U.S. patent application number 13/256990 was filed with the patent office on 2012-01-05 for environmentally clean process for utilizing pyrolysis products.
This patent application is currently assigned to T.D.E. RECOVERY TECHNOLOGIES LTD.. Invention is credited to Alexander P. Bronshtein, David Shalom Jakobowitch, Menachem L. Skop, Moshe Weiss.
Application Number | 20120000188 13/256990 |
Document ID | / |
Family ID | 42739249 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120000188 |
Kind Code |
A1 |
Bronshtein; Alexander P. ;
et al. |
January 5, 2012 |
ENVIRONMENTALLY CLEAN PROCESS FOR UTILIZING PYROLYSIS PRODUCTS
Abstract
A process for the recovery of sulfur from the products resulting
from the pyrolysis of sulfur-containing organic materials,
comprises the steps of: a) carrying out the combustion of liquid
pyrolysis products, thereby to obtain sulfur dioxide in the formed
exhaust gases; b) reacting hydrogen sulfide recovered from gases,
generated in the pyrolysis process, with said sulfur dioxide; and
c) reacting hydrogen sulfide recovered from gases, generated in the
gasification of solid pyrolysis products, with said sulfur dioxide,
and as a result to obtain elemental sulfur, pure gaseous fuel and
exhaust gases from liquid products combustion free from
sulfur-containing compounds.
Inventors: |
Bronshtein; Alexander P.;
(Beer Sheva, IL) ; Skop; Menachem L.; (Beer Sheva,
IL) ; Weiss; Moshe; (Tel Aviv, IL) ;
Jakobowitch; David Shalom; (Bnei Brak, IL) |
Assignee: |
T.D.E. RECOVERY TECHNOLOGIES
LTD.
Beer Sheva
IL
|
Family ID: |
42739249 |
Appl. No.: |
13/256990 |
Filed: |
March 16, 2010 |
PCT Filed: |
March 16, 2010 |
PCT NO: |
PCT/IL10/00219 |
371 Date: |
September 16, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61160842 |
Mar 17, 2009 |
|
|
|
Current U.S.
Class: |
60/282 ;
431/253 |
Current CPC
Class: |
F27D 3/16 20130101; F27B
7/00 20130101; C10J 2300/0956 20130101; Y02E 20/12 20130101; Y02P
20/143 20151101; F23G 5/20 20130101; F23G 5/0276 20130101; C10J
2300/094 20130101; F27B 7/20 20130101; F27B 7/362 20130101; C10J
3/66 20130101; C10J 2300/0973 20130101; C10B 53/07 20130101; C10J
2300/0946 20130101; C10B 1/10 20130101; C10B 49/04 20130101; C10B
51/00 20130101; F27B 7/42 20130101; F27B 7/10 20130101; B65G 11/206
20130101 |
Class at
Publication: |
60/282 ;
431/253 |
International
Class: |
F01N 3/18 20060101
F01N003/18; F23Q 2/32 20060101 F23Q002/32 |
Claims
1. A process for the recovery of sulfur according to claim 5,
comprising the steps of: a) carrying out the combustion of said
liquid pyrolysis products, thereby to obtain sulfur dioxide; b)
reacting said sulfur dioxide with hydrogen sulfide recovered from
said gases generated in the pyrolysis process and from said
generator gases; thereby to obtain elemental sulfur and, pure
gaseous fuel essentially free from sulfur-containing compounds,
wherein the total sulfur recovery is at least 99%.
2. A process according to claim 5, wherein sulfur dioxide is
contained in exhaust gases formed in a diesel
electro-generator.
3. A process according to claim 5, wherein the sulfur dioxide
formed during combustion of pyrolysis liquid products, reacts with
the recovered hydrogen sulfide in three sub-stages over catalysts
selected from the group consisting of: an activated alumina, a
mixture of activated alumina with titanium oxide (1:1) and, a
catalyst comprising iron and chromium oxides supported by
.alpha.-alumina or silica.
4. A process according to claim 5, being an efficient electrical
power production process, wherein: a) the fuels, which are
employed, comprise gaseous and liquid fractions of pyrolysed tire
shreds; b) the liquid fraction obtained from a pyrolysis step is
used directly for power production; c) the gaseous fraction of the
pyrolysis products, and the gas generated during the gasification
of solid pyrolysis products are cleaned from hydrogen sulfide,
using the monoethanolamine process or other similar process,
resulting in a hydrogen sulfide stream and in a clean gaseous
stream; and d) the exhaust gases from the power production of step
b) are mixed with said hydrogen sulfide stream of step c), and
reacted in a modified Claus process, such that essentially no
sulfur-containing compounds are released into the atmosphere;
wherein said final exhaust gases are free of sulfur dioxide, and
comprise less than 20 ppm hydrogen sulfide, preferably less than 10
ppm, and more preferably less than 1 ppm.
5. An environmentally friendly and energy-efficient process for the
pyrolysis of sulfur-containing organic materials and for recovery
of sulfur, wherein; a) the output of the pyrolysis, carried out in
a pyrolytic reactor, comprises gaseous, liquid and solid
sulfur-containing products; b) said liquid product is used as a
fuel for electric power generation, producing after its combustion
exhaust gases containing sulfur dioxide; c) the said solid,
carbonized product is gasified, whereby obtaining generator gas
which is used as a heat carrier for heating the raw material in
said pyrolytic reactor; d) said gaseous product in mixture with
said generator gas, partly cooled after separation from said
condensed liquid product, after leaving said pyrolytic reactor,
undergoes cleaning from hydrogen sulfide and provides a hydrogen
sulfide stream, and a pure gaseous fuel for electric power
generation, said gaseous fuel producing after its combustion final
exhaust gases essentially free from sulfur or sulfur-containing
compounds; and e) said hydrogen sulfide stream reacts with said
exhaust gases containing sulfur dioxide and provide regenerated
elemental sulfur said environmentally friendly process producing
electrical power in said steps b) and d), pure sulfur in said step
e), and final exhaust gases essentially free of sulfur or
sulfur-containing compounds in said step d).
6. A process according to claim 5, wherein said sulfur-containing
raw organic materials for pyrolysis are selected from discarded
tires, other sulfur vulcanized polymers, natural materials such as
coals, oil shales, bitumen, and mixtures thereof.
7. A process according to claim 6, wherein the liquid product of
pyrolysis is of a quality suitable for burning either in engine
electro-generators or in suitable furnaces for subsequent power
generation.
8. A process according to claim 6, wherein said raw material
comprises discarded tires, and wherein the solid product of the
pyrolysis consists of solid carbonized component, and steel
component in the form of wire cuts from tires cord.
9. A process according to claim 8, wherein the solid carbonized
product directed to gasification is first crushed and separated
from the steel by sieving or by electromagnetic separation.
10. A process according to claim 9, wherein the solid carbonized
product is gasified in gas generators with raised or with
horizontal flows or with pseudo-liquefied (boiling) bed using only
air or oxygen blowing, or blowing of said gases with steam,
resulting in up to 950-1000.degree. C. hot gaseous fuel containing
sulfur in the form of hydrogen sulfide.
11. A process according to claim 10, wherein the hot generator gas
is fed to a chamber to obtain a gaseous heat carrier by mixing with
the final cool gas of the process so as to form-a gaseous heat
carrier having a temperature of 650-700.degree. C. for directly
heating the pyrolytic reactor, or having a temperature of
700-800.degree. C. for indirectly heating the pyrolytic
reactor.
12. A process according to claim 5, wherein the heat of exhaust
gases, formed in the cleaned gaseous mixture combustion and in the
liquid pyrolysis product combustion, are utilized as a heat carrier
for the sulfur regeneration process.
13. A process according to claim 5, wherein said sulfur-containing
organic materials comprise discarded tires, and wherein in step e)
said hydrogen sulfide is in excess over said sulfur dioxide, in a
molar ratio of up to 3.7:1.
14. A process according to claim 5, wherein residual amounts of
hydrogen sulfide is removed from the processed exhaust gas in step
d) using a sorbent consisting of activated carbon or its mixture
with impregnated activated carbon, further comprising the
regeneration of said sorbent, and adding regenerated hydrogen
sulfide to said stream provided in step d).
