Method of removing sulfur oxides and nitrogen oxides in the flue gas

1. A method of removing sulfur oxides and nitrogen oxides in a regeneration flue gas of a catalytic cracking regenerator, wherein said method comprises the following steps:

(1) a mid-temperature zone reactor and a high-temperature zone reactor are provided;

(2) a catalyst of a noble metal active component and a rare earth metal active component on an inorganic oxide support is loaded in the high-temperature zone reactor; a catalyst of a rare earth metal active component and an optional transition metal active component on an inorganic oxide support is loaded in the mid-temperature zone reactor;

(3) the regeneration flue gas is sequentially passed through the high-temperature zone reactor and the mid-temperature zone reactor;

(4) a reductive gas is added to the high-temperature zone reactor and the mid-temperature zone reactor, wherein the reductive gas can enter the reactor(s) prior to, simultaneously with or posterior to the flue gas; and

(5) the flue gas and the reductive gas are reacted at 620-690° C. in the high-temperature zone reactor and the flue gas and the reductive gas are reacted at 500-550° C. in the mid-temperature zone reactor, wherein said reductive gas contains 0.01-90 vol % of hydrogen sulfide.

2. The method of claim 1 , wherein the mid-temperature zone reactor, a flue gas turbine expander and the high-temperature zone reactor are provided in the step (1), the catalytic cracking regenerator, the high-temperature zone reactor, the flue gas turbine expander and the mid-temperature zone reactor, are connected in the above mentioned order, after that a waste heat boiler is optionally connected, and then a cooler is optionally connected.

3. The method of claim 2 , wherein the waste heat boiler is present and a low-temperature zone reactor is disposed after the waste heat boiler and before the cooler, wherein the flue gas coming from the waste heat boiler and the reductive gas introduced into the low-temperature zone reactor are reacted at 150-250° C. in the presence of a catalyst, wherein said catalyst is one or more selected from alumina such as activated alumina, zirconia, titania and zinc oxide.

4. The method of claim 3 , wherein a sulfur recovery device is disposed in said low-temperature zone reactor.

5. The method of claim 3 , wherein said flue gas turbine expander has an inlet temperature of 630-680° C. and an outlet temperature of 520-550° C.; said waste heat boiler has an inlet temperature of 500-530° C. and an outlet temperature of 180-300° C.; and said cooler has an outlet temperature of 100-110° C.

6. The method of claim 3 , wherein a liquid sulfur recovery device is disposed in or after the waste heat boiler; and a solid sulfur recovery device is disposed in the cooler.

7. The method of claim 1 , wherein a catalyst of a noble metal active component and a rare earth metal active component on an inorganic oxide support is loaded in the high-temperature zone reactor,

wherein said noble metal active component is one or more selected from the group consisting of Pt, Pd, Rh and Au, said rare earth metal active component is one or more selected from the group consisting of La, Ce and Pr, and said inorganic oxide support is one or more selected from the group consisting of AlO 3 , SiO 2 , TiO 2 and ZrO 2 .

8. The method of claim 7 , wherein based on the total weight of the catalyst, the content of the noble metal (as oxide) in said catalyst is 0.1 wt %-5 wt %, and the content of the rare earth metal (as oxide) in said catalyst is 0.2 wt %-15 wt %.

9. The method of claim 1 , wherein a catalyst of a rare earth metal active component and an optional transition metal active component on an inorganic oxide support is loaded in the mid-temperature zone reactor, wherein said rare earth metal is one or more selected from the group consisting of La, Ce and Pr, said transition metal is one or more selected from the group consisting of Fe, Co, Ni, Cu, Zn, Ti, Mo and W, said inorganic oxide support can be one or more of Al 2 O 3 , SiO 2 , TiO 2 , ZrO 2 , SnO 2 and molecular sieve such as ZSM-5, HZSM-5, NaY, and mordenite, preferably one or more of Al 2 O 3 , TiO 2 , SiO 2 and ZrO 2 .

10. The method of claim 9 , wherein based on the total weight of the catalyst, the content of the rare earth metal (as oxide) in said catalyst is 0.2 wt %-16 wt %; and the content of the transition metal (as oxide) in said catalyst is 0.2 wt %-25 wt %.

11. The method of claim 1 , wherein said reductive gas is one or more of hydrogen, hydrogen sulfide, carbon monoxide and small molecule hydrocarbon(s) having the carbon number of 5 or less.

12. The method of claim 1 , wherein said reductive gas comprises or is a dry gas fraction obtained from a catalytic cracking plant.

13. The method of claim 1 , wherein the number of the mid-temperature zone reactor is one or more than one, wherein in the case that the number of the mid-temperature zone reactor is more than one, said reactors are connected in parallel; and/or the number of the high-temperature zone reactor is one or more than one, wherein in the case that the number of the high-temperature zone reactor is more than one, said reactors are connected in parallel.

14. An apparatus for removing sulfur oxides and nitrogen oxides in a regeneration flue gas of a catalytic cracking plant, wherein said catalytic cracking plant comprises a catalytic cracking reactor, a regenerator and a product separation system, wherein the regenerator has a flue gas outlet, and the product separation system has a dry gas outlet; wherein said apparatus comprises a mid-temperature zone reactor, an optional flue gas turbine expander and a high-temperature zone reactor,

wherein a catalyst of a noble metal active component and a rare earth metal active component on an inorganic oxide support is loaded in the high-temperature zone reactor;

wherein a catalyst of a rare earth metal active component and an optional transition metal active component on an inorganic oxide support is loaded in the mid-temperature zone reactor;

the flue gas outlet of the regenerator is connected to the high-temperature zone reactor, the inlet of the mid-temperature zone reactor is connected to the outlet of the high-temperature zone reactor; or in case that the flue gas turbine expander is present, the inlet of the mid-temperature zone reactor is connected to the outlet of the high temperature zone reactor through the flue gas turbine expander;

wherein the high-temperature zone reactor and the mid-temperature zone reactor respectively have one or more than one reductive gas inlets, wherein the flue gas outlet of the regenerator is connected through valve(s) to one or more than one reductive gas inlets of the high-temperature zone reactor or the mid-temperature zone reactor.

15. The apparatus of claim 14 , wherein said apparatus further comprises a subsequently connected waste heat boiler and optionally a cooler following the waste heat boiler.

16. The apparatus of claim 15 , wherein a liquid sulfur recovery device is disposed in or after the waste heat boiler; and a solid sulfur recovery device is disposed in the cooler.

17. The apparatus of claim 14 , wherein the number of the mid-temperature zone reactor is one or more than one, wherein in the ease that the number of the mid-temperature zone reactor is more than one, said reactors are connected in parallel; and/or the number of the high-temperature zone reactor is one or more than one, wherein in the case that the number of the high-temperature zone reactor is more than one, said reactors are connected in parallel.

18. The apparatus of claim 14 , wherein a low-temperature zone reactor is disposed after the waste heat boiler and before the optional cooler, said low-temperature zone reactor is loaded with one or more than one catalysts selected from the group consisting of alumina such as activated alumina, zirconia, titania and zinc oxide, and said low-temperature zone reactor has one or more reductive gas inlets.

19. The apparatus of claim 18 , wherein a sulfur recovery device is disposed in said low-temperature zone reactor.