Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
STEAM GENERATING HEAT EXCHANGER
BACKGROUND OF THE INVENTION
The present inventîon relates to a method and an apparatus
for cooling a high pressure, hot gas laden with ash particles, and
more particularly to a heat èxchanger design for recovering heat
from the high pressure combustible product gas produced in a
pressurized coal gasifier and utilizing said heat to produce
superheated steam.
A number oF coal gasification schemes have been developed
in the past few years which produce a combustible product gas wh;ch
can be upgraded to pipeline quality to supplement our nation's
natural gas resources. The chemical reactions occurring in these
gasification processes typically occur at temperatures ranging From
1350 to 1650 C. Further, pressures in the range of 1,7 to 10
megapascals are required in order to satisFy system requirements.
Other gas cleaning and processing steps are required subsequent to
the gasification reaction to produce a product gas suitable for
pipeline transmission. Prior to these gas cleaning and processing
steps, it is necessary to cool the product gas leaving the gasifica-
tion chamber from a temperature as high as 1650 ~ to a much lowergas handling temperature typically on the order of 200 to 350 C.
A major problem associated with cooling the product gas
leaving the gasification chamber is the high concentration of molten
ash in the product gas. The reduced gas volume associated with the
high gas pressure results in extremely high ash loadings. Typical
ash loadings encountered in pressurized gasiFier heat exchange
sections exceed 2500 kilograms ash per hour per square meter of
~low area as compared to typical ash loadings oF 50 to 250 kilograms
,.~
ash per hour per square meter of flow area in convent~onal coal-
fired power plant heat exchanger sections. Therefore, precautions
must be taken to avoid plugging o~ the heat exchanger with
accumulated ash deposits which would adversely affect the heat
transfer and pressure drop through the hea$ exchange section.
SUMMARY OF THE INVENTION
The steam generating heat exchanger of the present
invention comprises an inverted U-shaped pressure containment
structure having various heat exchange means disposed therein, said
pressure containment structure comprising a first pressure contain-
ment vessel, a second pressure containment vessel, and a pressure
containment pipe connecting the second pressure containment vessel
to the first pressure containment vessel.
The first pressure containment vessel comprises a
vertically elongated cylinder having a gas inlet at the bottom
thereof and a gas outlet at the top thereof. A radiant cooling
chamber formed of a plurality of vertically extending steam
generating heat exchange tubes is disposed within the first pressure
containment vessel and establishes a gas pass extending therethrough
Hot gases from the reaction chamber flow vertically upward through
the radiation chamber disposed within the first pressure containment
vessel with a major portion of the molten ash particles entrained in
the hot gases entering the radiation chamber depos~ting upon the
walls of the radiation chamber. The hot gases are cooled to a
temperature low enough to insure that any ash still entrained within
the cool product gas leaviny the radiation chamber is dry particulate
ash.
The second pressure containment vessel comprises a
vertically elongated cylinder having a gas inlet at the top thereof
and a gas outlet at the botto~ thereof. A convective cooling chamber
formed of a plurality of vertically extending steam generating heat
exchange tubes is disposed within the second pressure containment
vessel and establishes a vertical gas pass extending therethrough.
A plurality of heat exchange tube bundles are disposed within the
vertical gas pass formed by the convective cooling chamber to heat
and evaporate water.
~2
-- 3 --
The cooled gases leaving the rad;ant coo11ng chamber of
the first pressure containment vessel are conveyed to the in1et
of the convective cooling chamber through a conductor duct disposed
within the pressure containment pipe join;ng the first and second
pressure containment vessels. The gases are further cooled as they
flow vertically downward over various heat exchange tube bundles
disposed within the convective cooling chamber such that the gases
leave the second pressure containment vessel at a temperature of
200 to 350 C.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a sectional side elevational view of a steam
generating heat exchanger designed in accordance with the present
invention;
Figure 2 is a sectional plan view taken along line 2-2 of
Figure l;
Figure 3 is a sectional plan view taken along l;ne 3-3
of Figure l;
Figure 4 is a sectional plan view taken along line 4-4 of
Figure 1; and
Figure 5 is a cross-sectional view taken along line 5-5
of Figure 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Re~erring now to the drawings and more particularly to
Figure 1 thereof, there is depicted a steam generating heat exchanger
2 designed in accordance with the present invention, The steam
generating heat exchanger 2 comprises an inverted U~shaped pressure
containment structure having various heat exchange means disposed
therein. The pressure containment structure of the stea~ generating
heat exchanger 2 comprises a first vertically elongated cylindrical
pressure containment vessel 4 having a gas inlet 3 at the bottom
thereof and a gas outlet 5 at the top thereof, a second vertically
elongated cylindrical pressure containment vessel 6 having a gas
inlet 7 at the top thereof and a gas outlet 9 at the bottom thereof,
and a pressure containment pipe 8 connecting the gas inlet 7 of the
-- 4 --
second pressure containment vessel 6 to the gas outlet 5 of the
first pressure containment vessel 4.
