Methods for preventing formation of sulfuric acid and related products in combustion effluents
First Claim
1. A process for minimizing the formation of H2 SO4 in a combustion effluent having NO, at least 1 ppm SO3, and water vapor, the process comprising the step of contacting the combustion effluents with methanol, in an amount such that the mole ratio of the methanol to the sum of NO and SO3 is in the range of from about 0.8 to about 2.0, at a temperature in the range from about 500°
- C. to about 950°
C., said methanol reducing the SO3 in the combustion effluent to SO2, thereby minimizing the formation of H2 SO4.
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Abstract
The present invention is related to a method for preventing the formation of NH4 HSO4 during the noncatalytic reduction of nitric oxide by ammonia or ammonia precursors in combustion effluents. The present invention is also related to a method for preventing the formation of H2 SO4 in the absence of ammonia or its precursors. The formation of these corrosive substances is extremely detrimental. NH4 HSO4 formation is a limitation upon the usefulness of nitric oxide reduction processes, particularly in boilers, furnaces, and other combustion devices. The formation of H2 SO4 limits effective heat recovery in combustion equipment.
The present invention specifically teaches the use of methanol to reduce SO3 in the effluent stream to SO2. The noncatalytic reduction of SO3 by methanol is selective in that a large fraction of the SO3 is converted to SO2, while on a percentage basis very little oxygen is consumed. In addition, the process of the present invention allows the amount of methanol to be limited such that significant amounts of carbon monoxide are not produced and emitted with the effluent stream. By eliminating SO3, the formation of NH4 HSO4 and H2 SO4 can be blocked.
The present invention teaches contacting the methanol with the combustion effluent at a temperature ranging from approximately 500° C. to about 950° C. in order to assure proper operation of the process. It is also important to limit the reaction time used so that the carbon monoxide produced by the methanol oxidation is not itself oxidized to carbon dioxide.
38 Citations
24 Claims
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1. A process for minimizing the formation of H2 SO4 in a combustion effluent having NO, at least 1 ppm SO3, and water vapor, the process comprising the step of contacting the combustion effluents with methanol, in an amount such that the mole ratio of the methanol to the sum of NO and SO3 is in the range of from about 0.8 to about 2.0, at a temperature in the range from about 500°
- C. to about 950°
C., said methanol reducing the SO3 in the combustion effluent to SO2, thereby minimizing the formation of H2 SO4. - View Dependent Claims (2, 3, 4, 5, 6, 7)
- C. to about 950°
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8. A method of reducing SO3 to SO2 in a stream of combustion effluents, wherein the stream of effluents is at a temperature between approximately 500°
- C. and approximately 950°
C. and wherein the stream of effluents comprises at least 50 ppm SOx, water, and NO, comprising the step of introducing methanol into the stream of effluents such that the ratio of moles of methanol to the sum of the moles of SO3 and NO is in the range of from approximately 0.8 to approximately 2.0. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
- C. and approximately 950°
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17. A method for preventing the formation of H2 SO4 by reducing SO3 to SO2 in a stream of combustion effluents wherein the stream of combustion effluents comprises at least 1 ppm SO3, NO, and water vapor wherein the temperature of the stream of effluents is between approximately 500°
- C. and approximately 950°
C. comprising introducing methanol into the stream of effluents such that the ratio of the moles of methanol to the sum of the moles of SO3 and NO is in the range of approximately 0.8 to approximately 1.5. - View Dependent Claims (18, 19)
- C. and approximately 950°
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20. A process for removing SO3 a precursor of H2 SO4, in a combustion effluent having NO, at least 1 ppm SO3 and water vapor, the process comprising the step of contacting the combustion effluent with methanol in an amount such that the mole ratio of methanol to the sum of NO and SO3 is in the range of from about 0.8 to about 2.0, at a temperature in the range from about 500°
- C. to about 950°
C., said methanol contacting the combustion effluent in order to reduce the SO2 to SO3, thereby minimizing the formation of H2 SO4, the methanol being present in an amount insufficient to increase the amount of CO formed to unacceptable emission levels by the oxidation of methanol. - View Dependent Claims (21, 22, 23, 24)
- C. to about 950°
Specification