Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HEAT EXCHANGER
The present invention relates to a heat exchanger.
More specifically, the present invention relates to a
heat exchanger for the rapid cooling of high temperature
gas.
Even more specifically, the present invention relates
to a heat exchanger for the cooling of synthesis gas (syn-
gas) coming from the catalytic partial oxidation of light
hydrocarbons, for example methane, known as Catalytic Par-
tial Oxidation (CPO).
It is known that the preparation of syngas, a gaseous
blend containing H2 and CO in various proportions, can be
effected by the catalytic partial oxidation of natural gas,
methane or gaseous/liquid hydrocarbon mixtures, from refin-
ery or petrochemical facilities, in fixed bed tubular reac-
tors which can operate, depending on the catalyst used, at
a pressure ranging from 1 to 150 atm and temperatures
higher than 500 C, which, in some cases, can reach and ex-
ceed 1,000 C.
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The rapid cooling of syngas at the outlet of the reac-
tion unit is a necessity not to be neglected, as if this
gas is maintained at those temperatures, even for short pe-
riods of time, it can give undesired by-products, such as
alcohols or olefins (substantially ethylene and propylene)
or even regenerate the starting methane. Systems for rap-
idly cooling a gas which is at a high temperature, are men-
tioned in literature, for example in the patents US
2,896,927 and US 4,377,132. Some methods and relevant equipment include the
direct cooling of gas by means of water (quenching). This solution however has
the drawback of having to separate the cooled syngas from the aqueous vapour
formed.
Other industrial systems consist of equipment for in-
direct cooling, which allow the recovery of heat contained
in syngas, for the production of high pressure steam.
The object of the present invention relates to a de-
vice for the effective and rapid indirect cooling of syngas
in applications in which the thermal recovery of the sensi-
ble heat of the gas is not required, for engineering sim-
plicity or for economical reasons. For example in the pro-
duction of hydrogen in medium- small-scale systems.
The Applicants have therefore found a heat exchanger,
particularly suitable for the rapid cooling of gases which
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are at a temperature higher than 500 C, for example between
750 and 1100 C, and which allows to avoid any contact be-
tween the hot gas and the cooling liquid, normally water.
The object of the present invention therefore relates
to a heat exchanger for the rapid cooling of a gas at high
temperature, leaving a reaction unit/device, which com-
prises a coupling element to the reaction unit/device, a
gas cooling and transportation pipe and a covering shell,
in which:
a) the coupling element, substantially cylindrical, is situated between the
reaction
unit and the covering shell, it is internally cooled by means of a cooling
fluid, and
is axially connected, by means of a pass-through duct, to a feeding line of
hot
gas coming from the reaction unit;
b) the gas cooling and transportation pipe is fixed to the base of the
coupling
element, connected to the reaction unit, at the pass-through duct, said gas
cooling and transportation pipe consisting of two sections:
- a first section, substantially linear, is inserted in a coaxial position
into a second
pipe having a larger diameter which jackets it, so as to form an annular
hollow
space in which the cooling fluid, flows, an end of said first section forming
the
pass-through duct of the coupling element;
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,
- a second section, fixed in a continuous manner to the first section, at the
other
end, substantially curved in a semicircle, spirally envelopes, without
touching it,
at least part of said first section;
c) the covering shell is substantially cylindrical, closed at one end and open
at the
other end, connected to said coupling element and comprises at least one
opening for discharging the cooling fluid and the cooled gas.
According to the present invention, the coupling ele-
ment is axially crossed by the pass-through duct, connected
to the reaction device, for example a CPO reactor for the
production of syngas at a temperature ranging from 500 to
1100 C.
The external pipe which covers the first section of
the transportation pipe of the hot gas is connected, at one
end, to one or more specific feeding ducts of the cooling
liquid, which pass through the coupling element. The cou-
pling element, moreover, is independently cooled by means
of a duct which feeds the cooling liquid in correspondence
with its axis. Said fluid is discharged from the element,
after following a spiral path from the inside outwards, by
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means of an opening connected to the side surface of the
element itself.
