DE102010004011B3 - Process and plant for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process - Google Patents

Abstract

In the method according to the invention for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process, essentially the following method steps are carried out.
a. Preheating cement raw meal with hot exhaust gases in a preheater,
b. Calcining and / or sintering the preheated material into cement clinker in at least one furnace,
c. Cooling the cement clinker in a cooler,
d. Denitrification of the exhaust gas of the preheater in an SCR catalyst, the SCR catalyst is used in addition to the denitrification also for the adsorption of metallic mercury (Hg °) and for the desorption of ionic mercury (Hg _ion ) and then the de-nitrogen and ionic mercury-containing exhaust gas a mercury wash or an adsorption process for the removal of mercury is subjected.

Description

The invention relates to a method and a plant for the production of cement clinker and for the reduction of nitrogen oxides and deposition of mercury from the exhaust gases of the cement production process.

In the production of cement clinker exhaust gases usually contain a greater or lesser proportion of nitrogen oxides and a significant proportion of heavy metals. In particular, the SNCR process is used to reduce nitrogen oxides. Recently, however, the use of SCR catalysts has also been discussed, although the dusty exhaust gases from the cement production process are problematic for the operation of the catalyst.

In clinker production, mercury is introduced into the process via raw materials and fuels. Mercury is a volatile heavy metal that is already liquid at ordinary ambient temperatures. Because of these properties, mercury transfers completely into the flue gas in combustion processes, such as cement production, and emits through the chimney.

From the DE 40 00 795 A1 Therefore, a method for cleaning the exhaust gases of cement production is known, in which the exhaust gases are first dedusted after passing through a cooling tower or a tube mill and then fed to a filter consisting of three filter chambers. Wherein in a first filter chamber heavy metals are bound to a filter medium and discharged and in the second and third filter chamber by adding ammonia-containing agents denitrification of the exhaust gases is effected.

In the EP 0 461 305 B1 a three-stage filter zone is proposed for the purification of the exhaust gases from plants for the production of cement clinker, wherein in the first filter stage, a separation of dust, the second filter stage is designed as adsorption and denitrification of the exhaust gases takes place in the third filter stage. In order to avoid mercury accumulation in circuits, it is also proposed to create a corresponding depression by, for example, installing a gas bypass or discarding part of the filter dust.

In the earlier patent application 10 2009 036 950.3 a method for the separation of mercury from exhaust gases of a cement production process is further described, wherein the mercury is first sorbed on a sorbent and the sorbent is then discharged from the process and fed to a driven with a carrier gas expulsion reactor.

Mercury is adsorbed on sorbents such as lime, blast furnace coke and activated carbon or washed out of the flue gas with wet scrubbers. For both reduction methods, oxidation of the mercury is advisable. Certain oxidized forms of mercury, in particular HgCl ₂ , are water-soluble and also the adsorption is significantly more effective if the mercury is not elemental (Hg °).

Halides, preferably CaBr ₂ or CaCl ₂ , are currently used for the oxidation of the mercury. In the DE 102 33 173 B4 For example, bromine and / or a bromine-containing compound is used.

When using halides different reaction pathways are possible. These are listed below using the example of chlorine. In addition to the direct reaction between CaCl ₂ and Hg °, the oxidation can take place via the formation of HCl. CaCl ₂ + Hg ° + 0.5O ₂ → CaO + HgCl ₂ CaCl ₂ + H ₂ O → CaO + 2HCl Hg ° + 2HCl + 0.5O ₂ → HgCl ₂ + H ₂ O

Since the sorbent loaded with mercury is usually added to the cement clinker and ground together with the clinker to the cement, an entry of larger amounts of halogen is undesirable. For example, the chlorine content in the cement is limited to 0.1%.

Although alternative oxidants such as H ₂ O ₂ and ozone remain in the gas phase and do not affect the cement quality, but are relatively unstable due to their very high reactivity and thus difficult to store. In addition, they are subject to high safety requirements, so that the corresponding processes for storing and injecting the substances are very expensive. In addition, these substances are consumables and thus negatively affect the operating costs of the reduction process.

The invention is therefore based on the object of specifying a method and a plant for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process, so that in particular the cost of the deposition of mercury from the exhaust gases of the cement production process can be reduced.

