GB2267904A - Method of recovering and/or obtaining a sulphur moiety - Google Patents

Abstract

A method and an apparatus for recovering and/or obtaining a sulfur moiety are described. Waste gases (11) containing SOx and oxygen are contacted at elevated temperature with copper oxide supported on alumina (17 or 18) whereby the 50, is fixed as a copper sulfate compound and the resulting substantially SOx-free gases may be discharged to atmosphere (28). The supported copper sulfate compound is contacted with a reducing gas (e.g., a hydrocarbon gas and/or H2S (30, 79)) and thereby convened to re-usable copper oxide with the liberation of sulfur moiety (34) in at least one of the following forms: elemental sulfur, H2S or SO2. SO2 is reacted (60, 51) with H2S to produce elemental sulfur (43). Any 502 remaining (36, 39, 50) is reacted with H2S (62) in a Claus reactor (51, 60) and elemental sulfur is recovered (43). SO2-free gases (54) are recirculated (54) to mix with waste gases (11) or discharged to atmosphere (28). The waste gases (11) containing SOx and oxygen may be from a chemical and/or catalytic conversion step, e.g., the regenerator of a fluidised catalytic cracker. <IMAGE>

Description

METHOD OF RECOVERING AND/OR OBTAINING A SULFUR HOIETY The present invention relates to a method of recovering and/or obtaining a sulfur moiety.

It is already known (e.g., from GB 1089716, GB 1154008 and GB 1154009) to obtain a sulfur oxide-containing gas by reducing a compound comprising the reaction product of a sulfur oxide and a supported metal oxide, under oxidizing conditions, with a reducing gas selected from hydrogen, carbon monoxide and low molecular weight hydrocarbons. The said metal oxide is preferably a copper oxide.

The said compound is obtained by contacting a sulfur oxide-containing gas (e.g., flue gas) and particles of supported metal oxide under oxidizing conditions.

The present invention provides a method of recovering and/or obtaining a sulfur moiety comprising reducing a metal sulfate with a reducing gas wherein (i) either (a) the metal sulfate is reduced with an H2S-containing gas; and/or (b) the metal sulfate is reduced with a reducing gas containing at least one of the following : H2, H2S, a hydrocarbon and CO, and the resulting sulfur oxide-containing gas is reacted with H2S (optionally in the presence of a catalyst); and (ii) elemental sulfur is recovered from the resulting vapor-phase effluents.

As compared with prior processes, the method of the invention consumes less hydrogen for each mol of sulfur recovered.

The metal sulfate may be dispersed upon a support. The metal sulfate may comprise copper sulfate.

The metal sulfate may be obtained by the reaction of an oxide of the said metal with a gas containing a sulfur oxide, and optionally molecular oxygen. The said gas may be a flue gas.

In embodiments wherein metal sulfate is reduced (e.g., to reduced metal compounds including metal oxide) to liberate a sulfur moiety, and the metal sulfate is obtained by the reaction of a metal oxide with a sulfur oxide (e.g. SO2) under oxidizing conditions, the method of the invention may be performed as (or regarded as) a cyclic process in which in a first part of the cycle, the metal sulfatecontaining material is reduced to a metal oxide-containing material which is employed in a second part of the cycle to fix sulfur oxide to form metal sulfate-containing material in the first part of a subsequent cycle. The method may be performed employing fixed beds of metal sulfate and/or oxide containing material which are alternately exposed to the reducing and sulfur-fixing reactions, or the method may be performed in fluidized beds or moving beds or circulating beds adapted, as is known in the art, to cause particles comprising metal sulfate and/or metal oxide-containing materials to circulate between locations at which they are exposed, under reaction conditions, to sulfur oxide-fixing conditions in one location and metal sulfate-reducing conditions in another location. The particles may be circulated continuously or intermittently (e.g., in batches), in any of the ways known to those skilled in the art.

The flue gas may be obtained by the combustion of a sulfurcontaining solid or fluid carbonaceous material. The- carbonaceous material may be coke on particles of (1) coke or (2) cracking catalyst or (3) coal or lignite, and the combustion may be effected, at least in part, in either (i) the burner of a coking unit or (ii) the regenerator of a fluidised catalytic cracking unit or (iii) a coal or lignite-burning furnace. The carbonaceous material may be oil.

