U.S. patent application number 09/792469 was filed with the patent office on 2001-08-30 for heat exchanger for easily polymerizing substance-containing gas provided with gas distributing plate.
Invention is credited to Iwato, Hiroo, Mitsumoto, Tetsuji, Nishimura, Takeshi, Sakamoto, Kazuhiko.
Application Number | 20010017202 09/792469 |
Document ID | / |
Family ID | 26073280 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017202 |
Kind Code |
A1 |
Mitsumoto, Tetsuji ; et
al. |
August 30, 2001 |
Heat exchanger for easily polymerizing substance-containing gas
provided with gas distributing plate
Abstract
A heat exchanger for an easily polymerizing substance-containing
gas provided with a shell possessed of a heat-exchanging gas inlet
and a heat-exchanging gas outlet and a heat-exchanging part adapted
to circulate fluid introduced from outside the shell between the
gas inlet and said gas outlet, which heat exchanger is
characterized by being provided with a gas distributing plate
between the gas inlet and the heat-exchanging part. The heat
exchanger is characterized by the gas distributing plate having a
cross-sectional area in the range of 1.0-10.0 times the
cross-section of the gas inlet. When an easily polymerizing
substance-containing gas contacts a structure, the gas is condensed
on the contact surface of the structure and suffered to generate a
polymer. According to the heat exchanger of this invention, by
uniformly distributing a gas in the heat-exchanging part, it is
made possible to attain uniform distribution of heat, depress the
possible condensation of the gas, and prevent the easily
polymerizing substance from succumbing to polymerization.
Inventors: |
Mitsumoto, Tetsuji;
(Himeji-shi, JP) ; Nishimura, Takeshi;
(Himeji-shi, JP) ; Sakamoto, Kazuhiko;
(Himeji-shi, JP) ; Iwato, Hiroo; (Himeji-shi,
JP) |
Correspondence
Address: |
MATHEWS, COLLINS, SHEPHERD & GOULD, P.A.
100 THANET CIRCLE, SUITE 306
PRINCETON
NJ
08540
US
|
Family ID: |
26073280 |
Appl. No.: |
09/792469 |
Filed: |
February 23, 2001 |
Current U.S.
Class: |
165/174 ;
165/158 |
Current CPC
Class: |
B01J 19/002 20130101;
B01J 2219/00252 20130101; F28F 9/0278 20130101; F28D 7/1607
20130101; F28D 7/1623 20130101 |
Class at
Publication: |
165/174 ;
165/158 |
International
Class: |
F28F 009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2000 |
EP |
00307229.5 |
Feb 25, 2000 |
JP |
2000-49339 |
Claims
1. A heat exchanger for an easily polymerizing substance-containing
gas provided with a shell possessed of a heat-exchanging gas inlet
and a heat-exchanging gas outlet and a heat-exchanging part adapted
to circulate fluid introduced from outside said shell between said
gas inlet and said gas outlet, which heat exchanger is
characterized by being provided with a gas distributing plate
between said gas inlet and said heat-exchanging part.
2. A heat exchanger according to claim 1, wherein the
cross-sectional area of said gas distributing plate is in the range
of 1.0-10.0 times the cross section of said gas inlet.
3. A heat exchanger according to claim 1, wherein the distance
between said gas inlet and said gas distributing plate is in the
range of 0.5-3.0 times the diameter of said gas inlet and the
distance between said gas distributing plate and said
heat-exchanging part is in the range of 1.0-5.0 times the distance
between said gas inlet and said gas distributing plate.
4. A heat exchanger according to claim 2, wherein the distance
between said gas inlet and said gas distributing plate is in the
range of 0.5-3.0 times the diameter of said gas inlet and the
distance between the gas distributing plate and said
heat-exchanging part is in the range of 1.0-5.0 times the distance
between said gas inlet and said gas distributing plate.
5. A heat exchanger according to claim 1, wherein said gas
distributing plate is a perforated plate having a opening area
ratio in the range of 10-60%.
6. A heat exchanger according to claim 1, wherein the opening area
in one of the holes in said perforated plate is in the range of
20-1000 mm.sup.2.
7. A heat exchanger according to claim 1, wherein said gas
distributing plate forms a surface protruding from said gas inlet
toward said heat-exchanging part and said protruding surface is
such that the angle formed by the center of said gas distributing
plate and the outer peripheral part of said gas distributing plate
is in the range of 0.1-20.degree..
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a heat exchanger used for a gas
containing an easily polymerizing substance and provided between a
heat-exchanging gas inlet and a heat-exchanging part with a gas
distributing plate.
[0003] 2. Description of Related Art
[0004] The heat exchanger for transferring heat between two fluids,
the one having a high temperature and the other a low temperature,
is one of the chemical devices extensively used in the chemical
industry. The basis of the heat exchange resides in the exchange of
heat between a high temperature fluid and a low temperature fluid
through the medium of a heating surface.
[0005] Generally the heat exchanger fulfills the role of exchanging
heat by introducing into a heat-exchanging part thereof fluid
intended to be cooled or heated. The heat-exchanging part is known
in various types including the shell-and-tube type having a bundle
of numerous tubes inserted in a shell, the plate type having
heating plates each containing corrugated ribs or semicircular
ridges superposed and clamped through the medium of a gasket after
the fashion of a filter press and consequently enabled to enclose
thin flow paths of a rectangular cross section therewith and
allowing a high temperature fluid and a low temperature fluid to
flow through the flow paths on the alternating heating plates, and
the fin tube type having a heating tube provided on the inner
and/or outer wall surfaces thereof with fins intended to enlarge a
heating surface and heightening the effect of heat transfer, for
example.
