Note: Descriptions are shown in the official language in which they were submitted.
~9~
~'ROC~SS AND EQUIP~NT L`OR 'rll~ r~URNING
OF GASES CONTAINI~G 112S
The invention relates to a process for the
burning of H2S-containing gases with air and/or oxygen
to elclnelltary sulphur and for the separation of the
sulphur ~ormed from the reaction gas. The invention
also relates to equipment for carrying out this
process.
Processing of hydrogen-sulphide-containing gases
by the Claus method is effected in plants which may be
operated in a load range between 100 and 20~. Often,
however, it becomes necessary to keep the plant
operating at loads below 20%. This may be the case in
refineries, for example, where from time to time
lS very-low-suphur crude oils are processed and/or only a
fraction of the capacity is utilized.
This invention is based on the need to provide a
process and equipment for the~transformation of
H2S-containing gases into elementary sulphur in a load
range from 100 down to 5~, which ensures reliable
trouble-free operation even in the low-load range. In
the load range from 20 to 5% in particular, the
invention seeks to provide reliable burning of the
H2S-containing gas and mist-free separation of the
formed sulphurO
The invention is based on a process for the
burning of H2S-containing gases with air and/or oxygen
to elementary sulphur and the separation of the formed
sulphur from the reaction yas within a load range of
from 100 to 5%, in a burner-equipped combustion zone, a
subsequent reaction zone and several cooling zones, in
which the former sulphur is condensed and then
separated from the reaction gas. In a high-load range,
the H2S-containing gases are passed into the
combustion zone essentially by one or several main
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burners, and, ;n a low--load ranye, the yases are passed
inLo the combustion zone by a by-pass burner with
heating gas being additionally burned by a separate
burner in the low--load ranye and with the cooling
surfaces in the cooling zones, to which reaction gas is
admitted, being reduced. Because in the low-load range,
the H2S-containing gas is passed into the cornbustion
chamber by a separate by-pass-burner designed for this
load range, and because due to the burning of heating
gas in this load range a reaction l:emperature sufficient
for transforming the H2S into sulphur is maintained, a
reliable H2S conversion of more than 90% into
elementary sulphur is achieved even for a load range
from 20 to 5~. By reducing the cooling surface acted
upon by reaction gas in the low-load range, the
formation of sulphur mists in the cooling zones is
avoided thus achieving mist-free condensation of the
sulphur. ~here the reaction gases leaving the cooling
zones are re-heated in in-line burners, the reduction in
cooling surface in the low-load range has the added
advantage of saving on heating gas, if the in-line
burners are operated with heating gas, or of increasing
the sulphur recovery level of the whole process, if the
in-line burners are operated with acid gas
In the preferred embodiment of the process
according to the invention the switch-over between high-
load and low-load operation is effected at a load in the
15 - 40% range, preferably at a load of approximately
25%. In the high-load range for example, the main
burner may take 95 to 20% of the load, whilst the
by-pass-burner is supplied constantly with 5% of the
nominal load. When in the downward direction the load
has reached 25%, the switch-over may be made by
switching the main burner off and keeping only the
by-pass-burner running, whose load will increase from 5
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to 25% as the switch-over ls rnade.
Preferably the heating--gas burner is switched in
or out as a function of the temperature in the reaction
zone or the combustion zone. In this way the
temperature in the reaction zone may be maintained at
the optimum value required for the formation of sulphur
even in the low-load range, which optimum value cannot
be achieved in the low-load ranye solely by burning the
H2S. This temperature in the reaction zone achieved
by burning heating gas is generally 900 to 1150C in the
low-load range. The supply of heating gas to the
heating-gas burner is conveniently controlled by the
temperature in the reaction zone. In general, the
heating-gas burner is switched on, when the load has
dropped to 40% or less, preferably to 25% or less.
With the preferred embodiment of the process
according to the invention the change in the admission
of the reaction gas to the cooling surfaces is effected
at a load in the approximately 40 to 60~ range. If the
load drops below a value in this range, the cooling
surfaces acted upon by the reaction gas are reduced.
This has the effect of preventing an excessive drop in
the speed of the gas in the cooler and the formation of
elementary sulphur mists which are difficult to separate
in the usual sulphur condensers.
Furthermore provision should preferably be made
for the air supply to the combustion zone to be
controlled by a process chromatograph, in the high-load
range via the amount of air flowing to the main
burner(s) and in the low-load range via the amount of
air flowing to the heating-gas burner. The command
variable for controlling the air supply is the
H2S/SO2 ratio in the reaction gas at the exit of the
plant, that is after the last sulphur condensation
before the entry of the end gas into a thermal or
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catalytic post-burning stage. The control may be
efected by means of by-pass lines with control valves
provided on the main air valves of the air lines to the
mains burners/the heating gas burner, with the control
valves opening to a greater or lesser extent depending
upon the control commands coming from the chromatograph.
