JPS62258727A - Method for desulfurization and dust removal from waste gas - Google Patents

Abstract

PURPOSE:To prevent the lowering in desulfurization efficiency, by a method wherein O2-containing gas is introduced into the Ca-containing absorbing liquid of the zone contacting with waste gas containing SO2, HF, HCl and soot to hold the concn. of sulfite in the absorbing liquid to 5mmol/l or less. CONSTITUTION:The waste gas 1 containing SO2, HF, HCl and soot from a boiler is supplied to an absorbing part 6 and contacted with an absorbing liquid 8 containing a Ca-compound to be subjected to desulfurization and dust removal treatment while the waste gas 2 after treatment is exhausted. Air 3 is introduced into the absorbing liquid 8 and SO2 in the waste gas 1 is absorbed by the absorbing liquid to be immediately oxidized and a sulfate ion is formed to hold the concn. of sulfite to 5mmol/l or less. The absorbing liquid 8 is supplied to a solid-liquid separator 7 to separate gypsum 5 and CaCO3 4 being an absorbent is charged in the filtrate while the regenerated absorbing liquid is recirculated to the absorbing part 6. NaOH is supplied from a line 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a wet flue gas desulfurization and dust removal method, and more specifically to a method for reducing desulfurization performance due to soot, HF, and IIcI contained in flue gas, and , relates to a flue gas desulfurization and dust removal method that prevents a decrease in the reaction rate of limestone, reduces the COO value and nitrogen in the absorption liquid, reduces wastewater treatment, and further simplifies the equipment.

[Prior art]

In the wet flue gas desulfurization and dust removal method, dust removal is performed by gas-liquid contact, and the desulfurization is summarized by the reaction formula below.

S 02 + Ca CO3+ 1/2H20→Ca
S 03 ・1/2 H20+C02SO□+CaCo
, +1/202+2H20→Ca5o4-2H20+C
O2By the way, in addition to SO2 and soot, exhaust smoke from boilers that burn fossil fuels also contains N01IIF, llCl, and N01IIF.
Gases such as 113 are also included, and there are also impurities in the absorbent 1, so the reaction with the absorbent is extremely complicated.

Therefore, the effects on desulfurization performance are also diverse.

In the conventional desulfurization method using spray towers, packed towers, and grid towers, IIP present in flue gas,
HCI and soot caused drawbacks such as a decrease in the reactivity of absorbents such as lime and limestone, a decrease in desulfurization performance, a decrease in the quality of the obtained gypsum, and an increase in wastewater COD and nitrogen.

On the other hand, pollution control devices are always desired to be made simpler due to their purpose.

However, for exhaust gas containing IIF, llCl, and soot, a two-step method has been used in which the liver, llCl, and soot are removed, and then desulfurization is performed. A method of batch processing liver and HCI has been proposed, but the above-mentioned drawbacks tend to increase, and it has been considered difficult to simplify the apparatus by batch processing with the conventional method.

[Purpose of the invention]

The present invention solves the above-mentioned conventional drawbacks and reduces the amount of H contained in flue gas.
F, HCI, improves gypsum quality by preventing a decrease in desulfurization rate due to soot and dust and a decrease in reactivity of lime and limestone, improves desulfurization rate, further reduces COD and nitrogen in wastewater, and improves desulfurization and dust removal. The purpose is to process them all at once.

[Structure of the invention]

The flue gas desulfurization and dust removal method of the present invention, which achieves the above object,
In a flue gas desulfurization/dedusting method in which flue gas containing at least HF, HCI, and soot is brought into contact with an absorption liquid containing a calcium compound, an oxygen-containing gas is introduced into the absorption liquid in a zone in contact with the flue gas. The sulfite concentration in the absorption liquid was set to 511.
It is characterized by being kept at 1 mol/l or less.

Furthermore, in the present invention, at least one compound selected from the group consisting of caustic soda, soda carbonate and sodium sulfate can be added to the absorbent liquid in the zone in contact with the flue gas.

In the present invention, exhaust gas containing at least SO, HF, 11Cl, and soot is to be treated.

Here, the SO□ concentration in the flue gas to be treated may be within any range, and the contents of IIF, IIcI, and soot dust are not particularly limited, and vary depending on the type of coal; 200ppm, 5-20 of 11C1
0ppm, 20mg/Nm ~30g as soot and dust
/Nn? The content of each can be mentioned.

Further, in the present invention, an oxygen-containing gas is introduced into the absorption liquid containing the calcium compound in the zone that comes into contact with the flue gas.

Therefore, SO, in the highly active liquid that has just been absorbed, can quickly react with oxygen before reacting with limestone, etc., and therefore quickly generates highly acidic sulfate ions, causing the formation of limestone, etc. Melting can proceed smoothly.

