U.S. patent number 3,910,347 [Application Number 05/072,765] was granted by the patent office on 1975-10-07 for cooling apparatus and process.
This patent grant is currently assigned to Stone & Webster Engineering Corporation. Invention is credited to Herman N. Woebcke.
United States Patent |
3,910,347 |
Woebcke |
October 7, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Cooling apparatus and process
Abstract
An apparatus and process for effecting heat exchange between hot
effluent and a coolant. The heat exchange apparatus is
substantially tubular in shape and is provided with a divergent
inlet section having an angle of divergence less than 10.degree.,
and preferably 4.degree. to 7.degree..
Inventors: |
Woebcke; Herman N. (Wayland,
MA) |
Assignee: |
Stone & Webster Engineering
Corporation (Boston, MA)
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Family
ID: |
27535938 |
Appl.
No.: |
05/072,765 |
Filed: |
September 16, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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802790 |
Feb 27, 1969 |
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877575 |
Nov 26, 1969 |
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802790 |
Feb 27, 1969 |
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729878 |
May 10, 1968 |
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557005 |
Jun 13, 1966 |
3403722 |
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Current U.S.
Class: |
165/142; 165/147;
165/169; 422/201 |
Current CPC
Class: |
C10G
9/20 (20130101); F28D 7/12 (20130101); F28F
9/00 (20130101); F28D 7/0008 (20130101); B01D
51/10 (20130101); F28D 7/005 (20130101); F28D
7/103 (20130101); C10G 2400/20 (20130101); F28D
2021/0075 (20130101) |
Current International
Class: |
B01D
51/00 (20060101); B01D 51/10 (20060101); F28F
9/00 (20060101); F28D 7/10 (20060101); F28D
7/12 (20060101); C10G 9/00 (20060101); C10G
9/20 (20060101); F28D 7/00 (20060101); F28d
007/12 (); F28f 013/08 () |
Field of
Search: |
;165/142,1,157,158,141,155,135,169,146,147,40,159,143,7
;23/284,292,288.9 |
References Cited
[Referenced By]
U.S. Patent Documents
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779741 |
January 1905 |
Scheubner |
1884583 |
October 1932 |
Lucke et al. |
1884778 |
August 1965 |
Hood, Jr. et al. |
2904400 |
September 1959 |
Asendorf et al. |
|
Foreign Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Streule, Jr.; Theophie W.
Parent Case Text
CROSS REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part of applications Ser. No.
802,790 filed Feb. 27, 1969 and Ser. No. 877,575 filed Nov. 26,
1969 as a divisional application of Ser. No. 802,790, now
abandoned. Application Ser. No. 802,790 is a continuation-in-part
of application Ser. No. 729,878 filed May 10, 1968 now abandoned
which is a divisional application of application Ser. No. 557,005
filed June 13, 1966 now U.S. Pat. No. 3,403,722 granted Oct. 1,
1968. Additional applicants and patents which are relevant to the
subject matter of the present invention and which have a common
assignee therewith are: HEATING APPARATUS AND PROCESS, U.S. Pat.
No. 3,407,789 filed June 13, 1966 granted Oct. 29, 1968 COOLING
APPARATUS AND PROCESS, U.S. PAT. No. 3,403,722 filed June 13, 1966
granted Oct. 1, 1968; and COOLING APPARATUS AND PROCESS U.S. Pat.
No. 3,583,476 filed Feb. 27, 1969 granted June 8, 1971.
Claims
I claim:
1. A heat exchange apparatus comprising:
a divergently shaped inlet section for the flow of hot fluid
therethrough configured with a total divergence angle between
4.degree. and 7.degree.;
a downstream section for the flow of hot gases passing from the
inlet section which downstream section extends from the downstream
end of the inlet section and has a constant cross-sectional area
equal to the cross-sectional area of the downstream end of the
divergently shaped inlet section;
means for cooling the hot fluid flowing through the heat exchanger
apparatus;
whereby the flow of the hot gases is substantially turbulence-free
during the passage thereof through the heat exchange apparatus.
2. The apparatus of claim 1 wherein the total angle of divergence
of the inlet section is 5.degree..
3. The apparatus of claim 1 wherein the passage for the flow of hot
fluid is a centrally disposed tubular structure and the means for
cooling the hot fluid flowing therethrough is a cooling chamber
arranged therearound.
