Cyclone Separator Challenge

• Objectives :

• Perform an analysis of the given cyclone separator model by varying the particle diameter from 1 µm to 10 µm and calculate the separation efficiency in each case. Discuss the results. [Use both the velocity\'s as 3m/sec]
• Calculate the separation efficiency and pressure drop by varying the inlet velocity of both fluid and particle from 5 m/sec to 10 m/sec & Discuss the results. [Use particle diameter size as 5 µm.]

• Introduction :

Cyclone separators or simply cyclones are separation devices (dry scrubber) that use the principle of inertia to remove particulate matter from flue gases. Cyclone separators is one of many air pollutioncontrol devices known as precleaners since they generally remove larger pieces of particulate matter. This prevents finer filtration methods from having to deal with large, more abrasive particles later on. In addition, several cyclone separators can operate in parallel, and this system is known as a multicyclone.

It is important to note that cyclones can vary drastically in their size. The size of the cyclone depends largely on how much flue gas must be filtered, thus larger operations tend to need larger cyclones. For example, several different models of one cyclone type can exist, and the sizes can range from a relatively small 1.2-1.5 meters tall (about 4-5 feet) to around 9 meters (30 feet)—which is about as tall as a three story building!.

Cyclone separators work much like a centrifuge, but with a continuous feed of dirty air. In a cyclone separator, dirty flue gas is fed into a chamber. The inside of the chamber creates a spiral vortex, similar to a tornado. This spiral formation and the separation is shown in Figure 2. The lighter components of this gas have less inertia, so it is easier for them to be influenced by the vortex and travel up it. Contrarily, larger components of particulate matter have more inertia and are not as easily influenced by the vortex.

Since these larger particles have difficulty following the high-speed spiral motion of the gas and the vortex, the particles hit the inside walls of the container and drop down into a collection hopper. These chambers are shaped like an upside-down cone to promote the collection of these particles at the bottom of the container. The cleaned flue gas escapes out the top of the chamber.

Most cyclones are built to control and remove particulate matter that is larger than 10 micrometers in diameter. However, there do exist high efficiency cyclones that are designed to be effective on particles as small as 2.5 micrometers. As well, these separators are not effective on extremely large particulate matter. For particulates around 200 micrometers in size, gravity settling chambers or momentum separators are a better option.

Out of all of the particulate-control devices, cyclone separators are among the least expensive. They are often used as a pre-treatment before the flue gas enters more effective pollution control devices. Therefore, cyclone separators can be seen as \"rough separators\" before the flue gas reaches the fine filtration stages.

Seperation Efficiency : Separation efficiency is defined as the ratio of concentration that has been removed from the feed stream to the initial concentration in the feed stream. In our case it is ratio of number of trapped particles to total number of particles tracked.

Pressure Drop : Pressure drop is defined as the difference in total pressure between two points of a fluid carrying network. i.e Pressure drop = Total inlet pressure - Total Outlet Pressure( outlet top in this case).

• Geometry :

Uploading the 3D cad model of Cyclone seperator into space claim.

We need to extract fluid surface as we are concerned with it. Select edges as shown below.

Extracted volume will look as shown below. And we need to suppress the body for physics.

• Meshing :

Mesh Element Size = 4 mm.

Number of Nodes = 456576.

Number of Elements = 427841.

Meshing method : Cartesian.

• Case Setup :

Solver - Pressure based Absolute velocity formulation, with steady time.

Gravity - Enabled in y direction = -9.81.

Viscous Model - RNG K-Epsilon model considering swirl dominated flow.

Discrete Phase Modelling - Discrete Phase Modelling (DPM) is a method in which flow of discrete phase with a continous flow is modelled.

Injections - Injection type : Surface from Inlet

Particle type : Inert

Material type : Anthracite

X- velocity = As per case.

Diameter = As per case.

Flow rate = 1e-20 kg/s.

Boundary Conditions -

Inlet - Velocity = same as x-velocity of phase. DPM condition : Reflect.

Outlet top - Pressure = 0 Pa. DPM condition : Escape.

Outlet Bottom - Pressure = 0 Pa. DPM condition : Trap.

• Case I :

Create input parameter for diameter.

Create Output Parameter for Inlet and Outlet total pressure.

Velocity = 3m/s.

Standard Initialization and computing from inlet.

