JPS58124523A - Removal of carbon dioxide by packed solid calcium hydroxide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a method for removing carbon dioxide from a gas stream. The invention is particularly applicable to the fixation of radiocarbon present in industrial waste gas streams. For example, waste gas from nuclear power plants and similar facilities. However, the invention is not limited to such applications, but has application to the general removal of carbon dioxide from gas streams.

BACKGROUND OF THE INVENTION Known methods for removing carbon dioxide from gases include the following steps: (a) contacting the gas with a slurry of slaked lime; (b) an elevated temperature, typically between 550C and 450C.
and (c) contacting the solid barium hydroxide with the gas at the ambient temperature.

The reaction products of these methods, calcium carbonate or barium carbonate, are very stable and suitable for long-term storage. This provides a very attractive chemical form for the fixation and disposal of radioactive carbon isotopes. However, all three methods have drawbacks.

The slaked lime slurry method is contaminated with liquid effluent; the solid calcium hydroxide method requires operation at high temperatures; and the barium hydroxide hydrate method requires that barium hydroxide is toxic and expensive. It has a serious drawback. The inventors tested Okiya's calcium hydroxide method at ambient temperature (20Cγ250C) and found that the Oa of c a (OH)2
I finally found out that the conversion to O05 was about 3%, so
I knew that I would not be satisfied at all.

However, the inventors determined the humidity of the gas by measuring the layer temperature.
It has been discovered, quite by chance, that the solid calcium hydroxide process is very effective even at ambient temperatures when the relative humidity is raised to values of about 80% or higher. relative humidity is 80%
Even below, 0 of Oa (OH) 2 is higher than expected.
There is an uptake of carbon dioxide with conversion to aOOs, but this conversion only becomes economically useful when the relative humidity reaches about 80%. In fact, the relative humidity is between 80% and 100
% range, a rapid increase in conversion proceeds. However, if the water content exceeds the upper limit of this range, Ca(OH)
usage will decrease.

Furthermore, subsequent research revealed that the layer temperature may be as high as about 10 tZ' if the moisture content of the gas is increased appropriately. In this case, the relative humidity at layer temperature is approximately 90% to 100% for effective conversion or utilization of calcium hydroxide.
Should be between %. On the other hand, in the case of a higher layer temperature,
The relative humidity of the gas may be quite low, and if the layer temperature is
If it is C, it may be about 40%. Although the water content of the gas may be lowered at higher bed temperatures to provide effective calcium hydroxide conversion, at bed temperatures above about Effective utilization of the calcium hydroxide layer, which is operated at low temperatures, would be sacrificed.

To fully realize the benefits of the present invention, the layers should be 10C to S.
It should be operated in a temperature range of aC, preferably in a temperature range of 200-30C, whereby the moisture content of the shigas should be adjusted. David W.
.

Ho1laday) and Gary El Bag (Gary
U.S. Patent No. 4,162,29B by L. Haag)
No. 1, No. 1, No. 1, No. 1, No. 1, No. 1, 2003, 2003, discloses a method for removing carbon dioxide from industrial waste gases using a particle layer of a single permanent barium hydroxide at relative humidity of the gas in the range of 10% to 100%. However, no attempt has been made to apply this method to solid calcium hydroxide systems, which are believed to be unsuitable.

Furthermore, according to Holladay and Bagg's report presented at the 16th DIO/Nuclear Air Cleaning Conference in Sun Diego, California, October 19-24, 1980, research subsequently If the relative humidity of
) It was shown that even barium hydroxide systems are almost impractical because the Ba (OH) 2 particles collapse, resulting in a large pressure loss in the packed bed. The inventors have shown that calcium hydroxide systems do not have these drawbacks and are very effective even at very high relative humidity, where barium hydroxide is almost unusable.

SUMMARY OF THE INVENTION According to the present invention, the packed bed of calcium hydroxide is 10C to 5C.
Passing the gas stream through a packed bed of calcium hydroxide maintained at a temperature range of 0 C and such that the moisture content of the gas is maintained at a value in the range of 40% to 100% relative humidity at one layer temperature. A method for removing carbon dioxide from a gas stream is provided. To be commercially useful, the conversion of calcium hydroxide can be calculated using the following formula: at least o, i s (i.e., 15
%).

Here, R: gas flow rate, C: concentration of carbon dioxide upstream of the layer, T: time required for the downstream concentration of carbon dioxide to reach 5% of the upstream concentration, W: weight of calcium hydroxide in the layer. are shown respectively.

The numbers 22.4 and 74 are the molar volume of carbon dioxide and the molecular weight of calcium hydroxide, respectively.

The calcium hydroxide should be in a form that allows substantial gas flow of gas without excessive pressure loss, and thus
Such calcium hydroxide is preferably made by hydrating CaO, then drying and grinding to the required particle size of 0.25 m - 3 m.

In order to improve the gas flow, it is advantageous to arrange a number of packed beds in the form of relatively flat and regularly spaced layers of ground calcium hydroxide in succession with respect to the gas flow. turned out to be good.

In the experimental pilot plant, 20 to 50,000μ of carbon dioxide was added to the gas 11! The containing gas stream was treated in a carbon dioxide removal system. The gas flow is at its ambient temperature of 8
It was humidified to a relative humidity higher than 0% and passed through a stationary bed filled with solid calcium hydroxide. The results of chemical analysis of the absorption layer are shown in Table 1. However, it has been found that composition is not critical.

ca(oH)2870-900 0a0 24-55 0a 005 57 86H2o
In-is tests were also conducted at different layer temperatures and with varying moisture content of the humidifying gas. The conditions and results of the test are shown in Table 3.

The results of these tests show that carbon dioxide is removed from the gas stream at its ambient temperature, in fact in the temperature range 10C to 50C, and that if the gas is first conditioned to high humidity, the Oa
It shows that the conversion of (OH)2 to Ca(305) is highly accomplished.

the gas flow can exist at a temperature substantially higher than ambient temperature;
It should then be understood that the relative humidity at that elevated temperature is substantially less than 80%. Importantly, the moisture content of the gas must be adjusted to 40% and 10% at the bed temperature before passing through the bed.
It should correspond to a relative humidity of between 0% and the conversion of calcium hydroxide should be adjusted according to the layer temperature to be at least 15%.

For industrial waste gas disposal terminals, it is generally necessary to humidify the gas stream to raise its moisture content to the required value before passing it through the bed, as described above. However, if the initial humidity of the gas is higher than the required value, it is generally necessary to adjust the humidity by removing moisture, for example in the case of revbreathers.

DESCRIPTION OF EMBODIMENTS One embodiment of the invention is outlined in the accompanying figures. This is a system that removes radioactive carbon dioxide from waste gas generated at nuclear power plants.

In this figure, nuclear power generation is indicated by the number 10, and the waste gas is led by pipe 11 to a humidifier 12. Humidifiers are gas-water contact devices, atomizers or steam generators that increase the water content of the gas. The humidified gas is led from the humidifier 12 via line 13 to an absorption layer system 14 where it passes through successive layers of calcium hydroxide and, after removing carbon dioxide, is discharged via line 15. The layer temperature is preferably kept between about 2501 or 20C and 50G, and the moisture content of the gas humidified in this device should correspond to a relative humidity between 80% and 100%d at that temperature. No.

The device 14 in this embodiment consists of a vertical column 16 in which a number of packed beds 17 of calcium hydroxide are arranged;
The gas flows through each of them. Each layer 17
is in the form of a relatively flat layer and is spaced apart from the other layers to allow gas mixing and redistribution.

Effects of the Invention By humidifying the gas stream to raise the water content to the required value before passing it through the calcium hydroxide layer, carbon dioxide by the calcium hydroxide layer can be reduced at a low temperature convenient for handling. This is because it has been possible to increase carbon absorption efficiency to an extent that cannot be imagined from previous examples.

[Brief explanation of the drawing]

The figure shows a system for removing radioactive carbon dioxide from waste gas generated in a nuclear power plant. The main parts in the diagram are as follows. Nuclear power generation－－－－－１－＝－－－－－－－－－－－－
-------i. Humidifier------------------
−−−−=−−−−−−−−−−−−12 Piping・−−−
−−−−=−−−−−−−−−−−−−−−−−−−−
−−−−−−−−−−, 13 absorption layer system −−=−−==
−=−−−−−14 Piping・−−1−−−−−−−−−−
−−−−−−−−−−−−−・−−−−−−−−−−−
−15 columns, −−−−−−−=−−−−−−−−−
−−−−−−−−−−−−−−−−−16 layers−−−−−−
−−−−−−−−−−−−−−−−−−−−−1−−−
−−−−−−−−−−−−−17 Continued from page 1 Priority claim 04/23/1982■Canada (CA)
■401539 ■Applicant Roger William Grasse 2290 Wyandotte Drive, Oakville, Ontario, Canada

Claims (1)

Claims: 1. Removal of carbon dioxide from a gas stream by passing the gas stream through a packed bed of calcium hydroxide. In the method, the bed is maintained at a temperature in the range of 10C-50C, the moisture content of the gas is adjusted to a value corresponding to a relative humidity in the range of 40% to 100% under the bed temperature, and the final concentration of calcium hydroxide is A method of controlling the conversion rate to a value not smaller than 0.15 using the formula defined below. 22.4 74 In the formula, R = Gas velocity C: Concentration of carbon dioxide upstream of the layer T: Time required for the downstream concentration of carbon dioxide to reach 5% of the upstream concentration, W: Weight of calcium hydroxide in the layer, shows. 2. The method according to claim 1, wherein the layer temperature is maintained in the range 20C-[0C, and the moisture content of the gas stream corresponds to a relative humidity in the range of 80% to 100% at the layer temperature. . 3. There is an initial moisture content of the gas stream corresponding to a relative humidity of greater than 100% at the bed temperature, and the control comprises dehumidifying the gas before passing through the bed. Or the method of Fang 2. 4. The initial water content of the gas stream is lower than the minimum value of the relative humidity at the bed temperature, and the control comprises dehumidifying the gas before passing through the bed. Or the method of Fang 2. 5. A process for removing carbon dioxide from industrial waste gas by flowing a gas stream through a packed bed of calcium hydroxide maintained at a temperature in the range 10C to 50C, in the range 40% to 100% at bed temperature. A method for removing carbon dioxide comprising a step of humidification to increase the water content of the gas stream to a value corresponding to a relative humidity of , and such that the final conversion of calcium hydroxide is not less than the formula defined below. 22.4 74 Formula: Gas flow rate, C: Concentration of carbon dioxide upstream of the layer, T: Time required for the downstream concentration of carbon dioxide to reach 5% of the upstream concentration, W: Water in the layer Represents the weight of calcium oxide. 6. The layer is kept at a temperature in the range of 20C to 30C and the moisture content of the gas stream corresponds to a relative humidity in the range of 80% to 100% under the layer temperature. Method. 7. Hydrate 0aO, dry the obtained hydroxide, and (OH
) 2, the gas stream is brought into contact with water to increase the moisture content to a value corresponding to a relative humidity in the range 80% to 100% at bed temperature;
A method for removing and fixing carbon dioxide from a gas stream containing carbon dioxide with radioactive carbon as a component, comprising passing the humidified gas stream through a gas filter and converting calcium hydroxide to calcium carbonate. 8. The method according to claim 7, wherein the layer temperature is in the range of 20C to 30C. 9. A gas filter is formed of a column containing a number of relatively flat, regularly spaced layers of ground solid calcium hydroxide, the column defining a flow path for the gas, the layers being 8. The method of claim 7, wherein the layers are arranged in series with respect to the flow path of the gas, and the spaces between the layers are modified so that the gas flow is redistributed between the stages of the filter. 10. The method according to claim 9, wherein the temperature of the layer is 2DC-300.