Note: Descriptions are shown in the official language in which they were submitted.
11~4791
This invention relates to the method of preparing
sulphur dioxide used in the manu4acture o~ su~phuric acid
and in the pulp-and-paper industry.
~ nown in the prior ar-t is -the method of preparin~ sul-
phur dioxide o~ high concentration (to 90 per cent by ~oiume)
by burning sulphu~ in a gaseous mixture consisting of o~e
volume of oxygen and five volumes o- sulphur dioxide. ~he
pro-cess is xealized in special furnaces at a temperature o4
1200C. The furnace construction i5 characterized by the
presence o~ two nozzles for spraying sulphur, and heat exch~
angers ~or cooling return gas, the major part o~ which is
delivered into the reactor to maintain t~e required tempera-
ture conditions.
Disadvarltages of the known ~ethod are low intensity of
the process owing to recycling of the return gas in the reac-
tor, complexity o~ the process flow-sheet because of the
necessi-t~ of fine p~lrification o~ sulphur and the presence
of external heat-exchangers. It is alsc difficult to effect
the process at elevated pressures du~ to high process tempe-
ratu~es in the wor~ing zone o~ the fuxnace (1200C).
Known also in the prior art is another method o~ pxepar-
ing sulphur dioxide of high concentration by si~ultaneously
meltin~ lump sulphur, evaporating it, and oxidizing ~iith
ox~en blo~n throu~h a fluidized bed.
~ he disadvant~ge of this method is that lt is impposibl~
to realize the pxocess on an industrial scale because of a
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79~ j
sharp rise in tne process temperature i~ oxygen is used in '~
the blowing process instead of air. ~he tempera-ture rises
to above 2500C, and the problem of heat withdrawal is not
solved.
As the bed o~ an inert material is fluidized, sulphur
can get into its upper layers and its vapour can burn in the 7
zone above the bed.
Another disadvantage of this method is also impossibilit~
of carrying out the process under excess pressure since the
specific evolution o~ heat is intensified in proportion wit~
growing pressure.
Enown widely in the prior art is also a method of pre-
paring sulphur dioxide ~rom sulphur by bubbling primary air,
in the quantity of 0.5 - 1.0 per cent of the total volume of
the air, through a bed of molten sulphur with subsequent oxi-
dation of sulphur vapour in the combustion chamoer, where
the secondary air is delivered tange~tially, in a cyclone, to
ensure complete combustion of sulphur vapour.
Crushed lu~p sulphur is delivered by a screw feeder
into the lou~er part o~ the furnace, into the bubbling zone,
where it is melted by the heat of liquid sulphur. ~o accele-
rate this process, the primary air is delivered into the bed. ;
~he bubbling i~te~si~ies agitatio~ of the melt in the verti-
cal plane of the bed, and the melt surface is thus co~stantly
renewed. q'he tel~perature of the bubbled layer is 300 -380C,
and the boiling point (444C) i3 attai~ed at atmospheric
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pressure only at the interface. T~e main quantity o~ vapour
is generated at the sur~ace o~ the bed by this method.
~ he method suitable ~or vJork with impure sulphur, with
periodically removing the s~udge from the lower part of the
fur~ace. ~he heat stress of t~e furnace is higher than with
sprayer-type furnaces, and is about 1.7 X106 kcal/cu.m x hr.
The obtained sulphur dioxid\e has the concentration of 12 - j
18 per cent by volume.
The disadvantage of this method is the 10W concentration
of the obtained sulphur dioxide (not above 18 per cent by
volume)
The specific obaect of the invention is to prepare sul-
phur dioxide having high concentration (to 100 per cent by
volume) within a wide range of pressures, ~rom 1 to 35 atm.
~nother object of the invention is to intensily the
process of preparing sulphur dioxide 1.5 - 3.0 times. S
Still another object o~ the invention is to provide a
method that would rule out the action o~ high temperatures
on the furnace structures under elevated pressures.
