How to Design of Gas liquid Solid separator?
As the core device of the anaerobic reactor, three phase separator (Gas-Liquid-Solid separator) is mainly used in UASB and other anaerobic reactors to separate solid, liquid, and gas in the anaerobic reaction.
It is necessary to equip the UASB reactor with GLS separator device inorder to achieve highest possible sludge hold-up under operational conditions. Three phase separator plays an important role in the normal operation of the sludge bed and in obtaining good outlet quality water.
Three phase separator has the following two functions:
i) To collect the marsh gas generated in the reaction chamber under the separator,
ii) To precipitate the suspended substances above the separator.
The effect of three phase separation directly determines the success or failure of the anaerobic process so the design parameters of three phase separator are very important and precise.With good performance, the three phase separator is the guarantee of high load and stable operation of UASB and other anaerobic reactors.
Working principle of GLS separator
Anaerobic reaction occurs as wastewater comes in contact with sludge, then the production of marsh gas (The gas contains methane and carbon dioxide) causes perturbation in the sludge bed. Part of the marsh gas produced in the sludge remains attached to the sludge particles, and the free bubbles and bubbles with sludge particles rise to the top of the reactor. The bubbles rise up with the sludge particles and strike the bottom of the degassing baffle, which makes the bubbles burst and the entrapped gas is released.
The sludge particles then fall to the sludge bed, while the gas is collected in the reactor's gas collecting chamber. Liquid with solids and bio-particles enter into the sedimentation and they will go back to the sludge bed again after separating from the liquid. The liquid after separating solid gas continues to rise and flow out from the effluent weir, and finally discharge from the water collecting basin.
Working Condition of GLS separator
In an anaerobic reactor, the three-phase separator must fulfil the following requirements:
1. Before entering the settling chamber, the water and sludge combination must be separated.
2. The sedimentation zone's surface load should be less than 3.0 m3. The flow velocity of the mixed liquid via the input channel should not exceed the sedimentation speed of granular sludge before it enters the sedimentation zone.
3. Anaerobic sludge has a flocculation feature. When liquid flow rises and passes through the sludge layer, the sludge layer in the sedimentation zone can easily develop. The angle of the sloping wall in the sedimentation region should be adequate so that the sludge slides back to the reaction zone rapidly and does not collect on the sloping wall.
4. It is important to keep the gas chamber from creating a lot of foam; the height of the gas chamber should be kept under control to keep the scum from clogging the exit pipe.
Working of GLS separator
When the bubbles in the combination of gas, liquid, and solid reach the baffle board at the bottom of the three-phase separator, the gas is directed to the gas chamber, where it may be efficiently separated from the solid and liquid. Under the influence of gravity, some of the sludge separated from the bubbles returns to the reaction zone, while the rest rises with the fluid and reaches the sedimentation zone. Because there is no bubble in the liquid of the sedimentation zone, the density of the water column above the sludge reflux inlet is higher than that of the water in the reactor, so that the concentrated sludge can return to the reaction zone to achieve the purpose of solid-liquid separation.
Design of Gas Liquid solid (GLS) separator
The reflector, gas collecting basin, gas collecting pipe, and water collecting basin make up the three-phase separator.
The gas-water contact inside the dome is considered at a certain depth from the domes top. The height of the GLS separator can be thought of as 25% of the entire reactor height at first. The angle of the dome with the horizontal may be assumed to be 45o for determining the number of domes required at first, and the top width can be assumed to be 0.2 to 0.3 m.
It is possible to compute the number of domes necessary for a particular diameter (or breadth for a rectangular reactor). The flow rate shared by each dome must be approximated in proportion to the base area of each dome, including aperture width, to the overall area of the reactor once the number of domes has been determined.
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