GB2095653A - Producing CaSO4 and CaO from CaS - Google Patents

Abstract

Particles containing CaS are fluidized by an O2-containing gas in a first bed (compartment 1) under such conditions that some, but not all, the CaS is converted to CaSO4 with the liberation of heat but with substantially no evolution of sulfur moieties. Particles containing CaSO4 and the remaining CaS pass to another bed (between baffles 2 and 3) wherein they are fluidized by an O2- containing gas under such conditions that CaS is converted to CaO with the liberation of sulfur moieties, recoverable as (e.g.) SO2 or elemental sulfur. Particles containing CaSO4, CaO and unchanged CaS may be passed to a third bed (9) and fluidized therein by an O2-containing gas under such conditions that substantially all the CaS is oxidized to CaSO4 with no liberation of sulfur moieties. The resulting hot particles containing CaSO4 and CaO are preferably used for the oxidation and desulfurization of a sulfur-containing fuel in a fluidized bed (8) between the first and third beds. <IMAGE>

Description

SPECIFICATION Producing CaSO4 and CaO from CaS The present invention relates to a method of producing CaSO4 and CaO from CaS.

CaS is produced in a number of industrial processes, and its disposal presents problems since on exposure to moisture, it evolves H2S. In addition, the dumping of CaS may be regarded as a waste of the valuable sulfur content thereof.

In the process described in our European patent publication 0013590, a fuel is converted to a substantially inerts-free gas by a partial oxidation process in which the oxygen for the partial oxidation is furnished by CAST, which is reduced to CaS. The partial oxidation is performed in a fluidized bed at an elevated temperature, and the requirement for oxygen to convert the fuel is, generally speaking, low in comparison to the requirement for heat to maintain the conversion bed at the elevated temperature, so that the fluidized bed need contain only a small proportion of CaSO4 (e.g. equivalent to 0.5 to 2.5 wt % sulfur as sulfate preferably about 1 wt %) to provide the required oxygen, while the remaining part of the bed must be heated to maintain the fuel conversion reactions.Since most fuels contain sulfur, the remaining part of the bed may comprise CaO to capture or fix sulfur moieties during the conversion of the fuel, and the sulfur moieties are usually fixed as CaS. As a result, the gas leaving the fuel conversion bed has a very low content of sulfur moieties and the CaS produced by reduction of CaSO4 is augmented by CaS produced by the fixing of sulfur in the fuel conversion bed.

The present invention provides a method of treating solids containing CaS to produce CaS94 and CaO. According to the invention, there is provided a method of treating CaS-containing particles in a fluidized bed zone to produce a mixture of particles containing CaSO4 and CaO, the method comprising:: (a) passing the CaS-containing particles into an entrance region of a first fluidized bed of the fluidized bed zone, the first fluidized bed being fluidized by passing into the base thereof an 2- containing gas under such conditions that some, but not all, of the CaS is oxidized to CaSO4 with substantially no liberation of sulfur moieties into the gas leaving the top level of the first fluidized bed; (b) transferring particles containing CaS and CaSO4 from an exit region of the first fluidized bed to an entrance region of a second fluidized bed of the fluidized bed zone, the second fluidized bed being fluidized by passing into the base thereof an O2-containing gas under such conditions that at least some CaS is oxidized to CaO with the liberation of sulfur moieties into the gas leaving the top level of the second fluidized bed; and thereafter (c) recovering the particles comprising CaO and CaSO4 from the fluidized bed zone.

Preferably, the operation of the first fluidized bed is performed under such conditions that the gas leaving the top level thereof is substantially free of sulfur moieties.

Preferably, the gas leaving the top level of the first fluidized bed contains 02 and a portion of the O2-containing gas may be employed as at least some of the O2-containing gas passed into the base of the second fluidized bed.

Preferably step (b) is so performed that some, but not all, of the CaS is oxidized to CaO with the liberation of sulfur moieties, and the method may comprise the additional step (d) of transferring particles comprising CaS, CaO and CaSO4 from an exit region of the second fluidized bed to an entrance region of a third fluidized bed of the fluidized bed zone, the third fluidized bed being fluidized by passing into the base thereof an 2- containing gas having an 02content relative to the CaS in the third fluidized bed such that, under the conditions of operation, substantially all the CaS is oxidized to Ca SO4 with substantially no liberation of sulfur moieties into the gas leaving the top level of the third fluidized bed, step (d) being performed before the said step (c).

The method of the invention may be performed in such a manner that the sulfur moieties liberated in the second bed are recoverable as, e.g.

elements sulfur or SO2. For example, a reducing agent may be provided in at least the top region of the second fluidized bed to reduce at least some sulfur oxide(s) liberated therein to elemental sulfur which is recoverable from the gases leaving the top level of the second fluidized bed.

