Note: Descriptions are shown in the official language in which they were submitted.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
CONVERTING MIST FLOW TO ANNULAR FLOW
IN THERMAL CRACKING APPLICATION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to converting mist flow to annular
flow in a steam cracking application to enhance the flash drum removal
efficiency
of non-volatile hydrocarbons.
Description of Background. and Related Art
Steam cracking has long been used to crack various hydrocarbon
feedstocks into olefins. Conventional steam cracking utilizes a furnace which
has
two main sections: a convection section and a radiant section. The hydrocarbon
feedstock typically enters the convection section of the furnace as a liquid
(except
for light feedstocks which enter as a vapor) wherein it is typically heated
and
vaporized by indirect contact with hot flue gas from the radiant section and
by
direct contact with steam. The vaporized feedstock is then introduced into the
radiant section where the cracking takes place. The resulting olefins leave
the
furnace for further downstream processing, such as quenching.
Conventional steam cracking systems have been effective for
cracking high-quality feedstocks such as gas oil and naphtha. However, steam
cracking economics sometimes favor cracking low cost heavy feedstock such as,
by way of non-limiting examples, crude oil and atmospheric resid. Crude oil
and
atmospheric resid contain high molecular weight, non-volatile components with
boiling points in excess of 1100 F (590 C). The non-volatile, heavy ends of
these
feedstocks lay down as coke in the convection section of conventional
pyrolysis
furnaces. Only very low levels of non-volatiles can be tolerated in the
convection
section downstream of the point where the lighter components have fully
vaporized. Additionally, some naphthas are contaminated with crude oil during
transport. Conventional pyrolysis furnaces do not have the flexibility to
process
CA 02489876 2010-08-25
2
resids, crudes, or many resid or crude contaminated gas oils or naphthas,
which contain a large
fraction of heavy non-volatile hydrocarbons.
To solve such coking problem, U.S. Patent 3,617,493 discloses the use of an
external vaporization drum for the crude oil feed and discloses the use of a
first flash to remove
naphtha as vapor and a second flash to remove vapors with a boiling point
between 450 and
1100 F (230 and 600 C). The vapors are cracked in the pyrolysis furnace into
olefins and the
separated liquids from the two flash tanks are removed, stripped with steam,
and used as fuel.
U.S. Patent 3,718,709 discloses a process to minimize coke deposition. It
provides
preheating of heavy feed inside or outside a pyrolysis furnace to vaporize
about 50% of the heavy
feed with superheated steam and the removal of the residual liquid. The
vaporized hydrocarbons
are subjected to cracking.
U.S. Patent 5,190,634 discloses a process for inhibiting coke formation in a
furnace by preheating the feed in the presence of a small, critical amount of
hydrogen in the
convection section. The presence of hydrogen in the convection section
inhibits the
polymerization reaction of the hydrocarbons thereby inhibiting coke formation.
U.S. Patent 5,580,443 discloses a process wherein the feed is first preheated
and then
withdrawn from a preheater in the convection section of the pyrolysis furnace.
This preheated
feedstock is then mixed with a predetermined amount of steam (the dilution
steam) and is then
introduced into a gas-liquid separator to separate and remove a required
proportion of the
non-volatiles as liquid from the separator. The separated vapor from the gas-
liquid separator
is returned to the pyrolysis furnace for super-heating and cracking.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
3
The present inventors have recognized that in using a flash to
separate heavy non-volatile hydrocarbons from the lighter volatile
hydrocarbons
which can be cracked in the pyrolysis furnace, it is important to maximize the
non-volatile hydrocarbon removal efficiency. Otherwise, heavy, coke-forming
non-volatile hydrocarbons could be entrained in the vapor phase and carried
overhead into the furnace creating coking problems.
It has been found that in the convection section of a steam cracking
pyrolysis furnace, a minimum gas flow is required in the piping to achieve
good
heat transfer and to maintain a film temperature low enough to reduce coking.
Typically, a minimum gas flow velocity of about 100 ft/sec (30 m/sec) has been
found to be desirable.
When using a flash drum to separate the lighter volatile
hydrocarbon as vapor phase from the heavy non-volatile hydrocarbon as liquid
phase, the flash stream entering the flash drum usually comprises a vapor
phase
with liquid (the non-volatile hydrocarbon components) entrained as fine
droplets.