According to the invention, this object is solved by the features of claims 1 and 12.

• a. Vorwärmen von Zementrohmehl mit heißen Abgasen in einem Vorwärmer,
• b. Kalzinieren und/oder Sintern des vorgewärmten Materials zu Zementklinker in wenigstens einem Ofen,
• c. Kühlen des Zementklinkers in einem Kühler,
• d. Entstickung der Abgases des Vorwärmers in einem SCR-Katalysator, wobei der SCR-Katalysator neben der Entstickung auch zur Adsorption von metallischem Quecksilber (Hg°) und zur Desorption von ionischem Quecksilber (Hg_ion) verwendet wird und das entstickte und ionisches Quecksilber enthaltende Abgas anschließend einer Quecksilberwäsche oder einem Adsorptions-Verfahren zur Abscheidung des Quecksilbers unterzogen wird.

In the method according to the invention for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process, essentially the following method steps are carried out.

• a. Preheating cement raw meal with hot exhaust gases in a preheater,
• b. Calcining and / or sintering the preheated material into cement clinker in at least one furnace,
• c. Cooling the cement clinker in a cooler,
• d. Denitrification of the exhaust gas of the preheater in an SCR catalyst, the SCR catalyst is used in addition to the denitrification also for the adsorption of metallic mercury (Hg °) and for the desorption of ionic mercury (Hg _ion ) and then the de-nitrogen and ionic mercury-containing exhaust gas a mercury wash or an adsorption process for the removal of mercury is subjected.

• a. ein Vorwärmer zum Vorwärmen von Zementrohmehl mit heißen Abgasen,
• b. wenigstens ein Ofen zum Kalzinieren und/oder Sintern des vorgewärmten Materials zu Zementklinker,
• c. ein Kühler zum Kühlen des Zementklinkers,
• d. ein SCR-Katalysator zur Entstickung der Abgases des Vorwärmers, zur Adsorption von metallischem Quecksilber (Hg°) und zur Desorption von ionischem Quecksilber (Hg_ion) und
• e. eine dem SCR-Katalysator (6) nachgeschaltete Einrichtung zur Abscheidung von Quecksilber, die einen Quecksilberwäscher oder eine Adsorptions-Einrichtung zur Abscheidung des Quecksilbers umfasst.

In the system according to the invention for carrying out the above method, substantially the following system parts are provided.

• a. a preheater for preheating cement raw meal with hot exhaust gases,
• b. at least one furnace for calcining and / or sintering the preheated material into cement clinker,
• c. a cooler for cooling the cement clinker,
• d. an SCR catalyst for denitrification of the exhaust gas of the preheater, for the adsorption of metallic mercury (Hg °) and for the desorption of ionic mercury (Hg _ion ) and
• e. a SCR catalyst ( 6 ) downstream device for the separation of mercury, which comprises a mercury scrubber or an adsorption device for the removal of mercury.

The present invention takes advantage of the finding that the intended for the Abgasentstickung SCR catalyst can also be used for the adsorption of metallic mercury (Hg °) and for the desorption of ionic mercury (Hg _ion ). This adsorption-desorption mechanism of the mercury does not consume the SCR catalyst and, in effect, no consumables are needed to effect the oxidation of the mercury.

The oxidation of metallic Hg ° to ionic Hg _ion proceeds in several steps. Hg ° and halogens, such as chlorine adsorb at the active sites of the catalyst. Chlorine acts as an oxidant and is contained in the combustion exhaust gas in the form of Cl ₂ or HCl by the entry of raw materials and fuels. After the catalytic oxidation of metallic Hg ° to ionic Hg _ion , the desorption takes place in the form of HgCl ₂ .

The ionic mercury can then be subsequently deposited by means of mercury scrubbing or by an adsorption process, for example on charcoal, lime or a coal-lime mixture.

Further embodiments of the invention are the subject of the dependent claims.

Due to the high dust content of exhaust gases from the clinker production, it is expedient to at least partially reduce the dust content of the exhaust gas of the preheater before the SCR catalyst. In this case, the dust content before the SCR catalyst can be reduced by, for example, 10-60% in order to avoid clogging or impairment of the mode of action of the catalyst.

