Method for partial reduction of SO2

Abstract

The present invention relates to a method for partial reduction of SO.sub.2, wherein a SO.sub.2 stream, an oxidant and a gaseous fuel are fed to a burner and reacted in a flame reaction. The burner comprises at least one supply opening for the SO.sub.2 stream, at least one supply opening for the oxidant and at least one supply opening for the gaseous fuel, and a burner head (1) with first injection sets (7, 8) and second injection sets (9). First injection sets (7, 8) are arranged in a first section (4) of the burner head (1), and second injection sets (9) are arranged in a second section (5) of the burner head (1). The stoichiometric ratio of SO.sub.2, fuel and oxidant supplied through the first injection sets (7, 8) is different from the stoichiometric ratio of SO.sub.2, fuel and oxidant supplied through the second injection sets (9).

Claims

1. A method for partial reduction of SO.sub.2, wherein a SO.sub.2 stream, an oxidant and a gaseous fuel are fed to a burner and reacted in a flame reaction, wherein the burner comprises at least one supply opening for the SO.sub.2 stream, at least one supply opening for the oxidant and at least one supply opening for the gaseous fuel, and wherein the burner further comprises: a burner head (1) with first injection sets (7, 8) and second injection sets (9), the first injection sets (7, 8) arranged in a first section (4) of the burner head (1), the second injection sets (9) arranged in a second section (5) of the burner head (1), and a stoichiometric ratio of SO.sub.2, fuel and oxidant supplied through the first injection sets (7, 8) is different from a stoichiometric ratio of SO.sub.2, fuel and oxidant supplied through the second injection sets (9).

2. The method of claim 1, wherein at least one of the first and/or second injection sets (7, 8, 9) comprise a first port (7a, 8a, 9a) for oxidant, and a second port (7b, 8b, 9b) for fuel and/or SO.sub.2.

3. The method of claim 1, wherein the relative quantities of SO.sub.2, fuel and oxidant flowing through the first injection sets (7, 8) are within the flammability regime, and the relative quantities of SO.sub.2, fuel and oxidant flowing through the second injection sets (9) are outside the flammability regime.

4. The method of claim 1, wherein the first section (4) and the second section (5) do not overlap.

5. The method of claim 4 wherein the second injection sets (9) are more distant from the centre (3) of the burner head (1) than any of the first injection sets (7, 8).

6. The method of the claim 1, wherein the total quantities of fuel, SO.sub.2 and oxidant supplied to the burner are outside the flammability regime.

7. The method of claim 1, wherein the oxidant has an oxygen content of at least 90 percent by volume during normal operation.

8. The method of claim 1, wherein air is used as oxidant during stand by operation.

9. The method of claim 1, wherein the fuel comprises at least 80 percent by volume CH.sub.4.

10. The method of claim 1, wherein the burner head (1) comprises between three and ten first injection sets (7, 8), and/or between five and twenty second injection sets (9).

11. The method of claim 1, wherein one or more of the first injection sets (7, 8) and/or one or more of the second injection sets (9) comprise an inner pipe and a coaxial outer pipe, and an outlet of the inner pipe defines a first port (7a, 8a, 9a), and a ring-shaped outlet between the inner pipe and the coaxial outer pipe defines a second port (7b, 8b, 9b).

12. The method of claim 1, wherein the burner comprises a central area, and the first section (4) is defined by a cross section of the central area.

13. The method of claim 1, further comprising passing the fuel and/or SO.sub.2 through a space between the first injection sets (7, 8) and the second injection sets (9).

14. The method of claim 1, wherein the partial reduction of SO.sub.2 produces from at least 100 tons/day sulphur to at least 1000 tons/day sulphur.

15. The method of claim 1, wherein the ratio of SO.sub.2, fuel and oxidant supplied through the first injection sets (7, 8) is at a higher stoichiometric level than the ratio of SO.sub.2, fuel and oxidant supplied through the second injection sets (9).

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) For a more complete understanding of the present inventive embodiment disclosures and as already discussed above, there are several options to embody as well as to improve the teaching for the present invention in an advantageous manner. To this aim, reference may be made to the claims dependent on claim 1; further improvements, features and advantages of the present invention are explained below in more detail with reference to the following description of a preferred embodiment by way of non-limiting example and to the appended drawing FIGURE taken in conjunction with the description of the embodiment, of which:

(2) FIG. 1 shows the layout of a burner head for use in the invention.

