CN100346865C - Method for removing mercury for flue gas by using sulfo-halogen compound-supported modified adsorbent - Google Patents

Abstract

The present invention relates to a method for removing mercury in smoke gas by modified adsorption agents which contain sulfo-halogen compounds. Compounds which contain sulfur atoms and halogen atoms or precursors thereof are used as modifiers which are used for the load modification of adsorption agents, surface mercury absorption characteristics of the adsorption agents are changed, weight percentage of load capacity of sulfo-halogen compounds on the adsorption agents is from 0.01 to 10%, modified adsorption agents are filled or directly sprayed into smoke gas and contact the smoke gas, and the modified adsorption agents are directly used for removing mercury in the smoke gas. The capacity of adsorbing simple substance mercury in the smoke gas of the modified adsorption agents of the present invention is obviously increased, and adsorbed simple substance mercury is finally converted into stable mercury sulfide, and secondary pollution of the mercury is solved. Because the sulfo-halogen compounds can be easily loaded on the adsorption agents, the requirement of specific surface areas of the adsorption agents is low, and therefore, the selection range of the adsorption agents is widened, and modified fly ash or cheap inorganic substances can be used as adsorption agents for removing mercury.

Description

Method for removing mercury from flue gas by using sulfur-halogen compound-loaded modified adsorbent

technical field

The invention relates to a method for removing mercury from flue gas by using a sulfur-halogen compound-loaded modified adsorbent. By modifying the mercury-removing adsorbent, it can efficiently remove mercury in different forms in coal-fired flue gas, and It is converted into stable mercury sulfide, so as to achieve a more thorough treatment of mercury in flue gas.

Background technique

Mercury has strong physiological toxicity. Although its concentration in flue gas is low, its harm in the environment is quite serious. In March 2005, the United States officially promulgated the mercury emission control standard for thermal power plants, and other countries will also formally issue relevant standards. Due to the generally high mercury content in my country's coal combustion, and its huge coal consumption, my country has become the country with the most serious mercury pollution in the world. Therefore, it is very urgent to strengthen the control of mercury pollution in the process of coal combustion and waste incineration.

Mercury in flue gas mainly exists in three forms: particulate mercury (Hg ^p ), gaseous divalent mercury (Hg ²⁺ ) and gaseous elemental mercury (Hg ⁰ ). (mainly chlorine) content is very closely related, the lower the chlorine element, the higher the proportion of elemental mercury in the flue gas. Particulate mercury can generally be removed by dust removal devices; gaseous divalent mercury (mostly in the form of mercury compound vapor) is easily adsorbed by most adsorbents, or absorbed by wet desulfurization systems. However, elemental mercury is difficult to control. Even if the activated carbon flue gas injection (ACI) technology commonly used abroad is used, the removal effect of elemental mercury is not ideal, and the consumption of activated carbon is too high, which affects the reuse of fly ash. The use of wet desulfurization equipment can only remove divalent mercury in flue gas, but it has almost no removal effect on Hg ⁰ . Some people also try to use the catalytic oxidation method to oxidize the elemental mercury of Hg ⁰ in the flue gas, but because the sulfur dioxide in the flue gas has a poisonous effect on the catalyst, it is still difficult to find a catalyst that can be used stably for a long time, and this method requires additional A catalytic conversion unit increases the complexity and investment cost of the flue gas purification system, which is greatly limited in practical application.

In addition, some people try to use the recovery method to capture mercury in the flue gas, but it is difficult to realize because the mercury concentration in the flue gas is too low and the composition of the flue gas is too complex. In addition, in the mercury control methods currently explored, whether it is activated carbon adsorption or wet absorption, the mercury in the flue gas is directly transferred to the fly ash or desulfurization by-products, and the presence of mercury in these substances is not considered. safety and stability. In fact, most of the above-mentioned captured mercury exists in soluble mercury salts, which are easily leached by rainwater and cause secondary pollution and other problems.

In addition, in order to improve the adsorbent's ability to adsorb elemental mercury in flue gas, the adsorbent can be modified by using appropriate chemical treatment methods. Among them, the method of loading and modifying adsorbents with halogen molecules has attracted the most attention. However, if the adsorbent is directly modified with halogen molecules, although the chemical adsorption effect of the modified adsorbent on elemental mercury is better at low temperature, at a higher flue gas temperature (generally above 120°C), the adsorption The halogen molecules loaded on the agent are easy to lose, and the expected effect cannot be achieved. At the same time, the elemental mercury adsorbed on the adsorbent is oxidized into soluble mercury halides, and such compounds are easy to volatilize or be leached by water, causing secondary pollution. In addition, when using elemental sulfur (sulfur) as a load to modify the adsorbent, although the adsorbed elemental mercury can be converted into stable mercury sulfide, due to the poor reactivity of sulfur, the modified adsorbent The adsorption rate of elemental mercury is still too slow to meet the requirements of practical use.