In an alternative embodiment of the present invention,
the cooling fluid circulating inside the coupling element
(for independent cooling) can be discharged inside the vol-
ume contained in the shell of the exchanger.
The other end of the second pipe, which covers the
first section, is free and ends with the curved section,
substantially in a semicircle, so that the cooling liquid
can debouch freely, but in the opposite direction, into the
closed space of the shell, after flowing in the jacket be-
tween the two pipes.
The path of the liquid inside the shell volume is
guided by baffles, orthogonal to the axis, which also act
as a support for both sections of the gas transportation
pipe.
The second section of the transportation and cooling
pipe is substantially continuous to the first one, without
interruption, and develops in a spiral. In order to save
space, the spirals preferably envelop, without touching it,
the first section of the covered pipe. It is possible how-
ever for the spirals to develop downstream of the first
section.
The other end of the transportation pipe, i.e. the end
of the spiral section, is connected to an opening present
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on the shell for the discharge of the cooled gas outside
the heat exchanger, object of the present invention.
The shell has a substantially cylindrical form with
the diameter of the base substantially identical to that of
the coupling element and larger than the diameter of the
spirals. In this way, the shell includes in its inner space
the pipe system of the first and second section. The space
of the shell is filled with the cooling fluid, which is
discharged by the exchanger through a proper discharge
opening. In an alternative embodiment of the present inven-
tion, the circulating liquid, destined for the cooling of
the coupling element, also converges into the shell space.
The total liquid is discharged from the exchanger, object
of the present invention, through the proper opening situ-
ated on the shell. In any case, whether operating with the
first or second alternative embodiment, the pipe system of
the first and second section is completely immersed in the
cooling liquid.
The heat exchanger object of the present invention can
be better understood by referring to the schemes of the en-
closed figures which represent an illustrative but non-
limiting, embodiment, and wherein:
Figure 1 represents a longitudinal, flat sectional
view of the overall exchanger;
Figure 2 represents a front flat view of the scheme of
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Figure 1, produced according to the section ZZ.
With reference to the figures, the heat exchanger, ob-
ject of the present invention, comprises the coupling ele-
ment A, the pipe system for the gas transportation and
cooling B and the shell C.
The coupling element A also includes the ducts 1 and 2
for the feeding of the cooling fluid (water), which con-
verge into the coaxial duct 7, and the cooling duct 4, for
the independent cooling of the coupling element, which
feeds the water to the center of the spiral 4', from which
it exits through 5.
The gas transportation and cooling pipe system B com-
prises the first pipe section 6, the coaxial pipe which
jackets it 7 and the second section of the spiral pipe 8.
The first section of the pipe 6 includes, in turn, the
first end 3, coinciding with the axial pass-through duct of
the element A, and the second curvilinear end 3'. The coax-
ial pipe 7 jackets the first section starting from the end
3 until the curved end 3'. At this end (3') the coaxial
pipe is not closed, to allow the water to be discharged in-
side the shell, as will be described further on.
The shell C includes the discharge opening 9 of the
cooled gas, the discharge opening 10 of the water and the
supporting baffles 11 of the two sections of the gas trans-
portation pipe.
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The operation of the heat exchanger, object of the
present invention, will appear evident on the basis of the
drawings and what is described above. In particular, the
hot gas 12, leaving the reaction unit (not shown), is in-
troduced into the heat exchanger by means of the pass-
through duct 3 of the coupling element A. The gas flows
into the first section 6 of the cooling and transportation
pipe B and subsequently into the second section 8, to be
then discharged at a low temperature through the discharge
opening of the gas 9. As the gas flows through the first
section 6, it undergoes a first rapid cooling by means of
the water, fed through 1 and 2, which circulates inside the
annular hollow space between the pipes 6 and 7, up to the
end 3'. Here, the water flows freely in the closed space of
the shell, filling it, it further cools the gas flowing
through the section 8 of the cooling pipe and is discharged
from the opening 10.
During operation, in order to prevent overheating of
the coupling element, the latter is cooled by means of the
specific system consisting of the duct 4, which feeds water
to the system 4' developping in a spiral, and of the dis-
charge duct 5.
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