Elimination of SO.SUB.2 .and CO.SUB.2 .from a gas

Abstract

A process to treat/clean a gas, containing SO.sub.2, CO.sub.2 and O.sub.2 comprising the steps of: bringing the gas in contact with an activated carbon catalyst, converting SO.sub.2 to SO.sub.3/H.sub.2SO.sub.4 on the activated carbon catalyst, washing the SO.sub.3/H.sub.2SO.sub.4 from the activated carbon catalyst to obtain a sulfuric acid solution and a SO.sub.2 depleted gas; bringing the SO.sub.2 depleted gas in contact with an aqueous ammonia solution wherein CO.sub.2 is converted to obtain a SO.sub.2 and CO.sub.2 depleted gas containing ammonia; and bringing the SO.sub.2 and CO.sub.2 depleted gas containing ammonia in contact with the sulfuric acid solution obtained in step a. to form a solution containing ammonium sulfate and a treated, clean gas.

Claims

1. A process to treat or clean a gas containing SO.sub.2, CO.sub.2 and O.sub.2, said process comprising the steps of: (a) bringing the gas in contact with an activated carbon catalyst, converting SO.sub.2 to SO.sub.3/H.sub.2SO.sub.4 on the activated carbon catalyst, washing the SO.sub.3/H.sub.2SO.sub.4 from the activated carbon catalyst to obtain a sulfuric acid solution and a SO.sub.2 depleted gas; (b) bringing the SO.sub.2 depleted gas in contact with an aqueous ammonia solution wherein CO.sub.2 is converted to obtain a SO.sub.2 and CO.sub.2 depleted gas containing ammonia; (c) bringing the SO.sub.2 and CO.sub.2 depleted gas containing ammonia in contact with the sulfuric acid solution obtained in step (a) to form a solution containing ammonium sulfate and a treated, clean gas.

2. The process of claim 1, wherein the activated carbon catalyst is a mixture of an activated carbon catalyst and a filler material.

3. The process of claim 2, wherein the mixture contains no other solid ingredients than at least one of an activated carbon catalyst and a filler material.

4. The process of claim 2, wherein the filler material is chosen from fillers made of at least one of ceramic material, metal, plastic material and mixtures thereof.

5. The process of claim 2, wherein the filler material is a shape chosen among saddle shaped, ring shaped, ball shaped, torus shaped, prism shaped or irregular shaped.

6. The process of claim 2, wherein the mixture of the activated carbon catalyst and the filler material is in a fixed bed.

7. The process of claim 1, wherein the activated carbon catalyst is washed in step (a) with water or an aqueous solution in an amount between 5 l/hour/m.sup.3 of activated carbon catalyst and 100 l/hour/m.sup.3 of activated carbon catalyst.

8. The process of claim 1, wherein the activated carbon catalyst is washed by intermittent spraying with at least one of water and an aqueous solution in counter-flow to the gas.

9. The process of claim 1, wherein the gas containing CO.sub.2, SO.sub.2 and O.sub.2 is a natural gas, syngas, flue gas generated by at least one of: combustion of carbon and hydrogen-containing fuels; chemical processes; and metallurgical processes.

10. The process of claim 1, wherein the gas being brought into contact with the activated carbon catalyst has a temperature of between 10 and 150° C.

11. The process of claim 1 wherein the SO.sub.2 content of the gas is between 50 and 5,000 ppm.

12. The process of claim 1 wherein the CO.sub.2 content of the gas is between 2 and 20 v %.

13. The process of claim 1, wherein the O.sub.2 content of the gas is between 5 and 20% vol.

14. The process of claim 1, wherein the H.sub.2SO.sub.4 content of the H.sub.2SO.sub.4 solution is between 5 and 50% vol.

15. The process of claim 1, wherein the aqueous ammonia solution in step (b) comprises at least one of ammonia, urea and a mixture thereof.

16. The process of claim 1, wherein steps (a) and (c) take place in a same reactor.

17. The process of claim 16, wherein the reactor contains an upper bed of the activated carbon catalyst where step (a) takes place and a lower bed where step (c) takes place.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further details and advantages of the invention can be taken from the following detailed description of possible exemplary embodiments of the invention on the basis of the accompanying FIG. 1. in the drawings:

(2) FIG. 1 is a schematic view of the arrangement to treat/clean a gas, containing SO.sub.2, CO.sub.2 and O.sub.2, in accordance with various exemplary embodiments of the invention.

DETAILED DESCRIPTION

(3) The system contains three stages.

