WO2001087464A1 - Process for scrubbing flue gas using acids - Google Patents

Process for scrubbing flue gas using acids Download PDF

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Publication number
WO2001087464A1
WO2001087464A1 PCT/US2001/015483 US0115483W WO0187464A1 WO 2001087464 A1 WO2001087464 A1 WO 2001087464A1 US 0115483 W US0115483 W US 0115483W WO 0187464 A1 WO0187464 A1 WO 0187464A1
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Prior art keywords
sulfuric acid
contacting
nox
acid
remove
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PCT/US2001/015483
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French (fr)
Inventor
Francis Alix
Christopher Mclarnon
Claire Golden
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Powerspan Corp.
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Priority to AU2001263103A priority Critical patent/AU2001263103A1/en
Publication of WO2001087464A1 publication Critical patent/WO2001087464A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/60—Simultaneously removing sulfur oxides and nitrogen oxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/69—Sulfur trioxide; Sulfuric acid
    • C01B17/74—Preparation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/082—Compounds containing nitrogen and non-metals and optionally metals
    • C01B21/087—Compounds containing nitrogen and non-metals and optionally metals containing one or more hydrogen atoms
    • C01B21/093—Compounds containing nitrogen and non-metals and optionally metals containing one or more hydrogen atoms containing also one or more sulfur atoms
    • C01B21/094—Nitrosyl containing acids
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B21/00—Nitrogen; Compounds thereof
    • C01B21/20—Nitrogen oxides; Oxyacids of nitrogen; Salts thereof
    • C01B21/38—Nitric acid
    • C01B21/40—Preparation by absorption of oxides of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J15/00—Arrangements of devices for treating smoke or fumes
    • F23J15/003—Arrangements of devices for treating smoke or fumes for supplying chemicals to fumes, e.g. using injection devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/50—Inorganic acids
    • B01D2251/504—Nitric acid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/50—Inorganic acids
    • B01D2251/506—Sulfuric acid
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J2215/00—Preventing emissions
    • F23J2215/10—Nitrogen; Compounds thereof
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J2215/00—Preventing emissions
    • F23J2215/20—Sulfur; Compounds thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Definitions

  • This invention relates to pollution control equipment used for reducing emissions of nitrogen oxides and sulfur dioxide from the burning of fossil fuels.
  • Nitrogen oxides (“NOx”) and sulfur dioxide (“SO 2 ”) emissions are pollutants commonly emitted from the burning of fossil fuel. NOx (which is understood herein to be predominantly NO and N0 2 ) in the atmosphere creates ground level ozone, which is toxic when inhaled. Both SO 2 and NOx contribute to the formation of acid rain, which is harmful to plant and animal life, as well as property.
  • the typical method of reducing NOx emissions is the use of low NOx burners that cool the combustion temperature to a point where the bonds of nitrogen (“N 2 ”) present in combustion air are less likely to be broken.
  • Breaking the N 2 bond during combustion is what forms NOx in the emissions.
  • Using low NOx burners has the disadvantage of making combustion less efficient and increases particulate matter emissions.
  • Another method of reducing NOx emissions is to install expensive selective catalytic or non-catalytic reduction systems that use ammonia or urea injection. These devices are expensive to purchase and operate, are prone to fouling, degrade in performance over time, and take up scarce space at plant sites.
  • the typical methods of reducing SO 2 emissions are burning low-sulfur coal and employing flue gas desulfurization ("FGD") equipment. Burning low-sulfur coal reduces the particulate matter collecting efficiency of electrostatic precipitators that are commonly used to remove particulate matter emissions. Both of these methods are expensive to build and operate.
  • FGD flue gas desulfurization
  • a cost- effective process that reduces both NOx and S0 emissions from the combustion of fossil fuel is a two or three step process comprising at least the steps of first oxidizing and absorbing the SO 2 with nitric acid (“HNO ”) to form sulfuric acid (“H 2 S0 4 ”) and additional NOx and, second, absorbing the NOx with liquid sulfuric acid to form liquid nitrosylsulfuric acid and gas substantially free of NOx and S0 2 .
