WO2011140294A1

WO2011140294A1 - Method and apparatus for eliminating pollutants from a gas stream

Info

Publication number: WO2011140294A1
Application number: PCT/US2011/035289
Authority: WO
Inventors: James A. Wasas; Raymond C. Stenger; Wolfgang H. Koch
Original assignee: Swapsol Corp.
Priority date: 2010-05-07
Filing date: 2011-05-05
Publication date: 2011-11-10

Abstract

The present invention is directed to method of eliminating gaseous pollutants in a gas stream (12), such as flue gas stream, by reacting the gaseous pollutants with hydrogen sulfide (H2S) (24) in the presence of a catalyst (20) under conditions sufficient to convert the gaseous pollutants into products including one or more of elemental nitrogen, elemental sulfur, and water. In one embodiment, the invention is directed to a method of eliminating gaseous pollutants in a gas stream in which the gaseous pollutants include one or more of NOx, SOx, and combinations thereof. Additional pollutants that may be present in the gas stream and that may be eliminated in accordance with embodiments of the present invention include ozone (03) and carbonyl sulfide (COS).

Description

METHOD AND APPARATUS FOR ELIMINATING POLLUTANTS FROM

A GAS STREAM

FIELD OF THE INVENTION

The present invention relates generally to a method of eliminating pollutants from a flue gas, and more particularly, to the elimination of ΝΟχ and SOx pollutants in an exhaust gas stream.

BACKGROUND OF THE INVENTION

Today, many power plants produce electricity by combusting fuel, such as coal, oil, gas, biomass, etc. The combustion of such fuels results in the generation of an exhaust gas (also referred to as a flue gas) containing many undesirable byproducts that need to be removed prior to emitting the flue gas into the atmosphere. Examples of such byproducts may include nitrogen oxides (NO_x), sulfur oxides (SO_x), and the like.

Nitrogen oxides are typically formed in high temperature combustion processes and sulfur oxides are typically formed during combustion of sulfur in the fuel; these flue gases may also contain additional pollutants such as particulate matter, hydrocarbons and gasified metals.

The problems of pollutants in flue gases have been known for a long time, and reducing emissions from power plants is a concern all over the world. In particular, world organizations and international agencies, like the IEA, are concerned about the

environmental impact of burning fossil fuels. For instance, the combustion of coal has been linked to acid rain, air pollution, and has been connected with global warming.

Thanks to the development of "scrubbing" technologies, the amount of pollution released by modern day coal power plants has been significantly reduced. The most common method of reducing particulate emissions in flue gases from large plants is through a collection device that removes particles using an electrostatic force, an

Electrostatic Precipitator (ESP), which can clean more than 99.9% of particulate matter from flue gases. However, emission of pollutants in the form of flue gases containing nitrogen oxides and sulfur oxides continue to be a concern.

Sulfur oxides, such as sulfur dioxide (S0₂) and sulfur trioxide (SO3), are components of flue gas that cannot be removed via filtering. Since coal and oil contain sulfur compounds, their combustion generates mixed sulfur oxides (SO_x). When emitted to the air, sulfur oxides reacts with water and causes acidification of water and soil. The environmental impact of S0₂ emissions from fossil fuel combustion has been known for a long time, and the first cleaning technologies were introduced in the 1930s. Using fuels with less sulfur content was an early method of reducing SO_x emissions. More advanced and effective methods for treating sulfur oxide emissions were developed in the 1980s, including Flue Gas Desulfurization (FGD). In this method, the flue gases are cleaned using wet scrubbers or dry sorbants that absorb the sulfur oxides using limestone or other chemicals as an absorbing agent. However, FGD and other sulfur removing systems generally only have an efficiency rate on the order of 90 to 95%, and are generally not effective for the elimination of other flue gas components such as ΝΟχ. As a result, additional equipment and processing steps may be needed to effectively treat flue gases containing other pollutants.

In addition to sulfur oxides, combustion also generates nitrogen oxides as a result of nitrogen reacting with oxygen during combustion. Nitrogen oxides (ΝΟχ) have many adverse effects on the environment such as causing ground-level ozone that triggers respiratory problems, and contributing to acidification and eutrophication. ΝΟχ, and pollutants formed from NO_x , can be transported over long distances, following wind patterns.

