JPS60132626A - Removal of gaseous mercury in wet exhaust gas scrubbing equipment - Google Patents

Abstract

PURPOSE:To remove gaseous mercury in exhaust gas along with HCl and SOx with high efficiency, by scrubbing exhaust gas with an alkali solution to which thiourea and cuprous chloride are added. CONSTITUTION:Caustic soda 5, to which thiourea 2 and cuprous chloride 3 are added, is supplied to a gas scrubbing tower 13 while the exhaust gas 6 of a garbage incinerator is guided to said scrubbing tower 13 to be scrubbed with caustic sode 5. HCl and SOx in the exhaust gas are removed and, at the same time, 90% or more of gaseous mercury is removed. Purified exhaust gas is exhausted through a re-heater 25 while mixed with heated air 19.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for removing gaseous mercury in wet smoke cleaning equipment.

Conventional structure and problems Recently, heavy metals contained in waste gas from waste incineration plants, especially the content of mercury, which has a low boiling point, have become a major environmental problem (mercury is found in waste, such as thermometers with two dry batteries, etc.). (Included in fluorescent lights, etc.) However, in conventional wet smoke cleaning equipment consisting of Venturi scrubbers, trays, packed towers, etc., alkaline solutions (Na01(, Ca(OH))
The mercury removal rate (in soot and dust core gas) by z-CaCO5, etc. is 60 to 80% of the amount of mercury at the equipment inlet,
It was still inadequate.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for removing gaseous mercury in wet smoke cleaning equipment, which eliminates the above-mentioned conventional drawbacks.

Structure of the Invention In order to achieve the above object, the method for removing gaseous mercury using wet smoke cleaning equipment of the present invention is configured to perform wet smoke cleaning of exhaust gas with an alkaline solution to which thiourea and cuprous chloride are added. This makes it possible to remove about 90% or more of gaseous mercury at the same time as dehydrochlorination (HCI) and desulfurization oxides (SOx).

Examples and production Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the entire wet smoke cleaning equipment for applying the method of the present invention. In the figure, (1) is a caustic soda tank;
Thiourea (SC(NHz)2) (2) and cuprous chloride (
CuCl (X3) and dilution water (4) are added to the caustic soda (5). (0) is a caustic soda pump that draws out caustic soda (5) from the caustic soda tank (1), and (7) is the caustic soda (5) sent by the caustic soda pump (6) and stored in the hot water tank (8). The hot water pump sends caustic soda (5) to a cooling tower (9), and the caustic soda (5) cooled by the cooling tower (9) is sent to a cold water tank 00. (1η is the make-up water that is supplied to the cold water tank αQ as needed. (2) is the water that draws out the caustic soda (5) from the cold water tank Of3 and sends it to the gas scrubbing tower.
The cold water pump is configured to supply caustic soda (5) used in the dehumidification section a→ to the hot water tank (8). A portion of the caustic soda (5) sent from the hot water pump (8) to the cooling tower (9) is supplied to the cooling section (c) of the gas cleaning tower α.

On the other hand, 0Q is the incinerator exhaust gas supplied from the waste incinerator αη to the cooling section a→ of the gas cleaning tower α, and the a frame is the gas cleaning tower (
An air-gas mixer that mixes incinerator exhaust gas α and heated air α emitted from the upper end of the air-cooled plate brick ( The heated air (c) from ) is heat-exchanged with steam (2) in an air heater for white smoke prevention (e). Note that (c) is a drain. (2) is a gas reheater that reheats the exhaust gas DI mixed with air in the air-gas mixer (2) by exchanging heat with steam (E).The exhaust gas aQ that has passed through the gas reheater (2) is It is said to be guided to the chimney (b).

In addition, 2) is a drain.

(2) is a coolant circulation pump that circulates caustic soda (5) in the gas scrubbing tower (to), and the caustic soda (5) is appropriately supplied from the caustic soda pump (6) to the middle of the circulation path. ing. Further, the structure is such that the caustic soda (5) is appropriately drawn out from the middle of the circulation path and guided to the smoke cleaning exhaust material processing device. Nori is a drainage pump that draws out caustic soda (5) from the bottom of the gas scrubbing tower (to), and e is a liquid cyclone that separates the caustic soda (5) supplied from the drainage pump (81) into solid and liquid, and performs separation and regeneration. Caustic soda (
5) is returned to the cooling section (to) of the gas cleaning tower (to), and the waste material is guided to the smoke washing waste material processing device.

In wet smoke cleaning equipment with such a configuration, a gas cleaning tower (
By supplying caustic soda (5) containing thiourea (2) and cuprous chloride (3) to
1 dehydrochlorination and desulfurization oxides can be carried out,
At the same time, more than 90% of gaseous mercury can be removed.

Next, this will be specifically explained based on two experimental examples.

FIG. 2 shows the test equipment used in the first experiment (indoor test). In the figure, (8→ is an absorption bottle, (80 is a circulation line for gaseous mercury generated in the absorption bottle), and in the middle of the circulation line (86) there is a first switching cock, a desiccant ), absorption cell (88), diaphragm pump (
89), second switching hook (hooks are provided in order).

(4υ is a spectrometer installed on the - side of the absorption cell (38), (6) is its recorder, and (to) is a mercury lamp installed on the other side of the absorption cell (88). That is, This test device uses an atomic absorption spectrometry device using the reductive vaporization method.