  • the NOx produced in the first step is controlled to result in a molar ratio of NO to N0 2 that increases the efficiency of NOx removal in the second step.
  • the sulfuric acid produced in the first step also enhances the ability of the second step to remove NOx.
  • DRAWINGS Fig. 1 is a process schematic that describes the two-step process.
  • Fig. 2 is a process schematic that describes a three-step process.
  • Figure 1 shows the two-step process for removing NO x and S0 2 . It is comprised of a first step where SO 2 is absorbed and oxidized using nitric acid and a second step where NO x is absorbed using sulfuric acid. Flue gas 10, containing NO x and SO 2 is contacted 21 with liquid nitric acid 25. This contact produces a liquid stream 22 containing a mixture of nitric and sulfuric acids and a gas stream 11 substantially reduced in SO 2 . While gas stream 11 is greatly reduced in SO 2 , the quantity of NO x has been greatly increased, which is ordinarily an undesirable effect, and why oxidizing and absorbing S0 2 with nitric acid has not been used before as a pollution control process.
  • This step also produces sulfuric acid, which is not often desired.
  • the first step has not been used for pollution control before, the likely chemical reactions that take place are described in U.S. Patent No. 5,788,949, issued to O'Brien on August 4, 1998, that is not admitted to be prior art by its inclusion herein.
  • O'Brien teaches a process for converting a source of S0 2 to concentrated H 2 SO 4 in the field of sulfuric acid manufacture. He uses hydrogen sul ide as a source instead of flue gas.
  • the likely reactions that take place in the first step are as follows: ( ⁇ ) S0 2 + HN0 3 + H 2 0 -» HN0 2 + H 2 S0 4 (2) 2HNO 2 - NO + N0 2 + H 2 0
  • liquid 22 produced by absorbing and oxidizing SO 2 with nitric acid is a mixture of sulfuric and nitric acids.
  • the liquid mixture 22 enters a separator 23 where the nitric acid and sulfuric acids are separated. This separation may proceed by flash evaporation, evaporation, or other means common to the chemical processing industries.
  • Nitric acid 25 is pumped 24 back to the contactor 21 for reuse in the absorption and oxidation of S0 2 .
  • Sulfuric acid produced in the separator 23 is pumped 26 to the second step of the two-step process 27 or withdrawn as product sulfuric acid 28.
  • Flue gas 11 from the first process step containing NO x in the form of NO and NO 2 , is brought into contact 41 with sulfuric acid 45.
  • Reactions taking place in the second process step are described in the paper Absorption of NOx Fumes in Sulfuric Acid, by A. Kaldas, C-I- L Inc., September 1985, which is not admitted to be prior art by its inclusion herein.
  • the major reactions in the second step are as follows: (3) NO 2 + NO ⁇ N 2 0 3 (4) N 2 0 3 + 2H 2 S0 4 ⁇ 2NOHS0 4 + H 2 O
  • the NOx is converted in the sulfuric acid scrubbing step to liquid nitrosylsulfuric acid ("NOHS0 ”) and violet acid ("NO-H 2 S0 4 "). Violet acid is unstable, and decomposes into nitrosylsulfuric acid.
  • the liquid stream 42 containing sulfuric acid and nitrosylsulfuric acid, is drained from contactor 41.
  • a gas stream 13 is produced which is substantially free of NOx and SO 2 .
  • Nitrosylsulfuric acid in the liquid stream 42 produced by the absorption of NO and N0 2 is treated in a processor 43, producing a stream of sulfuric acid 45 substantially free of nitrosylsulfuric acid, pumped by a pump 44 for reuse in the sulfuric acid contactor 41. Removal of nitrosylsulfuric acid in a processor 43 produces nitric acid and is achieved through stream stripping or other methods common to the commercial manufacture of sulfuric acid. Nitric acid produced from nitrosylsulfuric acid is pumped 46 to the first process step 47 to make up for nitric acid consumed in the absorption and oxidation of S0 2 . Nitric acid produced excess of that needed for absorption and oxidation of SO 2 is withdrawn from the process 48.