[0006] The heat exchanger is extensively utilized generally as
sorted by the nature of use into (1) a heater, i.e. a heat
exchanger to be used for the purpose of heating a given fluid to a
required temperature without changing the phase, (2) a preheater,
i.e. a heat exchanger to be used for the purpose of heating a given
fluid in advance and consequently exalting the efficiency of the
subsequent step, (3) a superheater, i.e. a heat exchanger to be
used for the purpose of heating a given fluid till a superheated
state, (4) an evaporator, i.e. a heat exchanger to be used for the
purpose of vaporizing a given fluid by heating, (5) a re-boiler,
i.e. a heat exchanger to be used for the purpose of causing fluid
condensed in a device to be heated again till vaporization, (6) a
cooler, i.e. a heat exchanger to be used for the purpose of cooling
a given fluid till a required temperature, (7) a chiller, i.e. a
heat exchanger to be used for the purpose of cooling a given fluid
till a very low temperature below 0.degree. C., (8) a condenser,
i.e. a heat exchanger to be used for the purpose of cooling a
condensable gas till condensation and liquefaction, (9) a total
condenser, i.e. a heat exchanger to be used for the purpose of
thoroughly condensing a given condensable gas, and (10) a partial
condenser, i.e. a heat exchanger to be used for the purpose of
causing a given condensable gas to be partly condensed and
liquefied and allowing the remainder thereof to be released in the
gaseous state into the subsequent step, for example.
[0007] One example of the shell-and-tube type heat exchanger for
one-pass operation will be described below with reference to FIG.
1. It is provided, however, that the heat-exchanging gas and/or the
fluid may be led in or led out respectively through the inlet or
the outlet in the opposite direction indicated in the following
description, the gas may be led in or led out respectively through
the fluid inlet or the fluid outlet or, by the same token, the
fluid may be led in or let out respectively through the inlet or
the outlet for the heat-exchanging gas, depending on the purpose or
the necessity. Furthermore, the direction in which the heat
exchanger is installed does not need to be limited to verticality
but may be selected to suit the kind of the gas or the fluid to be
handled and the purpose for which the heat exchanger is used.
[0008] With reference to FIG. 1, 10 stands for a shell, 11 for a
fluid outlet, 12 for a fluid inlet, 13 for a tube sheet, 14 for a
heat-transfer tube, 15 for a baffle plate, 16 for a impingement
plate, 20 and 21 each for a channel, 22 for a heat-exchanging gas
inlet, and 23 for a heat-exchanging gas outlet. In FIG. 1, the part
interposed between the two tube sheets (13) inside the shell
corresponds to a heat-exchanging part (30).
[0009] In this heat exchanger, the gas subjected to exchange of
heat is supplied through the gas inlet (22) disposed in the channel
(20), then introduced into the heat-transfer tube (14), and
thereafter discharged through the heat-exchanging gas outlet (23)
disposed in the channel (21). The fluid, for example heating
medium, is introduced through the fluid inlet (12) disposed in the
shell (10), caused to exchange heat efficiently with the gas in the
heat-transfer tube (14) through the medium of the heat-transfer
tube (14) as guided along the flow path altered by the baffle plate
(15), and led out through the fluid outlet (11). By interposing the
impingement plate (16) between the fluid inlet (12) and the
heat-transfer tube (14), the fluid can prevent from inducing
erosion on the surfaces of the tubes which is generated by fluid
contacting directly the outer wall surfaces of the bundled tubes.
Generally, the cross-sectional area of the gas inlet is smaller
than the area of the heat-exchanging inlet part. The reason for
this difference is that when the cross-sectional area of the gas
inlet is equalized with that of the heat-exchanging inlet part, it
will become necessary to enlarge the gas pipe and heighten the
cost.
[0010] The difference in cross-sectional area between the gas inlet
and the heat-exchanging part, however, forms a cause for lowering
the ratio of heat exchange because the heat-exchanging gas is
supplied in a large amount to the central part of the heat
exchanger and in a small amount to the peripheral part thereof. The
heat-transfer tube for introducing the heat-exchanging gas,
however, has never been accorded any consideration about the
adoption of a device for rendering the supply of the gas uniform.
Barely, the wall thickness, cross-sectional area, tube layout, and
pitch of the heat-transfer tube have been studied and the shape and
disposal of the baffle plate have been studied.
[0011] Particularly when the ratio of heat exchange is ununiform
where the heat-exchanging gas happens to be an easily polymerizing
substance-containing gas, the easily polymerizing substance tends
to succumb to polymerization due to condensation. Absolutely no
measure has been devised against this detriment. In the
shell-and-tube type heat exchanger which has gas pipes drawn in
from the top of a distillation column, for example, the vapor
abounding in a low boiling component and ascending to the top of
the distillation column is cooled and condensed inside the
heat-transfer tubes. This vapor tends to succumb to polymerization
inside the heat exchanger when the substance subjected to
distillation happens to be such an easily polymerizing compound as
acrylic acid. For, the acrylic acid gas which has been obtained
prevalently by the catalytic gas phase oxidation of propylene, for
example, contains such impurities as water, acetic acid, and
acrolein and tends to induce polymerization of acrylic acid easily.
This polymerization cannot be prevented fully satisfactorily even
by adding to the process a varying polymerization inhibitor such
as, for example, phenothiazine, hydroquinone, methoquinone, cresol,
phenol, or t-butyl catechol. Since such a polymerization inhibitor
is a high boiling substance, the temperature conditions capable of
gasifying the easily polymerizing substance fail to bring though
incorporation of the polymerization inhibitor in the gas to be
formed under such conditions. It follows that the slender
heat-transfer tubes are liable to induce polymerization in their
interiors and suffer deposition of a polymer on the inner walls
thereof because the composition itself is in a very easily
polymerizing state and, moreover, the polymerization inhibitor does
not effectively discharge its own function in a gas.
[0012] The problems regarding the uniformity of the ratio of heat
exchange, the distribution of the heat-exchanging gas, and the
generation of a polymer by the easily polymerizing substance which
are encountered by the heat exchanger are not limited to the
shell-and-tube type heat exchanger mentioned above but are entailed
by the fin tube type heat exchanger and the plate type heat
exchanger as well.
