Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Reexamination Certificate
2001-07-31
2003-08-26
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
C423S244060, C423S393000, C423S395000, C423S400000, C423S522000, C423S544000, C423S548000, C423SDIG005
Reexamination Certificate
active
06610263
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the systems and processes for removal of pollutants, such as oxides of sulfur, oxides of nitrogen, fly ash, mercury compounds, and elemental mercury from gases generated from the burning of fossil fuels and other process gases with electronic control of operational parameters such as, differential pressure across the system, gas temperature, and removal efficiency. The systems and processes of the invention employ oxides of manganese as the primary sorbent to effect removal of pollutants, such as oxides of sulfur and/or oxides of nitrogen, and may further employ other sorbent materials and chemical additives separately and in conjunction with oxides of manganese to effect the removal of other target pollutants, e.g., using alumina to remove mercury.
BACKGROUND OF THE INVENTION
During combustion of fuels that contain sulfur compounds, oxides of sulfur (SO
X
), such as sulfur dioxide (SO
2
), and sulfur trioxide (SO
3
) are produced as a result of oxidation of the sulfur. Some fuels may contain nitrogen compounds that contribute to the formation of oxides of nitrogen (NO
X
), which are primarily formed at high temperatures by the reaction of nitrogen and oxygen from the air used for the reaction with the fuel. These reaction compounds, SO
X
and NO
X
, are reported to form acids that may contribute to “acid rain.” Federal and state regulations dictate the amount of these and other pollutants, which may be emitted. The regulations are becoming more stringent and plant operators are facing greater difficulties in meeting the regulatory requirements. Many technologies have been developed for reduction of SO
X
and NO
X
, but few can remove both types of pollutants simultaneously in a dry process or reliably achieve cost effective levels of reduction.
In the past to meet the regulatory requirements, coal-burning power plants have often employed a scrubbing process, which commonly uses calcium compounds to react with SO
X
to form gypsum. This waste product is normally discarded as a voluminous liquid slurry in an impoundment and ultimately is capped with a clay barrier, which is then covered with topsoil once the slurry is de-watered over time. Alternatively, some power-plant operators have chosen to burn coal that contains much lower amounts of sulfur to reduce the quantities of SO
X
emitted to the atmosphere. In the case of NO
X
, operators often choose to decrease the temperature at which the coal is burned. This in turn decreases the amount of NO
X
produced and therefore emitted; however, low temperature combustion does not utilize the full heating value of the coal, resulting in loss of efficiency.
Turbine plants normally use natural gas, which contains little or no sulfur compounds, to power the turbines, and therefore virtually no SO
X
is emitted. On the other hand at the temperature that the turbines are commonly operated, substantial NO
X
is produced. In addition to Selective Catalytic Reduction (SCR) processes for conversion of NO
X
to nitrogen, water vapor, and oxygen, which can be safely discharged, some operators choose to reduce the temperature at which the turbines are operated and thereby reduce the amount of NO
X
emitted. With lower temperatures the full combustion/heating value of natural gas is not realized, resulting in loss of efficiency. Unfortunately for these operators, newer environmental regulation will require even greater reduction of SO
X
and NO
X
emissions necessitating newer or more effective removal technologies and/or further reductions in efficiency.
Operators of older coal-burning power plants are often running out of space to dispose of solid wastes associated with use of scrubbers that use calcium compounds to form gypsum. Operators of newer plants would choose to eliminate the problem from the outset if the technology were available. Additionally, all power plants, new and old, are faced with upcoming technology requirements of further reducing emissions of NO
X
and will have to address this issue in the near future. Thus, plants that currently meet the requirements for SO
X
emissions are facing stricter requirements for reduction of NO
X
for which there has been little or no economically feasible technology available.
The nitrogen oxides, which are pollutants, are nitric oxide (NO) and nitrogen dioxide (NO
2
) or its dimer (N
2
O
4
). The relatively inert nitric oxide is often only removed with great difficulty relative to NO
2
. The lower oxide of nitrogen, nitrous oxide (N
2
O), is not considered a pollutant at the levels usually found in ambient air, or as usually discharged from air emission sources. Nitric oxide (NO) does however; oxidize in the atmosphere to produce nitrogen dioxide (NO
2
). The sulfur oxides considered being pollutants are sulfur dioxide (SO
2
) and sulfur trioxide (SO
3
).
Typical sources of nitrogen and sulfur oxide pollutants are power plant stack gases, automobile exhaust gases, heating-plant stack gases, and emissions from various industrial process, such as smelting operations and nitric and sulfuric acid plants. Power plant emissions represent an especially formidable source of nitrogen oxides and sulfur oxides, by virtue of the very large tonnage of these pollutants and such emissions discharged into the atmosphere annually. Moreover, because of the low concentration of the pollutants in such emissions, typically 500 ppm or less for nitrogen oxides and 3,000 ppm or less for sulfur dioxide, their removal is difficult because very large volumes of gas must be treated.
Of the few practical systems, which have hitherto been proposed for the removal of nitrogen oxides from power plant flue gases, all have certain disadvantages. Various methods have been proposed for the removal of sulfur dioxide from power plant flue gases, but they too have disadvantages. For example, wet scrubbing systems based on aqueous alkaline materials, such as solutions of sodium carbonate or sodium sulfite, or slurries of magnesia, lime or limestone, usually necessitate cooling the flue gas to about 55° C. in order to establish a water phase. At these temperatures, the treated gas requires reheating in order to develop enough buoyancy to obtain an adequate plume rise from the stack. U.S. Pat. No. 4,369,167 teaches removing pollutant gases and trace metals with a lime slurry. A wet scrubbing method using a limestone solution is described in U.S. Pat. No. 5,199,263.
Considerable work has also been done in an attempt to reduce NO
X
pollutants by the addition of combustion catalysts, usually organo-metallic compounds, to the fuel during combustion. However, the results of such attempts have been less successful than staged combustion. NO
X
oxidation to N
2
is facilitated by ammonia, methane, et al. which is not effected by SO
X
is described in U.S. Pat. No. 4,112,053. U.S. Pat. No. 4,500,281 teaches the limitations of organo-metallic catalysts for NO
X
removal versus staged combustion. Heavy metal sulfide with ammonia is described for reducing NO
X
in stack gases in U.S. Pat. No. 3,981,971.
Many fuels, and particularly those normally solid fuels such as coal, lignite, etc., also contain substantial amounts of bound or fuel sulfur with the result that conventional combustion produces substantial amounts of SO
X
pollutants which are also subject to pollution control. It has generally been the opinion of workers in the art that those conditions employed in staged combustion, particularly two-stage rich-lean combustion for NO
X
reduction, will likewise lower the level of SO
X
emissions. However, it has been found that little or no reduction in SO
X
emissions can be obtained in a two-stage, rich-lean combustion process. Indeed, it has been found that the presence of substantial amounts of sulfur in a fuel also has a detrimental effect on NO
X
reduction in a two-stage, rich-lean process.
Considerable effort has been expended to remove sulfur from normally solid fuels, such as coal, lignite, etc. Such processes include wet scrubbing of stack gases from coal-fired burners. However, su
Axen Steve G.
Boren Richard M.
Carlton Steve C.
Hammel Charles F.
Huff Ray V.
EnviroScrub Technologies Corporation
Fredrikson & Byron , P.A.
Silverman Stanley S.
Vanoy Timothy C.
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