4. The apparatus of claim 1 wherein the passage for the flow of hot
fluid is a centrally disposed tubular structure and the means for
cooling the hot fluid flowing therethrough is comprised of an
annular array of tubes arranged in direct contact with the outer
surface of the centrally disposed chamber.
5. The apparatus of claim 4 further comprising cooling manifolds at
each end of the heat exchanger and wherein the annular array of
tubes arranged in direct contact with the surface of the centrally
disposed chamber communicate with the manifolds.
6. The apparatus as in claim 5 where the cooling manifolds arranged
to communicate with the annular array of tubes are toroidal in
configuration.
7. The apparatus as in claim 3 wherein the cooling chamber has a
coolant inlet located in proximity to the inlet of the centrally
disposed chamber for hot fluid and an outlet located in proximity
to the outlet of the centrally disposed chamber for hot fluid.
8. The apparatus of claim 7 wherein the cooling chamber surrounds
the entire centrally disposed chamber for hot fluid.
9. The apparatus of claim 1 wherein the passage for the flow of hot
fluid is annular.
10. The apparatus of claim 9 wherein the increase in
cross-sectional area of the divergent inlet section is equivalent
to the increase in cross-sectional area per unit length of a
conical pipe having an angle of divergence of 5.degree..
11. The apparatus of claim 9 wherein the means for cooling the hot
fluid flowing through the annular passage is a cooling passage
arranged concentrically with and interiorly of the inner wall of
the annular passage.
12. The apparatus of claim 11 wherein the cooling passage arranged
concentrically with and interiorly of the inner wall of the annular
passage is comprised of a tubular central cooling chamber arranged
axially in the heat exchanger, which central cooling chamber has an
inlet at one end and an outlet at the opposite end; an annular
cooling chamber defined by the outer wall of the tubular central
chamber and the inner wall of the annular hot fluid passage; and
communication means between the tubular central chamber and the
annular cooling chamber.
13. The apparatus of claim 12 wherein the diverging inlet for the
annular hot fluid passage is defined by a cone extending from the
end of the inner wall of the annular hot fluid passage near the hot
fluid inlet and a converging wall surrounding the cone, which
converging wall extends from the outer wall of the annular hot
fluid passage to the hot fluid inlet.
14. The apparatus of claim 13 wherein the cone has an angle of
25.degree. to 30.degree. and the converging wall extending from the
outer wall of the annular hot fluid passage surrounding the cone
has an angle of 20.degree. to 25.degree..
15. The apparatus of claim 9 wherein the cone has an angle of
25.degree. to 30.degree. and the converging wall extending from the
outer wall of the annular hot fluid passage surrounding the cone
has an angle of 20.degree. to 25.degree..
16. The apparatus of claim 14 further comprising cooling means
arranged around the outer wall of the annular hot fluid
passage.
17. The apparatus of claim 16 wherein the cooling means arranged
around the outer wall of the annular hot fluid passage is a cooling
chamber.
18. The apparatus of claim 17 further comprising cooling fins
extending from the outer wall of the annular hot fluid passage into
the outer cooling chamber.
Description
The present invention relates generally to an apparatus and process
for cooling a fluid and, in particular, to an apparatus and process
for rapidly cooling a fluid. The apparatus and process of the
present invention are especially suitable for rapidly cooling
furnace effluent issuing from a hydrocarbon cracking furnace.
The present invention comprises an apparatus and process which is
used to rapidly cool hot fluids. The apparatus comprises a means
whereby a hot fluid is contacted on cooling surfaces to provide
rapid decrease in the temperature of the hot fluid. The cooling
means is suitable for cooling fluids at elevated pressures. The
apparatus of the present invention can be used to rapidly cool hot
gases without substantial pressure change.
The cooling means has particular and advantageous application when
used in conjunction with a process for the production of olefins by
cracking hydrocarbon feeds at high temperature and short residence
time, using a high radiant heat furnace having relatively short
conduits of small diameter. The cooling means is used to provide
rapid reduction in the effluent product gas temperature from the
furnace without substantial pressure drop.
Cracking furnace effluent gas temperatures are very high, and at
these high temperatures the cracking reactions proceed at a rapid
rate. In order to substantially stop the reactions in the effluent
gas and to minimize the production of undesirable by-products, it
is necessary to rapidly cool the effluent gas after it leaves the
reactor to a temperature at which the reactions substantially
cease. There are several means available for doing this, most of
which have one or more drawbacks. Conventional means of cooling,
e.g., a shell and tube heat exchanger, result in substantial
pressure loss of the effluent gas. This type of heat exchanger
employs multiple tubes and is fitted with an inlet head. The
residence time of the hot gases in this head alone at the
temperatures employed is significant and results in product
degradation and the formation of coke precursors and coke, either
of which can accumulate in the heat exchanger.
In cooling high temperature hydrocarbon gas effluents from a
hydrocarbon cracking process used to produce olefins, the
temperature of the cooling means be sufficiently low to cool the
gases the desired amount and sufficiently high to prevent
condensation of high boiling hydrocarbon by-products on the cooling
surfaces.
Cooling techniques and apparatus of the present invention are
particularly useful in cooling the effluent gases from a process
for the thermal cracking of hydrocarbons. In the thermal cracking
of hydrocarbons, in the process described hereinafter, the
hydrocarbon feed can be heated to high temperature, maintained at
high temperature for a short residence time and selectively
converted to desired products. In accordance with the present
invention, the hot gas reaction products are rapidly quenched or
cooled in such a manner that the conversion is substantially
stopped after the desired residence time.
The quenching apparatus and process of cooling of the present
invention is particularly suitable for use in cooling the hot gas
effluent issuing from a pyrolysis furnace. However, the concept
used can be readily applied to other processes for cooling hot
product streams, for heat recovery and/or for heating fluids. The
cooling means and process can be used for rapidly cooling hot
gaseous products from other cracking processes. The quenching
apparatus provides indirect cooling on surfaces. The apparatus is
simple in design and easy to operate. The apparatus can be of any
size and is normally designed for a specified service. The
apparatus can be horizontally or vertically disposed. The cooling
unit rapidly cools hot fluilds while not substantially changing the
pressure of the fluid. That is, the pressure of the cooled fluid at
the outlet of the cooling unit is substantially the same as the
inlet pressure. The material to be cooled can be upflow or
downflow. The operation of the unit can be such that the coolant
circulation rate can be self-regulating and within limits adjust
itself to the heat load. Alternatively, the coolant circulation
rate can be controlled by suitable auxiliary pumping means.
SUMMARY OF THE INVENTION
Basically, the heat exchanger of the present invention is comprised
of a passage for the flow of hot fluid therethrough and at least
one coolant passage. The hot fluid passage and the coolant passage
or passages are arranged with common walls through which indirect
heat exchange occurs. The inlet of the hot fluid passage is
configured in the form of a diverging nozzle having an angle of
divergence of from 4.degree. to 10.degree., and preferably
4.degree. to 7.degree..
A variation of the basic heat exchanger design consists essentially
of three concentric pipes,, pipes, walls of which form two annular
chambers and one central chamber. The cooling fluid can be fed into
the top of the unit and flow into the central chamber. The central
chamber at the end opposite from the inlet thereof is in
communication with the first annular chamber. The cooling fluid can
flow downwardly in the central chamber and upwardly in the first
annular chamber and exit through an opening at or near the top of
the first annular chamber. The outer wall of the second concentric
pipe forms a cooling surface. The hot gaseous material to be cooled
can enter at the bottom of the cooling device through an opening in
the third concentric pipe and pass upwardly through the second
annular chamber and be cooled by direct contact with the cooling
surface. The cooled material can pass out of the cooling device
through an outlet located near the top of the second annular
chamber.
The invention will be better understood and made more apparent when
considered in conjunction with the accompanying drawings
wherein:
FIG. 1 is a schematic flow diagram of an overall thermal cracking
system with the gas cooling apparatus of the present invention
embodied therein;
FIG. 2 is a cross-sectional elevational view of an embodiment of
the cooling or quench apparatus;
FIG. 3 is a cross-sectional view of the cooling apparatus of FIG. 2
taken through line 3--3 showing a cross section of the concentric
pipes and cooling tubes;
FIG. 4 is a cross-sectional elevational view of another embodiment
of the cooling or quench apparatus of the present invention;
FIG. 5 is a cross-sectional view of the cooling apparatus of FIG. 4
taken through line 5--5 showing the concentric pipes and cooling
fins;
FIG. 6 is a cross-sectional elevational view of another embodiment
of the cooling or quench apparatus of the present invention;
FIG. 7 is a cross-sectional view of the cooling apparatus of FIG. 6
taken through line 7--7;
FIG. 8 is a cross-sectional elevational view of another embodiment
of the cooling or quench apparatus of the present invention;
FIG. 9 is a cross-sectional view of the cooling apparatus of FIG. 8
taken through line 9--9;
The heat exchanger of the present invention will be described as
part of a system for thermally cracking hydrocarbons to produce
olefins. Basically, the heat exchanger of the present invention is
an indirect heat exchanger having a passage for the flow effluent
therethrough and at least one coolant chamber with a common wall
therebetween.