The H2S may be obtained, at least in part, from the products of oil refining.

The invention also provides a hydrocarbon conversion process wherein a sulfur-containing hydrocarbon feedstock is contacted with hot particles in a reaction step under conversion conditions thereby converting the feedstock to converted products and causing the deposition of sulfur-containing carbonaceous material on the particles, contacting particles from the reaction step with an oxygen-containing gas in a regeneration step to remove carbonaceous material therefrom in an exothermic oxidation reaction which heats the particles, employing at least some heated particles from the regeneration step in a subsequent reaction step to convert further amounts of sulfur-containing feedstock, contacting a sulfur oxidecontaining flue gas from the regeneration step with a metal oxidecontaining material under oxidizing conditions to fix at least some sulfur oxide as metal sulfate, and recovering or obtaining a sulfur moiety from the metal sulfate by the method described herein.

Particles may be stripped with a stripping medium in a stripping step, following the reaction step, before being subjected to the regeneration step. The particles may comprise coke or cracking catalyst.

The reaction step may be performed in a reaction zone, the stripping step may be performed in a stripping zone, the regeneration step may be performed in a regeneration zone, and particles may be circulated between the zones.

At least some of the said H2S may be recovered from converted products obtained from the reaction step.

Metal sulfates, and other compounds formed by the reaction of a sulfur oxide and metal oxide, are available either in nature (e.g., as gypsum) or as the product of industrial desulfurization processes, such as the removal of sulfur oxide from flue gas. The method of the present invention enables elemental sulfur to be recoverable therefrom instead of a stream of sulfur oxide-containing gas. Elemental sulfur is not an environmental pollutant, is relatively easily storable, and has numerous industrial uses. For these and other reasons, elemental sulfur is a more preferred sulfur moiety than the sulfur oxide-containing gases of the prior art.

In some regions or areas, there are limits imposed by law or local regulations on the amount of sulfur oxide (SOx) which can be discharged to atmosphere by an industrial plant such as a fluidized catalytic cracking unit ("FCCU"). The amount of SOx produced by a FCCU depends upon the sulfur-content of the feedstock. If the SOx emission limit is attained by a FCCU, the throughput of feedstock to the FCCU can be increased only by employing a feedstock of lower sulfur content. Since the cost of a fuel or chemical feedstock or refinery feedstock depends upon factors such as sulfur content, the use of a lower sulfur (costlier) feed reduces the operating profitability of a FCCU. The process of the present invention enables a FCCU to operate with a higher sulfur (cheaper) feed and/or with a higher feed throughput, both of which factors enhance the operating profitability of a FCCU.

The invention will now be further described with reference to embodiments thereof, given by way of non-limitative examples, and with reference to the accompanying drawings, in which: FIGURE 1 is a flow-sheet of the principal parts of a plant for recovering elemental sulfur from a supported metal oxide sorbent which fixes sulfur oxide from the flue gas of an industrial facility such as a catalytic cracker or a fluid coker or an installation for combusting a sulfur-containing fuel (such as coal or lignite or oil); and FIGURE 2 is a diagrammatic depiction of the principal parts of another plant according to the invention.

A waste gas from a regenerator of a fluidized coker or a fluidized catalytic cracking unit ("FCCU") or fossil fuel combustion plant is conducted via line 11 to a heat-recovery unit 12 (e.g., a heat exchanger) and a de-duster 13 (which may include an electrostatic precipitator, not shown). Fluidized cokers and FCCUs are well-known and will not therefore be described. If the waste gas contains CO, the heat-recovery unit may include a CO-boiler (not shown) which is a common and well-known item of equipment at oil refineries.

The de-dusted gas leaving the de-duster 13 contains sulfur oxide(s), herein denoted SOx, and molecular oxygen, and is recovered in line 14 and directed by three-way valve 15 and a circulation fan 16 to one of two substantially identical reactors 17 and 18 via lines 19, 20, 21 and valves 22 and 23. One reactor 17 or 18 is employed for fixing sulfur oxide from the gas while the other is being operated to recover and/or obtain a sulfur moiety therefrom.

Each reactor 17, 18 contains a bed, or (as shown) at least two beds A and B, of sulfur oxide-fixing material vertically-separated by a space 24. The sulfur oxide-fixing material is preferably a copper oxide material (or a precursor thereof) dispersed on particles of a porous refractory oxide support material, preferably alumina.

Suitable compositions of sulfur-oxide-fixing material are described in patent documents GB-A-1089716; GB-A-1154008 and GB-A-1154009, inter alia.

For the purpose of describing the equipment of the drawing, it is assumed that valve 22 is open and valve 23 is shut, so that SOx- containing gas passes into reactor 17 where it initially contacts SOx-fixing material in bed B, then after traversing the space 24, passes through bed A. SOx is fixed in the material of the beds B and A under oxidizing conditions, and the gas leaving reactor 17 via line 25 is substantially free of SOx or has a residual amount therein which is within the limits acceptable for discharge to the environment, depending upon the relative amounts of SOx-fixing material in the reactor 17 and the amount of SOx introduced thereto, and also the reaction conditions therein.

The relatively SOx-free flue gas is discharged to a stack (not shown) from line 25 via an open control valve 26 and discharge lines 27 and 28.

A by-pass line 29 extends between the three-way valve 15 and the discharge line 28 for the discharge of untreated flue gas from the de-duster 13 to the stack when the reactors 17 and 18 are both out of service (e.g., for repairs and/or maintenance).

While the reactor 17 is being used for the fixing of S0x from flue gas, the reactor 18 is being operated to recover and/or obtain sulfur moiety from supported metal sulfate material previously formed during a SOx-fixing operation such as that described with reference to reactor 17. The SOx-fixing step will herein be designated the "reaction step" and the operation to obtain and/or recover sulfur moiety from supported metal sulfate material will be designated the "regeneration step".

The regeneration step can be performed in more than one way. In one mode, an H2S-containing gas is passed through both or one of the beds in reactor 18 at a regeneration temperature sufficiently high to cause the following reaction:

CuS04 + 2H2S -- > CuO + 3H20 + 4S ..... (1) Other reactions may also occur.

The H2S-containing gas may be introduced via lines 30 and 31, valve 32 (when open) and line 33 into one end of the reactor 18.

Reaction (1) occurs and a gas containing elemental sulfur is recovered from the other end of reactor 18 in lines 21 and 34 under the influence of a circulation fan 35 in line 34.

The sulfur-containing gas stream is diverted into line 36 by valve 37, when closed, and may be passed directly to a sulfur condenser 38 via lines 39 and 40 when valve 41 (in line 36) is closed. Liquid sulfur is recovered in line 42 and received in a sulfur pit 43. The heat discharged by condensing the sulfur is recovered by heating water and/or a hydrocarbon feed from line 44 to a higher temperature, and recovering the heated fluid in line 45.

The resulting substantially desulfurized gas may either be discharged to atmosphere via line 46, valve 47 (when open) and line 48, or it may be circulated via valve 49 (when open) and line 50 to a reactor 51 maintained at a temperature below the solidification temperature of sulfur whereby if there should be any elemental sulfur entrained with the desulfurized gas, it will deposit as a sulfurfrost on the packing (not shown) of the bed in the reactor 51 from where it can be recovered by purging the reactor 51 with a suitable hot gas. Sulfur deposited in the reactor 51 can be recovered by operating reactor 51 alternately with another reactor (e.g., of the Claus type) (e.g., reactor 60, mentioned below), and periodically substituting the sulfur-capture operation of the reactor 51 and the sulfur-liberation operation of the other reactor (e.g., reactor 60).

When the other reactor (e.g., reactor 60) is operating to capture sulfur (e.g., as a sulfur frost), the reactor 51 is heated by hot gas from line 36 and other sources (e.g., a Claus kiln 65, referred to below) to cause liberation of previously deposited sulfur which is thereafter recovered in the sulfur pit 43. Alternatively, the desulfurized gas from the sulfur condenser 38 may be passed to a second sulfur condenser 52 by a suitable arrangement of pipes and valves (not shown), further condensed sulfur being passed by a conduit 53 to the sulfur pit 43. Waste gas may be discharged to atmosphere, e.g., by a connection 54 to the CO-boiler 12 (as shown), or directly to pipe 29.