In such a test device, first, an absorption bottle (goods) is used.
mercuric chloride solution (o, ooo5q as mercury)
, then add the stannous chloride solution and immediately operate the diaphragm pump φ. Then, the mercury ions in the water are reduced and vaporized by the soot chloride to metallic mercury, which circulates through the circulation line as gaseous mercury.

Therefore, while watching the recorder (6), when the reduction had sufficiently progressed, the gaseous mercury was switched to an absorption bottle containing various absorption liquids using the switching cock +aft (40), and the mercury was absorbed. As shown in the laboratory test results in Table 1, the type of absorption liquid was determined by combining the denitrification agent with thiourea and other ingredients (neutral pH), and absorption with pure water and potassium permanganate-sulfuric acid solution. compared with the rate. Note that the potassium permanganate-sulfuric acid solution is an absorption liquid used in the analysis of gaseous mercury, and is said to have an absorption efficiency of 100%.

The following can be inferred from this test result.

(1) A solution in which thiourea and copper coexist is effective in removing mercury.

(2) Thiourea alone has poor mercury absorption compared to pure water.

(3) In a solution in which thiourea and iron coexist, it is about the same as in the case of pure water.

Table 1 Note 1) Heating treatment at 65-70℃ is heated to 80℃ to the same temperature as on-site.
Warmed for minutes. The absorption test was conducted after cooling to avoid the influence of water vapor on the mercury measuring device (raw water absorption spectrometer needle).

Note 2) The absorption rate of gaseous mercury was calculated using the peak height on the recording paper after 8 minutes as the treated gas mercury concentration.

FIG. 8 shows the test equipment used in the second experiment (outdoor test). In the figure, ■ is the exhaust gas from the garbage incinerator ■ (
46) a cooling tower fed through a pump (4'l);
(2) is supplied with exhaust gas from the cooling tower (a circulation pump that circulates sodium hydroxide (NaOH) or calcium carbonate (CaC03) (49) from the cooling tower). (Hydrogen chloride, sulfur oxide from 4ψ.

An absorption tower for absorbing mercury fume, (51) is the absorption tower -
A circulation pump that circulates calcium carbonate φ to which thiourea and cuprous chloride have been added;
The exhaust gas (46) that has passed through the reheater is guided to the chimney (b). In other words, this test device adds thiourea and cuprous chloride to a caustic soda tank for gas cooling and gas absorption liquid replenishment in conventional wet smoke cleaning equipment.
46) It is intended to remove gaseous mercury in.

In addition, in the figure, <A><B><C><D><E> indicate measurement points, respectively.

In such a test device, the exhaust gas @ 6) is humidified and cooled in the cooling tower (→), and hydrogen chloride is dissolved and absorbed by sodium hydroxide or calcium carbonate (49). Plus hydrogen chloride.

Sulfur oxides and mercury fume are absorbed. Table 2 shows the results of this test.

The following results were obtained from this test.

(1) Mercury removal rate of the entire device 86.6-99.5%
(2) Equipment outlet (7) Mercury concentration 0.002 to 0.08
1J/Nm (3) Mercury removal rate in cooling tower 71.8-9
4.296(4) Mercury removal rate in absorption tower 62.2~9
7.9% (5) Cooling tower absorbent NaOH and CaCO3
There is almost no difference in the mercury removal rate.

(6) Circulation amount in cooling tower and absorption tower There is almost no difference in the mercury removal rate depending on the amount of circulation.

(7) Concentration of thiourea (SC(Nl2)+) There is almost no difference in the mercury removal rate depending on the concentration.

(8) Number of leakage stages of absorption tower There is almost no difference in the mercury removal rate depending on the number of stages.

Therefore, considering the results of the first and second experiments together, it can be seen that in the second experiment, the mercury removal rate was about 90% or more,
The mercury concentration at the device outlet is 0. Since a treatment result of O8fEf/Nd or less was obtained, it is thought that a solution in which thiourea and copper coexist is effective in absorbing and removing gaseous mercury. A solution containing copper is considered to be effective in removing gaseous mercury.

In addition, although the exhaust gas has been explained by taking as an example the exhaust gas from a garbage incinerator, it is clear that similar results can be obtained with the exhaust gas from an industrial waste incinerator.

That is, the method of the present invention can be widely applied to wet smoke cleaning equipment for mercury-containing exhaust gas.

Effects of the Invention According to the present invention, about 90% or more of gaseous mercury in the exhaust gas (in the dust core gas) can be removed at the same time as dehydrochlorination (HCI) and desulfurization oxides (SOx).

[Brief explanation of the drawing]

Figure 1 is a flow diagram of wet smoke cleaning equipment for applying the method of the present invention, Figure 2 is a flow diagram of the test equipment used in the first experiment, and Figure 8 is a flow diagram of the test equipment used in the second experiment. It is a flow diagram. (2)...thiourea, (3)...cuprous chloride, (5
N...Caustic soda, bales Q...Incinerator exhaust gas agent Yoshihiro Morimoto

Claims (1)

[Claims] 1. A method for removing gaseous mercury using wet smoke scrubbing equipment, which is characterized by wet scrubbing exhaust gas with an alkaline solution containing thiourea and cuprous chloride.