[0013] Absolutely no study has ever been made as to the
distribution of the heat-exchanging gas. Particularly in the heat
exchange of an easily polymerizing gas, the problems such as the
generation of a polymer in portion of the heat-exchanging part due
to the degradation of the heat-transfer efficiency resulting from
ununiform supply of the gas and also due to the concentration of
the feed gas, the forced suspension of the entire system, and the
decline of the heat-transfer efficiency resulting from the
deposition of a polymer on the heat-transfer surface remain yet to
be solved.
SUMMARY OF THE INVENTION
[0014] The present inventor has performed an elaborate study on the
structure of a heat exchanger and has consequently found that the
provision of a gas distributing plate between the heat-exchanging
part and the heat-exchanging gas inlet allows the gas to be
uniformly supplied to the heat-exchanging part and that the
generation of the polymer can be effectively depressed by the
disposition of the gas distributing plate. This invention has been
perfected as a result.
[0015] To be specific, this invention is aimed at providing the
following intellectual achievement.
[0016] A heat exchanger for an easily polymerizing
substance-containing gas provided with a shell possessed of a
heat-exchanging gas inlet and a heat-exchanging gas outlet and a
heat-exchanging part adapted to circulate fluid introduced from
outside the shell between the gas inlet and the gas outlet, which
heat exchanger is characterized by being provided with a gas
distributing plate between the gas inlet and the heat-exchanging
part.
[0017] According to this invention, since the heat-exchanging gas
containing an easily polymerizing substance is uniformly
distributed in the heat-exchanging part inside the heat exchanger,
the generation of a polymer which possibly occurs when the gas is
ununiformly supplied to the heat-exchanging part can be repressed.
When an easily polymerizing substance-containing gas contacts a
structure where the distribution of a gas is not uniform, the gas
touching the surface of the structure is caused to condense and
stagnate and consequently give rise to a polymer. In the heat
exchanger of this invention, it is made possible by effecting
uniform distribution of the gas in the heat-exchanging part to
repress the stagnation of the gas subsequent to the condensation
and prevent the easily polymerizing substance from
polymerizing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram of the conventional
shell-and-tube type heat exchanger.
[0019] FIG. 2 is a partial diagram illustrating one mode of
embodying the shell-and-tube type heat exchanger of this invention
which is provided with a gas distributing plate. In this diagram,
the flow of a heat-exchanging gas is indicated by filled arrow
marks and the flow of fluid by empty arrow marks.
[0020] FIG. 3 is a perspective view illustrating a square gas
distributing plate possessed of numerous circular holes and used in
the heat exchanger of this invention.
[0021] FIG. 4 is a plan view illustrating a circular gas
distributing plate possessed of numerous circular holes of varying
diameters and used in the exchanger of this invention.
[0022] FIG. 5 is a partial diagram illustrating one mode of the
heat exchanger of this invention, wherein the gas distributing
plate has a protruding surface.
[0023] FIG. 6 is a perspective view illustrating schematically one
mode of the plate type heat exchanger of this invention. In this
diagram, the flow of the heat-exchanging gas is indicated by filled
arrow marks and the flow of the fluid is indicated by empty arrow
marks.
[0024] FIG. 7 is a cross section illustrating schematically one
mode of the fin tube type heat exchanger of this invention. In this
diagram, the flow of the heat-exchanging gas is indicated by filled
arrow marks and the flow of the fluid is indicated by empty arrow
marks.
[0025] FIG. 8 is a diagram illustrating schematically a heat
exchanger furnished with a vacuum generating device (50) and used
in a working example.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] This invention concerns a heat exchanger for an easily
polymerizing substance-containing gas provided with a shell
possessed of a heat-exchanging gas inlet and heat-exchanging gas
outlet and a heat-exchanging part adapted to circulate fluid
introduced from outside the shell between the gas inlet and the gas
outlet, which heat exchanger is characterized by being provided
with a gas distributing plate between the gas inlet and the
heat-exchanging part. Now, a preferred embodiment of this invention
which is provided in a shell-and tube type heat exchanger with a
gas distributing plate will be described below with reference to
FIG. 2.
[0027] First, FIG. 2 is a partial diagram illustrating in type
section a shell-and-tube type heat exchanger for one-pass operation
with respect to the relation between the fluid gas inlet and the
heat exchanging part. With reference to FIG. 2, 10 stands for a
shell, 13 for a tube sheet, 14 for a heat-transfer tube, 20 for a
channel, 22 for a heat-exchanging gas inlet, 30 for a
heat-exchanging part, and 40 for a gas distributing plate. The gas
which has been introduced through the heat-exchanging gas inlet
(22) into the heat exchanger is distributed through the medium of
the gas distributing plate (40) and distributed uniformly on the
surface of the tube sheet (13) exposed to the gas. The gas,
therefore, is uniformly introduced to the numerous heat-transfer
tubes (1) fitted to the tube sheet (13). Specifically, this
invention is characterized by providing the gas distributing plate
(40) between the gas inlet and the heat-exchanging part.
Consequently, the heat-exchanging gas can be uniformly distributed
thereby increasing the ratio of heat exchange in the
heat-exchanging part. Particularly when the heat-exchanging gas
happens to be an easily polymerizing substance-containing gas, the
uniform distribution can prevent the partial condensation of the
easily polymerizing substance-containing gas, the consequent
generation of a polymer, and the deposition of the formed polymer.