Thus, for both the denitrification and for the adsorption and desorption mechanism of mercury is an optimal temperature range, the temperature of the exhaust gas before introduction into the SCR catalyst at 150 ° C to 500 ° C, preferably at 200 ° C to 400 ° C, can be adjusted. For example, a heat exchanger arranged upstream of the SCR catalytic converter is also suitable for this purpose.

The clinker production is usually carried out in two operating states, the composite and the direct operation. After leaving the preheater, the dust-laden exhaust gas is fed in a composite operation of a crushing unit, in particular a raw mill, where the raw material is ground and dried by the thermal energy of the exhaust gases. In direct operation, the exhaust gas is not routed through the shredding unit.

For denitrification, a usually ammonia-containing reducing agent is added to the exhaust gas before it is introduced into the SCR catalyst. 2NO + 2NH ₃ + 0.5O ₂ → 2N ₂ + 3H ₂ O

In addition, since ammonia and metallic mercury compete for the free adsorption sites on the catalyst, it may be advantageous to switch on a selective non-catalytic reduction of the NO (SNCR).

By prior ammonia dosing a part of the NO is already implemented before the SCR catalyst. On the catalyst below a smaller amount of NH _{3 is} required. A smaller amount of NH ₃ on the catalyst increases the number of adsorption sites for Hg ° and thus its oxidation.

As the adsorbent for the mercury is particularly suitable coal (for example, activated carbon or Herdofenkoks), lime or coal-lime mixtures.

The adsorption of the ionic mercury can take place both on a solid adsorber and in the flow-through method. In the combined operation, a large part of the mercury in the crushing unit is adsorbed on the raw material, so that in this operation under certain circumstances further mercury removal is unnecessary.

Since mercury oxidation is hindered at high SO ₂ partial pressures, measures for SO ₂ reduction may have to be taken. This includes, for example, the dry sorption of calcium hydroxide.

Furthermore, in the case of mercury removal in scrubbers or the adsorption device, desulfurization of the exhaust gas can take place at the same time.

Further advantages and embodiments of the invention will be explained in more detail below with reference to the description of some embodiments and the drawings.

In the drawing show

1 1 is a block diagram of a plant for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process according to a first exemplary embodiment,

2 a block diagram of a plant for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process according to a second embodiment,

3 a block diagram of a plant for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process according to a third embodiment and

4 a block diagram of a plant for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process according to a fourth embodiment.

The plant for the production of cement clinker is in 1 shown schematically. It consists essentially of a pre-heater designed as a cyclone preheater 1 , an oven designed as a rotary kiln 2 and a cooler 3 , Also, one with the exhaust gases 4 operated shredding device 5 be provided for grinding the raw materials.

Furthermore, an SCR catalyst 6 provided with the exhaust gases 4 of the preheater is acted upon. Before the SCR catalyst 6 can be a device 7 be provided for exhaust treatment and / or dust conditioning, for example, the dust content of the exhaust gas 4 at least partially reduce. But it is also possible to condition the dust contained in the exhaust gas in other ways, for example, to charge, to an impairment and / or blockage of the subsequent SCR catalyst 6 counteract.

In the SCR catalyst 6 finds on the one hand the conventional denitrification of the exhaust gas 4 instead, wherein for the Entstickungsreaktion the addition of a reducing agent usually ammonia-containing is required. The active catalyst material of the SCR catalyst 6 consists for example of TiO ₂ , WO ₃ / MoO ₃ , V ₂ O ₅ and other constituents, such as binders, plasticizers and excipients.

That in the exhaust 4 of the preheater 1 contained mercury is present in the form of metallic mercury (Hg °) and ionic mercury (Hg _ion ). As studies have shown, the ratio of Hg °: Hg _{ion is} about 80:20. The catalyst material not only serves for denitrification but also causes adsorption of the metallic mercury and subsequent desorption of ionic mercury. In this conversion of mercury no catalyst material is consumed and there are basically no additional consumables necessary to effect this oxidation of the mercury. Increases the preferred ionic content for the deposition.

The de-nitrogenized and ionic mercury contained exhaust gas 4 ' is then connected in composite mode on the shredder 5 or in direct operation via a cooling tower 8th a dust filter 10 fed. The de-embroidered and dedusted exhaust 4 '' is then in a mercury scrubber or in an adsorber 9 where the mercury is washed out and removed or adsorbed and separated by exchange of the sorbent.