Therefore, the flash stream is two-phase flow. At the flow velocities required
to
maintain the required boundary layer film temperature in the piping inside the
convection section, this two-phase flow is in a "mist flow" regime. In this
mist
flow regime, fine droplets comprising non-volatile heavy hydrocarbons are
entrained in the vapor phase, which is the volatile hydrocarbons and
optionally
steam. The two-phase mist flow presents operational problems in the flash drum
because at these high gas flow velocities the fine droplets comprising non-
volatile
hydrocarbons do not coalesce and, therefore, cannot be efficiently removed as
liquid phase from the flash drum. It was found that, at a gas flow of 100
feet/second (30 m/s) velocity, the flash drum can only remove heavy non-
volatile
hydrocarbons at a low efficiency of about 73%.
The present invention provides a process for the effective removal
of non-volatile hydrocarbon liquid from the volatile hydrocarbon vapor in the
flash drum. The present invention provides a process that converts a "mist
flow"
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
4
regime to an "annular flow" regime and hence significantly enhances the
separation of non-volatile and volatile hydrocarbons in the flash drum.
SUMMARY OF THE INVENTION
The present invention provides a process for treating a heavy
hydrocarbon feedstock which comprises preheating the heavy hydrocarbon
feedstock, optionally comprising steam, in the convection section of a steam
cracking furnace to vaporize a portion of the feedstock and form a mist stream
comprising liquid droplets comprising non-volatile hydrocarbon in volatile
hydrocarbon vapor, optionally with steam, the mist stream upon leaving the
convection section having a first flow velocity and a first flow direction,
treating
the mist stream to coalesce the liquid droplets, the treating comprising first
reducing the flow velocity followed by changing the flow direction, separating
at
least a portion of the liquid droplets from the vapor in a flash drum to form
a
vapor phase and a liquid phase, and feeding the vapor phase to the thermal
cracking furnace.
In one embodiment of the present invention, the vapor phase is fed
to a lower convection section and radiant section of the steam cracking
furnace.
In one embodiment, the treating of the mist flow comprises
reducing the flow velocity of the mist stream. The mist stream flow velocity
can
be reduced by at least 40%. The mist stream velocity can be reduced to less
than
60 feet/second (18 m/s).
According to another embodiment, the mist stream flow velocity is
reduced and then is subjected to at least one centrifugal force, such that the
liquid
droplets coalesce. The mist stream can be subjected to at least one change in
its
flow direction.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
In yet another embodiment in accordance with the present
invention, the mist stream droplets are coalesced in a distance of less than
25 pipe
diameters, preferably in less than 8 inside pipe diameters, and most
preferably in
less than 4 inside pipe diameters.
5
According to another embodiment, the mist stream flows through a
flow path that comprises at least one bend. The flow path can further comprise
at
least one expander. Preferably, the flow path comprises multiple bends. The
bends can be at least 45 degrees, 90 degrees, 180 degrees, or combination
thereof.
In yet another embodiment, the mist stream is converted into an
annular flow stream. The flash efficiency can be increased to at least 85%,
preferably at least 95%, more preferably at least 99%, and most preferably at
least
99.8%. The mist stream can be converted into an annular flow stream in less
than
50 pipe diameters, preferably in less than 25 pipe diameters, more preferably
in
less than 8 pipe diameters, and most preferably in less than 4 pipe diameters.
Also according to the present invention, a process for treating a
hydrocarbon feedstock comprises: preheating a hydrocarbon feedstock,
optionally
including steam, in the convection section of a thermal cracking furnace to
vaporize a portion of the feedstock and form a mist stream comprising liquid
droplets comprising hydrocarbon in hydrocarbon vapor, optionally with steam,
the
mist stream upon leaving the convection section having a first flow velocity
and a
first flow direction, treating the mist stream to coalesce the liquid
droplets,
separating at least a portion of the liquid droplets from the vapor in a flash
drum to
form a vapor phase and a liquid phase, and feeding the vapor phase to the
steam
cracking furnace, wherein the flash comprises introducing the mist stream
containing coalesced liquid droplets into a flash drum, removing the vapor
phase
from at least one upper flash drum outlet and removing the liquid phase from
at
least one lower flash drum outlet.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
6
The present invention also discloses another embodiment in which
the mist stream is tangentially introduced into the flash drum through at
least one
tangential drum inlet.
BRIEF DESCRIPTION OF THE FIGURE
Figure 1 illustrates a schematic flow diagram of a steam cracking
process.
Figure 2 illustrates the design of expanders.
Figure 3 illustrates the design of a flash drum in accordance with
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Unless otherwise stated, all percentages, parts, ratios, etc. are by
weight.
Unless otherwise stated, a reference to a compound or component
includes the compound or component by itself, as well as in combination with
other compounds or components, such as mixtures of compounds.
Further, when an amount, concentration, or other value or
parameter, is given as a list of upper preferable values and lower preferable
values, this is to be understood as specifically disclosing all ranges formed
from
any pair of an upper preferred value and a lower preferred value, regardless
whether ranges are separately disclosed.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
7
Also as used herein:
Flow regimes are visual or qualitative properties of fluid flow.
There is no set velocity and no set drop size. Mist flow refers to a two-phase
flow
where tiny droplets of liquid are dispersed in the vapor phase flowing through
a
pipe. In clear pipe, mist flow looks like fast moving small rain droplets.
Annular flow refers to a two-phase flow where liquid flows as
streams on the inside surface of a pipe and the vapor flows in the core of the
pipe.
The vapor flow velocity of annular flow is about 20 feet/second (6 m/s). In
clear
pipe, a layer of fast moving liquid is observed. Few droplets of liquid are
observed in the core of the vapor flow. At the pipe exit, the liquid usually
drips
out and only a small amount of mist is observed. The change from mist to
annular
flow usually includes a transition period where mist and annular flow exist
together.
The feedstock comprises at least two components: volatile
hydrocarbons and non-volatile hydrocarbons. The mist flow, in accordance with
the present invention, comprises fine droplets of non-volatile hydrocarbons
entrained in volatile hydrocarbon vapor.
The non-volatile removal efficiency is calculated as follows:
Non-volatile Non-volatiles in the vapor phase leaving flash (mass/time)
Removal Efficiency = [1 - ] * 100%
Non-volatiles in the hydrocarbon entering the flash (mass/time)
Hydrocarbon is the sum of vapor (generally volatile) and liquid
(generally non-volatile) hydrocarbon. Non-volatiles are measured as follows:
The boiling point distribution of the hydrocarbon feed is measured by Gas
Chromatograph Distillation (GCD) by ASTM D-6352-98. Non-volatiles are the
fraction of the hydrocarbon with a nominal boiling point above 1100 F (590 C)
as
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
8
measured by ASTM D-6352-98. This invention works very well with non-
volatiles having a nominal boiling point above 1400 F (760 C).
The fraction of non-volatile 1100 to 1400 F (590 to 760 C) in the
whole hydrocarbon to the furnace and a sample of the flash drum overhead after
water is removed are analyzed by ASTM D-6352-98.
A process for cracking a hydrocarbon feedstock 10 of the present
invention as illustrated in Figure 1 comprises preheating a hydrocarbon
feedstock
by a bank of exchanger tubes 2, with or without the presence of water 11 and
steam 12 in the upper convection section 1 of a steam cracking furnace 3 to
vaporize a portion of the feedstock and to form a mist stream 13 comprising
liquid
droplets comprising non-volatile hydrocarbons in volatile hydrocarbon/steam
vapor. The further preheating of the feedstock/water/steam mixture can be
carried
out through a bank of heat exchange tubes 6. The mist stream upon leaving the
convection section 14 has a first flow velocity and a first flow direction.
The
process also comprises treating the mist stream to coalesce the liquid
droplets,
separating at least a portion of the liquid droplets from the hydrocarbon
vapor in a
flash 5 to form a vapor phase 15 and a liquid phase 16, and feeding the vapor
phase 8 to the lower convection section and the radiant section of the thermal
cracking furnace.