(4) In a first stage, a gas containing 15% v/v CO.sub.2, 500 ppm SO.sub.2 and 14% v/v O.sub.2, is transferred into a first reactor 1. In this particular gas, an exhaust gas from a clinker plant was used.

(5) In this particular design, the first reactor 1 contains two vertically stacked beds 3, 4 of an activated carbon catalyst, each with a height between 0.5 and 2.0 meters. It is clear that one could also have used two separate reactors.

(6) The gas 2, with for example 18% v/v O.sub.2, 15 v % of CO.sub.2, and 500 ppm of SO.sub.2 (the rest being N.sub.2), passes through the upper bed 3 of an activated carbon catalyst and travels from the bottom to the top of the activated carbon bed 3 by means of a fan (not shown). In this step only SO.sub.2 is removed and converted to sulfuric acid on the activated carbon catalyst's surface according to the following reaction:
SO.sub.2+½O.sub.2+nH.sub.2O.Math.H.sub.2SO.sub.4.Math.(n−1)H.sub.2O

(7) The sulfuric acid is then washed from the upper activated carbon catalyst bed and then sprayed on top of the lower activated carbon catalyst bed 4.

(8) In the second stage, the CO.sub.2 contained in the gas is removed by absorption in an aqueous ammonia solution with formation of ammonium bicarbonate.

(9) After removal of SO.sub.2 and formation of sulfuric acid, the gas stream with CO.sub.2 (7) is transferred in a first absorber 8 and then in a second absorber 9 containing an aqueous ammonia solution. The formation of ammonium bicarbonate or ammonia carbonate or ammonium carbamate takes place at these two absorbers 8, 9 by reaction of CO.sub.2, water and ammonia.
CO.sub.2+H.sub.2O+NH.sub.3.fwdarw.(NH.sub.4)(HCO.sub.3)

(10) The produced ammonia bicarbonate, or ammonia carbonate or carbamate solution is cooled-down in a heat exchanger (not shown) and then transferred to a precipitator (not shown) in which the crystallized product is separated from the liquid phase. This liquid, containing still some ammonia, is transferred back to the two absorbers 8, 9.

(11) Third Stage: Avoid the release of ammonia slip into the air.

(12) In the third stage, the gas leaving the two absorbers 8, 9 contains now some ammonia evaporated from the aqueous ammonia solution and this ammonia rich gas stream 10 passes through a reactor 11 containing a bed of activated carbon, with a height between 0.5 and 2.0 meters. In this reactor 11, wash water is added countercurrent on top of the reactor. This water reacts with ammonia, contained in the gas on the surface of activated carbon, and ammonium hydroxide is produced and taken up by the aqueous solution in the reactor:
H.sub.2O+NH.sub.3.fwdarw.NH.sub.4OH

(13) The ammonium hydroxide solution is enriched with gaseous NH.sub.3 and then transferred to the two-reactor system 8, 9.

(14) In parallel, the gas stream which still contains NH3 is transferred via a gas conduct 12 to the final scrubber unit 6 (in the first reactor) which contains the sulfuric acid produced on the activated carbon catalyst bed 3 during the first stage of the process. Ammonia and sulfuric acid react and form ammonium sulfate according to the following reaction.
H.sub.2SO.sub.4+2NH.sub.3.fwdarw.(NH.sub.4).sub.2SO.sub.4

(15) The cleaned gas is released to the chimney/stack 14.

(16) Results from Pilot Tests

(17) TABLE-US-00001 Test 1: The test was carried out under the following conditions: Raw gas volume flow min. 260 m.sup.3/h max. 310 m.sup.3/h SO.sub.2 content (inlet) min. 400 ppm max. 800 ppm CO.sub.2 content (inlet) min. 5.5 v % max. 6.5 v % Waste gas temperature min. 78 ° C. max. 82 ° C. O.sub.2 content >20 v %

(18) The reactor is made of inert glass fiber reinforced plastics material, has a volume of approximately 2 m.sup.3 and is filled with 0.6 m.sup.3 of an activated carbon catalyst of the Norit®_RST-3 type.

(19) The test system was run for approximately 5 hours with the exhaust from a clinker production. The SO.sub.2 and CO.sub.2 content of the flue gas was measured at the inlet of the first reactor 3 and at the outlet of the stack 14 as described above. In addition, the ammonia slip was measured at the stack. The SO.sub.2 and CO.sub.2 concentration fluctuated repeatedly between 500 ppm and 700 ppm for SO.sub.2 and around 6 v % for CO.sub.2, with a SO.sub.2 removal efficiency superior to 98% and a CO.sub.2 conversion efficiency of 51%. The ammonia solution was added continuously over 5 hours and the measured ammonia slip outlet was below 15 ppm over this time period.

