Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TS 8516
AN APPARATUS FOR COOLING SOLIDS LADEN HOT GASES
The present invention to an apparatus for cooling
solids laden hot gases.
A solids laden gas is, for example, synthesis gas
obtainable from a coal gasification process. The coal
gasification process is a well-known process for partial
oxidation of finely divided solid carbonaceous fuel
wherein an oxygen-containing gas, which is applied as an
oxidiser, and a finely divided solid carbonaceous fuel
are supplied to a gasification zone wherein substantially
autothermically under appropriate conditions of
temperature and pressure a gaseous stream containing
synthesis gas (which is substantially a gaseous mixture
of hydrogen and carbon monoxide) is produced. Further,
solid impurities such as fly ash particles are usually
present in the synthesis gas. Such particles may be
sticky. The oxygen-containing gas, which is applied as an
oxidiser, is usually air or (pure) oxygen or steam or a
mixture thereof.
The above partial oxidation reaction usually takes
place in a gasification reactor. In order to control the
temperature in the reactor a moderator gas (e.g. steam,
water or carbon dioxide or a combination thereof) can be
supplied to said reactor.
Those skilled in the art will know the conditions of
supplying oxidiser and moderator to the reactor.
Advantageously, the said carbonaceous fuel
(optionally with a moderator gas) and the said oxygen-
containing gas, applied as oxidiser (optionally with a
moderator gas) are supplied to the reactor via at least a
burner. The hot raw effluent gas stream leaving the
reactor, usually at or near its top, is optionally
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quenched and is usually cooled in an indirect heat
exchanger such as a convection cooler.
Conventionally, the raw gas stream is cooled off by
means of convective heat transfer surfaces arranged in a
gascooler located next to the gasification reactor and
connected through a duct to the said reactor.
The gases are solids laden and therefore problems may
arise with respect to erosion of the heat transfer
surfaces (when the gas velocity is too high) or with
respect to fouling/blocking the gas passages between the
heat transfer surfaces (when the gas velocity is too
low).
Generally, during cooling processes the gas velocity
will decrease when operating at a constant throughput and
pressure, to such an extent that fouling/blocking of the
equipment may occur (e.g. by sticky particles) and
expensive rapping devices are required to avoid
fouling/blocking.
Therefore, there is a need for coolers which
rely on a self-cleaning effect of the solids
laden gas, are fouling/blocking-free and erosion-free and
under normal operating conditions can be operated without
the use of (complicated) rapping equipment.
The invention therefore provides an apparatus with
reduced fouling and erosion for cooling a solids laden hot
gas, said apparatus comprising a vessel with a gas inlet
and a gas outlet and heat transfer structure comprising a
plurality of heat transfer surfaces extending in the vessel
between said inlet and said outlet in a longitudinal
direction and forming a plurality of gas passages in the
said structure, wherein the said plurality of heat transfer
surfaces is arranged in such a way that the overall
_ cross-sectional inlet area of the said gas passages in
the said structure is larger than the overall cross-
35 sectional outlet area between said gas passages and that
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the said gas passages are arranged in such a manner that,
in operation, the velocity of the gas flowing through the
said gas passages, is kept substantially constant between
the cross-sectional inlet area of the said gas passages
and the cross-sectional outlet area of the said gas
passages.
The invention will now be described in more detail by
way of example by reference to the accompanying drawings,
in which:
fig. 1 represents schematically a longitudinal
section of a gascooler of the invention;
figs. 2a and 2b represent schematically partial side
views of header arrangements applied in the gascooler of
fig. 1;
figs. 3a and 3b represent schematically cross-
sectional views of the heat transfer structure applied in
the gascooler along the lines I-I and II-II respectively
of fig. 1; and
fig. 4 represents a partial side view of an
advantageous embodiment of a detail of figs 3a and 3b.
Referring to fig. 1 a vessel 1, made of any material
suitable for the purpose, is shown. The vessel 1 has a
vessel wall la and is provided at its upstream side with
an inlet 2 for solids laden gas A from a reactor (not
shown for reasons of clarity) and at its downstream side
with an outlet 3 for cooled gas B which is supplied in
any suitable manner to any suitable further gas treating
and processing equipment (not shown for reasons of
clarity). Advantageously, the inlet 2 is located at or
near the top of vessel 1 and the outlet 3 is located at
or near the bottom of vessel 1.
Generally, the gascooler is substantially cylindrical
and arranged substantially vertically, but it will be
appreciated by those skilled in the art that any
arrangement suitable for the purpose can be applied. The
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cooler 1 is internally provided in any suitable manner
with a heat transfer structure comprising a plurality of
panels 4 of (convective) heat transfer surfaces arranged
in such a manner, that a plurality of gas passages 13
from said inlet to said outlet extending in downstream
direction is provided (i.e. in the direction of
decreasing process temperature). In particular, the
arrangement of the heat transfer surfaces is such that
the overall cross-sectional inlet area of the gas
passages 13 is larger than the overall cross-sectional
outlet area of the gas passages 13. For reasons of
clarity only nine panels 4 have been shown in fig. 1 but
it will be appreciated any number of panels suitable for
the purpose can be applied. The height of the heat
transfer structure is M, whereas the distances between
the outer heat transfer surfaces of said structure are Wi
(inlet) and W2 (outlet) respectively.