15. A process according to claim 5, wherein the heat for sulfur
regeneration process in all its sub-stages is provided by exhaust
gases.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an energy-efficient and
environmentally friendly process for the pyrolysis of
sulfur-containing organic materials. More particularly the
invention relates to processes for the recycling of
sulfur-containing products, such as vulcanized polymers. A
particularly interesting process of this type is the recycling of
used tires by a process that does not release sulfur containing
compounds into the atmosphere.
BACKGROUND OF THE INVENTION
[0002] Many methods for the conversion of discarded tires are known
in the art, to produce useful products such as fuels. Also known in
the art are methods for cleaning obtained products from polluting
compounds. However, process known in the art suffer from a variety
of drawbacks, such as they release polluting gaseous sulfur
compounds into the atmosphere or require expensive purification
steps to remove them prior to the release of exhaust gases. Other
processes end with other liquid or gaseous polluting discharges or
require cleaning steps that are not economically efficient;
furthermore, prior art processes often fail to exploit the
pyrolysis products in an efficient manner.
[0003] For instance, U.S. Pat. No. 4,240,587 discloses a process,
in which the tires are first cryogenically fragmented and then
pyrolysed at 450-500.degree. C. in a rotary inclined cylinder,
which is heated indirectly. The remaining pyrolysis oil may either
be further utilized as an initial component for manufacturing
chemical compounds, such as lubricants, or it may be used as a fuel
propellant. The remaining pyrolysis gas is utilized for the direct
operation of a gas turbine. However, all the suggested products of
this invention contain sulfur and therefore their combustion
products cause sulfur dioxide pollution of the atmosphere.
[0004] An illustrative cleaning process is found in US
http://patft.uspto.gov/negacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&-
p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&1=50&s1=4,806,232.PN.&OS=PN/-
4,806,232&RS=PN/4,806,232-h0#h0http://patft.uspto.gov/netacgi/nph-Parser?S-
ect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=-
G&1=50&s1=4,806,232.PN.&OS=PN/4,806,232&RS=PN/4,806,232-h2#h24,806,232,
which describes a method for the desulphurization of
sulfur-containing heavy fuels or used oil, in which the fuels are
mixed with solid basic additive (preferably lime) and metal in
finely divided form (preferably iron powder). The mixture obtained
is injected into the pyrolysis and the sulfur is absorbed or
chemically bonded to the basic additive and separated. The
permanent gas formed in the pyrolysis and the simultaneously formed
condensate may be directly fired as low-sulfur fuel. This method is
expensive and cumbersome to perform and, therefore, has not found
broad application in the art.
[0005] It is therefore clear that it would be highly desirable to
provide a simple process by which pyrolysis products can be
obtained, which are free from harmful sulfur product or could be
used as fuels without release into the environment of harmful
sulfur-containing products.
[0006] It is therefore an object of the present invention to
provide a process that overcomes the drawbacks of the prior art. It
is another object of the invention to provide an
environmentally-friendly process for the recycling of
sulfur-containing high-molecular and other organic materials. It is
yet another object of the invention to provide an efficient
recycling process that maximizes the utilization of the products of
pyrolysis.
[0007] Other objects and advantages of the invention will become
apparent as the description proceeds.
SUMMARY OF THE INVENTION
[0008] In an aspect of the present invention there is provided a
process for the recovery of sulfur from the products resulting from
the pyrolysis of sulfur-containing high-molecular weight organic
material, comprising the steps of: [0009] a) carrying out the
combustion of liquid pyrolysis products, thereby to obtain sulfur
dioxide; [0010] b) reacting hydrogen sulfide recovered from gases
generated in the pyrolysis process with said sulfur dioxide; and
[0011] c) reacting hydrogen sulfide recovered from generator gases,
if any, with said sulfur dioxide; thereby to obtain elemental
sulfur, gaseous products essentially free from hydrogen sulfide and
exhaust gases essentially free from sulfur dioxide.
[0012] According to one embodiment of the invention sulfur dioxide
is contained in diesel exhaust gases formed in a diesel
electro-generator.
[0013] The invention can be usefully exploited in a process for the
treatment and utilization the products of the pyrolysis of
sulfur-containing high molecular weight organic materials, to
generate electric power without environmental contamination and
without the formation of non-usable by-products. The process
includes the gasification of the solid organic materials and the
use of the produced hot gas, together with pyrolysis gas, as a
direct heat carrier for a pyrolytic reactor, and the subsequent use
of both gas mixtures, after cleaning from hydrogen sulfide, for
electric power generation.
[0014] In another embodiment of the invention the processing of
hydrogen sulfide produced resulting from processes pyrolysis and
gasification accordingly the known Claus process is not needed for
the thermal stage of the process for obtaining sulfur dioxide, as
it is done usually in the Claus process (and as described e.g. in:
Ulmann's Encyclopedia of Industrial Chemistry, 2003, Sixth,
Completely Revised Edition, volume 34, pp. 605-627). Thus, such
very complicated thermal stage is eliminated.
[0015] In the process of the present invention only the second,
catalytic stage, of the Claus process:
2H.sub.2S+SO.sub.2.fwdarw.3S+2H.sub.2O
is in principle used. This reaction runs over a catalyst: activated
alumina at 240-330.degree. C. in different steps of the process.
The stream of hydrogen sulfide interacts with exhaust gases from
the liquid product combustion, which contain sulfur dioxide. For
the complete purification of the exhaust gases from H.sub.2S
residue, the third sub-stage is used for oxidizing H.sub.2S
directly over a suitable catalyst according to the reaction:
2H.sub.2S+O.sub.2=2S+2H.sub.2O.
[0016] In the final stage the exhaust gases undergo treatment by a
suitable sorbent.
[0017] In an embodiment of the present invention the total physical
heat of the exhaust gases, those containing sulfur dioxide, and
those that do not contain sulfur dioxide (formed in a clean gaseous
fuel combustion) is enough for the said total catalytic process,
i.e., an additional heat source is not required for heating the
reaction mixtures after their cooling at each stage of the process
for sulfur vapors condensation. This obviates also the need for
equipment for heating the reaction mixture, which is a prerequisite
in the classical Claus method.
[0018] In another aspect the invention encompasses an efficient
electrical power production process, wherein: [0019] (a) the fuels
are gaseous and liquid products of the organic material (e.g.,
discarded tire shreds) pyrolysis, and the gaseous product of the
pyrolysis solid product gasification; [0020] (b) the liquid product
obtained from a pyrolysis step is used directly for power
production; [0021] (c) the solid carbonized product is gasified in
a gas generator resulting in gaseous fuel (generator gas)
containing hydrogen sulfide. The hot generator gas, which is
partially cooled by mixing with cool gas of the total process, is
directed into the pyrolysis reactor as a heat carrier; [0022] d)
the mixture of gases, formed through the pyrolysis of raw material,
and said gaseous heat carrier outgoing from the pyrolysis reactor
together with the formed vapors, after cooling and separation from
condensed liquid product, undergoes purification from hydrogen
sulfide by known methods, e.g., by the monoethanolamine process.
After this step two streams are obtained: the separated hydrogen
sulfide stream and the mixed cleaned gas that is used as a fuel for
electric power generation;
[0023] (e) the exhaust gases resulting from the combustion of the
liquid pyrolysis products, which contain sulfur dioxide, are
interacted with the said separated hydrogen sulfide stream,
resulting in sulfur-free final exhaust gases, and sulfur as a
recycled product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic illustration of a total pyrolysis
process according to one embodiment of the present invention;
and
[0025] FIG. 2 is a detailed illustration of the sulfur recycling
process according to one embodiment of the process of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The process that is schematically illustrated in FIGS. 1 and
2 can be carried out using a variety of different equipment and
arrangements and, as will be apparent to the skilled person, is not
limited to any particular arrangement of equipment and process
steps, as long as the composition resulting from the process at its
outlets is essentially comparable to the one that will be described
in greater detail hereinafter.
[0027] Without departing from the generality of the above, one
exemplary process will be described in greater detail, with
reference to FIG. 1, which is a schematic flow sheet of a pyrolytic
process for discarded tires, provided for the purpose of
illustration.
[0028] The discarded tires are pyrolysed in a pyrolytic reactor
after having been shredded into large pieces of size 250-300 mm,
which are fed through a feeding system schematically indicated at
numeral 1. The pyrolysis reactor can be of any suitable type and is
therefore not described herein, for the sake of brevity. In the
reactor the tire pieces are heated up to a typical temperature of
480-500.degree. C., e.g., by a gaseous heat-carrier indicated at 2.
