GB2228929A

GB2228929A - Desulphurization of gaseous effluents

Info

Publication number: GB2228929A
Application number: GB9001164A
Authority: GB
Inventors: Claude Dezael; Gerard Martin; Frederic Kolenda
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 1989-01-19
Filing date: 1990-01-18
Publication date: 1990-09-12
Anticipated expiration: 2010-01-18
Also published as: JP3005690B2; FR2642663B1; GB9001164D0; GB2228929B; FR2642663A1; JPH02245222A; DE4000188A1

Description

S DESULPHURIZATION OF GASEOUS EFFLUENTS The invention relates to a process

for the desulphurization in a flowing fluidized bed of gaseous streams containing substantial quantities of sulphur compounds such as sulphur trioxide, sulphur dioxide, hydrogen sulphide, sulphur, carbon hydroxy5 sulphide and mercaptans by a regeneratable absorbent mass.

It more particularly applies to the desulphurization of gaseous streams produced during the regeneration of catalysts on which coke has been deposited during the catalytic cracking of a hydricarbon charge. These gaseous streams generally contain sulphur pollutants diluted in smoke gases and under these conditions it is difficult to increase the value thereof.

US Patent 429089 describes the introduction into a catalytic cracking unit of regeneratable absorbent masses, which fix the sulphur dioxide released during the combustion of the coke deposited on the cracking catalyst. These absorbent masses flow in fluidized bed form with the catalyst into the regenerator and reactor (riser) and are decomposed in the latter releasing hydrogen sulphide. Part of the sulphur introduced with the charge is directed towards the fractionating column and then to a Claus-type unit. Although of interest from the cost standpoint, because no significant extra costs are involved, this desulphurization procedure still suffers from disadvantages. The absorbent masses used have particular properties, namely the chemical composition and specific surfaces, which can lead k I - to relatively unselective cracking reactions. Moreover, the necessary absorbent quantities are considerable and consequently contribute to the dilution of the catalyst leading to a reduction of the conversion.

As the operating conditions of the reactor or riser are regulated so as to maximize the production of the sought, valorizable hydrocarbons and are not a function of the desulphurization performance characteristics, the desulphurization levels reached under these conditions leave much to be desired.

The prior art is also illustrated by US Patent 4283380, where there is a desulphurization of the smoke gases in a fluidized bed in an absorption zone by an absorbent constituted by alumina, optionally containing an oxide of a metal of group VB and VIII at a tem perature not exceeding 4000C, so as to bring about no deterioration of the porous structure of the alumina. This desulphurization is followed by a regeneration in a fluidized bed of the alumina which flows by gravity. However, this process cannot be directly applied to catalytic cracking regeneration effluents, due to their thermal level generally corresponding to temperatures between 600 and 8000C.

Finally, the prior art can be illustrated by European Patent applications EP-A-0214910, 215709, British patent application and US Patent US-A-444219.

Moreover, the regeneration effluents contain sulphur polluting products in a low concentration and their subsequent valorization is made more difficult, particularly in Claus-type units.

The process according to the invention makes it possible to obviate these disadvantages and solve the problem, whilst still obtaining excellent desulphurization yields and good regeneration of the absorbent. It can be more particularly applied to the desulphurization of the smoke gases resulting from the regeneration of a catalytic cracking catalyst. It also makes it poss- ible to enhance the value of the sulphur compounds resulting from the smoke gases to be treated.

Thus, the invention specifically relates to a process for the desulphurization of a gaseous stream incorporating a substantial quantity of sulphur compounds such as SO 2' so 3 and/or H 2 S having a stage of absorbing these compounds on an absorbent mass in an absorption zone under absorption conditions in the presence of an oxygen- containing gas, a stage of regenerating the absorbent mass enriched with sulphur compounds in the form of sulphates in a regeneration zone under regeneration conditions in the presence of a reducing gas and a stage of recycling at least part of the absorption mass, which has at least partly been regenerated in the absorption zone; characterized in that the absorption stage comprises:

a) the introduction at a first end of the absorption zone of particles of the absorbent mass comprising at least one zeolite in a matrix, magnesium oxide, nickel oxide, iron oxide, vanadium oxide and optionally aluminium oxide, cerium oxide, cobalt oxide, platinum oxide and/or palladium oxide, in appropriately chosen proportions, the absorbent mass having a grain size distribution between 5 and 5000 micrometre3 and a specific surface between 0.1 and 500 m 2 /9; b) the introduction of the gaseous stream at a temperature bet- ween approximately 400 and 1000 0 C at said end of the absorption zone in such a way that the surface velocity in the absorption zone is between 0.3 and 40 m/s; c) the contacting, in the flowing fluidized bed, of the gaseous stream and said particles in the presence of an oxygen-containing gas under absorption conditions such that the sulphur content of said gaseous stream is reduced and a mixture is obtained of particles enriched with the sulphate of the metal introduced in stage a) and sulphur-depleted gaseous effluent; d) the at least partial separation of said sulphate-enriched particles from said sulphur-depleted gaseous effluent in a seperation zone at the opposite end of the absorption zone; e) the recovery of the f,-;--nt cffl-.ucnt having a.---d.-,ced.

sulphur content; The process also being characterized in that the regeneration stage comprises:

f) the contacting in the regeneration zone of at least part of said sulphur-enriched particles in a flowing fluidized bed and the reducing gas at a temperature between 400 and 1000 0 c and with a surface velocity of the resultant gases in the fluidized bed of 0.3 to 40 m/s, so as to obtain a mixture of regenerated particles and a second sulphur-enriched effluent; g) the at least partial separation of the regenerated particles and the second effluent in a separation zone downstream of the regeneration zone; and h) the second effluent is recovered.

Compared with the prior art, the inventive process has the advantage of a better contact between the particles and the gas in the desulphurization and regeneration zones due to the use of a zeolitic material. It is also possible to treat regeneration effluents of catalysts obtained in both stages, whereof one was performed in -- reducing medium.

Unlike in US Patents 4240899 and 4175275, the absorption and regeneration zones according to the present process are separate and Rppnrated by a regeneratiOn and =talytic --rack4-.-g reaction zone from the coke-charged catalyst, which makes it possible to optimize the temperatures of the absorption and regeneration zones of the absorbent mass.

The regeneration effluent resulting from the process of the invention and which is highly enriched with sulphur, particularly sulphur dioxide, can be valorized either by passing into a Claustype unit where all the sulphur compounds are converted into sulphur, or by passing into a sulphuric acid production unit.

According to a particular embodiment, the regeneration effluent could be treated by reducing to H 2 S on a catalytic bed in the presence of at least part of a reducing torch or fuel gas from the distillation of a catalytic cracking effluent. The products resulting from the catalytic reduction reaction are then treated in a conventional manner in an amine unit and then in a Claustype unit.

According to a feature of the process, the oxygen quantity introduced in stage (q) necessary for the more or less complete combustion reactions of the gaseous stream, catalyzed by metal oxides of the absorbent mass and for the desulphurization reactions by the metal oxides, is such that the first gaseous effluent containing at least 2% by volume of oxygen, e.g. 2 to 5% of oxygen is recovered.

The main reactions -ns follows:

the combustion reactions catalyzed by the metal oxides of the absorbent mass:

CO + 1/2 (0 2 + 4 N 2)_-5C02 + 2N2 H 2 + 1/2 (0 2 + 4 N 2) 4H 2 0 + 2N 2 COS + 3/2 (0 2 + 4 N 2)---lco 2 + SO 2 + 6N 2 H 2 S + 3/2 (0 2 + 4 N 2)--IH 2 0 + SO 2 + 6N 2 so + 1/2 (0? + 4 N + 2N 2 2) 'S03 2 the desulphurization reactions by metal oxides:

so 3 + mo---- so 4 m so 2 + 1/2 (0 2 + 4N 2) + MO --->SO 4 M + 2N 2 the metal MO oxide o. so 4 m = sulphate of the metal.

The mass absorbing the sulphur compounds from the gaseous stream comprises a zeolite in a matrix more particularly containing the silica in a weight proportion equal to 5 to 25% for 75 to 95% of matrix, impregnated by/or mixed advantageously with magnesium oxide, nickel oxide, vanadium oxide, iron oxide and optionally platinum oxide, palladium oxide, aluminium oxide, cobalt weight oxide in the followingiproportions:

1 zeolite + matrix 30 to 98.97% M 9 0 1 to 30% preferably 10 to 20% coo, 0 to 2000 ppm preferably 0 to 100 ppm Ni 0 100 to 2000 ppm preferably 500 to 1000 ppm Fe203 100 to 2000 ppm preferably 100 to 1000 ppm V 2 0 5 100 to 2000 ppm preferably 500 to 1000 ppm Al 203 0 to 30% preferably 10 to 30% CeO 2 Pto PdO 0 to 10% preferably 1 to 10% 0 to 100 ppm preferably 5 to 50 ppm 0 to 100 ppm preferably 5 to 50 ppm The zeolite used can be an aluminosilicate-based zeolite. a ZSM5 zeolite, an e.g. Y faujasite used for the catalytic cracking of petroleum charges and which can contain at the most 5% by weight coke, e.g. 1 to 3%.