Generally, a polymerization inhibitor is added to a purification
column which is operated for purifying a gaseous easily
polymerizing substance, which is prevalently a high boiling
substance. Thus, the easily polymerizing substance-containing gas
does not sufficiently contain the polymerization inhibitor and,
therefore, tends to succumb to condensation and consequently
generate a polymer of the easily polymerizing substance. The
condensation and the generation of a polymer, when the ratio of
heat exchange is not uniform, are liable to entail generation of a
polymer because the condensate stagnates in part of the heat
exchanger for a comparatively long period of time. When the
introduced gas is an easily polymerizing substance, therefore, the
heat exchange, when performed after the gas has been uniformly
distributed, exalts the efficiency of heat exchange and prevents
the generation of a polymer as well. It has been heretofore held
that an addition to the structure results in increasing the surface
of contact with the easily polymerizing gas and promoting the
partial stagnation of the condensate and the fluid. It has been
ascertained, however, that in accordance with this invention, the
occurrence of the polymerization of an easily polymerizing
substance can be effectively prevented by interposing the gas
distributing plate between the gas inlet and the heat-exchanging
part.
[0028] The easily polymerizing substance is only required to assume
a gaseous state at the time that it is introduced into the heat
exchanger. The discrimination between the gaseous state and the
liquid state prevailing under the standard conditions is
irrelevant. As concrete examples of the easily polymerizing
substance answering the requirement, acrylic acid, methacrylic
acid, maleic acid, and esters thereof, and styrene and
acrylonitrile may be cited. The easily polymerizing substances may
further contain high boiling substances and solvent, subliming
substances, and mixtures thereof. Particularly advantageous easily
polymerizing substances include acrylic acid, methacrylic acid, and
esters thereof. They may further contain solvents and other
mixtures. In the case of acrylic acid and acrylic esters, for
example, acetic acid, propionic acid, acrolein, maleic acid, water,
and formalin mixture which are by-produced when acrylic acid is
obtained by the reaction of catalytic gas phase oxidation may be
cited. Then, in the case of methacrylic acid and methacrylic
esters, for example, methacrolein, acrylic acid, and acetic acid
mixtures which are by-produced when methacrylic acid is obtained by
the reaction of catalytic gas phase oxidation may be cited.
[0029] This invention has the gas distributing plate interposed
between the gas inlet and the heat-exchanging part. The
cross-sectional area of this gas distributing plate (40) is
preferably in the range of 1.0-10.0 times, more preferably in the
range of 1.2-8.0 times, and particularly preferably in the range of
1.5-6.0 times the cross-sectional area of the gas inlet. Since the
gas inlet is connected to the gas pipe, the cross-sectional area of
the gas inlet is generally smaller than the cross-sectional area of
the heat-exchanging part. Generally, the cross-sectional area of
the heat-exchanging part is 2-100 times the cross-sectional area of
the gas inlet. The cross-sectional area has been set in the range
mentioned above for the following reason: If the cross-sectional
area of gas distributing plate falls short of 1 times the
cross-sectional area of the gas inlet, some of the gas will escape
being distributed by the gas distributing plate and thorough gas
distribution will be obtained with difficulty. Conversely, if the
cross-sectional area in question exceeds 10.0 times the
cross-sectional area of the gas inlet, the excess will possible
cause the distributing plate to induce formation of a polymer.
[0030] The gas distributing plate can dispense with a through hole.
When it is furnished with holes, the holes are effective in more
uniformizing the distribution of a gas and preventing the gas
distributing plate itself from inducing polymerization. Properly,
the plate containing such holes has a opening area ratio in the
range of 10-60%, more preferably in the range of 20-55%, and
particularly preferably in the range of 40-50%. If the opening area
ratio falls short of 10%, the shortage will unduly increase the
proportion of the gas which fails to pass through the distributing
plate, prevent the distribution from uniformly proceeding for the
incorporation of holes, and force the distributing plate to induce
formation of a polymer. Conversely, if the opening area ratio
exceeds 60%, the excess will unduly increase the proportion of the
gas which passes through the distributing plate possibly to the
extent of rendering uniform distribution infeasible. The term
"cross-sectional area of the gas distributing plate" as used in the
specification hereof means the surface area of a flat surface part
existing in the case of a opening area ratio of 0%. When the gas
distributing plate is possessed of numerous openings as illustrated
in FIG. 3, the actual surface area of the flat surface is found by
this formula: cross-sectional area.times.(100-opening area ratio(%)
)/100. The opening area ratio (%) is defined by this formula:
(opening area/cross-sectional area of gas distributing
plate).times.100.
[0031] FIG. 3 illustrates a preferred mode of the gas distributing
plate. FIG. 3 depicts a tetragonal plate furnished with circular
through holes. The gas distributing plate (40) contemplated by this
invention is only required to be shaped like a plate having a
circular or elliptic shape, or a polygonal figure such as a
triangle or a tetragon, for example. The holes (41) opened in the
plate do not need to be in a circular or elliptic shape exclusively
but may be in a polygonal shape such as, for example, a triangle or
a tetragon. Incidentally, the holes are preferred to be uniformly
distributed in the gas distributing plate but are not required to
be identical in shape. FIG. 4 illustrates a circular gas
distributing plate (40) furnished with circular through holes
having varying diameters. In this invention, the holes varying in
size may be distributed as illustrated in FIG. 4.
[0032] In the distributing plate (40) to be used in this invention,
the opening area in one of the hole in the distributing plate (41)
is in the range of 20-1000 mm.sup.2, preferably in the range of
50-700 mm.sup.2, and particularly in the range of 100-500 mm.sup.2.
If the opening area falls short of 20 mm.sup.2, the shortage will
force the holes to be blocked with a polymer and finally prevent
the gas from being uniformly distributed in the heat-exchanging
part and possibly entail the generation of a polymer in the
heat-exchanging part. Conversely, if the opening area exceeds 1000
mm.sup.2, the excess will possibly prevent the gas from being
thoroughly distributed during its passage through the gas
distributing plate and force the gas to entail formation of a
polymer in the heat-exchanging part.