(20) TABLE-US-00002 Test 2: The test was carried out under the following conditions: Raw gas volume flow min. 270 m.sup.3/h max. 320 m.sup.3/h SO.sub.2 content (inlet) min. 350 ppm max. 700 ppm CO.sub.2 content (inlet) min. 6 v % max. 7 v % Waste gas temperature min. 58 ° C. max. 62 ° C. O.sub.2 content >20 v %

(21) The reactor is made of inert glass fiber reinforced plastics material, has a volume of approximately 2 m.sup.3 and is filled with 0.6 m.sup.3 of an activated carbon catalyst of the JACOBI_EcoSorb® VRX-Super type.

(22) The test system was run for approximately 7 hours with the exhaust from a clinker production. The SO.sub.2 and CO.sub.2 content of the waste gases was measured at the inlet to the first reactor and at the outlet of the stack as described above. In addition, the ammonia slip was measured at the stack. The SO.sub.2 and CO.sub.2 concentration fluctuated repeatedly between 500 ppm and 650 ppm for SO.sub.2 and around 6.2 v % for CO.sub.2, with a SO.sub.2 removal efficiency superior to 98% and a CO.sub.2 conversion efficiency of 49%. The ammonia solution was added continuously over 7 hours and the measured ammonia slip outlet was below 15 ppm over this time period.

(23) TABLE-US-00003 Test 3: The test was carried out under the following conditions: Raw gas volume flow min. 270 m.sup.3/h max. 320 m.sup.3/h SO.sub.2 content (inlet) min. 320 ppm max. 740 ppm CO.sub.2 content (inlet) min. 7 v % max. 11 v % Waste gas temperature min. 58 ° C. max. 62 ° C. O.sub.2 content >20 v %

(24) The reactor is made of inert glass fiber reinforced plastics material, has a volume of approximately 2 m.sup.3 and is filled with 0.6 m.sup.3 of an activated carbon catalyst of the CHEMVIRON CENTAUR® HSV type.

(25) The test system was run for approximately 11 hours with the exhaust from a clinker production. The SO.sub.2 and CO.sub.2 content of the waste gases was measured at the inlet to the first reactor and at the outlet of the stack as described above. In addition, the ammonia slip was measured at the stack. The SO.sub.2 and CO.sub.2 concentration fluctuated repeatedly between 500 ppm and 650 ppm for SO.sub.2 and around 9 v % for CO.sub.2, with a SO.sub.2 removal efficiency superior to 98% and a CO.sub.2 conversion efficiency of 50%. The ammonia solution was added continuously over 11 hours and the measured ammonia slip outlet was below 15 ppm over this time period.

(26) TABLE-US-00004 Test 4: The test was carried out under the following conditions: Raw gas volume flow min. 200 m.sup.3/h max. 300 m.sup.3/h SO.sub.2 content (inlet) min. 0 ppm max. 10 ppm CO.sub.2 content (inlet) min. 7 v % max. 18 v % Waste gas temperature min. 20 ° C. max. 45 ° C. O.sub.2 content >5 v %

(27) The reactor is made of inert glass fiber reinforced plastics material, has a volume of approximately 2 m.sup.3 and is filled with 0.5 m.sup.3 of an activated carbon catalyst of the Norit®_RST-3 type.

(28) The test system was run for approximately 6 hours with the exhaust from a clinker production. The SO.sub.2 and CO.sub.2 content of the waste gases was measured at the inlet to the first reactor which is in this particular case a so called Sulfacid® reactor and at the outlet of the stack as described above. In addition, the ammonia slip was measured at the stack. The SO.sub.2 and CO.sub.2 concentration fluctuated repeatedly between 0 ppm and 10 ppm for SO.sub.2 and around 9 v % for CO.sub.2, with a SO.sub.2 removal efficiency superior to 99% and a CO.sub.2 conversion efficiency of 50%. The ammonia solution was added continuously over 6 hours and the measured ammonia slip outlet was below 4000 ppm over this time period.

(29) Test 4 underlines the necessity of SO.sub.2 inlet for reduction of ammonia slip!

(30) Although the present invention has been described in considerable detail with reference to certain exemplary versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.

(31) All the features disclosed in this specification (including any accompanying claims, abstract, and drawings) can be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar.