Note: Descriptions are shown in the official language in which they were submitted.
? ~
This invention relates to a process
of purifylng a gas which con~ains combusti~le components
as well as carbon dioxids and sulfur compounds, parti~
cularly H2S, in that ~he ~as i~ scrubbed in a scrubbing
z.one with a scrubbing solution, which is regenerated and
re-used, whereill the sc~llbbing solution to ~e regene-
rated is pressure-relieved, stripped, and heated in a
hot regenerating zone, an exhaust ~'G3 rich in H2S pro-
duc~d in the l!ot regenerati~g zone is processed to form
ele~enbary sulfur and a residual gas which contains
H2S, an~ the residual gas i3 contacted with scrubbing
solution~
`~uropean ~atent 0 054 772 describes
a process which s of that ~ind and in which the exhaust
gas that is supr.lied to the Claus proces~ plan~ contains
considerable amounts o~ ~,C, i n addition to ~S. That
exhaust ~as i5 proces~:ed rurther in a relatively ex-
pe.nsive Claus process Dlant~ which inlcudes two or three
. .,.. . .
.. ..
,' `
S ~
catalytic stages, in which after a partial com~ustion
of H2S to S02 the exhaust ias is catal,~tically con-
verted as completely as possible to elementary sulfur
and water by the Claus re~ction
H2S + ~2 -' 3 S + 2 H20
ae~ore and behind each of ~ d catalytic stages, elemen~
tary sulfur is condensed ~rom the mi~ed gases and is
removed. In the l{nown proces,~ the catalytic conversion
stages are succeeded c~ a hydro~enation and the exhaust
gas is therea~ter recycled to the scrubber.
Those catalytic processing stages give
rise tc conserable costs and have the disadvantage
that they render the star~-up of the plant from stand-
still expensive and time-consuming. There is also a risk
that in case of frequent start-ups and shutdowns and of
extreme load changes the catalysts will soon lose their
activity.
It is an object of the invention so to
process the exhaust gas rich in H2S that is formed
in the hot regenerating zone that a fast start-up from
a standstill can be effected in a simple manner and
even a frequent load change will not be problematic.
In the process which has been described first herein-
before this is accomplished in accordance with the in-
vention in that the exhaust gas which is rich in H2S
and has been produced in the hot regenerating zone is
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partly combusted in a combustion chamber with oxygen,
oxygen-containing ga~ or air; a ~,as mixture which is
at a temperature in the range from lO00 to 2000C and
in which ~ e percent of the sulfur supplied to
the combustion chamber are contained a~ elementary sulfur
and which also contains the components H2S and S02 in
a molar ratio of 4:l to 1:1 is produced in the combustion
the
chamber; ~as mixture is cooled below the dew point tem-
perature of sulfur; condensed elementary sulfur is re-
moved; the gas ~ixture is subsequently heated to tem-
peratures of 180 to 280C and is th~n directl~ subjected
to a catalytic hydrogenation and/or hydrolysis, wherebg
the residual content o~ S02 is substantiall~ converted
to H2S ;
and at least part of the gas which
has thus been treated is contacted as an H2S-containing
residual gas with scrubbing solution. The process in
accordance with the invention is particularly desir-
able for the desulfurization of fuel gases to be used
as fuel in a gas turbine-steam turbine power pla~.
In the process in accordance with
the invention, ca~ is taken to ensure that the ga~ which
is rich in H2S and supplied to the combustion chamber
is highly enriched with H2S so that a large share of
the hydrogen sulfide is reacted to elementary sulfur
by the reaction
,
.~ "
.
H2S + 2 ~ S ~ H20
in and immediately after the combustion chamber and
there is no longer a need for a further processing
of the gas mixture by a catalytic reaction of -H~S and
S2 according to the Claus reaction
2 H2$ ~ S02 = 3 S + 2 H20
reaction of H2~ to a lower degree i5 in~entionally
tolerated and this will also increase the demand for
hydrogen for the hydrogenation. But in the process in
accordance with the invention the h~per rate of hydro-
genation requires that the h~drogenation catalyst is
cooled and in the process in accordance with the in-
vention that cooling can be effected by the ~eeding of
a cooling gas, which ma~ also be used to supply the de-
ficient hydrogenatin~ hydro~en.
'~he residual ~as which is ~igh in ~I2S and
has been produced iD the hydro~enating and/or hydrolyzing
stage may be recycled, e.~., to the scrubbing zone or
to the regeneratin~ stage. Alternatively, part of that
residual .sas may directl~ be supplied to the combustion
chamber and this will be recommendable particularl~ if
oxygen and an exhaust ~as which is highly enriched with
H2S are supplied to the com~ustion chamberO
;''he hot regenerat~on proauces an exhaust
~as which has a low C02 content not in excess of l~o
by volume or will have a much lower C02 content if the
laden scrubbing solution ;`rom -;he ;crubbirg zone is
pressure-relieved iD at least ~10 re~en~atin~ columns
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~ 4 , ~i!