[0033] Generally, the distribution of a gas is varied with the
location of the gas distributing plate. The layout of the
distributing plate (40) to be used in this invention will be
explained with the aid of FIG. 2. In this invention, the distance
(Ln) between the gas inlet and the gas distributing plate is in the
range of 0.5-3.0 times, preferably in the range of 0.6-2.5 times,
and particularly in the range of 0.8-2.0 times the equivalent
diameter of the gas inlet, and the distance (Lt) between the gas
distributing plate and the heat-exchanging part is in the range of
1.0-5.0 times, preferably in the range of 1.1-4.0 times, and
particularly in the range of 1.2-3.0 times the distance (Ln)
between the gas inlet and the gas distributing plate. If the Ln
falls short of 0.5 times the equivalent diameter mentioned above,
the shortage will tend to prevent the gas entering the gas inlet
from being distributed throughout the entire surface of the gas
distributing plate and force the gas to entail formation of a
polymer on the surface of the gas distributing plate. Conversely,
if it exceeds 3.0 times the equivalent diameter, the excess will
decrease the amount of the gas contacting the gas distributing
plate and consequently bring insufficient distribution of the gas.
If the Lt falls short of 1.0 times the Ln mentioned above, the
shortage will prevent the gas from being sufficiently distributed
in the heat-exchanging part located most closely to the gas
distributing plate. Conversely, if it exceeds 5.0 times the Ln, the
excess will be at a disadvantage in necessitating an addition to
the length of the channel of the heat exchanger. The gas inlet does
not need to assume a circular shape exclusively but may assume a
polygonal shape like a triangle or a tetragon, for example. The
easily polymerizing substance-containing gas tends to stagnate in
angular parts and consequently entail formation of a polymer
because of the stagnation. When the gas inlet is in a circular
shape lacking a corner, therefore, it is at an advantage in
preventing the easily polymerizing substance from polymerizing.
When the gas inlet is in a circular shape, the equivalent diameter
of the gas inlet means the inside diameter thereof. When the gas
inlet is not in a circular shape, the magnitude found by the
calculation of the formula, 4.times.cross-sectional area of gas
inlet/inner circumferential length of gas inlet, is used as the
equivalent inside diameter in the calculation of the distance (Ln)
between the gas inlet and the gas distributing plate. The gas
distributing plate (40) is preferred to be disposed parallelly or
nearly parallelly to the surface of the heat-exchanging part
approximating most closely to the gas distributing plate which is
exposed to the gas. In FIG. 2, the tube sheet (13) corresponds to
the gas-contacting surface of the heat-exchanging part
approximating most closely to the gas distributing plate.
[0034] Then, FIG. 5 illustrates part of the heat exchanger having
disposed therein the distributing plate (40) which forms a surface
protruding from the gas inlet toward the heat-exchanging part. The
protruding surface of this sort is advantageous in enabling the gas
to be distributed as far as the outer peripheral part of the
heat-exchanging part. This protruding surface is properly such that
the angle (.theta.) falls in the range of 0.1-20.degree.,
preferably in the range of 1-15.degree., and particularly in the
range of 3-10.degree.. If this angle falls short of 0.10, the
shortage will tend to induce distribution of the gas in the outer
peripheral part of the heat-transfer surface. Conversely, if this
angle exceeds 20.degree., the excess will be at a disadvantage in
entailing insufficient distribution of the gas in the outer
peripheral part. When the gas distributing plate has a shape other
than a circle, the angle formed between the center of gravity of
the gas distributing plate and the outer peripheral part most
distant from the center of gravity is required to fall in the range
specified above. Incidentally, when the distributing plate has such
a protruding surface as illustrated in FIG. 5, the distance from
the gas inlet to the most protruding part of the gas distributing
plate corresponds to the distance (Ln) between the gas inlet and
the gas distributing plate and the distance from the protruding
surface to the position approximating most closely to the
heat-exchanging part corresponds to the distance (Lt) between the
gas distributing plate and the heat-exchanging part.
[0035] The heat exchanger of this invention is possessed of the gas
distributing plate (40). The disposal of this distributing plate
(40) is easily implemented by having the gas distributing plate
suspended with one or more gas distributing plate-supporting
members (42) as illustrated in FIG. 5. For the purpose of effecting
heat exchange on an easily polymerizing substance-containing gas,
the absence of a structure from the interval between the gas inlet
and the heat-exchanging part is intrinsically preferred. When the
easily polymerizing substance-containing gas contacts an
intervening structure, if any, it tends to condense and stagnate on
the contacting surface of the structure and entail generation of a
polymer. For the purpose of enabling the introduced gas to be
distributed more uniformly, it is permissible to have a plurality
of such distributing plates disposed in the range mentioned above.
The provision of the plurality of gas distributing plates possibly
add to the uniformity of the distribution.
[0036] It is proper to use steel as the materials for the gas
distributing plate (40) and the gas distributing plate-supporting
member (42). On account of the ease of welding, such items of known
steel as austenite steel, austenite ferrite steel, and ferrite
steel can be used preferably. The reason for this preference is
that the steel of interest avoids reacting with an easily
polymerizing substance, degenerating an easily polymerizing
substance, or corroding a heat-transfer tube itself.
[0037] Further, when the gas distributing plate or the gas
distributing plate-supporting member forms a protruding part on the
surface thereof, it automatically gives rise to a depressed part.
In this depressed part, the easily polymerizing
substance-containing gas condenses and stagnates and consequently
tends to generate a polymer. This invention, therefore, prefers the
gas distributing plate to have such an outer surface that the
magnitude, Ry, which is specified in JIS (Japanese Industrial
Standard) B0601 (-1994) is not more than 12.5, preferably not more
than 3.2. This surface roughness of the gas distributing plate can
be accomplished by treating the surface of this plate.
[0038] For the surface treatment of this sort, such mechanical
polishing as buffing and electropolishing are available. The
buffing is a method of polishing which is adopted when a flat
smooth surface or a glossy surface is to be obtained. For the
buffing, coarse polish with a stationary abrasive, a medium polish
with a semisolid or free abrasive, and finish polish are available.
