JPS5855027A - Removing method for sulfur dioxide in waste gas - Google Patents

Abstract

PURPOSE:To remove the sulfur dioxide in waste gases effectively with combination of a tray tower and a spray tower in the stage of removing the sulfur dioxide from the waste gases by using the tray tower first then the spray tower. CONSTITUTION:Waste gases contg. sulfur dioxide are first conducted through a line 3 into a tray tower 1, where the gases are brought into contact with the absorbing liquid from a line 11, whereby 60-90% the sulfur dioxide to be removed is removed. Then the waste gases are conducted through a line 5 into a spray tower 2, where the flow of the gases is regulated with flow regulating plates 6 and the gases are brought into counter current contact with the absorbing liquid from spray nozzles 7, whereby the sulfur dioxide is removed. Thus the tray tower is used when the concn. is high and said tower is used in combination with the spray when the concn. is low, whereby the short paths in the spray tower are prevented and the sulfur dioxide is removed effectively in high yields.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for effectively removing 801 from exhaust gas containing sulfur dioxide (hereinafter referred to as SO).

It is well known that various devices (commonly referred to as flue gas desulfurization devices) using various methods are in operation in order to remove oxidants contained in boiler exhaust gas. The mainstream is the absorption of 808 in the absorption liquid, and as an absorbent, 803
It is common to use a product that contains a component that reacts with the chemical in some way. This is called the reaction absorption method. This s
O! In some cases, the absorbent liquid that has absorbed it may be discharged, but! From an economic standpoint, the absorbent liquid is often regenerated and recycled. The device for absorbing 80 tons of gas is generally called a gas absorption device, and is designed to efficiently bring the gas into contact with the absorption liquid.

Increase the absorption effect and SO! This will improve the removal rate. When gas absorption devices are classified based on their type, they are classified into gas dispersion layers and liquid dispersion lids. It's normal.

(Reference: Chemical Engineering Handbook Revised Edition P522) For example, 8
A typical example of the 0s reaction absorption method is absorption using a dilute aqueous solution of sodium sulfite. This method has a regeneration process that uses a reversible reaction.

The following reaction is occurring.

0C Nap so=+ 80x+ Mountain 0→2NaH80s
(1) 100C 2NaH801→ Na1804+ 801110H
,0↑ (2) In this process, o=+ in the exhaust gas
According to Son, ShoNal 80B is oxidized (
The side reaction 3) occurs and 9Na-so4 is produced.

HaB 80g + +Os→H smell 804
(3) This Na1804 needs to be taken out of the system, which results in a loss of reaction absorption components, so it is economically disadvantageous that the oxidation reaction proceeds.

The following problems arise when designing an SO absorption device using this fresh and thick sodium sulfite aqueous solution.

1. The concentration of SO contained in the exhaust gas is low, and the 80sfajF in the gas after absorption must be absorbed at a very low source of 11Kt, approximately 100 ppm or less (this is a common problem with all absorption methods). Increase collection efficiency by increasing the flow rate ratio of liquid to gas.

2. Since the nine chemical reactions shown in equation (1) above are relatively fast reactions, it seems that the absorption mechanism is gas-dominated and liquid dispersion type is suitable, but as shown in equation (3) This also makes the progress of side reactions more efficient.

That balance is important.

In the end, in consideration of the above two points, as an actual device, a gas dispersion type multi-stage tower is used, and each stage circulates the absorption liquid.
Designs have been made to increase the substantial liquid-to-gas ratio.

A spray tower can be considered as a representative example of the liquid dispersion type, but this type has the problem of competition with the side reactions mentioned above, as well as the difficulty of suppressing the shut path of the exhaust gas. This problem arises because the amount of boiler exhaust gas is generally large.

To prevent sheet pass, it is necessary to increase the number of sprays, but this increases the amount of absorbed liquid and produces side reaction products.
Snow 1104 There was a large amount of cram school, a large amount of absorption liquid was extracted, and a large amount of collected liquid was replenished.

However, it has the disadvantage of being industrially disadvantageous.

As a result of intensive studies by the present inventors to solve the above-mentioned problems, the limitations of the gas dispersion type column column in the absorption operation in the low-complexity region of SO after several collections, the concentration of which is about 100 p- or less, and the low IN direct region. It has been discovered that by combining the effectiveness of the spray tower for the liquid fraction *m in the absorption operation, it is possible to suppress the paper-making and side reactions, and based on this knowledge, the present invention has been completed.

That is, in the present invention, when removing sulfur dioxide from exhaust gas using a gas absorption device, 60 to 90 liters of sulfur dioxide to be removed is removed by a tray column, and the remaining residue is removed by a spray column. The present invention provides a method for removing sulfur dioxide from exhaust gas.

Next, the process of the present invention will be explained in detail according to the drawings.

FIG. 1 is a process diagram showing an example of a process according to the present invention. In Figure K>-, 1 is a tray tower, and 2ti is a spray tower. The exhaust gas containing 980 snow supplied from the 2-in-3 plate tower IK passes through the 3-stage perforated plate 4 while contacting the absorption liquid (for example, a concentrated aqueous solution of sodium sulfite) supplied from the line 11 to the 0-stage column. In I, it should be removed from exhaust gas @
SO, 60-90 g is removed, after which the exhaust gas is fed to the spray tower 2 via line 5.

The exhaust gas that has been rectified by the rectifying plate 6 comes into contact with an absorbing liquid (for example, a concentrated aqueous solution of sodium sulfite) injected from the spray nozzle 7 in a countercurrent manner to remove 802, and then the accompanying absorbing liquid is separated by the mist separator 8. and is discharged from line 9.

On the other hand, the absorption liquid is supplied to the spray column 2 and the tray column 1 through supply lines 10 and 11. The absorption liquid supplied to the spray tower 2 is circulated by the circulation pump 12, and then supplied to the tray column through the overflow line 14, or extracted to the outside of the absorption system through the extraction line 15 as necessary. It will be done. The absorption liquid supplied to the plate column from 11 is extracted from the discharge 2-in 13 after 80 liters of absorption.

The tray column in the present invention is generally equipped with 3 to 5 stages of perforated plates. Spray towers are typically equipped with 10 to 20 nozzles. The superficial contact time in both absorption devices is usually 10 to 15 seconds. Although the treatment temperature does not directly affect SO removal efficiency, it is generally advantageous to carry out the treatment at 60 to SOC, preferably 40 to 50C.

The pressure can be reduced, normal pressure, or increased pressure, but normal pressure is preferred to 1%.The ratio of the amount of absorption liquid circulated in the spray tower to the exhaust gas is usually 0.5 to 3.0 (bar).

When carrying out the present invention when a tray column is already used as an absorption column, it is possible to remove a part of the upper part of the first column, attach a spray to that part, and use it as an integrated absorption column. can. Furthermore, when manufacturing a new absorption tower, one equipped with a spray in the upper part and trays in the lower part (a device in which the tray tower and the spray tower are integrated) is suitably used in the present invention.

In the stage 4F of the present invention, it is necessary to remove 0.60 to 90% of the SO to be removed from the exhaust gas. If it is less than 60 liters, the amount of Na1804 generated will increase due to side reactions, and if it exceeds 9G concentration.

The absorption efficiency of the tray column is greatly reduced, and the absorption efficiency of the absorption column as a whole is reduced, which is undesirable.The absorption liquid company according to the present invention is generally a mixture of sulfite and the main component, but l
f! fK is not limited. In other words, any liquid that can effectively absorb 80 g of water may be used.

The absorption liquids used in the tray column and the spray column may be the same or different.

Next, the present invention will be explained in detail.

That is, first, 80. Removal rate: 60-90
By removing 802 and using a spray absorption tower after the attack, (1) the oxidation of sulfites, which was considered to be the biggest drawback of spray absorption towers, is reduced to the same level as a tray tower! fKt can be significantly reduced. Compared to the use of a 9-stage column alone, the reduction in absorption rate in the latter stage of absorption can be significantly improved, resulting in a
03 If you keep the removal rate to a high removal rate of 95 or more, 1ti,i
I can do L things.

Examples according to the present invention will be described below.

Example 1 After a plate tower consisting of three perforated plates, the effective spray height was 1.
5m1I%G (spray circulation liquid volume/exhaust gas volume) = 1 to 2
(J/l/) spray tower combination device (Figure 1)
Using this method, SO was removed from boiler exhaust gas by varying the amount of absorption liquid supplied. The absorption liquid mainly contained in the plate column and the spray column K Nsg Boz was used, and a system was adopted in which the absorption liquid was supplied to the first column after the use of the spray column. In addition,
The heavy oil used in the boiler is C heavy oil containing about 2.7 liters of sulfur, and its flow rate is 6,000 to 7,000 k17ufa.

The results of the above evacuation are shown in ■ in FIG. As can be seen from the figure, the method of the present invention is 80 times better than the conventional method described later (using only a three-stage column with perforated plates). Excellent removal rate. In addition, the amount of sulfite oxidation (NallK)4 generated is not much different from the case using only the conventional plate column (3 stages of perforated plates), and in both cases, the amount of oxidation of sulfite (NallK)4 is 80 to 10 OvH at the absorption liquid volume VH-.
■It is.

On the other hand, reverse K 80. When operating with the removal rate fixed at 90 liters, the SO removal rate improves, so the operating cost of the gas absorption equipment, including the regeneration cost and absorption liquid replenishment cost, is:
This is a 30% reduction compared to the conventional three-stage column with perforated plates.

Comparative Example 1 SO was removed from the boiler exhaust gas under the same conditions as in Example 1 except for using only the tray column consisting of three stages of perforated plates used in the conventional method. The results are shown in Figure 2 (■).

[Brief explanation of drawings]

FIG. 1 is a sheet showing an embodiment of the apparatus 7 used in the present invention, and FIG. 80 in Comparative Example IK. FIG. 3 is a diagram showing the relationship between removal rate and absorption liquid supply amount. l・・・・・・・・・・・・Tanto 2...
・・・・・・・・・・・・Spray tower patent applicant
Japan Synthetic Rubber Co., Ltd.

Claims (2)

[Claims] (1) When removing sulfur dioxide from exhaust gas using a gas absorption device, 60 to 90% of the sulfur dioxide to be removed
1. A method for removing sulfur dioxide from exhaust gas, which comprises removing sulfur dioxide using a tray tower and removing residue using a spray tower. (2) The method according to claim (1), characterized in that an apparatus in which a tray column and a spray column are integrated is used.