  • Product sulfuric acid 28 and nitric acid 48 from the two step process may be sold as commercial acid, utilized in the production of fertilizer, neutralized, or used in other ways as is common for sulfuric and nitric acids.
  • the nitric acid scrubbing step 21 could be performed by merely spraying nitric acid into the flue gas stream.
  • Other specific methods include using a packed scrubbing tower, a series of towers, or other mass transfer devices such those that are well known in the pollution control art.
  • the sulfuric acid scrubbing step 41 may be performed using a packed scrubbing tower, or a series of packed towers or other mass transfer devices that are well known in the pollution control art.
  • the present invention is suitable for removing NOx and S0 2 from the combustion of many types of fossil fuels.
  • the invention may have its broadest application in coal burning electric power plants. However, it should be recognized that this invention could also be used with the combustion of natural gas, propane, oil, diesel fuel, gasoline, wood, biomass, and any other fossil fuel or industrial process that contains sulfur and emits NOx and S0 2 .
  • liquid nitric acid in contact with gaseous S0 2 substantially reduces the S0 2 concentration (from 1512 to 88 ppm) while producing copious amounts of NO (from 527 to 955 ppm) and N0 2 (from 44 to 1000 ppm). It can also be seen that liquid sulfuric acid substantially reduces the gaseous concentration of NO (from 955 to 126 ppm) and N0 2 (from 1000 to 47 ppm).
  • nitric acid at a concentration between about 0.1 and 65 percent by weight at a temperature between about 32 and 138° C is effective to absorb and/or oxidize, and therefore remove, S0 2 in the nitric acid contacting step.
  • a mixture of nitric acid of between about 0.1 and 65 percent nitric acid by weight and between about 0.1 and 80 percent sulfuric acid by weight will also be effective in the nitric acid contacting step.
  • the first step consists of S0 2 removal utilizing HN0 or a mixture of HN0 3 in H 2 S0 4 as described previously.
  • Flue gas 11 from the first step is contacted 31 with sulfuric acid 35 to absorb water vapor creating a flue gas stream 12 that is substantially free of S0 2 and H 2 0.
  • Water removal is accomplished to increase the rate of NOx absorption in the third step by allowing the acid 45 utilized in contactor 41 to be more concentrated and at a lower temperature than in the two step process.
  • the affinity of H 2 S0 4 for water, a common constituent in flue gas steams making up from about three to about fifteen percent of the total volume, is well known.
  • Diluted sulfuric acid stream 32 is then treated in separator 33 producing a sulfuric acid stream 34 returned for additional water absorption.
  • Water from separator 33 is pumped 36 from the process for general use 38 or disposal, as needed. Removing water in a separate processing step allows for optimal choice of acid concentration and temperature to accomplish the water removal and recover it from the dehydrating acid stream. It also limits water absorption in the NO x removal step , allowing it to be run at an optimal concentration and temperature for NOx absorption.
  • Make up sulfuric acid 29 for the water removal step is supplied by the excess sulfuric acid produced in the absorption and oxidation of S0 2 .

Abstract

A process that reduces both NOx and SO2 emissions from the combustion of fossil fuels, comprising at least two steps, is provided. First, the flue gas is contacted with nitric acid (21) to remove SO2. Then the flue gas is contacted with sulfuric acid (41) to remove NOx. Optionally, a second sulfuric acid contacting step (31) may be used to remove water from the flue gas before the sulfuric NOx removing sulfuric acid contacting step (41) so that the temperatures and concentrations of each step may be optimized.

Description

PROCESS FOR SCRUBBING FLUE GAS USING ACIDS by Francis R. Alix, Christopher R. McLarnon, and Claire A. Golden
BACKGROUND a. Field of the Invention.
This invention relates to pollution control equipment used for reducing emissions of nitrogen oxides and sulfur dioxide from the burning of fossil fuels. b. Description of the Related Art. Nitrogen oxides ("NOx") and sulfur dioxide ("SO2") emissions are pollutants commonly emitted from the burning of fossil fuel. NOx (which is understood herein to be predominantly NO and N02) in the atmosphere creates ground level ozone, which is toxic when inhaled. Both SO2 and NOx contribute to the formation of acid rain, which is harmful to plant and animal life, as well as property. The typical method of reducing NOx emissions is the use of low NOx burners that cool the combustion temperature to a point where the bonds of nitrogen ("N2") present in combustion air are less likely to be broken. Breaking the N2 bond during combustion is what forms NOx in the emissions. Using low NOx burners has the disadvantage of making combustion less efficient and increases particulate matter emissions. Another method of reducing NOx emissions is to install expensive selective catalytic or non-catalytic reduction systems that use ammonia or urea injection. These devices are expensive to purchase and operate, are prone to fouling, degrade in performance over time, and take up scarce space at plant sites.
The typical methods of reducing SO2 emissions are burning low-sulfur coal and employing flue gas desulfurization ("FGD") equipment. Burning low-sulfur coal reduces the particulate matter collecting efficiency of electrostatic precipitators that are commonly used to remove particulate matter emissions. Both of these methods are expensive to build and operate.
One of the features of these methods that make them so expensive to install and operate is that plants purchase and install a separate control device for each pollutant.
Installing a separate device for each pollutant wastes space and money, if a method can be devised that treats more than one pollutant. Also, using one process per pollutant makes it very unlikely that pollutant removal devices can operate synergistically or in a complimentary manner. For the foregoing reasons, there is a need for a cost-effective process that reduces both NOx and SO2 emissions from the combustion of fossil fuel in a single synergistic process in which the byproducts of the removal of one pollutant aid in the removal of the other pollutant.
SUMMARY
The present invention is directed to a process that satisfies these needs. A cost- effective process that reduces both NOx and S0 emissions from the combustion of fossil fuel is a two or three step process comprising at least the steps of first oxidizing and absorbing the SO2 with nitric acid ("HNO ") to form sulfuric acid ("H2S04") and additional NOx and, second, absorbing the NOx with liquid sulfuric acid to form liquid nitrosylsulfuric acid and gas substantially free of NOx and S02. The NOx produced in the first step is controlled to result in a molar ratio of NO to N02 that increases the efficiency of NOx removal in the second step. The sulfuric acid produced in the first step also enhances the ability of the second step to remove NOx. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawing and description.
DRAWINGS Fig. 1 is a process schematic that describes the two-step process.
Fig. 2 is a process schematic that describes a three-step process.
DESCRIPTION
Figure 1 shows the two-step process for removing NOx and S02. It is comprised of a first step where SO2 is absorbed and oxidized using nitric acid and a second step where NOx is absorbed using sulfuric acid. Flue gas 10, containing NOx and SO2 is contacted 21 with liquid nitric acid 25. This contact produces a liquid stream 22 containing a mixture of nitric and sulfuric acids and a gas stream 11 substantially reduced in SO2. While gas stream 11 is greatly reduced in SO2, the quantity of NOx has been greatly increased, which is ordinarily an undesirable effect, and why oxidizing and absorbing S02 with nitric acid has not been used before as a pollution control process. This step also produces sulfuric acid, which is not often desired. Although the first step has not been used for pollution control before, the likely chemical reactions that take place are described in U.S. Patent No. 5,788,949, issued to O'Brien on August 4, 1998, that is not admitted to be prior art by its inclusion herein. O'Brien teaches a process for converting a source of S02 to concentrated H2SO4 in the field of sulfuric acid manufacture. He uses hydrogen sul ide as a source instead of flue gas. The likely reactions that take place in the first step are as follows: (ϊ) S02 + HN03 + H20 -» HN02 + H2S04 (2) 2HNO2 - NO + N02 + H20
As taught by O'Brien, these reactions can take place in the liquid phase at temperatures ranging from about 20° C to about 150° C with concentrations of nitric acid from about 0.1 M to about 16 M. Whereas O'Brien teaches that each mole of S02 is converted to a half mole of NO and a half mole of NO2, we submit only that controlled molar proportions of some sort are important for the second step.
