Note: Descriptions are shown in the official language in which they were submitted.
This inYention relates to a method for thermal cracking
sulfuric acid wherein sulfuric acid is passed into an ultrasonic
field provided by an ultrasonic atomizer while simultaneously
combusting fuel to provide sulfuric acid thermal cracking
temperatures, and to ultrasonic atomizers useful in practicing
the method for thermal cracking sulfuric acid.
In a number of chemical processes, waste sulfuric acid
containing varying amounts of impurities are obtained. The
lmpurities may be organic or inorganic such as the ammonium,
iron, and sodium sulfate salts, and water. Generally, these
impurities can only be removed from the waste sulfuric acid by
expensive procedures. It has been proposed that sulfur values
can be recovered from waste sulfuric acid by thermal cracking
the sulfuric acid to provide a sulfur dioxide gas which can be
removed from the impurities. The sulfur dioxide-containing
gas can be conventionally processed, e.g. by the contact method,
to obtain concentrated sulfuric acid or oleum.
Heretofore, thermal cracking of waste sulfuric acid
has been accomplished by, for instance~ injecting the waste
acid into a reaction chamber which is maintained at thermal
cracking temperatures, e.g. 800 to 1300C., by the simultaneous
combustion of fuel in the rea¢tion chamber. ~he acid is gener-
ally in;ected into the reaction chamber by means of pressure ato-
mizers or rotary atomizers. A number of, for example~ oil burners
are provided in the reaction chamber to provide the necessary
thermal energy for thermal cracking of sulfuric acid. Frequently,
the reaction chamber is cylindrical and vertical, and the waste
acid is injected centrally at the ceiling with the burners
being disposed radially or tangentially into the reaction chamber.
Problems occurred with the use of pressure or rotary atomizers
in that they tended to clog rapidly and thus were prone to dis-
turbances, especially since a flnely-divided ~istribution of
sulfuric acid is desired for efficient thermal cracking.
Ultrasonic atomizers operating with an ultrasonic
generator (Hartman generator) are known and have found applica-
tion as ultrasonic oil burners~ Unlik~ heating oil which is a
practically h~mogeneous li~uid, contaminated waste sulfuric
acids which are subjected to thermal cracking re~uently either
initially contain solids or precipitate solids during atomiza-
tion. Consequently, waste sulfuric acid must be introduced
in a considerably larger layer thickness into the ultrasonic
field than the thicknesses emploved wi~h heating oil. Moreover,
the presence of solid c~mponents in as well as changes in the
composition of waste acid as well may affect the degree of ato-
mization. Irregular atomization may cause the thermal cracking
to be susceptible to disturbances such as flame cooling.
My prior U. S. Patent No. 3,908,904, issued September
30, 1975, with Friedrich Mahler and Heinrich Petexs as co~
inventors, discloses usin~ ultrasonic atomiæers for atomizing
waste sulfuric acid in acid cracking furnaces. In ul~rasonic
atomization, the effec~ of mechanical injection thxough a
nozzle is further intensi~iëa by an ultrasonic field in the
zone in front of the nozzle. Thus, a desirably fine dispersion
of the waste acid can be obtained using a coarse spray. The
dispersion of the waste acid may be subjected to thermal
cracking by ~hermal energy provided by fuel burners disposed
within the furnace. The fuel burners may be placed axially
on the ceiling of the furnace such that already hot gases en~er
the thermal cracking zone parallel ~o the acid mist. In this
manner, there is no danger of flame subcoolin~.
, ~ ' J
When the cracked gas is processed to obtain sul~uric
acid or oleum, the amounts of gaseous diluents in the cracked
gas is of substantial concern. A highly diluted cracked gas
may require increased expenditures for additional and larger
apparatus in the sulfllric acid plant to process the larger vol-
ume of gas and will require increased power costs. The use of
more concentrated oxygen-providing gases for combustion with
fuel to reduce the amount of diluent gases from that providing
using air as the oxygen source, may lead to the production of
high temperatures, for instance, in excess of 2000C. using
oxygen as the oxygen source, which may result in damage to con-
-ventional oil burners and the lining of the combustion chamber.