In one embodiment of the method of the invention, particles recovered in step (c) are passed into an entrance region of a fourth fluidized bed of the fluidized bed zone, the fourth bed being fluidized by passing into the base thereof a gas which is substantially free of inert substances but which contains a mediator which is capable of mediating the transfer of oxygen from CaSO4 to a hydrocarbon fuel and/or carbonaceous fuel within the fourth bed under mediating conditions, and passing hydrocarbon and/or carbonaceous fuel into the fourth fluidized bed whereby the fuel is converted to at least partially oxidized fuel products which leave the top level of the fourth bed.

The invention is now further described by way of non-limitative examples thereof and with reference to the accompanying drawing which is an isometric diagram of the principal features of an apparatus for performing one embodiment of the process of the invention The apparatus is in the form of a parallelepiped having, above the base, a false bottom which is adapted to serve as a distributor to distribute gases from beneath the false bottom into a fluidized bed of solid particulate material supported on the false bottom. The interior of the parallelepiped is divided into compartments by vertical walls or baffles which extend beneath the false bottom, and slots or ports are provided in the vertical walls or baffles above, but close to, the false bottom whereby each compartment communicates with adjacent compartments.

Compartment 8 contains a fluidized bed of particles including particles comprising CaO and CaSO4. A sulfur-containing fuel is passed into the fluidized fuel-conversion bed by suitable means (not shown) and CaSO4 is reduced to CaS as the fuel is gasified to partially oxidized products which leave the top of the fluidized fuel-conversion bed.

Sulfur from the fuel is fixed as CaS by reaction with CaO. The bed is fluidized with a substantially inerts-free gas, preferably de-tarred product gas and optionally steam, whereof the H2 and/or other constituents thereof substantially suppress the liberation of sulfur moieties from the bed. Thus a good quality fuel gas/synthesis gas is produced in the fuel-conversion bed at a suitable fuel conversion temperature (e.g. in the range 850 to 1 500 C, preferably 900 to 10000 C, e.g. about 9500C).

Bed solids pass from the fuel-conversion bed in compartment 8 to a first CaS-conversion bed in compartment 1 wherein the particles are fluidized by air or other gas containing molecular oxygen under conditions which allow the temperature of the bed to be about 970 and 103O0C, preferably about 1 0000C substantially without sulfur moiety being released from the first CaS-conversion bed.

The suppression of the release of sulfur moiety is conveniently ensured by fluidizing the first CaS conversion bed with sufficient oxygen so that there is a small amount of oxygen (e.g. 0.5 to 5 vol %, preferably 1 to 3 vol % 2) in the gas leaving the top of the bed. Under these conditions, some CaS is selectively converted to CaSO4.

Bed solids pass from the first CaS-conversion bed via a port between the false bottom of the apparatus and the partition 2 into a compartment 10 defined between the partition 2 and a similar partition 3 having a port at its bottom. The bed solids are fluidized in compartment 10 by a regeneration gas containing molecular oxygen (e.g. air) suppied from plenum 4 at a fluidization velocity which is low enough to ensure that no oxygen appears in the gas leaving the top of the bed in the compartment 10. Under these conditions, the temperature in the compartment 10 is maintained at a value in the range 1050 to 10900C, preferably about 10700C, and some CaS is exothermically converted to CaO with the liberation of sulfur moieties in the gas leaving the bed.The sulfur moieties may be SO2 in a relatively high concentration, e.g. up to 14 vol %, although more usually in the range 6 to 8 vol %.

Alternatively, if a reducing component such as some of the fuel or char or other fuel residue is provided e.g. as a layer at the top of the bed, the sulfur moiety may leave the bed as elemental sulfur.

Bed particles including particles containing CaO, CaSO4 and uncoverted CaS pass via the port between the false bottom and the partition 3 into a compartment 9 wherein they are fluidized in a bed of air (or other gas containing molecular oxygen) which is provided at such a rate that the gas leaving the top of the bed contains molecular oxygen thereby substantially suppressing the liberation of sulfur moieties into the gas leaving the bed. The remaining reactive CaS is exothermically oxidized to CaSO4 thereby maintaining the temperature of bed solids in the compartment 9 at 1050 to 1 000C, e.b. 1060 to 1080"C.

Bed particles pass from the compartment 9 to the compartment 8 via a slot-shaped transfer port 7. The enthalpy of the particles entering the compartment 8 from compartment 9 serve to maintain the temperature of the fluidized bed in the compartment 8 whereby further quantities of fuel may be converted to fuel gas therein.

For continuous operation of the apparatus, the amount of sulfur moiety liberated in the compartment 10 must match the amount of sulfur from the fuel which is fixed to CaS in the fuelconversion bed. This matching may be effected in a number of ways - e.g. by monitoring the amount of sulfur moiety produced in compartment 10 and varying the rate of air supply to compartment 10 from plenum 4. Alternatively, the off-gases leaving the bed in compartment 10 may be monitored for oxygen and the air supply rate to plenum 4 reduced when molecular oxygen is detected in the off-gases. In yet a further method, the temperature of the bed and/or off-gases is monitored and the rate of air supply to the plenum 4 is regulated to maintain the bed temperature within the range at which sulfur moieties are liberated into the off-gases.Other methods for maintaining a substantially constant inventory of sulfur moiety in the solids circulating in the illustrated apparatus may be employed to regulate the liberation of sulfur moieties in compartment 10, and any combination of methods, including those specifically referred to, may also be employed.

