JPS6094138A - Adsorbent for removing mercury and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an adsorbent adsorbing mercury traces contained in a waste gas and waste water by providing the condition that sulphuric acid or sulfur oxide and vapor are adsorbed to an activated carbon. CONSTITUTION:After a waste gas produced in a combustion furnace 1 is desulfurized by an SO2 adsorption tower 2 via a flue 7 of the waste gas, said gas is discharged from a stack 5 via a flue 8 of the desulfurized gas to the atmosphere. The adsorbent adsorbed SO2 is conveyed to an SO2 desulfurized tower 3 through a conveying path 9 of the used adsorbent and is heated to produce concd. gaseous SO2 and is regenerated. The regenerated adsorbent is returned from the tower 3 to the tower 2 and is reutilized to desulfurize the waste gas, but the adsorbent subjected to abrasion and pulverization is drawn out on the way, and the pulverized carbon is used as an adsorbent of mercury.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adsorbent for removing mercury and a method for producing the same.
In particular, the present invention relates to an adsorption solution made of carbonaceous solid suitable for adsorbing and removing trace amounts of mercury in exhaust gas and wastewater.

Mercury has long been used in agricultural chemicals, medicine, metal processing, etc., but in recent years, as the harms of mercury have become clearer, its use and emissions have been regulated. Currently, mercury in wastewater is regulated to be removed until it is undetectable, but there are technical problems with mercury in exhaust gas, such as removal methods and analysis methods.
Regulations are delayed compared to wastewater, and zinc! ! A device for removing mercury from exhaust gas is installed only in cases where high concentrations and large amounts of mercury are generated, such as in salt processing factories and salt electrolysis.
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However, even in general industry, water 6! When coal with a high content is used, there is a possibility that mercury will be emitted along with the exhaust gas, so a device for removing mercury will be required. In other words, it is now becoming clear that inorganic mercury in the natural world is becoming organic and accumulating in living things, albeit in minute amounts compared to these measuring instruments, and in some situations it may be regulated, and devices to remove mercury from exhaust gas may become necessary in the future. Conceivable.

Conventionally, devices for removing mercury from exhaust gas have used cleaning with water, sulfuric acid, etc. in the case of high concentrations of mercury, and adsorption with activated carbon in the case of low concentrations. In order to reduce the mercury in exhaust gas to 1 ppm or less, activated carbon must be used. However, this method of using activated carbon has the following problems.

In other words, manufacturing activated carbon requires a large amount of heat and labor;
υ1 Gas treatment G It is impossible to use a large amount of activated carbon adsorbent due to cost considerations, and activated carbon for gas treatment cannot adsorb a large amount of mercury unless it is specially processed. Processing methods for increasing the amount of mercury adsorbed on activated carbon include a method of adding chlorine, potassium iodide, etc. to the activated carbon in advance, and a method of oxidizing the surface of the activated carbon with a liquid such as nitric acid.

However, these processing processes are complicated and may also cause secondary pollution.

The object of the present invention is to provide an adsorbent for mercury removal that eliminates the disadvantages of activated carbon mentioned above, does not require special processing, is easily available and inexpensive, and has excellent mercury adsorption performance, and a method for producing the same. It is in.

The present invention is an adsorbent for removing mercury whose main component is a porous carbonaceous solid that repeatedly adsorbs and desorbs sulfur oxides, resulting in decreased adsorption performance. In the present invention, waste adsorbent periodically generated in a sulfur recovery type desulfurization device for boiler exhaust gas is preferably utilized as the mercury adsorbent.

As a result of examining activated carbon used in sulfur recovery type desulfurization equipment, the inventor found that the adsorption performance of sulfur oxides decreased due to repeated use in desulfurization. The present invention was developed based on the finding that the oxide is the same as the oxide produced when the mercury is used, and that it promotes the adsorption of mercury.

Hereinafter, the history and basis of the present invention will be explained based on experimental results.

Activated carbon was repeatedly used to desulfurize exhaust gas containing sulfur oxides, and its mercury adsorption performance and other properties were measured before and after.