The cooling apparatus can use any desired cooling fluid. The
cooling fluid can be a liquid that, on heating, partially or
completely vaporizes. The preferred cooling fluids are liquids.
Suitable liquids are Dowtherm, water, etc.
The preferred cooling liquid is water. In the present embodiment,
the cooling apparatus is used to produce high temperature, high
pressure steam. The heat energy recovered in cooling can be used
for power generation or heating service.
A typical reactor furnace and cooling unit will be described with
reference to FIG. 1 of the drawings. A petroleum naphtha fraction
boiling in the range of 90.degree. to 375.degree. F. is fed through
line 1 into convection preheat section 7 wherein it is heated from
about ambient temperature to a temperature of about 1000.degree. to
1100.degree. F. Steam, at a ratio of steam to hydrocarbon of about
0.4 to 0.8 by weight, is introduced into preheat section 7 through
lines 8 and/or 9 at a point where the naphtha feed is approximately
80% vaporized. The preheated hydrocarbon and steam and steam
mixture at about 1000.degree. to 1100.degree. F. is then fed to
manifold 2 and subsequently into the inlets of coils 3-6. The feed
is heated in the coils from about 1000.degree. to 1100.degree. F.
to a coil outlet temperature of about 1650.degree. F. Under the
recited conditions the hydrocarbon partial pressure at the coil
outlet is about 12 to 14 PSIA. The residence time of the fluid in
the radiant section of the furnace is about 0.20 to 0.25 seconds.
The mass velocity of the hydrocarbon and steam in the coils is
about 18 to 26 pounds per second, per square foot of
cross-sectional area of the coil. The radiant coil inlet pressure
is about 45 PSIA and the coil outlet pressure of the effluent gases
is about 25 PSIA. The hot effluent gases are fed from the outlet
manifold 11 through line 12 to the cooling apparatus 14 at a gas
velocity of about 800 ft./sec. The hot gases are introduced into
the cooler through inlet 13 at a temperature of about 1650.degree.
F. The cooled gases are withdrawn from the cooler through outlet 15
which is in communication with line 16. The gases are cooled
rapidly in about 10-20 milliseconds to a temperature of about
1200.degree. to 1400.degree. F. and may be conveyed to a
conventional cooling means for further cooling and to a
conventional olefin separation plant for separation and recovery of
ethylene. The gas pressure in line 16 is about 25 PSIA.
Basically, the heat exchanger 14 of the present invention can be
adapted to rapidly cool the furnace effluent by 100.degree. to
600.degree. F.; that is, from about 1500.degree. to 1650.degree. F.
down to about 1000.degree. to 1400.degree. F. The cooling step is
carried out very rapidly after the effluent leaves the radiant
section of the furnace in about 1 to 30 milliseconds, preferably in
about 5 to 20 milliseconds. The rapid cooling step is critical in
the high temperature, short residence time process for cracking
hydrocarbons to produce olefins. It is found that if the cooling
step takes substantially more than about 30 milliseconds, there may
be substantial coke deposits in interior passages of the cooling
unit and downstream equipment.
When high temperature and short residence time are used to crack
hydrocarbon to form olefins, it is necessary to rapidly cool the
furnace effluent sufficiently below the reaction temperature to
substantially stop the reaction. If this is not done, the reaction
continues after the effluent has left the reaction zone and can
result in degradation of product, reduction of ethylene yield, and
increased production of polynuclear aromatics and/or compounds of
low volatility. Such products tend to cause deposition of coke on
the walls of the downstream equipment. At 1600.degree. F. reaction
rates are so high that the residence time in a quench zone at times
as short as 50 milliseconds results in a significant amount of
reaction taking place. It is, therefore, important to quench the
effluent very soon after it leaves the furnace to a temperature at
which substantially no deleterious reaction takes places, e.g.
below 1100.degree. to 1400.degree. F.