Moreover, since the cracked gases are generally cooled and
cleaned before they are fed to the sulfuric acid plant, unre-
duced sulfuric acid, and in some cases sulfuric acid compounds
in the cracked gases, together with other gas impurities, can
lead to corrosive attacks on treating equipment. Furthermore,
during scrubbing~ hexavalent sulfuric moieties in the gas may
at least partially be dissolved in the scrubbing water and thus
20 are lost from the system. Consequently, it is desired to provide -
essentially complete thermal cracking of sulfuric acid with
minimal dilution of the thermal cracked product with inert
gases.
By the method of this invention, sulfuric acid, which
may be waste sulfuric acid, for instance, containing suspended
solids or dissolved salts which precipitate upon atomization of
the acid, and fuel are passed into an ultrasonic field whereby
the ultrasonic field atomizes sulfuric acid. Combustion of -
fuel with oxygen is conducted within the ultrasonic field to pro-
j 30 vide sulfuric acid thermal cracking temperatures, e.g. about
~ 800 to 1300C., preferably about 900 to 1100C. Thermal
cracking yields of SO2 provided by the method of this inve~ltion
may be high, e.g. at least about 99 or about 99.5%, and the
thermal cracking is not unduly susceptible to disturbances.
Since the thermal cracking is almost complete, corrosion in the
processing equipment downstream from the thermal cracking may
be minimal. External fuel burners such as employed in conven-
tional sufluric acid thermal cracking furnaces may be omitted,
resulting in a reduction of equipment costs and elimination of
periodic conventional maintenance. Conveniently, an ultrasonic
atomizer for providing the ultrasonic field is adapted to inject
fuel and waste acid into the ultrasonic field. In view of the
finely~divided form of the liquid, combustion of fuel with oxy-
gen and thermal cracking of sulfuric acid to provide sulfur di-
oxide occurs quickly and requires a thermal cracking zone of less
volume than if the entire source of thermal energy were provided
by fuel burners outside the ultrasonic field. The ultrasonic
field may also be employed for atomization of waste solutions
containing salts, e.g. ammonium salts, of sulfur-containing
acids.
In one aspect of this inventiong a mixture of fuel and
sulfuric acid is prepared, and the mixture is injected into the
ultrasonic fieId. The fuel may desirably be liquid, e.g. fuel
oil, and may be dispersed in the acid by means of conventional
apparatus for dispersing a liquid in a second liquid which is
immiscible with the first liquid. Such apparatus include mixing
nozzles for liquids, e.g. Venturi-type mixing nozzles. The fuel
is often employed in amounts less than the amounts of sulfuric
acid to be thermally cracked~ and thus an oil-in-water dispersion
is generally formed.
37
In another aspect of this invention, the fuel and
sulfuric acid to be thermally cracked may be passed through
separate nozzle openings into the ultrasonic field. In this
manner, fuel and sulfuric acid are separately, but simulta-
neously, injected into the ultrasonic field. An ultrasonic
atomizer for use in this aspect of the method o~ this invention
provides for the separate injection of fuel, sulfuric acid, and
sound gas, i.e. operating medium, which is gas passed through the
atomizer to provide ultrasonic vibrations. The fuel and sulfuric
acid may be released from the nozzle in, for instance, concentric
patterns, into the ultrasonic field, and the patterns in the
ultrasonic field may conveniently overlap. The liquid passing to
the ultrasonic field may be ln the form of finely-divided drops,
; for instance, having a size of about 0.2 to 2 millimeters.
Advantageously, the fuel is injected into the ultrasonic field
concentrically around a separate, central injection of sulfuric
acid; however, the sulfuric acid may be concentrically injected
around a separate, central injection of fuel. Conveniently, the
ultrasonic field surrounds both the sulfuric acid nozzle and the
fuel nozzle.