That is, sulfur dioxide (hereinafter represented by the molecular formula SO2) was produced under conditions not shown in Table 1 for activated reconstitution prepared using bituminous coal as a raw material through the steps of carbonization and steam activation.

) adsorption and desorption were repeated 20 times, and then the temperature was increased to 45
(Heat at +'C for 30 minutes to completely eliminate SO2.

The mercury adsorption fib, SO2 adsorption performance, oxygen source Table 1 collection amount in the activated carbon, and p■-■ value of the activated carbon-water slurry of the sample (activated carbon B) produced in this way were measured. The mercury adsorption performance is based on the inner diameter of 0.3g sample
The amount of mercury adsorbed in the sample and the SO2 adsorption performance after filling a glass tube of 011I11 and flowing 500 ml of nitrogen gas containing 0.02 VO]% of mercury vapor at 1 N/min for 12 hours while maintaining it at an arbitrary temperature. , Analysis value of 502 in activated carbon after treatment under the adsorption conditions shown in Table 1, Activated carbon -
The pH value of the water slurry was determined as the Op H value of a slurry prepared by pulverizing a sample to 200 mesh or less and adding distilled water.

Table 2 shows the measurement results of the sample before and after adsorption and desorption treatment.

From the results shown in Table 2 below, it is clear that by repeating SO2 adsorption and desorption, the amount of SO2 adsorbed by activated carbon decreases, but on the contrary, the amount of mercury adsorbed increases.

It was also observed that the amount of mercury adsorbed decreased as the temperature increased, and that mercury was no longer adsorbed when the temperature exceeded 200°C.

Furthermore, from Table 2, as the amount of oxygen element in the adsorbent increases, the pH
It can be seen that the value is acidic. This is considered to be because the repeated S02 adsorption/desorption process produced acidic oxides on the surface of the activated carbon that improve the mercury adsorption performance, similar to the liquid phase oxidation process using nitric acid or the like.

Next, we investigated at what point during SO2 adsorption and desorption the surface oxides of activated carbon are generated. The test was carried out in Example 1.
The activated carbon immediately after the first SO2 adsorption treatment was collected, and the amount of oxygen in the activated carbon after sulfur oxides were extracted by water washing.
#I elementary element amount in activated carbon after heating at 00°C for 6 hours,
And the amount of oxygen element in the activated carbon immediately after the first S02 desorption treatment was analyzed. As a result, an increase in the amount of oxygen element was observed only in activated carbon immediately after S02 desorption. From this, the oxygen compounds on the activated carbon surface are S02 and 02 in the gas, H2C
It is thought that it is generated when H2SO4 accumulated in the adsorbent is desorbed. Estimating these reactions is as follows. Here, A and C indicate activated carbon bodies.

When S02 is adsorbed: SO2→-□0□+■(20 When S02 is desorbed: H2so4+71.,C・□C 1toA−C H2SO4toA,C−C −1−−−−−−−−・A, C-C-○+S○21+
+-+207 (oxygen compounds on the surface of activated carbon) The temperature at which S02 is adsorbed on activated carbon and sulfuric acid is produced is 20
0℃ or below, and the temperature at which sulfuric acid is desorbed is 250℃)
, above. As a result of the test, the amount of acidic oxide produced when sulfuric acid is desorbed was determined at a heating rate of 2°C/min and 100°C/min.
The maximum heating temperature is 320℃ and 450℃.
It was found that it did not change with C, but was determined simply by the amount of sulfuric acid released.

The acidic oxide thus generated dissociates from the activated carbon surface as CO as the temperature rises further. This tendency is negligible at 450℃, but at 600℃
If the temperature exceeds 600°, the desorption treatment temperature becomes significant.
It turns out that it needs to be C or lower.

From the above, in manufacturing the adsorbent of the present invention, activated carbon (porous carbonaceous solid) is coated with sulfuric acid at a temperature of 200°C or less.
Alternatively, it has been found that it is necessary to adsorb sulfur oxides, oxygen, and steam, and then desorb sulfuric acid while heating at a temperature of 250 to 600°C.

