Treatment of flue gases

• US 4,049,399 A
• Filed: 01/26/1976
• Issued: 09/20/1977
• Est. Priority Date: 04/08/1975
• Status: Expired due to Term

• Current Assignee: Research-Cottrell Incorporated
• Original Assignee: Teller Environmental Systems Incorporated
• Inventors: Teller, Aaron Joseph
• Primary Examiner(s): Adee, John
• Application Number:
  US05/652,634
• Time in Patent Office: 603 Days
• Field of Search: 55/63, 55/68, 55/73, 55/74, 55/76, 55/77, 55/79, 55/89, 55/90, 55/93, 55/94, 55/223, 55/226, 55/228, 55/229, 423/223
• US Class Current: 95/36
• CPC Class Codes: B01D 53/501 by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound

Abstract

Process and apparatus are disclosed for the treatment of flue gases to remove particulates, sulfur oxides, hydrogen sulfide and organic sulfur compounds using an alkaline scrubbing liquor containing activated carbon.

Claims

1. A process for treating an effluent gas containing entrained particulates a portion of which are below 1 micron in size, acid gas components, and a compound selected from the group consisting of H₂ S, lower alkyl mercaptans, lower alkyl sulfides and lower alkyl disulfides, said gas having a temperature above 150°

F., which comprises;

a. initiating nucleation of the particulates in a first enclosure by treating the gas to increase its turbulence and to increase its humidity substantially to saturation at a temperature above about 150°

F. to about 212°

F. under substantially adiabatic conditions, the pressure drop of said gas in said first enclosure being less than about 20 inches of water;

b. passing said saturated gas which is at a temperature above about 150°

F. to about 212°

F. in a substantially horizontal path through a second enclosure containing packing;

c. passing a scrubbing liquor comprising an aqueous alkaline slurry of activated, oxygenated carbon downwardly over said packing under laminar flow conditions;

d. exhausting said gas from said second enclosure; and

,

e. collecting at least a portion of said liquid after passage through said packing and recirculating said liquid portion to said packing, said recirculating liquid portion containing at least about 15% non-volatile material by weight.

2. The process of claim 1 wherein the increase in turbulence of the gas stream is sufficient to reduce the particulate content of said exhausted gas to not more than about 0.08 gr/sdcf.

3. The process according to claim 1 wherein the turbulence of the gas is increased in said first enclosure to a Reynolds number greater than about 10,000, the pressure drop of the gas in passing through said first enclosure being below about 20 inches of water.

4. The process of claim 3 wherein said increase in turbulence and increase in humidity is by the step of passing said gas stream through a venturi and simultaneously quenching it by contact with an aqueous quenching liquor.

5. The process of claim 3 wherein said increase in turbulence and increase in humidity is by the step of passing said gas stream through a set of baffles which are continuously washed with an aqueous washing liquor.

6. The process of claim 3 wherein said increase in turbulence and increase in humidity is by the steps of passing said gas stream through a venturi and simultaneously quenching it by contact with a recirculated portion of said scrubbing liquor and passing the gas stream through a set of baffles which are continuously washed with a recirculated portion of said scrubbing liquor.

7. The process according to claim 1 wherein said slurry has a pH below about 9.5 and a concentration of activated carbon between about 0.03% and about 0.6% by weight.

8. The process according to claim 1 wherein said slurry is recirculated through said packing at a substantially constant temperature, which is approximately the same as the gas which is above about 150°

F. to about 212°

F.

9. The process of claim 1 comprising the further step of bringing said gas from said second enclosure into contact with an aqueous washing liquid which is at a temperature below that of the gas to remove a further portion of residual contaminants.

10. The process according to claim 1 wherein a portion of said slurry is recirculated to said first enclosure to provide moisture for saturation therein, and another portion of said slurry is recirculated through said packing, said slurry having a constant heat content except for withdrawal of a slipstream and addition of makeup materials sufficient to maintain the volume, concentrations and pH thereof.

11. The process according to claim 1 wherein the flow rate of slurry is greater in upstream portions of said packing than in downstream portions of said packing, said upstream and downstream portions being with respect to the direction of flow of the gas, whereby greater amounts of alkali and carbon contact the gas at locations where the gas has relatively high concentrations of components to be removed therefrom.

12. The process according to claim 1 wherein said slurry is collected in a sump below said packing and wherein said carbon is oxygenated in said sump.