For the buff abrasive, besides such soft materials as leather and
cloth which are intended for polishing a surface, oily, non-oily,
or spray solvents containing tripolysilicate, silicon carbide,
fused alumina, calcined alumina, and chromium oxide as an abrasive
can be used.
[0039] The electropolishing is a method for smoothing a metallic
surface while melting it. As the electropolishing solution which
fits the gas distributing plate made of iron or steel, perchloric
acid type, sulfuric acid type, phosphoric acid type, sulfuric
acid-phosphoric acid can be used. Since the iron and the steel have
their textures largely varied not only with their compositions but
also with the degrees of heat treatment and fabrication, they can
be properly selected so as to suit the particular gas distributing
plate to be used. It, therefore, suffices to make this selection
properly, depending on the amount of acetic anhydride to be added
generally to a perchloric acid type electrolyte, the temperature of
electrolysis, the density of electric current, the voltage, the
duration of electrolysis, etc. Optionally, the gas distributing
plate may be subjected to mechanical polishing and further to
electropolishing.
[0040] This invention contemplates using the gas distributing plate
(40) not only for distributing a gas but also for preventing an
easily polymerizing substance from forming a polymer. When the heat
exchanger happens to be a shell-and-tube type heat exchanger,
therefore, it does not need to impose any particular limit on the
specification excepting the requirement that the gas distributing
plate mentioned above can be interposed between the gas inlet and
the heat-exchanging. The heat exchanger does not need to be limited
to one-pass operation inside and outside the tubes. The number of
passes of operation can be selected arbitrarily on either side.
[0041] Further, the heat exchanger of this invention permits
arbitrary selection of the type of a partition plate among the
separation with a cover plate, the integration with a cover plate,
and the integration with a tube sheet. Likewise, the form of fixing
a tube sheet and a shell may be freely selected among the type
using a stationary tube sheet, the type using a externally sealed
floating tubesheet, and the type using a pull through floating
head. The outside diameter and the length of heat-transfer tubes to
be laid inside the shell may be properly selected so as to suit the
size, shape, and purpose of use of the heat exchanger to be used.
On the condition that the heat exchanger is possessed of the
structure described above, this heat exchanger may be produced with
a baffle plate, an longitudinal baffle plate, a impingement plate,
a channel side shell flange, a shell cover side shell flange, a
shell side nozzle, a floating head cover, tie rods and spacers, a
gas vent connection, instrument connections, a supporting saddle, a
lifting lug, a liquid level gauge connection, an expansion joint,
and a device for resisting inflation which are used in ordinary
heat exchangers.
[0042] The heat exchanger of this invention is embodied in various
types such as, for example, the shell-and-tube type which, as
illustrated in FIG. 8, comprises tube sheets attached inside a
shell, heat-transfer tubes constrained in position at the terminals
thereof at least on one side, and fluid adapted to be circulated
around the outer peripheries thereof, the plate type which, as
illustrated in FIG. 6, comprises corrugated ribs or heat-transfer
plates forming hemispherical projections thereon superposed and
clamped through the medium of gaskets after the fashion of a filter
press thereby interposing a thin flow path of a rectangular cross
section between the adjacent plates and a high temperature fluid
and a low temperature fluid adapted to flow through the alternating
flow paths thereby effecting necessary heat exchange between the
two fluids, and the fin tube type which, as illustrated in FIG. 7,
comprises heat-transfer tubes provided on the inner surfaces and/or
outer surfaces thereof with fins.
[0043] The heat exchanger of this invention can be used in any of
(1) a heater, i.e. a heat exchanger to be used for the purpose of
heating a given fluid to a required temperature without changing
the phase, (2) a preheater, i.e. a heat exchanger to be used for
the purpose of heating a given fluid in advance and consequently
exalting the efficiency of the subsequent step, (3) a superheater,
i.e. a heat exchanger to be used for the purpose of heating a given
fluid till a superheated state, (4) an evaporator, i.e. a heat
exchanger to be used for the purpose of vaporizing a given fluid by
heating, (5) a re-boiler, i.e. a heat exchanger to be used for the
purpose of causing fluid condensed in a device to be heated again
till vaporization, (6) a cooler, i.e. a heat exchanger to be used
for the purpose of cooling a given fluid till a required
temperature, (7) a chiller, i.e. a heat exchanger to be used for
the purpose of cooling a given fluid till a very low temperature
below 0.degree. C., (8) a condenser, i.e. a heat exchanger to be
used for the purpose of cooling a condensable gas till condensation
and liquefaction, (9) a total condenser, i.e. a heat exchanger to
be used for the purpose of thoroughly condensing a given
condensable gas, and (10) a partial condenser, i.e. a heat
exchanger to be used for the purpose of causing a given condensable
gas to be partly condensed and liquefied and allowing the remainder
thereof to be released in the gaseous state into the subsequent
step, for example.
[0044] The heat exchanger of this invention can be further used as
the reactor for the reaction of catalytic gas phase oxidation. The
reaction of catalytic gas phase oxidation is a reaction which is
induced by supplying a given raw material in a gaseous state to a
catalyst for the reaction of catalytic gas phase oxidation
contained in advance in a multiple of tubes with a view to
oxidizing the raw material into the target product or an
intermediate thereof. It is generally a exothermic reaction. It is,
therefore, common for this reaction to circulate fluid around the
outer peripheries of the multiplicity of tubes for the sake of heat
exchange. When the intermediate of the reaction of catalytic gas
phase oxidation happens to be an easily polymerizing
substance-containing gas and this intermediate is intended to be
converted by the reaction of catalytic gas phase oxidation into the
target product, the known reactor for the reaction of catalytic gas
phase oxidation is not different at all from the shell-and-tube
type heat exchanger in respect that it is possessed of a gas inlet
part and a heat-exchanging part. By interposing the gas
distributing plate between the heat-exchanging part and the gas
inlet of the reactor, therefore, it is made possible to implement
effectively the uniform distribution of the easily polymerizing
substance-containing gas to be supplied to the multiplicity of
tubes individually.
