JPH1170315A - Treatment of high temperature gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating high temperature gas in which activated carbon hard to cause dust explosion is used. SOLUTION: Powdery activated carbon, in which total oxygen amount calculated from pyrolysis gas at 950 deg.C is 1.5 wt.% and amount of ash content is not less than 15 wt.%, is used in a method for treating high temperature gas suitable for treatment of exhaust gas of an incinerator in particular. Various kinds of materials such as botanical wood, sawdust, coconut shell, pulp waste liquid, fossil fuel-based coal, petroleum heavy oil or coal/petroleum pitch obtained by thermally cracking them, a synthetic polymer, phenol resin, furan resin, polyvinyl chloride resin, polyvinyliden chloride resin, plastic waste and a waste tire are used as the raw material of activated carbon. A method for producing activated carbon from these raw materials differs by the raw materials. Such a method is cited that in general, firstly the raw material is pulverized and then granulated to uniformly carbonize it and thereby pellets of uniform size are produced, carbonized and activated and thereafter again pulverized. When amount of ash content in the obtained activated carbon is insufficient, the raw material is pulverized and thereafter inorganic oxide is added and the mixture is granulated and carbonized. Alumina, silica and iron oxide or the like are favorable as the used inorganic oxide at this time from a point of safety.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating high-temperature gas for removing harmful substances such as dioxins contained in high-temperature exhaust gas generated from incinerators such as municipal waste using activated carbon. The present invention relates to a method for safely processing hot gas without danger of ignition or explosion.

[0002]

2. Description of the Related Art Toxic substances in exhaust gas generated when incinerators such as municipal waste and industrial waste are incinerated include acid gases such as hydrogen chloride and sulfur oxides, heavy metals such as mercury, and highly toxic dioxins. And controlling dioxin emissions is becoming a global problem.

[0003] The dioxin formation reaction in the incineration process is complicated and has not been elucidated yet, but the precursor generated by the combustion of chlorine-containing waste undergoes a resynthesis reaction in the exhaust gas cooling process to form dioxins. It is believed that. The most effective method for removing the generated dioxins is adsorption removal with activated carbon, and treatment with activated carbon has the advantage that many harmful substances such as mercury can be removed in addition to dioxin.

[0004] Exhaust gas treatment by activated carbon can be roughly divided into two methods. One is a method of spraying activated carbon powder into a flue and collecting and discharging activated carbon adsorbing harmful substances with fly ash together with fly ash.The other is installing a separate adsorption tower filled with granular activated carbon, This method is installed downstream of a dust collector to adsorb and remove harmful substances.The former method is particularly used in ordinary incineration plants to remove acidic gases such as hydrogen chloride and sulfur oxides. Since equipment similar to the equipment for spraying slaked lime powder can be used, there is a great advantage in terms of equipment, and many existing incineration plants are introducing this method.

[0005]

The high-temperature gas treatment method using powdered activated carbon as described above has the advantages of high harmful substance removal efficiency and simple equipment, but on the other hand, combustible in high-temperature gas. Because it will blow fine powder of nature,
There is a risk of a dust explosion in the flue or a fire accident during discharge from the dust collector.

[0006] In the event of such an explosion or ignition accident, incinerated ash or activated carbon containing a large amount of harmful substances may scatter around and cause serious environmental pollution.
Although studies are being made on lowering the temperature of exhaust gas and dust collectors, there is a limit to lowering the temperature due to the problem of the dew point of the exhaust gas. Therefore, there has been a demand for a method of treating high-temperature gas using powdered activated carbon, which is less likely to cause a dust explosion or an ignition accident and which can be safely treated. SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides a method for treating high-temperature gas using powdered activated carbon which is less likely to cause a dust explosion and a fire accident, is safe and has a high treatment efficiency.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the invention having the following structure has been reached. The method for treating a high-temperature gas according to the present invention is characterized by using powdered activated carbon having a total oxygen content of 1.5 wt% or less and an ash content of 15 wt% or more calculated from a pyrolysis gas at 950 ° C.

Hereinafter, the present invention will be described in detail. The ignition mechanism of activated carbon is considered as follows. When the activated carbon is heated in the presence of oxygen, carbon atoms on the surface of the activated carbon are oxidized, releasing oxidation heat and forming an oxygen-containing functional group. At this time, not all carbon atoms on the activated carbon surface are oxidized uniformly, but carbon atoms existing at so-called active sites are preferentially oxidized. Further, when the temperature rises, the formed oxygen-containing functional group is eliminated from the activated carbon surface as carbon monoxide or carbon dioxide, and a new oxygen-containing functional group is formed. The reaction surface propagates through the activated carbon while repeating the process of generating and desorbing the oxygen-containing functional groups, and when the amount of heat of oxidation accompanying this exceeds the amount of heat released, the temperature rises spontaneously and the oxidation rate rapidly increases. Increases, leading to ignition. Further, in the state where the activated carbon powder is suspended in the gas, the reaction proceeds more violently and may cause a dust explosion due to a large supply amount of oxygen to the activated carbon.

In order to suppress such ignition or explosion and to safely process high-temperature gas, activated carbon in which oxygen-containing functional groups are easily formed is small, and the activated carbon is not easily propagated in the activated carbon. It is effective to use. The amount of active sites on the activated carbon surface corresponds to the amount of oxygen-containing functional groups present on the activated carbon surface. The amount of surface oxygen-containing functional groups can be determined from the total amount of oxygen calculated from the pyrolysis gas of activated carbon at 950 ° C. To use activated carbon with few active points, select activated carbon with few oxygen-containing functional groups. It is necessary to. In addition, it is considered that ash in activated carbon is effective for suppressing propagation of the oxidation reaction surface. From these viewpoints, the properties and ignition characteristics of various powdered activated carbons were examined. As a result, the total oxygen content calculated from the pyrolysis gas at 950 ° C. was 1.5 wt% or less, and the ash content was 15 wt%. The present inventors have found that the risk of ignition of activated carbon can be suppressed by using the powdered activated carbon described above, and have reached the present invention.

As the raw material of the activated carbon used in the present invention, many carbonaceous substances can be considered. However, industrially, it is difficult to activate the raw material, the quality of the raw material, the price, the availability of the raw material in large quantities and stably, and the like. Is the selection condition. Raw materials include plant-based wood, sawdust, coconut shell, pulp waste liquid, fossil fuel-based coal, petroleum heavy oil, or thermally decomposed coal and petroleum pitch, synthetic polymers, phenolic resins, It is widely used for furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, plastic waste, and waste tire. The method of producing the activated carbon used in the present invention from these raw materials varies depending on the raw materials.In general, the raw materials are first powdered for uniform carbonization and then granulated to obtain pellets of uniform size. After carbonization and activation, and then powdering again. If the ash content of the obtained activated carbon becomes insufficient, the raw material may be powdered, and then the inorganic oxide may be added, followed by granulation and carbonization.
As the inorganic oxide used at this time, alumina, silica, iron oxide and the like are preferable from the viewpoint of safety. In this way, the ash content is 15 wt% or more, more preferably 15 wt%.
% To 50 wt% or less, it is possible to obtain activated carbon that is less likely to cause a dust explosion, without substantially reducing the adsorption capacity. Activation methods after carbonization are roughly classified into gas activation and chemical activation. In the gas activation method, chemical activation is chemical activation, whereas physical activation is also called physical activation, and the carbonized raw material is contact-reacted with steam, carbon dioxide, oxygen, and other oxidizing gases at high temperatures. This is a method for producing fine porous adsorbed carbon, and a method using steam is the mainstream industrially. The chemical activation method is a method in which a raw material is uniformly impregnated with an activating chemical, heated in an inert gas atmosphere, and a fine porous adsorbed carbon is produced by a dehydration and oxidation reaction of the chemical. The chemicals used include zinc chloride, phosphoric acid, sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate,
There are potassium sulfate, calcium carbonate and the like. The raw material and production method of the activated carbon used in the present invention are not particularly limited, and activated carbon produced by any raw material or method can be used in the present invention.

The particle size of the powdered activated carbon used in the present invention is not particularly limited, but is preferably 0.0
1 μm or more and 300 μm or less, more preferably 0.1 μm or less
It is preferable that the thickness be not less than μm and not more than 100 μm. This is because if the activated carbon is too fine, handling is troublesome, and even if harmful components are adsorbed at an angle, there is a possibility that it will be difficult to recover the harmful components thereafter. On the other hand, if the particle size is too large, the efficiency of adsorption is likely to decrease this time. The specific surface area of the powdered activated carbon used in the present invention is not particularly limited, but is preferably 100 m ² / g or more and 2000 m ² or more.
² / g or less, more preferably 300 m ² / g or more, 1
It is better to be 500 m ² / g or less.

The calculation of the total amount of oxygen from the pyrolysis gas at 950 ° C. can be performed by the following method. The activated carbon sample is placed in a quartz reaction tube, evacuated to 10 ^-2 mmHg, and the reaction tube is inserted into a furnace maintained at 950 ° C., and gas generated over 30 minutes is collected. The amounts of carbon monoxide and carbon dioxide in the gas are calculated from the amount of generated gas and the composition of the gas determined by gas chromatography. The amount of generated carbon monoxide and the amount of oxygen contained in carbon dioxide are calculated, the weight percentage with respect to the amount of activated carbon in the reaction tube is determined, and the total amount is calculated from the pyrolysis gas at 950 ° C. It is an essential requirement of the present invention that this be 1.5 wt% or less. It should be noted that if the amount of the activated carbon sample put in the reaction tube is too large, the thermal decomposition is not completed within the specified time and the total oxygen amount is estimated to be lower.