FIG. 1 of the drawing illustrates the thermosiphon cooling
embodiment of the present invention. Coolant water from steam drum
17 is introduced through line 18 at a temperature of about
600.degree. F. and a pressure of about 1600 PSIA. The coolant flows
through line 18 into a torus 19 and upwardly in tubes 20, in which
tubes the water is partially converted to steam. The steam and
water mixture flows into torus 21 and through line 22 back to steam
drum 17. The water being more dense than the mixture of steam and
water sets up a thermosiphon flow of coolant water through the
cooling apparatus. Within design limits the cooling apparatus is
self-regulating and the higher the temperature and flow rate of
gases into the cooling unit the faster will be the coolant liquid
circulation rate.
Saturated steam at a temperature of about 600.degree. F. and a
pressure of about 1600 PSIA can be withdrawn from steam drum 17
through line 23 and the heat energy recovered. Boiler feed water is
fed to steam drum 17 through line 24.
The heat exchanger of the present invention can be used in other
known processes but it is particularly suitable for service in a
hydrocarbon cracking system. However, it will be obvious that the
cooling apparatus has many uses for cooling process streams, heat
exchange, and other uses that will appear to those skilled in the
art.
The heat exchange apparatus of the present invention comprises a
means whereby the hot furnace effluent is cooled in a heat
exchanger passage. If the heat exchanger passage is annular, either
or both of the surfaces comprising the annular passage can be a
heat transfer surface. This cooling apparatus is particularly
adapted to rapid quench of hot gas with a small decrease or
substantially no change in the pressure of the fluid being cooled
while generating high pressure steam economically.
One basic embodiment of the present invention is depicted in FIGS.
2 and 3. Basically, the heat exchanger 14 is an indirect heat
exchange apparatus which cools furnace effluent or similar hot
fluid and generates high pressure steam. Also, the inlet end of the
heat exchanger is designed to gradually lower the velocity of the
furnace effluent steam so that the velocity head or kinetic energy
is converted to static pressure. The pressure recovery realized can
partially or entirely offset the friction pressure drop through the
device depending upon the specific dimensions of the apparatus and
the conditions under which it is operated. Rapid cooling of the gas
if effected by passing the gas through a tubular passage which is
cooled.
The heat exchanger 14 is comprised of a centrally disposed pipe 25
that extends about the length of the apparatus and terminates in an
outlet 26. The inner wall 27 of the pipe 25 defines the passage or
chamber 28 through which the effluent passes to be quenched. At the
top of the pipe 25 there is provided connecting means 29 to connect
the heat exchanger 14 to the transfer line pipe.
The wall of pipe 25 can be provided with a multiplicity of equally
spaced tubes 20 which tubes are connected to and are in close
contact with the outer wall 31 of the pipe 25. These tubes run the
approximate length of the wall and, at the upper and lower ends,
flare outwardly by curved portions 32 and 33 respectively, and are
in communication with torus 21 at their upper end and torus 19 at
their lower end. Torus 19 has a connecting conduit 36 through which
coolant fluid passes through inlet 37 into the torus 19 and flows
upwardly through tubes 20. Tubes 20 are in communication with upper
torus 21 and the cooling fluid flows out of torus 21 through outlet
38 and conduit 39.
Pipe 25 at a position proximate to the end at which effluent enters
the quench apparatus tapers inwardly to form inlet opening 40. The
cross-sectional area of inlet 40 is such that the passage 28
gradually increases in cross-sectional area from inlet 40 to the
quench chamber to form an inlet diffuser section 41.
The cooling apparatus can be disigned and sized to accommodate any
desired cooling service. Suitable apparatus for use in the present
invention can have an overall length of the cooling apparatus from
gas outlet 26 to hot gas inlet 40 of 10 to 50 feet. The inside
diameter of the pipe 25 can be 2.5 to 5 inches. Tubes 20 can be
about 1 to 2 inches in inside diameter. The inside diameter of tori
19 and 21 can be about 3 to 6 inches. The cross-sectional area of
gas inlet 40 can be about 3 to 14 square inches, gradually
increasing in cross-sectional area to about 4 to 20 square inches
in the straight portion of pipe 25. The total coolant flow through
tubes 20 can be about 10 times the flow of hot effluent gases based
on weight.
Hot gases at a velocity of 700 to 800 ft./sec. enter the cooling
apparatus through inlet 40 and pass into chamber 28 where they are
slowed to about 400 to 500 ft./sec. and pass out of the apparatus
at the end of the chamber through outlet 26. Coolant water enters
the bottom torus 19 through inlet 37 and flows upwardly in tubes 20
providing indirect contact cooling for the hot furnace effluent
gases at the inner wall surface 27 of pipe 25. The inner surface 27
of pipe 25 provides the cooling surface for the hot gas.
The mixture of steam and water moves upwardly in tubes 20 into
torus 21 and through outlet 38.
The inlet diffuser section 41 provides for gradual increase in
cross-sectional area of the gases entering through inlet 40 which
gradually increases the pressure of the hot gases as the gas
velocity is reduced. The diffuser section 41 insures uniform gas
distribution over the cooling surface 27 without the production of
large eddy currents in the gas flow. In accordance with the present
invention, the pressure increase in the gas caused by the gradual
increase in cross-sectional area in the inlet compensates for a
substantial portion of the pressure loss in the gas due to
friction. The cooled outlet gas pressure will be about the same as
the hot inlet gas pressure. Passage 28 is sized to provide the
gradual increase in cross-sectional area through which the hot
gases flow. The gradual increase is provided by the tapered shape
of the wall of diffuser section 41.
The gradual increase in cross-sectional area provides a gradual
decrease is gas velocity which is accompanied by an increase in gas
pressure to conserve total energy.
The total angle of divergence of the entering pipe of the diffuser
section 41 is in the range of 4.degree. to 10.degree., preferably
4.degree. to 7.degree., e.g. 5.degree..
FIG. 3 shows a cross section of the cooling apparatus taken through
line 3--3 of FIG. 2. FIG. 3 shows an end section of tubes 20 and
the manner in which they are connected by welds 42 to the outer
wall of pipe 25. A suitable heat transfer material 43 can be used
to fill the space between tubes 20 in order to improve the heat
transfer between the hot gases and coolant.
Another embodiment of the cooling apparatus is illustrated by FIGS.
4 and 5 of the drawings. In this embodiment cooling of the hot
gases is provided by direct contact with the outer wall of the
concentric pipe 25. In order to improve the heat transfer between
pipe 25 and the cooling fluid, pipe 25 can possess a multiplicity
of cooling fins 44 which project into the coolant passage 45.
The diffuser section 41 immediately adjacent the cooling chamber
inlet 40 is again formed of an entering pipe section which makes a
total divergence angle of between 4.degree. and 10.degree.,
preferably 4.degree. to 7.degree..
The coolant chamber 45, however, completely surrounds the inner
quenching chamber 28 thereby providing direct exposure of the tube
25 with the fluid passing through the cooling chamber or jacket 45.
Coolant enters inlet 46 which is near the hot effluent inlet 40,
passes through chamber 45 and discharges through outlet 47 thereby
providing cooling of the chamber 28 from the inlet 40 to the
discharge opening 26.
Another embodiment of the cooling apparatus is depicted in FIGS. 6
and 7 of the drawings. Referring to FIG. 6 of the drawings, the
cooling device can comprise three concentric cylinders or pipes
which are vertically disposed, the outer cylinder of which is
provided with a multiplicity of equally spaced tubes. The hot
effluent gases are introduced into the coolant apparatus and
rapidly cooled by indirect heat exchange by contact with two
cooling surfaces.
The central concentric pipe 132 has an inlet 173 at its upper end
and depends downwardly to form the central passage 131. The second
concentric pipe 134 at its upper end just short of inlet 173 curves
inwardly and abuts and terminates at the wall of central pipe 132.
The outer wall of pipe 132 and the inner wall of pipe 134 form
annular space 133. Spacers 148 maintains pipe 132 equidistant from
the inner wall of pipe 134. Pipe 134 at its lower end forms a
rounded chamber terminating in rounded end member 137. The third
concentric pipe 136 extends about the length of the apparatus and
terminates short of the top of pipe 134. Above the point at which
pipe 136 terminates, conduit 174 is in communication with annular
space 133 through outlet opening 175. The inner wall of pipe 136
and the outer wall of pipe 134 form the second annular chamber 135.
Near the top of annular passage 135 there is provided baffle ring
146 which prevents stagnant product gases from accumulating in the
upper end of the annular chamber. Also near the top of annular
chamber 135 there is provided connecting means 144 which is in
communication with annular passage 135 through outlet opening 145.
Baffle ring 146 and spacers 147 maintain concentric pipe 134 in the
center of annular chamber 135.
An important feature of the cooling apparatus is the nose cone 138.
The nose cone 138 is arranged axially with the pipe 134, the base
of the nose cone 138 being attached to the rounded end member 137
and the apex extending in the direction of the inlet opening 143.
The concentric pipe 136 at a position proximate to the end of the
straight portion of concentric pipe 134 tapers inwardly in the
general direction of the nose cone 138 to form inlet opening 143.
The cross-sectional area of inlet 143 is such that the annular
passage 140 gradually increases in cross-sectional area from inlet
143 to the annular space formed by the walls of pipes 134 and
136.
The outer wall of concentric pipe 136 can be provided with a
multiplicity of equally spaced tubes 161 defining passages 167,
which tubes are connected to and are in close contact with outer
wall 136. These tubes run the approximate length of outer wall 136
from about the bottommost portion of wall 136 up to conduit 144.
Tubes 161 at the upper and lower ends flare outwardly by curved
portions 160 and 162, respectively and are in communication with
torus 150 at their upper end and torus 149 at their lower end.
Torus 149 has a connecting conduit 164 through which coolant fluid
passes through inlet 163 into the torus 149 and flows upwardly
through tubes 161. Tubes 161 are in communication with upper torus
150 and the cooling fluid flows out of torus 150 through outlet 166
and conduit 165.
The cooling apparatus can be designed and sized to accommodate any
desired cooling service. Suitable apparatus for use in the present
invention can have an overall length of the cooling apparatus from
coolant inlet 173 to hot effluent gas inlet 143 of 20 to 24 feet.
The inside diameter of the third concentric pipe 136 can be 8 to 10
inches. Tubes 161 can be about one to two inches in inside
diameter. The inside diameter of tori 149 and 150 can be about 3 to
4 inches. The cross-sectional area of central chamber formed by
pipe 132 can be 7 square inches. The length of the central chamber
can be 18 to 20 feet. The cross-sectional area of the first annular
chamber 33 can be about 12 square inches and can have a length of
about 18 to 20 feet. The cross-sectional area of the second annular
chamber 135 can be about 20 square inches and the chamber can have
a length of about 16-18 feet, excluding the inlet section. The
cross-sectional area of gas inlet 143 can be about 12 to 13 square
inches, gradually increasing in cross-sectional area to about 19 to
20 square inches in the straight portion of pipe 134. Tapered nose
cone 138 can have an angle at its apex of about 28.degree. to
30.degree.. The total cross-sectional area of tubes 161 can be
about 10-11 square inches. The total coolant flow through tubes 161
and first annular passage 133 can be about 10 times the flow of hot
effluent gases based on weight.
Hot gases at a velocity of 700 to 800 ft./sec. enter the cooling
apparatus through inlet 143 and pass into second annular chamber
135 where they are slowed to about 400 to 500 ft./sec. and pass out
of the apparatus at the end of the chamber through outlet 145. The
coolant water is introduced through inlet 173 and flows downwardly
in the central chamber 131 of concentric pipe 132 and a mixture of
water and steam flows upwardly in first annular passage 133 and
passes out near the top of the first annular passage through outlet
opening 175. Coolant water enters the bottom torus 149 through
inlet 163 and flows upwardly in tubes 161 providing indirect
cooling for the hot furnace effluent gases at the inner wall
surface of pipe 136. The inner surface of pipe 136 and the outer
surface of pipe 134 provide the two cooling surfaces for the hot
gas.
The mixture of steam and water move upwardly in tubes 161 into
torus 150 and through outlet 166.
The inlet diffuser 140 formed by wall 139 and nose cone 138
provides for gradual increase in cross-sectional area of the gases
entering through inlet 143 which gradually increases the pressure
of the hot gases as the gas velocity is reduced. The diffuser 140
ensures uniform gas distribution between cooling surfaces 136 and
134 without the production of large eddy currents in the gas flow
which would reduce the extent of pressure increase. In accordance
with the present invention, the pressure increase in the gas caused
by the gradual increase in cross-sectional area in the inlet
compensates for a substantial portion of the pressure loss in the
gas due to friction. The cooled outlet gas pressure will be about
the same as the hot inlet gas pressure. Passage 140 is sized to
provide the gradual increase in cross-sectional area through which
the hot gases flow. The gradual increase is provided by the tapered
shape of nose cone 138 and the converging wall 139 of pipe 136.
The gradual increase in cross-sectional area provides a gradual
decrease in gas velocity which is accompanied by an increase in gas
pressure to conserve total energy.
The angle of the nose cone 138 and the entering pipe 139 are
selected so that the increase in cross-sectional area of the
annular space formed between cone 138 and pipe 139 per unit length
is equal to the increase in cross-sectional area per unit length of
a conical pipe having an angle of divergence of 4.degree. to
10.degree., preferably 4.degree. to 7.degree., e.g. 5.degree.. The
angle of the cone 138 and extent to which converging wall 139
corresponds to the angle of cone 138 provide the necessary gradual
increase in cross-sectional area. The nose cone angle can be
25.degree. to 30.degree.. The angle of converging wall 139 if taken
to an apex can be 20.degree. to 25.degree.. The length of cone 138
can be 8 to 12 inches. The cooling chamber that is the second
annular chamber 135 has the same cross-sectional area throughout
its length.
FIG. 7 shows a cross section of the cooling apparatus taken through
line 7--7 of FIG. 6. FIG. 7 shows an end section of tubes 161 and
the manner in which they are connected by welds 170 to the outer
wall of concentric pipe 136. A suitable heat transfer material 171
can be used to fill the space between tubes 161 and to improve the
heat transfer between the hot gases and coolant.
Another embodiment of the cooling apparatus is illustrated by FIGS.
8 and 9 of the drawings. In this embodiment cooling of the hot
gases is provided primarily by direct contact with the outer wall
of concentric pipe 134. In order to improve the heat transfer
between pipe 134 and the hot gases, pipe 134 can contain a
multiplicity of cooling fins 156 which project into the hot gases
in annular space 135.
The cooling apparatus or quenching unit of the present invention
provides rapid cooling for hot fluids by indirect heat exchange on
cooling surfaces. The heat exchanger can be used to cool liquids or
gases and/or for heat recovery and generation of steam. Typically,
when used to cool a hot gaseous hydrocarbon effluent from a
cracking furnace, the inlet gas temperature to the quench unit will
be about 1350.degree. to 1650.degree. F. While in the heat
exchanger the effluent will be cooled by 100.degree. to 600.degree.
F. The hot gases are fed to the quench unit at a velocity of 350 to
1000 ft./sec., and preferably at 500 to 900 ft./sec. The heat flux
at the inlet to the cooling apparatus can be as high as 80,000
BTU/hr./sq. ft. and the cooling apparatus can have an average heat
flux of about 40,000 BTU/hr./sq. ft. In the operation of the unit,
at the pressures described below, about 10 to 15 lbs. of water are
circulated for each pound of steam produced. The design and
operation of the unit can provide that there be substantially no
decrease in pressure between the hot gas inlet and the quenched gas
outlet. The pressure decrease of the fluid to be cooled can be kept
down to 3 PSI and preferably less than 1 PSI. The water is
introduced to the unit at a pressure of 200 to 2000 PSIA and at a
temperature of about 388.degree. to about 635.degree. F. and
preferably, the coolant water is introduced at a pressure of 1500
to 1800 PSIA and at a temperature of about 595.degree. to
620.degree. F. In the embodiment of the invention where the coolant
circulation is provided by thermosiphon effect, the circulation
rate can be self-regulating within design limits and automatically
adjusts for variations in cooling service required.
When cooling high temperature hydrocarbon streams which contain
some relatively high boiling constituents, it is necessary to
maintain the cooling surfaces at a temperature high enough to
prevent condensation and deposition of the high boiling
constituents on the cooling surfaces, but it is also necessary to
maintain the cooling surfaces cold enough to carry out the rapid
cooling of the effluent stream that is required.
* * * * *