Contents of the invention

The purpose of the present invention is to address the shortcomings of the existing mercury pollution control technology, and propose a method for removing mercury from flue gas by using sulfur-halogen compound loaded modified adsorbent, which can significantly improve the adsorption effect of elemental mercury in flue gas and reduce the adsorption The amount of agent used can avoid secondary pollution to the environment.

In order to achieve this goal, in the technical solution of the present invention, a compound containing both sulfur and halogen atoms or its precursor is used as a modifying agent to carry out load modification on the adsorbent, so that the modified adsorbent can resist the pollutants in the flue gas. The adsorption capacity of elemental mercury is significantly improved, and the adsorbed mercury is finally converted into stable mercury sulfide. Firstly, the sulfur-halogen compound or its precursor is heated and vaporized, and then contacted with the adsorbent, so that the sulfur-halogen compound is loaded on the surface of the adsorbent in the form of adsorption, so that the surface mercury adsorption characteristics of the adsorbent are changed, and the sulfur-halogen compound is adsorbed. The weight percentage of the load is 0.01-10%, and the modified adsorbent is in contact with the flue gas in the form of filling or directly spraying into the flue gas, and is directly used for removing mercury from the flue gas.

The study found that the chemical modification of the adsorbent by using compounds containing both sulfur and halogen atoms (or its precursors) can combine the characteristics of halogen molecules and sulfur: it can quickly adsorb the elemental mercury in the flue gas to the improved On the active adsorbent, mercury can be converted into stable mercury sulfide. In addition, such substances are easily loaded on the adsorbent and are not easy to be lost at high temperatures. Moreover, some sulfur-halogen compounds themselves have high oxidation activity to elemental mercury. The oxidation of elemental mercury by sulfur halide compounds and the stabilization of mercury can be represented by the following two reactions:

Hg+S _m X _n (loaded on sorbent) → HgS, HgX ₂ (occurred on sorbent) (1)

HgX ₂ +S _m X _n (loaded on adsorbent)+H ₂ O (steam)→HgS+HX+others (2)

Wherein, S _m X _n represents a sulfur-halogen compound (m is the number of sulfur atoms in the molecule, generally 1-3; n is the number of halogen atoms, generally 2 or 4). In reaction (1), S _m X _n corresponds to the oxidative chemisorption of elemental mercury, forming HgS and HgX ₂ simultaneously. The reaction (2) is carried out in the presence of water vapor (such as flue gas or water vapor in natural air), S _m X _n reacts with water vapor to generate S ^2- and sulfur (also has a small amount of sulfate) , using S ^2- and sulfur to convert HgX ₂ into HgS.

It can be seen that if the adsorbent can be properly modified so that it can adsorb different forms of mercury and convert the adsorbed mercury into stable mercury sulfide, it is an ideal way to purify flue gas.

Method of the present invention is specifically as follows:

1. Using the sulfur halogen compound or the precursor of the sulfur halogen compound to carry out load modification on the adsorbent, so that the weight percentage of the sulfur halogen compound loading on the adsorbent is 0.01-10%. in,

a) When using sulfur halogen compounds for modification, the sulfur halogen compounds are heated and vaporized, and the gas flow containing the sulfur halogen compound vapors is quickly passed into an adsorption container equipped with an adsorbent, and the sulfur halogen compounds in the gas flow are passed through by continuous mixing. adsorbed on the adsorbent.

b) Carry out step-by-step modification with the precursor of the sulfur-halogen compound, first heat and vaporize the sulfur-containing precursor, so that the weight percentage of the sulfur loading on the adsorbent is within 5%; then heat and vaporize the halogen-containing precursor , so that it is loaded on the adsorbent containing sulfur, and the weight percentage of the loaded amount is also within 5%, and the sulfur and halogen precursors adsorbed on the adsorbent are converted into sulfur-halogen compounds through reaction.

2. Use the above-mentioned loaded modified adsorbent to adsorb mercury in the flue gas. The adsorbent is in contact with the flue gas in the form of filling or directly spraying into the flue gas, so that the elemental mercury and other forms of mercury in the flue gas are absorbed The modified adsorbent is adsorbed and gradually converted into mercury sulfide, so that the mercury in the flue gas can be completely removed. When the filling type is used, the thickness of the adsorbent filling layer is 1-200mm; when the form of direct spraying into the flue gas is adopted, the ratio of the volume of the adsorbent sprayed into the flue gas to the flue gas is 10-2000mg/m ³ .