Advantageously, each panel 4 of heat transfer
surfaces arranged in the gas cooler comprises a plurality
of cooling tubes (not shown in fig. 1 for reasons of
clarity) in mutual mechanical connection by any suitable
means such as a webbing, through which tubes any suitable
cooling fluid flows (e.g. water or steam, advantageously
in counter current flow with the gas) and these panels
are designed such that the cross-sectional areas of the
passages between the heat transfer surfaces are in
tapering arrangement aiming at keeping the gas velocity
substantially constant, advantageously in the velocity
region of 6-12 m/s. Advantageously, the tubes are
provided with fins.
The overall cross-sectional area decrease of the gas
passages between the said heat transfer surfaces is such
that the gas flow A is smoothly directed to the said
surfaces and the gas flow impingement represented by the
arrow C on the heat transfer surfaces is at small angles
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g
a such that the gas flows substantially parallel to the
said surfaces from erosion point of view. The angle a is
defined as follows:
a = tan 4 (W1- W2)
M
An advantageous impact angle a of the gas flow is 2.5
degrees.
The gascooler is provided at its one end with a
plurality of inlet headers feeding the panels of cooling
tubes with any suitable cooling medium.
The gascooler is provided at its other end with a
plurality of outlet headers. For reasons of clarity the
inlet headers, outlet headers and the mechanical
connections of the tubes with said headers have not been
shown in fig. 1.
Each end of a cooling tube of a panel is connected to
an outlet header 6 and inlet header 5 respectively as
will be explained in more detail below referring to figs.
2a and 2b.
Further, in practice, the arrangement of the panels
and tubes is such that a so-called membrane pipe wall is
formed, the (ring-shaped) inlet of which and the (ring-
shaped) outlet of which have been represented
schematically in fig. 1 by reference numerals 8 and 9
respectively. The membrane pipe wall forms within the
vessel la a "cage" surrounding the said panels and will
be shown in more detail below by reference to figs. 3a
and 3b.
Fig. 2a represents a partial side view of the inlet
header arrangement applied in the gascooler of the
invention as shown in fig. 1. For reasons of clarity only
7 tubes have been shown. The inlet header 5 is in any
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suitable manner connected to each cooling tube 10 of a
panel 4. Reference numeral la represents the vessel wall.
The tubes 10 of the panel 4 are mechanically
connected via webbings l0a (e.g. by welding).
Further, the end or outer tube 10' of a panel 4 is
part of the "cage" formed by the membrane pipe wall and
is in fluid-connection to the inlet 8 (Fig. 1). The
membrane pipe wall tube is not connected to the inlet
header 5. It will be appreciated that where appropriate
the tubes of the membrane pipe wall are suitably bent to
provide space for the connecting tubes between the panel
4 and the inlet header 5.
Fig. 2b represents a partial side view of a similar
arrangement for an outlet header 6 applied in the
gascooler of the invention as shown in fig. 1. For
reasons of clarity only 7 tubes have been shown. The same
reference numerals as in fig. 2a have been used and where
appropriate the tubes of the membrane pipe wall are
suitably bent. The end or outer tube 10' is part of the
"cage" and is in fluid-connection to the outlet 9
(fig. 1).
Fig. 3a represents a cross-sectional view of the
arrangement of heat transfer surfaces along the line I-I
of fig. 1. In this case thirteen panels 4 have been
shown, each panel 4 comprising a plurality of cooling
tubes 10 and end or outer tubes 10'.
The tubes 10 of each panel are connected via webbings
10a.
The end or outer tubes 10' of each panel 4 are
connected to the end or outer tubes 10' of the adjacent
panel 4 via tubes 7. The outer tubes 7 and 10' form the
"cage" 11.
The tubes 7 (except two which are arranged in a
symmetry-plane of the arrangement) are diminishing in
diameter from top to bottom so that a tapering
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arrangement and a sloping position of the panels 4 at
both sides of a symmetry-plane are obtained. For reasons
of clarity, only a limited number of tubes 10 of each
panel 4 is represented.
Reference numeral 13 represents the gas passages
between the heat transfer surfaces.
The panel distance C1 at the inlet side of the panels
is larger than the panel distance at the outlet side (C2)
due to the arrangement of tapering tubes 7 arranged
between the outer tubes 10' of each panel 4.
Thus, the cage overall dimensions are V x W1 (inlet)
and V x W2 (outlet) wherein W1 > W2 and V remaining
constant.
Fig. 3b represents a top view of the outlet header
arrangement of fig. 1. The same reference numerals have
been used as in previous figures.
Fig. 4 represents an advantageous embodiment
(partially represented) of a tapering tube 7 of the
"cage", arranged between the outer tubes 10' of each
panel 4 (vide figs. 3a and 3b). Z represents a tapered
webbing.
The diameter of the tube 7 decreases gradually from
inlet end to outlet end with a suitable tapering angle (3
(e.g. 2.5 ) for the plurality of tapered parts of the
said tube. In an advantageous embodiment of the invention
the diameter of the tube is gradually decreasing in
downflow direction from 60 to 30 mm and the length M is
25-35 m.
It will be appreciated by those skilled in the art
that any number of headers suitable for the purpose can
be applied. E.g. two headers per panel of tubes can be
used.
It will also be appreciated by those skilled in the
art that the invention is not restricted to counter
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current flow of the cooling fluid with the process gas.
Advantageously, co-current flow can be applied.
In an advantageous embodiment of the invention the
webbings between the tubes are provided with openings.
More advantageously, the webbings are 25-90% open.
Various modifications of the present invention will
become apparent to those skilled in the art from the
foregoing description. Such modifications are intended to
fall within the scope of the appended claims.