One method of limiting ΝΟχ production is through a controlled combustion in which combustion temperature and oxygen concentration are controlled. However, such methods generally require precise controls and may limit the efficiency of the combustion process.

Other methods of limiting ΝΟχ production include the catalytic treatment of flue gas. For example, Selective Catalytic Reduction (SCR) reduces NO_xin flue gases by reacting ΝΟχ with ammonia in the presence of a catalyst. The ammonia reacts with the nitrogen oxides in the flue gas, forming elementary nitrogen (N₂) and water. Urea can also be used, but with the additional release of C0₂. However, SCR catalysts are generally expensive and are not useful in eliminating pollutants such as SO_x. Thus, there still exists a need for improved methods and equipment for eliminating pollutants found in flue gases.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to methods of eliminating gaseous pollutants in a gas streams, such as flue gas streams, by reacting the gaseous pollutants with hydrogen sulfide (H₂S) in the presence of a catalyst under conditions sufficient to convert the gaseous pollutants into products including one or more of elemental nitrogen, elemental sulfur, and water. Advantageously, the present invention provides a method, system and apparatus for the elimination of multiple pollutants in a gas stream that can be carried out in a continuous process with the use of a single catalytic material. As a result, additional cleaning steps and additional equipment are not required to remove NO_x and SO_x from a gas stream.

In one embodiment, a gas stream is provided in which the gas stream includes one or more gaseous pollutants that include at least one of ΝΟχ and SOx molecules as pollutants. A stream of gaseous H₂S is then introduced into the gas stream to form a stream comprising a combination of H₂S and at least one of NO_x or SO_x. The gaseous stream containing H₂S and ΝΟχ or SOx is then introduced into a catalyst in which the H₂S reacts with ΝΟχ or SOx present in the gas stream to convert the ΝΟχ or SOx pollutants into one or more of elemental sulfur, elemental nitrogen, water, and mixtures thereof.

The present invention is also directed to an apparatus for eliminating pollutants from a gas stream in which the apparatus includes a catalytic reactor having a catalyst in which H₂S reacts with at least one of ΝΟχ or SOx to produce reaction products including one or more of elemental sulfur, elemental nitrogen, water, and mixtures thereof.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a schematic side view of an apparatus for eliminating pollutants in a gas stream having a catalytic reactor for reacting H₂S with at least one of ΝΟχ or SOx; and FIG. 2 is a schematic side view of an alternative apparatus for eliminating pollutants in a gas stream that includes a nozzle for introducing a stream of water into the catalytic reactor. DETAILED DESCRIPTION OF THE INVENTION The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

The present invention is directed to method of eliminating gaseous pollutants in a gas stream, such as flue gas stream, by reacting the gaseous pollutants with hydrogen sulfide (H₂S) in the presence of a catalyst under conditions sufficient to convert the gaseous pollutants into products including one or more of elemental nitrogen, elemental sulfur, and water. In one embodiment, the invention is directed to a method of eliminating gaseous pollutants in a gas stream in which the gaseous pollutants include one or more of ΝΟχ, SOx, and combinations thereof. Additional pollutants that may be present in the gas stream and that may be eliminated in accordance with embodiments of the present invention include carbonyl sulfide (COS).

In one embodiment, a gas stream is provided in which the gas stream includes one or more gaseous pollutants that include at least one of NO_x and SO_x molecules as pollutants. A stream of H₂S is then introduced into the gas stream to form a stream comprising a combination of H₂S and at least one of ΝΟχ or SOx. The gaseous stream containing H₂S and ΝΟχ or SOx is then introduced into a catalyst in which the H₂S reacts with ΝΟχ or SO_x present in the gas stream to convert the NO_x or SO_x pollutants into one or more of elemental sulfur, elemental nitrogen, water, and mixtures thereof.

