JPS61268342A - Method for controlling concentration of hydrogen chloride in exhaust gas - Google Patents

Abstract

PURPOSE:To rapidly control the concn. of hydrogen chloride in exhaust gas, by changing the amount of air for atomizing an alkali solution corresponding to the change in the concn. of residual hydrogen chloride after alkali spraying treatment to change the particle size of the liquid droplets of the alkali solution. CONSTITUTION:Exhaust gas containing hydrogen chloride supplied to a hydrogen chloride removing tower 1 from above is contacted with the alkali solution sprayed from nozzles 2 and taken out from an outlet 5 while hydrogen chloride therein is removed. The concn. of residual hydrogen chloride (a) in exhaust gas at the outlet is measured and, when said concn. rised so as to exceed the prescribed concn., a valve 4 is opened to increase the amount of air supplied to the nozzle 2 and liquid droplets are made minute to be increased in a surface area and the removal capacity of hydrogen chloride is enhanced. At this time, because the concn. and supply amount of the alkali solution 6 are always constant and only the amount of air is changed, correspondence is extremely rapid and operation is also simple.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for controlling hydrogen chloride concentration in exhaust gas.

[Prior art]

In recent years, as the amount of plastic, particularly polyvinyl chloride, in municipal garbage has increased, the amount of hydrogen chloride in the combustion exhaust gas from municipal garbage incinerators has become a problem.

Therefore, in order to reduce the hydrogen chloride concentration in the exhaust gas, a method of spraying an alkaline solution into the exhaust gas is generally adopted.

In the conventional method of spraying an alkaline solution, the alkali concentration or the amount of atomized alkaline solution is adjusted depending on the hydrogen chloride concentration in the exhaust gas, especially the hydrogen chloride concentration in the exhaust gas discharged from the hydrogen chloride removal tower after the alkali treatment. The hydrogen chloride concentration at the outlet of the hydrogen chloride removal column was controlled by increasing or decreasing the amount of hydrogen chloride. However, the method of changing the alkali concentration of the atomized alkaline solution has the disadvantage that the operation is complicated and that it cannot quickly respond to changes in the hydrogen chloride concentration in the exhaust gas at the outlet of the removal tower. Further, the method of increasing or decreasing the amount of atomized alkaline solution has the problem that the spray pattern of the alkaline solution changes, making it impossible to perform stable hydrogen chloride removal, and furthermore, the temperature of the exhaust gas at the exit of the removal tower is not constant.

[Purpose of the invention]

The present invention has a quick response to changes in the concentration of hydrogen chloride in the exhaust gas at the outlet of the hydrogen chloride removal tower, is simple to operate, and has a nearly constant spray pattern. The purpose is to provide a method for controlling

[Structure of the invention]

To achieve the above object, the present invention provides a method for controlling the concentration of hydrogen chloride in the exhaust gas by spraying an alkaline solution into the exhaust gas containing hydrogen chloride. The present invention is characterized in that the amount of air supplied to the nozzle that sprays the alkaline solution is changed accordingly. Hereinafter, the present invention will be explained based on the process diagram shown in FIG.

In FIG. 1, exhaust gas containing hydrogen chloride is supplied to the hydrogen chloride removal column 1 from above the hydrogen chloride removal column 1 along arrow A, flows down inside the hydrogen chloride removal column 1, and is taken out in the direction of arrow B. .

A nozzle 2 is provided in the hydrogen chloride removal column 1,
The alkaline solution 6 supplied through the valve 3 is sprayed from this nozzle 2 along the direction in which the exhaust gas flows. In the present invention, the exhaust gas containing hydrogen chloride flows upward from the bottom of the hydrogen chloride removal tower 1, and the alkaline solution is sprayed downward from the top of the removal tower 1, thereby controlling the flow of the exhaust gas and the alkaline solution. It is also possible to countercurrent the flow.

Here, in the present invention, the amount of alkaline solution sprayed from the nozzle 2 is always kept constant, and the alkali concentration that can be omitted from the alkaline solution is also kept constant. Note that NaOH, Na2 CO3, etc. are used as the alkali.

In the present invention, the amount of atomizing air supplied from the valve 4 is controlled in accordance with changes in the concentration of hydrogen chloride in the exhaust gas discharged from the outlet 5 of the hydrogen chloride removal tower 1, and the amount of atomizing air is After that, it is supplied to valve 2.

That is, the concentration of hydrogen chloride in the exhaust gas at the outlet 5 of the hydrogen chloride removal tower is measured, and when this concentration rises above the specified concentration, the valve 4 is opened to increase the amount of air supplied to the nozzle 2, while at the outlet When the hydrogen chloride concentration in the exhaust gas at step 5 decreases, valve 4 is closed and the amount of air supplied to valve 2 is reduced.

By changing the amount of air supplied to the nozzle 2 in this manner, the gas-liquid ratio in the nozzle 2 is changed, and the droplets are miniaturized.

That is, as the amount of air increases, the diameter of the droplet decreases, and as the amount of air decreases, the diameter of the droplet increases. If the droplets become smaller, the surface area of the droplets will increase even if the amount of atomized alkaline solution is constant, and the performance of removing hydrogen chloride from exhaust gas will be improved.

Conversely, when the hydrogen chloride concentration at the hydrogen chloride removal tower outlet 5 is low, the amount of atomizing air is small and the diameter of the alkaline solution droplets may be large.

Note that the hydrogen chloride concentration in the exhaust gas at the outlet 5 is automatically measured, and the valve 4 is automatically opened and closed in accordance with this value.

The method of the present invention can also be used to remove toxic gases other than hydrogen chloride by appropriately selecting the type of spray solution. It can also be applied to slurry spraying.

〔Effect of the invention〕

As described above, according to the present invention, since the amount of air supplied to the nozzle that sprays the alkaline solution is simply changed, the atomization can be performed quickly in response to changes in the concentration of hydrogen chloride remaining in the exhaust gas after the alkaline spray treatment. The particle size of the alkali solution droplets can be varied.

The response to changes in the hydrogen chloride concentration at the outlet 5 of the removal tower is significantly faster than the conventional method of changing the amount of alkaline solution sprayed or the alkali concentration.

In addition, the operation is extremely simple, and the hydrogen chloride removal rate is 70 to 9.
It can be easily adjusted within the range of 0% (in case of Na/Cl ratio -2.0).

Furthermore, since the amount of atomized alkaline liquid does not liquefy, the spray pattern hardly changes even if the amount of atomized air changes, and stable gas-liquid contact can be achieved.

Furthermore, even if the hydrogen chloride concentration at the outlet of the hydrogen chloride removal column changes, there is also the advantage that the alkaline concentration of the alkaline solution can be kept constant.

Examples of the present invention will be described below.

〔Example〕

When the amount of atomized alkaline solution is constant, the relationship between changes in the amount of atomized air and the hydrogen chloride removal rate was investigated for exhaust gas with a hydrogen chloride concentration of 450 ppm at the inlet of the hydrogen chloride removal tower.

The results are shown in Figure 2.

In FIG. 2, curve A shows the case where the Na/Cl ratio is 3.0°, curve B shows the case where the Na/Cl ratio is 2.0°, and curved curve shows the case where the Na/Cl ratio is 1.0.

It is clear from FIG. 2 that as the amount of atomizing air increases and as the alkali is present in excess of hydrogen chloride, the hydrogen chloride removal rate increases.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of the present invention, and FIG. 2 is a diagram showing changes in the hydrogen chloride removal rate with respect to changes in the amount of atomizing air. 1... Hydrogen chloride removal column, 2... Nozzle, 4... Air valve, 5... Hydrogen chloride removal column outlet, 6... Alkaline solution.

Claims (1)

[Claims] In a method for controlling the hydrogen chloride concentration in exhaust gas by spraying an alkaline solution into exhaust gas containing hydrogen chloride, a nozzle that sprays the alkaline solution in accordance with the concentration of hydrogen chloride remaining in the exhaust gas after the alkaline solution is sprayed. A method for controlling hydrogen chloride concentration in exhaust gas, characterized by changing the amount of air supplied to the exhaust gas.