The adsorbent of the present invention can be manufactured by a manufacturing method that satisfies the above-mentioned conditions, but in general, waste adsorbent used in a sulfur recovery type desulfurization device can be used as described below.

Hereinafter, the present invention will be specifically explained with reference to Examples. 1st
The figure shows the flow of a combustion exhaust gas desulfurization apparatus that produces an adsorbent for mercury removal as a by-product according to the present invention. This device adsorbs sulfur oxides in exhaust gas on activated carbon, then activates F1.
This is a device that heats J-charcoal to recover concentrated SO2 gas and converts it into sulfur (s). In Fig. 1, J and II gases generated in a furnace 1 that burns fossil fuels pass through a υF gas flue 7, are desulfurized in an SO2 adsorption tower 2, pass through a desulfurized gas flue 8, and enter the atmosphere from a chimney 5. is released. S.O.
The adsorbent that has adsorbed SO2 in the adsorption tower 2 is sent to the SO2 desorption tower 3 via a used adsorbent conveyance path 9, where it is heated, generates concentrated SO2 gas, and is regenerated. Concentrated SO2 gas tank S
It is sent to the recovery section 4, converted into S by a reduction process, and recovered. If mercury is included in the exhaust gas, mercury is also S.
It is 4-condensed by adsorption and desorption with O2, and when SO2 is converted to S, it becomes mercury sulfide, which is included as an impurity in the recovered S, so it can be separately recovered by sedimentation separation. The recycled adsorbent is removed from the SO2 desorption tower 3.
It is returned to the O2 adsorption tower 2 and used again for 1-NO-1 sulfur desulfurization, but during the process, worn and powdered adsorbent is extracted and new adsorbent is supplied. The adsorbent discharged from the SO2 desorption tower 3 is passed through an adsorbent sieve 4. It is sieved by a J-type machine 6, and the degree of pulverization is separated and taken out from the degree of pulverization extraction pipe 14. The degree of pulverization decreases due to repeated use of desulfurization, and much of the adsorbent is pulverized, resulting in a decrease in its SO2 adsorption performance and, conversely, an improvement in its mercury adsorption performance. If the desulfurization performance of the equipment decreases, it is not the degree of pulverization, but
The adsorbent is extracted from the oxidized carbon extraction pipe 15, and new adsorbent is supplied in the same amount from the new adsorbent supply pipe 13. In addition, in the figure, 10 is a regenerated adsorbent conveyance path, 11 is a concentrated S02 discharge pipe,
12 is a tail gas exhaust pipe.

In this way, adsorbents with reduced degree of pulverization and SO2 adsorption performance produced by sulfur recovery type desulfurization equipment have acidic oxides formed on their internal surfaces, and are used as adsorbents for excellent mercury removal from exhaust gas and wastewater. can do. In addition, in the desulfurization equipment shown in Figure 1, mercury in J-11 gas is also adsorbed and removed, and is finally separated and recovered as mercury sulfide precipitation in the recovered sulfur, so another mercury removal process is required. No equipment is required.

Therefore, the mercury removal method of the present invention is suitably used for exhaust gas or waste water from boilers and combustion furnaces that are not equipped with a desulfurization device that simultaneously adsorbs and removes mercury.

Figure 2 shows υ using the adsorbent for mercury removal according to the present invention.
1 shows a device for removing mercury in gas. In FIG. 2, exhaust gas generated in a combustion furnace 18 that burns coal containing mercury is washed/γ1 with an alkaline cleaning liquid in a cleaning tower 19.
Acidic components in the gas such as SO2 and HCI are removed, and mercury in the gas is also partially removed. The remaining mercury in the flue gas is adsorbed and removed by the adsorbent in the mercury adsorption tower 2o, and then transferred to the chimney 2o.
The adsorbent used in the mercury adsorption tower 20 is a waste adsorbent produced as a by-product in the sulfur recovery type desulfurization equipment, and is transported to the oxidized carbon feeder 17 by transportation means such as trucks and conveyors. The gas from which mercury has been removed in the mercury adsorption tower 2° is processed and discharged from the chimney 21 (11) through the flue 23. The cleaning tower 19 Some of the mercury that has migrated from the exhaust gas to the cleaning solution must be removed through wastewater treatment.

