Page 187 - Applied Process Design For Chemical And Petrochemical Plants Volume II
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176 Applied Process Design for Chemical and Petrochemical Plants
Liquid throw: The horizontal distance traveled by the liq- Ffactor: The vapor kineticenergy parameter, often used
uid after flowing over a weir. as a correlating term for flooding velocity, foam density, etc.
DualJlow: Both liquid and vapor pass through the per- Souder and Brown equation: G/A = K[dv (dL - dv)]1/2,
forations on the tray; there are no downcomers. where G/A = superficial vapor flow, lb/ (hr) (ft2), and d,
Radialflow: Liquid flowing radially from, or to, an inlet and dL = vapor and liquid densities, lb/ft3. See Equation
(or outlet) located at the center of the tray, to (or from) 8-219.
downcomers (or inlets) at the tray periphery.
Reverseflow: Liquid flowing from the inlet on one side of Tower Diameter
the tray (around a center baffle) reverses its direction at
the other side of the tray, and flows back to the downcom- The tower diameter may be calculated for first approxi-
er on the same side of the tray where the inlet is. mation by the Souders-Brown method; however, this has
SpZitflow: Liquid flow across the tray is split into two or been found to be conservative, since it is based on no liq-
more flow paths. uid entrainment between trays. Actually, some entrain-
Double pass: A split-flow tray with two liquid flowpaths on ment can be tolerated at negligible loss in efficiency or
each tray. Each path handles half of the total liquid flow. capacity.
Blowing: A condition where the rising vapor punches There are several approaches to column diameter
holes through the liquid layer on a tray and usually carries design [65, 741 as well as the proprietary techniques of
major industrial and engineering designers. Some of these
large drops and slugs of liquid to the next tray. use the proprietary Fractionation Research Institute meth-
Coning: A condition where the rising vapor pushes the ods which are only available on a membership basis and
liquid back from the top of the hole, and passes upward do not appear in the technical literature.
with poor liquid contact. In general, a better first approximation and often a
Dumping: A condition caused by low vapor rates where more economical tower diameter is determined using Fig-
all of the liquid falls through some holes (rather than over ure 8-121 [33].
the weir) to the tray below, and vapor rises through the e, = 0.22 (5)
remaining holes. (:) 3.2
Raining: A condition similar to dumping (no liquid goes (8 - 250)
over the weir) except that, because of higher vapor rates,
the liquid fall through the holes is more uniform. S' = St - 2.5 h, (8 - 251)
Weeping: A condition occurring when the vapor rate is
not large enough to hold all the liquid on the tray, so that where e, = weight of liquid entrained/unit weight of vapor
part of the liquid flows over the outlet weir while the rest flowing in sieve tray column
falls through the holes. (J = liquid surface tension, dynes/cm
Hooding: A condition that gives rise to a sharp decline in v, = vapor velocity based on column cross-section,
ft/sec
tray efficiency and a sharp increase in pressure drop. S' = effective tray spacing, distance between top of
Flooding is commonly due to either an excessive carryover foam and next plate above, in.
of liquid to the next tray, or to an inability of the system to h, = height of clear liquid in bubbling zone, in.
convey the liquid flow to the tray below.
Oscillation: A wave-type motion of the liquid on the tray, This is based on a frothed mixture density of 0.4 that of
perpendicular to the normal direction of flow. the clear liquid on the tray, and has been found to be a
Seal point: The point at which a weeping condition reasonable average for several mixtures.
changes to raining. Entrainment values of 0.05 lbs liquid/lb vapor are usu-
Injection regime: A condition in which the liquid above ally acceptable, with 0.001 and 0.5 lb/lb being the
the plate is in the form of individual drops dispersed in extremes. The specific design dictates the tolerance on
the vapor; thus, there is virtually no mixing in the main entrainment. From the calculated vapor velocity, v,, the
bulk of the liquid. diameter of the column can be calculated using:
Stable regime: The preferable hydrodynamic condition of
the aerated liquid on a sieve tray. The aerated material
exists as a stable froth; gas-liquid contact is good. (8 - 252)
Turndown ratio: A term used by designers to denote ratio
of minimum-allowable to operating throughput. Entrainment does not usually become a problem until
Segmental downcomer: The channel for liquid flow the tray is operating at 85-100% of the flooding condition.
formed by an enclosed segmental tray section. Figure 8-121 is convenient for solving for %.