As noted, the feedstock is a hydrocarbon. Any hydrocarbon
feedstock having heavy non-volatile heavy ends can advantageously be utilized
in
the process. Such feedstock could comprise, by way of non-limiting examples,
one or more of steam cracked gas oil and residues, gas oils, heating oil, jet
fuel,
diesel, kerosene, gasoline, coker naphtha, steam cracked naphtha,
catalytically
cracked naphtha, hydrocrackate, reformate, raffinate reformate, Fischer-
Tropsch
liquids, Fischer-Tropsch gases, natural gasoline, distillate, virgin naphtha,
crude
oil, atmospheric pipestill bottoms, vacuum pipestill streams including
bottoms,
wide boiling range naphtha to gas oil condensates, heavy non-virgin
hydrocarbon
streams from refineries, vacuum gas oils, heavy gas oil, naphtha contaminated
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
9
with crude, atmospheric resid, heavy residium, C4's/residue admixture, and
naphtha residue admixture.
The heavy hydrocarbon feedstock has a nominal end boiling point
of at least 600 F (310 C). The preferred feedstocks are low sulfur waxy
resids,
atmospheric resids, and naphthas contaminated with crude. The most preferred
is
resid comprising 60-80% components having boiling points below 1100 F
(590 C), for example, low sulfur waxy resids.
As noted, the heavy hydrocarbon feedstock is preheated in the
upper convection section of the furnace 1. The feedstock may optionally be
mixed with steam before preheating or after preheating (e.g., after preheating
in
preheater 2) in a sparger 4. The preheating of the heavy hydrocarbon can take
any
form known by those of ordinary skill in the art. It is preferred that the
heating
comprises indirect contact of the feedstock in the convection section of the
furnace with hot flue gases from the radiant section of the furnace. This can
be
accomplished, by way of non-limiting example, by passing the feedstock through
a bank of heat exchange tubes 2 located within the upper convection section 1
of
the pyrolysis furnace 3. The preheated feedstock 14 before the control system
6
has a temperature between 600 and 950 F (310 and 510 C). Preferably the
temperature of the heated feedstock is about 700 to 920 F (370 to 490 C), more
preferably between 750 and 900 F (400 and 480 C) and most preferably between
810 and 890 F (430 and 475 C).
As a result of preheating, a portion of the feedstock is vaporized
and a mist stream is formed comprising liquid droplets comprising non-volatile
hydrocarbon in volatile hydrocarbon vapor, with or without steam. At flow
velocities of greater than 100 feet/second, the liquid is present as fine
droplets
comprising non-volatile hydrocarbons entrained in the vapor phase. This two-
phase mist flow is extremely difficult to separate into liquid and vapor. It
is
necessary to coalesce the fine mist into large droplets before entering the
flash
drum. However, flow velocities of 100 ft/sec or greater are normally necessary
to
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
practically effect the transfer of heat from the hot flue gases and reduce
coking in
convection section.
In accordance with the present invention, the mist stream is treated
5 to coalesce the liquid droplets. In one embodiment in accordance with the
present
invention, the treating comprises reducing the velocity of the mist stream. It
is
found that reducing the velocity of the mist stream leaving convection section
14
before the flash 5 (location 9 in Figure 1) helps coalesce the mist stream. It
is
preferred to reduce the mist stream velocity by at least 40%, preferably at
least
10 70%, more preferably at least 80%, and most preferably 85%. It is also
preferred
to reduce the velocity of the mist flow stream leaving the convection section
from
at least 100 feet/second (30 m/s) to a velocity of less than 60 feet/second
(18 m/s),
more preferably to less than 30 feet/second (27 to 9 m/s), and most preferably
to
less than 15 feet/second (27 to 5 m/s).
Annular flow can be achieved by reducing flow velocity due to
friction in large diameter pipes. In order to achieve the required reduction
to
convert mist flow into annular flow, a substantial length of piping is
necessary.
The required length of piping is defined in terms of the number of inside pipe
diameters. Engineering practices require that after reducing the mist now
velocity
to 60 feet/second (18 m/s), the friction from 50 to 150 pipe diameters of
straight
pipe (for instance 24 inches x 100 = 200 feet or 0.6 meters x 100 = 60 meters)
is
needed to establish annular flow.
The reduction of velocity of the mist flow stream is accomplished
by including in the piping outside the convection section one or more
expanders.
In a close system, at least one expander is believed necessary to achieve the
preferred reduction of velocity. By way of non-limiting examples, the expander
can be a simple cone shape 101 or manifolds 102 as illustrated in Figure 2.
With
the cross section area of the outlet end greater than the cross section area
of the
sum of all the inlets. In a preferred embodiment in accordance with this
invention,
the mist flow is subject to at least one expander first and then to at least
one bend,
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
11
preferably multiple bends, with various degrees. When the mist flow stream
flows
through the expander(s), the velocity will decrease. The number of expanders
can
vary according to the amount of velocity reduction required. As a general
practice
rule, more expanders can be used if high velocity reduction is required. Any
expanders, for example, a manifold, can be used in the present invention.
Although expanders alone will reduce the velocity such that
annular flow will be established, it is preferred that at least one bend is
used
following the reduction in velocity. The bend acts like a centrifuge. The
liquid
droplets flow to the outer wall of the bend where they can coalesce.
The present invention enables the conversion of mist flow to
annular flow in significantly less piping. According to the present invention,
the
mist stream droplets are coalesced in less than 25, more preferably less than
8, and
most preferably less than 4 inside pipe diameters.
In accordance with the present invention, treating of the mist
stream comprises subjecting the mist stream to at least one expander and one
centrifugal force downstream of the expander such that the liquid droplets
will
coalesce. This can be accomplished by subjecting the mist stream to at least
one
change in its flow direction. The piping outside the convection section is
designed
to include at least one bend in order to convert a mist flow stream into an
annular
flow stream. The bends can be located throughout the piping downstream of the
expander between the control system 17 and just before the flash drum.
Different angle bends can be used. For example, 45 degree, 90
degree, and/or 180 degree bends can be used in the present invention. After an
expander, the 180 degree bend provides the most vapor core velocity reduction.
In one embodiment of the present invention, the process includes at least one
bend
of at least 45 degrees. In another embodiment, the process includes at least
one
bend of 90 degrees. In yet another embodiment, the process includes at least
one
bend of 180 degrees.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
12
It is found that using the inventions disclosed herein, a flash drum
removal efficiency of at least 85% can be accomplished. A preferred flash
efficiency of at least 95%, a more preferred flash efficiency of at least 99%,
and a
most preferred flash efficiency of at least 99.8% can also be achieved using
the
present invention.
After the required reduction of velocity, e.g., in a combination of
expanders, the fine droplets in the mist flow stream will coalesce in one or
more
bends and thus are easily separated from the vapor phase stream in the flash
drum
5. Flash is normally carried out in at least one flash drum. In the flash drum
5,
the vapor phase stream is removed from at least one upper flash drum outlet
and
the liquid phase is removed from at least one lower flash drum outlet.
Preferably,
two or more lower flash drum outlets are present in the flash for liquid phase
removal.
Also according to the present invention, a process for treating a
hydrocarbon feedstock comprises: heating a liquid hydrocarbon feedstock in the
convection section of a thermal cracking furnace to vaporize a portion of the
feedstock and form a mist stream comprising liquid droplets comprising
hydrocarbon in hydrocarbon vapor, with or without steam, the mist stream upon
leaving the convection section having a first flow velocity and a first flow
direction, treating the mist stream to coalesce the liquid droplets,
separating at
least a portion of the liquid droplets from the hydrocarbon vapor in a flash
drum to
form a vapor phase and a liquid phase, and feeding the vapor phase to the
radiant
section of the steam cracking furnace, wherein the flash comprises introducing
the
stream containing coalesced liquid droplets into a flash drum, removing the
vapor
phase from at least one upper flash drum outlet and removing the liquid phase
from at least one lower flash drum outlet.
A flash drum in accordance to the present invention is illustrated in
Figure 3. The removal efficiency of the flash drum decreases as liquid droplet
size entering the flash drum decreases. The droplet size decreases with
increasing
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
13
gas velocity. To increase separation efficiency, a sufficient length of pipe,
expanders, and bends are required to establish a stable droplet larger size at
a
lower velocity.
