JPS6133605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying malodorous gas by washing and purifying malodorous gas with an aqueous hypochlorite solution.

In the process of converting a gas containing malodorous components into an odorless or almost odorless treated gas by washing the gas with an aqueous hypochlorite solution, if the concentration of malodorous components is high, The concentration of hypochlorite in the aqueous solution becomes extremely low, almost zero, and when the concentration of malodorous components is low, it becomes abnormally high, resulting in a decrease in the removal performance of malodorous components and deodorization. This causes inconveniences such as increased operating costs for the device.

This kind of problem can be solved by making the hypochlorite concentration in the cleaning solution follow the concentration fluctuations of the malodorous components, but in this case, it is possible to measure the hypochlorite concentration without changing the properties of the measurement solution. The important issue is to do so.

This invention measures the concentration of hypochlorite in a cleaning solution from the ultraviolet absorption intensity of the cleaning solution in a wavelength range of 270 to 330 mμ, corrects changes in this absorption intensity due to PH, and uses this measured value to measure the concentration of hypochlorite in the cleaning solution. By controlling the hypochlorite concentration of the cleaning liquid by adjusting the acid salt replenishment rate, the present invention provides a method for purifying malodorous gas that is excellent both in terms of performance and economy.

Figure 1 shows the ultraviolet absorption spectrum of a sodium hypochlorite aqueous solution with an effective chlorine concentration of 200 ppm at PH = 5 and temperature of 28°C (the effective length of the measurement cell is 10 mm).
This shows that. A compound that exhibits a maximum absorption intensity around 240 nm is hypochlorous acid (hereinafter referred to as HClO), and a compound that exhibits a maximum absorption intensity around 290 nm is hypochlorite ion (hereinafter referred to as ClO ^- ). These two compounds have a chemical equilibrium relationship as shown in formula (1).

HClOClO ^- +H ⁺ …………(1) Therefore, even at the same concentration of hypochlorite,
The absorption intensity is shown by curve A in Figure 2 (this curve A is calculated using the effective chlorine equivalent of 400 nm sodium hypochlorite aqueous solution at a temperature of 28°C and an effective absorption cell length of 10 mm).
The absorption intensity at around 290 nm varies depending on the PH value, as shown in 2).

For the above reasons, the PH of the liquid to be measured needs to be kept at a constant value or adjusted to a highly alkaline region of PH = 9, where the absorption intensity changes slowly. There are some difficulties as follows.

In other words, in order to maintain the pH of the cleaning solution at a constant level, and even to adjust it to a high alkaline range, installation of an alkaline tank, injection pump, mixer, etc. is required, making the equipment complex. Not only that, but the liquid to be measured is highly alkaline, so the pH must be readjusted if this liquid is to be discharged or returned to the washing tower.

However, in this invention, since changes in absorption intensity due to pH changes are electrically corrected, the above-mentioned difficulties are not encountered, and the hypochlorous acid concentration can be measured without changing the properties of the measurement liquid.

In other words, it is known that the concentration ratio of HClO and ClO ^- has the following relationship: log ([ClO ^- ]/[HClO]) = -7.49 + PH …………(2), so based on equation (2) By electrically correcting the absorption intensity, it is possible to correct variations in the maximum absorption value due to pH. In this case, the theoretical curve based on equation (2) becomes as shown in curve C in Figure 2, and the deviation from the actual measured value becomes large at pH below neutrality, resulting in a somewhat less accurate approximation, but the second If the actually measured curve A is approximated by three straight lines as shown by the broken line B in the figure, more accurate correction is possible.

It is easy to perform such a correction operation electrically. Moreover, PH measurement of cleaning liquid is usually performed in almost all gas cleaning cases, and the output signal of an existing PH measuring device can be used without installing a new PH measuring device.

FIG. 3 shows an embodiment of the method of this invention. In the figure, 1 is a cleaning liquid containing hypochlorite (liquid to be measured), 2 is a PH meter, 10 is a concentration calculator, 20 is a gas to be treated, 21 is a cleaning tower, and 22 is a hypochlorite aqueous solution (cleaning liquid), 23 is a circulation pump, 24 is a hypochlorite aqueous solution storage tank, and 25 is a replenishment pump, the driving of which is controlled by the electric output (control signal) of the concentration calculator 10. 26 is an overflow liquid, 27 is a pump for extracting the liquid to be measured 1, 28
is an ultraviolet spectrophotometer, 29 is a processing gas, 30 is a cleaning tower, 31 is a circulation pump, 32 is a reducing agent aqueous solution, 3
3 is a blower, 34 is a reducing agent storage tank, 35 is a replenishment pump, and 36 is an overflow liquid.

The ultraviolet spectrophotometer 28 is constructed as shown in FIG. 4 or 5. In the figure, 1 is a cleaning solution containing hypochlorite, 2 is a PH meter, 3 is a measurement cell, 4 is a light source (a deuterium lamp, a xenon lamp, etc. that has an emission band around 300 nm wavelength), 5 is ultraviolet light, 6 is an optical filter, 7 is a light receiver (photomultiplier tube, phototube, etc.), 8 is an electrical signal that is the output of the PH meter 2, 9 is an output electrical signal of the light receiver 7, 10 is the A concentration calculator 11 calculates the concentration by inputting both electrical signals 8 and 9. Reference numeral 11 is the electrical output of this calculator 10, which serves as a control signal for the replenishment pump 25. 12 is the measuring solution, 13 is the reducing solution, 1
4 is a control cell, 15 and 17 are semi-transparent mirrors, 16 is a total reflection mirror, and 19 is a tipper. The length of the measurement cell 3 corresponds to the hypochlorite concentration to be measured based on Lambert-Beer's law and the extinction coefficient σ of hypochlorite ion = 4.1 × 10 ^-3 ppm ^-1 cm ^-1. The absorbance is approx.
Set the value to be between 0.1 and 2. for example,
If the hypochlorite concentration is 300 ppm and the pH is 6 to 9,
The length of the measurement cell should be 0.08 cm or more and 1.6 cm or less. The reducing agent 13 may be a sodium thiosulfate aqueous solution, a sodium sulfite aqueous solution, or a mixture of the two, which has a reducing power against hypochlorite, and whose compound itself or its oxidized product is within the measurement wavelength range. Use a material that does not absorb.

The gas to be treated 20 is introduced into a cleaning tower 21 and is cleaned with an aqueous hypochlorite solution 22 . The hypochlorite aqueous solution 22 is circulated by the circulation pump 23, and the overflow liquid 26 is intermittently or continuously pumped from the storage tank 24 by the replenishment pump 25.
The corresponding amount will be replenished.

During such circulation, a part of the cleaning liquid flows into the liquid to be measured 1.
The water is introduced into the PH meter 2 by a pump 27, and then returned to the washing tower 21 via an ultraviolet spectrophotometer 28. The electrical signals from the PH meter 2 and the ultraviolet spectrophotometer 28 (generation of these signals will be described later) are as follows.
It is input to the concentration calculator 10, and an electrical output corresponding to the calculated hypochlorite concentration in the cleaning liquid is sent to the replenishment pump 25 as a control signal 11.
The drive of the replenishment pump 25 is controlled by the control signal 11, and as a result, the amount of replenishment of hypochlorite is adjusted, and the concentration of hypochlorite in the circulating cleaning liquid is maintained at a constant value.

On the other hand, the processing gas 29 that has exited the cleaning tower 21 is introduced into the cleaning tower 30 for the next treatment process, and is fed to the circulation pump 3.
Reducing agent aqueous solution 32 being circulated by the operation in step 1
Cleaned by. Thereafter, it is discharged to the outside by the action of the blower 33. A reducing agent aqueous solution (such as a thiosulfate aqueous solution, a sulfite aqueous solution, or a mixed aqueous solution thereof) 32 is replenished from a storage tank 34 by a replenishment pump 35 intermittently or continuously. A liquid amount corresponding to this replenishment amount is discharged as overflow liquid 36.

Next, a system for measuring hypochlorite concentration in an aqueous solution will be described in detail. The cleaning liquid 1 is introduced into the measurement cell 3, and the PH meter 2 measures the pH, and the ultraviolet spectrophotometer 28 measures the absorption intensity.

That is, the cleaning liquid 1 introduced into the measurement cell 3 passes between the light source 4 and the light receiver 7. At this time, the ultraviolet rays 5 radiated from the light source 4 are absorbed by the hypochlorite of the cleaning liquid 1. This absorption amount and hypochlorite concentration are related by the Lambert-Beer law. The ultraviolet light 5 that has passed through the measurement cell 3 is passed through an optical filter 6 and enters a light receiver 7 as monochromatic light around 290 nm. However, this monochromatic light
Not limited to 290nm, but the range where ultraviolet absorption by hypochlorite ions is observed, i.e.
It can be any wavelength between 270 and 330 nm, and it can be broad light over the entire region.

The electric signals 8 and 9 obtained by the PH meter 2 and the light receiver 7 in this way become inputs to the concentration calculator 10, and by calculating these signals 8 and 9, hypochlorite in the liquid to be measured 1 is determined. Output 11 corresponding to acid ion concentration
is obtained. The liquid 12 after measurement is pushed out of the measurement cell 3 and discharged or returned to the washing tower 21.

In the configuration shown in FIG. 5, a stoichiometrically excessive reducing agent 13 is added to the solution 12 after measurement with respect to the hypochlorite concentration in this solution, so that the hypochlorite concentration is reduced. After reduction, it is introduced into the control cell 14, where the ultraviolet absorption intensity is measured again. Then, the amount of ultraviolet absorption in measurement cell 3 and control cell 1
The difference between the amount of ultraviolet absorption at 4 and the amount of ultraviolet light absorbed is applied to the calculator 10 as an electric signal 9. For this purpose, the ultraviolet rays 5 from the light source 4 are split into two directions by the semi-transparent mirror 15,
One side is a control cell 14, a total reflection mirror 16, and a semitransparent mirror 17.
The other beam passes through a total reflection mirror 18, a measurement cell 3, a semi-transparent mirror 17, and a filter 6 and reaches a light receiver 7.The light from the two directions is transmitted through a chopper 19. It is switched periodically by

By using the double beam method in this way, it is possible to eliminate measurement errors caused by zero-base drift caused by cloudy liquid or dirt on the cell window, or by the coexistence of compounds that have absorption in the measurement wavelength range but do not have oxidizing power. can.

In the above description, the measurement wavelength range is 270 to 330 nm corresponding to hypochlorous acid ion, but the absorption wavelength range of hypochlorous acid 230 to 260 nm may also be used. however,
In that case, if the pH is above neutral, the ultraviolet absorption in that wavelength range will be smaller than in the case of 270 to 330 nm, and in the acidic range it will be relatively large, but the evaporation of hypochlorous acid into the gas phase Overall, it is preferable to observe the ultraviolet absorption of hypochlorite ions in the range of 270 to 330 nm, since problems such as concentration instability arise due to increased chemical reactivity. Furthermore, in the case of the double beam method, the overflow liquid 36 can be used as the reducing liquid 13.

As described above, according to the present invention, when cleaning gas containing malodorous components with a hypochlorite aqueous solution, the hypochlorite concentration can be determined from the ultraviolet absorption intensity of the aqueous solution in the wavelength range of 270 to 330 nm. At the same time, it automatically corrects the change in absorption intensity due to PH, and uses the electric signal of this measurement value to adjust the amount of hypochlorite replenishment to control the hypochlorite concentration in the aqueous solution. Concentration detection can be performed without changing the properties of the liquid, and even when the concentration of malodorous components changes, it is possible to automatically maintain the hypochlorite concentration under good processing conditions. We can expect stable and economical gas processing.

[Brief explanation of the drawing]

Figure 1 is an ultraviolet absorption spectrum diagram of an aqueous sodium hypochlorite solution, Figure 2 is a curve diagram showing the change in absorption intensity at around 290 nm of an aqueous sodium hypochlorite solution with respect to pH, and Figure 3 is a diagram showing the implementation of the method of this invention. FIGS. 4 and 5 are block diagrams illustrating the configuration of the concentration measurement system, respectively. 1... Liquid to be measured, 2... PH meter, 3... Measurement cell, 4... Light source, 5... Ultraviolet light, 6... Optical filter, 7... Light receiver, 8, 9... Electric signal, 10
... Concentration calculator, 11 ... Control signal, 12 ... Measurement liquid, 13 ... Reducing liquid, 14 ... Control cell, 1
5, 17...Semi-transparent mirror, 16,18...Total reflection mirror,
19...Chiyotsupa, 20...Gas to be processed, 21...
...Cleaning tower, 22...Hypochlorite aqueous solution, 23...
... Circulation pump, 24 ... Hypochlorite aqueous solution storage tank, 25 ... Replenishment pump, 30 ... Washing tower, 32
...Reducing agent aqueous solution. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In a method for purifying malodorous gas by washing and purifying malodorous gas with an aqueous solution containing hypochlorite, the ultraviolet absorption intensity and PH in the wavelength range of 270 mμ to 330 mμ of the aqueous solution are measured. The hypochlorite concentration in the aqueous solution is calculated from both values, and the hypochlorite concentration in the aqueous solution is controlled by adjusting the supply amount of hypochlorite based on this calculated value. A method for purifying foul-smelling gas. 2. A first step in which the gas to be treated containing malodorous components is washed with an aqueous hypochlorite solution adjusted to pH 6 to 9 to remove the malodorous components, and a process for removing the malodorous components from the treatment in the first step. 270 m of the aqueous solution in the first step includes a second step of removing oxidizing substances and residual malodorous components by washing with an aqueous reducing agent solution.
Ultraviolet absorption intensity and PH in the wavelength range μ~330mμ
The hypochlorite concentration in the aqueous solution is calculated from both values, and the hypochlorite concentration in the aqueous solution is controlled by adjusting the amount of hypochlorite supplied based on this calculated value. A foul-smelling gas purification method characterized by: