Process for treating the off gas from a carbon black plant to recover sulphur

Abstract

The present application relates to a process for treating the off gas from a carbon black process, said process comprising the steps of: providing an off gas from a carbon black process, reacting said off gas in a first reaction step forming water and S, and condensing the S at a temperature Tcon where S is in a liquid phase and the water is in gas form thereby achieving a gaseous stream comprising water and a liquid stream comprising S, and wherein the first reaction step is carried out over a monolith catalyst.

Claims

1. A process for treating off gas from a carbon black process, said process comprising the steps of: providing an off gas from a carbon black process; reacting said off gas in a first reaction step forming water and S; and condensing the S at a temperature T.sub.con where S is in a liquid phase and the water is in gas form thereby achieving a gaseous stream comprising water and a liquid stream comprising S, wherein the first reaction step is carried out over a monolith catalyst at an inlet temperature of 180-250° C.

2. Process according to claim 1, wherein the monolith catalyst is corrugated from sheet metal or fiber glass web or is extruded.

3. Process according to claim 1, wherein the condensation temperature T.sub.con is in the interval between the dew point of water and the dew point of elemental Sulfur.

4. Process according to claim 1, wherein, the condensation is carried out at atmospheric pressure.

5. Process according to claim 1, wherein the composition of the carbon black off gas is 1-15% CO, 1-15% H.sub.2, 0.1-5% CO.sub.2, 50-5000 ppm H.sub.2S, 15-40% water, balance N.sub.2.

6. Process according to claim 1, wherein the carbon black off gas comprises 10-2000 ppm CS.sub.2 and/or 10-500 ppm COS.

7. Process according to claim 1, comprising a hydrolysis step upstream the first reactor.

8. Process according to claim 1, wherein O.sub.2 and/or air is added upstream the first reaction step in a stoichiometric amount according to the reaction H.sub.2S+0.5O.sub.2.fwdarw.S+H.sub.2O.

9. Process according to claim 1, wherein the monolith catalyst comprises oxides of Fe, Cr and/or Zn based on alumina and/or or Silica carriers optionally promoted by Na.sub.2O.

10. A process for treating off gas from a carbon black process, said process comprising the steps of: providing an off gas from a carbon black process; reacting said off gas in a first reaction step forming water and S; and condensing the S at a temperature T.sub.con where S is in a liquid phase and the water is in gas form thereby achieving a gaseous stream comprising water and a liquid stream comprising S, wherein the first reaction step is carried out over a monolith catalyst, and wherein the gaseous stream comprising water from the condensation step is reacted in a hydrogenation step.

11. Process according to claim 10, where the hydrogenation is carried out over a catalyst comprising Ni, Co and/or Mo on an alumina carrier.

12. Process according to claim 10, wherein the hydrogenation may comprise an oxidation step.

13. Process according to claim 10, wherein the hydrogenation takes place in the gas mixture as it is or alternatively with H.sub.2 added.

14. Process according to claim 10, wherein the effluent stream from the hydrogenation reactor may comprise CO, H.sub.2, CO.sub.2, H.sub.2S, H.sub.2O, N.sub.2 to balance.

15. Process according to claim 10, wherein at least part of the effluent from the hydrogenation reactor is treated in a H.sub.2S absorption unit, obtaining a substantially H.sub.2S free stream.

16. Process according to claim 15, wherein at least part of the effluent from the hydrogenation reactor bypasses the H.sub.2S absorption step as a bypass stream.

17. Process according to claim 15, wherein the bypass stream and the substantially H.sub.2S free stream may be mixed or separately treated downstream.

18. Process according to claim 15, wherein the H.sub.2S absorption unit is regenerative.

19. Process according to claim 18, wherein the regeneration is carried out under low O.sub.2 conditions.

20. Process according to claim 19, wherein, at low O.sub.2 conditions, the regeneration off gas comprises H.sub.2S, and the regeneration off gas comprising H.sub.2S is recycled upstream the first reactor.

21. Process according to claim 18, wherein the regeneration is an oxidation process, wherein the regeneration off gas comprises SO.sub.2, and wherein the regeneration off gas comprising SO.sub.2 is fed to a WSA process.

22. A plant arranged to carry out the process according to claim 1, comprising a hydrogenation reactor wherein water from the condensation step is reacted.