Advantageously the particles of the absorbent mass can have a grain size distribution between 20 and 100 micrometres and preferably between 20 and 50 micrometres. This prevents sedimentation of the catalyst in the apparatus, which would lead to an efficiency loss of the absorbent mass. The surface velo- city of the resultant effluent gas in the fluidized bed in the absorption zone is advantageously between 8 and 30 m/s.

According to another feature of the process the magnesium oxide used in stage (c) and the sulphur compounds contained in the 9 - gaseous stream are in a molar ratio between 1 and 20 and preferably between 1 and 10.

On operating in this way at temperatures advantageously between 500 and 8000C an excellent desulphurization rate exceeding 98% was obtained. Under these conditions it is possible to directly desulphurize cracking catalyst regeneration smoke gases, whereof the temperature on leaving the regenerator is essentially of the same order of magnitude.

The stage of regenerating the particles of the absorbent in the form of metal sulphate (Mg, V, Ni, Fe and optionally Al, Ce, Co, Pt and Pd) can be carried out in a fluidized bed regenerator in the presence of a reducing gas, which is usually hydrogen, methane, hydrogen sulphide, sulphur in vapour form or torch/ fuel gas at a temperature advantageously between 500 and 800 0 C, the torch gas preferably resulting from the distillation of the catalytic cracking effluent. Regeneration generally takes place in counter-current manner with a surface velocity of the effluent gases in the fluidized bed between 0.3 and 1 m/s.

For example with methane, the reactions are as follows, as a function of the desired stoichiometry and the operating conditions 4 MSO 4 + 3CH 4 ---.4S + 3C0 2 + 6H 2 0 + 4M0 4 MSO 4 + CH4--- 4SO 2 + 2H 2 0 + C09 + 4M0 MSO 4 + CH 4 ----M 2 S + H 2 0 + CO 2 + MO According to another feature of the invention, the zeolitic catalyst used for the production of the desulphurizing mass can result from catalyst purging of a fluidized bed catalytic cracking unit, the latter already containing elements constituting the desulphurizing mass according to the invention, e.g. nickel, cobalt, iron, vanadium, platinum, optionally supplied by the charge to te treated or by the catalyst. It is merely necessary to add thereto in this case complementary absorption agents MgO or MgO and optionally Al 2 0 3 According to another feature of the process, the reducing gas is conventionally introduced into the regenerating zone in a molar ratio with respect to the metal sulphates contained in the particles generally between 1 and 20 and preferably between 2 and 10.

According to another feature of the process, it is possible to check the temperature of the regeneration zone either by bringing about an at least partial circulation of sulphate-enriched particles in a heat exchange zone operating in fluidized bed manner upstream of the regeneration zone, or by carrying out a partial combustion of the reducing gas in the regeneration zone in such a way that the temperature is between 400 and 10000C.

According to another feature of the process, it is possible 1 1 tale regenerated at Cast part 0A.

to Circu a at - L &..L es separated after stage (g) into a second heat exchange zone, the same as in the previous case e.g. operating in a fluidized bed, prior to carrying out the recycling stage of the particles in the absorption zone. The gaseous stream to be desulphurized can come from any random refining unit. It can in particular result from the regeneration of a spent catalytic cracking catalyst in at least one regeneration zone. When the cracking unit has two regeneration zones, the gaseous stream can come from the first regeneration zone, the second zone, or both zones.

In this case, it can contain a substantial oxygen quantity intro duced in excess during the regeneration of the spent catalyst.

The desulphurizing mass can be prepared in different ways.