ΝΟχ compounds that can be eliminated in accordance with the present invention include nitric oxide (NO), nitrogen dioxide (N0₂), nitrogen pentoxide (N₂0₅), nitrogen tetraoxide (N₂04), nitrogen trioxide (N₂0₃), nitrous oxide (N₂0), nitrous acid (HN0₂), and nitric acid (HNO3), and combinations thereof. In a preferred embodiment, the ΝΟχ compounds include nitric oxide (NO), nitrogen dioxide (N0₂), or a combination thereof. The chemical reaction of the H₂S with the various ΝΟχ compounds are represented by Equations 1-8, below:

Reaction (1): NO + H₂S -> H₂0(g) + 1/2N₂ + S;

Reaction (2): N0₂ + 2H₂S -> 2H₂0(g) + 1/2N₂ + 2S;

Reaction (3): N₂0₅ + 5H₂S -> 5H₂0(g) + N₂ + 5S;

Reaction (4): N₂0₄ + 4H₂S -> 4H₂0(g) + N₂ + 4S; Reaction (5): N₂0₃ + 3H₂S -> 3H₂0(g) + N₂ + 3S;

Reaction (6): N₂0 + H₂S -> H₂0(g) + N₂ + S;

Reaction (7): 2HN0₂ + 3H₂S -> 4H₂0(g) + N₂ + 3S;

Reaction (8): 2HN0₃ + 5 H₂S -> 6H₂0(g) + N₂+ 5S.

The thermodynamic values for the reaction of H₂S with ΝΟχ compounds are described in Table 1 , below.

TABLE 1 : Thermodynamic values for reaction of H₂S with ΝΟχ compounds,

thermodynamic constants from CRC Handbook

SO_x compounds that can be eliminated in accordance with the present invention include sulfur dioxide (S0₂), sulfur trioxide (S0₃), and combinations thereof. The chemical reaction of the H₂S with the various SO_x compounds are represented by

Equations 9-10, below:

Reaction (9): S0₂ + 4H₂S -> 4H₂0(g) + 3S₂;

Reaction (10): S0₃ + 3H₂S -> 3H₂0(g) + 2S₂.

The thermodynamic values for the reaction of H₂S with SOx compounds are described in Table 2, below.

TABLE 2: Thermodynamic values for reaction of H₂S with SOx compounds,

thermodynamic constants from CRC Handbook

As can best be seen from the enthalpy values in Tables 1 and 2, above, the process of catalytically reacting H₂S with ΝΟχ and SOx pollutants found in the gas stream is highly exothermic. As such, it may be desirable to control the temperature of the gas stream during the conversion reaction so that it is maintained at a temperature that is less than about 500° F. More preferably, the temperature of the gas stream is controlled so that the temperature is less than about 305° F. In some embodiments, the temperature of the gas stream is from about room temperature to 305° F, and in particular, from about 100° F to about 150° F. It should be recognized that in some embodiments, higher temperatures may be employed. For example, temperatures ranging from about 500° to 1500° F may also be employed, although not necessarily with equivalent results.

Advantageously, embodiments of the present invention provide a method of eliminating substantially all ΝΟχ and SOx pollutants in a gas stream with the same catalyst material. In particular, the present invention helps to solve some of the problems associated with the prior art, and in particular, provides a single step process for removing both ΝΟχ and SOx. As a result, multiple separate steps for the removal of ΝΟχ and SOx from a gas stream can be eliminated or reduced.

As used herein, the term "substantially" includes at least 90% removal, but removal may be as much as 100%. Preferably, at least 95%, more preferably, at least 98%, and most preferably, at least 99% of the pollutants are removed during the inventive process.

Embodiments of the present invention are also directed to an apparatus and system for the elimination of gaseous pollutants in a gas stream. In this regard, FIG. 1 illustrates a system 10 in accordance with the present invention in which a gas stream, such as flue gas stream, containing pollutants is reacted with H₂S in the presence of a catalyst to eliminate the pollutants in the gas stream. As shown in FIG. 1, a gas stream 12 is introduced into a gas duct 14 from a gas source 16. As will be appreciated by one of skill in the art, the gas stream can be a result of any combustion or manufacturing process that generates pollutants such as NO_x and SO_x. For example, the gas source can be a furnace or combustion chamber that burns fuel, such as coal, gas, oil, and the like. Alternatively, the gas source can be any industrial or commercial process that generates a gas stream containing pollutants, such as ΝΟχ and SOx.

