FI106365B - Method for the separation of hazardous substances from waste gases - Google Patents

Description

, 106365

Method for the separation of hazardous substances from exhaust gases

The invention relates to a process for separating hazardous substances from a waste gas stream which is passed through a granular adsorbent mass. Preferably, the hazardous substances are mercury or mercury compounds, but also polycyclic or polynuclear aromatic hydrocarbons, especially dioxins and furans, as well as other heavy metals and / or heavy metal compounds.

In particular, the removal of metallic mercury from gases is known, U.S. Patents 4,101,631, 4,500,327 and 4,814,152 use zeo-10 hits or activated carbon saturated with sulfur for this purpose. The process known from DE-A 4 326 450 uses low aluminum zeolites which may also be sulfur impregnated.

Gases of different origins, such as waste gases from waste incineration plants, include e.g. dust, unburned hydrocarbons, halogenated hydrocarbons and sulfur oxides, nitrogen oxides, heavy metals and heavy metal compounds, but also dioxins and furans. Different purification methods are used to separate these substances. In particular, in order to separate the mercury and mercury compounds and the dioxins and furans, an additional separation step is usually required before the furnace. Carboniferous powder or pulps of 20 granular activated carbon are used for this. Harmful to these carbonaceous materials is the inherent danger of fire, which may also cause self-ignition. In addition, the adsorption of other gas constituents, such as, for example, SO 2 residues, results in rapid adsorption and soaking or sintering of the adsorbent, which usually requires changing.

The invention must be based on an attempt to prevent the risk of fire and the problem of soot and sintering of the pulp in the process mentioned above. The present invention relates to a process for separating hazardous substances from a waste gas stream passed through a mass of granular adsorbent 30. The process is characterized in that the pulp consists of a mixture of granular high carbon material and granular inert material, wherein the high carbon material is activated carbon, activated coke or lignite coke and the inert material is silicate rock, pumice, lava, slag, glaze, 8 to 3 times the bulk density of the carbonaceous material, the carbonaceous material having a grain size in the range 0.5 to 10 mm and the inert material having a grain size in the range 1 to 6 mm, 106365 2 having a high carbon content in the mass of 5 to 80% by weight; are between 20 and 200 ° C when the gas stream is passed through it. The mixing of the inert material allows for long service lives and especially high separation capacities for heavy metals, dioxins and furans. In continuous operation, there are no ignition or self-heating phenomena, and soot and sintering also do not occur. The heat of adsorption released binds to the inert material and is removed so that no heat concentration occurs.

The gas can flow through the granular mixture of the carbon-rich material and the inert material either vertically or horizontally. The pulp is usually placed in a container as a fixed or mobile layer. It has proved expedient to pass gas through the pulp at an empty tube speed of 0.1 to 0.5 m / s.

The residence time of the gas in the mass depends on the concentration of the substances to be separated and is usually in the range of 0.5 to 5 seconds.

15 Examples of high carbon materials used are activated carbon, activated carbon or lignite coke. The high-carbon material may be impregnated with, for example, sulfur or sulfur compounds, such as siliceous rock, pumice, lava, slag, vitrified waste or crushed stone. The proportion of high carbon material in the pulp is from 5 to 80% by weight and preferably from 20 to 75% by weight. When the gas stream is passed through the pulp, the temperatures in the pulp are about 20-200 ° C. The inert material should be hydrophobic. Preferably, the inert material has a water retention capacity of less than 15% by mass at equilibrium when using a gas having a relative humidity of 65%.

The high carbon material used in the pulp, as well as the inert material, has a grain size in the range of 0.5 to 10 mm. Preferably, the inert material is somewhat coarser with at least 80% by weight of the granules in the range of 1 to 6 mm.

Using different mixture ratios, the Hg difference in the layers of the invention was measured. With a proportion of only 30% by mass of active form. For 30 carbons, and with a gas residence time of only 1 s, separation rates of, for example, • primary compounds or metallic mercury, which were more than 99% for extended periods of time, could be assigned. Thus, the mixture need only contain a small amount of carbonaceous material. Furthermore, the alloy has the advantage that the resolution capacities can be varied by adjusting the alloy ratio within wide limits. Thus, there is also elasticity with respect to the layer thickness 35 and the gas pressure drop directly dependent on it. Furthermore, by using coarse-grained materials, such as formulated activated carbon, sulfur impregnation can be added to achieve even higher resolution efficiencies of 3 106365 or also the selective separation of heavy metals, particularly mercury, as high vapor pressure elements.

Such a solid bed mass as a final step before the furnace can also fulfill the function of a safety filter 5 for all hazardous substances if the above exhaust gas cleaning passes through the gases and also serves as a filter for residual dust. The inert material binds only trace amounts of SO 2 and forms only trace amounts of sulfuric acid. On the one hand, the ability to store activated carbon and, on the other hand, the separation effect of the inert material prevents the mass from wetting and sticking by the soaking. It was found that even with a sulfuric acid loading of more than 70% by weight of activated carbon there was no soot. When using pure activated carbon or activated coke, the carbonation begins already with substantially lower acid loads.

The Federal Institute for Material Research and Testing (Bundesanstalt fur 15 Materialforschung und -priifung) in Berlin conducted studies on mixtures of activated carbon and volcanic rock (lava) in mass ratios of 70:30, 50:50 and 30:70. In this case, no signs of dangerous heat evolution with the possibility of auto-ignition were observed.

Example 1 In a long-term experiment of 18 months, the exhaust gas of a high-tech waste incineration plant is passed through an adsorption filter with a solid bed of a mixture containing 30% by weight of activated carbon and 70% by weight of lava. At the end of the experiment, the separation efficiency of Hg and Hg is invariably greater than 95% and no soot, temperature increase or CO-25 development is observed.

Example 2

In a laboratory test, the mass consists of 70% by weight of pumice stone with a grain size of 2 to 6 mm and 30% by weight of activated carbon having a grain size of ": about 4 mm. HgCl2-containing air is passed up through the bed after 700 hours. The HgCl 2 concentration is reduced.

Mass diameter: 36 mm

Mass height: 360 mm

Temperature in the mass: 80 ° C

Gas temperature: 60 ° C

35 Gas velocity, real: 30cm / s

Measured (Hg-A = Hg at the inlet, Hg-B = Hg at the outlet): 4 106365

Operating time (h) Hg-A (pg / m3) Hg-B (μg / m3) Difference% 70 273 1 99.6 550 271 1 99.6 715 113 2 98.2 932 113 2 98.2

Example 3

In another laboratory test, the temperature of the gas containing HgCl2 is about 70 ° C, otherwise work as in Example 2. The results were obtained: 5

Operating time (h) Hg-A (pg / m3) Hg-B (pg / m3) Difference% 240 60 1 98.3 1595 98 1.8 98.2 2095 91 1 98.9 3072 130 1.6 99.2 3720 137 1 99.2 4647 129 1 99.2 6110 128 1.5 99.8 6686 171 1 99.4 7690 93 1 98.9 m

Claims (4)

1. A process for separating hazardous substances from an exhaust stream conducted through a mass of a granular adsorbent, characterized in that the mass consists of a mixture of a granular carbon rich material and a granular inert material, wherein as carbon rich material is used active koi, active coke or lignite coke and as inert material silicate rock material, pumice, lava, slag, glaze residue or finch ice is used, that the bulk density of the inert material is 0.8 - 3 times the bulk density of the carbonaceous material. that the carbonaceous material has a grain size in the range 0.5 - 10 mm and the inert material has a grain size in the range 1-6 mm, that the proportion of carbon rich material in the pulp is 5 - 80 pulp%, and that the temperatures in the pulp are 20 - 200 ° C as the gas stream is passed through it. Process according to claim 1, characterized in that the pulp forms in a container a fixed bed or a movable bed, the exhaust flowing vertically or horizontally through the bed. 3. A process according to claim 1 or 2, characterized in that heavy metals and / or heavy metal compounds and / or polycyclic or multi-core aromatic hydrocarbons, especially dioxins and furans, are removed from the gas stream. 4. A process according to any one of claims 1-3, characterized in that heavy metals in elemental form are removed from the exhaust stream, using carbonaceous material which is at least partially impregnated with sulfur. s1 l,