The sulfur halogen compound described in the present invention is disulfur difluoride, sulfur difluoride, sulfur tetrafluoride, sulfur hexafluoride, disulfur dichloride, sulfur dichloride, sulfur tetrachloride, dibromide disulfide Sulfur, disulfur diiodide, one or more of them are used.

Among the precursors of sulfur-halogen compounds described in the present invention, the sulfur-containing precursors are sulfur, metal sulfides and polysulfides; Substances, such as hypochlorous acid, chlorine dioxide, bromine dioxide, hypochlorous acid, hypobromous acid, halogen acid, perhalogen acid, etc.; use one or more of them.

The adsorbent of the present invention includes coal-fired fly ash, different types of activated carbon, ceramic-carbon composite material, ceramic material, clay, bauxite, sepiolite, volcanic rock ash, etc., and one or more of them are used.

The features of the present invention are:

1) After the adsorbent is loaded and modified by this method, the adsorption capacity and adsorption rate of elemental mercury are significantly increased, and the amount of adsorbent used in the flue gas treatment process is significantly reduced;

2) Quickly oxidize the adsorbed elemental mercury and finally form stable mercury sulfide, reducing the possibility of secondary pollution to the environment;

3) The sulfur-halogen compound used is relatively easy to be loaded on the adsorbent, and the specific surface area of the adsorbent is not required to be high, so that the selection range of the adsorbent is widened, and the modified fly ash or cheap inorganic substances can be used as Mercury removal sorbent.

Description of drawings

Figure 1 is a diagram showing the effect of adsorption and removal of elemental mercury by using different activated carbons in Example 1.

In Fig. 1, 1 ^# : adsorption curve of elemental mercury by activated carbon modified by disulfur dichloride; 2 ^# : adsorption curve of elemental mercury by activated carbon modified by sulfur; 0 ^# : adsorption curve of elemental mercury by unmodified activated carbon Mercury adsorption curve.

Detailed ways

The technical solution of the present invention will be further described below through specific examples. The following examples are not intended to limit the present invention.

Embodiment 1 (activated carbon supported disulfur dichloride)

Loading method: take 5 mL of disulfur dichloride (analytical purity, >98%), and put it into a 50 mL glass vaporizer. Immerse 2/3 of the volume of the vaporizer in an oil bath, and use the oil bath to control the temperature of the vaporizer. In addition, 100 g of activated carbon with a particle size of 100-120 mesh was weighed, and it was placed in a three-necked flask with a volume of 500 mL as an adsorption bottle. One port of the flask is used to install the stirrer, and the other two ports are respectively used as the inlet and outlet of sulfur dichloride vapor. Connect the gas outlet of the vaporizer bottle to the gas inlet of the adsorption bottle.

Turn on the heating power of the oil bath to keep the temperature of the vaporizing bottle at about 120°C, disulfur dichloride is continuously evaporated and vaporized, and its vapor is introduced into the adsorption bottle. The stirrer in the adsorption bottle continuously stirs the activated carbon at a speed of 100 rpm, so that it can be well mixed with disulfur dichloride vapor and quickly absorbed by the activated carbon. When the adsorption time is 10 minutes, the loading rate of disulfide dichloride on activated carbon is about 1%.

Stop heating the vaporizing bottle, and use the activated carbon loaded with disulfur dichloride to carry out the adsorption experiment of elemental mercury, and compare it with the activated carbon without loaded disulfur dichloride. The method is as follows:

Weigh 0.02 g of activated carbon with a disulfide dichloride loading rate of 1%, put it into a U-shaped glass tube with a diameter of 6 mm and a length of 100 mm, and plug both ends with quartz wool to form an activated carbon adsorption layer. The thickness of the activated carbon adsorption layer is It is about 2mm; it is heated by an oil bath heating device, and the temperature of the adsorption layer is controlled at 140°C. Mercury-containing simulated exhaust gas was prepared by using mercury permeation tube and flowing air, so that the concentration of elemental mercury in the gas was 90 μg/m ³ . When the air flow continuously passes through the activated carbon adsorption layer at a flow rate of 200ml/min, the concentration of elemental mercury in the adsorbed gas is measured to determine the removal effect of the adsorption layer on elemental mercury. Similarly, a comparative experiment was also carried out using activated carbon not loaded with sulfur halogen compounds and activated carbon loaded with 1% sulfur, and the amount of activated carbon used was 0.02 g. When the temperature of the adsorption layer is 140°C, the adsorption results of different activated carbons for elemental mercury in the gas stream are shown in Figure 1.

It can be seen from Figure 1 that the activated carbon (1 ^# ) loaded with disulfide dichloride has the best adsorption effect on elemental mercury, and the removal rate of elemental mercury has remained above 90% within 50 minutes after the start of adsorption. The effect of activated carbon (0 ^# ) not loaded with other substances is very poor. When the adsorption time is 10 minutes, the removal efficiency of elemental mercury drops to about 20%. Although the adsorption performance of activated carbon loaded with sulfur (2 ^# ) was slightly improved, the effect was much lower than that of activated carbon loaded with disulfur dichloride.

Example 2

Using a loading method similar to that of Example 1, disulfur dibromide was vaporized at 200° C., and the activated carbon powder was fumigated and loaded with its steam, so that the loading of dibromide on the activated carbon was about 0.5%. 0.02g of activated carbon was weighed as an adsorbent, and the main experimental conditions were the same as in Example 1 for the adsorption experiment of mercury-containing gas.

It was found that activated carbon loaded with disulfur dibromide had a better adsorption effect on elemental mercury. When the adsorption time was 100 minutes, the removal rate of elemental mercury was still above 92%.

Example 3

Using a loading method similar to that of Example 1, sulfur and disulfur dibromide were vaporized at a temperature of 200° C., and loaded on different coal-fired fly ash, respectively, with a loading amount of about 0.5%. Weigh 0.1 g of the modified adsorbent respectively, so that the thickness of the adsorption layer is about 2 mm. The adsorption experiment conditions of mercury-containing gas are also the same as in Example 1.

It was found that the fly ash loaded with disulfide dibromide had a better adsorption effect on elemental mercury. When the adsorption time was 30 minutes, the removal rate of elemental mercury was still above 85%. And under the same situation, when using the fly ash loaded with sulfur or the fly ash not loaded with any substance, the adsorption effect on elemental mercury is very poor. When the adsorption time is 5 minutes, the removal rate of elemental mercury drops below 20%. .

Embodiment 4 (precursor loading)

A method similar to that of Example 1 was adopted, but the load substances used were sulfur and bromine, the precursors of sulfur chlorobromine compounds. First, sulfur is vaporized at 200°C, and it is loaded on the fly ash by fumigation, so that the sulfur load on the fly ash is about 0.5%; then, elemental bromine is vaporized at a temperature of 40°C, and the sulfur loaded The fly ash is fumigated to load about 1% bromine. It was found that elemental bromine was easily adsorbed on the fly ash loaded with sulfur, and reacted quickly to form disulfur dibromide. However, fly ash not loaded with sulfur has a weak adsorption capacity for elemental bromine, and it will be lost quickly when the temperature is slightly higher.

Weighed 0.1 g of the above-mentioned modified fly ash, and carried out an adsorption experiment on mercury-containing gas, and the experimental conditions were also the same as in Example 1 (the thickness of the filling layer was 2 mm). The results found that when sulfur and elemental bromine were used as precursors for step-by-step modification, the modified fly ash also showed a good adsorption effect on elemental mercury. When the adsorption time was 30 minutes, the removal rate of elemental mercury Around 85%.

Example 5

The experiment was carried out in a simulated flue gas duct. A glass tube with an inner diameter of 30mm and a length of 500mm was placed vertically, and the temperature was kept at 150°C by electric heating. It is configured to simulate mercury-containing flue gas, so that the concentration of elemental mercury in the gas flow is about 55 μg/m ³ , and the gas flow flows through the glass tube from top to bottom. The average flow rate of the gas flow is 10m ³ /h. A small Cyclone.

Adopting the method similar to embodiment 1 to obtain disulfur chloride loading is 1% gac 500g; Modified gac is sprayed in the glass tube from the top of glass tube with the feed rate of 2g/h (the content of gac in the air-flow The ratio to the gas volume is 200mg/m ³ ), so that it is quickly mixed with the airflow, and the activated carbon flowing out from the lower part of the glass tube with the airflow is removed by the cyclone dust collector.

The concentration of elemental mercury in the airflow entering and exiting the glass tube under the above conditions was measured, and the results showed that activated carbon modified with disulfide dichloride had a high adsorption efficiency for elemental mercury, averaging over 90%. However, the removal efficiency of elemental mercury was less than 30% under the same operating conditions when activated carbon without disulfur dichloride was used.

Example 6

Using a method similar to that of Example 1, disulfur dibromide was vaporized at a temperature of 200° C. and loaded on coal-burning fly ash, and the loadings were all about 0.5%. The preparation conditions of simulated flue gas are the same as in Example 5.

Spray the fly ash loaded with disulfur dibromide into the glass tube from the upper part of the glass tube at a feed rate of 6g/h (the ratio of the content of the fly ash in the airflow to the volume of the gas is 600mg/m ³ ), so that it can quickly and The airflow is mixed, and the activated carbon flowing out from the lower part of the glass tube with the airflow is removed by the cyclone dust collector.

The concentration of elemental mercury in the airflow entering and exiting the glass tube under the above conditions was measured, and the results showed that the fly ash modified with disulfide dibromide had a high adsorption efficiency for elemental mercury, averaging above 85%.

Example 7

Based on Examples 1-6, the chemical conversion products of elemental mercury adsorbed by the adsorbent were analyzed, and the mercury-containing products in the adsorbent were leached and analyzed by ethanol and concentrated sodium sulfide solution respectively. It was found that more than 60% of elemental mercury can be converted into mercury sulfide by disulfur dichloride or disulfur dibromide loaded on the fly ash, and the rest is mercury chloride or mercury bromide. Good stabilizing transformation. When the above adsorbent is placed in natural air (relative humidity 30%-60%) for 2 days, the conversion rate of mercury sulfide is greater than 70%.

Claims (4)

1. A method for removing mercury from flue gas by using a sulfur-halogen compound-loaded modified adsorbent, characterized in that it comprises the following steps: 1) modifying the adsorbent by using a sulfur halogen compound or a precursor of a sulfur halogen compound, so that the weight percentage of the sulfur halogen compound loading on the adsorbent is 0.01-10%; wherein, a) modifying the adsorbent by using a sulfur halogen compound When the sulfur-halogen compound is heated and vaporized, the airflow containing the sulfur-halogen compound vapor is flowed into the adsorption container equipped with an adsorbent, and through continuous mixing, the sulfur-halogen compound in the airflow is loaded on the adsorbent by adsorption; b ) is carried out step by step when using the precursor of the sulfur-halogen compound to carry out the modification, first heating and vaporizing the sulfur-containing precursor, so that the weight percentage of the sulfur loading on the adsorbent is within 5%; then heating and vaporizing the halogen-containing precursor, Make it loaded on the adsorbent containing sulfur, the percentage by weight of the loaded amount is also within 5%, and the sulfur and halogen precursors adsorbed on the adsorbent are converted into sulfur halogen compounds through reaction; 2) Use the above-mentioned loaded modified adsorbent to adsorb mercury in the flue gas, and the adsorbent contacts the flue gas in the form of filling or directly spraying into the flue gas, so that the elemental mercury in the flue gas is adsorbed by the modified adsorbent , and gradually converted into mercury sulfide, so that the mercury in the flue gas is removed; when the filling type is used, the thickness of the adsorbent filling layer is 1-200mm; when the form of direct injection into the flue gas is used, the mercury injected into the flue gas The volume ratio of adsorbent to flue gas is 10-2000 mg/m ³ . 2. The method for removing mercury from flue gas by using sulfur-halogen compound loaded modified adsorbent according to claim 1, characterized in that said sulfur-halogen compound is disulfur difluoride, sulfur difluoride, sulfur tetrafluoride, hexafluoride One or more of sulfur fluoride, disulfur dichloride, sulfur dichloride, sulfur tetrachloride, disulfur dibromide, and disulfur diiodide is used. 3. The method for removing mercury from flue gas by using sulfur-halogen compound-loaded modified adsorbent according to claim 1, characterized in that the sulfur-containing precursors of the sulfur-halogen compound are sulfur, metal sulfides and polysulfides, wherein one or more; the halogen-containing precursor of the sulfur-halogen compound is a simple substance of fluorine, chlorine, bromine, iodine or an oxide with a valence above zero, including hypochlorous acid, chlorine dioxide, bromine dioxide, hypochlorous acid One or more of chloric acid, hypobromous acid, halogen acid, and perhalogen acid are used. 4. The method for removing mercury from flue gas by using sulfur-halogen compound-loaded modified adsorbent according to claim 1, characterized in that the adsorbent is coal-fired fly ash, activated carbon, ceramic-carbon composite material, ceramic material, clay, Bauxite, sepiolite, volcanic rock ash, adopt one or more of them.

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