Cyclones Applications for cyclones Efficiency of cyclones Estimating costs of cyclones Fisher Klosterman, Inc Hannigan, Inc

streamlines Brownian Motion (diffusion) impaction interception Removal mechanisms for particles in a gas stream.

Cheap No moving parts (low maintenance) Removes solid or liquid particles (non-corrosive particles) Harsh conditions (high temperatures) Time-proven technology (1940s) Low efficiency for small particles (dp<10 um) High pressure drops  High operating costs Can’t do sticky particles General cyclone thoughts IMPACTION! Mechanism=

What happens to the collected particles?? Airlock system

When would I use a cyclone??? Particles are coarse (Dp>10  m) Concentrations are high (Conc. > 1 gr/ft 3 ~ 2 g/m 3 ) Size classification is desired High efficiency is not required Cyclones are often used as a pre-cleaning device.

Types of Cyclones High efficiency cyclones (Papa Bear) High pressure drop High collection of small diameter particles (dp<10 um) High throughput cyclones (Baby Bear) Low pressure drop High flow rate Low collection of small dp Conventional ‘standard’ cyclones (Mama Bear) In-between high efficiency and high throughput

W DeDe D Top View Standard (involute) Cyclone Side view H DeDe D S DdDd LbLb LcLc Book gives relative dimensions of different cyclone parts, e.g., H/D = 0.5 for conventional standard cyclone

Gas flow rate  Gas velocity Flow rate (Q) = volume/time = length 3 /time Cyclone inlet Velocity (V) = length/time H W Q V=Q/A Area (A) = length 2 For a cyclone: V i =Q/(HW)

Calculating cyclone efficiency Number of revolutions the carrier gas spins through during the downward part of the spiral: Gas residence time during the downward part of the spiral: R=D/2 = circum*revs/velocity W D R Particle has to hit wall in to be removed. Maximum radial distance a particle will travel:W H LbLb LcLc

Centrifugal force Drag force Velocity for collection to occur > But we know how to calculate particle terminal velocity: Centrifugal force = 1/ 

Smallest particle that will be collected: What factors improve efficiency of cyclone (i.e., decrease d p )? Putting it all together:

Particle size ratio ( d p /d pc ) efficiency 50% 1

Sometimes operating conditions change: temperature density loading flowrate Need to calculate change in cyclone performance (Table 4.2 in text) Example: Decide to sample Asian dust instead of sea salt. (1) How does collection efficiency change? (2) How does cutpoint diameter change?  ss  85%, d pc =2.2  m  ss = 2.2 g/cm 3  ad = 2.8 g/cm 3

Pressure drops in cyclones Variety of empirical formulas for determining pressure drop. 12<K<18 Important for figuring out power requirements: Power = Q Tells you how big a fan you need to pull the dirty air through the cyclone. Bigger fans cost more money. H v =‘velocity head’

Costs for Cyclones Purchase Costs: collection efficiency gas volume throughput design pressure drop material of construction Alternatively: key parameter is area of cyclone inlet P c = 6520A P v = 273A See Table 4.3 Cyclone cost Airlock valve

Impactors Stokes number (Stk) is ratio of stopping distance over characteristic dimension of system. Stopping distance is distance a particle traveling at velocity v will travel in the absence of applied force. S= V p  V p Similar principle to cyclone Use ‘impaction’ to size segregate particles. Not a pollution control device

Efficiency of collection:  i = (  /2)Stk i = Impactors typically have sharper cutoff efficiency than cyclone (see Figure 4.3 in text book)