High pressure, hot product gas laden with molten ash
passes from a reaction chamber wherein it ;s produced, such as a
pressurized coal gasifier, to the steam generating heat exchanger
2 to be cooled therein prior to subsequent gas c1eaning and
processing operations conducted downstream of the heat exchanger.
Such a gas would typically be passed to the steam generating heat
exchanger 2 at a pressure of 15 to 105 kilogra~s per square
centimeter and at a temperature of 1350 to 1650 C. The hot gas from
the reaction chamber, not shown, passes into the steam generating
heat exchanger 2 through refractory lined inlet tee 10. The hot gas
from the reaction chamber enters inlet tee 10 horizontally and turns
90 degrees passing vertically upward out of the inlet tee 10 into gas
inlet 3 of the ~irst pressure containment vessel 4. It is estimated
that 25 to 50 percent of the molten ash particles entrained in the
hot gas entering inlet tee 4 will precipitate out of the gas stream
as the gas stream turns upward to enter vesse1 4. This ash will drop
vertically downward out of the inlet tee for collection in slag/ash
hopper (not shown) disposed directly beneath and secured to inlet
tee 10.
Housed within the interior of the ~irst pressure containment
vessel 4 is a radiant cooling chamber 12 formed of a plurality of
steam generating heat exchange tubes 14 arranged side-by-side to form
a waterwall extendin~ generally vertically upward ~rom one or more
radiant waterwall inlet headers 16 disposed in the lower portion of
the first pressure containment vessel 4 at a location near the gas
inlet 3 to one or more radiant waterwall outlet headers 18 disposed
in the uppermost region of vessel 4, so as to establish a gas pass
extending therethrough from the gas inlet 3 to the gas outlet 5 of
the vessel 4. The hot product gas must traverse radiant cooling
chamber 14 as it passes through the first pressure containment vessel
. The gas inlet 3 is lined with helical heat exchange tube coils
17 through which cooling water is circulated to cool that portion of
vessel 4 surrounding the gas inlet 3. Tube coils 17 also serve as a
gas barrier to prevent the hot gas entering vessel 4 from contacting
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the radiant waterwall inlet headers 16. Alternatively, the gas inlet
3 may be lined with refractory brick rather than heat exchange coi1s.
In the preferred embodiment of the invention, as illustrated
in F;~ures 2 and 3, the steam generat;ng heat exchange tubes 14 turn
upwardly and outwardly from the radiant waterwall inlet header 16 to
the interior wall of the first pressure containment vessel 4, thence
extend vertically upward lining the interior of the vessel 4, and
thence bend inwardly and upwardly in the upper portion of vessel 4
before extending vertically upward again to the radiant waterwall
outlet header 18 in the form of a rectilinear outlet duct 13 having
sidewalls formed of heat exchange tubes 14C, a front wall formed of
heat exchange tubes 14A, and a rear wall formed of heat exchange tubes
14S. Heat exchange tubes 14A which form the front-wall of the outlet
duct 13 bend to extend horizontally across the top of outlet duct 13
to form the roof thereof.
The hot product gas passing through radiation chamber 12 is
cooled to a temperature sufficiently below the initial deformation
temperature of the entrained ash particles to insure that only dry
ash particles remain in the cooled product gas leaving chamber 12.
Preferably, the temperature of the cooled gas flowing from radiant
cooling chamber 12 into outlet duct 13 is approximately 980 C.
If superheated steam is desired, a superheater tube bundle
20 may be disposed in outlet duct 13 immediately above the radiant
cooling chamber 12 as shown in the preferred embodiment illustrated
in Figure 1. Superheater tube bundle 20 typically comprises a
plurality oP horizontal tube rows disposed in vertical planes parallel
to the sidewalls of outlet duct 13 and spaced across the width thereof
at sufficiently wide intervals to insure that the free area between
neighboring tube rows is not bridged by deposits of ash particles
precipitating from the cooled product gas leaving the radlant cooling
chamber 12. Each of the tubes formin~ the superheater tube bundle
20 is connected at its inlet end to superheater inlet header 22 and
at its outlet end to superheater outlet header 24, both headers being
located out of the gas stream in the void space between the inner
surface of vessel 4 and the waterwall defined by heat exchange tubes
14. If required, soot blowers may be incorporated into radiation
chamber 12 and outlet duct 13 to provide a means for cleaning ash
deposits from the walls thereof and from the superheater surface
disposed therein.