The gas duct is in communication with a catalytic reactor 18. The catalytic reactor includes a catalyst 20 for the conversion of pollutants in the gas stream. The stream of gas flows from the gas source and is introduced into the catalytic reactor 18 via inlet 22.

Preferably, the gas stream has been filtered to remove particulate matter prior to being introduced into the catalytic reactor. For example, in some embodiments the gas stream may be passed through a particulate collection device, such as an electrostatic precipitator (ESP) prior to be introduced into the catalyst.

A source of H₂S 24 provides a stream of H₂S that is introduced into the gas stream via supply line 26. A nozzle 28 in communication with supply source 24 is positioned upstream of the catalyst to introduce the H₂S stream into gas stream 14. The H₂S stream mixes with the gas stream and is carried downstream to the catalyst 20 where the H₂S and pollutants in the gas stream (e.g., NO_x, SO_x) react on the catalyst 20 to convert the pollutants into one or more products including elemental sulfur, nitrogen gas and water. The resulting clean flow is then discharged from the catalytic reactor 18 through outlet 30.

Monitoring sensors and computer controlled valves may be used to control the injection of H₂S into the gas stream 14 so as to use only just enough H₂S to maintain the correct stoichiometric ratio of H₂S to pollutants in the flue gas to effect elimination of both the H₂S and flue gas contaminants.

Examples of catalyst that may be used in accordance with the present invention include copper compounds, such as carbonates, hydroxides, oxides or sulfides of copper, vanadium compounds, such as oxides or sulfides of vanadium, and tungsten compounds, such as oxides or sulfides of tungsten, and mixtures thereof, but any other catalyst that accelerates the reaction may be used. Exemplary catalysts include, but are not limited to, minerals, such as malachite and azurite, and chemicals, such as vanadium pentoxide, vanadium sulfide, nichrome wire, chromium oxides, tungsten sulfide, tungsten oxides, molybdenum sulfide and titanium dioxide, and combinations thereof. Preferably, the catalyst comprises a material that is capable of accelerating the reaction between NO_x, SO, and H₂S. Other catalysts include those specified in U.S. Pat. No. 6,099,819.

In one embodiment, the catalyst comprises a mixture of sulfides and oxides of aluminum, cobalt, copper, iron, magnesium, manganese, and nickel. In certain

embodiments, the catalyst material may also include trace amounts in the low parts per million of rhodium, chromium, and silver, and combinations thereof.

The catalysts may be in any form, including powders, pellets, and other shapes suitable for a given reactor. In one embodiment, the catalyst is in the form of a particulate material having average particles sizes ranging between 100 and 100,000 microns, and in particular, from about 500 to 25,000 microns, and more particularly, from 1 ,000 to 5,000 microns. In one embodiment, the particles have average sizes ranging from 1,000 to 2,500 microns.

The catalyst may be a coating on a carrier, such as rings or beads, or may be particles that are not so fine as to prevent the flow of the gases through the catalytic bed. For example, the catalyst may be comprised of vanadium shavings with an oxidized surface. The catalyst is, preferably, placed in a column of such composition as to be structurally stable and resistant to attack by the gas passing through the reactor and placed above or in contact with a outlet for receiving, or draining, water, sulfur and purified gas, including nitrogen gas, from the catalyst. Multiple stages and additional filtration may be employed as desired to assure the elimination of entrained particulates.

As shown in FIG. l, the catalytic reactor is configured so that the gas stream flow flows downwardly through the catalyst. That is, the gas stream and any reaction products formed in the catalyst flow downwardly in the direction of gravity. This is particular advantageous as the reaction between NO_x and SO_x typically creates a slurry material containing water vapor, nitrogen gas, and element sulfur. The resulting slurry flows downwardly and exits the catalytic reactor via outlet 30.