DETAILED DESCRIPTION OF THE DRAWINGS; BEST WAY OF EMBODYING THE PRESENT INVENTION

(3) Before explaining the present inventive embodiment in detail, it is to be understood that the embodiment is not limited in its application to details of construction and arrangement of parts illustrated in the accompanying drawing, since the present invention is capable of other embodiments and of being placed or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

(4) In the following description, terms such a horizontal, upright, vertical, above, below, beneath and the like, are used solely for the purpose of clarity illustrating the present invention and should not be taken as words of limitation. The drawings are for the purpose of illustrating the present invention and are not intended to be to scale.

(5) The burner head 1 shown in FIG. 1 is used for partial reduction of SO.sub.2 by combusting SO.sub.2 with natural gas as fuel and oxygen. SO.sub.2, natural gas and O.sub.2 are supplied as separate feed streams to the burner (not shown). The separate feeds allow to adjust the respective gas velocities in order to optimize the reaction conditions at different flow rates or when the process is switched from normal operation to stand-by or vice versa.

(6) The burner head 1 comprises a first section 4 of circular shape circular arranged coaxial with the burner axis 3. The circumference 2 of the first section 4 divides the cross-sectional area of the burner head 1 into the first section 4 and a second section 5. The first section 4 is of circular shape and the second section 5 is ring-shaped.

(7) Within the first section 4 there are six first injection sets 7, 8. Each first injection set 7, 8 consists of an inner pipe 7a, 8a and an outer pipe 7b, 8b coaxial with the inner pipe 7a, 8a. One first injection set 7 is centrally arranged in the burner head 1. The other five first injection sets 8 are equally distributed on a circle around first injection set 7.

(8) Within the second section 5 there are arranged twelve second injection sets 9. The second injection sets 9 are equally distributed on a circle around the center 3 of the burner head 1. Each second injection set 9 consists of an inner pipe 9a and an outer pipe 9b coaxial with the inner pipe 9a.

(9) Oxygen is passed through the inner pipes 7a, 8a, 9a of the first and second injection sets 7, 8, 9. However, the flowrate of oxygen passed through the inner pipes 7a, 8a is different from the oxygen flowrate through the inner pipes 9a of the second injection sets 9 as will be explained below.

(10) A mixture of SO.sub.2 and CH.sub.4 is passed through the outer pipes 7b, 8b, 9b of the first and second injection sets 7, 8, 9. The flowrate of the SO.sub.2CH.sub.4-mixture passed through the outer pipes 7b, 8b is different from the SO.sub.2CH.sub.4-mixture flowrate through the outer pipes 9b.

(11) Further, a mixture of reactants could also be sent through the annular space inside the shell 10 of the burner head 1. The fuel mixture flows through the intermediate space between the first and second injections sets 7, 8, 9.

(12) Burner 1 is used in a thermal stage of a sulphur recovery unit for partial reduction of SO.sub.2. SO.sub.2, natural gas and technical pure oxygen are supplied to the burner. The overall composition of the reactants falls outside of the flammability region. Thus, the combustion of such a composition of the reactants will not be stable.

(13) According to the invention the (inner) first section 4 and the (outer) second section 5 are provided with the reactants in different compositions. The stoichiometric ratio of SO.sub.2, natural gas (CH.sub.4) and O.sub.2 supplied through the first injection sets 7, 8 is different from the stoichiometric ratio of SO.sub.2, natural gas and oxygen supplied through the second section 5.

(14) The mixture in section 4the inner circlecould lead to a stable combustion and generate high flame temperature required. This instantaneous reaction will also result in starting the reaction at the outer circle section 5. The temperature in section 5 will be much lower than the flame centre in section 4. Therefore, this could provide protection to the reaction furnace wall from the very hot central flame. This means a flame temperature profile well suited for such application.

(15) The inner and outer circle stoichiometric levels can be adjusted according to the specific requirement for each design. This can be achieved through using different numbers of injectors and different size of injectors, as well as different layout of the injectors.

LIST OF REFERENCE SIGNS

(16) 1 burner head 2 circumference of first section 4 3 burner axis or centre of burner head 1 4 first section of burner head 1 5 second section of burner head 7, 8 first injection set 7a, 8a first port or inner pipe of first injection set 7, 8 7b, 8b second port or outer pipe of first injection set 7, 8 9 second injection set 9a first port or inner pipe of second injection set 9 9b second port or outer pipe of second injection set 9 10 shell of burner head 1