The essence of the invention consists in that in the
met~od for preparing sulphur dioxide from sulphur by melting
the latter, evaporating it in a bubbled bed, and-oxidizing
the obtairled sulp~ur vapour into the end product, according
to the invention, sulphur is evaporated by bubbling oxygen
through molten sulphur, while the formed sulphur vapour is
oxidized ~ith oxygen in a ~luidized bed of an inert material.
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~ 4791
T~s proposed method makes it possible to burn sulphur f
directly in a stream of oxygen, which intensi~ies the proce3s
of preparing sulphur dioxide.
It is recommended that sulphur be evaporated by bubbling
oxygen through molten sulp~ur at the temperature o~ its-boil-
ing point, which ensures maximum evaporation o~ sulp~ur.
Sulphur can be evaporated and the vapour oxidized under
a pressure o~ from 1 to 35 atmospheres.
It is recommended that quartz sand, silica gel or alu-
mino~ilicate be used as the inert material.
~ he ~urther des~ription o~ the invention will be illu
strated by a process flow-sheet given in the appended draw-
ing. Crushed sulphur is melted in chamber 1, heated by steam
through coils 2, or by any other suitable method. Molten
sulphur is then purified by pa~sing throu~h a ~ilter chamber
3. ~he molten and purified sulphur, at a temperature o~ 140 -
150C, is delivered by a pump 4 into a bubbling chamber 5 o~
the furnace, where oxygen is sparged through the molten bed
7 of sulphur by a bubbler 6.
The oxygen delivery rate is calculated ~ith respect to
the heat and material balance, and depends on the process
parameters. Unlike in the known bubbling met~od, the oxida-
tion and evaporation processes in the proposed method occur
inside a ~as bubble. Because o~ the chain character o~ the
burning process, sulphur vapour burns in oxygen in tenth
~rac~ions o~ a second. ~he temperature inside a bubble rises
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4791
suddenly and attains the point close to the theoretical te~-
perature of adiabatic burning of sulphur in o~ygen (about
3000 - 3500C)~
As the gas bubble rises through the molten sulphur, it
exchanges its heat with the m~lt 7, the heat-exchange process
being completed at the depth of 1 - 1.5 m ~rom the melt sur-
~ace to the bubbler (experimental data). During the process,
the gas bubbles do not come in direct contact with the ele-
ments of the apparatus, and the walls of the reaction chamber
are not heated a~ove the temperature of the melt. ~he c~mposi-
tion of the vapour-gas mixture, as it issues ~rom the bubbli
chamber 5, is determIned by the process parameters, such as
pressure, temperature, and heat loss. In the proposed method,
the heat of the reaction in the bubbling zone of the furnace
is con~umed to evaporate sulphur, and to heat the melt to the
working temperature.
~ he composition of the mixture can be regulated b~ with-
drawing part of heat using special heat-exchangers 8 located
in the bubbling bed.
Sulphur vapour and par~ of sulphur diexide are passed
through a gas distributing grating 9 into the fluidized bed
o~ inert material 10. ~he secondary oxygen is delivered
, . . .
through the bubbler 11 in a small excess (1 - 1.5 per cent
with resl~ect to stoichiometric) i~ 100 per cent S02 is requi-
red. By va~ying the amount of excess oxygen, the required
concentrations of S02 in the gas are obtained. ~Ieat-exchang-
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~1~4~91
ers 12 serve to withdraw heat ~rom the ~luidized bed zone. -
~he hig~ values of the heat transfer coefficien~ in the
fluidized bed make it possible to rnaint-ain the ternperature
in the bed at 600 - 700C. Common lining and construction
materials can thus be u~ed in the manufacture of the appara-
tus.
~ he holding capacity of the apparatus for preparing
sulphur dioxide under pressure, decreases with the growing
pressure. ~he specific capacity o~ the furnace for the manu-
facture of sulphur dioxide by the proposed method, is about j~
2 - 3 times higher than of the apparatus used in the known
method~ I
Realization of the proposed method o~ preparing sulphur ;
dioxide under pressure, increases the pro~uctivity to 2000 k~
per square metre of the bed surface per hour, the pressure
being 10 - 35 atm, and the intensity being 3000 - 3500
kg/sq.m x hr undsr a pressure of 1 - 10 atm.
The proposed method has the following advantages:
1. The concentration of S02 in the obtained gas increa-
ses to 100 per cent.
2. ~he concentration o~ oxygen in the blowin~ gas can
be as high as 100 per cent by vol.
3. Bubbling of oxygen t~rough molten sulphur at a te~-
perature of its boiling point, or at lower temperaturs, mar-
kedly increases the surface of evaporation to intensify the
pro~ess 1.5 - 3 times as compared with the known methods.
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11Ç~47~1 ~
4. The temperature of the medium at the bubbling stage
does not exceed 700 - 800C, which makes it possible to use
com~on (non-refractory) construction materials.
5. Burning o~ sulphur in a fluidized bed of an inert
material makes it psssible to remove the heat, liberated
during o~idatio~ ~ sulphur by oxygen, directly from the
reaction zone.
6. Oxidation of sulphur in a ~luidized bed of an inert
material in the form of vapour, intense mixing of the v~pour
with oxygen, make~ it possible to complete the process in the
bed~ the temperature in the zone above the bed not exceeding
the temperature of the bed.
7, ~he intensity of sulphur burning in the form of va-
pour in a fluidized bed o~ an inert material incxeases 2-3
times as compared with the kno~m methods.
8. ~he proposed method makes it possible to obtain sul- i
phur dioxide gas ha~ing the concentration of 100 per cen~ !
out of sulphur and oxygen under a pressure of up to 35 atm.
~ or a better understandin~ of the invention, the follow-
ing exa~ples of its practical embodiment are given by way of
illustration.
~ :amPle 1
Crushed sulphur containing to 5 per cent by weight of
admixtures is delivered into a melting zone by a screw feeder
at a rate of 7740 kg/hr. ~ sulphur melts, it is purified,
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4791
and pumped at a temperature of 140 - 150C into t~e bubbling
chamber of the ~urnace. The cross section area of the bubbl-
ing chamber is about 3 s~.m, and the diameter is 2 metres.
The height of -the sulphur melt is maintained at 1 metre, (in !
the stationary conditions). Th`e bubbling chamber is a separa-
te apparatus, 3.5 m high. ~he height of the separation space
above the melt is 0.8 m, and of the settling zone 1.2 m. ~he
consumption rate of puri~ied sulphur is 7~70 kg/hr. ~echnical~
oxygen, containlng to 2 per cent by volume of inert gas, is
used in the manufacture o~ sulphur dioxide. The process is
effected u~der a pressure of 10 atm and at a te.~perature of
the melt equal to the boili~g point of sulphur at a given
pressure (646.1C), This temperature is maintained in the
bubbling chamber by the heat liberated in the reaction of
oxidation of part of sulphur with ox~gen as it is bubbled
through the moltsn sulphur. The quantitg of oxygen at a tem-
perature of 15 - 20C used for bubbling, under stabilized
process conditions, i5 626.5 ~g/hr or 438.5 cu.m/hr (at STP).
~he quantity of inert gas that is bubbled together with oxy~-
en is 28.9 k~/hr or 23.1 cu.m/hr (at STP). In the startin~
period, oxygen is heated to a temperature of 350 - 400C. As
the process conditions get stabilized) the oxygen reacts in
the melt with the sulphur vapour. ~he reaction inside the gas
bubbles is complete. A vapour-gas mixture is formed as a re-
sulk in the space above the molten sulphur, the mixture con
sisting of sulphur vapour (6743 kg/hr or 4720 cu.m/hr~ at
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S~P), sulphur dioxide (1253 kg/~r or 433.5 cu.m/hr, at STP),
and inert gases (28.9 kg/hr or 23.1 cu.m/hr, at S~P). ~he
output capacity of the bubbling chamber is 2500 kg/hrx sq.m.