After exiting the catalytic reactor 18, the treated material flows into a separation unit 32 in which the gaseous components (e.g., water vapor and nitrogen) are separated from the liquid and solid components. The now cleaned gaseous components can then be introduced into a stack 36 via line 38 from which the gaseous components can be discharged into the atmosphere. The remaining mixture having liquid and solid components is sent to a second separation unit 40 for separating solids from and liquid that may remain. The solid components, such as sulfur, can then be recovered in a subsequent step.

As briefly noted above, the reaction of H₂S with NO_x and SO_x is highly

exothermic. As a result, it may be desirable to treat the gas stream so that the temperature of the gas stream is maintained within a desired temperature range. In one embodiment, it has been found that introducing water into the gas stream prior to the catalyst helps to maintain the temperature within a desired range, such as below 500° F, and preferably, below about 200° F. In this regard, FIG. 2 illustrates an embodiment of the invention in which the apparatus include a nozzle 50 for introducing a stream of water 52 into the gas stream. The stream of water can be introduced as a liquid, mist, or a vapor. Water, owing to its high heat capacity, is capable of absorbing heat that is produced during the reaction of H₂S with one or more of the pollutants. The water removes the heat from the system so that the temperature within the catalytic reactor can be controlled. As in the embodiment described in FIG. 1, the water and reaction products are discharged from the catalytic reactor via an outlet of the catalytic reactor that feeds into a gas separator. After the cleaned gases are removed, the water can be separated and recovered from the solid components as discussed above. As shown in FIG. 2, the recovered water can then be recycled for reintroduction into the catalytic reactor as described above. Other methods of controlling the temperature may include introducing ambient air into the gas stream, using heat exchanges and/or air coolers. The process may also vary the H₂S injection location or include multiple locations for H₂S injection.

In some embodiments, the catalytic reactor may also include a means for mixing the H₂S stream and the gas stream. For example, the apparatus may also include a mixing element (not shown) that helps in the uniform distribution of the H₂S into the gas stream. The mixing element is typically disposed downstream of the H₂S injection nozzle 28. In one embodiment, the mixing element comprises a fin device, such as fan, having fins or blades such that as the gas stream flows through the mixing element, the path of the path of the gas stream is disturbed creating a turbulent flow of the gas stream on downstream side of the mixing device. As a result, the H₂S stream introduced into the exhaust stream can be more uniformly distributed therein. Other forms of mixing the H₂S stream and gas stream include projections and similar structures positioned within the catalytic reactor and that are configured to disturb the flow of the gas stream, helical coils, and the like.

The following Examples are provided for illustration purpose only and should not be construed as limiting the invention.

EXAMPLES

The following Examples illustrate embodiments of the invention in which H₂S was used to eliminate various gases from a nitrogen gas stream.

Experimental Procedure

A catalytic column was prepared using a Pyrex glass tube having a 25 millimeter (mm) outer diameter (OD) and a 22 mm inner diameter (ID), or a stainless steel tube having an outer diameter of 1 inch and an inner diameter of 7/8 of an inch. The column was packed with about 80 grams of a catalyst material having an average particle size ranging from 1,000 to 2,000 microns. The catalyst material was comprised of a mix of sulfides and oxides of aluminum, cobalt, copper, iron, magnesium, manganese, and nickel. The catalyst material also included traces of rhodium, chromium, and silver. The apparent density of the catalyst material was about 2 grams/cm and the catalyst bed in the column was about 110 mm deep.

The catalytic column was heated with an exterior resistance wire to a temperature ranging from about 30° C to about 250 ° C. The temperature within the catalytic column was measured with a Type K direct contact thermocouple that was positioned inside of the catalyst bed. The experiments were carried out with both a dry catalytic column and a water showered catalytic column. The temperature of the water showered catalytic column was maintained in the range of about 30 ° C to about 90° C, and the dry catalytic column was maintained at a temperature up to about 150° C.

A stream of hydrogen sulfide gas was injected into a nitrogen carrier gas containing a targeted flue gas. The resulting stream was then introduced into the catalytic column in which the flue gas constituents were reacted with hydrogen sulfide. The reaction products were then discharged from the column through an outlet at the base of the column. The reaction products included a gas and a water slurry containing various impurities. The gas was collected and analyzed with a SRI Model 86 IOC gas

chromatographer (GC) equipped with a MG #2 configuration. The detection limit of the GC for SO_x was 500 ppb, for NO_x was 300 ppm and for H₂S and COS was about 4 ppb.

