JPS6019019A - Dry purifying method of waste gas - Google Patents

Abstract

PURPOSE:To allow an absorbent to absorb an acidic noxious substance contained in waste gas within a short treating time, by a method wherein the absorbent comprising fine particulate quick lime or slaked lime with a particle size of 10mum or less is dispersed in the waste gas containing the acidic substance and the treated gas is subsequently subjected to dust collecting treatment. CONSTITUTION:Powdery quick lime or slaked lime is mutually impinged in a grinder 1 by a jet stream of high pressure air or overheated steam to be finely pulverized. The obtained fine particulate absorbent is introduced into waste gas along with high pressure air or overheated steam in a dispersing machine 2 to be uniformly dispersed throughout the waste gas. The dispersed fine particulate absorbent absorbs the acidic noxious substance in the exhaust gas. As a dust collecting apparatus 3, a bag filter is pref. used. The particle size of the absorbent is pref as small as possible but, with due regard to the operation cost of a jet mill, the absorbent having a particle size of 5mum or less and sharp particle size distribution curve is especially pref.

Description

[Detailed description of the invention] This invention relates to a dry purification method for II gas.

Sulfur oxidation f is present in boiler exhaust gas and waste incinerator exhaust gas.
It contains a large amount of acidic and harmful substances such as 4f/J (SOx), HCJ, and HF, and it is mandatory to remove these substances as a pollution control measure. Conventionally, as a method for removing the above-mentioned acidic harmful substances, a wet method has been generally used in which an absorbing liquid or slurry containing an alkaline absorbent is brought into contact with exhaust gas to clean the exhaust gas. However, in this method, the removal rate was high, but on the other hand, it was difficult to treat the waste water, it was necessary to heat the exhaust gas, and the equipment and operating costs were high.

From this point of view, various methods have been used in place of the wet method, such as activated carbon to eliminate harmful substances. Proposed methods include an activated carbon adsorption method that deposits and then desorbs harmful substances, a semi-dry method that sprays slaked lime slurry into the exhaust gas, and a method that sprays lime powder into the exhaust gas or uses a moving bed of lime to absorb harmful substances. ing. However, none of these methods has achieved sufficient results. Among the above-mentioned 1ilff methods, the lime powder spraying method is considered promising because it uses inexpensive equipment and can be easily performed, but in this case as well, the utilization rate of powdered lime as an absorbent is low. The removal rate was low, and therefore this method was not put to practical use except in special cases where trench regulations were extremely lax.

The reason why the utilization rate of the powdered lime is low is as follows. That is, the acidic harmful components in the dry gas react with an absorbent consisting of quicklime and slaked lime according to the following reaction formula, and 1 is absorbed by the absorbent.

Ca O(-S O2-+ Ca S 03Ca (O
H) 2 +S O2→Ca S 03 +H20C+
+, O-1-2HCl -Ca Cj' 2 +H2
0Ca (OH) 2 +2 H(J'-+Ca C1
2+2 H20SO3 and HF are also absorbed by the polymer absorbent according to the above reaction formula. Conventional absorbents have a particle size of 10
Therefore, according to the kinetic study of the above reaction, the reaction rate between the acidic component and the absorbent is extremely fast, or the acidic component is diffused inside the particles of the absorbent. If the rate of reaction is Z<, the reaction occurs only at the surface of the particle or within 3 to 4 microns from the surface, and most of the interior of the particle does not participate in the reaction.

Therefore, the utilization rate of the absorbent could not be lower than 40%. In this case, in order to obtain a removal rate comparable to that of the wet method, it is necessary to keep the contact time between the absorbent and the exhaust gas extremely long, but such treatment is completely impractical.

In view of the above-mentioned circumstances, the present inventor has conducted extensive research with the aim of developing a dry purification method for IJ gas that can obtain a removal rate as high as that of the 111) method (at least 90%). As a result, they obtained the knowledge that the size of lime particles greatly affects the removal rate, and completed this invention.

The purification method according to the present invention involves dispersing an adsorbent made of fine particulate quicklime or slaked lime with a particle size of 10 microns or less in exhaust gas containing acidic substances, and then collecting dust from the exhaust gas to form an adsorbent that has adsorbed acidic substances. It is characterized by removing.

Boiler gas and waste incineration exhaust gas are usually 100 to 400
℃ or higher than JJ+gas temperature, the carbon dioxide in the antagonist gas converts into an absorbent or CaCO3, and its utilization rate decreases. Therefore, in order not to reduce the utilization rate of the absorbent, it is necessary to
The range of 0°C is preferably 17″0 and this type of #l’ j
fs contains acidic harmful substances such as SOx, J (Cj2. HF, etc.).

In order to treat such harmful gases, an adsorbent made of particulate quicklime or slaked lime with a particle size of 10 microns or less, preferably 6 microns or less is used. In addition, 1) As the first agent in the form of granulated particles, it is preferable that the first agent draws a sharp particle size distribution curve, i. The smaller the particle size of the adsorbent, the better; however, taking into consideration the operating cost of a jet mill, an adsorbent with a sharp particle size distribution curve of 5 microns or less is particularly preferred. Adsorbents containing coarse particles are not preferred. For example, in the case of an adsorbent containing 10 weight percent of particles with a particle size of 40 microns, the adsorption efficiency is approximately 7.
%descend.

The flow of the purification method according to the present invention is shown in FIG. In the figure, the crusher (1) is preferably a jet mill, but is not limited thereto. In a jet mill, quicklime or slaked lime powder is atomized by colliding with each other by a jet of high-pressure air or superheated steam. The particulate absorbent is introduced into the U[gas] together with high-pressure air or superheated steam in the disperser (2), and is uniformly dispersed in the υl·gas.