The cooled gas leaving the radiant cooling chamber 12
passes through outlet duct 13 into gas pass 15 of connector duct 26.
Connector duct 26 is formed of a plurality of heat exchan~e tubes
disposed side-by-side to form a gas pass extending from an opening
in the sidewall of outlet duct 13 through the gas outlet 5 of the
first pressure containment vessel 4, thence through the pressure
containment pipe 8, and thence through the gas inlet 7 of the second
pressure containment vessel 6.
Housed within the second pressure containment vessel 6 is
a convective cooling chamber 30 formed of a plurality of vertically
extending steam generating heat exchange tubes 28 disposed side-by-
side within the vessel 6 so as to establish a gas pass extending
therethrough froln the gas inlet 7 ~o the ~as outlet 9 thereof. An
opening is provided in the upper portion of the convective cooling
chamber to mate with connecting duct 26 so as to receive the cooled
product gas leaving the first vessel 4 through gas pass 15.
The heat exchange tubes 28 forming the convective cooling
20 chamber 30 extend vertically from one or more convective cooling
chamber waterwall inlet headers 32 disposed in the bottom portion of
vessel 6 at an elevation near the gas outlet 9 of vessel 6 upward to
one or more convective cooling chamber waterwall outlet headers 34
disposed in the uppermost portion of vessel 6. At least one convec-
tive heat exchanger, such as an economizer or evaporator, is disposedwithin the convective cooling chamber 30 such that the ash and gas
passing therethrough must traverse the heat exchanger thereby pro-
viding for the further cooling of the product gas.
In the preferred embodiment of the present Invention, the
convective cooling chamber 30 is of rectilinear cross section, as
shown in Figure 4, having a front wall formed of heat exchange tubes
28A, a rearwall formed of heat exchange tubes 28B, and sidewalls
formed of heat exchange tubes 28C. Heat exchange tubes 28B which
form the rearwall of convective cooling chamber 30 are bent to
extend horizontally across the top of the convective cooling chamber
to form the roof thereof.
As illustrated in Figure 1, disposed within the convective
cooling chamber 30 are heat exchangers 36 and 38 comprising an
economizer and an evaporator, respectively. Economzier 36, preferably
disposed in the lower portion of the convective cool;ng chamber 30,
comprises a plurality of vertically arrayed tube banks of horizontal
tube rows connected between an economizer inlet header 40 disposed
beneath economizer 36 and an economizer outlet header 42 disposed in
the upper portion of vessel 6. Evaporator 38, preferably disposed in
the upper portion of the convective cooling chamber 30, comprises a
plurality of vertically arrayed tube banks of horizontal tube rows
connected between an evaporator inlet header 44 and an evaporator
outlet header 46.
In the preferred embodiment of the present invention, the
connector duct 26, which provides a gas pass for conveying the gases
from the outlet duct 13 of the radiant cool;ng chamber 12 of the
first pressure containment vessel 4 to the convective cooling chamber
30 of the second pressure containment vessel 6, is formed of heat
exchange tubes 14 and 28 as shown in Figure 5. More specifically, a
- portion of the heat exchange tubes 14A which form tne front wall and
roof of the outlet duct 13 of radiant cooling chamber 12 extend
through containment pipe 8 to the convective csoling chamber waterwall
outlet header 34 thereby forming the roof of the connector duct 26.
Additionally, a portion of the heat exchange tubes 14B which form the
rearwall of the outlet duct 13 of the radiant cooling chamber 12 are
turned to extend horizontally through containment pipe 8 to the
convective cooling chamber 30 thereby forming the floor of connector
duct 26. The sidewalls of connector duct 26 are similarly formed by
bending a portion of the heat exchange tubes 28A which form the front
wall of the convective cooling chamber 30 to extend horizontally out
of the gas inlet 7 of the second pressure containment vessel 6 and
through containment pipe 8 ;nto the outlet duct 13 within the first
pressure containment vessel 4.
The cooled reaction gases leaving the outlet duct 13 of
the radiant cool;ng chamber 12 are further cooled to a tempera~ure
preferably in the range of 200 to 350 C as they pasC through the
water-cooled connector duct 26 and flow vertically downward through
the convective cooling chamber 30 traversing heat exchanger 36 and
38 d;sposed therein. As the vertically downward ~lowing product
gases leave the convective cooling chamber 30, they turn within the
bottom of the second pressure containment vessel 6 through a U-shaped
path to leave vessel 6 horizontally through the gas outlet 9 thereof.