To ensure that the H2S-containing gas is reliably
burned even at very low load, the process air is
conveniently controlled on the air line to the heating-
gas burner. Conveniently the air supply to theby-pass-burner is limited to a load range from 8 to 25%.
If the reaction gas is re-heated after condensation of
the sulphur by means of in-line-burners, the supply of
air to the by-pass-burner is omitted for loads below 8%,
whilst in cases not employing in-line-burners the supply
of air to the by-pass-burner is maintained down to 5%.
The air supply to the by-pass-burner is set to a
constant ratio in relation to the H2S-containing gas,
whereby the control is effected, as explained above, by
the air supply to the heating gas burner, which is
always operating in the low-load range.
The equipment for carrying out the process
according to the invention comprises a combustion
-furnace including a combustion chamber, a reaction
chamber and burners for H2S-containing gas and heating
gas, further a reaction gas cooler and at least one
sulphur condenser/separator. At least one main burner
for the high-load range and a by-pass-burner and a
heating-gas burner for the low-load range are provided
in the wall of the combustion chamber, and the cooling
surfaces of the sulphur condenser/separator are divided
enabling part of the cooling surfaces to be shut off.
~hilst with the previous Claus furnaces a heating-gas
burner was only used for the start-up, its purpose with
the equipment according to the invention is to prevent
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the reaction temperature from dropping in the low-load
ranye due to insufficient heat generation from the
burning of the H2S. The heating--gas burner thus has a
permanent function in the low-load range. Shutting~down
a part of the cooling surfaces ensures that in the
low-load range, the mass speed in the cooling tubes does
not drop below a certain value, thus avoiding the
formation of sulphur mists in the gas phase. If the
sulphur condenser/separator comprises a bank of tubes
surrounded by a coolant, separate gas inlet pipes are
preferably provided for the central tubes and for the
tubes of the outer circumferential area, and a shut-off
device is arranged in the gas line supplying the central
tubes. In the low-load range the central tubes may be
disconnected from the gas flow by means of the shut-off
device. Shutting-off the central tinner) tubes ensures
that the central (shut-off) tubes are surrounded by a
sufficiently heated coolant ~water), so that the sulphur
is prevented from consolidating in these tubes not acted
upon by the reaction gas.
The invention will now be described in detail by
way of example with reference to the drawings in which:
Figure 1 is a schematic illustration of the
combustion furnace with the burners for acid gas and
heating gas;
Figure 2 is an enlarged illustration of part of
the combustion furnace showing the gas feeds and the
associated control devices;
Figure 3 is a schematic illustration of that
part of the equipment according to the invention which
is arranged downstream of the combustion furnace, and
Figure 4 is an enlarged illustration of one of
the sulphur condensers built into the equipment
according to the invention.
Figure 1 shows the combustion furnace 1
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col-nprising a combustion chamber la and a rcaction
chamber lb, attached to which is the first stage of
the process gas cooler lC. A restriction has been
created between chambers la and lb by means of a
baffle plate. The acid gas advanced through line 2 may
be passed to the main burner 3 via line 2a, whereby
main burner 3 is shaped as a multi-jet burner. The acid
gas may also be passed to a by-pass-burner 4 via the
by-pass-line 2b~ Furthermore the combustion chamber
la has a central heating-gas burner 5 which is
supplied with heating gas via line 6.
As shown in Figure 2, the acid gas lines 2a
and 2b and also the heating-gas line 6 contain control
valves 8a, 8b and 9 respectively, the importance of
which will be described further on. Oxygen and air are
passed to the burners 3, 4, 5 from the line 7 via the
part lines 7a, 7b and 7C respectively, also
equipped with control valves 10a, 10b and 10C
respectively. Acid gas to the in-line-burners is
supplied via line 2C.
As can be seen ~rom Figure 2, valves 8a, 8b,
9 and loa to 10C form part of an integrated control
~ystem allowing the controlled supply of acid yas,
heating gas and air to the burners 3 to 5. Actuation of
the heating gas valve 9 is controlled by a temperature
sensor 11 in the reaction chamber lb of the furnace,
and similarly air valve 10C in the associated air line
7c is controlled via a ratio control. The combustion
air is controlled by a process chromatograph (not
shown), which detects the H2S/SO2-ratio in the
reaction gas at the exit, i.e. after the last sulphur
condensation before entry of the gas into a thermal or
catalytic post-burning stage. The purpose of this
command variable is to control the amount of combustion
air flowing through line 7a to valve loa by means of
1~'34~(3
a valve 12 in the by-pass-line 13 in the load ranye
hetween 25 and 100%. For loads below 25% the supply of
combustion air to the heating-gas burner 5 is controlled
by the process chroinato~raph via control line 14 by
means of valve 15 which is arranged in a by-pass 16 to
the air valve lOC.