Returning to Figure 1, liquid 22 produced by absorbing and oxidizing SO2 with nitric acid is a mixture of sulfuric and nitric acids. The liquid mixture 22 enters a separator 23 where the nitric acid and sulfuric acids are separated. This separation may proceed by flash evaporation, evaporation, or other means common to the chemical processing industries.
Nitric acid 25 is pumped 24 back to the contactor 21 for reuse in the absorption and oxidation of S02. Sulfuric acid produced in the separator 23 is pumped 26 to the second step of the two-step process 27 or withdrawn as product sulfuric acid 28.
Flue gas 11 from the first process step, containing NOx in the form of NO and NO2, is brought into contact 41 with sulfuric acid 45. Reactions taking place in the second process step are described in the paper Absorption of NOx Fumes in Sulfuric Acid, by A. Kaldas, C-I- L Inc., September 1985, which is not admitted to be prior art by its inclusion herein. The major reactions in the second step are as follows: (3) NO2 + NO ^ N203 (4) N203 + 2H2S04 ■ 2NOHS04 + H2O
(5) 2N02 - N204
(6) N204 + H2S04 ■» NOHSO4 + HNO3
(7) NO + H2SO4 - NO-H2SO4
By these reactions, the NOx is converted in the sulfuric acid scrubbing step to liquid nitrosylsulfuric acid ("NOHS0 ") and violet acid ("NO-H2S04"). Violet acid is unstable, and decomposes into nitrosylsulfuric acid. The liquid stream 42, containing sulfuric acid and nitrosylsulfuric acid, is drained from contactor 41. A gas stream 13 is produced which is substantially free of NOx and SO2. These reactions occur at a higher rate with higher H2SO4 concentration and lower temperature.
Nitrosylsulfuric acid in the liquid stream 42 produced by the absorption of NO and N02 is treated in a processor 43, producing a stream of sulfuric acid 45 substantially free of nitrosylsulfuric acid, pumped by a pump 44 for reuse in the sulfuric acid contactor 41. Removal of nitrosylsulfuric acid in a processor 43 produces nitric acid and is achieved through stream stripping or other methods common to the commercial manufacture of sulfuric acid. Nitric acid produced from nitrosylsulfuric acid is pumped 46 to the first process step 47 to make up for nitric acid consumed in the absorption and oxidation of S02. Nitric acid produced excess of that needed for absorption and oxidation of SO2 is withdrawn from the process 48.
Product sulfuric acid 28 and nitric acid 48 from the two step process may be sold as commercial acid, utilized in the production of fertilizer, neutralized, or used in other ways as is common for sulfuric and nitric acids. In practice, the nitric acid scrubbing step 21 could be performed by merely spraying nitric acid into the flue gas stream. Other specific methods include using a packed scrubbing tower, a series of towers, or other mass transfer devices such those that are well known in the pollution control art.
The sulfuric acid scrubbing step 41 may be performed using a packed scrubbing tower, or a series of packed towers or other mass transfer devices that are well known in the pollution control art.
The present invention is suitable for removing NOx and S02 from the combustion of many types of fossil fuels. The invention may have its broadest application in coal burning electric power plants. However, it should be recognized that this invention could also be used with the combustion of natural gas, propane, oil, diesel fuel, gasoline, wood, biomass, and any other fossil fuel or industrial process that contains sulfur and emits NOx and S02.
The process of this invention requires at least two steps to accomplish in a commercially viable system. O'Brien, in U.S. Patent Application No. 09/190,730, filed on 11/10/1998, teaches that S02 and NOx oxidation can be accomplished in a single step utilizing a mixture of sulfuric and nitric acids. However, experiments treating flue gas representative of that produced by the combustion of fossil fuels have shown that the single step process produces NOx in the treated gas in excess of the amount contained in the incoming gas, due to the slow rate of NOx absorption. A second step, where NOx absorption takes place without additional SO2 absorption, is required to achieve a substantial reduction in the emission of nitrogen oxides.
Laboratory experiments conducted in two series packed columns show the ability of the two-step process to remove both S02 and N0X from simulated flue gas streams. Each column consisted of a 3.8 cm ID glass tube packed to a height of about 46 cm with glass Raschig rings. Simulated flue gas containing S02, NO, N02, 02 and N2 was passed through the series columns. Nitric acid was circulated through column 1 and sulfuric acid circulated through column 2. Results in the table below show the acid concentration, temperature and flow rate through each column, the gas temperature, flow rate and concentrations of S02, NO and N02 at the column inlet and the concentrations of S02, NO and NO2 at the column outlet.
Figure imgf000006_0001
It can be seen in the table that liquid nitric acid in contact with gaseous S02 substantially reduces the S02 concentration (from 1512 to 88 ppm) while producing copious amounts of NO (from 527 to 955 ppm) and N02 (from 44 to 1000 ppm). It can also be seen that liquid sulfuric acid substantially reduces the gaseous concentration of NO (from 955 to 126 ppm) and N02 (from 1000 to 47 ppm).
It has been determined that nitric acid at a concentration between about 0.1 and 65 percent by weight at a temperature between about 32 and 138° C is effective to absorb and/or oxidize, and therefore remove, S02 in the nitric acid contacting step. Likewise, a mixture of nitric acid of between about 0.1 and 65 percent nitric acid by weight and between about 0.1 and 80 percent sulfuric acid by weight will also be effective in the nitric acid contacting step.
In a separate embodiment, shown in Fig.2, removal of S02 and NOx is accomplished in three processing steps. The first step consists of S02 removal utilizing HN0 or a mixture of HN03 in H2S04 as described previously. Flue gas 11 from the first step is contacted 31 with sulfuric acid 35 to absorb water vapor creating a flue gas stream 12 that is substantially free of S02 and H20. Water removal is accomplished to increase the rate of NOx absorption in the third step by allowing the acid 45 utilized in contactor 41 to be more concentrated and at a lower temperature than in the two step process. The affinity of H2S04 for water, a common constituent in flue gas steams making up from about three to about fifteen percent of the total volume, is well known. Diluted sulfuric acid stream 32 is then treated in separator 33 producing a sulfuric acid stream 34 returned for additional water absorption. Water from separator 33 is pumped 36 from the process for general use 38 or disposal, as needed. Removing water in a separate processing step allows for optimal choice of acid concentration and temperature to accomplish the water removal and recover it from the dehydrating acid stream. It also limits water absorption in the NOx removal step , allowing it to be run at an optimal concentration and temperature for NOx absorption. Make up sulfuric acid 29 for the water removal step is supplied by the excess sulfuric acid produced in the absorption and oxidation of S02.
Although the preferred embodiments of the invention are described herein, it will be understood by those skilled in the art that changes and modifications may be made thereto without departing from the spirit of the invention or the scope of the appended claims. Accordingly, this specification is intended to encompass all such changes and modifications that fall within the scope of the present invention.

Claims

CLAIMSWe claim:
1. A process for removing S02 and NOx from a gas stream comprising the steps of
a. contacting the gas with a nitric acid solution to remove S02 and produce sulfuric acid and NOx, then
b. contacting the gas with a sulfuric acid solution to remove NOx and produce nitrosylsulfuric acid.
2. The process of claim 1 wherein the solution contacting the gas to remove S02 is nitric acid at a concentration of between 0.1 and 65 percent by weight and at a temperature of between 32 and 138°C.
