone can be designed for a specific volume and pressure drop to achieve a specific result. In order for this to happen the external system must also be designed properly. If the system static pressure is not compatible with the fan the entire system will suffer, including the cyclone. A cyclone may be designed to operate at 10000 ACFM @ 6" w.g. pressure drop but if the system fan is not selected to compensate for the total system static pressure, the cyclone may actually suffer a loss in volume, pressure drop and efficiency. If the equipment performance is suspect, and the actual pressure drop is measured at 4" ?P instead of 6" ?P the volume may become 6 = (10000)2 4 (New VQ)2 New volume @ 8165 ACFM This volume effect to a given single cyclone could reduce the efficiency to well below an acceptable level.

The Multiple Cyclone Effect

In many cases splitting the flow into multiple cyclones in parallel is preferred because of the efficiency gain at no loss in pressure drop combined with the height reduction benefit it provides. To illustrate this effect, figure 1 was based on the following initial data input to the cyclones. Case I Case II Volume = 10000 ACFM 8165 ACFM Gas = Air (dry) at sea level at 14.7 psia Density = .075 lbs/ft.3 Specific Gravity of Particulate = 2.0 Grain Loading of Particulate = 5 grains/ACF (428 lbs/hr) Particle Size Distribution given as: Micron (Stokes) Percent Finer Than 1 .01 50 50 100 100

ACFMVOLUME ?P@ Conditions SingleCyclone Eff. DualCyclone Eff. QuadCyclone Eff. Standard HighEfficiency Model 810510000 4.00" w.g. 6.00" w.g. 91.646 93.226 93.454 94.336 95.1 96.1 Ultra HighEfficiency Model 816510000 4.00" w.g. 6.00" w.g. 98.98 99.17 99.23 99.42 99.51 99.63

Figure 1 From Figure 1 example it is easy to visualize the basic system effect on the end results utilizing two different models of cyclones as single units, duals and quads at the stated conditions. It is important to emphasize that variations in density, specific gravity, grain loading and particle size distribution will provide a new set of results.

Efficiency vs Outlet Emissions

Most people do not properly equate efficiency to outlet emissions. Many people think that a 99% efficiency means, we are collecting basically all of the material but can not understand why it appears that the outlet is visibly discharging a lot of material.

In our example at 10,000 ACFM with a grain loading of 5 grains/ACF (428 lbs/hr) if we collect 99% we will capture 423.7 lbs/hr and lose 4.28 lbs/hr (.05 gr/ACF). 0.05 gr/ACF is approximately twice the outlet emission required to become invisible at the stack or emission point. To cut the emissions load in half to reach the point of no visibility an efficiency of 99.5% would be required in this example.

Cyclone Maintenance

A properly installed cyclone assembly consists of three key elements: 1) A properly designed cyclone 2) A properly designed vortex reduction hopper (receiver) 3) A properly designed air locked discharge (for both positive and negative systems Given these components, maintenance should be nil, assuming that the equipment is leak proof.

Operation Maintenance

It is recommended that a log be maintained initially and whenever tests are conducted, record the conditions of operation and results. There is nothing more valuable than a record of flows, pressure drops, temperatures, material conditions, etc. taken initially for use in identifying potential problems, if they develop from a change in operations later.

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