According to Figure 3 the reaction gas flows
from the furnace 1 initially through a first reaction
cooler lC, in which it is cooled to a temperature of
at least 10 to 20C above the sulphur melting point,
thus substantially avoiding any sulphur condensation.
The cooling of the gas is effected by generating medium-
pressure steam. The reaction gas is then cooled down to
a temperature below the sulphur melting point in a
cooler/condenser/separator 20. During this process a
large part of the formed sulphur is separated~ The
temperature of the cooled reaction gas will be in the
range between 180 and 220C for example. Subsequently
the gas is heated in a cornbustion chamber 21 to 220 -
300C for example, by means of an in-line burner. This
is achieved by burning acid gas supplied through line 22
with air supplied through line 23 in the combustion
chamber 21. The gas is then further transformed at a
Claus contact 24, followed by a cooler/condenser 25,
where it is freed from the sulphur which has Eormed.
The gas, cooled down to-140 - 180C, is re-heated in a
further combustion chamber 26 to 180 - 250C for
example, by burning acid gas (line 27) with air (line
28), it is then further transformed at the Claus contact
29 and finally cooled down in the cooler/condenser 30 to
allow the sulphur to condense. When it has cooled to
120 - 150C and the sulphur has separated out, the gas
reaches a third and possible fourth Claus contact stage
and/or a post-burning facility.
The cooler/separator 20, 25, 30 illustrated in
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Fiyure 3 can be seen dimensiona]ly enlaryed in Figure 4.
It has a bank of tubes between t~be plates with central
tubes 34 to which gas may be admitted through a pipe
socket 38b, and tubes 35 in the annular area
surrounding tlle central tubes 34, to which gas may be
admitted through a pipe socket 38a. The gas is
supplied to the condenser 30 through line 32, whereby
the central tubes 34 are supplied by line 32b
containing the shut-off device 33, whilst the tubes 35
in the annular area are supplied via partial line 32a.
Downstream of the bank of tubes is the separator, where
the sulphur droplets which have formed are separated.
The liquid sulphur collects in the trap 39 and is drawn
off by line 37. The reaction gas leaves the separator
through line 31. This design permits the cooling
surface to be reduced to the tubes 35 in the annular
area by shutting off line 32b, when the load has
dropped to a certain value, for instance to 50%.
Operating methods
1. Operation in a load range from 100 to 25%.
5% of the H2S-containing gas are advanced at a
controlled rate to the by-pass-burner 4 and directed
into combustion zone la without combustion air. The
remaining 20 to 95% are burned together with the
required quantity of air at a controlled pressure in the
main burner 3, whereby the quantity of acid gas required
for the in-line burners 21, 26 may be deducted from this
quantity. The heating-gas burner 5 which is not in
operation is purged with part of the combustion air or
an inert gas, in order to prevent the intrusion of
sulphur vapours into the burner. When the reaction
temperature, in general approximately 1000C, drops
below this value in the combustion chamber la or the
reaction chamber lb, the heating-gas burner 5 is
ignited and the purging stops. The process
3~
chromatograph controls the air quantity admitted to the
main burner 3.
2. Operation in the load range from 25 to 5%.
~hen a load of 25% is reached, i.e. 20% to the
main burner 3 and 5% to the by-pass burner 4, the main
burner 3 is switched off and purging with an inert gas
begins. The acid quantity is burned at a controlled
pressure in the by-pass burner 4 with the quantity of
air required for the process. If the heating-gas burner
is not in operation, it is ignited at this stage at the
latest, in order to ensure reliable operation down to a
load of 5%. The process air quantity from the process
chromatograph is controlled by valve 15 in the by-pass
16 to the air valve 10C of air line 7C to burner 5.
3. Load range from 25 to 5~ employing in-line
burners operated with acid gas.
The burning of acid gas in the in-line burners
21, 26 and possibly further in-line burners is effected
in the range between the stoichiometric air quantity for
burning to SO2 ( ~ = 0.9 to 0.95) and that for burning
to sulphur for the purpose of avoiding an 2 surplus.
In order to prevent the air/acid gas ratio going to the
by-pass burner 4 from dropping below the minimum value
(maintaining the flame), this ratio is preset and used
to operate the by-pass burner 4 at a value below the
stoichiometric value. The fine adjustment of the
process air quantity is effected as indicated in 2.
When a minimum quantity of acid acid is reached, e.g. 10
to 15% (as a function of the acid gas concentration and
the acid gas quantity to the in-line-burners) the air
supply to the by-pass burner 4 is switched off. Air
control is effected as previously, via the combustion
air for the heating gas. The transformation into
elementary sulphur is then effected, in the main, in the
reaction zone lb of the combustion furnace 1.
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With the process accordiny to the invention the
variations in the load may be caused by changes in the
gas throughp~t, and also by fluctuations in the
H2S-concentration.