EXAMPLE 1 : Elimination of NO_x and COS using H₂S

A stream of nitrogen gas containing 7.8% nitrous oxides supplied by Matheson TriGas was used in this example. A stream of hydrogen sulfide (H₂S 99.5%, COS 0.5%>) as supplied by Matheson TriGas was injected into the impure nitrogen stream. The resulting gas stream was then introduced into a prepared catalytic column as described above. The catalytic column was pre-heated with an exterior resistance wire to temperatures ranging from 30° C to 150° C. A water slurry and a gas emerged from the bottom of the column. The gas was separated from the water slurry and analyzed with the GC. The gas comprised nitrogen, and no nitrogen oxides, hydrogen sulfide or carbonyl sulfide detected in the gas stream.

The Experiment was repeated using a water showered catalytic column, which was maintained at a temperature of about 30° C to about 90° C. No nitrogen oxides, hydrogen sulfide or carbonyl sulfide was detected in the nitrogen gas stream.

EXAMPLE 2: Elimination of 0₃, COS and H₂S.

Ozone was generated in air with a high voltage sparker and fed into the catalytic column, which was pre-heated with an exterior resistance wire to temperatures ranging from 30° C to 150° C while hydrogen sulfide (H₂S 99.5%, COS 0.5%) as supplied by Matheson Trigas was injected into the air stream. A water slurry and a gas emerged from the bottom of the column. The gas was separated from the water slurry and analyzed with the GC for the presence of contaminants. The gas comprised nitrogen and oxygen; no contaminants were detected in the gas stream. EXAMPLE 3: Elimination of SOx, COS and H₂S.

Sulfur oxides were mixed into nitrogen as supplied by Matheson TriGas and fed into a catalytic column pre-heated with an exterior resistance wire to temperatures ranging from 30° C to 150° C. As in the process described above, a stream of hydrogen sulfide (H₂S 99.5%, COS 0.5%) as supplied by Matheson TriGas was injected into the impure nitrogen stream. A water slurry and a gas emerged from the bottom of the column. The gas was separated from the water slurry and analyzed with the GC for the presence of contaminants. The gas comprised nitrogen, and no contaminants were detected in the gas stream. The water slurry included sulfur.

EXAMPLE 4 A: Elimination of mixed pollutants using H₂S.

Nitrous oxides and sulfur oxides were mixed into a nitrogen stream and introduced into a catalytic column as described above. As in the process described above, a stream of hydrogen sulfide (H₂S 99.5%>, COS 0.5%>) as supplied by Matheson TriGas was injected into the impure nitrogen stream. A water slurry and a gas emerged from the bottom of the column. The gas was separated from the water slurry and analyzed with the GC for the presence of contaminants. No nitric oxides, sulfur oxides, hydrogen sulfide or carbonyl sulfide were detected in the resulting nitrogen gas stream.

EXAMPLE 4B:

Nitrous oxides and sulfur oxides were mixed into nitrogen and fed into a catalytic column as described above and that was pre-heated with an exterior resistance wire to

250° C. As in the process described above, a stream of hydrogen sulfide (H₂S 99.5%>, COS 0.5%) as supplied by Matheson TriGas was injected into the impure nitrogen stream. A water slurry and a gas emerged from the bottom of the column. The gas was separated from the water slurry and analyzed with the GC for the presence of contaminants. The gas comprised nitrogen, and no nitric oxides, sulfur oxides, hydrogen sulfide or carbonyl sulfide were detected in the gas stream.

EXAMPLE 4C.

Nitrous oxides and sulfur oxides were mixed into nitrogen and fed into a catalytic column as described above and that was pre-heated to 70° C with an exterior resistance wire. As in the process described above, a stream of hydrogen sulfide (H₂S 99.5%>, COS 0.5%) as supplied by Matheson TriGas was injected into the impure nitrogen stream. A water slurry and a gas emerged from the bottom of the column. The gas was separated from the water slurry and analyzed with the GC for the presence of contaminants. No nitric oxides, sulfur oxides, hydrogen sulfide or carbonyl sulfide were detected in the gas stream.

