Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Sulfur or sulfur containing component
Reexamination Certificate
2002-01-31
2003-08-12
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Sulfur or sulfur containing component
C423S547000
Reexamination Certificate
active
06605263
ABSTRACT:
BACKGROUND OF INVENTION
a. Field of the Invention
This invention relates to methods and apparatuses for removing SO
2
from a gas stream.
b. Description of the Related Art
Fossil fuels are burned in many industrial processes. Electric power producers, for example, burn large quantities of coal, oil, and natural gas. Sulfur dioxide (“SO
2
”) is one of the unwanted byproducts of burning any type of fossil fuel. It is known to cause acid rain, and to have serious negative health effects on people, animals, and plants. A great deal of research has been done to find a way to economically remove SO
2
from flue gas streams before it enters the atmosphere.
SO
2
is often removed from gas streams (“desulfurization”) by scrubbing the gas with an aqueous ammonium sulfate solution containing ammonia. Examples of this process are disclosed in U.S. Pat. Nos. 4,690,807, 5,362,458, 6,221,325, and 6,277,343, which are not admitted to be prior art by their mention in this Background section. The absorbed sulfur compounds react with ammonia to form ammonium sulfite and ammonium bisulfite, which are then oxidized to form ammonium sulfate and ammonium bisulfate. The ammonium bisulfate is further ammoniated to form ammonium sulfate.
The patents referenced above teach, among other things, that the pH of the ammonium sulfate solution should be kept between about four and six. This range is the result of a compromise between competing factors. On one hand, ammonium sulfate solution is capable of absorbing SO
2
more rapidly when its pH is higher. The ability to absorb SO
2
better implies that the size of the scrubbing tower can be smaller, thus saving capital costs. In addition, the liquid to gas (“L/G”) ratio can be smaller, meaning less liquid will be required and operating costs will be lower.
On the other hand, higher pH levels are also associated with the release of free ammonia from solution, often termed “ammonia slip.” In addition to incurring an economic loss because of lost ammonia, free ammonia in the scrubbed flue gas reacts with uncaptured sulfur dioxide and trioxide to create an ammonium sulfate/bisulfite aerosol that is visible as a blue or white plume in the stack discharge, leading to secondary pollution problems. Controlling the amount of free ammonia in the desulfurization process is in part a function of the ammonia vapor pressure, which results from a combination of pH and levels of unoxidized ammonium sulfite that remain in the absence of sufficient oxygen. Therefore, high pH values and high levels of unoxidized ammonium sulfite promote ammonia slip.
One exception is a method disclosed in U.S. Pat. No. 6,063,352 in which the pH is kept between 4.5 and 7. However, this method avoids the formation of aerosols by maintaining a very high ratio of ammonium sulfite to ammonium sulfate. The ratio is on the order of 15:1 to 3:1. Maintaining this ratio in a scrubber on a commercial scale would be very difficult.
In the past, the solution to the problem of removing SO
2
from a gas stream prior to the present invention has been a compromise between these two competing factors: maintaining the pH of the ammonium sulfate solution to between about four and six. It is recognized that a pH of greater than six is likely to produce ammonia slip. If the aerosols could be removed from the gas stream, the SO
2
removal process could be made much more efficient without the need for compromise. What is needed, therefore, is a process that removes SO
2
from a gas stream that can occur at a pH greater than six, and minimizes ammonia slip.
SUMMARY OF INVENTION
REFERENCES:
patent: 4028071 (1977-06-01), Langlois
patent: 4029482 (1977-06-01), Postma et al.
patent: 4029739 (1977-06-01), Senjo et al.
patent: 4035470 (1977-07-01), Senjo et al.
patent: 4120671 (1978-10-01), Steinmeyer
patent: 4155726 (1979-05-01), Steinmeyer
patent: 4193774 (1980-03-01), Pilat
patent: 4345916 (1982-08-01), Richards et al.
patent: 4435260 (1984-03-01), Koichi et al.
patent: 4650555 (1987-03-01), Rzad et al.
patent: 4690807 (1987-09-01), Saleem
patent: 4726940 (1988-02-01), Kobayashi
patent: 4735927 (1988-04-01), Gerdes et al.
patent: 4735930 (1988-04-01), Gerdes et al.
patent: 4806320 (1989-02-01), Nelson
patent: 4892718 (1990-01-01), Peter et al.
patent: 4971777 (1990-11-01), Firnhaber et al.
patent: 5023063 (1991-06-01), Stiles
patent: 5176888 (1993-01-01), Stiles
patent: 5229091 (1993-07-01), Buchanan et al.
patent: 5308385 (1994-05-01), Winn
patent: 5362458 (1994-11-01), Saleem et al.
patent: 5547648 (1996-08-01), Buchanan et al.
patent: 5624649 (1997-04-01), Gal
patent: 5658547 (1997-08-01), Michalak et al.
patent: 5715764 (1998-02-01), Lyngfelt et al.
patent: 5753012 (1998-05-01), Firnhaber et al.
patent: 5792238 (1998-08-01), Johnson et al.
patent: 5846301 (1998-12-01), Johnson et al.
patent: 5871703 (1999-02-01), Alix et al.
patent: 6063352 (2000-05-01), Risse et al.
patent: 6117403 (2000-09-01), Alix et al.
patent: 6132692 (2000-10-01), Alix et al.
patent: 6159440 (2000-12-01), Schoubye
patent: 6168709 (2001-01-01), Etter
patent: 6183708 (2001-02-01), Hei et al.
patent: 6193934 (2001-02-01), Yang
patent: 6221325 (2001-04-01), Brown et al.
patent: 6277343 (2001-08-01), Gansley et al.
patent: 6277344 (2001-08-01), Hei et al.
patent: 6284022 (2001-09-01), Sachweh et al.
patent: 6302945 (2001-10-01), Altman et al.
patent: 6312505 (2001-11-01), McQuigg et al.
patent: 6531104 (2003-03-01), Borio et al.
patent: 2001/0033817 (2001-10-01), Sander
patent: 2001/0045162 (2001-11-01), McQuigg et al.
patent: 37 33 319 (1989-04-01), None
patent: WO-99/47268 (1999-09-01), None
patent: WO-01/87464 (2001-11-01), None
patent: WO-02/062453 (2002-08-01), None
Lee, etal. “The Effect of In Situ Generated Ammonia—Sulfur Aero sols on the Removal of NOx in a Wet ESP”, Aug. 20, 2001, Mega Symposium, Chicago, IL pp. 1-11.
Alix Francis R.
Duncan Joanna L.
McLarnon Christopher R.
Decker Phillip E.
Powerspan Corp.
Silverman Stanley S.
Vanoy Timothy C.
LandOfFree
Sulfur dioxide removal using ammonia does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sulfur dioxide removal using ammonia, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sulfur dioxide removal using ammonia will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3077238