The ash content can be measured by the following method. Put the activated carbon sample in a magnetic crucible,
Heat at 15 ° C. for 5 hours or more. After cooling, the mass of the remaining ash is measured, and the weight percentage with respect to the amount of activated carbon put in the crucible is determined to be the ash content. It should be noted that if the amount of the activated carbon sample put in the crucible is too large, the incineration does not end within the specified time and the amount of ash is overestimated, so care must be taken. The method for treating a high-temperature gas in the present invention is performed by bringing the above-mentioned activated carbon into contact with a high-temperature gas, particularly a high-temperature gas of 150 ° C. or higher. The method of contact is not particularly limited, but when used in an incinerator, it is preferable to spray it on a flue.

[0014]

The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Using three different types of coal as starting materials, three types of powdered activated carbon were produced by a steam activation method (Examples 1 to 3), and their properties and ignition characteristics were measured. Table 1 shows the results. In addition, in order to examine the performance of removing harmful substances, each activated carbon powder was sprayed into the exhaust gas of an incinerator, and the dioxin concentrations in front of the activated carbon spray port and at the bag filter outlet were measured, and the results were shown.

[0015] The specific surface area was measured using a "SORPOMATIC 2100" manufactured by Carlo Elba, using BE by nitrogen adsorption.
Performed by the T method. The particle size was measured using a laser diffraction particle size distribution analyzer “LA-500” manufactured by “HORIBA” and the median diameter was determined. The total oxygen amount was the total oxygen amount calculated from the pyrolysis gas at 950 ° C., and was measured by the following method. About 0.5 g of activated carbon sample was placed in a quartz reaction tube, evacuated to 10 ^-2 mmHg, and the reaction tube was inserted into a furnace maintained at 950 ° C., and gas generated over 30 minutes was collected. The amounts of carbon monoxide and carbon dioxide in the gas were calculated from the amount of generated gas and the composition of the gas determined by gas chromatography. The amount of oxygen contained in the generated carbon monoxide and carbon dioxide was calculated, and the weight percentage with respect to the amount of activated carbon in the reaction tube was obtained, and the result was defined as the total amount of oxygen.

The ash content was measured by the following method.
Put 1-2 g of activated carbon sample in a magnetic crucible,
Heat at 5 ° C. for 6 hours. After cooling, the mass of the remaining ash was measured, and the weight percentage with respect to the amount of activated carbon put in the crucible was determined to be the ash content. The ignition point of each sample was measured as the ignition characteristic. It is determined that the higher the ignition point, the lower the risk of ignition of the activated carbon. The ignition point was measured by the following method using a differential thermal analyzer. 5 mg of an activated carbon sample was put in a sample container made of quartz, and the sample was applied to a differential thermal analyzer.
The temperature was raised at 10 ° C./min while flowing air at a flow rate of ml / min. When the ignition point is reached, the sample heats up rapidly, so the results are plotted with the horizontal axis representing the sample temperature and the vertical axis representing the differential temperature, and the intersection of the extension of the temperature line before the rapid rise and the extension of the temperature line after the sudden rise The corresponding sample temperature was taken as the ignition point.

A dust explosion test at 200 ° C. in air was performed by the Hartmann method. The internal volume was 21 and the dust formation conditions were as follows: gas reservoir pressure 3.0 kg / cm ² , blowing time 1
Seconds, ignition delay time 1 second, spark time 1 second. As an ignition source, in addition to electric sparks, cotton powder (0.1 mol N
0.1 g of aNO ₂ + cotton (1 g) was used. Ignition energy is a total of 370 of electric spark 170J and cotton powder 200J.
J. Dust concentration of 200 g / m ³ and 500 g / m ³
A dust explosion test was performed at n = 10. Table 1 shows the results
Shown in

[0018]

[Table 1]

Comparative Example Commercially available powdered activated carbon (NORIT)
GL-50) and its properties and ignition characteristics were measured in the same manner as in the examples. Table 1 shows the results.

According to the above examples and comparative examples, 950
1.5wt% of total oxygen calculated from pyrolysis gas at ℃
The powder activated carbon having an ash content of 15% by weight or more has a high ignition point, and it can be understood that the use of the activated carbon makes it possible to safely and efficiently treat the exhaust gas.

[0021]

According to the hot gas processing method of the present invention,
Dust explosions and fire accidents are unlikely to occur, and safe and efficient high-temperature gas treatment can be performed.

Claims (4)

[Claims] 1. A method for treating a high-temperature gas, comprising using activated carbon powder having a total oxygen content calculated from a pyrolysis gas at 950 ° C. of 1.5 wt% or less and an ash content of 15 wt% or more. 2. A method for treating exhaust gas from an incinerator using the method according to claim 1. 3. The processing method according to claim 1, wherein the high-temperature gas contains dioxins. 4. The processing method according to claim 1, wherein the temperature of the high-temperature gas is 150 ° C. or higher.