The method of this invention enables oxygen and air-
enriched with oxygen as well as air to be used as the oxygen-
containing gas to support combustion of the fuel without such
high temperatures occurring as to damage the combustion chamber
or the ultrasonic atomizer. Due to inkimate mixing of fuel and
sulfuric acid by the method of this invention, the endothermic
thermal crackin~ of the sulfuric acid serves as a heat sink,
without undue subcooling, to the interspersed exothermic fuel
combustion thereby tending to abate undeslrable peaks of high
temperature on even a local basis in the combustion zone. The
dispersion of fuel and sulfuric acid may be essentially uniform,
but in any event, the mixing is sufficient to avoid localities
in the ultrasonic field of excessively high temperature which
may be deleterious to the equipmenf,. The oxygen-containing
gas is preferably employed in an amount in excess of that re-
quired for complete combustion of the fuel, i.e. for hydrocarbon-
containing fuels, to carbon dioxide and water or for elemental
sulfur-containing fuels, to sulfur dioxide, on a stoichiometric
basis. The gases from the thermal cracklng zone may fequently
contain about 1 to 9, preferably about 2 to 4, volume percent
free oxygen. The oxygen-containing gas may, for instance, con-
tain at least about 25 volume percent free, or molecular, oxygen.The capability Or employing oxygen or air enriched with oxygen
as the oxygen-containing gas provides numerous advantages to the
method of this invention. For instance, since the oxygen-con-
taining gas may contain less inert gases than air, the amount
of fuel employed can be reduced while still maintaining the same
thermal cracking temperature. Particularly in conventional
sulfuric acid thermal cracking units employing air as the oxygen-
containing gas, it has been necessary to provide a preheater
ror the air. Such an air preheater may not be required in meth-
ods of thls invention in view of the reduced amounts of gas toheat and hi8her combustion kemperatures which can be achieved
using more oxygen rich oxygen-containing gases than air. ~y
using oxygen as the oxygen-¢ontaining gas, the volume of effluent
gases from the thermal cracking zone may be about 40% lower than
the amount of gases provided when air is used. Since the con-
centration of sulfur dioxide is correspondingly greater in the
effluent gases, the volume of~ for instance, a ~onventional
sulfuric acid plant to convert sulfur dioxide to concentrated
sulfuric acid or oleum may be substantially less and may result
in a cost savings of about 30 percent over the costs required
for the sulfuric acid plant to treak effluent gases when air
,
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-;:' - ' ., ' ' ~ '
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~ h~
is used as the oxygen-containing gas. A savings o~ about 30
percent in electrical energy costs may also be real~zable.
The ultrasonic field is provided by the action of the
ultrasonic atomizer on the passage therethrough of compressed
operating medium, i.e. sound gas. The frequency of the ultra-
sonic field is suitably bet~een about 10 and 1000 kilohertz,
especially between about 20 and 100 kilohertz. The sound gas
may be generally provided at a pressure of about o.6 to 10,
pre~erably o.6 to 4, atmospheres absolute. The ultrasonic field
atmoizes liquids passing therethrough and droplets in the range
of between about 1 and 200 microns, especially between about
50 and 80 microns, may be obtained. Conveniently, the oxygen-
containing gas for combustion with fuel is employed as the sound
; gas although other gases may also be employed such as steam
which can be condensed from the effluent gases prior to passing
to a sulfuric acid plant. Oxygen-containing gas may also be
supplied by secondary oxygen supply ports, but preferably the
oxygen-containing gas is supplied ln whole or part as the sound
gas. `
Ultrasonic atomizers which may be beneficially employed
in the method of this in~ention generally contain feed duct or
ducts centrally arranged in the sound generation portion of the
ultrasonic atomizer. Inkegral with the feed duct is a nozzle
through which ~eed enters the ultrasonic field. Surrounding the
feed duct or ducts is a sound gas conduit. At the operative end
~ face of the sound generator is positioned a deflector for the
- sound gas for guiding the sound gas from the sound gas conduit
into a resonance chamber whereat ~ibrations are for~ed. The
deflector and resonance chamber are preferably disposed concen-
trically around the nozzIe portion of the feed duct, and the
resonance chamber includes an outlet opening into the operative
-7-
end face. In one aspect of the apparatus of this invention, a
single feed duct is preceded by a mixer which mixes and provides
a fine dispersion of liquid ruel in sulfuric acid ~or passing to
the ultrasonic field. The mixer may be a mixing nozzle such
as a Venturi-type mixer. In another aspect, two concentric
feed ducts are provided, one for sulfuric acid, e.g. the inner
duct, and the other for fuel. The fuel and acid are separately
inJected into the ultrasonic field and are mixed in the ultra-
sonic field.
