JPH07308542A - Method for removing mercury in waste gas - Google Patents

Abstract

PURPOSE:To miniaturize equipment by improving the capacity of an absorbent more than the conventional DOWA method being comparatively effective in removing the mercury does and also securing durability of the efficiency with lapse of time. CONSTITUTION:Waste gas in company with gaseous or mist-like mercury is passed through a packed bed of an absorbent consisting of that which a mixture which pyrite (FeS2) is added to synthetic lead sulfide (PbS) by about 50wt.% to form is deposited on pumice powder to form, to remove the mercury by adsorption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a trace amount of mercury contained in a gas or a mist in exhaust gas from a metal smelter, a boiler or the like.

[0002]

2. Description of the Related Art Generally, as a method for removing metal components in a gas including mercury, a scrubber method in which dust and mist are brought into contact with washing water to separate them, a filter dust collection by a bag filter, and a centrifugal separation are used. There are various physical methods such as cyclone separation, gravity settling method using a dust chamber, and electric dust collection using a cotrel.

Further, as disclosed in Japanese Examined Patent Publication No. 54-8475, "A solution containing SO ₂ having a dew point pH value of 1.0 or more and being accompanied by gaseous or mist-like mercury. The acidic exhaust gas is guided to a packed bed of an absorbent composed of a non-carbonaceous inorganic porous material carrier on which at least one metal sulfide selected from the group consisting of ZnS, CdS and PbS is carried, and A method of chemically fixing mercury in exhaust gas by passing it through (hereinafter referred to as the Dowa method) is known.

Usually, among the harmful substances, especially mercury compounds are likely to be metallic, and easily become metallic mercury by heating or the presence of a slight reducing agent. Metallic mercury is a substance that has a very large vapor pressure and is easily volatilized. For example, the following is borrowed from the description in "Chemical Handbook".

Temperature Vapor pressure 20 to 30 ° C. (normal temperature) 10 ⁻³ mmHg 50 to 60 ° C. 10 ⁻² mmHg 100 ° C. 10 ⁻¹ mmHg 120 to 130 ° C. ^{1 to 2} mmHg 180 to 190 ° C. 10 to 20 mmHg and mercury halogen Compounds (generally chlorides) also have a very high vapor pressure. Therefore, harmful substances such as mercury are not only scattered as solid so-called smoke ash and also scattered, but in many cases they are contained in the gas as gaseous fumes, so physically perform operations such as washing and sedimentation. In many cases, it cannot be removed, and a part is often contained in the gas as fine mist.

[0006]

Therefore, it has been difficult to completely remove the gaseous metal containing mercury and a trace amount of harmful substances even if the above physical dust removal methods are used alone or in various combinations. .

The above-mentioned Dowa method, which is a type of chemical treatment method, allows an exhaust gas containing mercury to pass through a packed bed of an absorbent comprising a metal sulfide supported on an inorganic porous carrier, so that a packed tower is used. There is a problem that the pressure loss of the column increases and the packing column becomes large in order to suppress the pressure loss and perform sufficient mercury removal.

Therefore, an object of the present invention is to further improve the mercury absorbing capacity of the absorbent as compared with the conventional Dowa method using a porous material carrier carrying a metal sulfide which has a relatively good effect on mercury removal, and An object of the present invention is to provide a method of removing mercury in exhaust gas, which can economically ensure the sustainability of efficiency and thus enables downsizing of the apparatus.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above-mentioned object. As a result, PbS mixed with a specific ratio of iron sulfide (FeS ₂ ) was supported on a porous substance carrier. If the gas is passed through the packed layer of the absorbent, the mercury content is higher than that in the case of the above-mentioned dowa method (using the absorbent supporting at least one metal sulfide selected from ZnS, CdS and PbS). The inventors have found that the absorption rate, that is, the removal rate, of S.

That is, the present invention is an absorbent comprising a mixture of lead concentrate or artificially synthesized lead sulfide and naturally occurring iron sulfide or synthetic iron sulfide supported on a porous material carrier. The method for removing mercury in exhaust gas is characterized in that mercury is adsorbed and removed by passing exhaust gas accompanied by gaseous or mist-like mercury through the packed bed.

[0011]

The absorbent used in the present invention contains 5% by weight of pyrite (pyrite) or marcasite (markersite) as iron sulfide with respect to inexpensive lead concentrate or artificially synthesized lead sulfide (PbS). As described above, the mixture is preferably mixed at a ratio of about 50% by weight, and the mixture is adsorbed on a porous substance with a pelletizer or the like.

In this case, artificial Fe is used instead of pyrite.
The same effect is exhibited when S ₂ is used. Mixing ratio is 5
Below 50% by weight, there is not much difference from the case of using lead sulfide alone, and even if 75% by weight is added, there is no difference from around 50% by weight, so about half the cost of lead sulfide is mixed in terms of cost. Is good.

Further, as the porous substance, when the exhaust gas temperature is high or the corrosiveness of the exhaust gas is strong, inorganic substances such as porous volcanic emissions generally called pumice are preferable, and the low temperature and When it is not corrosive, organic substances such as activated carbon, coal or sponge rubber can be used as well.

When the above-mentioned absorbent is used, it is necessary that water be present in the absorbent, and the sufficient ability to remove and absorb mercury in gas cannot be exhibited without water.

Basically, the more the water content is, the more the absorption efficiency is improved. However, when the water content is too much, the pressure loss in the packed bed increases.
Since the performance will drop and the sulfide will fall off, we decided to maintain the activity of the mercury absorbent by adjusting the humidity in the gas.

[0016]

EXAMPLE FIG. 1 is a graph showing changes in mercury removal rate with time for the mercury absorbent used in this example and other absorbents used for comparison. FIG. 2 is a graph showing the amount of pyrite added to synthetic PbS. It is a graph which shows the relationship with the mercury removal rate one hour after passing the gas, and will be described below with reference to these graphs.

(1) First, an aqueous solution of sodium hydrosulfide was added to an aqueous solution of lead acetate to prepare synthetic PbS.

(2) To 200 mg of synthetic PbS, 200 mg of each sulfide prepared by adding pyrite at a ratio of 20, 50, 100 and 150 mg respectively was taken, and 5 g of pumice powder (30 to 100 mesh) and Purified water 1
It was mixed with g to obtain a mercury absorbent.

(3) Each of these mercury absorbents has an inner diameter of 2
Fig. 2 shows the mercury removal rate for each absorbent after 1 hour after filling a 0 mm absorption tower with a gas having a mercury concentration of 1.0 mg / Nm ³ at a rate of 9 L / min. It was In addition, in the figure, the case of adding only PyS without adding pyrite is shown as an addition amount of zero.

From the results shown in FIG. 2, the mercury removal rate was maintained at around 35% at 20 mg (10% by weight of PbS),
The highest removal rate was obtained with 100 mg (50% by weight of PbS).

Next, 200 mg of sulfide prepared by adding about 50% by weight of pyrite to the synthesized PbS was mixed with 5 g of pumice powder (30 to 100 mesh) and 1 g of purified water to obtain a mercury absorbent as described above. The time course of the mercury removal rate was obtained through the gas in the same manner as in (3), and the results are shown in the graph of FIG. 1, and the removal rate values immediately after passing the gas, one hour after, and four hours after are shown in Table 1. It was

[0022]

[Comparative Examples 1 to 4] For comparison with the examples, synthetic PbS
In the case of plain, in the case of pyrite alone, in the case of the dowa absorbent and in the case of lead concentrate alone, 200 mg of each sulfide, pumice and purified water were mixed in the same manner as in the example, and then filled in an absorption tower. Then, the mercury removal rate for each absorbent was determined by the same operation as in the example and is shown in FIG. 1 and Table 1. Note that, in FIG. 1, the substantially horizontal dotted line shows the result of the blank test.

[0023]

[Table 1]

From the results shown in FIG. 1 and Table 1, in the case of the method of the present invention, the removal rate immediately after passing through the gas is as high as 80%, and economically, it is compared with the conventional metal sulfide alone as the absorbent. It was confirmed that the absorption capacity was maintained for a long time.

[0025]

As described above, as compared with the absorbent which supports only the metal sulfide selected from ZnS, CdS and PbS in the conventional method, the iron sulfide mixed with the lead sulfide by the method of the present invention is mixed with the porous material. Since the absorbent supported on the carrier for solid substances can be used stably for a long time and also has a high mercury absorption efficiency, the ability to remove mercury per unit weight of the absorbent is high, and the packing layer that fills the absorbent is miniaturized. The effect of being able to be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a graph showing changes in mercury removal rate with time for a mercury absorbent used in Examples of the present invention and an absorbent used in Comparative Examples.

FIG. 2 is a graph showing the relationship between the amount of pyrite added to synthetic PbS and the mercury removal rate after 1 hour of passing gas.

Claims (1)

[Claims] 1. A bed of absorbent material comprising a mixture of lead concentrate or artificially synthesized lead sulfide and naturally occurring iron sulfide or synthetic iron sulfide supported on a porous material carrier. A method for removing mercury in exhaust gas, which comprises adsorbing and removing mercury by passing exhaust gas accompanied by gaseous or mist-like mercury.