[0045] This reaction of catalytic gas phase oxidation can be
adopted particularly advantageously when any of the raw material
gas, the reaction product, and the intermediate contains an easily
polymerizing substance and the reaction is an exothermic reaction.
More specifically, acrylic acid, methacrylic acid, acrolein, and
methacrolein which are produced by subjecting such raw material
gases as propylene, propane, isobutylene, and methacrolein to
catalytic gas phase oxidation with a molecular oxygen-containing
gas in the presence of an oxidizing catalyst may be cited, for
example.
[0046] Further, the heat exchanger of this invention can be used as
a condenser for producing (meth)acrylic acid. Now, the method for
producing (meth)acrylic acid by incorporating therein a step of
operating the heat exchanger of this invention as a condenser will
be described.
[0047] First, the method for producing acrylic acid according to
this invention comprises a step for obtaining a (meth)acrylic
acid-containing gas, a step for absorbing acrylic acid in an
absorbent, and a step for separating a low boiling substance and a
high boiling substance from the absorbent and obtaining
(meth)acrylic acid in a purified form.
[0048] As the step for obtaining (meth)acrylic acid-containing gas,
the production of (meth)acrylic acid-containing gas is attained by
subjecting propylene, acrolein, isobutylene, t-butyl alcohol, or
methacrolein to the reaction of catalytic gas phase oxidation.
[0049] Then, the step for absorbing (meth)acrylic acid in an
absorbent is a step for absorbing (meth)acrylic acid by the use of
a known (meth)acrylic acid absorbent. This step is allowed to
effect simultaneous discharge of a gas containing a small amount of
organic substance.
[0050] The step for separating a low boiling substance and a high
boiling substance from the absorbent and obtaining (meth)acrylic
acid in a purified form is a step for separating low boiling
impurities and high boiling impurities by means of distillation
from the (meth)acrylic acid-containing solution obtained by the
step of collection and obtaining crude (meth)acrylic acid. The step
of interest may incorporate therein a step for adding an aldehyde
treating agent to the crude (meth)acrylic acid and subsequently
distilling the resultant mixture thereby expelling the aldehyde and
obtaining (meth)acrylic acid of high purity.
[0051] When a gas containing the organic substance mentioned above
is obtained, the gas is wholly or partly circulated to the step for
obtaining the (meth)acrylic acid-containing gas and the remainder,
if any, is disposed of by incineration, for example. This step may
further incorporate there in a step for disposing by incineration,
for example, the whole amount of the gas discharged from the step
for collection and subsequently circulating the gas wholly or
partly to the step for obtaining the acrylic acid-containing
gas.
[0052] The heat exchanger of this invention can be utilized as a
reactor for catalytic gas phase oxidation in the step for obtaining
(meth)acrylic acid-containing solution, as a heat exchanger
attached to a circulation pipe and/or a heat exchanger disposed in
the device for disposing the waste gas at the step for circulating
the gas, and as a condenser attached to a distillation column at
the step for obtaining (meth)acrylic acid in a purified form,
respectively in the method for production mentioned above.
[0053] Now, the use of the heat exchanger of this invention as a
condenser will be described below with reference to FIG. 8
depicting the case of handling acrylic acid as an easily
polymerizing substance. First, the acrylic acid-containing gas is
introduced through a gas inlet (22) and then distributed through
the medium of a gas distributing plate (40). Then, the gas is
uniformly distributed throughout the entire surface of a tube sheet
(13), subsequently transferred inside heat-transfer tubes (14), and
discharged through a lower tube sheet (13). As the fluid for
cooling the heat-transfer tubes, water may be used. It is supplied
through a fluid inlet (12) to a heat-exchanging part (30), advanced
through a flow path having the course thereof altered with a baffle
plate (15), and discharged through a fluid outlet (11). Thus, the
fluid has fulfilled its roll in the operation of heat exchange.
FIG. 8 represents the mode of arbitrarily attaching a vacuum
generating device (50) capable of being connected to the heat
exchanger.
[0054] In the supply of the acrylic acid-containing gas to the heat
exchanger of this invention, the linear velocity of this gas in the
feed pipe is generally in the range of 5-60 m/s and the temperature
of the feed gas is generally in the range of 40-100.degree. C.
[0055] Generally, a polymerization inhibitor is added to the
interior of a distillation column which is attached to the heat
exchanger. As the polymerization inhibitor for this purpose, any of
the known polymerization inhibitors which are intended for such
easily polymerizing substances as acrylic acid can be used. Among
other such known polymerization inhibitors, at least one member
selected from the group consisting of hydroquinone, methoquinone,
cresol, phenol, t-butyl catechol, diphenyl amine, phenothiazine,
and methylene blue, p-phenylene diamines such as p-phenylene
diamine, N-oxyl compounds such as 4,-hydroxy-2,2,6,6-tetramethyl
piperidinoxyl, and molecular oxygen-containing gases are used
particularly advantageously. The compounds enumerated above may be
used either singly or in the form of a combination of two or more
members. From the view point of the effectiveness manifested in
inhibiting polymerization, the resistance to corrosion of a
distillation device, and the ease with which the waste liquid
emanating from the distillation device is disposed, phenothiazine
and/or N-oxyl compounds, and molecular oxygen-containing gases are
used particularly advantageously. Though the amount of the
polymerization inhibitor to be used does not need to be
particularly restricted, the total amount of the polymerization
inhibitor is preferred to be in the range of 1-1000 ppm (by weight)
based on the amount of the vapor of acrylic acid to be
generated.
