Mixing apparatus for gases

1. A mixing apparatus for mixing a first gas and a second gas, which mixing apparatus comprises:

i) a linear first tube for supply of the first gas, said first tube comprising an inlet for the first gas at an upstream end and tapering to form a nozzle at a downstream end, said nozzle having an opening of internal area of less than 10 mm 2 at the outlet for the first gas and providing a pressure drop in the supply of the first gas through said first tube, and

ii) a linear second tube for supply of the second gas, said second tube comprising an inlet for the second gas at an upstream end, a first portion which forms an annulus around the outer surface of the first tube upstream of the nozzle, which annulus has a length of 5 to 50 mm and a cross-section area of 2 to 10 times the area of the opening of the nozzle and which acts to provide a pressure drop in the supply of the second gas through said second tube, and a second portion which forms a sheath around the nozzle of the first tube and which forms an area of expanded cross-section compared to the annulus,

and wherein:

a) the dimensions of the nozzle and annulus are such that the pressure drops caused in the supply of the first and second gases are in a ratio of 2:1 to 1:2,

b) the angle of the external taper of the nozzle is less than 12° compared to the longitudinal axis of the first tube, and

c) any change in diameter of second tube in the second portion takes place by a slope or a taper with an angle of less than 12° compared to the longitudinal axis of the second tube.

2. The mixing apparatus according to claim 1 wherein the angle of the taper of the nozzle is less than 7° compared to the longitudinal axis of the first tube and any change in diameter of the second tube in the second portion takes place by a slope or a taper with an angle of less than 7° compared to the longitudinal axis of the second tube.

3. The mixing apparatus according to claim 1 wherein the internal area of the opening of the nozzle is from 0.5 to 5.0 mm 2 .

4. The mixing apparatus according to claim 3 wherein the internal area of the opening of the nozzle is less than the internal cross-sectional area of the linear first tube other than at the nozzle, the opening thus setting the pressure drop in the linear first tube, which pressure drop is in the range 10 to 400 kPa.

5. The mixing apparatus according to claim 1 wherein any changes in external diameter of the linear first tube take place by a slope or a taper with an angle of less than 12° compared to the longitudinal axis of the linear first tube.

6. The mixing apparatus according to claim 1 wherein the annulus is of a length of 5 to 30 mm.

7. The mixing apparatus according to claim 6 wherein the annulus has a length of 5-30 mm and the annulus cross-section is in the range 5-60 mm 2 , the annulus setting the pressure drop in the linear second tube, which pressure drop is in the range 10 to 400 kPa.

8. The mixing apparatus according to claim 1 wherein the nozzle and annulus are arranged such that the pressure drops are in a ratio of 1:1 to 1:1.5.

9. The mixing apparatus according to claim 1 wherein upstream of the annulus, the linear second tube has a wider internal cross-section compared to the portion at the annulus, the linear second tube narrowing in the downstream direction at an angle of less than 12° to the diameter required for the annulus.

10. The mixing apparatus according to claim 1 wherein any change in the internal diameter of the linear second tube downstream of the nozzle also takes place by a slope or a taper with an angle of less than 12° compared to the longitudinal axis of the linear second tube.

11. The mixing apparatus according to claim 1 wherein the mixing apparatus comprises at least 100 linear first and second tubes.

12. A reactor for the mixing and reaction of a first gas and a second gas, which reactor comprises a mixing zone comprising the mixing apparatus as claimed in claim 1 and a reaction zone downstream of the mixing zone.

13. A process for the mixing and reaction of a first gas and a second gas, which process comprises feeding said first gas and said second gas to, respectively, one or more linear first tubes and one or more linear second tubes in a mixing apparatus as described in claim 1 and subsequently passing the gaseous mixture obtained to a reaction zone downstream of the mixing zone.

14. A process for the production of one or more olefins, said process comprising mixing an oxygen containing gas and a paraffinic hydrocarbon-containing gas by passing the oxygen-containing gas as the first gas and the paraffinic hydrocarbon-containing gas the second gas to a mixing apparatus as claimed in claim 1 , passing the gaseous mixture obtained to a reaction zone via a porous resistance zone, and partially combusting in the reaction zone the gaseous mixture to produce the one or more olefins.

15. A process according to claim 14 wherein the partial combustion of the gaseous mixture in the reaction zone is carried out in the presence of a catalyst which is capable of supporting combustion beyond the fuel rich limit of flammability.