It can e.g. be prepared by impregnating a catalytic mass (zeolite + matrix) with a solution containing soluble salts of magnesium, nickel, vanadium, iron and optionally platinum, palladium, alum inium, cobalt and in particular the nitrate, sulphate, acetate or chloride of said metals, drying and calcining in air the product obtained. The salt concentration of the solution will obviously depend on the desired oxide content in the mass and the solubility of said salts in the solution. It will e.g.

be between 10 and 26 g of SO 4 Mg for 100 g of water, or between and 50 g of magnesium acetate for 100 g of water, between 0.001 and 0.050g of vanadyl sulphate for 100 g of water, between 0.001 and 0.050 g of ferric nitrate for 100 g of water and bet ween 0 and 0.001 g of platinum chloride, between 0 and 0.001g of pailat!-um --hloride and beenreen 0 and 0.050 a of nickel nitrate r 0 for 100 g of water.

Impregnation can take place once or several times with drying of the product obtained after each operation. The drying temperature is advantageously between 100 and 1500C. After drying, the product obtained is calcined in a furnace under air at a temperature between 400 and 8000C.

It can also e.g. take place by intimately mixing a catalytic mass (zeolite + matrix) and a powder containing the said oxides and having an appropriate grain size distribution of 5 to 5000 micrometres and advantageously 20 to 100 micrometres.

The powder can be obtained by all means giving a powder of metal oxides, e.g. by drying by atomizing between 350 and 5500C an alumina suspension treated by an acid in such a way as to obtain a gel and a magnesium oxide suspension containing in solution nickel, vanadium, platinum, palladium, cobalt, cerium and iron salts.

The grain size of the magnesium oxide used is advantageously between 5 and 500 and preferably between 20 and 100 micrometres.

The concentration of soluble salts in the suspension of alumina and magnesia is calculated so as to obtain the desired content of said oxides in the absorbent mass. It is advantageously between 0 and 0.001% by weight for the platinum and palladium salts, 0 and 0.05% by weight for the cobalt salts and 0.001 and 0.05% by weight for the vanadium, nickel and iron salts.

1 The invention will be better understood from fig. 1 showing in an illustrative, diagrammatic manner an apparatus for performing the process. The drawing illustrates a fluidized bed cracking unit with two regenerators supplying a gaseous stream cont- aining sulphur compounds to an apparatus for desulphurizing said gaseous stream. In the drawing the apparatus comprises a riser 1 supplied at its bottom with vapour by line 2, with hot cracking catalyst by line 3 and with a hydrocarbon charge containing sulphur by line 4.

After cracking, the mixture of catalyst and effluent hydrocarbon vapours is fed into the stripper 5, supplied with vapour by line 6. The hydrocarbon vapours, freed from particles, leave the stripper through line 15 and are sent to a not shown fractionating column.

is A line 7 from stripper 5 feeds the spent catalyst containing coke and sulphur compounds to the base of a first regenerator 8, where under per se known first regeneration conditions there is a partial combustion of the constituents deposited on the catalyst in the presence of air supplied by a line 9. The partly regenerated catalyst then passes into a second regenerator 12 via a pipe 10 (lift) supplied with vapour by line 11, whilst the first regeneration effluents, after dust removal in at least one internal or external cyclone 14a, are collected in order G be passed at a terperature f,'L Of. 1, L. m approximately 700 - by a p-pe 17 to the subsequently described inventive apparatus. These first regeneration effluents, which are particularly rich in hydrogen, hydrogen sulphide, unburnt hydrocarbons and carbon monoxide are generally at a pressure above that prevailing in the second regenerator. They can be expanded in an energy reco- very turbine 16, whose inlet is connected to the cyclone 14a by a pipe 17 and whose outlet is connected to pipe 20, on which is arranged a flow regulating valve 19a.

The second regenerator 12 receives the partly regenerated catalytic particles and permits an almost total regeneration of the latter under per se known second regeneration conditions by an oxygen supply delivered to the base of the second regenerator 12 by a pipe 13. The catalytic particles are then recycyled to the riser supply by line 3.

Dust is removed from the second regeneration effluents by an internal or external cyclone 14b with respect to regenerator 12. They are particularly enriched with sulphur dioxide, carbon dioxide and also generally contain an oxygen excess. They are at a temperature of approximately 800 0 C. They are supplied by a pipe 18 from the outlet of cyclone 14b of the second regen- erator 12 to a tubular desulphurization reactor 21, generally in the first half of the fluidized bed and preferably in the first third thereof. However, the effluent from the first regenerator supplies the bottom of the reactor, preferably substan4-4 "Ily at the s=e pressure as that of the secvad rcgenerator tiall - is - effluent introduced above the dense phase present in the bottom of the reactor. Pressure checking valves for the effluents 19a and 19b are located respectively on pipes 20 and 18. The desulphurization reactor 21 has an elongated tubular shape and preferably a circular cross-section. Injection means such as not shown venturi tubes make it possible to obtain a substantially axial injection of the first regenerat-4-on effluents and injection means such as nozzles permit a substantially radial injection of the second regeneration effluents at the lower end 22 of the reactor.

If the air excess of the second regenerator is inadequate for ensuring in the desulphurization reactor the complete combustion of the effluents from the first regenerator, as well as the sulphatization of the absorbent, a complementary air supply can be provided by the pipe issuing into said reactor, preferably between the two effluent inlet levels.

The particles of absorbent, e.g. ZSMS zeolite dispersed in a silicaalumina matrix and containing the oxide of magnesium, nickel, iron and vanadium in appropriately chosen proportions and which come from the subsequently described recycling means also supply the reactor 21 by conventional introduction means located at the end of a pipe 29. It is optionally possible to directly supply the regenerated particles to absorption zone 91 1,- lines- 44 and 44a.

Fresher particles from another source and representing the losses by purging can be introduced by line 23. These two lines preferably issue between the two introduction levels for the gaseous effluents 18 and 20.

Under these conditions, all the absorbent particles in contact with the gaseous effluent stream flow in co-current manner from bottom to top in the fluidized bed in reactor 21 for a time during which combustion and desulphurization can take place over essentially the entire height of the reactor, the fluidiz10 ation rate in the bed being between 0.3 and 40 m/s.

Desulphurized effluents are separated from the particles in at least one cyclone 26, whose inlet is connected to the upper end 25 of reactor 21 and are collected in a waste heat boiler, not shown in the drawing, by a line 27.

The particles leave cyclone 26 by an outlet 26b and drop into a fluidized bed cooling enclosure 28 with at least two fluidized compartments 30,31 separated by a partition 32 over part of the enclosure height. The first compartment 30 receives the hot absorbent, which can optionally be reinjected level with 20 the lower end of the desulphurization reactor by pipe 29.

A valve 35 for checking the flow rate of the hot particles makes it possible to limit their quantity in the reactor, so that there is-an overflow of said hot particles into compartment 31 cooled by a conventional exchanger means 33 immersed in the bed. The cooled particles are then delivered from compartment 31 to the end of a generator 37 by a pipe 36 controlled by a flow regulating valve 34.

If the need arises, the particles of the absorbent enriched with sulphates by the combustion and culphatization reaction in the reactor 21 can be cooled, because said reaction is exothermic, by passing into the compartment 31 containing the heat exchanger 33. Control valves 34,35, respectively on lines 36,29, make it possible to control the flow of particles in the various compartments and the intensity of the heat exchange. Line 36 transfers particles in the form of metal sulphates to the base of thecylindrical regenerator 37 operating in fluidized bed form and of a conventional nature. A reducing gas, such as methane is introduced by a line 38 connected to injectors 39, which ensure the fluidization of the particles in regenerator 37. As the absorbent regeneration reaction is endothermic, if the temperature in the regenerator is not sufficiently high, it is possible to introduce means 40 able to bring about a par20 tial combustion of the reducing gas.

The regeneration of the absorbent into metal oxide takes place with a flow of particles and reducing gas in co-current manner, the surface velocity of the effluent gas in the regenerator be-ing betucen 0.3 --d 40 mils. Once r-cgcncrat--d, t.e particles are partly separated from the regeneration effluents in an internal or external cyclone 41 located in the upper part of the regenerator. The concentrated effluents are partly evacuated by a pipe 42 to an e.g. Claus-type unit. The absorbent particles regenerated in metal oxides are supplied to another cyclone 43 by a line 44 using means 45 (gas lift), which is supplied with vapour. The effluents are discharged by line 46 to the upper part of the cyclone and are also directed towards the Claus unit. The separated particles are cooled in the aforementioned cooling enclosure 28 and are then recycled by line 29 to the bottom of the absorption column 21.

At least periodically, it is possible to carry out absorbent particle purges at various points of the apparatus, e.g. at the base 22 of column 21 by a line 47, or at the base of cyclone 43 by line 48.

The invention is further illustrated by the following illustrative and non-limitative examples.

Example 1

A catalytic cracking catalyst is regenerated in a catalytic cracking unit with two regenerators, as indicated in fig. 1.

The effluents from the two regenerators have the composition, flow rate and temperature indicated hereinafter (Table I).

1 TABLE I

Vol. % First regenerator N 2 CO CO 2 H 2 0 so 2 + H 2 S so 2 + SO 3 0 2 70.68 4.48 11.52 13.08 0.232 flow rate (Nm 3 /h) 119.481 T 0 c 6500C Vol. % Second regenerator 75.48 0.0037 15.82 6.54 0.213 1.94 48.951 8000C The absorbent mass has the following weight composition: ZSM 5 zeolite: 25%, silica-alumina matrix 73.05%, MgO = 1.5%, NiO: 0.1% V 2 0 5 = 0.15%, PtO = 4 ppm, Fe 2 0 3 = 0.2%, its grain size being between 40 and 60 micrometres and its specific surface being 150 m 2 /g.

The absorbent mass and the gaseous flow of the first regenerator are introduced into the lowest zone of the 16 m high, 5 m inter- nal diameter fluidized bed absorption reactor, whilst the flow from the second regenerator is introduced at a higher point an the lateral part.

r The combustion and oxidation air for the sulphur compounds is introduced at a rate of 31000 Nm 3 /h, so that at the reactor outlet is obtained an effluent gas containing approximately 2% oxygen. The surface velocity of the effluent gas in the fluidized bed is approximately 10 m/s and the temperature controlled by the heat exchanger downstream of the separator is 600 0 C. The total circulating flow rate of the absorbent mass in lines 29 and 36 is approximately 800 t/h.

The purified gas leaving the cyclone separator 26 has the foll owing composition:

N 2 74.4%, CO 2 so 2 40 ppm.

13.9%, H 2 0: 9.6%, 0 2 = 2%, CO = 10 ppm, The desulphurization yield is approximately 95.7%. Part of the mass which has absorbed the sulphur compounds is supplied at a flow rate of 51 t/h to the bottom of the regenerator (height 2m, diameter 1.6 m), where fluidization of the bed is ensured by a torch gas with the following volume composition:

H 2 = 23.5%, CH 4 = 55.7%, C 2 H 6 = 3.7%, CO 2 = 0.4%, N 2 = 16.8%.

The torch gas is introduced at a flow rate of 150 Nm 3 /h, its surface velocity level with the fluidized bed being 0.4 m/s.

1 1 The molar ratio of reducing compounds contained in the gas to the metal sulphates absorbing the sulphur compounds contained in the absorbent particles is approximately 1.11. The fluidized bed temperature is 6000C.

The composition of the effluent gas on leaving the regenerator is as follows:

so 2 H 2 0: CO N 2:

47% by volume 33% 14.5% 3.8% H 2 S: traces S traces H 2 "'1% CH 4: '-' 1 % is There is a characteristic SO 2 enrichment of the effluent, which can then be fed to a Claus-type unit. The regeneration rate of the mass is equal to 99%.

Example 2

A catalytic cracking catalyst is regenerated in a catalytic cracking unit having one regenerator, the effluent from the I OW . ion --age Ale regenerat - t..aving Lollowing composition, 1 rate and temperature:

N 2 76.745 vol. %, CO = 0.005%, CO 2 = 13%, H 2 0 = 8%, SO 2 + so 3 0.25%, 0 2 = 2%, flow rate: 150,000 NJ /h, temperature 7S&C.

The absorbent mass has the following weight composition: fauja- -5 site zeolite 12% magnesia-silica matrix 85.67%, MgO: 1%, NiO:

0.07%, V 2 0 5 = 0.11%, Ce 2 0 3 = 1%, Fe 2 0 3: 0.15%, its grain size being 60 to 100 micrometres and its specific surface 200 m 2 /g.

The absorbent mass and the gaseous flow from the cracking regenerator are introduced into the lowest zone of the absorption reactor of the fluidized bed comparable to that of example 1.

The velocity of the effluent gas in the fluidized bed is approx imately 10 m/s and the temperature controlled by a heat exchanger downstream of the separator is 5500C.

The purified gas leaving the cyclone separator 26 has the follow- ing composition:

N 2 = 77% vol. %, CO - 0.01%, CO 2: 13%, H 2 0 = 8%, SO 2 + SO 3 = 0.004%, 0 2 = 2%.

The purification yield is 98.4%.

Part of the mass which has absorbed the sulphur compounds is at a A"Lcw rate jj, 50 t/h tei thIle of the rzgener- ator, where fluidization of the bed is ensured by a CH 4 -rich gas having the following composition:

CH 4 = 80 vol. %, C 2 H 6 = 2%, N 2 = 18%.