3. The process of claim 1 wherein the solution contacting the gas to remove S02 is a mixture of nitric acid of between 0.1 and 65 percent by weight and sulfuric acid of between 0.1 and 80 percent by weight.
4. The process of claim 1 wherein the solution contacting the gas to remove NOx is sulfuric acid at a concentration of between 65 and 96 percent by weight operating at a temperature of between 21 and 149 °C.
5. The process of claim 1 further comprising the step of treating the nitrosylsulfuric acid from the removal of NOx to produce nitric acid.
6. The process of claim 5 wherein at least some of the nitric acid produced is returned to the S02 removal step.
7. A process for removing S02 and NOx from a gas stream comprising the steps of:
a. contacting the gas with a nitric acid solution to remove S02 and produce sulfuric acid and NOx, then
b. contacting the gas with a sulfuric acid solution to remove water vapor from the gas stream, then
c. contacting the gas with a sulfuric acid solution to remove NOx and produce nitrosylsulfuric acid.
8. The process of claim 7 wherein the sulfuric acid solution contacting the gas to remove water vapor is provided at a concentration and temperature suitably adapted to remove the water vapor and permit recovery of the water from the sulfuric acid solution.
9. The process of claim 7 wherein the sulfuric acid solution contacting the gas to remove NOx is provided at a concentration and temperature suitably adapted to remove the
NOx and form nitrosylsufuric acid.
10. An apparatus for removing S02 and NOx from a gas stream comprising
a. at least one nitric acid contacting means for contacting the gas stream with nitric acid and thereby removing S02, said nitric acid contacting means having an inlet for receiving a gas stream containing S02 and NOx and an outlet, and
b. at least one sulfuric acid contacting means for contacting the gas stream with sulfuric acid and thereby removing NOx, said sulfuric acid contacting means having an inlet for receiving the gas stream from the outlet of said nitric acid contacting means, and an outlet for exhausting the gas stream with S02 and NOx removed.
11. The apparatus of claim 10 further comprising a separator means for separating nitric acid from sulfuric acid collected from the nitric acid contacting means.
12. The apparatus of claim 10 further comprising a processor means for producing nitric acid from nitrosylsulfuric acid collected from the sulfuric acid contacting means.
13. The apparatus of claim 10 further comprising at least one sulfuric acid contacting means for contacting the gas stream with sulfuric acid and thereby removing water, said sulfuric acid contacting means having an inlet for receiving the gas stream from the outlet of said nitric acid contacting means, and having an outlet for exhausting the gas stream with S02 and water removed to said sulfuric acid contacting means for removing NOx.
14. The apparatus of claim 13 further comprising a separator means for separating sulfuric acid from water collected from the sulfuric acid contacting means for removing water.
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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6605263B2 (en) 2001-12-06 2003-08-12 Powerspan Corp. Sulfur dioxide removal using ammonia
WO2004092425A1 (en) * 2003-04-16 2004-10-28 Shapovalov Viatcheslav Dmitrie Method for processing sulfide minerals and concentrates
US6974565B2 (en) 2000-08-01 2005-12-13 Enviroscrub Technologies Corporation System and process for removal of pollutants from a gas stream
US6991771B2 (en) 1996-10-09 2006-01-31 Powerspan Corp. NOx, Hg, and SO2 removal using ammonia
US7247279B2 (en) 2000-08-01 2007-07-24 Enviroscrub Technologies Corporation System for removal of pollutants from a gas stream