Diameter (m)	Tracked	Escaped	Incomplete	Trapped	Separation Efficiency (%)	Inlet Pressure (Pa)	Outlet Pressure (Pa)	Pressure Difference (Pa)
1.00E-06	378	150	90	138	36.5	31.15	4.27	26.88
2.00E-06	378	129	99	150	39.68	31.17	4.27	26.9
3.00E-06	378	101	113	164	43.38	31.19	4.27	26.92
4.00E-06	378	77	76	225	59.52	31.21	4.27	26.94
5.00E-06	378	74	78	226	59.78	31.22	4.27	26.95
6.00E-06	378	67	58	253	66.93	31.24	4.27	26.97
7.00E-06	378	79	36	263	69.57	31.25	4.27	26.98
8.00E-06	378	61	25	292	77.24	31.27	4.27	27
9.00E-06	378	66	15	297	78.57	31.28	4.27	27.01
1.00E-05	378	52	27	299	79.1	31.3	4.27	27.03

• Case II :

Create input parameter for velocity.

Create Output Parameter for Inlet and Outlet total pressure.

Diameter = 5e-6m.

Standard Initialization and computing from inlet.

Velocity	Tracked	Escaped	Incomplete	Trapped	Separation Efficiency (%)	Inlet Pressure (Pa)	Outlet Pressure(Pa)	Pressure Difference (Pa)
5m/s	378	80	13	285	75.39	91.32	12.61	78.71
6m/s	378	79	0	299	79.1	133.23	18.47	114.76
7m/s	378	74	0	304	80.42	183.47	25.53	157.94
8m/s	378	66	0	312	82.53	241.67	33.72	207.95
9m/s	378	66	0	312	82.53	308.1	43.09	265.01
10m/s	378	65	0	313	82.8	380.96	53.42	327.54

• Results :

1. Seperation efficiency depends on both diameter and velocity of the particles.
2. Increase in diameter and velocity increases seperation efficiency.
3. Velocity has greater impact as compared to diameter of particle.
4. Pressure drop is dependant on velocity. For constant velocity with varying diamtere size the pressure drop remains almost constant.
5. Increase in velocity causes the pressure drop to rise exponentially.

Write a few words about any four empirical models used for cyclone separator efficiency.

1. IOZIA AND LEITH MODEL
Iozia and Leith (1990) logistic model is a modified version of Barth (1956) model which is developed based on force balance. The model assumes that a particle carried by the vortex endures the influence of two forces: a centrifugal force, Z, and a flow resistance, W. Core length, zc and core diameter, dc
The addition made by Iozia and Leith on the original Barth (1956) model are the core length zc and slope parameter β expression which is derived based on the statistical analysis of experimental data of cyclone with D = 0.25 m.

2. LI AND WANG MODEL
The Li and Wang (1989) model includes particle bounce or re-entrainment and turbulent diffusion at the cyclone wall. A two-dimensional analytical expression of particle distribution in the cyclone is obtained. Li and Wang model was developed based on the following assumptions:
• The radial particle velocity and the radial concentration
profile are not constant, for uncollected particles within the
cyclones.
• Boundary conditions with the consideration of turbulent
diffusion coefficient and particle bounce re-entrainment on
the cyclone wall are:

c = c0 , at θ = 0

Dr = (1- α)wc, at r = D/2

• The tangential velocity is related to the radius of cyclone by: uRn = constant.

3. KOCH AND LICHT MODEL
Koch and Licht (1977) collection theory recognized the inherently turbulent nature of cyclones and the distribution of gas residence times within the cyclone. Koch and Licht describe particle motion in the entry and collection regions with the additional following assumptions:
• The tangential velocity of a particle is equal to the tangential velocity of the gas flow, i.e. there is no slip in the tangential direction between the particle and the gas.
• The tangential velocity is related to the radius of cyclone by: uRn = constant.

A force balance and an equation on the particles collection yields the grade efficiency ηi.

4. LAPPLE MODEL
Lapple (1951) model was developed based on force balancewithout considering the flow resistance. Lapple assumed that a particle entering the cyclone is evenly distributed across the inlet opening. The particle that travels from inlet half width to the wall in the cyclone is collected with 50% efficiency. The semi empirical relationship developed by Lapple (1951) to calculate a 50% cut diameter.