METHOD FOR SEPARATING MERCURY FROM FLUE GAS

Abstract

The invention relates to a method for separating mercury (Hg) from furnace gases of combustion plants, wherein a catalytically active material having a mean grain diameter <35 ?m is metered into the furnace gas, the elemental mercury in the furnace gases is oxidized, and resulting oxidized mercury is separated in the process using adsorption and absorption techniques in preexisting plant technology. The intensified formation of oxidized mercury is performed within a temperature range <500? C.

Claims

1-6. (canceled)

7. A method for oxidizing and removing mercury from a power plant flue gas, comprising: preparing a powdery, catalytically active material comprising iron(III) oxide with a mean grain diameter <35 ?m; injecting the material into the flue gas downstream of a combustion chamber, thereby causing an increased formation of oxidized mercury at a temperature range <500? C.; and removing the oxidized mercury and the powdery, catalytically active material comprising iron(III) oxide from the flue gas in a flue gas cleaning device.

8. The method as in claim 7, wherein the powdery, catalytically active material comprising iron(III) oxide is incurred as a waste product during treatment and remediation processes of waters or bodies of water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The following figures are referenced in the following detailed explanation: FIG. 1 shows several block diagrams illustrating options of injecting a catalytic material to a flue gas;

[0039] FIG. 2 is a table showing results of a first exemplary embodiment of a method for separating mercury from flue gas; and

[0040] FIG. 3 is a table showing results of a second exemplary embodiment of a method for separating mercury from flue gas.

DETAILED DESCRIPTION

[0041] As illustrated in FIG. 1, in a lignite combustion power plant the injection 6 of a catalytic material according to the invention takes place downstream of a boiler/combustion 1 and/or an air preheater 2 and/or a dedusting system 3. In this case, the catalytically active material is injected into the furnace gas via known injection devices, such as screw conveyors or blowers. A typical lignite combustion plant comprises the boiler/combustion 1, followed by an air preheater 2, a dedusting system 3, a desulfurization system 4 and a chimney/cooling tower 5.

[0042] If the material according to the invention is to be used in a bituminous coal combustion power plant, the injection takes place in the ongoing process downstream the boiler/combustion 1, the air pre-heater 2 and/or the catalytic denitrification 7 and/or the dedusting system 3. After the dedusting system 3, desulfurization 4 takes place towards the chimney/cooling tower 5.

[0043] If the method according to the invention is used in sewage sludge or waste incineration, the addition of the material according to the invention is carried out by way of process engineering via the boiler/combustion 1, the air preheater 2, the dedusting system 3. After dedusting 3, the desulfurization 4, the catalytic denitrification 7 takes place towards the chimney/cooling tower 5. Customary injection devices, such as screw conveyors or blowers, are used for the feeding of the produced material into the furnace gas, as already described.

Example 1

[0044] The material, preferably iron(III) oxide, was added to the flue gas of a lignite-fired power plant at temperatures around 320? C. in in front of the air preheater. The feed of the catalyst was carried out via a pneumatic conveyor line from the silo via a lance system having 12 injection points distributed over the cross section of the waste gas duct. The separation of the catalyst was carried out together with the filter dust via electrostatic filter. The mean grain diameter of the iron-containing catalyst was 1.5 ?m. Concentrations in the crude gas were adjusted between 35-150 mg/Nm.sup.3f and oxidation results achieved are shown in Table 1, FIG. 2.

[0045] Without injection of catalyst material, the oxidized Hg content was <4 ?g/Nm.sup.3tr in the usual range of total Hg inventory of 15 ?g/Nm.sup.3tr. After electrostatic filter, this results in a proportion of about 25% oxidized Hg. This proportion increased to almost 50% with injection quantities around 35 mg/Nm.sup.3f. A proportion of oxidized mercury of 57% was reached with maximum cat concentration of 150 mg/Nm.sup.3f.

Example 2

[0046] The material, preferably iron(III) oxide, was added to the flue gas in the lignite-fired power plant after air preheater/before electrostatic filter at temperatures around 170? C. The feed of the catalyst was carried out via a pneumatic conveyor line from the silo via a lance system having 12 injection points distributed over the cross section of the waste gas duct. The separation of the catalyst was carried out together with the filter dust via the subsequent electrostatic filter in the process.

[0047] The mean grain diameter of the iron-containing catalyst was 1.5 ?m. Concentrations in the crude gas of 50 and 210 mg/Nm.sup.3f were tested and the oxidation results achieved are shown in Table 2, FIG. 3.

[0048] In the case of a catalyst concentration of 50 mg/Nm.sup.3f, a concentration of 12.6 ?g/Nm.sup.3 of oxidized Hg was determined (approximately 75% proportion oxidized Hg from the Hg inventory). A significant increase in the dose to 200 mg/Nm.sup.3 cat material achieved no increase of the oxidized Hg concentration.

REFERENCE NUMERALS

[0049] 1. Boiler/combustion [0050] 2. Air preheater [0051] 3. Dedusting System [0052] 4. Desulfurization System [0053] 5. Chimney/cooling tower [0054] 6. Optional injection point of catalytic material for Hg oxidation [0055] 7. Catalytic denitrification