--5--
before the hot re~eneration. In ~,hat c~se it wiil
be recommendable to feed at least ~art of ~he flashed-
off gas as a stripr,ing gas to u~e E!recedinLr s~a~e. Lr
addition, inert gas ~ay be used as a stripping gas in
the hot regenerating ~oneO
The process is particularl~ desir-
able for effecting a desulfurization oi` gases which
have a high heatin~ value and are intended for use in
a gas turbine-steam turbine po~ver plant~ Such gases
having a high heatin~ value ma~- be ~roduced in a manner
known per se, e.~ y a gasification oi` solid fuels.
'rhe gas may be purified by means of
various ~crubbing solutions, which ~re selec~ite for
~l2S and which are known per se and may consist, e~g., of
physicallù~ acting scrubbing solutions, such ~IS ;netne;nol,
N-methyl pyrrolidone, methyl diethanol~mine or also
dimethyl ether of polyethylene glyc~ he ~as is scrub-
bed in most cases under pressures in the ran~e from 5 to
100 hars and at the ~no~rn te~peratures which are ~ypical
of the scrub~ing solution employed and lie in the range
from -80C to ~100C. ~ha e].emen',Gry sulfur is produced
under pressures of about 1 to ,~0 bars or even ligrher
pressures. Pressure~ o~ 1 to 10 bars are presently pre-
ferred.
Further features of the process will
be explained with reference to the ~Irawing. Figures 1,
3, ~nd 4 are flow schemes illustratinLr various variants
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of the process. ~igure 2 is a simplified represen~
tation of an example of the Claus ~rocess plant which
may be used in accordance with +~he inven~ion, Pu~ps
and compressors have been omitted in t;he drawing for the
sake of simplicity and of a clearer arrangement~
In the process illustrated in
Figure 1 ~e gas which is to be desulfurized is fed in
l~ne 1 to a scrubbing zone 2, which is supplie~1 with
regenerated scrubbing solution through line 3. Purified
~as is withdrawn in line 4. Laden scrubbing solution~
which contains H2S and C02, is supplied in line 5 with
a partial pressure relief to a re-absorber 6. ~he re-
absorber consists OL` a regenerating column, ~vhich
contains mass transfer-promo~in~ elements known per se 9
such as liquid- and gas-permeable plates. I~he re-
absorber 6, C02 is substantially stripped off whereas as
much H2S as possible is ~ept in the scrubbing solution.
~or thls purpose the re-absorber is supplied at its top
through line ~ with regenerated scrubbing solution,
which prefercntially takes up the sulf'ur compounds from
the rising gases. Y2S-containing ~ases from lines 10
and 11 are SUPP1ierI to the lower portiun of the re-ab-
sorber and in the re-absorber 6 act as stri-~ing gases
to strip off particularly C02. ~n exhaust ~as which is
rich in C02 is withdrawn from the re-absorber through
line 12 and becnuse it has substantiallv been ~lesul-
furized may be combined for most appllcation with the
Oas frQm line 4.
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l`he scrubbing solution from the re~
absorber 6 is supplied in line 13 to a heat exchanger
14 and is heated therein and then flo~ls in line 15 to
the hot regenerating apparatus 16, in which a reboiler
17 effects the temperature rise which is required for
a release of impurities, particularly H2S, which are
bound to the scrubbing solution. In case of need,
a strip~in~ gas may additionall~- be supplied through
the line 18, which is indicated by a dotted linè. ~hat
stripping gas may consist7 e.g., ot` hydrogen rr nitrogen
or of a desulfurized exhaust gas.
~ egenerated scrubbing solution le~ves
the hot regenerating zone 16 in line 20 and is cooled
in the heat exchanger 1~ and in line 21 is recycled to the
scrubbing zone 2 and to the re-absor`oer 6. ~xhaust gas
which is rich in H2S is withdrawn in line 23 from the
top of the hot regenerating apparatus 16 and a partial
stream thereor is supplied in line 24 to a Claus process
plant, vhich consists of a burner section ~ and a suc-
ceeding hydrogenati~g ~ection Ho Details of the Claus
process plant consisting of sections ~ and H will be
explained hereinafter with reference to Figure 2. and it
ill also be explained that the hydrogenating section H
comprises a hydrogenating and/or hydrolyzing 5 ~age. Re-
maining exhaust gas i5 withdrawn in line 23 from the hot
regenerating apparatus 16 and is supplied through a
cooler 26 and through line 11 to the re-absorber 6.
