JPS58143821A - Method for deodorizing malodorous gas - Google Patents

Abstract

PURPOSE:To operate an apparatus smoothly and develop stable deodorizing effect, by holding the concn. of NaHCO3 and/or Na2CO3 in a basic NaClO washing liquid in an absorptive oxidation method to a predetermined value or less to control the amount of replenishing water. CONSTITUTION:In supplying a basic NaClO washing liquid 6 to a washing liquid tank 5, the concn. of NaHCO3 and/or Na2CO3 in the washing liquid 6 is measured by a carbonate densitometer 16. By this measured value, an electromotive valve 17 is controlled to adjust the replenishing amount of fresh water 8 so as to hold the concn. of the washing liquid in the tank 5 to 4,000ppm or less, especially, 1,500-3,000ppm. Thus adjusted washing liquid is injected from the liquid distributor 3 of a washing tower 1 to be contacted with a malodorous gas 13 such as H2S contg. accompanied CO2. As the result, H2S is converted to S or Na2SO4 to carry out deodorizing while CO2 is converted to a proper amount of carbonates in the aforementioned concn. and the adhesion of carbonates to the liquid contact part of a deodorizing apparatus is prevented to smoothly operate the apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for deodorizing malodorous gas, and more specifically, to deodorizing malodorous gas containing carbon dioxide by an absorption oxidation method (hereinafter referred to as absorption oxidation method) using sodium hypochlorite as an alkaline cleaning liquid. Regarding deodorizing methods. Note that the term "foul-smelling gas" here refers to gases that are the cause of malodor complaints, including exhaust gases from factories and business establishments that are subject to regulations under the Offensive Odor Prevention Act and local pollution control ordinances.

Deodorization by the absorption oxidation method, which uses sodium chloride as an alkaline cleaning solution, is particularly often used for large-scale deodorization in public environmental facilities such as sewage treatment plants, human waste treatment plants, and garbage treatment plants. A general configuration of the device M will be explained with reference to the attached drawings.

In the figure, 1 is a cleaning tower in the form of a packed column.

It comprises a demister 2, a liquid distributor 3 and a packing layer 4. Reference numeral 5 denotes a cleaning liquid tank, and although the figure shows one separated from the cleaning tower 1, there is also a tank that is integrally formed at the bottom of the cleaning tower.

There is also a type that integrates multiple cleaning towers into one body and separates their functions with partition walls. 6 in the figure is the sodium chlorate liquid storage tank,
7 is a sodium hydroxide liquid storage tank, 8 is a water pipe, 9 is a pH indicating controller, and 10 is a concentration meter for instructing the next IIE sodium hydroxide concentration adjustment. I 1.12 is a drug infusion pump, and both are linked with the instrument described in it I (
The chemical solution (corresponding pump and meter connections are shown by dotted lines) is injected into the cleaning solution from each storage tank in a controlled manner to maintain the cleaning solution's pi value and the concentration of sodium chlorate at a predetermined value. (indicated by a thick solid line) passes through the cleaning tower 1 from the inlet 13, comes into contact with the cleaning fluid that is circulated from the liquid tank to the top of the tower by the cleaning fluid circulation pump 14, and is sprayed, and is deodorized and released into the atmosphere from the outlet 15. 16 is a carbonate concentration meter related to the present invention, which detects the concentration of hydrogen carbonate and/or sodium carbonate in the alkaline absorption liquid, and sends a signal to the electric valve 17 to transmit the signal by opening and closing. The amount of water supplied from the water pipe 8 to the cleaning liquid tank is adjusted.

18 is a drain pipe for overflowing and discharging a part of the cleaning liquid. In addition, in actual devices, devices are often configured in combination with other methods such as acid cleaning and activated carbon adsorption.

The basic principle of the absorption oxidation method is to change the odor components in malodorous gas and make it odorless and stable through the oxidizing action of IJium (hypochlorous acid). For example, water sulfide, which is the main target component, is changed into chemically stable sulfur or sodium sulfate in alkaline conditions as shown in formula (3).

H2S + 2 NaOH= Na2S + 2 H2O
--"・beat--(11Na2S +NaCl0+HtO
= S+Nacl+2NaOH--f21Na2S+4
NaCIO= Na, So, +4NaC7-・-・old・
・The reactions of f3J(1+ and (3) occur simultaneously, and one of them becomes the main reaction depending on the pH of the solution.The purpose of replenishing fresh water to the cleaning solution and overflowing a part of the solution is to: 1) Reaction products ( For example, this prevents the deodorizing efficiency from decreasing due to the high concentration of NaC1) in the liquid, which reduces the gas absorption rate of the liquid.

2) Floatable or sedimentary products such as S and carbonates described below) are allowed to flow out to prevent trouble in the operation of the equipment due to their arrival.

These two points allow the device to maintain its deodorizing ability. However, the method of controlling the amount of fresh water to be replenished is
Not established so far. For example, PPM19
July 1981 issue, pages 1-13, "Standard deodorizing equipment for human waste treatment plants" and August 1981 issue, pages 32-39, "Deodorizing equipment for sewage treatment plants and pumping stations using special fillings"
describes the absorption oxidation method, but does not provide any information on the amount of make-up water. The reality is that the supply of fresh water to existing equipment is carried out in a way that is based on the experience of the installer. By the way, if the amount of make-up water is large, the amount of chemicals discharged due to overflow will increase, causing problems. Especially sodium hypochlorite is 0.3p
It has sterilizing power at about pm, and deodorizes at 100 to 2000 p.m.
Since it is used within the concentration range of pm, discharging a large amount as deodorizing equipment wastewater will have an adverse effect on aquatic life. In addition, the amount of hypochlorous acid is not negligible from the point of view of economic efficiency.
Emissions from IJum overflow reached 23% of total consumption.

On the other hand, if foul-smelling gas containing carbon dioxide is processed in a situation where there is little make-up water, precipitates mainly composed of carbonates will form and adhere, blocking the absorption liquid circulation path and damaging the instrumentation sensors. The deodorizer becomes dirty, causing an error in the detected value and deteriorating the function of the deodorizing device. Not only pH meters, but especially 5-sodium hypochlorite concentration meters that have recently become popular, contamination of the wetted parts by deposits is a problem, regardless of whether they use the ift electrode method or the photoelectric photometry method. This is a major hindrance factor.

The present inventor believes that the occurrence of this deposit is related to the concentration of carbonates in the cleaning liquid, and that if the concentration of carbonates is taken as an index for controlling the injection of make-up water, the amount of fresh water to be refilled can be achieved without impairing the deodorizing effect of the device. The present invention was completed by discovering that it is possible to adjust the

That is, the present invention is a deodorizing method using an absorption oxidation method, in which the *i of sodium bicarbonate and/or sodium carbonate in the IJium cleaning solution is preferably 4000 ppm or less, preferably rl: 1500 to 300.
This method of deodorizing foul-smelling gas is characterized by controlling the amount of water added to the liquid so as to maintain it at 0 ppm.

Reduce the amount of water supplied to the cleaning solution to reduce the carbonate concentration to 4.
If it exceeds 000 ppm, precipitation will occur within a short period of time and will adhere to the wetted parts of the deodorizing device.

Can you increase the amount of water again? # Reduce the concentration to 1500 ppm or less
6- Otherwise, the number of sodium hypochlorite needles discharged from the device will be increased unnecessarily, resulting in the above-mentioned disadvantages. According to the present invention, an appropriate amount of fresh water can always be supplied to the absorption oxidation deodorizing equipment, so the above-mentioned problems are eliminated, and the equipment can operate smoothly with less impact on the environment due to its wastewater, resulting in stable operation. A deodorizing effect can be obtained. In carrying out the present invention, 5. Although any method may be used to detect and control the detection, for example, the Winkler method may be used for detection. Further, as a device that automatically detects the concentrated JJi and outputs the open side 1 signal, Dlgi Chem3000 (manufactured by Yuasa Ionics Co., Ltd.) or the like may be used.

Sodium hydrogen carbonate and sodium carbonate are produced when carbon dioxide contained in the malodorous gas that is treated by the device reacts with hydroxide (injected to adjust pH) in the cleaning solution.

In general, anaerobic fermentation is often involved in the generation of malodorous gases, and most of them contain carbon dioxide, whose concentration is constantly changing. Therefore, the influence of carbonates on the deodorization of malodorous gases is unavoidable, and the present invention is a useful method for dealing with this.

Example: A packed tower type (2000φX5
A deodorizing device consisting of a cleaning tower of 200H, filling height 1.9m, and packing material Tricarno ξtsukin P-164) removes 100 ppm of hypochlorous acid from the cleaning solution.
When treated under the conditions of pH 10 and liquid/gas ratio of 2 kg/kg, carbonate in the cleaning solution was... [: (11k degree of Na2CO3 and NaHCO3 according to Winkler biography) is 3000
Above 4000 ppm, a sticky precipitate will form.
Once it reached pm, the secondary chlorine meter became unusable within a short time. The amount of replenishing water at that time was 3 to 5 min.

Furthermore, when the concentration of carbonate was kept below 3000 pprn, no adhesive precipitation occurred (replenishment swimwear 7-101/rn
ln). In addition, the removal rate of hydrogen sulfide (ra
The removal rate by passing through the device is 99 for +z approximately 1 to 4 ppm.
It was 5% or more.

[Brief explanation of drawings]

The drawing is a schematic diagram of an apparatus for implementing the present invention. 1... Washing tower, 2... Demister-13... Liquid distributor,
4. Filling snort, 5. Cleaning liquid tank, 6. Sodium hypovolite liquid storage tank, 7. Sodium hydroxide liquid storage tank, 8
... Water pipe, 9 ... pH indicator controller, 10 ... Hypochlorous acid (IJ) meter, 11.12 ... Liquid medicine injection pump, I3 ... Malodorous gas inlet, 14.・Cleaning liquid circulation I pump, 15...Deodorizing gas outlet, 16...Carbonate concentration meter, 17...Electric valve 18...Drain pipe 9-

Claims (1)

[Claims] 1. Hypochlorous acid) In a method of deodorizing a malodorous gas containing accompanying carbon dioxide by an absorption oxidation method using IJium as an alkaline cleaning solution, the concentration of sodium bicarbonate and/or sodium carbonate in the cleaning solution is
A deodorizing method characterized by controlling the amount of fresh water added to the cleaning solution so as to keep the concentration below 4000 ppm.