WO2010036748A1 (en) * 2008-09-26 2010-04-01 Praxair Technology, Inc. Multi-stage process for purifying carbon dioxide and producing sulfuric acid and nitric acid
CN101905872A (en) * 2010-07-30 2010-12-08 金川集团有限公司 Device for absorbing SO3 generated in process of preparing sulfuric acid
FR2961409A1 (en) * 2010-06-22 2011-12-23 Air Liquide Purifying flue gas comprises contacting gas rich in carbon dioxide and containing sulfur dioxide, nitrogen oxides and oxygen with acid, separating sulfuric acid and concentrating gas into sulfur dioxide, nitric oxide and nitrogen dioxide
WO2017070466A3 (en) * 2015-10-21 2017-06-22 8 Rivers Capital, Llc Systems and methods for removing combustion products from a power generation cycle
CN112938906A (en) * 2021-02-02 2021-06-11 呼伦贝尔驰宏矿业有限公司 Application of concentrated nitric acid as reddening inhibitor in production of industrial sulfuric acid

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Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6991771B2 (en) 1996-10-09 2006-01-31 Powerspan Corp. NOx, Hg, and SO2 removal using ammonia
US6974565B2 (en) 2000-08-01 2005-12-13 Enviroscrub Technologies Corporation System and process for removal of pollutants from a gas stream
US7247279B2 (en) 2000-08-01 2007-07-24 Enviroscrub Technologies Corporation System for removal of pollutants from a gas stream
US7052662B2 (en) 2001-12-06 2006-05-30 Powerspan Corp. NOx, Hg, and SO2 removal using alkali hydroxide
US6605263B2 (en) 2001-12-06 2003-08-12 Powerspan Corp. Sulfur dioxide removal using ammonia
US6936231B2 (en) 2001-12-06 2005-08-30 Powerspan Corp. NOx, Hg, and SO2 removal using ammonia
US7048899B2 (en) 2001-12-06 2006-05-23 Powerspan Corp. Removing NOx, SO2, and Hg from a gas stream using limestone regeneration
US7682419B2 (en) 2003-04-16 2010-03-23 Viatcheslav Dmitrievich Shapovalov Method for processing sulfide minerals and concentrates
GB2415192B (en) * 2003-04-16 2007-06-13 Viatcheslav Dmitrie Shapovalov Method for processing sulfide minerals and concentrates
GB2415192A (en) * 2003-04-16 2005-12-21 Viatcheslav Dmitrie Shapovalov Method for processing sulfide minerals and concentrates
WO2004092425A1 (en) * 2003-04-16 2004-10-28 Shapovalov Viatcheslav Dmitrie Method for processing sulfide minerals and concentrates
US7927573B2 (en) 2008-09-26 2011-04-19 Praxair Technology, Inc. Multi-stage process for purifying carbon dioxide and producing acid
US7927572B2 (en) 2008-09-26 2011-04-19 Praxair Technology, Inc. Purifying carbon dioxide and producing acid
WO2010036748A1 (en) * 2008-09-26 2010-04-01 Praxair Technology, Inc. Multi-stage process for purifying carbon dioxide and producing sulfuric acid and nitric acid
FR2961409A1 (en) * 2010-06-22 2011-12-23 Air Liquide Purifying flue gas comprises contacting gas rich in carbon dioxide and containing sulfur dioxide, nitrogen oxides and oxygen with acid, separating sulfuric acid and concentrating gas into sulfur dioxide, nitric oxide and nitrogen dioxide
CN101905872A (en) * 2010-07-30 2010-12-08 金川集团有限公司 Device for absorbing SO3 generated in process of preparing sulfuric acid
WO2017070466A3 (en) * 2015-10-21 2017-06-22 8 Rivers Capital, Llc Systems and methods for removing combustion products from a power generation cycle
AU2016341977B2 (en) * 2015-10-21 2019-10-31 8 Rivers Capital, Llc Systems and methods for removing combustion products from a power generation cycle
EA035992B1 (en) * 2015-10-21 2020-09-10 8 Риверз Кэпитл, Ллк System and method for removing combustion products from a power generation cycle
CN112938906A (en) * 2021-02-02 2021-06-11 呼伦贝尔驰宏矿业有限公司 Application of concentrated nitric acid as reddening inhibitor in production of industrial sulfuric acid
CN112938906B (en) * 2021-02-02 2022-10-21 呼伦贝尔驰宏矿业有限公司 Application of concentrated nitric acid as reddening inhibitor in production of industrial sulfuric acid

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