As the gases turn at the bottom of vessel 6, much of the dry ash
particles still entrained therein precipitate out and collect in an
ash hopper, not shown, disposed therebeneath. If required, soot
blowers may be incorporated into chamber 30 to provide a means for
cleaning ash deposits from the walls thereof and from the heat
exchange tube bundles disposed therein.
It should be noted at this point, that the walls forming
the radiant cooling chamber 12, the connector duct gas pass 15, and
the convective cooling chamber 30 need not be designed to withstand
the high pressure of the product gas. A portion of the cool prodwct
gases leaving the convective cooling chamber 30 turn in the bottom
of vessel 6 and enter the void space 70 through the open gap between
the outer surface of chamber 30 and the inner surface of vessel 6.
These cooled gases eventually fill the entirety of void space 70,
thereby eliminating any pressure differential across the walls forming
the radiant cooling chamber 12, the connector duct gas pass 15~ or
the convective cooling chamber 30. If desired, a purge system, using
a noncorrosive gas such as nitrogen or carbon dioxide, is provided
for purging the void space 70 of any product gases when the heat
exchanger is taken out of service.
In the steam generator of the present invention, feedwater
is supplied to the economizer inlet header 40 through feedwater supply
lines 50 and heated as it circulates through economizer 36 in heat
exchange relationship with the product gases flowing through the
convective cooling chamber 30. The heated water leaving the economizer
30 is collected in economizer outlet header 42 and fed therefrom to a
water and steam drum (not shown) located outside of and above the
pressure containment structure of heat exchanger 2 through economizer
link 52 which penetrates the wall of vessel 6.
Saturated or slightly subcooled water flows from the water
and steam drum through downcomers (not shown) for distribution to the
steam generating circuit of heat exchanger 2. A portion of the
downcomer water ;s supplied to the radiant waterwall inle-t header 16
:~ t
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through feedline 54. The water then flows upwardly throuyh steam
generating heat exchange tubes 14 forming the radiant cooling chamber
12 and the outlet duct 13 thereto. A water and skeam mixture is
generated w;th;n tubes 14 as water vaporizes upon absorbing heat
radiated by the hot product gases passing through the radiant cooling
chamber 12. The steam and water mixture 1eaving tubes 14 is col1ected
in the radiant waterwall outlet header 18 and returned to the steam
and water drum through riser pipe 56 which penetrates the wall of
vessel 4. Similarly, the st~am and water mixture flowing through
that portion of heat exchange tubes 14A which form the roof of the
outlet duct 13 and the connector duct 26, and the steam and water
mixture flowing through that portion of heat exchange tubes 14B which
form the flow of connector duct 26 are collectcd in the convective
cooling chamber waterwall outlet header 34 and passed to the steam
and water drum through riser pipe 58 which penetrates the wall of
vessel 6.
Simultaneously with the circulation of water through tubes
14 of the radiant cooling chamber 12, another portion of the down-
comer water is supplied to the convective cooling chamber waterwall
inlet header 32 through feedlines 60. The water th~n flows upwardly
through steam generating tubes 28 ~orming the convective cooling
chamber 30. A steam and water mixture is generated within tubes 28
as the water absorbs heat from the product gases flowing through the
convective cooling chamber 30. The steam and water mixture leaving
tubes 28 is collected in the convectlve cooling charnber waterwall
outlet header 34 and returned to the steam and water drum through
riser pipe 58. The steam and water mixture flowing through that
portion of heat exchange tubes 28 which forms the sidewall of the
connector duct 26 is collected in the radiant waterwall outlet header
18 and returned to the steam and water drum through riser pipe 56.
A third portion of downcomer water is simultaneously
supplied to the evaporator inlet header 44 through feedline 62. The
water then flows through evaporat~r 38 in heat exchange relationship
with the product gases flowing therethrough the convective ccoling
chamber 30. In so doing, a steam and water mixture is generated
within evaporator 38 as a portion oF the water vaporizes upon
absorbing heat from the product gas. The steam and water mixture is
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collected in evaporator outlet header 46 and returned to the steam
and water drum through riser pipe 64 which penetrates the wall of
vessel 6.
Saturated steam from the water and steam drum is passed
to superheater inlet header 22 via line 66. The steam is then
superheated to a predetermined desired temperature as it flows
through superheater 20 in heat exchange relationship with the product
gases leaving the radiant cooling chamber 12 via outlet duct 13. The
superheated steam is collected in superheater outlet header 24 and
passed fro~ the steam generating heat exchanger 2 through steam line
68 which penetrates the wall of vessel 4. The superheated steam may
be used in a number of processes related to the gasification of coal
but is particularly useful in the production of hydrogen gas from
the coal through well-known reactions.