23. Plant according to claim 22, further comprising a first reactor comprising a monolith catalyst for reacting a carbon black off gas to water and S, and a condensation step downstream the first reactor.

24. Plant according to claim 23, wherein the monolith catalyst comprises oxides of Fe, Cr and/or Zn based on alumina and/or or silica carriers optionally promoted by Na.sub.2O.

25. Plant according to claim 22, wherein said hydrogenation reactor comprises a catalyst comprising Ni, Co and/or Mo on an alumina carrier.

26. Plant according to claim 22, wherein said hydrolysis reactor is upstream the first reactor, and wherein said hydrolysis reactor comprises at least one catalyst comprising TiO.sub.2 and/or alumina.

27. Plant according to claim 22, further comprising a H.sub.2S absorption unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a first embodiment of the present invention;

(2) FIG. 2 shows a second embodiment of the present invention;

(3) FIG. 3 shows a third embodiment of the present invention; and

(4) FIG. 4 shows a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 The carbon black off gas exits the bag filter at 180-260 C and is mixed with air fed directly to the first reactor. The reaction H.sub.2S+0.5O.sub.2.fwdarw.S+H.sub.2O is catalysed and elemental sulfur is formed. The elemental sulphur is condensed in the Sulphur condenser at a temperature where the sulphur is still in the liquid phase but the water content in the gas stream is still in the vapour form. The gas from the condenser is then fed to a CO boiler or gas engine for heat and power production.

(6) FIG. 2 The carbon black off gas exits the bag filter at 180-260 C and is mixed with air fed directly to the first reactor. The reaction H.sub.2S+0.5O.sub.2.fwdarw.S+H.sub.2O is catalysed and elemental sulfur is formed. The elemental sulphur is condensed in the Sulphur condenser at a temperature where the sulphur is still in the liquid phase but the water content in the gas stream is still in the vapour form. The gas from the condenser is then fed to a hydrogenation reactor where residual elemental sulfur vapour and SO.sub.2 is hydrogenated to H.sub.2S around at 200 C and a part of the gas stream is led to a H.sub.2S absorption unit where the gas is further purified and depending on the gas purity required downstream is led directly (or after mixing with the bypass stream) to a CO boiler or gas engine for heat and power production.

(7) FIG. 3 The carbon black off gas exits the bag filter at 180-260 C and is mixed with air fed directly to the first reactor. The reaction H.sub.2S+0.5O.sub.2.fwdarw.S+H.sub.2O is catalysed and elemental sulphur is formed. The elemental sulphur is condensed in the Sulphur condenser at a temperature where the sulphur is still in the liquid phase but the water content in the gas stream is still in the vapour form. The gas from the condenser is then fed to a hydrogenation reactor at around 200 C where residual elemental sulphur vapour and SO.sub.2 is hydrogenated to H.sub.2S and a part of the gas stream is led to a H.sub.2S absorption unit where the gas is further purified. The H.sub.2S absorption unit is regenerative and the regenerated off gas containing H.sub.2S is routed back upstream from the first reactor to a CO boiler or gas engine for heat and power production.

(8) FIG. 4 The carbon black off gas exits the bag filter at 180-260 C and is mixed with air fed directly to the first reactor. The reaction H.sub.2S+0.5O.sub.2.fwdarw.S+H.sub.2O is catalysed and elemental sulphur is formed. The elemental sulphur is condensed in the Sulphur condenser at a temperature where the sulphur is still in the liquid phase but the water content in the gas stream is still in the vapour form. The gas from the condenser is then fed to a hydrogenation reactor where residual elemental sulphur vapour and SO.sub.2 is hydrogenated to H.sub.2S around 200 C and a part of the gas stream is led to a H.sub.2S absorption unit where the gas is further purified. The H.sub.2S absorption unit is regenerative and the regenerated in a manner where the outlet gas is converted to SO.sub.2 which is further converted to sulfuric acid in for example a WSA plant. The purified gas is led to a CO boiler or gas engine for heat and power production.

(9) Depending on the composition of the carbon black off gas each of the embodiments according to FIGS. 1 to 4 may further be arranged to hydrolyse one or more sulphur compounds to H.sub.2S in a hydrolysing step before the first reactor.