[0056] To the heat exchanger of this structure, a molecular
oxygen-containing gas can be supplied. The supply of the molecular
oxygen-containing gas is intended to prevent the easily
polymerizing gas from yielding to polymerization. The molecular
oxygen-containing gas may be directly mixed with the acrylic
acid-containing solution by bubbling or indirectly mixed there with
by solution in a solvent. Properly, the molecular oxygen-containing
gas is generally supplied at a rate in the range of 0.1-1 vol. %
based on the volume of the vapor of acrylic acid to be
generated.
[0057] Though the production of methacrylic acid overlaps the
production of acrylic acid in many points, it differs there from in
the following points. For example, a methacrylic acid-containing
liquid, prior to its introduction into the distillation column, is
led to a step for extraction for the purpose of extracting
methacrylic acid from the methacrylic acid-containing liquid by the
use of a solvent. Even in this case, by fulfilling the conditions
specified by this invention, the possible polymerization in the
shell-and-tube type heat exchanger can be prevented.
EXAMPLES
[0058] Now, this invention will be described more specifically
below with reference to working examples.
Example 1
[0059] Heat exchange was performed on acrylic acid gas by the use
of a shell-and-tube type heat exchanger illustrated in FIG. 8. In
this heat exchanger, the inside diameter of a shell was 900 mm, the
outside diameter of heat-transfer tubes was 34 mm, the length of
heat-transfer tubes was 3000 mm, the number of heat-transfer tubes
was 305, and the diameter of an acrylic acid gas inlet was 200 mm.
A gas distributing plate 300 mm in diameter was disposed parallelly
to a heat-exchanging part at a position 200 mm from the acrylic
acid gas inlet and 600 mm from a tube sheet. The gas distributing
plate was a perforated plate containing a plurality of openings 12
mm in diameter at a opening area ratio of 20%.
[0060] Water as a heat-transfer fluid for the heat exchanger was
supplied to a heat-exchanging part and, at the same time, acrylic
acid gas containing 200 wt. ppm of phenothiazine as a
polymerization inhibitor and 1 vol. % of air was introduced at a
flow rate of 700 kg/h from the gas inlet toward the heat-transfer
tubes. The temperature of the acrylic acid gas was 85.degree. C. at
the inlet of the heat-exchanging part. The acrylic acid gas was
wholly condensed by adjusting the flow rate of the heat-transfer
fluid, then cooled to 40.degree. C., and discharged from the
heat-exchanging part.
[0061] The heat exchanger and the vacuum generation device
positioned on the downstream side thereof were found to have
absolutely no sign of polymerization during six months' operation.
When the interior of the heat exchanger was inspected after
termination of the operation, the heat-transfer tubes showed no
sign of clogging with a polymer. Though the supporting member for
the gas distributing plate showed a sign of adhesion of a trace of
polymer, the amount of adhesion was not so large as to affect the
function of the heat exchanger.
comparative Example 1
[0062] Heat exchange was performed on acrylic acid gas by following
the procedure of Example 1 while excluding the gas distributing
plate from the shell-and-tube heat exchanger.
[0063] In the acrylic acid gas supplied in the same flow rate as in
Example 1, condensation was attained only in a portion of about 660
kg/h. Acrylic acid flowed into the vacuum generation device on the
downstream side, lowered the ability of this device to generate
vacuum, incited generation of polymer in the vacuum generating
device, and consequently forced the heat exchanger to stop
operation on the day following the start of operation. When the
heat exchanger was inspected after the stop of the operation,
adhesion of an acrylic acid polymer and clogging with the polymer
were observed in 105 heat-transfer tubes approximating closely to
the outer periphery of the bundle of heat-transfer tubes in the
heat-exchanging part.
Example 2
[0064] Acrylic acid was cooled by following the procedure of
Example 1 while using a flat plate having the same diameter and
containing no opening in the place of the gas distributing plate.
Though the cooling could be continued till 40.degree. C. during the
initial stage of the operation, the temperature of the acrylic acid
ascended with the elapse of time. After one month of the operation,
the device was stopped at the time that the cooling temperature
subsequent to the condensation reached 55.degree. C. When the
interior of the heat exchanger was inspected, clogging with an
acrylic acid polymer was observed in 31 heat-transfer tubes
approximating closely to the center of the bundle of heat-transfer
tubes. The operation of the device never the less could be
continued for one month. Further, adhesion of about 3 kg of polymer
was observed on the rear sides of the gas distributing plate and
the distributing plate-supporting member. The vacuum generation
device was observed at this time to suffer an increase of load with
the elapse of time. The inspection of this device after the stop of
operation, however, failed to detect any polymer.
Example 3
[0065] Acrylic acid was cooled by following the procedure of
Example 1 while having the gas distributing plate disposed at a
position of 600 mm from the gas inlet. When the operation was
discontinued after two months and the interior of the heat
exchanger was inspected, clogging with an acrylic acid polymer was
observed in 8 heat-transfer tubes approximating closely to the
outer periphery of the bundle of heat-transfer tubes and in 3
heat-transfer tubes approximating closely to the center of the
bundle of heat-transfer tubes. The heat exchanger nevertheless
could be stably operated continuously for two months. At this time,
the vacuum generation device showed no sign of abnormality. The
amount of adhesion of the polymer to the gas distributing plate and
the supporting member was on a per with that in Example 1. It was
not so much as to affect the ability of the device to exchange
heat.
Example 4
[0066] Acrylic acid was cooled by following the procedure of
Example 1 while using a perforated plate having a diameter of 700
mm and containing a plurality of openings 12 mm in diameter at a
opening area ratio of 20%. When the heat exchanger was stopped
after two months' stable operation and the interior of the heat
exchanger was inspected, the heat-transfer tubes showed no sign of
clogging with an acrylic acid polymer. Adhesion of about 1 kg of a
polymer was observed in the outer peripheral part of the gas
distributing plate. At this time, the vacuum generation device
showed no sign of abnormality.
* * * * *