In addition, unlike in conventional spray towers where oxidation is mainly carried out by oxygen in flue gas, the oxygen in oxygen-containing gas has a high oxygen partial pressure and is directly absorbed into the highly active liquid. The oxidation rate is greatly improved due to contact with the absorbing liquid containing a low concentration of SO□.

Therefore, a small amount of oxygen-containing gas can minimize the sulfite concentration in the absorption liquid.

Furthermore, oxidation of sulfite occurs in the SO absorption part, so 502
It becomes possible to rapidly reduce the partial pressure, and it is possible to improve the desulfurization rate.

The sulfite concentration can be easily controlled by the amount of oxygen-containing gas supplied, and the concentration is 5 amol/j!
If the temperature exceeds 20%, the reactivity of the absorbent decreases, resulting in a decrease in the absorbent utilization rate, a decrease in the desulfurization rate, and nitionate salts, which are problematic in terms of wastewater regulations, and imidodisulfonate salts, which are generated by the absorption of NOx. There is an increase in the concentration of N-5 compounds such as N-5, which poses a problem in a simplified process of desulfurization and dedusting.

In the present invention, the sulfite concentration in the absorption liquid is 5n+m
ol/ff or less, preferably 3 mmol or less.

Furthermore, in the present invention, at least one compound selected from the group consisting of caustic soda, sodium carbonate, and sodium sulfate can be added to the absorption liquid in the absorption zone.

These compounds are considered to have the function of increasing the solubility of lime and limestone because they increase the sulfate ion concentration in the absorption liquid and decrease the calcium ion concentration from the solubility product.

Dissolution of lime and limestone proceeds rapidly in the flue gas-absorbent contact zone.

On the other hand, IIP, IIcI, soot dust, etc. are thought to inhibit the dissolution of these limes and limestones, and therefore, such dissolution inhibition becomes greater in the flue gas-absorbent contact zone.

However, by adding caustic soda etc. to the absorption liquid which is the flue gas-absorption liquid contact zone, the /8 decomposition inhibiting effect by IIF etc. can be efficiently reduced, and Ca
The desulfurization rate can be improved by promoting the reaction between SO□ and SO□.

It is also believed that the addition of highly alkaline Na to the absorption liquid, which is the SO2 absorption part, promotes SO2 absorption.

The amount of these compounds added is not particularly limited;
2. Although it varies depending on the concentration of HF, llCl, and soot, the Na concentration in the absorption liquid is usually 50 to 2000 pp.
m.

As described above, by adding caustic soda or the like to the absorption liquid in the flue gas-absorption liquid contact zone, a sufficient effect can be achieved with a small amount.

The calcium compound used in the present invention is not particularly limited, and conventionally used lime, limestone, etc. can be used.

Further, as the oxygen-containing gas, air, oxygen, oxygen-enriched air, or the like can be used, and the amount to be supplied is not particularly limited, and for example, twice the theoretical amount or more of SO□ is used.

〔Effect of the invention〕

As described above, according to the present invention, an oxygen-containing gas is introduced into the absorption liquid in the zone in contact with flue gas, so that the sulfite concentration in the absorption liquid is maintained at 5 mmol/R, and the absorption liquid in the contact zone is Since caustic soda and the like are added to the solution, the following effects can be achieved.

+11 It is possible to prevent deterioration of desulfurization performance due to soot, IIF, and HCI contained in flue gas.

In normal spray towers, packed towers, and grid towers, oxidation is mainly carried out by oxygen in the flue gas in the flue gas-absorbent contact zone, and if necessary, in the lower part of the absorption tower that is not in the flue gas-absorbent contact zone. Circulating liquid tank (liquid reservoir) located
Air is introduced into the absorption liquid inside to perform liquid phase oxidation of S02.

Therefore, sulfites are temporarily accumulated in the absorption liquid flowing down in contact with the flue gas in the absorption tower, and the soot and dust in the flue gas, l(F
, HCI inhibits the dissolution of lime and limestone, reducing desulfurization performance.

Also, since sulfites accumulate, nithionic acid (+
1 Yu S Yu 0. ) is generated, the COD of the absorbent increases, and the concentration of N-3 compounds increases.

According to the present invention, such conventional drawbacks can be completely eliminated.

(2) In the above conventional method, the concentration of So in flue gas is 30
When the concentration exceeds 0 ppm, the concentration of sulfite in the absorbent increases particularly significantly, the inhibition of dissolution of lime and limestone by IIF etc. in the flue gas increases, and the desulfurization performance deteriorates sharply.

Further, even when the oxygen concentration in the flue gas is about 2.8% or less, the desulfurization performance deteriorates significantly due to insufficient oxidation and IIF, etc., which cannot be solved by introducing air into the liquid m part.