A furnace for thermal cracking of sulfuric acid which
may beneficially be employed in accordance with this invention
comprises one or more ultrasonic atomizers centrally arranged
in the furnace. The furnace, which may be brick-lined, may
conveniently be of a cylindrical configuration and be vertically
oriented with the ultrasonic atomizer positioned on the ceiling.
The furnace may contain a furnace body constriction at a spacing
from the furnace ceiling of about 1 to 4, preferably 1.5 to 3,
times the diameter of the furnace. By this arrangement of the
furnace, ultrasonic atomizer and furnace body constriction, a
gaseous flow is achieved in the furnace which enables almost
all of the sulfuric acid to be thermally cracked in a relatively
small furnace volume. The residence time of the gases in the
thermal cracking zone may be from about 0.1 to 5, preferably
1 to 4, seconds. The ultrasonic atomizer may also be selected
to provide a beneficial configuration of the mixture of sulfuric
acid and fuel for thermal cracking of the acid.
Various liquid or gaseous fuels under the conditions
of injection into the furnace may be employed in the method of
this inventi~n. Typical ~uels include hydrocarbon-containing
liquid fuels such as fuel oil~ molten sulfur, or hydrocarbon-
containing gaseous fuels such as fuel gas. The fuel selected
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s..Juld in any ev~nt be capable of pr~vidlng surriclent h~zt to
maintain thermal cracklng temperatures ln the furnace during
operation.
The invention is further illustrated with reference to
the drawings in which
Figure 1 is an axial schematic sectional representa-
tion of a thermal cracking furnace for sulruric acid, and
Figure 2 is an axial schematic sectional representa-
tion Or a head of an ultrasonic atomizer for atomization and
mixing of separate streams Or fuel and sulfuric acid.
With reference to Figure 1, ultrasonic atomizer 12
ls centrally positioned on the ceiling 10~ of vertical thermal
c;racking furnace 10. Air is supplied to the ultrasonic atomizer
as the sound gas via line 16 by means of blower 14 ~hich draws
air through filter 1~. Waste sulfuric acid to be atomized is
supplied to mixing nozzle 13 via line 18, and is intimately
mixed therein with fuel oil passing to the mixing nozzle through
pipe 17 to form an oil-in-acid dispersion. The oil-in-ac~d
dispersion passes through feed duct 12a to the head of ultra-
sonic atomizer 12 and is injected into the ultrasonic field in
- thermal cracking zone lOb. Fire bridge, or furnace body con-
striction, 11 is provided in the furnace to enhance thermal
cracking of sulfuric acid to provide sulfur dioxide. The sulfur
dioxide-containing effluent is discharged from the furnace
through line 19~ The effluent may be transported to a sulfuric
acid plant to convert sulfur dioxide to sulfuric acid or oleum.
Figure 2 illustrates head 1 of an ultrasonic atomizer
for separately injecting sulfuric acid and ~uel~ e.g. fuel gas~
into the ultrasonic field, Central feed duct 2 is adapted to
pass sulfuric acid to the thermal cracking zone. At the front
of central duct 2 is pressure atomizer nozzle 5. Annular feed
,'i. .
duct 3 is adapted to pass ~uel gas to and through annular open-
ing 6 at face of the ultrasonic atomizer. The sound gas is
passed via outer annular sound gas conduit 4 to the face of the
ultrasonic atomizer ~here it impinges on deflector surface 8
and is deflected into resonance chamber 7 to provide ultrasonic
vibrations and ultrasonic field for atomizing and mixing the
fuel and sulfurlc acid.
