Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a device for the heat exchange
between a recycle gas leaving an NH3 converter and water, the
device having recycle gas-charged heat exchanger tubes which have
a gastight connection to at least one tubesheet separating a
pressure-resistant channel from a heat exchange chamber, the tube-
sheet being additionally provided with cooling bores for a stream
of water or of a water/steam mixture.
Such a device is, for instance, known from the
applicant's European patent application 0 130 361. The tubesheet
described there is arranged substantially horizontally and provided
at least sectionally with cooling bores which are closed towards
the hot side and which are provided with an additional inner tube
so that the heat exchanger water is sucked into the tube by natural
flow, the water vaporizes in the cooling bores, and the water/steam
mixture formed flows back to the heat exchanger.
Although this method of cooling thick-walled structural
elements which are hot at least on one side offers special advan-
tages, at least one disadvantage ensues from the fact that, in
this case, the natural flow requires the structural elements to be
arranged in a substantially horizontal position so as to allow the
cooling water to enter the cooling bores with a safe recycle
quantity, to vaporize, and to leave in form of a water/steam
mixture
: The object of the present invention is to provide for
a solution which allows cooling to be safely maintained even for
an arrangement of the tubesheets other than horizontal, i.e.
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cooling should be effective independently of the position of
installation of the tubesheet.
The invention provides apparatus for heat exchange
between a recycle gas leaving an NH3-converter and water,
comprising heat exchanger tubes through which the recycle gas
flows and which are gas-tightly connected to at least one tube
plate separating a pressure-resistant pre-chamber and a heat
exchanger chamber, wherein the pre-chamber has at least one bell
for supplying the recycle gas and a collecting chamber surrounding
the bell for carrying away the cooled recycle gas, characterized
in that the tube plate is additionally provided with cooling bores
through which flows a water/steam mixture and which do not
completely pass through the tube plate from the heat exchanger
side and which communicate in their base regions by way of feed
bores with a water supply through which the supplied water is fed
into the heat exchanger chamber by way of the cooling bores, and
that the supply conduit to the externally cooled bell is arranged
in the associated outlet connection of the pre-chamber and the
remaining annular space in the outlet connection has cooled
recycle gas flowing therethrough.
This invention makes use of the cooling bores
representing the state of the art but abandons the natural flow of
the cooling water. In addition, feed bores have been provided for
supplying cooling water to the base area of the cooling bores. A
natural flow may, of course, also be applied for this purpose, but
it is expedient to use conveying means.
On principle, quite a series of different designs of
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such heat exchangers are known, as shown, for instance, in DE-OS
20 07 528 or 30 22 480. In these cases, too, a relief of the hot
tubesheet has been realized by a particular synthesis gas routing.
The cooling hores provided in the present invention
should, in any case be distributed uniformly over at least the hot
2a
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area of the tubesheet. Depending upon the design, it may, in
certain cases, be sufficient to cool only particularly hot zones.
Thus an embodiment of the invention provides for the tubesheet
being equipped but sectionally with cooling bores connected via
feed bores to the cooling water supply line.
It may also be expedient to design the cooling water
supply line as branch from the feedwater supply line, i.e. part of
the feedwater the heat exchanger is charged with is introduced
directly through the cooling bores.
Instead of the direct connection between the feedwater
supply line and the cooling water supply line, the latter may be
connected to the water cycle of the steam generator, which is, of
course, not excluded due to the measure mentioned before.
According to a special embodiment of the invention,
the channel is of the split type having at least two recycle gas
intake bells for different NH3 converter outlet gases as well as
the pertaining collecting chambers for the cooled recycle gases.
This measure conditions a particularly compact structural concept.
A stepwise cooling of one and the same recycle gas at different
temperature stages can also take place in a common housing.
In a further embodiment of the invention at least one
of the feed lines for the bells cooled from the outside is arranged
in the associated outlet nozzle, the design providing for a cooled
recycle gas flow through the annular space. This also contributes
to a relief of the structural elements, in particular to cooling
the inlet nozzles of the device.
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As already mentioned, there exist quite different heat
exchanger designs. The heat exchangers may be arranged in vertical,
horizontal, or inclined position. They may be equipped with one
tubesheet only and the recycle gas-bearing tubes may be designed
as long U-shaped tube coils, i.e. tubes that start in the tubesheet
and also end there, however, in another segment. The invention is,
however, not limited to this design. Thus the device mightbe
equipped with two tubesheets and with two channels, the invention
providing in such a case that the second channel, too, is split
into two deflection chambers for two different NH3 converter outlet
gases and that at least one of the tubesheets is equipped with
cooling bores. Pursuant to a further embodiment of the invention,
cooling bores are incorporated at least sectionally in both tube-
sheets.
The invention is described in more detail in the
following, with reference to the attached drawings, wherein:-
Figure 1 is a longitudinal sectional view of a device
for heat exchange, with cooled tubesheet;
Figure 2 shows a further embodiment with two tubesheets,
at least one of which is cooled;
Figure 3 shows a further embodiment of the design as
per Figure 2;
Figure 4 shows a heat exchanger with tubes in opposed
direction and with channels and deflection chambers, each of the
two tubesheets being cooled at least sectionally;
Figure 5 shows a further embodiment of a heat exchanger
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with two tubesheets which are cooled at least sectionally;
Figures 1 to 5 are sectional drawings reflecting the principle of
the device;
Figure 6 is a cross section of a channel of one embodi-
ment;
Figure 7 is the same representation of a channel of
another embodiment;
Figure 8 shows the arrangement of bores and cooling
bores in the tubesheet for an embodiment as in Figure 6;
Figure 9 shows the bores in a tubesheet for an embodi-
ment as in Figure 7.
Initially it is pointed out that in all figures the same
reference numbers have been used for parts which are identical or
similar in function. In some cases variations have been marked by
small letters.
The heat exchange device illustrated consists of a
pressure-resistant casing 2 with two chambers, viz. a heat exchange
chamber 3 and a channel 5 split by a partition wall into the two
channel sections 5a and 5b. The channel 5 and the heat exchange
chamber 3 are separated by a tubesheet 6.
The special feature of the embodiment represented in the
figures is that two heat exchangers are accommodated in housing
2, which requires the channel 5 to be split by a partition wall 4.
It must be noted that the invention is, however, not limited to
such an embodiment. The essential feature is the design of the
tubesheet which is referred to below in more detail. First the
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basic design of the device 1 is described.
The channel sections 5a and 5b are equipped with nozzles
7a and 7b represented only schematically which, in turn, are
provided with an inner inlet tube 8a and 8b being arranged central-
ly in the nozzle 7a and 7b so that an annular space 9a and 9b is
produced. The inlet tube nozzles 8a and 8b lead to the hot gas
chambers or bells lOa and lOb which charge the tubesheet 6 section-
ally. The heat exchanger tubes lla and llb are U-shaped in the
embodiment of Figure 1, i.e. their arrangement in the heat exchange
chamber 3 is such that they start from the tubesheet, describe a
bow at the upper end and then return to the tubesheet 6. The
cooled gases flow back to the channel sections 5a and 5b and are
discharged via the annular space 9a and 9b. It is thus possible
to keep the tube nozzles 7a and 7b at the same low temperature as
the walls of channel 5.
The design of the channels as well as of the gas routing
permits, of course, a plurality of modifications. Some variations
to which the invention is, however, not limited are described
below in more detail. The essential design features of the follow-
ing embodiments are identical.
Particularly important for the invention is the design
of the tubesheet 6. As can be seen from the representation, the
tubesheet is provided with a series of cooling bores 12 which are
open towards the side wall of the heat exchange chamber 3. These
bores do not penetrate the tubesheet 6 completely and are inter-
connected in their base area via feed bores 13. The feed bores 13
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are connected at the outside to a water supply line 14 which, by
way of example, surrounds the device 1 as a semi-circular cooling
ring 15.
The heat exchange fluid, e.g. water, for producing
steam or a water/steam mixture is introduced via a feed nozzle 16
of the heat exchange chamber 3 and the heated or vaporized fluid
or a mixture of both leaves the heat exchange chamber 3 via a
nozzle 17.
It is crucial for the invention that the fluid cooling
the tubesheet 6 is the same as the heat exchange fluid that enters
the heat exchange chamber 3 via nozzle 16 since these fluids mix
directly as desired, the water entering via water supply line 14
being fed directly to the heat exchange chamber 3 via the cooling
bores 12.
The embodiment of Figure 2 shows essentially the same
design of device 1. The difference is that two tubesheets 6 and
18 have been provided, with two channels 5a and 5b and two deflec-
tion chambers l9a and l9b.
Figure 3 shows a further embodiment with two tubesheets
6 and 18. However, the fluid to be cooled is led without deflec-
tion through the heat exchange chamber 3. In this case the channel
nozzles 7a and 7b are cooled separately by means of a cooling agent
entering via the tube nozzles 20a and 20b. The cooling agent may,
of course, be the process gas leaving the chambers 21a and 21b via
the tube nozzles 22a and 22b, or any other fluid.
Whereas in the embodiments as per Figure 2 and 3 only
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one of the two tubesheets 6 and 18 is cooled (namely tubesheet 6),
Figure 4 shows a further embodiment with two tubesheets cooled at
least sectionally. Therefore, both tubesheets are given the
reference number 6a. In this case the two heat exchangers are
charged with a counter-current flow in a common housing. Each of
the channels Sa and 5b has its own deflection chamber l9a and l9b.
Due to the special tubesheet cooling, two water supply lines 14a
and 14b have been provided.
Figure 5 shows a further embodiment of a heat exchanger
in the hozizontal position. The other embodiments are, of course,
also suitable for the horizontal position; this is not decisive
for the invention.
According to the design as per Figure 5, the channels
and deflection chambers are not of the split-type. The two gas
streams charging the heat exchange chamber 3 in counter-counter
enter via the two hot gas inlet nozzles 8c and 8d and pass through
the chambers lOc and lOd before reaching the heat exchanger tubes
in the tubesheets 6b. The tubesheets 6b are cooled with water at
least sectionally.
If the fluid is e.g. a hot recycle gas fed to the cham-
ber lOc via tube nozzle 8c, a bypass line 23 extending through the
entire heat exchanger and equipped with control facilities, if
required, may additionally be provided for securing a flow through
the annular space 24 around the tube nozzle 8d. This annular space
24 is cooled at its outside by the cooled process fluid traversing
a surrounding annular space 25.
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Figure 6 is a cross-sectional view of a channel 5 follow-
ing nearly line VI-VI marked in Figure 1. The pertinent distribu-
tion of the bores in tubesheet 6 is given in Figure 8. It is
evident that the feed bores 13 must be relatively long to reach
even the cooling bores 12 arranged centrally.
A further embodiment is shown in Figures 7 and 9. In
this case the chambers 10a and 10b are arranged relatively close
to the tubesheet periphery so that only short feed bores 13a
(Figure 9) have to be provided. This may facilitate fabrication
and save costs.
The embodiments of the invention described before by way
of example permit, of course, a plurality of modifications without
departing from the basic idea of the invention. As already men-
tioned, the invention is not necessarily limited to a cooling with
water. Other fluids may be used as well. Variations as regards
the cooling bores etc. are also feasible.
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