13. The process according to claim 11 wherein the packing comprises a plurality of toroidal elements, said elements being larger in upstream portions than in downstream portions of said packing, said upstream and downstream portions being with respect to the direction of flow of the gas therethrough.

14. The process of claim 1 wherein contact between said effluent gas and said slurry causes oxidation and removal of at least a portion of said sulfur compounds, the process including as a further step, subsequently contacting said effluent gas with oxidizing agent means more powerful than oxygen and scrubbing the gas with an alkaline aqueous liquid to remove additional sulfur compounds therefrom.

15. The process of claim 14 wherein said oxidizing agent means is chromic acid, a chlorine containing gas, or an alkali metal or alkaline earth metal hypochlorite, permanganate or chromate.

16. The process of claim 15 wherein said oxidizing agent means is chlorine and said alkaline aqueous liquid has a pH less than about 9.5.

25. The process of claim 1 comprising the further subsequent step of passing said gas horizontally through an additional enclosure containing packing, and passing a fluid cooler than said gas downwardly over said packing to recover heat from the gas.

17. A process for treating effluent gases from a pulp recovery boiler, said gas containing particulates a portion of which are below 1 micron in size, oxides of sulfur, hydrogen sulfide and organic sulfur compounds, said effluent gases having a temperature above about 150°

F., said process comprising as steps;

a. treating said gas in a first enclosure to increase its turbulence to a Reynolds number of at least about 10,000 and to increase its humidity to saturation at a temperature above about 150°

F. and under substantially adiabatic conditions, said first enclosure including a low energy venturi, the pressure drop of the gas in passing through said first enclosure being less than about 20 inches of water,

b. thereafter passing said gas in a substantially horizontal path through a second enclosure containing packing elements,

c. passing an aqueous alkaline slurry of oxygenated, activated carbon downwardly over said packing and through said second enclosure under substantially laminar flow conditions, the flow rate of the slurry through upstream portions of the packing exceeds the flow rate through downstream portions of the packing, said upstream and downstream portions being with respect to the direction of gas flow through the packing,

d. recirculating said slurry at a pH of less than about 9.5, at a non-volatile content of between at least about 15% by weight, a carbon concentration of between about 0.03% to 0.6% by weight, and at a substantially constant temperature approximately the same as said gas saturation temperature which is above about 150°

F. to about 212°

F., and

e. exhausting said gas from the second enclosure.

18. The process according to claim 17 wherein the consumption of carbon is less than about 0.6 pounds and the consumption of caustic as NaOH is less than about 25 pounds per ton of air dried pulp processed.

19. The process according to claim 17 wherein a portion of said slurry is recirculated to said first enclosure to provide the water to saturate said gas, the slurry being recirculated at constant heat content except for withdrawal of a slipstream and addition of makeup sufficient to maintain volume, concentration and pH thereof.

20. The process according to claim 19 wherein said slurry is collected in a sump below at least one of said enclosures and wherein said carbon is oxygenated in said sump.

21. The process according to claim 17 wherein the packing elements in an upstream portion of the packing are larger than the elements in a downstream portion.

22. The process of claim 17 comprising the further step of bringing said gas from said second enclosure into contact with an aqueous washing liquid which is at a temperature below that of the gas to remove a further portion of residual contaminants.

23. The process according to claim 17 wherein said gas is introduced into said first enclosure by means of a fan wetted with an aqueous liquid.

24. The process of claim 17 comprising as a further subsequent step, mixing chlorine with the gas and scrubbing additional sulfur compounds therefrom with an alkaline aqueous liquid having a pH less than about 9.5.

26. The method according to claim 17 wherein said slurry has a concentration of activated carbon of low density between about 0.03% and about 0.2% by weight.

27. Apparatus for treating effluent gas having a temperature above about 150°

F. and containing contaminants to be removed, said apparatus comprising (a) a first enclosure and within said first enclosure, a washed venturi for increasing the turbulence of the gas and for saturating the gas with moisture under substantially adiabatic conditions at a temperature above about 150°

F. up to about 212°

F., said venturi having a gas pressure drop therethrough less than about 20 inches of water;

(b) a second enclosure and, within said second enclosure, a packing material;

means for passing said gas in a substantially horizontal path through said second enclosure;

means for passing an aqueous alkaline carbon slurry downwardly over said packing in substantially laminar flow, means for varying the flow rate of slurry over said packing such that portions of the packing upstream can receive a greater flow than downstream portions, said upstream and downstream portions being with respect to the direction of gas flow therethrough;