The CH 4 -rich gas is introduced at a rate of 112.5 Nm 3 /h, its surface velocity level with the fluidized bed being 0.3 m/s. The molar ratio between the methane contained in the gas to the metal

sulphates absorbing the sulphur compounds contained in the absorbent particles is approximately 0.275.

The fluidized bed temperature is 650 0 C. The composition of the effluent gas on leaving the regenerator is as follows:

so 2 H 2 0 C0 2 N 2 H 2 S S H 2 CH 4 C 2 H 6 55.2 vol.% 27. 6 vol.% 13.8 vol.% 3.4 vol.% traces 11 IT 1% 0.5% The SO 2 -enriched effluent can be supplied to a Claus-type unit.

The regenerated absorbent mass is fed to the absorption stage.

The regeneration level of the mass is equal to 99% Example 3

Treatment takes place of the effluents of a cracking catalyst regeneration performed in a unit having two regenerators, like those described in example 1. The effluents are identical as regards composition, flow rate and temperature to those of example 1 given in Table 1.

The desulphurizing mass is formed by a spent catalyst used in the catalytic cracking unit, to which has been added a magnesia- alumina powder obtained by the atomization of an alumina-magnesia suspension.

This alumina-magnesia suspension is obtained in the following way:

- mixing an alumina powder with demineralized water, - addition of concentrated nitric acid to bring about the peptization of the alumina and to produce the alumina gel, which will be used as the binder, - addition of a magnesia suspension, accompanied by vigorous stirring.

The solid content of the alumina gel and the magnesia suspension are calculated so as to obtain a compound, whose compositions by weight or mass are respectively 30% MgO and 70% A1 2 0 3 This colloidal solution is then shaped by drying by atomizing with air at 5000C. This gives spherical particles with an average size of approximately 50 to 60 micrometres.

The absorption-regeneration unit is started up in the following way. Into the absorption and regeneration reactor is introduced a spent catalyst having the following composition by weight:

ZSMS zeolite = 12% Silica-alumina matrix = 85.8 Pt - 5 ppm NiO = 1. 7% v 2 0 5 = 0.35% Fe 2 0 3 = 0.15% Regenerated catalyst is then removed from the catalytic cracking unit (2 t/day) by line 50 and into it is incorporated 0.2 t/day of alumina-magnesia powder obtained by atomization, the regenerated catalyst and powder being mixed in a rotary drum. This mixture is introduced at a rate of 2.2 t/day into the sulphur compound absorption section by line 23. The total weight of the absorbent mass in the absorption reactor is maintained by drawing off approximately 2.2 t/day of mass with line 51.

1 After 8 days operation under the conditions of example 1, the mean weight composition of the absorption mass is as follows:

ZSM5 zeolite: 10.9%, silica matrix = 78, alumina: 6.36 MgO: 2.73%, NiO: 1.54 %, V 205: 0.32 %, PtO: 4.5 ppm, Fe 2 0 3:A 136%. The purified gas leaving cyclone 26 has the follo- wing composition by volume N2 74.4%, CO 2: 13.9%, H 2 0: 9.6%, 0 2: 2%, CO 4. 10 ppm, so 2 40 ppm. The desulphurization yield is identical to that of example 1, i.e. 95.7%.

The regeneration conditions are identical to that of example 1, as is the composition of the effluent gas.

After 8 days operation, the spent catalyst drawing off rate is brought to 0.5 t/day, that of the MgO-alumina mixture addi tion to 0.05 t/day and that of the drawing off at the absorption reactor to 0.55 t/day.

Under these new conditions, the SOX purification and the regeneration rates remain unchanged.

0 1

Claims

CLAIMS is 1. Process for the desulphurization of a gaseous stream

comprisinga substantial quantity of sulphur compounds such as SO 21 so 3 andlor H2S having a stage of absorbing these compounds on an absorbent mass in an absorption zone under absorption conditions in the presence of an oxygen-contain- tage of regenerating the absorbent mass enriched ing gas, a st with sulphur compounds in the form of sulphates in a regeneration zone under regeneration conditions in the presence of a reducing gas and a stage of recycling at least part of the absorption mass, which has at least partly been regenerated,in the absorption zone; in which the absorption stage comprises:

a) the introduction at a first end of the absorption zone of particles of the absorbent mass comprising at least one zeolite -In a matrix, magnesium oxide, nickel oxide, iron oxide, vanadium oxide and optionally aluminium oxide, cerium oxide, cobalt oxide, platinum oxide and/or palladium oxide, in appropriately chosen proportions, the absorbent mass having a grain size distribution between 5 and 5000 micrometres and a specific surface between 0.1 and 500 M2 /g; - 28 b) the introduction of the gaseous stream at a temperature between approximately 400 and 10000C at said end of the absorption zone in such a way that the surface velocity in the absorption zone is between 0.3 and 40 m/s;

c) the contacting, in the flowing fluidized bed, of the gaseous stream and said particles in the presence of an oxygen-containing gas under absorption conditions such that the sulphur content of said gaseous stream is reduced and a mixture is obtained of particles enriched with the sulphate of the metal introduced-in stage a) and sulphurdepleted gaseous effluent; d) the at least partial separation of said sulphate-enriched particles from said sulphur-depleted gaseous effluent in a separation zone at the opposite end of the absorption zone; and e) the rerovery of the first gaseous effluent having a reduced sulphur content; and the regeneration stage comprises:

f) the contacting in the regeneration zone of at least part of said sulphur-enriched particles in a flowing fluid ized bed and the reducing gas at a temperature between 1 1 400 and 1000oC and with a surface velocity of the resultant gases in the fluidized bed of 0.3 to 40 =/a, so as to obtain a mixture of regenerated particles and a second sulphurenriched effluent; is g) the at least partial separation of the regenerated particles and the second effluent in a separation zone downstream of the regeneration zone; and h) recovery of the second effluent.

2.

Process according to claim 1, wherein the oxygen quantity introduced in stage (c) is such that the first gaseous effluent containing at least 2% by volume of oxygen is recovered.

3. Process according to claims 1 or 2, wherein the absorbent mass comprises a zeolite in a matrix containing silica in a proportion of 5 to 25% by weight for 75 to 95% by weight of matrix impregnated by/or mixed with magnesium oxide, nickel oxide, iron oxide, vanadium oxide and optionally platinum oxide, aluminium oxide, palladium oxide, cobalt oxide and cerium oxide in the following proportions:

I zeolite + matrix 30 to 98.97% by weight Mgo 1 to 30% 11 NiO 100 to 2000 ppm Fe 2 0 3 100 to 2000 ppm v 205 100 to 2000 ppm A1 203 0 to 30% CeO 2 0 to 10% Pt 0 0 to 100 ppm Pd 0 0 to 100 ppm co 0 0 to 2000 ppm ', Process according to one of the claims 1 to 3, wherein the molar ratio of magnesium oxide to sulphur compounds during stage (c) is between 1 and 20 and preferably between 1 and 10.

5. Process according to one of the claims 1 to 4, wherein the molar ratio of the reducing gas to the sulphates of said metal contained in the particles in the regeneration zone is between 1 and 20 and preferably between 2 and 10.

6. Process according to one of the claims 1 to 5, wherein the regeneration zone temperature is controlled either by circulating at least part of the sulphate-enriched particles into a heat exchange zone operating in fluidized bed form upstream of the regeneration zone, or by the h 1 partial combustion of the reducing gas in the regeneration zone, in such a way that the temperature is between 400 and 10000C.

Process according to one of the claims 1 to 6, wherein the temperatures of the absorption zone and the regeneration zone are between 500 and 8000C.

8. Process according to one of the claims 1 to 7, wherein the grain size distribution of the particles is between 20 and 100 and preferably between 20 and 50 micrometres.

9. Process according to one of the claims 1 to 8, wherein at least part of the regenerated particles separated after stage (g) is made to circulate in a second heat exchange zone operating in fluidized bed form, prior to carrying out the stage of recycling particles in the absorption zone.

10. Process according to one of the claims 1 to 9, wherein the gaseous stream results from the regeneration of a spent catalytic cragking catalyst in at least one regeneration zone.

11. Process according to one of the claims 1 to 10, wherein the zeolite is a silica-alumina and/or a silica-magnesia.

1 1 32 12. A process according to Claim 1 carried out substantially as hereinbefore described in any one of the foregoing Examples.

13. A process according to Claim 1, carried out in apparatus substantially as hereinbefore described with reference to the accompanying drawings.

14. A desulphurized gas stream obtained by a process according to any one of the preceding claims.

Published 1990 at The Patent Office. State House. 66 71 High Holborn. London WClR 4TP- Purther copies maybe obtained from The PatentOfflc e Wes Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray, Kent, Con- V87