The heat-carrier is preferably--but not limitatively--a gas 10
produced by the gasification of the solid carbonized product 7 and
partly cooled by mixing in a mixing chamber, using cooled and
cleaned final gases, up to 650-700.degree. C.
[0029] In the example of FIG. 1 the hot heat-carrier passing
through the pyrolysis reactor is partially cooled by its contact
with the tire pieces and is mixed in the reactor with the gases and
vapors formed during tire shreds pyrolysis. The combined stream
leaves the reactor at numeral 3 and is cleaned from dust in a
dedicated separator 4, for example a Vortex system, manufactured by
Vortex Co., Israel. Then the vapor-gas stream 4 is directed to a
system for cooling and vapor condensation, which includes two
stages. In the first stage the vapor-gas stream is cooled in an air
cooler by means of air stream 8, directed from a source of air,
typically up to about 130.degree. C. Here part of the vapors is
condensed. The cooler provides also flushing of the vapor-gaseous
stream from the remainder of dust, by part of condensate formed in
the process. The hot air 13 leaving the cooler is directed to the
gas generator, where its heat is utilized, thus utilizing part of
the heat of the vapor-gaseous pyrolysis products and of the
gasifying gases. The formed liquid and the stream of gas and of
non-condensed vapors 14 from the air cooler enter the gas-liquid
separator, after which the first liquid product 15 is directed for
treatment to a centrifuge, where the liquid is cleaned from the
last dust, and is directed to its oil collector. The gas and
non-condensed vapors 16 enter the second stage cooler-condenser,
where it is cooled to about 15-20.degree. C. The condensed second
liquid and the gas come into a separator (see 17) and after their
separation are directed as follows: the gas 22--to cleaning from
hydrogen sulfide and the liquid product is directed to its
collector or is mixed with heavier liquid 19. The produced oil is
ready to be used as a fuel for diesel or other electro-generators,
accordingly the requirements for their type of engine. This fuel
combustion, as previously mentioned, is accompanied in the prior
art by the emission of sulfur dioxide in the exhaust gases. The
sulfur recovery process according to the invention solves the
environmental problems associated with the use of said liquid
fuels, as further discussed below.
[0030] The cooled gas separated from the oil, as hereinbefore
mentioned, enters at numeral 22 into a system where it is cleaned
from hydrogen sulfide by monoethanolamine. The clean gas can be
combusted without damage to the environment and is used as a
gaseous fuel for electric power generation by means of
electro-generators. Illustrative examples of such generators are,
for example, those manufactured by GE Jenbacher GMBH & CO OHG
(Austria) with gas engines from 342 kWe up to 3,119 kWe. Part of
the cleaned gas is directed to a mixing chamber for partially
cooling the hot gas stream 10 from the gas generator and preparing
the heat carrier 11 for the pyrolysis reactor. Another part of the
cooled and cleaned gas 25 acts as a fuel in a burner for a heat
exchanger, which is used to control the final temperature of the
gaseous heat carrier 2 that is fed to the pyrolytic reactor.
[0031] The recovered hydrogen sulfide 24 is reacted with exhaust
gases 21 obtained from the combustion of the liquid fuel obtained
from the pyrolysis. The reaction runs as a modified Claus catalytic
reaction, as already discussed above. The resulting exhaust gases
are sulfur dioxide-free and are non-polluting.
[0032] The sulfur that is formed in the reaction between hydrogen
sulfide and sulfur dioxide (from the exhaust gases), is collected
and is a marketable product.
[0033] The solid pyrolysis product formed during the pyrolysis of
discarded tire shreds, is evacuated at 6 from the reactor; it
comprises solid carbonized material and steel cord in the form of
wire. The carbonized material is fragile and when treated in a
suitable crusher, such as a hammer crusher, it can be readily
reduced in size and thereafter separated from the cord by sieving
or by electromagnetic separation. The crushed carbonized solid
product separated from cord steel is directed at 7 to rising- or
fluidized bed gasification and the cord steel can be recycled.
[0034] The solid carbonized product gasification can be carried out
as a steam-air (respectively 9-13) process without the introduction
of external heat. Resulting from such process, taking place at
temperatures around 1,000.degree. C., a semi-water generator gas is
formed. The generator gas 10 undergoes cleaning from dust in a
cyclone system known per se in the art and therefore not described
herein in detail. Further, the generator gas is partial cooled by
its mixing with cool gas 25 so that the temperature of the mixture
is decreased to 650-700.degree. C. The mixture of gases so obtained
is a gaseous heat carrier 2, which can be used to heat the pieces
feedstock in the pyrolytic reactor.
[0035] The above description, as stated, is not intended to limit
the invention in any way but it does provide a more comprehensive
understanding of a practical scenario in which the invention can be
advantageously implemented. Of course, the skilled person will be
able to devise alternative scenarios and setups in which the
invention can be advantageously carried out.
[0036] Reverting now to FIG. 2, the process of the present
invention for the sulfur regeneration is shown in detail. The
regeneration of sulfur comprises: [0037] a) The recovery of
hydrogen sulfide contained in gaseous products resulting from the
pyrolysis of sulfur-containing organic material, as well as in
gases resulting from gasification of solid pyrolysis product;
[0038] b) The recovery of sulfur contained in sulfur-organic
compounds present in liquid products.
[0039] According to the present invention hydrogen sulfide 24 (FIG.
1) recovered from pyrolysis and generator gases interacts with
sulfur dioxide, which is contained in exhaust gas 21 (FIG. 1)
formed in an electro-generator during the combustion of liquid
pyrolysis products. The reaction is a modified Claus catalytic
reaction that runs through three sub-stages. The molar ratio
H.sub.2S to SO.sub.2 in the reaction mixture entering the first
sub-stage is up to 3.7. The operating temperature in this sub-stage
is preferably about 320.degree. C. This temperature promotes the
hydrolysis of COS and CS.sub.2, which can be formed during the
liquid fuel combustion. Activated alumina, which is the known Claus
catalyst, is used. With this catalyst the H.sub.2S oxidation by
oxygen present in the exhaust gases (in a small amount) is minimal.
The gaseous reaction mixture after cooling, and the formed sulfur
condensation, are fed to the second sub-stage which is previously
heated in heater 210; the reaction runs at 200-220.degree. C. over
a mixture of alumina and titanium dioxide catalysts where the
reaction between residual hydrogen sulfide and sulfur dioxide
reaches completion. The processing exhaust gas still contains
residues of H.sub.2S. In order to remove said H.sub.2S the residual
hydrogen sulfide is directly oxidized into sulfur over the
appropriate catalyst. This can be done by means known in the art;
for instance, U.S. Pat. No. 5,262,135 discloses a complete stage of
the Claus process as contacting the tail gas preliminary admixed
with oxygen and heated preferably up to 220.degree. C. in a fixed
bed with a catalyst comprising at least 80% by weight TiO.sub.2 and
containing of an impregnate selected from the group consisting of
nickel, iron and cobalt. In this case air is introduced into the
processed stream and hydrogen sulfide is oxidized accordingly the
reaction
2H.sub.2S+O.sub.2.fwdarw.2S+2H.sub.2O
[0040] After the said reaction the stream is cooled to obtain
sulfur condensation. In one embodiment of the invention it is
preferred to organize the oxidizing stage using the known
Superclaus catalyst--iron and chromium oxides supported by
.alpha.-alumina or silica (described in Ulmann's Encyclopedia of
Industrial Chemistry referred to above) or using the catalyst
disclosed in U.S. Pat. No. 6,506,356, that do not depend on the
presence of steam.
[0041] In principle, according to WO 1987/002653, a practically
complete after-treatment is achieved in the last stage by passing
the gases through the solid metal oxide sorbent, e.g. zinc oxide,
combined with a porous carrier material and iron, cobalt and nickel
oxides with further regeneration of the sorbent. According to the
present invention the temperature (usually about 450.degree. C.)
and heat content of both exhaust gases (21 and 26, FIG. 1) is
sufficient for carrying out all stages of the modified Claus
catalytic reaction. This obviates the need for additional heat and
heating equipment for in each sub-stage of the process, which is a
prerequisite in the classical Claus method.
Process Description
[0042] The process flow diagram for sulfur recovery according to
one embodiment of the invention is shown in FIG. 2. The exhaust
gases 202 and 202.1 (21, 26 in FIG. 1) from the electro-generators
enter the heater 210 (FIG. 2) of the second sub-stage of the
process. Here they heat the reaction mixture 209, formed after
cooling the stream in the first sub-stage by cooler 207, from
140.degree. C. up to 200-220.degree. C. Then the partially cooled
exhaust gas 202 (21 in FIG. 1) containing sulfur dioxide is fed to
the mixing and heating into a chamber 203, where it mixes with the
hydrogen sulfide stream and thus a hot reaction mixture is formed
for the first sub-stage of the catalytic reaction of hydrogen
sulfide with sulfur dioxide contained in the exhaust gas; if it is
necessary to raise the temperature of the reaction mixture, the
clean exhaust gas 202.1, which is free of sulfur dioxide, goes
through a heat exchanger of the chamber 203 and heats the said
reaction mixture.
[0043] The reaction mixture 204 enters reactor 205, where the Claus
catalytic reaction takes place over an activated alumina catalyst.
According to one alternative embodiment of the invention instead of
a fixed bed reactor-converter a rotating horizontal
reactor-converter is used. The rotating reactor is equipped with a
horizontal shaft provided with mixing blades. At low speed of
rotation (0.2-3 rpm) sufficient mixing is achieved while avoiding
catalyst abrasion and improving the contact between gaseous
reaction mixture and the catalyst surface. Application of modern
catalysts in the form of balls with a diameter 4.8 mm and more
having enough high strength showed a slight dust formation in an
actual test. The feeding of the gaseous reaction mixture is carried
out through a distribution manifold installed outside the reactor
at its bottom. The gases leave through the outlet pipe in the upper
part of the reactor and further pass through the said Vortex
chamber for cleaning from the said slight amount of dust. A
periodic withdrawal of part of the spent catalyst for regeneration
is performed simultaneously with its completion without stopping
the reactor by means of charging and discharging lock chambers
preventing leaking the gases into the atmosphere.
[0044] After leaving the reactor, stream 206 containing the formed
sulfur is cooled down to 140.degree. C. in cooler 207, the
condensed sulfur is separated from the gas stream in liquid state
and is removed at 208 from the cooler. The reaction mixture is fed
(at 209) to the second sub-stage of the catalytic reaction. Here
the mixture is heated again in the heater 210 by exhaust gas
streams 202 and 202.1, as previously discussed, and enters the
reactor 212 (at 211) for the second sub-stage of the catalytic
reaction over alumina and titanium dioxide catalysts. Then the
mixture 213 leaves the reactor 212 and is cooled in cooler 214 down
to the temperature required for sulfur condensation (140.degree.
C.), separated and removed (215). Furthermore air is injected into
the reaction mixture and the mixture is heated again up to
220.degree. C. in a heater 217 by means of the exhaust gas 202.1
leaving the first sub-stage heat exchanger (placed in chamber 203).
The heated reaction mixture is fed to reactor 219 for the direct
oxidation of the tail hydrogen sulfide with sulfur formation, over
the Superclaus catalyst or over the catalyst containing oxides of
vanadium, titanium, and of element selected from group of Fe,
Mn,Cr, Ni, Sb and Bi (see U.S. Pat. No. 6,506,356).
[0045] For reliability in the complete purification the processed
exhaust gases 202 from hydrogen sulfide they are passed through a
sorbent consisting of activated carbon, particularly the granular
non-impregnated GC Sulfursorb Plus for H.sub.2S Treatment or the
Spectrum XB-17 (50/50 blend of activated carbon with granular media
impregnated with potassium permanganate) which are produced in
General Carbon Corp., USA. AQIVID (Air Quality Management District)
publishes results of Carbon Scrubber Hydrogen Sulfide Removal
Performance (2006 year), wherein when the inlet ELS concentration
in air is 10-20 ppm the outlet concentration can be between
0.01-0.1 ppm (the allowable concentration is 1 ppm). This
demonstrates the possibility of complete after-purification of
exhaust gases from H.sub.2S.
EXAMPLE
[0046] Checking the Interaction of Exhaust Gases, Resulting from
the Combustion of Pyrolysis Liquid Fuel in a Diesel Engine and
Containing Sulfur Dioxide, with the Stream of Hydrogen Sulfide.
[0047] The liquid fuel was produced from the pyrolysis of discarded
tire shreds in an experimental, 7 liter reactor. The final
pyrolysis temperature averaged 493.degree. C. The average yields of
pyrolysis products are, in mass %;
[0048] gas--10.9;
[0049] liquid--44.4;
[0050] solid--44.7 (including steal cord wire).
[0051] The liquid product density is 0.890; the sulfur content
0.95%.
[0052] The system for the sulfur regeneration testing included
equipment for carrying out three sub-stages of catalytic reaction:
three reactors, two heaters and three coolers and also the exhaust
gases source. The exhaust gases containing sulfur dioxide were
produced by a motorcar ("Renault") operating on diesel fuel. The
exhaust gases were passed through an intermediate box and further
transported by a blower into the reactor, where they displaced the
air from the box and from the reactor, which was preliminarily
filled up to 2/3 of its volume with catalyst. Then the car was
refueled by 6 kg pyrolytic liquid (6.7 liter) and continued to work
(without motion) and burned all the fuel in 134 min. In the inlet
tube the exhaust gas was mixed with H.sub.2S flow from a balloon,
thereby forming the reaction mixture. The rate of the H.sub.2S flow
was 1.1 liter per minute, which corresponds to the flow of H.sub.2S
extracted from pyrolysis and gasification gases while 6 kg of
liquid are produced. The molar ratio between H.sub.2S and SO.sub.2
was 3.7:1, as it is in real conditions in the recycling process for
discarded tires shown in FIG. 1.
[0053] The reactor-converter for the Claus catalytic reaction was a
horizontal cylindrical vessel of 7 liters volume with side covers
that was equipped with a horizontal rotating shaft and with mixing
blades. It was also provided with devices for the charging and
discharging of the catalyst, as previously discussed and can be
heated electrically by means of a spiral located around its outer
surface. In the first reactor the activated alumina catalyst was
used in the form of balls of 4.8 mm diameter. The reaction mixture
after the reactor was fed to the cooler and was cooled down to
140.degree. C. The formed sulfur was condensed and fed to the
separator (the lower empty part of the cooler). There the vapors
and gases were separated from sulfur and were fed to the tube
heater that was heated by an electric coil up to 220.degree. C.,
and was fed to the second preliminary heated reactor, which was
similar to those described above. The catalyst mixture used was
activated alumina and titanium dioxide. After passing the reactor,
the reaction mixture was fed to the second sub-stage cooler and
after separation of the formed sulfur it was fed to the third
sub-stage. The residual hydrogen sulfide was directly oxidized by
injected air over the Superclaus oxidizing catalyst
(.alpha.-alumina supported iron and chromium oxides) at 220.degree.
C. Further the reaction mixture was cooled in the third sub-stage
cooler down to 140.degree. C. and was separated from the condensed
sulfur. For the extraction of any H.sup.2S residue the exhaust gas
was additionally fed to an absorber filled with activated carbon of
type GS Sulfursorb Plus with the addition of Activated Carbon
impregnated with soda caustic.
[0054] The following experimental results were obtained:
[0055] Amount of Regenerated Sulfur:
[0056] in the first sub-stage--164.2 g
[0057] in the second stage--87.0 g
[0058] in the third stage--18.1 g
[0059] in the adsorption stage H.sub.2S--0.7 g
[0060] The total sulfur recovery was 99.7%.
[0061] The H.sub.2S concentration in the cleaned exhaust gas was 7
ppm, which is less than the Occupational Safety and Health
Administration (OSHA, USA) acceptable ceiling limit in the
workplace (20 ppm). It is also less than the limit set by the
National Institute for Occupation Safety and Health (NIOSH, USA),
which recommends 10 ppm in the work place.
[0062] As discussed above, the total after-purification from
H.sub.2S could be obtained here using an activated carbon scrubber
of greater capacity, where the hydrogen sulfide concentration can
be decreased down to 0.1 ppm and less, i.e. less than the allowable
concentration in atmospheric air.
[0063] All the above description of the process, system and
examples has been given for the purpose of illustration and is not
intended to limit the invention in any way. Many modifications can
be effected to the various process steps, materials and equipment,
and many different raw materials may be processed, all without
exceeding the scope of the invention.
* * * * *
References