In one alternative method of regeneration of the supported sulfate material of reactor 18, a reducing gas is supplied to the reactor 18 from line 30. The reducing gas may be any convenient reducing gas such as H2, CO or a light hydrocarbon (e.g., C1 to C3) or any mixture of two or more of the foregoing. Mixtures of light hydrocarbon gases such as methane and ethane are commonly available at oil refineries as by-products of refining and conversion processes. Such gas mixtures may also contain hydrogen and some sulfurous material (e.g., H2S and/or COS). The gas mixture is passed through reactor 18 at a temperature which is sufficiently high to reduce the sulfated material and liberate sulfur as, e.g., sulfur oxide. H2S entering with reducing gas from line 30 reacts directly with the sulfate and/or with SO2 liberated by reaction with the reducing gas, according to the Claus reaction. The support (e.g., A1203) for the copper oxide may catalyse the well-known Claus reaction empirically given as S02 + 2H2S -- > 2H2O + 3S. Temperatures in the range 300 to 500"C are suitable, preferably 300 to 450"C (e.g., in the range 325 to 440or, such as 350 to 430 C).

The resulting SOx-containing gas mixture is recovered in line 34 and circulated by fan 35 into a Claus reactor 60, a valve 61 in line 39 being closed.

H2S-containing gas is added to the gas entering the Claus reactor 60 from line 62. The mixture of gases is at a temperature (e.g., 450"C and thereabouts) at which the well-known Claus reaction occurs.

Sulfur-containing gas leaves the reactor 60 via line 40 and passes to the sulfur condenser 38 for sulfur-recovery in the sulfurpit 43 as described herein. Gas containing unreacted SO2 and H2S passes from the sulfur condenser 38 and via line 50 to the reactor 51 which contains a Claus catalyst to promote a further stage of the Claus reaction with sulfur recovery via the sulfur condenser 52 and line 53 to the sulfur pit 43. The resulting desulfurized gas may be conducted via line 54 to mix with SOx-containing flue gas in line 11 or it may be further desulfurized by the method described in European patent document EP-A-0332373 and either then discharged to atmosphere or circulated into line 11.

The temperature of the gas mixture entering the reactor 60 may be maintained at a Claus-reaction temperature by providing an in-line heater (not shown) of any known type in line 36 and/or in line 62.

Alternatively or in addition, the H2S-containing gas in line 62 may be gas from a Claus furnace 65 wherein H2S, entering at line 66, is partially burned with air (or other oxygen-containing gas) from line 67 to produce a mixture of H2S and S02, and heat. The heat raises the temperature of the gas mixture to a level which will maintain the operation of the Claus reactor(s) 60 and/or 51. The H2S conversion in the furnace 65 is regulated by adjusting the air rate entering at line 67 to ensure that the gas mixture entering the Claus reactor(s) 60 and/or 51 is about optimum for the Claus reaction. Any unreacted SO2 and/or H2S in the gas leaving the reactor(s) 60 and/or 51 may be subjected to further sulfur-recovery processing (as described) by circulating it via line 54 to mix with the flue gas in line 11.

Heat is recovered from the Claus furnace 65 by fluid (water or hydrocarbon) passing from line 68 to line 69 via heat exchanger 70.

Sulfur formed in the furnace 65 is recovered via line 71 and passed to the sulfur pit 43.

In yet another embodiment, reducing gas and an H2S-containing gas are both employed to recover or obtain sulfur moieties from the sulfated material in the reactor 18. Reducing gases (H2, CH4, C2H6, C3H8 and C2/C3 olefins) are readily available at oil refineries, as also are gas streams containing H2S. Indeed, such reducing gases and H2S-containing gas streams are available as by-products from refining (e.g., hydrofining) and conversion processes (e.g., fluid coking and catalytic cracking).

In this embodiment, a reducing gas stream is supplied from lines 30 and 31 to one end of the reactor wherein it passes through bed A, the space 24 between beds A and B, and then through bed B to reduce sulfated material in the beds A and B in endothermic reactions as described. A gas distributor 75 is disposed in space 24 and is connected via line 76, valve 77, and line 78 to a line 79 which contains a hydrogen sulfide-containing gas. H2S is introduced into the space 24 and passes through bed B causing an endothermic redox reaction which can be represented empirically as follows:

CuSO4 + 3H2S -- > CuO + 3H20 + 4S.