The invention may be further understood by reference
to the following examples. A sulfuric acid thermal cracking
operation of the prior art is provided in Example 1.
EXAMPLE 1
A cylindrical, vertical waste sulfuric acid thermal
cracking furnace is provided with an ultrasonic atomizer for
waste acid disposed centrally on the ceiling of the furnace and
six conventional oil burners directed radially into the furnace
chamber. Approximately 23.1 tons per hour of waste sulfuric
acid are passed through the ultrasonic atomizer into the furnace
chamber. The waste sulfuric acid is obtained from a methyl
methacrylate production plant and contains about 11.3 weight
percent sulfuric acid, 53.5 weight percent ammonium bisulfite,
1.0 weight percent ammonium sulfate, 2 weight percent disul-
fonic acid, 1.6 weight percent other organic components, and
30.6 weight percent water. Air ls passed to the thermal crack- -
ing zone at a rate of 11,570 Nm3 (cubic meters at standard
temperature and pressure) per hour. The total consumption of
fuel oil including the oil required in preheating the air is
4,120 kilograms per hour. Approximately 72,700 ~m3 per hour
of wet effluent from the thermal cracking zone are obtained,
3o and the wet effluent contains about 4.2 volume percent sulfur
dioxide and about 3.1 volume percent molecular oxygen. The wet
,
--10--
.
effluent is dried to provide about 50,380 Nm3 per hou.r of dried
gas containing 6.o volume percent sulfur dioxide and 4.5 volume
percent molecular oxygen. The energy consumption inclusive of a
sulfuric acid plant is about 40,000 kilowatt hours per day.
The following examples are illustrative of sulfuric
acid cracking operations in accordance with the method of this
invenkion.
EX~MPLE 2
A sulfuric acid cracking furnace of the type described
in connection with Figure l is employed in connection with this
example. A wa~te sulfuric acid stream having essentially the
same composition and flow rate as described in Example 1 is
intimately admixed with 2.38 tons per hour of fuel oil to pro-
vlde a fuel oil in acid dispersion. The dispersion is fed to
the reaction chamber through an ultrasonic atomizer. The sound
gas for the ultrasonic atomizer is a mixture of 8,100 Nm3 per
; hour of air and 5,300 Nm3 per hour of molecular oxygen. Free
oxygen comprises about 51 volume percent of the sound gas. ~bout
~ 20 36,725 Nm3 per hour of wet effluent containing 8.4 volume per-
; cent sulfur dioxide and 2.3 volume percent molecular oxygen are
obtained. No oil burners are provided, and the necessary thermal
energy is provided by combuskion of fuel in the ultrasonic field.
~fter drying, about 16,350 Nm per hour of effluent containing
18.9 volume percent sulfur dioxide and 5.2 volume percent
molecular oxygen are obtained. The energy consumption inclu-
sive of a sulfuric acid plant is about 25,000 kilowatt hours per
day. The cost of the waste sulfuric acid thermal cracking unit
and sulfuric acid plant is estimated to be about 67 percent of
the cost of the installakions for Example 1.
~9 ~
~XAMPLE 3
Essentially the same procedure as described in Example
2 is repeated except 6,900 Nm3 per hour of molecular oxygen are
employed as the sound gas. The total fuel oil consumption is 2.3
tons per hour. The thermal cracking apparently proceeds without
deleterious effects from combusting fuel with essentially pure
oxygen. ~bout 30,180 Nm3 per hour of wet effluent containing
10.2 volume percent sulfur dioxide and 2.8 volume percent
molecular oxygen are obtained, and upon drying the gas, 10,100
Nm3 per hour o~ a gas containing 30.5 volume percent sul.fur
dioxide and 8.4 volume percent molecular oxygen are provided.
Examples 2 and 3 illustrate that the method for thermal
cracking sul~uric acid Or this invention provides a sulfur
dioxide-containing gas which can be of substantially higher con-
centration than that o~ conventional thermal cracking units.
'rhus, lesser operational and equipment costs are incurred by
employing the method of this invention, especially when the sul-
fur dioxide is processed to provide sulfuric acid or oleum.
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