Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Sulfur or sulfur containing component
Reexamination Certificate
1999-11-19
2001-07-03
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Sulfur or sulfur containing component
C423S243090, C423S555000
Reexamination Certificate
active
06254843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to methods of reclaiming large amounts of calcium sulfite, as is produced by lime-based flue gas desulfurization (FGD) systems. More particularly, this invention is directed to a process and equipment capable of being retrofitted to an existing FGD facility at minimal cost and with minimal interruption of the existing scrubbing operation, and which efficiently converts the stock of calcium sulfite produced by the FGD facility to calcium sulfate.
2. Description of the Prior Art
A significant number of facilities exist that produce and/or store large amounts of calcium sulfite. Primary examples are lime-based flue gas desulfurization (FGD) systems that remove substances such as acidic constituents and particulate matter from combustion or flue gases produced by utility and industrial plants. Limebased flue gas desulfurization processes have typically involved the use of limestone (calcium carbonate; CaCO
3
) slurries or hydrated lime (calcium hydroxide; Ca(OH)
2
) slurries formed by action of water on lime (calcium oxide; CaO). Intimate contact between these calcium-based slurries and acidic gases that are present in flue gases, such as sulfur dioxide, hydrogen chloride (HCl) and hydrogen fluoride (HF), result in the absorption of the gases by the slurry and the formation of salts, such as calcium sulfite (CaSO
3
.½HOH), calcium sulfate (CaSO
4
.2HOH), calcium chloride (CaCl
2
) and calcium fluoride (CaF
2
) precipitates, which must be collected for disposal, recycling or sale.
Calcium sulfite is the primary byproduct of lime-based FGD operations, but has no commercial value and is difficult to dispose of. In contrast, calcium sulfate (gypsum) is a saleable byproduct, is significantly easier to handle, and can be more readily stored long-term. In more modem FGD facilities, scrubber units are adapted for in situ forced oxidation of the slurry (typically within the gas-liquid contactor) to ensure that all of the sulfites are reacted to form sulfates, thereby maximizing the production of gypsum. However, many existing facilities are not equipped for in situ forced oxidation, and as a result accumulate large amounts of calcium sulfite slurry that is typically stored for long periods in holding ponds prior to disposal. During storage, calcium sulfite can leach into the surrounding soil, posing a hazard to plant life and ground water. As a result, processes have been proposed for reclaiming and converting calcium sulfite in holding ponds. One such method utilizes a liquid source of acid that is introduced into a storage tank into which the slurry is pumped. An amount of acid is added to sufficiently lower the pH of the mixture to enable the sulfite precipitate to become dissolved in the mixture, which is then aerated with compressed air to oxidize the calcium sulfite and produce calcium sulfate. This type of system is expensive to operate, primarily due to the cost of the acid when compared to the value of the final sulfate product.
In view of the above, it would be desirable if a method were available that was practical for reclaiming and converting calcium sulfite slurry accumulated from lime-based flue gas scrubbing operations that do not have the capability for in situ oxidation. To be practical, such a method must be capable of being adapted for use with existing FGD facilities without requiring major renovations to the existing FGD scrubber units, capable of being installed and commenced with minimal interruption of the scrubbing process, and operate without the necessity for adding an additional acidification agent.
SUMMARY OF THE INVENTION
The present invention provides a process and appropriate equipment that can be added to an existing flue gas scrubbing facility to reclaim accumulated calcium sulfite slurry and produce calcium sulfate. The invention is particularly suitable for retrofitting an existing facility that scrubs sulfur dioxide-containing flue gases, as is typical with plants that burn fossil fuels. Such facilities typically employ a gas-liquid contactor to absorb sulfur dioxide from the flue gases, producing a calcium sulfite-containing slurry that is accumulated or otherwise held in a reservoir apart from the gas-liquid contactor. The calcium sulfite within the slurry is in precipitate form, has essentially no commercial value, and is difficult to store and dispose of.
A flue gas scrubbing facility modified in accordance with this invention generally includes a vessel through which acidic gases flow, and to which the calcium sulfite-containing slurry is delivered from the reservoir so that an amount of the acidic gases is absorbed by the slurry to lower the pH of the slurry to a level sufficient to enable the sulfite to dissolve. The acidic gases required to acidify the calcium sulfite-containing slurry are preferably drawn from the combustion source of the flue gases intended for treatment by the existing facility, which are then delivered to the gas-liquid contactor of the same facility for scrubbing, such that the overall acid emission level from the combustion source is reduced. After contacting and absorbing the acidic gases, the slurry is accumulated in a receptacle where the calcium sulfite dissolved in the slurry is oxidized and converted to calcium sulfate. The calcium sulfate precipitates can then be removed from the receptacle for sale or storage.
Based on the above, the present invention provides a method by which a large amount of accumulated calcium sulfite can be safely and efficiently reclaimed from a lime-based flue gas scrubbing operation that does not have the capability for in situ oxidation. Furthermore, the method and its associated equipment are readily capable of being adapted for use with an existing FGD facility without requiring major renovations to the FGD scrubber unit, and can be installed and commence operation with minimal interruption of the scrubbing process.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
REFERENCES:
patent: 5266287 (1993-11-01), Johnson
patent: 5695727 (1997-12-01), College et al.
patent: 6090357 (2000-07-01), Hammer et al.
patent: 288 100 A5 (1991-03-01), None
patent: 62-225226A (1987-10-01), None
patent: WO 89/07576 (1989-08-01), None
U.S. Application No. 08/335,589, Laslo.
Brown Gregory N.
Mengel Michael L.
Griffin Steven P.
Hartman Domenica N. S.
Hartman Gary M.
Marsulex Environmental Technologies, LLC
Vanoy Timothy C
LandOfFree
Process for the reclamation of calcium sulfite produced by a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the reclamation of calcium sulfite produced by a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the reclamation of calcium sulfite produced by a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2485665