Week 8 - Simulating Cyclone separator with Discrete Phase Modelling
Aim:- To perform CFD analysis on cyclone separator and calculate the separation efficiency and pressure drop.
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.
Working of cyclone separator:
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. 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 separtors 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.
Effectiveness
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.
To write a few words about any four empirical models used to calculate the cyclone separator efficiency.
Simulation Setup:
Geometry
Load the geometry in the space claim, Using volume extract tool separate the fluid volume and select suppress for physics for thicken2 component.
Meshing
Create named selections like Inlet, outlet-1, outlet-2.
Insert>Method>Cartesian>element size 5mm and generate mesh.
Mesh Metrics
Fluent Solver setup
Boundaries.
At outlet-2 set dpm as trap.
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.]
Case-1:
Particle dia= 1 μm , vel=3m/sec.
Scaled residuals
Vortex Region
Anthracite particle time:
Separator Efficiency=325/378=85.97%
Case-2:
Particle dia= 2 μm , vel=3m/sec.
Scaled residulas:
Anthracite particle time:
Separator Efficiency=324/378=85.71%
Case-3:
Particle dia= 3 μm , vel=3m/sec.
Scaled residuals
Anthracite particle time:
Separator Efficiency=157/378=41.54%
Case-4:
Particle dia= 4 μm , vel=3m/sec.
Scaled residuals
Anthracite particle time:
Separator Efficiency=290/378=76.71%
Case-5:
Particle dia= 5 μm , vel=3m/sec.
Scaled residuals
Anthracite particle time:
Separator Efficiency=250/378=66.13%
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]
Case-1:
Particle dia= 5 μm , vel=1m/sec.
Scaled residuals
Inlet Pressure:
Outlet Pressure
Separator Efficiency=312/378=82.53%
Case-2:
Particle dia= 5 μm , vel=2m/sec.
Scaled residuals
Outlet pressure
Separator Efficiency=289/378=76.45%
Case-3:
Particle dia= 5 μm , vel=3m/sec.
Scaled residuals
Anthracite particle time:
Separator Efficiency=325/378=66.13%
Case-4:
Particle dia= 5 μm , vel=4m/sec.
Scaled residuals
Inlet Pressure
Outlet Pressure
Separator Efficiency=260/378=68.78%
Case-5:
Particle dia= 5 μm , vel=5m/sec.
Scaled residuals
Inlet ppressure
Outlet pressure
Separator Efficiency=284/378=75.13%
Conclusions:
CFD simulation of Cyclone separator is carried out by keeping the flow velocity constant and by varying the particle diameter
and separation efficiency is calculated for each case.
CFD simulation of Cyclone separator is carried out by keeping the particle diameter constant and by varying the flow velocity, separation efficiency is calculated for each case.