When it is desired that the sulfur moiety liberated in compartment 10 is elemental sulfur, a fluidized bed of char or petroleum coke may be superimposed on the bed in the compartment 10, as described in our UK patent specification 1 541434. The char may be at least some of the char which would be entrained out of the fuel conversion bed in compartment 8 when the fuel is a solid fuel such as coal or lignite. Any char not used for this purpose may be returned to the fuel conversion bed in compartment 8.

It will be appreciated that the geometric arrangement of beds shown in the drawing is one of several that may be used to produce the same results. For example, if sulfur, moieties are to be discarded, e.g. to the atmosphere as, e.g. SO2, compartment 10 may be dispensed with by the elimination of one of its partition walls 2 or 3, and also the corresponding wall of the plenum 4 beneath compartment 10.

Claims (14)

1. A method of treating CaS-containing particles in a fluidized bed zone to produce a mixture of particles containing CaSO4 and CaO, the method comprising: (a) passing the CaS-containing particles into an entrance region of a first fluidized bed of the fluidized bed zone, the first fluidized bed being fluidized by passing into the base thereof an 2- containing gas under such conditions that some, but not all, of the CaS is oxidized to CaSO4 with substantially no liberation of sulfur moieties into the gas leaving the top level of the first fluidized bed:: (b) transferring particles containing CaS and CaS04 from an exit region of the first fluidized bed to an entrance region of a second fluidized bed of the fluidized bed zone, the second fluidized bed being fluidized by passing into the base thereof an 02-containing gas under such conditions that at least some CaS is oxidized to CaO with the liberation of sulfur moieties into the gas leaving the top level of the second fluidized bed: and thereafter (c) recovering the particles comprising CaO and CaSO4 from the fluidized bed zone.

2. A method as in claim 1 in which the operation of the first fluidized bed is performed under such conditions that the gas leaving the top level thereof is substantially free of sulfur moieties.

3. A method as in claim 2 in which the gas leaving the top level of the first fluidized bed contains 02, and a portion of said gas is employed as at least some of the 02-containing gas passed into the base of the second fluidized bed.

4. A method as in any one of claims 1 to 3 in which in step (b), some, but not all, of the CaS is oxidized to CaO with the liberation of sulfur moieties, and in which the method comprises the additional step (d) of transferring particles comprising CaS, CaO and CaS04 from an exit region of the second fluidized bed to an entrance region of a third fluidized bed of the fluidized bed zone, the third fluidized bed.being fluidized by passing into the base thereof an O2-containing gas having an 02 content relative to the CaS in the third fluidized bed such that, under the conditions of operation, substantially all the CaS is oxidized to CaS04 with substantially no liberation of sulfur moieties into the gas leaving the top level of the third fluidized bed, step (d) being performed before step (c).

5. A method as in claim 4 in which the operation of the third fluidized bed is performed under such conditions that the gas leaving the top level thereof contains 02 in a concentration which is at least sufficient to substantially suppress the liberation of sulfur moieties into the gas leaving the top level of the third fluidized bed.

6. A method as in claim 4 or claim 5 in which a portion of the gas leaving the top level of the third fluidized bed is employed as at least part of the O2-containing gas passed into the base of the second fluidized bed.

7. A method as in any one of claims 1 to 6 in which a reducing agent is provided in at least the top region of the second fluidized bed to reduce at least some sulfur oxide(s) liberated therein to elemental sulfur which leaves the top level of the second fluidized bed in the gases leaving the top level thereof.

8. A method as in any one of claims 1 to 7 in which the CaS-containing particles passed into the first fluidized bed also contain and/or are mixed with CaO.

9. A method as in any one of claims 1 to 8 in which the fluidized beds of the fluidized bed zone are contained in a single vessel.

10. A method as in any one of claims 1 to 9 in which particles recovered in step (c) are passed into an entrance region of a fourth fluidized bed of the fluidized bed zone, the fourth bed being fluidized by passing into the base thereof a gas which is substantially free of inert substance but which contains a mediator which is capable of mediating the transfer of oxygen from CaSO4 to a hydrocarbon fuel and/or carbonaceous fuel within the fourth bed under mediating conditions, and passing hydrocarbon and/or carbonaceous fuel into the fourth fluidized bed whereby the fuel is converted to at least partially oxidized fuel products which leave the top level of the fourth bed.

11. A method of treating CaS-containing particles in a fluidized bed zone to produce a mixture of particles containing CaSO4 and CaO substantially as hereinbefore described.

12. At least partially oxidized fuel products made by the method of claim 10.

13. Sulfur and/or sulfur oxides and/or other sulfur moiety made by the method of any one of claims 1 to 11.

14. Apparatus for performing the method of any one of claims 1 to 11 substantially as described.