(c) means for collecting and recirculating said slurry;

(d) means for oxygenating said carbon;

(e) means for withdrawing portions of said slurry and means for adding fresh alkali and carbon to maintain a predetermined volume of slurry in the apparatus and to maintain the pH, the carbon concentration, and the non-volatile content;

(f) a third enclosure filled with packing material downstream of said second enclosure with respect to the gas flow path, said third enclosure being disposed substantially vertically across the horizontal flow path of said gas, and means for passing water at a temperature below the temperature of the gas downwardly over said packing in the additional enclosure in heat exchange contact with the gas; and

(g) means for exhausting said gas.

28. Apparatus according to claim 27 wherein said apparatus is housed in a single, compact housing and wherein the means for collecting the slurry comprises a sump within the housing and below at least one of said enclosures, the means for oxygenating said carbon being located in said sump.

29. Apparatus according to claim 27 further comprising an additional enclosure containing packing material, said additional enclosure being disposed substantially vertically across the horizontal flow path of said gas downstream of said second enclosure, means for passing an aqueous alkaline liquid downwardly over said packing, means for collecting and recirculating said liquid, means for contacting said gas with an oxidizing agent in the third enclosure or in a space between said second and third enclosures, and means for adding fresh alkali to said liquid to maintain substantially constant volume and pH.

30. A process for treating an effluent gas at a temperature above about 150°

F. and containing particulates a portion of which are below 1 micron in size, acid gas components, and oxidizable hydrogen and lower alkyl compounds of sulfur, the process comprising as steps;

a. treating said gas in a first enclosure to increase its turbulence to a Reynolds number of at least about 10,000 and to increase its humidity to saturation at a temperature above about 150°

F. and under substantially adiabatic conditions, the pressure drop of the gas in passing through said first enclosure being less than about 20 inches of water;

b. thereafter passing said gas in a substantially horizontal path through a second enclosure containing packing;

c. passing an aqueous alkaline slurry of oxygenated, activated carbon downwardly over said packing and through said second enclosure under substantially laminar flow conditions;

d. recirculating at least a portion of said slurry at a substantially constant temperature approximately the same as said gas saturation temperature, approximately the same as the saturated gas which is above about 150°

F. to about 212°

F., a pH of less than about 9.5, a non-volatile content of at least about 15% by weight, and a carbon concentration of between about 0.03 percent to 0.6 percent by weight;

e. passing said gas in a substantially horizontal path through an additional enclosure containing packing in heat exchange relation with water cooler than said gas, said water passing downwardly over said packing; and

f. exhausting said gas.

31. The process of claim 30 comprising the additional step, after passage through said second enclosure, of contacting the gas with oxidizing means more powerful than oxygen and cross-flow scrubbing additional oxidized compounds of sulfur from the gas with an alkaline aqueous liquid.

32. The process of claim 31 wherein said oxidizing means is chlorine.

33. In a process for the adsorption, oxidation and removal of odoriferous sulfur-containing compounds from a gas stream containing a member selected from the group consisting of H₂ S, lower alkyl mercaptans, lower alkyl sulfides, and lower alkyl disulfides by contact with an aqueous alkaline slurry of activated carbon, the improvement wherein said slurry is oxygenated and introduced to the top of an enclosure containing packing and passed downwardly over said packing under laminar flow conditions, and said gas is passed transversely through the packing in contact with said slurry;

whereby the carbon has a greater effective concentration at the contacting surface than in the bulk of said slurry.

34. The process according to claim 33 wherein said packing comprises a plurality of toroidal packing elements.

35. The process according to claim 33, wherein the carbon concentration in said slurry is between about 0.03 and about 0.6% by weight, the slurry has a pH below about 9.5, and said slurry is recycled at a substantially constant temperature with a non-volatile content of at least about 15% by weight.

36. The process according to claim 33 comprising the further step of recoverying heat by passing said gas, after contaact with said alkaline carbon slurry, transversely through another packed enclosure, and passing water cooler than the gas downwardly over said packing in heat exchange contact with the gas.

37. The process according to claim 33 comprising a second oxidative step of contacting said gas, subsequent to exposure to said carbon slurry, with an oxidizing agent more powerful than oxygen and cross-flow scrubbing additional compounds of sulfur therefrom with an alkaline aqueous liquid.