The resulting gas mixture is recovered in line 34 and is circulated by fan 35 to line 36 wherein it is mixed with H2S and S02 from the Claus furnace 65 before passing to the Claus reactor 60.

The relative amounts of H2S and SO2 in the gas in line 62 are adjusted, by regulation of the amount of air entering at line 67, to provide approximately sufficient H2S to react stoichiometrically with the S02 in the gas from the reactor 18 in the presence of the catalyst within the Claus reactor 60. Sulfur from the Claus reactor 60 is recovered in the sulfur pit 43 via line 42. The resulting desulfurized gas may then be passed either to the Claus reactor 51 and/or via vents directly to the atmosphere via lines 48, and/or discharged to line 54 for circulation with the feed gas in line 11.

If the heat generated by the regeneration reaction(s) in the bed(s) A and B is insufficient to maintain adequately high temperatures for efficient regeneration, additional heat may be supplied from suitable sources. One such source is shown in the drawing as a so-called in-line burner 80 (of any of the well-known types) which burns a low-cost fuel (e.g., surplus light hydrocarbons) with air in the burner 80 or at least partly within line 81 which provides a connection between the outlet end of the reactor 18 and the inlet end thereof. Some of the gases leaving the reactor 18 are circulated via control valve 37 into line 81, where they mix with hot gas from the burner 80, and the resulting hot gas mixture is circulated via a control valve 82 to line 31 and into the inlet end of the reactor 18.

In-line burners may be provided elsewhere in the plant to maintain and/or raise temperatures therein, where desirable or necessary.

When the reactor 18 has been regenerated at least to some extent, and the reactor 17 has fixed SOx from the flue gas in line 14, the roles of the two reactors are swapped, so that the reactor 18 is used to fix SO, from flue gas in conduit 14 and the beds A and B of sulfated material in reactor 17 are regenerated (as described supra with reference to reactor 18) to recover and/or obtain sulfur moieties (e.g., elemental sulfur) therefrom. The swapping of roles is effected by closing valves 22 and 32, and opening valves 23 and 132 (in line 131 which connects lines 25 and 31), and additionally opening valve 88 in line 89 (which connects lines 20 and 34), closing valve 188 in line 34 and opening valve 126 in line 33. These alterations in the valve settings cause flue gas from line 14 to pass into and through reactor 18 to lines 33, 27 and 28, and cause reducing gas and/or H2S-containing gas to pass via lines 31, 131 and 25 into the reactor 17 so that gas containing recovered sulfur moieties is received in lines 20, 89 and 34 for passage to line 36 and treatment for recovery and/or obtaining of sulfur moieties therefrom (as described supra with reference to reactor 18).

An H2s-containing gas can be distributed into the space 24 of reactor 17 between the beds A and B from a distributor 175, the gas being supplied from line 79 and via line 176 and valve 177 (which should then be open). The plant shown in the flow-sheet of the drawings is then operated in a manner similar to that described supra, before the roles of the reactors 17 and 18 are reversed.

The direct reduction of metal sulfate (e.g., copper sulfate) in the beds A, B of the reactors 17 and 18 favourably reduces the utility demand (e.g., H2 and/or hydrocarbon) and the equipment size and cost of the Claus plant 65 and the reactors 51 and 60 thus contributing to economics in investment and operating costs. The recycle of unconverted (and marginal) amounts of H2S and/or S02 via line 54 to the reactors 17 and 18 mitigates discharges of sulfurous waste to the environment.

When the beds A, B in a reactor 17 or 18 are being regenerated, reducing gases are passed therethrough as described. At the end of a regeneration period, it is highly desirable to purge the reactor beds of reducing gas to avoid the risk of fire or explosion during a subsequent SOx-fixing step performed under oxidizing conditions. A suitable purge gas is steam. Steam can be passed through a reactor from line 150 using an appropriate setting of the inlet and outlet valves governing flows through the reactors. The purged reducing gases and steam are vented to line 27 for discharge to the atmosphere via line 28. Alternatively (and/or in addition), an in-line burner (not shown) may be connected to line 150. When the reactor 17 is at the end of an SOx-adsorption period, there will be oxygen in the reactor 17. The on-line burner could optionally be operating, if necessary, to provide hot combustion gas to maintain the operating temperature of the reactor 17. If the fuel and air supply to the on-line burner is changed to give an excess of fuel relative to air, carbon monoxide (inter alia) will be passed from the on-line burner to the reactor 17 which will both purge and react with oxygen therein, and with suitable regulation, the production of a potentially explosive atmosphere in the reactor 17 can be avoided.

