What is the Downcomer?
Downcomers are tubes that start from the steam drum and supply water to the lowest points of the furnace walls and boiler banks.
What is Downcomer in distillation column?
Downcomers are conduits having circular, segmental, or rectangular cross sections that convey liquid from upper tray to a lower tray in a distillation column. The minimum limit for flow path length is 400 mm in order to provide good contacting between vapour and liquid.
What is flooding velocity in distillation column?
Vapour flow velocity is dependent on column diameter. Weeping determines the minimum vapour flow required while flooding determines the maximum vapour flow allowed, hence column capacity.
What is Downcomer in boiler?
Downcomers are pipes leading from the top to the bottom of the boiler. Downcomers carry the water from steam drum to the bottom part of the boilers where it enters the distribution headers to be heated in the combustion zone.
What is wet riser and downcomer?
Wet risers are a form of internal hydrant sytem in a building where it is pumped from ground level sump through a pressure pump to different areas of the building according to the design of the system Wet riser system comprises duty fire pump with standby pump discharging into riser pipe with landing valves at each …
What is the function of a Downcomer?
The primary function of downcomers on trays is to facilitate countercurrent liquid flow down the column with vapor flowing up through the tray openings on sieve and valve trays.
What is the function of weir and Downcomer?
The gas flows through the holes, and the downcomer ensure the flow of the liquid down from one plate to the other. The weir is the element which retains a liquid quantity on the plate in order to ensure the contact between the two phases before flow into the next plate.
What is weir length in distillation column?
The outlet weir height typically is 51 mm, this is the height that has been used in obtaining most of the FRI data with the trays with downcomer. In vacuum distillation, operating in the spray regime, typical weir height is 0 to 25 mm, while absorbers and strippers may use 102 mm weir height(1).
What is Jet flooding?
Jet flooding, also called entrainment flooding, is caused by massive entrainment of liquid to the tray above. As the tray loading increases, a two-phase mixture of spray or froth begins to occupy more and more of the clear vapor space between the trays.
What is the flooding velocity?
Point e is known as the flooding point. The gas velocity at this point is known as the flooding velocity (limiting velocity). – at constant liquid rate, gas pressure drop increases with gas velocity. – at constant gas velocity, the gas pressure drop is higher at larger liquid rate.
What is distillation flooding?
Flooding is a common abnormal process condition wherein the distillation column stops generating a separation, thus causing the quality of the top and/or bottom products to go off specification.
Why is the downcomer cross sectional area the same?
It will work OK at high loads, but at reduced throughput there will be not enough liquid to maintain the hydraulic seal. Downcomer cross-sectional area remains the same because it is independent from downcomer length. The D/C area is what you see when looking at the tray from the top perspective.
What are the counter current conditions in downcomer?
Counter-current flow conditions in full-scale downcomer for strongly subcooled ECC water, distribution of subcooled temperatures. The test was carried out at a reactor typical steam upflow of 320 kg/s and ECC water injection (subcooling 115 K) into the three intact loops.
Is the inlet weir height the same as the downcomer?
Downcomer area has probably remained the same since inlet weir height needs to be increased for the same amount as downcomer clearance, in order to maintain liquid seal on the trays. The best thing is to check directly with the vendor.
Why is there a seal on the downcomer?
The downcomer seal prevents vapor from the tray from bubbling into the downcomer (see Figure 13-1 ), whether the trays are bubble cap, valve or sieve types.