Of course, the cleaning fluid that has degraded and migrated to mercury after being used to clean the exhaust gas is cleaned through the extraction pipe 25 of the cleaning tower 19. & is extracted to the preparation device 27, where it is regenerated, and the cleaning liquid supply pipe 2
4 and returned to the washing tower 19 for reuse. A part of it is branched, subjected to neutralization treatment and oxidation treatment, and then discharged from the system through waste cleaning liquid discharge pipes 29 and 30. If this liquid still contains a trace amount of mercury, use the waste cleaning liquid drain pipe 2.
In the middle of step 9, the degree of pulverization for mercury removal is added from the degree of pulverization supply device 26, so that mercury can be adsorbed. At this time, the degree of pulverization after adsorption of mercury can be determined by sedimentation and separation in the sink pond 28. After being used for mercury adsorption, the adsorbent can be regenerated by desorbing concentrated mercury vapor by combustion.

According to this embodiment, mercury in the exhaust gas can be easily removed by using the degree of pulverization produced as a by-product in the sulfur recovery type desulfurization device as an adsorbent for mercury removal.

As described above, according to the present invention, it is possible to obtain an excellent adsorbent for removing mercury using carbonaceous solid as a raw material, and in particular, waste adsorbent generated in large quantities in dry desulfurization equipment for exhaust gas can be used as an adsorbent for removing mercury. As a result, an adsorbent for mercury can be obtained at low cost without requiring any special processing. Incidentally, the waste absorbent (LJ charcoal) from dry desulfurization equipment has conventionally been used for incineration, landfilling, etc., but the present invention is of great significance as it opens the way to its effective use.

[Brief explanation of the drawing]

FIG. 1 (J) is a flow diagram showing an example of a combustion furnace flue gas desulfurization apparatus for producing the adsorbent according to the present invention, and FIG. 2 is an example of an apparatus using the adsorbent according to the present invention to remove mercury from exhaust gas and waste water. It is a flow diagram showing the following.■, ... Combustion furnace, 2, ... SO2 adsorption tower, 3, ...
・S 02 desorption tower, 4,...S recovery section, 5,...chimney, 6,...adsorbent sifter, 7,...exhaust gas flue, 8,...desulfurization Processed gas flue, 9,... Spent adsorbent path, 10,... Regenerative adsorbent IN path, 11,...
・Concentrated SO2 discharge pipe, 12, ・Tail gas discharge pipe, 1
3,... New adsorbent supply pipe, 14,... Powdered coal extraction pipe, 15,... Oxidized carbon extraction pipe, 16,... Recovery S extraction pipe, 17,... Oxidized carbon feeder, 1B, ... combustion furnace,
19,...shoulder/? Tower, 20, ... Mercury adsorption tower, 21
,...chimney, 22,...exhaust gas flue, 23,...
Processing gas flue, 24,...Cleaning liquid supply pipe, 25,...
・Cleaning liquid extraction pipe, 26,... Powdered charcoal supply device, 27, ・
...Washing liquid preparation device, 2B, ...Sedimentation tank, 29, ...Waste washing liquid discharge pipe, 30, ...Drain pipe. Agent Patent Attorney Nagare Kawakita

Claims (3)

[Claims] (1) An adsorbent for mercury removal whose main component is a porous carbonaceous solid that repeatedly adsorbs and desorbs sulfur oxides, resulting in decreased adsorption performance. (2) A gas containing sulfur oxide, oxygen, and water vapor and/or sulfuric acid are adsorbed onto a porous carbonaceous solid at a temperature of 200°C or less, and then heated to a temperature of 250 to 600°C. ; A method for producing an adsorbent for removing mercury, which is characterized by causing the adsorbent to be desorbed from the heart. (3) In claim (2), the carbonaceous solid adsorbent that has adsorbed the gas and/or sulfuric acid is a waste adsorbent that has been used in a sulfur recovery type desulfurization device and has decreased adsorption performance for sulfur oxides. A method for producing an adsorbent for removing mercury, characterized by the following.