Week 8 - Simulating Cyclone separator with Discrete Phase Modelling
Cyclone separator
Cyclone separators or simply cyclones are separation devices (dry scrubbers) that use the principle of inertia to remove particulate matter from flue gases. Cyclone separators is one of many air pollution control 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!
How it works
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.
Cyclone separators are generally able to remove somewhere between 50-99% of all particulate matter in flue gas. How well the cyclone separators are actually able to remove this matter depends largely on particle size. If there is a large amount of lighter particulate matter, less of these par0ticles are able to be separated out. Because of this, cyclone separators work best on flue gases that contain large amounts of big particulate matter.
There are several advantages and disadvantages in using cyclone separators. First, cyclone separators are beneficial because they are not expensive to install or maintain, and they have no moving parts. This keeps maintenance and operating costs low. Second, the removed particulate matter is collected when dry, which makes it easier to dispose of. Finally, these units take up very little space. Although effective, there are also disadvantages in using cyclone separators. Mainly because the standard models are not able to collect particulate matter that is smaller than 10 micrometers effectively and the machines are unable to handle sticky or tacky materials well.
Empirical models used to calculate separation efficiency
SIMULATION
1. geometry
2. Meshing
3. setup images
4.results
Geometry
Geometry profile
From this we have to extract the fluid volume and uncheck the same for physics
Extracted fluid volume
Meshing
After running the simulation once, it was established that the no of particles that get tracked depends on the mesh and mesh size. So, smaller the mesh size, more the number of particles that get tracked. So, particle size of the main mesh is 10mm and that of the inlet face is 5mm. i have applied the cartesian method for meshing so that i get a hexahedral mesh.
the mesh profile is given in the image below.
SETUP and IMAGES
Here we are selecting a steady state solver with gravity enabled. we choose the k-`epsilon`model with RNG with swirl dominated flow. This enhances the accuracy of swirl flows. Discrete phase modeling is used in this simulation. There are 2 types of modeling a) coupled flows and b) uncoupled flows. The coupled flow model has interaction between the discrete phase and continous flow, and the latter being the opposite.We require coupled flow model for this simulation.
Case P1V3 :
Particle size 1 micrometre
velocity 3m/s
BOUNDARY CONDITION
Inlet velocity 3m/s
INLET
OUTLET 1 (TOP)
OUTLET 2 (BOTTOM COLLECTOR)
Solution Initialisation
The above setup is the same for all the cases ecxcept the parameters changed
changed parameters are velocity and Particle size. Below you can find the images of all the results with all the cases (number after P is the particle size in micrometre and number after V is the velocity in metre/sec )
P1V3
The number of cells trapped and tracked will help us calculate the separation efficiency.
Tracked : 378
Trapped : 114
Vorticity
P3V3
Tracked : 378
Trapped :125
Vorticity
P5V3
Tracked : 378
Trapped : 205
Vorticity region
P5V5
Tracked : 91
Trapped : 68
Vorticity
P5V1
Tracked : 91
Trapped : 37
Vorticity region
From the images above, we can conclude that case P5V5, which consists of 5 micrometre particles injected from the inlet at 5metres per secon velocity.
Separation efficiency can be calculated
`("no. of cells trapped")/("no. of cells tracked")`
The table below shows the separation efficiency of the above cases
With the results in the table we can say that for the setup given, the best efficiency is achieved by case P5V5.