Method and plant design for reduction of start-up sulfur oxide emissions in sulfuric acid production
The invention is a method and a sulfuric acid plant design for reduction of start-up SO 2 , SO 3 and H 2 SO 4 emissions in sulfuric acid production, in which SO2 is converted to SO 3 in n successive catalyst beds, where n is an integer >1. The final catalytic beds are used as absorbents for SO 2 to SO3 during the start-up procedure, and one or more of the m beds downstream the first bed are purged, either separately or simultaneously, with hot gas, where m is an integer >1 and m<n, during the previous shut-down. Also, one separate purge with hot gas is used on the final bed.
1. A method for reduction of start-up SO 2 , SO 3 and H 2 SO 4 emissions in sulfuric acid production, in which SO 2 is converted to SO 3 in a set of successive catalyst beds connected in series, the method comprising:
flowing a waste gas stream comprising SO 2 through the set of catalyst beds;
shutting down the catalyst beds, the shutting down comprising:
isolating at least one final downstream catalyst bed from the set of catalyst beds;
leaving all other catalyst beds of the set connected in series;
flowing a first heated purge gas stream through the at least one final downstream catalyst bed;
flowing a second heated purge gas stream through the other catalyst beds;
starting up the set of catalyst beds, the starting up comprising:
placing the at least one final catalyst beds back in series with the other catalyst beds; and
absorbing SO 2 and SO 3 into a catalyst of the at least one final downstream catalyst bed during the starting up.
2. A method according to claim 1 , wherein the shutting down comprises:
isolating at least two final downstream catalyst beds from the set of catalyst beds;
configuring the penultimate catalyst bed and final downstream catalyst beds in series; and
flowing the first hot purge gas stream through the penultimate catalyst bed prior to the final downstream catalyst bed.
3. A method according to claim 1 , wherein the shutting down comprises:
isolating two or more beds from the other catalyst beds, downstream of the first catalyst bed; and
purging each isolated catalyst bed separately with hot purge gas.
4. A method according to claim 1 , wherein the shutting down comprises:
isolating two or more beds from the other catalyst beds, downstream of the first catalyst bed; and
purging each isolated catalyst bed simultaneously with hot purge gas.
5. A method according to claim 1 , where the catalyst comprises a vanadium(V) compound, sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate and alkali metals, such as Li, Na, K, Rb or Cs, on a porous carrier.
6. A method according to claim 5 , wherein the porous carrier of the catalyst comprises silicon dioxide (SiO 2 ).
7. A method according to claim 6 , wherein the porous carrier of the catalyst comprises SiO 2 with less than 10 wt % of alumina.
8. A method according to claim 7 , wherein the porous carrier of the catalyst comprises SiO 2 with less than 2 wt % of alumina.
9. A method according to claim 8 , wherein an alkali metal content of the catalyst is 2-25 wt %.
10. A method according to claim 9 , wherein the alkali metal content of the catalyst is 8-16 wt %.
11. A method according to claim 1 , wherein the first heated purge gas stream is air fed to the final catalyst bed at a temperature of 400-600° C.
12. A method according to claim 5 , wherein the catalyst contains 1-15 wt % of a vanadium(V) compound such as V 2 O 5 .
13. A method according to claim 5 , wherein the catalyst contains 1-25 wt % sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate.
14. A method according to claim 13 , wherein the catalyst contains 2-20 wt % sulfur, in the form of sulfate, pyrosulfate, tri- or tetrasulfate.
15. A method according to claim 14 , wherein the catalyst contains 4-16 wt % sulfur in the form of sulfate, pyrosulfate, tri- or tetrasulfate.
16. A method according to claim 12 , wherein the catalyst contains 2-12 wt % of a vanadium(V) compound such as V 2 O 5 .
17. A method according to claim 16 , wherein the catalyst contains 4-10 wt % of a vanadium(V) compound such as V 2 O 5 .
18. A method according to claim 7 , wherein the porous carrier of the catalyst comprises SiO 2 with not greater than 5 wt % of alumina.
19. A method according to claim 8 , wherein the porous carrier of the catalyst comprises SiO 2 with not greater than 1 wt % of alumina.
20. A sulfuric acid plant design provided with means for securing reduced start-up emissions of SO 2 , SO 3 and H 2 SO 4 , said plant design comprising a set of successive catalyst beds connnected in series, wherein:
a waste gas stream comprising SO 2 is flowed through the set of catalyst beds;
at least one final downstream catalyst bed is isolated from the set of catalyst beds during shut down, leaving all other catalyst beds of the set connected in series
a first heated purge gas stream is flowed through the at least one final downstream catalyst bed during shut down;
a second heated purge gas stream is flowed through the other catalyst beds during shut down;
the at least one final catalyst beds are placed back in series with the other catalyst beds; and
SO 2 and SO 3 is absorbed into a catalyst of the final downstream catalyst bed during start up.