Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Reexamination Certificate
1998-02-25
2001-03-13
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
C423S230000, C095S273000, C095S285000
Reexamination Certificate
active
06200543
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to reducing the carbon dioxide (CO
2
) content of an air stream and more particularly, to apparatus and methods for reducing the CO
2
content of an air stream used in the manufacture of hydrated lime.
BACKGROUND OF THE INVENTION
During the manufacture, conveyance, and storage of calcium hydroxide, Ca(OH)
2
, sometimes referred to as hydrated lime, the presence of CO
2
in the air which comes in contact with the hydrated lime can compromise the chemical integrity of the hydrated lime. While hydrated lime has a greater moisture stability than calcium oxide, hydrated lime is perishable unless adequately protected from CO
2
absorption. Hydrated lime has a strong affinity for CO
2
even in dilute concentrations. When hydrated lime absorbs CO
2
from the air, an undesirable reaction known as recarbonation occurs and the Ca(OH)
2
is converted to calcium carbonate, CaCO
3
. It is known that CaCO
3
can deposit as scale on the walls of conduits in pneumatic conveying systems. As these deposits build up, they can sometimes totally occlude the conduit.
Hydrated lime in storage containers can absorb CO
2
from the air in the storage container. Also, as hydrated lime is milled into smaller particles during manufacturing, the hydrated lime becomes more susceptible to CO
2
absorption. This is because as the lime is milled into smaller particles, the surface area per unit volume of lime increases. The increased surface area per unit volume will increase the CO
2
absorption rate of the lime making it susceptible to chemical degradation.
The chemical integrity of hydrated lime can be protected using an inert gas such as nitrogen for blanketing storage containers, milling machines, and conveying systems. However, commercial generators of nitrogen are expensive to install and maintain.
It would be desirable to provide inexpensive, easy to maintain apparatus and methods that provide air with a reduced CO
2
content. The reduced CO
2
content air could then be used in manufacturing, conveying and storing hydrated lime such that the chemical integrity of the hydrated lime is not degraded.
SUMMARY OF THE INVENTION
These and other objects may be attained by apparatus and methods for generating a reduced CO
2
content air stream by injecting hydrated lime into an air stream. The lime reacts with the CO
2
in the air stream to form calcium carbonate, CaCO
3
. As a result of this reaction, the CO
2
content of the air stream is reduced. The reduced CO
2
content air stream can then be used, for example, in a hydrated lime manufacturing process. Particularly, the reduced CO
2
content air may be used to blanket storage containers, milling machines, and conveying systems. The reduced CO
2
content air also may be used in pneumatic conveying systems.
More specifically, a method for reducing CO
2
content of an air stream in accordance with one embodiment of the present invention includes the steps of injecting hydrated lime into an air stream containing CO
2
. The hydrated lime reacts with the CO
2
in the air stream to form CaCO
3
. The air stream is then directed into a lime storage container having a dust collector. As air is drawn through the dust collector, hydrated lime and CaCO
3
are collected on the filter bags. The air drawn through the dust collector has a reduced CO
2
content as compared to the air prior to being injected with hydrated lime. The reduced CO
2
content air stream exhausted from the dust collector can then be directed to the different parts of the hydrated lime manufacturing process.
An apparatus for reducing CO
2
content of an air stream in accordance with one embodiment of the present invention includes a lime storage container, and an air and lime inlet conduit connected to an inlet of the lime storage container. A dust collector is attached to and in flow communication with the storage container, and a dust collector exhaust fan is connected to, and in flow communication with, the dust collector by an exhaust air line.
A rotary airlock valve with a variable speed drive, for dispensing hydrated lime from the storage container, is located at an outlet of the storage container and connected to a hydrated lime feed line. The feed line extends from a blower to the air and lime inlet conduit. The blower supplies air to pneumatically convey hydrated lime through the feed line to the air and lime inlet conduit where the lime is injected into the air stream.
Prior to the operation, the lime storage container is at least partially filled with hydrated lime. In operation, lime from the storage container flows through the rotary airlock valve into the lime feed line. The lime in the lime feed line is pneumatically conveyed, e.g., by air from the blower, to the air and lime inlet conduit and is injected into a CO
2
containing air stream flowing in the inlet conduit. The hydrated lime reacts with CO
2
in the air stream to form CaCO
3
, which reduces the CO
2
content of the air stream as it is directed into the storage container.
Air inside the storage container is drawn into and through the attached dust collector by a dust collector blower. Hydrated lime and CaCO
3
are collected in the dust collector as the reduced CO
2
content air is exhausted from the dust collector. The reduced CO
2
content air exhausted from the dust collector can then be directed to different hydrated lime manufacturing processes, such as the milling process, and may be used in conveying and storing the hydrated lime.
As mentioned above, the reduced CO
2
content air can be utilized to reduce the amount of CaCO
3
formed while processing and storing hydrated lime. As a result, very little scaling of conduits will occur and the chemical integrity of the hydrated lime is maintained.
REFERENCES:
patent: 2332887 (1943-10-01), Biederbeck et al.
patent: 3847837 (1974-11-01), Boryta
patent: 4559211 (1985-12-01), Feldman et al.
patent: 5227144 (1993-07-01), Perez de la Garza
patent: 5678959 (1997-10-01), Griffard et al.
Perry et al. (editors)Chemical Engineers' Handbook, 5th Edition McGraw-Hill Book Co. USA; ISBN 0-07-049478-9, pp. 20-89 to 20-94, 1973.
Lime—Handling, Application and Storage, National Lime Association 1995, No. 213, Chapter 2, pp. 9-26.
Allebach William S.
DeGenova Mark G.
Griffard Randy J.
Lutman Gary F.
Armstrong Teasdale LLP
Griffin Steven P.
Mississippi Lime Company
Vanoy Timothy C.
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