In contrast, in the present invention, oxygen-containing gas is introduced into the absorption liquid, which is the contact zone between the flue gas and the absorption liquid.
It is possible to oxidize SO to sulfate ions almost simultaneously with the absorption of Oyu, reducing 1 degree sulfite in the absorption liquid to 5 mmol/
1 or less, and even if the SO concentration is 300 ppm or more and the oxygen concentration in flue gas is 2.8% or less, the utilization rate of absorbent such as limestone, gypsum quality, and desulfurization performance can be sufficiently increased. .

(3) In the above conventional method, air is blown into the liquid reservoir after contact with the flue gas, so there is soot, dust, 11F, and HCI in the flue gas.
The presence of So2 oxidation efficiency is particularly reduced, a larger amount of air is required, and a complicated oxidation method is required to improve the oxidation efficiency, resulting in economical problems.

According to the present invention, since oxygen-containing gas is introduced into the absorption liquid in the zone that comes into contact with flue gas, the amount of oxygen-containing gas used can be reduced, and the device can be made smaller and simpler. can.

(4) In the flue gas-absorbent contact zone, in order to increase the S02 oxidation efficiency by oxygen in the flue gas, even in the conventional method of using Fe or Mn as an oxidation catalyst, sulfite in the absorbent It is difficult to keep the concentration below 5 mmol/1, which requires increasing the L/G (liquid/gas ratio), increasing the size of the absorption tower, controlling catalyst concentration, and recovering the catalyst. This was not satisfactory in terms of simplification of the device.

The method of the present invention sufficiently overcomes the drawbacks of such conventional methods.

Examples of the present invention will be described below.

〔Example〕

Example 1 Using the flue gas desulfurization and dust removal equipment shown in FIG.
000 pp, approximately 3000 N rt of flue gas from a coal-fired boiler containing 4% oxygen and soot and dust. /h is supplied to the absorption section 6, and the absorption l&8 containing calcium compounds is supplied.
Desulfurization and dust removal treatment were carried out by contacting with the gas, and the treated flue gas 2 was discharged.

On the other hand, air 3 was introduced into the absorbent liquid 8 that came into contact with the flue gas 1 in the absorber 6, and 802 in the exhaust gas 1 was absorbed into the absorbent liquid 8 and simultaneously oxidized to generate sulfate ions.

The absorption liquid 8 is discharged from the absorption section 6, and the solid-liquid separator 7 removes the gypsum 5.
was separated, and calcium carbonate 4 as an absorbent was added to the filtrate and circulated to the absorption section 6.

Additionally, caustic soda and the like were supplied from line 9.

The results are shown in Table 1 below.

In addition, the concentration of nitionate in the absorption liquid was 10 mmol/
I! and the N-8 compound is also 10 mmol/
It was 1 or less.

Furthermore, the COO values in the wastewater were all below 5 ppm, even though no nithionic acid decomposition equipment was installed.

(Hereinafter, overlapping margins) Table 1 Example 2 Using the equipment shown in Figure 1, the boiler combustion method was changed and flue gas was desulfurized and dedusted with the oxygen concentration reduced to 2.0%. went.

The results are shown in Table 2 below.

As is clear from Table 2, no decrease in the sulfur rate was observed.

Table 2 Example 3 Desulfurization and dust removal were carried out under the same conditions as in Example 1 using the absorption apparatus shown in FIG.

The results are shown in Table 3 below.

Table 3 Comparative Examples The same flue gas as in Example 1 was subjected to a desulfurization and dedusting test using a spray tower absorption device.

The oxidizing air was introduced into the circulating liquid tank in an amount 20 times the theoretical molar amount of SO□. The results are shown in Table 4 below.

Table 4 In addition, when the pH of the absorption liquid was 4.5 or higher, operation was poor.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing a contact portion between an absorbing liquid, exhaust gas, and oxygen-containing gas in the present invention, and FIG. 2 is a schematic diagram showing another example of this contact portion. 1- Smoke exhaust, 3- Air, 8- Absorbing liquid.

Claims (1)

[Claims] 1. In a flue gas desulfurization/dedusting method in which flue gas containing at least SO_2, HF, HCl, and soot dust is brought into contact with an absorbing liquid containing a calcium compound, the absorbing liquid in a zone in contact with the flue gas is A flue gas desulfurization and dust removal method characterized by introducing an oxygen-containing gas to maintain the sulfite concentration in the absorption liquid at 5 mmol/l or less. 2. At least one compound selected from the group consisting of caustic soda, soda carbonate, and sodium sulfate is added to the absorbing liquid in the zone that contacts the flue gas.
Flue gas desulfurization and dust removal method described in Section 1.