The reducing gases from the on-line burner can be employed for a short time solely to remove oxygen from the reactor 17 during the period when it changes roles with reactor 18, or it may be continued thereafter in order to supplement, or even wholly replace, the reducing gases from lines 79 and/or 30 on a temporary or permanent basis. The same arrangements involving the use of the on-line burner may also be employed for the same purpose when reactor 18 completes its SO2-absorption period and is reverting to its previous role in which sulfur moieties are recovered therefrom under reducing conditions.

Reference is now made to the embodiment of Figure 2. The embodiment can be regarded as an adaption of the Figure 1 embodiment for continuous circulation of the sulfur oxide-fixing material between a sulfur oxide-fixing zone and a regeneration zone. In Figure 2, items which serve the same function as items in the Figure 1 embodiment have the same reference numerals. For the purpose of illustration, it is assumed that the sulfur oxide-fixing material of Figure 2 is copper oxide on alumina (CuO/A1203) optionally comprising suitable promoters.

Active and/or regenerated CuO/A1203 is received in a bed 100 in a hopper 101 from an elevator or riser 102 and distribution line 103.

The CuO/A1203 is preferably in the form of durable pellets, pills or prills which may be of the types, sizes and shapes employed in so-called moving bed technology (e.g., as used in moving bed catalytic crackers).

Waste gas (e.g., flue gas) containing sulfur oxide(s), SOx, and oxygen in line 11, passes via heat recovery unit 12, line 14 and valve 15 to circulation fan 16 which circulates the gas via line 19 into a lower region of the bed 100. The temperature of contact of the waste gas and bed material in the bed 100 is adequately high to facilitate a sulfur oxide fixing reaction, such as the empirical reaction: 2CuO + 2SO2 + 02 -- > 2CuSO4. SOx-depleted waste gas leaves the top of the hopper 101 and is recovered in line 27 and then passed by line 28 to suitable solids-removal equipment 13 such as one or more cyclone separators and/or physical/mechanical filters (e.g., bag-type filters) and/or electrostatic precipitators and/or gaswashing apparatus, all of which are well-known in the art.

Relatively solids-free, SOx-depleted waste gas is discharged (e.g., to the atmosphere) from conduit 28.

The hopper 101 has a frusto-conical bottom having a central orifice 105 connected to a solids-discharge tube 106 containing a star valve 107 or other means maintaining a substantially gas-tight seal in the tube 106 while facilitating the transfer of solids downwardly through the tube 106. Steam or another suitable inert gas is injected into the tube 106 from line 108 to maintain a degree of agitation and/or incipient mutual separation of particles in the tube 106 in order to prevent particles packing and blocking flow via the tube 106.

The tube 106 discharges solids into a bed 109 maintained in a lower vessel 110. The roof of the vessel 110 is formed by the conical bottom 104 of the hopper, and the vessel 110 has a frustoconical bottom 112 with a central orifice 113 connected to a solidsdischarge tube 114 containing a star valve 115 to facilitate the passage of solids via the tube 114 while maintaining a substantially gas-tight seal.

A hydrogen-sulfide-containing gas from line 79 is passed into the bed 109 via line 76 and suitable distributors 117 Inverted 'V'-angle members (e.g., of mild steel) 118 are disposed above the distributors 117 to prevent their blockage by solids. The distributors 117 are disposed about half-way up the depth of the bed 109. The contacting temperature of the H2S-containing gas and the particles in the bed is within the range at which the following empirical reaction occurs: CuSO4 + H2S -- > CuO + 2H20 + 3S.

The gases and reaction products are circulated downward through the lower half B of the bed 109 and removed therefrom by the action of a fan 35 which sucks the gases etc. via line 34 and discharges them via line 36. Some product gas etc. in line 36 may be circulated to the bed 109 according to the settings of valves 37, 77 and 78.

Additionally or alternatively to the injection of H2S into the lower part B of bed 109, a reducing gas may be passed through both an upper part A and the lower part B of bed 109. The reducing gas may comprise one or more of the reducing gases or gas mixtures which are commonly available at oil refineries and chemical works, e.g., H2, CH4, C2H6, C2H4, C3H8, C3H6, CO, H2S, etc. and any mixture containing the foregoing. The reducing gas may conveniently be introduced from lines 122, 123 and distributing pipes 124. The pipes 124 are preferably above the top level of the solids in the bed 109, but they may be immersed in the bed.

The H2S-containing gas from line 79 and/or the reducing gas from line 122 reduces CuSO4 with the liberation of sulfur moieties, as described with reference to Figure 1. In-line burners (not shown) of any known type may be provided to ensure that the temperature of the reducing gas passing through the bed 109 is sufficiently high to react with CuSO4 in the bed and to liberate sulfur moieties (e.g., S02 and/or S).

The gas and sulfur moieties in line 36 are circulated by fan 35 to Claus reactors (not shown) corresponding with the Claus reactors 51 and 60 shown in Figure 1 wherein the same type of sulfur-recovery steps are performed. The product from a Claus kiln (not shown), corresponding with the product in line 62 of Figure 1, may also be added to the materials in line 36 for the purposes explained in connection with Figure 1. Waste gas from the Claus reactors is recovered in line 54 and discharged to line 11, as shown.

Reduced particles are recovered from the base of the bed 109 via tube 114 and star valve 115. Steam (or other inert gas) is injected from line 130 into a lower region of tube 114 to prevent particles packing in, and blocking, tube 114.

Claims (13)

1. A method of recovering and/or obtaining a sulfur moiety comprising reducing a metal sulfate with a reducing gas wherein (i) either (a) the metal sulfate is reduced with an H2S-containing gas; and/or (b) the metal sulfate is reduced with a reducing gas containing at least one of the following : H2, H2S, a hydrocarbon, CO, and the resulting sulfur oxide-containing gas is reacted with H2S (optionally in the presence of a catalyst); and (ii) elemental sulfur is recovered from the resulting vapor-phase effluents.

2. The method of claim 1 wherein the metal sulfate is dispersed upon a support.

3. The method of claim 1 or claim 2 wherein the metal sulfate comprises copper sulfate.

4. The method of any one of claims 1 to 3 wherein the metal sulfate is obtained by the reaction of an oxide of the said metal with a gas containing a sulfur oxide, and optionally molecular oxygen.

5. The method of claim 4 wherein the said gas is a flue gas.

6. The method of claim 5 wherein the flue gas is obtained by the combustion of a solid or liquid sulfur-containing carbonaceous material.

7. The method of claim 6 wherein the carbonaceous material comprises coke on particles of (1) coke or (2) cracking catalyst or (3) coal or lignite, and the combustion is effected, at least in part, in either (i) the burner of a coking unit or (ii) the regenerator of a fluidised catalytic cracking unit or (iii) a coal or lignite-burning furnace.

8. The method of any one of claims 1 to 7 wherein the H2S is obtained, at least in part, from the products of oil refining.

9. A hydrocarbon conversion process wherein a sulfurcontaining hydrocarbon feedstock is contacted with hot particles in a reaction step under conversion conditions thereby converting the feedstock to converted products and causing the deposition of sulfurcontaining carbonaceous material on the particles, contacting particles from the reaction step with an oxygen-containing gas in a regeneration step to remove carbonaceous material therefrom in an exothermic oxidation reaction which heats the particles, employing at least some heated particles from the regeneration step in a subsequent reaction step to convert further amounts of sulfurcontaining feedstock, contacting a sulfur oxide-containing flue gas from the regeneration step with a metal oxide-containing material under oxidizing conditions to fix at least some sulfur oxide as metal sulfate, and recovering or obtaining a sulfur moiety from the metal sulfate by the method of any one of claims 1 to 8.

10. The process of claim 9 wherein, following the reaction step, particles are stripped with a stripping medium in a stripping step before being subjected to the regeneration step.

11. The process of claim 9 or claim 10 wherein the particles comprise coke or cracking catalyst.

12. The process of any one of claims 9 to 11 wherein the reaction step is performed in a reaction zone, the stripping step is performed in a stripping zone, the regeneration step is performed in a regeneration zone, and particles are circulated between the zones.

13. The process of any one of claims 9 to 12 wherein at least some of the said H2S is recovered from the converted products obtained from the reaction step.