It is indicated in ~igure 1 that in addition
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h.~ . .. ..
to the exhaust ~as which is rich in H2S and conducted
in line 24 the Claus ~rocess plant is supplied through
line 28 with oxygen or a.ir or oxygen-enriched air, that
elementary sulfur is ~thdrawn in line 30, that exhaust
gas which contains H25 and S02 is supplied in line 45
to the hydrogenating sectiorl H, and that a part of the
H2S-containing residual as frcm the hydrogenating
section is recycled in line lOa for a control of the
temperature in the hydrogenating re~ctor. ~he scrubbing
zo~e 2, the re-absorber ~j an~ t~e hot regenerating appa-
ratus 16 may contain elements known per se, such as
plates, for im?roving the mass transfer.
'rhe ~aus process plant which i~
shown in ~etail in ~igure 2 essentially consists of the
burner section ~ (between items 24 and 40) and the hydro-
genating section H (bet~ieen items 45 and 50) and is o~erat-
ed as follows: ~xhaust gas from line 24 and oxygen-con-
tainin~ gas from line 28 are initially sup~lied to a Claus
process burner 31 ~ or a plurality of burners - provided
with an integrated combustion chamber. Details of such a
combuster are described in Published German Application
37 35 002 and in U.S. r~tent 4,632,~19. By the combustion,
a gas mixture at temperetures of~b`out lO00 to 2000C is
produced and the oxygen in line 28 is metered to ensure
that the mole ratio of ~2~ to ~2 in the gas mixture
lies between 4:1 and 1:1 and preferably at about 2:1.
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_9_
The succe~ding indirect cooler 32 is provided with a
feed ~fJater sup?ly line 34 and ~,vith a ~Jater v~por-
withdr~wing line 33 and is used -to cool the gas mixture
below the dew point temperature of sulfur so that ele-
mentary sulfur ls condensed. ~hat elementary sulfur is
delivered in line ~Oa to ~ collectir.g bin Z5.
~ he cooled gas mi:~ture ~lows in ;ine
~7 ~o a further indirect cooler ~8, which i9 used to
improve the yield of elementary sulfur. That elementar~
sulfur flows in line ~Ob also to the bin 35. The gas in
line 40 is still at temperatures of about 125 to 135C
and is heated in an indirect heat exchan~er 430 ~he
thus preheated gas is supplied at tem~eratures of 180
to 280C in line 45 to a catalytic h~Jdrogenator 46,
which .vill be supplied through line 46a with hydrogen-
co~taining gases if the hydro~en produced in ~he com-
bustion chamber 31 is not sufficient. The h~drogenator
may be used entirely or in part as a hJdrolyzer and is
used in known manner mainly ~o convert S02 co H2S.
Co~t-molybdenum catalysts ma~ be used, for instance,
fo~ that purpose. The gas mixture from the h~drogenator
46 is initially precooled in the cooler 47 and is ther
fed to a direct cooler 48 for a remo~Jal of water~
The cooler 48 is 5upplied with cooli~g ~ater, which is
circulated throu~h an indirect cooler 49. Surplus wa~er
is withdrawn in line 50. H2S-containing residual gas at
temperatures of a~out 20 to 40~ leaves ~he cooler 48
in line 10 and a partial stream of tha~ residual gas is
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recycled in line lOa -to the hydrogenator 46 to control
the temperature in the nydrogenator. Lines lOa and 46a
may alternatively open in~o line 45. The residual gas
flOw~ng in line 10 will be ~rocessed further in the
manner that is ex~ained with reference to Figures 1, 3,
and 4.
The p~ocess variants illustrated in ~'igures
3 and 4 agree with the rrocess of Figure 1 in part so that
like reference characters are employed and reference is
made to the explan~tions furnished with reference to
~igure 1. In accordance with Figure 3, gas which is to
be desulfurized is supplied in line la and after it has
been mixed with the gas flowing in line 10 is supplied
in line 1 tothe scrubbing zone 2. In the processes
illustrated in ~'igures 3 and 4 the regenerating appara-
tus also compriSQs two regenerating columns 7 and 51, in
which the scrubbing solution i9 partly pressure-relieved
and is treated with a strip~ing gas. The stripping gas
for the column 7 comes from line 52 and consists of an
exhaust gas which comes fxom the regenerating
column 51 and has flown through the cooler 53. In accordance
with Figure 3 a part of the exhaust gas from column 7
is supplied in line 60 to the scrubbing zone 2 and the
remainder flows through line 61 to the hydroge~atiDg
section H of the Claus process plant~ Hydrogen-contain-
ing gas is added through line 46a and may be tapped, e.g.,
from the pure gas flowing in line 4 if that pure gas is
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: :.