The particulate absorbent dispersed in 6 follows the reaction formula described above.
#l Harmful substances are absorbed by the acid in the gas.

Although a bag filter is preferable as the dust collector (3), an electric dust collector or the like may of course be used instead. A mixture of particulate absorbent that has absorbed acidic substances and soot is removed from the exhaust gas by a bag filter. In this case, the contact time between the 1" gas and the absorbent inside the bag filter increases and is maintained for a long time, further promoting the absorption of acidic substances.

Next, the structure of the apparatus used in the horn 1 gas purification method of the present invention will be explained.

In Figure 2, an air supply pipe (13) with an air compressor (11j and an air tank (12)) is arranged in a jet mill (14) with a quicklime supply port (14, a). ) has a single sheet machine (16
A bag filter (17) is installed (J) on the downstream side of the bag filter (17).
An absorbent supply pipe (J8) is arranged in the disperser (16). Variance i (1(i+ to bag filter (I7)
The distance is set to ensure sufficient contact between the gas and the absorbent. Then, in the jet mill (14), the granular quicklime supplied from the quicklime supply port (14-a, ) is made to collide with each other using the air flow energy of compressed air to become fine particles.

It consists of a fixed vane (20) and an absorbent discharge valve 1 provided at the downstream end of the core body (19) so as to open in the downstream direction. Then, the plurality of fixed blades (20) are each cut long), twisted in the horizontal direction, and injected I]51! l is the absorbent supply pipe (
18) or connected. The exhaust gas increases the flow velocity while passing through the internal passage tube of the disperser (16), which is narrowed by the core body (19), and is rotated by the fixed vane (19).
l) Circulation is performed. Further, fine particulate absorbent is discharged from the absorbent discharge 1 base. As a result, the particulate absorbent is uniformly dispersed in the first gas by the high-speed swirling flow of the first gas. The dispersed absorbent beam adsorbs acidic substances in contact with the gas, is collected together with soot and dust by the bag filter (17), and is removed via the low-Q intertary valve.

Example First, an experimental apparatus consisting of the flow shown in FIG. 5 was constructed.

In the figure, a zilter was used as the crusher f211, and an electric heater was used as the heating device (27). In addition, the flow rate regulator (2G) measures SO2 and rice, and the analyzer (29) measures SO2, HCj', and CO.
2 O 6 and H 2 O, and the humidity control device (28)
Then, the temperature of the circulating exhaust gas was adjusted.

The quicklime used in the experiment was Ca095%, (: a C03
3.5% and other 1.5%, slaked lime contains Ca
It consisted of 296% (OH), 33% CaCO, and 1% other.

In the experimental apparatus with the above configuration, a simulated U[gas containing SO2, HC4CO2, and H20 was circulated in the direction of the arrow at a flow rate of 2000 NyytI/H, and quicklime or slaked lime was atomized with compressed air in a jet mill. , dispersed in the circulating phase gas in a disperser (22). After the W setting conditions became stable, operating data under various conditions was collected and summarized in Table 7 below.

Furthermore, the relationship between particle size and removal rate is shown in FIG. Note that the particle size of the absorbent in the same table means that 95% or more of fine particles having the indicated particle size are contained.

The stoichiometric ratio of the absorbent is (CaO in the supplied absorbent)
or %/l/number of Ca(OH)2)/(reacted SO
It represents the number of moles of reacted HCl (XI/2).

As is clear from the above table and Figure 6, when the particle size is 10 microns or more, the removal rate of acidic components is low, or the particle size is 1.
The removal rate and absorbent utilization rate (that is, the reciprocal of the absorbent stoichiometric ratio) reached 90% or more when the particle size was 0 microns, especially when the particle size was 6 microns or less. Furthermore, when the temperature of the exhaust gas exceeded 200°C, a decrease in the utilization rate of the absorbent was observed due to the formation of CaCO3.

Comparative Example In the experimental apparatus used in the example, an absorbent made of commercially available slaked lime having the particle size distribution shown in Table 2 below was used instead of the fine particulate absorbent, and H2O11 was used at a temperature of 245°C.
, 3%, HCj'1228p 11 nl was dispersed in a simulated exhaust gas to remove H(4). At an equivalent ratio of absorbent/HCl of 1.02, the removal rate of HCp was 52.2. Table 2 Particle size distribution of slaked lime in % As is clear from the results, even if 43% of particles with a particle size of 10 microns or more were contained, the removal rate was significantly reduced.

As described above, in the dry purification method according to the present invention, an absorbent made of fine particulate quicklime or slaked lime with a particle size of 10 microns or less is used. The acidic substances can be absorbed into the absorbent in a short treatment time of a few minutes, and therefore the acidic substances can be removed with a high removal rate.

[Brief explanation of drawings]

Figure 1 is a flow diagram of the υ gas purification method, Figure 2 is a schematic diagram of the exhaust gas purification device, Figure 3 is a partially cutaway side view of the dispersion machine,
Figure 4 is a cross-sectional view along Jv-IV Mj in Figure 3;
FIG. 5 is a flow diagram of the experimental apparatus, and FIG. 6 is a graph showing the relationship between particle size and removal rate. that's all

Claims (1)

[Claims] An adsorbent made of fine particulate quicklime or slaked lime with a particle size of 10 microns or less is dispersed in exhaust gas containing acidic substances,
This is a dry purification method for exhaust gas, which is characterized by collecting the residual gas and removing the adsorbent that has adsorbed acidic substances.