The vapour-gas mixture is delivered through a gas-di-
stributing grating into the chamber having the inner section
diameter of 1.7 m and the ~eight of 3.4 m. The chamber is an
apparatus where crushed quartz, having particles sizing
1.5 mm, is fluidized. The height of the fluidized bed is
Ho = 1.2, which ensures complete combustion of sulphur vapor
in an oxygen stream at a te~perature of 650C. Excess h~t
of the reaction is withdra~n by heat-exchangers located di-
- rectly in the fluidized bed. ~he temperature of the gas at
the exit ~rom the apparatus has the same value.
The quantity of oxygen to be delivered into the fluidi-
zed bed should be cal~ulated on the assemption t~at the
obtained sulphur dioxide will be furt-her ~ to sulphur
trioxide. ~or t~is reason, the total required quantity o~
oxygen (~or ~he suimary reaction) should be delivered into
the ~urnace. Sincs part of oxygen is bubbled, the total re-
quired quantity o~ oxygen is 11274 kg~hr, the excess factor
being ~ = 0.02. Thus, 7453.4 cuOm/br (at S~P) o~ oxygen are
delivered into the fluidized bed of an inert material thro-
ugh a special device. ~e composition of the gas issued from
the furnace is as follows: oxyge~ 32.9 per cent by volume,
~hich is equivalent to 3905 kg/hr or 2733 cu.m/~r (a~ STP),
sulphur dioxide 62.1 per cent by volume, ~lhich is equivalerlt
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~4791
to 14,740 kg/hr or 5159 cu.m/hr (at S~P), and inert gases
5 per cent by volume, which is equivalent to 5~8 kg/hr or
415 cu.m/hr (at STP).
~ he product1on capacity of the furnace, with respect to !~
sulphur dioxide gas having -the specified composition, is
8300 cu.m/hr (at STP).
Exam~le 2
The process is carried out as described in ~xample 1,
except that the pressure is 15 atm, and the temperature o~
the molten sulphur is maintained at 650C, which is below
the melting point o~ sulphur at this pressure. ~i~uid sulphur
(20412 kg/hr) is evaporated in the bubbling chamber by pass-
ing 1113.9 kg/hr of technical oxygen containing 15 per cent
by weight of inert gas admixtures. As a result, 19~47.5 kg/hr
of sulphur vapour, ~130 kg/hr of sulphur dioxide, and 49 kg/br
of nitrogen are obtained in the fluid bed having the height
of 1.5 m and the inner diameter of the section o~ 3.3 m. ~he
vapour-gas mixture is delivered into the fluidized bed of
silica gel having particles o~ 1.5 mm. The height of ~he bed
is Ho = 1..2 m, the diameter o~ the apparatus in the working
zone is 1~6 m, and the gas velocity, in the ~orking condi-
tions, is wp = 0,75 m/second. Oxygen is delivered into the
fluidized bed in the ~uantity required for complete oxidation
of sulphur vapour an~ sulphur dioxide to sulphur trioxide.
~aking into account t~e excess ratio factor ~ = 0,02, this
~uantity is 30166 k~/hr, or 21,116 cu.m/hr (at STP). Technical
oxygen containing 5 p~r cent by volume of inert gas is used
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~ 47 9
B in the process. The temperature in the fluidized bed~ ~
maintained at 650C~ The ~ollowing products are obtained at
the exit from the furnace:
sulphur dioxide 40,824 kg/~r, or 14,290 cu.~/hr
(at STP),
oxygen 10,819 kg/hr, or 7571 cu.m/hr
(at STP),
nitrogen 1437 kg/hr, or 1149 cu.m/hr (at STP).
~he composition o~ sulphurous acid gas i8:
S2 62.1 per cent by volume
2 32.g per cent bg volume
N2 5 per cent by volume.
EscamPle ~
~ he process i~ realized as de3cribed in Example 1,
except that the pressure is 25 atm, and the temperature o~
the molten sulphur in the bubbling chamber is 650C which is
below the melting point of sulphur at this pressure.
EXcess heat is withdrawn by heat-exchangers that are
located directly in the molten sulphur bed.
~ iquid sulphur having the temperature o~ 140 - 150~C is
delivered i~to the bubbling chamber at a rate of 30234 kg/hr
The height of the molten sulphur bed is 1.5 metre. ~he diame-
ter of the apparatus is 3 metres, and its height is 16 me~res.
Technical oxygen is delivered into the apparatus under
a pressure of 25 atm at a rate o~ 4559.9 kg/hr. ~he amount
of delivered nitro~en is 20 kg/hr.
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11~4791
,
The gaseous mixture discharged ~rom the bubbli~g cham-
ber consists of sulphur dioxide (9120 kg/hr, which is 18.4
per cent by volume), sulphur vapour (25675 kg/hr, 81.2 per
cent by ~olume) and inert gases (20 kg/hr, 0.42 per cent by
volume). ~he mixture is delivePed into the ~luidized bed of
silica gel (particle size, 1.5 mm). Technical oxygen contain-
ing nitrogen (183.5 kg/hr) is delivered in~o the fluidized
bed at a rate of 41,699 kg/hr. Sulphur vapour is completely
oxidized in the ~.~uidized bed at a temperature of 650C,
which is maintained at this point by withdrawing excess heat
from the fluidized bed. The resultant gas consists o~ sulphur
~ioxide, 64.95 per cent by volume (60,468.6 kg/hr), oxygen
34,55 per cent by volume (16,024 kg/hr), and inert gases,
0.5 per cent by volume (203,5 kg/hr).
~ !
'~he process is carried out under a pressure of to 35 atm
on a pilot plant. ~rom a melting chamber, having a capacitg
of one cubic metre, sulphur is loaded periodically into the
bubbling chamber in the quantity of 0.017 cu.m. The diameter
of the chamber is ~.3 m, the bed height is 1 m. ~he total de-
livery of oxygen is 60 cu.m/hr (~P). ~he quantity o~ ox~ygen
- spent ~or bubbling is 20 per cent o~ the to~al quantity o~
oxygen. ~he production capacity of the svaporator is 130
kg/hr, t~e intensity o~ evaporation being 2000 kg per square
meter of the sur~ace per hour. ~he inert material used in t~e
fluidized bed is specially treated aluminosilicate catalyst
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11~4791
having particles o~ 1.5 mm. The height of the bed is
- 0.5 m. ~he temperature in the ~luidized bed is mai~tain-
ed at 600 - 615C. ~he composition of the gas discharged
~rom the furnace is
S02 48 - 50 per cent by volume
2 ~ - 40 per cent b~ volume
S03 1.8 - 2 per ce~t by volume.
inert gases to make 100 per cent.
Example 5
~ he process is carried out on a pilot plant under
atmosp~eric pressure Pure sulphur is loaded periodically
into a cylindrical apparatus, having the diameter of 0.008 m
and a height o~ 1.2 m, and provided with an ex*ernal electric
heater. ~he cover of the apparatus has t~o connections, for
a bubbler tube and for taking gas samples. ~he bubbling
height in the c~linder varies from 0.5 m to 1 metre. '~he con-
sumpticn of oxygen for bubbling varies from 0.5 to 3 cu.m~hr
(S~P). The analysis of gas taken from the zone above the mel~
has shown a ~00 ~er cent o~idation of sulphur with oxygen,
the height of bubbling being 0.5 metre. ~he temperature of
the melt varies from 300 to ~00C. Electric heating is used
to commence the process at smaIl rates of air consumption
(0.5 - 1 cu.m/hr, at S~P). ~e bubbler chamber comprises a
cooling coil through which water is passed when sulphur boils.
A vapour-~as mixture is formed in the ~pace above the surfacc
o~ the molten sulphur. The Dixture consists of sulphur vapour
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11~4791
(17.0 cu.m/hr, STP) and sulphur dioxide (3 cu.m/hr, S~P).
The obtained quantity of sulphur vapour is oxidized in the
~luidized bed o~ aluminosilicate (1 mm particles) at a tem-
perature of 650 - 700C. ~he concentration of the obtained
sulphur dioxide is 98 - 99 per cent by volume.
~ he capacity of the apparatus is 3000 - 3500 ~cg per
sq.m per hour.
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