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--11
suitable for the purposeO
StripDin, gas is supplied i~ line
18 also t~ the hot regenerating apparatus 16, and a
part of the exhaust gas from the hot regenerating appa-
ratus flows through the control valve 66 and line 67
as a stripping gas to the second regenerating column
51. ~he scrubbing solu~ion from line 15 flo~s throush
the pressure relief valve 15a and subsequently enters
the column 51. H2S-containing residual gas from-the hy-
drogenating section H is admixed from line 10 to the
gas to be purified, which flows in line lo
The proce~s illustrated in Figure 4
is similar to that shown in Figure 3. In that case the
H2S-containing residual gas from line 10 is used as an
additional stripPing g~s in the first regenerating column 7
and the entire exhaust gas from that column is supplied
through line 60 to the scrubbing zone 2. ~he sntire ex-
haust gas which is rich in H2S and comes from the hot
regenerating apparaGus 16 is supplied in line 24 to ~he
Claus process plant. ~itrogen, e.g., is used as a
stripping ~as in the second regenerating column 51 and
is supplied in line 62. Hydrogen usually coming ~rom an
extraneous source is sup~lied as a hydrogenating gas
through line 46a ~o ~he hydrogenati~g section H. Alter-
natively, a partial stream of the scrubbed gas in line
4 may be used as a hydrogenating gas.
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~xample 1
In R processing system as shown in
Figure 3, comprisiDg a Claus process plant as shown
in Figure 2, a dedusted product gas from the gasifi-
cation of coal is treated with NMP as a scrubbing
solution. Data indicating the rates, pressures and
~as components in various lines are apparent from the
following tables. All rates, also those of the compo-
nents,are stated in all examples in kilomoles per hour.
Line 1a 4 5 10 60 61
;~ateloooo 10039.4 395-7 192.5 247 119.9
(bars) 37 36 37 1.1 1.4 1.4
Components:
2 1650 1656.4 294 104.3 196.8 95.7
s 33 - 75 22.7 19.3 9.4
~2 4317 431404 11 2.8 7.5 3.5
co 4000 3993.6 15.5 0.4 10.5 5.0
N2 - 75 002 62.3 1209 603
Line 13 24 46a 52 54 67
.
~ate 124.4 lC3.8 4.4 95.6 65.9 37.1
Pressure
(bars) 105 1.8 36 1.6 108 1.8
Components:
C2 49.2 105 C.7 47.7 2 o.5
H2S 74-9 4603 - 28.6 63 1607
2 - 1.9 _ _
co - - 1.8
~2 0. 3 56 _ 19.3 o O 9 19.9
..
.
,-,
, . ..
~ f~ J~
.~itrogen at a rate of 75 kilomoles
per hour is conducted as a strippin~ g~s through line
18. Pure oxygen at a rate of 21 kilomoles per hour is
supplied through line 28 ~o the combustion chamber 31.
The laden scrubbing solution in line 5 is at a tempe-
rature of 37C. ~lementar~J sulfur is collected in the
bin 35 at a rate of 33 kilomoles per hour. In the
hydrogenator 46, a cobalt-mol~Jbdenum catalyst is used,
which comprises a carrier consistin~ of activated alu-
mina, A partial stream of the pure gas in liue 4 is
supplied in line 46a as an additional hydrogenating
gas. 35.6 kilomoles of water at 70C are withdrawn per
hour in line 50.
Example 2
A processing s~stem as shown in
Figure 4 combined with the Claus process plant of
Figure 2 is used to process a gas that has been produced
by a gasification of coal and is supplied in li~e la.
NMP is used as a scrubbing solution. Nitroge~ at a rate
of 45 kilomoles per hour is supplied as a stripping gas
in line 62. ~he combustion in the combustion chamber 31
is effected with pura 2 supplied at a rate of 12.1
kilomoles per hour, and elementary sulfur at a rate of
19 kilomoles per hour is collected in the bin 35. '~ater
at a rate of 24.1 kilomoles per hour is withdrawn in
line 50. Further data are stated in the following tables,
,
,
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-14-
in which all rates, also those of the components, are
stated in kilomoles per hourO
Line 1 4 5 10 13 24
.
Rate 10000 10026.8 372.6 9 128.127.2
(bars) 37 36 37 1.4 1051.8
~emperature (C) 3 38 36 3 31
Components:
~2 1650 1650 3 ~ 27
H2~ 19 _ 4603 6.3 100~52503
H2 + C0 8331 8331.8 26.3 008 - _
N - 45 - 1.9 0.61.9
Line 46a 52 54 60
Rate 6 14509 2702 399.4
Pressure
(bars) 2.5 104 1.8 1~3
~emperature (C) 30 30 31
Components:
C2 ~ 27 - 300
H2~ ~ 7502 2503 2703
H2 ~ C0 6 - _ 2701
_ 43.7 1.9 45.0
. . ...
.