EXAMPLE 4D.

Nitrous oxides and sulfur oxides were mixed into nitrogen and fed into a catalytic column as described above. The catalytic column was pre-heated to 70° C with a water shower introduced into the column. As in the process described above, a stream of hydrogen sulfide (¾S 99.5%, COS 0.5%) as supplied by Matheson TriGas was injected into the impure nitrogen stream. A water slurry and a gas emerged from the bottom of the column. The gas was separated from the water slurry and analyzed with the GC for the presence of contaminants. The gas comprised nitrogen. No nitric oxides, sulfur oxides, hydrogen sulfide or carbonyl sulfide were detected in the gas stream.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED:

1. A method for eliminating gaseous contaminants from a gas stream, comprising:

introducing a stream of H₂S into a gas stream having one or more gaseous contaminants therein, the gaseous contaminants including at least one of NO_x or SO_x in the gas stream;

reacting the H₂S with said at least one of one of NO_x or SO_x in the presence of a catalyst and under conditions to convert the one of NO_x or SO_x into one or more of elemental sulfur, elemental nitrogen, water, and mixtures thereof.

2. The method of claim 1, further comprising the step of combusting a fuel to generate said gas stream.

3. The method of claim 2, wherein the fuel is selected from the group consisting of natural gas, coal, oil, peat, and waste, and combinations thereof.

4. The method of claim 1 , wherein the NO_x is selected from the group consisting of nitric oxide (NO), nitrogen dioxide (N0₂), nitrogen pentoxide (N₂0₅), nitrogen tetraoxide (N₂04), nitrogen trioxide (N₂0₃), nitrous oxide (N₂0), nitrous acid (HN0₂), and nitric acid (HNO3), and combinations thereof.

5. The method of claim 1, wherein the NO_x is nitric oxide (NO), nitrogen dioxide (N0₂), or a combination thereof.

6. The method of claim 1, wherein the SOx is sulfur dioxide (S0₂), sulfur trioxide (SO3), and combination thereof.

7. The method of claim 1, further comprising the step of maintaining the temperature of the gas stream during the step of reacting the H₂S with said gaseous contaminants at a temperature that is less than about 500° F.

8. The method of claim 7, wherein the temperature of the gas stream is less than about 250° F.

9. The method of claim 7, wherein the temperature the temperature of the gas stream is less than about 150° F.

10. The method of claim 1, further including the step of introducing a stream of water into the catalyst during the reacting step.

11. The method of claim 1 , wherein the catalyst comprises carbonates, hydroxides, oxides or sulfides of one or more of aluminum, cobalt, copper, iron, magnesium, manganese, and nickel.

12. The method of claim 1, wherein the catalyst includes trace amounts of rhodium, chromium, or silver, or combinations thereof.

13. A system for eliminating gaseous contaminants from a gas stream, the system comprising:

a gas stream having one or more gaseous contaminants therein, the gaseous contaminants including at least one of NO_x or SO_x, in the gas stream;

a source of H₂S that is configured to introduce a stream of H₂S into the gas stream; and

a catalytic column disposed downstream of the gas stream and the source of H₂S, the catalytic column including a catalytic material, wherein the contaminants react with H₂S in the presence of the catalytic material to convert the one of NO_x, or SO_x into one or more of elemental sulfur, elemental nitrogen, water, and mixtures thereof.

14. The system of claim 13, wherein the catalytic material comprises carbonates, hydroxides, oxides or sulfides of one or more of aluminum, cobalt, copper, iron, magnesium, manganese, and nickel, and combinations thereof.

15. The system of claim 13, further comprising a furnace in which a fuel is combusted to produce said gas stream.

16. The system of claim 15, wherein the fuel is selected from the group consisting of natural gas, coal, oil, peat, and waste, and combinations thereof.

17. The system of claim 15, further comprising a source of water that is configured to introduce a stream of water into the gas stream.

18. The system of claim 15, wherein the catalytic material is in the form of particles having average sizes ranging from 1,000 to 2,500 microns.