Cyclone Separator Challenge
Aim: To perform analysis on cyclone separator and calculate the separator efficiency and pressure drop.
Objective:-
- To write a few words about any four empirical models used to calculate the cyclone separator efficiency.
- To perform an analysis on a given cyclone separator model by varying the particle diameter from 1 μm to 5 μm and calculate the separation efficiency in each case. Discuss the results. [Use both the velocity's as 3m/sec.]
- To perform an analysis on a given cyclone separator model by varying the particle velocity from 1 m/sec to 5 m/sec and calculate the separation efficiency and pressure drop in each case. Discuss the results. [Use particle diameter size as 5 μm for all cases & keep flow velocity same as particle velocity]
Introduction:
Theory:
Cyclone separator: These are devices used to remove particulate matter from flue gases by using the principle of inertia. cyclone separators is one of many air pollution control devices known as precleaners since they generally remove large 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 called as multicyclone. cyclones can vary drastically in size and the size largely depends on how much of flue gases much be filtered so larger operation need larger cyclones.
Working principle: cyclone separator works as a centrifuge but has continuous feed of dirty air . Dirty flue gases are fed into the chamber. The inside of the chamber creates a spiral vortex similar to a tornado. The lighter components of gas have less interia so it is easy for them to be carrried away by vortex and travel up.The heavier particles due to high inertia and weight they settle down at the bottom.
Larger particles have a tendency to settle down due to inertia and before that they hit the walls of the separator and fall down and collected in a hopper. Cyclone separator can remove particulate matter less than 10 micrometer in diameter. There are separator which can even remvove a particulate size of 2.5 micrometer..
Empircal models used in calculating cyclone separator efficiency:
1. Iozia and Leith model:
Iozia and leith logistic model is a modified version of Barth model, which is developed based on force balance. The model assumes that a particle carried by the vortex endures the influence of two forces that are centrifugal force Z and a flow resistance W. The collection efficiency `eta underseti` of particle diameter dpi can be calculated from
`beta`is an expression for slope diameter
2. Li and wang model:
The Li and wang model includes particle bouncing or entrainment and turbulent diffusion at cyclone wall. A two dimensional analytical expression of particle distribution in the cyclone is obtained.
Assumptions were made in making the model:
i.The radial particle velocity and the radial concentration profile are not constant for uncollected particles within the cyclone.
ii.Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce re- entrainment on the cyclone wall are:
The collection efficiency of particle of any size is given as:
3. Koch and litch model:
kotch and litch collection theory recognized the inherently turbulent nature of cyclones and the distribution of gas residence times within the cyclone. kotch and litch described the particle motion in the entry and collection regions with additional following assumptions:
- The tangential velocity of a particle is equal to the tan- gential 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: uR^n= constant.
Grade efficiency
4. Lapple model:
Lapple model was developed based on force balance without 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 to calculate a 50% cut diameter.
The efficiency of collection of any size of particle is given by :
Modelling approach:
- Import the geometry in spaceclaim and extract the volume.
- Mesh the model with a finer mesh size around 10 mm.
- Two parts of the problem is to be considered i.e varying diameter with velocity constant v=3m/s
- velocity variable by keeeping diameter constant d= 5micrometer
- set up the fluent with pressure based solver and gravity on.
- use k-epsilon RNG swirl dominated flow.
- Setup the discrete phase model with anthracite injection
- Use steady state solver.
- post process the results.
Case table:
Geometry:
Base model: Extract volume model:
Named selections:
Inlet outlet up outlet down
Boundary condition:
Inlet and wall:- Reflect
Outlet(Top):- Escape
Outlet(Bottom/dustbin) - Trap
----------------------------------------------------------------------------------------------------Part 1---------------------------------------------------------------------------------------------
Mesh:
10 mm mesh size is taken for the analysis for part 1
fluent setup:
Boundary condition:
Discrete phase model:
solution initialization:
Case 1:Analysis on cyclone separator model with flow and particle velocity at 3m/s with particle diameter of 1 micrometer.
fluent setup:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 31/124
=0.25
Separator efficiency=25%
Residuals:
Anthracite particle time:
Pressure contour:
Velocity contour:
Pressure difference between inlet and outlet top:
pressure difference= inlet - outlet top
=19.52-2.70
=16.82 pascals
Swirl strength:
swirl strength values 0.0024/0.08//0.28
Animation case 1:
Case 2:Analysis on cyclone separator model with flow and particle velocity at 3m/s with particle diameter of 2 micrometer
Fluent setup:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 95/124
=0.766
Separator efficiency=76.6%
Residuals:
Anthracite particle time:
Note: Since the velocity of the particle and the flow are same, the pressure and velocity values and contours will be same that of case 1
Note : The swirl strength would give the same results as that of case1
Animation case 2:
Case 3:Analysis on cyclone separator model with flow and particle velocity at 3m/s with particle diameter of 3 micrometer:
Fluent setup:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 102/124
=0.822
Separator efficiency=82.2%
Residuals:
Anthracite particle time:
Note: Since the velocity of the particle and the flow are same, the pressure and velocity values and contours will be same that of case 1
Note : The swirl strength would give the same results as that of case1
Animation case 3:
Case 4:Analysis on cyclone separator model with flow and particle velocity at 3m/s with particle diameter of 4 micrometer:
Fleunt setup:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 108/124
=0.871
Separator efficiency=87.1%
Residuals:
Anthracite particle time:
Note: Since the velocity of the particle and the flow are same, the pressure and velocity values and contours will be same that of case 1
Note : The swirl strength would give the same results as that of case1
Animation case 4:
Case 5:Analysis on cyclone separator model with flow and particle velocity at 3m/s with particle diameter of 5 micrometer:
Fluent setup:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 118/124
=0.951
Separator efficiency=95.1%
Residuals:
Anthracite Particle time
Animation case 5:
Results table for part 1 all cases:
-------------------------------------------------------------------------------------------------------------------Part 2------------------------------------------------------------------------------------------------
In this part we keep the particle diameter as 5 micrometer for every case and vary the velocity from 1 to 5 m/s
fluent setup remains same except that the flow velocity and partice velocity changes in each case.
Mesh:
Case 1:Analysis on cyclone separator model with flow and particle velocity at 1m/s with particle diameter of 5 micrometer.
fluent setup:
Residuals:
Anthracite particle time:
Pressure contour and values:
Velocity contour and values:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 168/348
=0.4827
Separator efficiency=48.27%
Pressure drop between inlet and outlet top:
pressure diffference= Inlet - outlet top
= 1.86-0.18
=1.68 pascals
Pressure drop= 1.68 pascals.
Animation case 1:
Case 2 : Analysis on cyclone separator model with flow and particle velocity at 2m/s with particle diameter of 5 micrometer
fluent setup:
Residuals:
Anthracite particle time:
Pressure contour and value:
velocity contour and value:
velocity streamlines:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 186/348
=0.5344
Separator efficiency=53.44%
Pressure drop between inlet and outlet top:
pressure diffference= Inlet - outlet top
= 8.05-0.92
=7.13 pascals
Pressure drop= 7.13 pascals.
Animation case 2:
Case 3 : Analysis on cyclone separator model with flow and particle velocity at 3m/s with particle diameter of 5 micrometer
fluent setup:
Residuals:
Anthracite particle time:
Pressure contour and value:
velocity contour and value:
velocity streamlines:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 231/348
=0.6637
Separator efficiency=66.37%
Pressure drop between inlet and outlet top:
pressure diffference= Inlet - outlet top
= 19.5-2.44
=17.06 pascals
Pressure drop= 17.06 pascals
Animation case 3:
Case 4 : Analysis on cyclone separator model with flow and particle velocity at 4m/s with particle diameter of 5 micrometer
fluent setup:
Residuals:
Anthracite particle time:
Pressure contour and value:
velocity contour and value:
velocity streamlines:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 232/348
=0.6666
Separator efficiency=66.66%
Pressure drop between inlet and outlet top:
pressure diffference= Inlet - outlet top
= 37.86-5.17
=32.7 pascals
Pressure drop= 32.7 pascals.
Animation case 4:
Case 5 : Analysis on cyclone separator model with flow and particle velocity at 5m/s with particle diameter of 5 micrometer
fluent setup:
Residuals:
Anthracite particle time:
Pressure contour and value:
velocity contour and value:
velocity streamlines:
Separator efficiency:
Defined as ratio of concentration that has been removed from the feed stream to that of the initial concentration in the feed stream.
Separator efficiency = No of particles trapped/No of particles tracked
= 292/348
=0.8390
Separator efficiency=84%
Pressure drop between inlet and outlet top:
pressure diffference= Inlet - outlet top
= 64.84-8.99
=55.85 pascals
Pressure drop= 55.85 pascals.
Animation case 5:
Swirl strength for one case :
swirl strength 0.01/0.04/0.07
Part 2 cases table results:
-------------------------------------------------------------------------------------------------Discussion and conclusion--------------------------------------------------------------------------
final table:
Conclusion and Inferences:
- Both the parts have different mesh sizes and method. Part 2 has finer mesh size and inflation layer added to capture the velocity and pressure drop with more accuracy.
- In part 1 we can infer that as the particle diameter size increased the separator efficiency increased.
- In part 2 we can infer that as the flow and particle velocity increases the separator efficiency increased and pressure drop increased.This confirm the accuracy of simulation.
- By this we can understand that particle size and velocity plays and important role is separator efficiency.
- Discrete particle model allows us to inculcate better control for velocity and particle size.
- Increase in velocity leads to higher pressure drop which yields better results.
- The highest separator efficiency obtained is 95.1% for particle velocity 3m/s and particle diameter 5 micrometer.