To further increase the removal efficiency of the non-volatile
hydrocarbons in the flash drum, it is preferred that the flash stream 9 of
Figure 1
enters the flash drum tangentially through at least one tangential flash drum
inlet
201 of Figure 3. Preferably, the tangential inlets are level or slightly
downward
flow. The non-volatile hydrocarbon liquid phase will form an outer annular
flow
along the inside flash drum wall and the volatile vapor phase will initially
form an
inner core and then flow upwardly in the flash drum. In one preferred
embodiment, the tangential entries should be the same direction as the
Coriolis
effect.
The liquid phase is removed from one bottom flash drum outlet.
Optionally, a side flash drum outlet (203) or a vortex breaker can be added to
prevent a vortex forming in the outlet. The upward inner core flow of vapor
phase
is diverted around an annular baffle 202 inside the flash drum and removed
from
at least one upper flash drum outlet 204. The baffle is installed inside the
flash
drum to further avoid and reduce any portion of the separated liquid phase,
flowing downwards in the flash drum, from being entrained in the upflow vapor
phase in the flash drum. The vapor phase, preferably, flows to the lower
convection section 7 of Figure 1 and through crossover pipes 8 to the radiant
section of the pyrolysis furnace.
The invention is illustrated by the following Example, which is
provided for the purpose of representation, and is not to be construed as
limiting
the scope of the invention. Unless stated otherwise, all percentages, parts,
etc., are
by weight.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
14
Example 1
The vapor/liquid separation efficiency of a flash drum separation is
highly dependent on droplet size. Stoke's law teaches that the terminal
velocity of
a drop or a particle is proportional to its diameter squared. Hence, if a very
fine
mist enters a flash drum, the upward gas velocity will be greater than the
terminal
velocity of the droplets causing entrainment. Extensive coalescing of droplets
into
annular flow produces very large droplets which separate easily in a flash
drum.
Annular flow can be effected by reducing the bulk flow velocity
and allowing sufficient time and friction for coalescing of droplets. After
the bulk
velocity is reduced, roughly 100 pipe flow diameters are required to coalesce
drops. Air/water flow tests were conducted to determine how to produce annular
flow in less than 100 pipe diameters. Two 6 HP blowers produced a high
velocity
gas in 2" ID pipe. The air from the two blowers combine in a Y-fitting and
flow
into the 2" ID clear pipe. Just before the clear pipe is a T-fitting where
water is
added to produce the mist flow. An anemometer at the end of the piping system
measures the fluid velocity.
Various piping bends, for example 45 degrees, elbows, and return
bends, and expanders were tested to observe whether the fine droplet in the
mist
flow stream coalesced. They are summarized below in Table 1.
CA 02489876 2004-12-17
WO 2004/005431 PCT/US2003/020375
TABLE 1
Observation of Droplet Coalescing
Test Description Observation
1 Added 6 GPM of water to the air producing two Fine droplet mist flow in
phase flow at 110 ft/sec bulk velocity 2" ID pipe
2 Added a 90 bend to provide a centrifugal force Mist flow is intensified
3 To the end of the straight 2" ID pipe added an Mist flow throughout the
expander and 6 ft of 3" clear pipe 6 ft or 25 IDs of 3" clear
pipe
4 Added 12 ft more of 3" clear pipe to test 3 for a Some droplet coalescing
total of 18 ft or 75 diameters but mist still exists
5 To the end of the straight 2" ID pipe added an Significant coalescing of
expander to 3" ID, a 90 elbow and 6 ft. of 3" droplet drops - annular
clear pipe - velocity 50 ft/sec flow with some mist.
6 To the end of the 2" ID pipe added an expander to Annular and stratified
6" ID, 90 elbow, 4 ft of 6" ID pipe, 90 elbow flow with less than a
and 4 ft of 6" ID pipe trace of mist
The conclusions of the observations are as follows: Test 2 showed
5 that a bend alone at high velocity does not coalesce droplets and may even
produce a finer mist. Tests 3 and 4 showed that an expander alone did not
coalesce droplets enough even after 75 pipe diameters of the larger diameter
pipe.
Tests 5 and 6 showed that expanders followed by bends with short lengths of
straight pipe did coalesce droplets. The larger the expanders followed by
bends,
10 the more complete the droplet coalescing into annular and even stratified
flow.