The adsorption mechanism of mercury in the SCR catalyst 6 is hindered at high SO ₂ partial pressures. In this case, appropriate measures for SO ₂ reduction make sense. For this example, calcium hydroxide (Ca (OH) ₂ ) before the SCR catalyst 6 the exhaust 4 be added.

By the mercury separation in 'tail-end circuit' allows process variant 1 to operate the scrubber (or adsorber) at low process temperatures. This has an advantageous effect on the deposition.

In 2 is used instead of stationary deposition by means of mercury scrubber or adsorber 9 a mobile adsorption, the airflow method provided. As adsorbent in particular coal, such as activated carbon or Herdofenkoks, lime or a coal-lime mixture into consideration.

The adsorbed on the adsorbent mercury is in the dust filter 10 deposited.

By Flugstromadsorption the embodiment has in 2 the lowest investment costs and the lowest investment costs. In addition, the sorbent injection and thus the mercury deposition can also be done only at high mercury loads, such as occur in direct operation. In the other embodiments, this would require an additional bypass.

The SCR catalyst 6 is in the embodiments of 1 and 2 in a high-dust or with pre-dedusting ( 7 ) are arranged in a semi-Dust circuit.

However, the high dust load of exhaust gases from the cement production is not entirely unproblematic for the operation of the SCR catalyst, since in particular blockages or clogging of the catalyst material can occur. Therefore, additional measures (dust conditioning, eg by electrical charging) or special configurations of the catalytic converter (sound, vibration devices) are usually required.

In this respect, the arrangement of the SCR catalyst 6 in a low-dust circuit, as judged by the 3 and 4 is explained in more detail below, quite an alternative.

In the embodiment according to 3 become the exhaust gases 4 of the preheater 1 first in a cooling tower 8th cooled or over the shredder 5 the filter 10 be fed to dedusting. The exhaust gas is then in a heat exchanger 13 on the for the SCR catalyst 6 optimal temperature heated up. The de-nitrogenized and ionic mercury contained exhaust gas 4 ' is in a heat exchanger 14 cooled and then the mercury scrubber or adsorber 9 fed, where the mercury is removed from the exhaust gas.

In the embodiment according to 4 is after the heat exchanger 14 a sorbent 11 injected into the exhaust gas. In a second filter ( 12 ) the sorbent is separated again.

The advantage of this design is the option for regeneration and recirculation of the sorbent.

Claims (13)

Process for the production of cement clinker and for the separation of nitrogen oxides and mercury from the exhaust gases of the cement production process, comprising the following steps: a. Preheating cement raw meal with hot exhaust gases in a preheater, b. Calcining and / or sintering the preheated material into cement clinker in at least one furnace ( 2 ) and c. Cooling the cement clinker in a cooler ( 3 ), d. Denitrification of the exhaust gas ( 4 ) of the preheater ( 1 ) in an SCR catalyst ( 6 ), wherein the SCR catalyst is used in addition to the denitrification also for the adsorption of metallic mercury (Hg °) and for the desorption of ionic mercury (Hg _ion ) and the de-nitrogen and ionic mercury-containing exhaust gas then a mercury or an adsorption process for deposition is subjected to the mercury. A method according to claim 1, characterized in that the dust content of the exhaust gas ( 4 ) of the preheater ( 1 ) prior to introduction into the SCR catalyst ( 6 ) is partially reduced. Method according to claim 1, characterized in that the exhaust gas ( 4 ) before and / or after the SCR catalyst ( 6 ) is supplied to a heat exchanger. Method according to claim 1, characterized in that the temperature of the exhaust gas ( 4 ) prior to introduction into the SCR catalyst ( 6 ) is adjusted to 150 ° C to 500 ° C, preferably to 200 ° C to 400 ° C. Method according to claim 1, characterized in that the exhaust gas ( 4 ) of the preheater ( 1 ) wholly or partly of a shredding unit ( 5 ), in particular a mill, is supplied. Method according to claim 1, characterized in that the exhaust gas ( 4 ) prior to introduction into the SCR catalyst ( 6 ) an ammonia-containing agent is added. A method according to claim 1, characterized in that are used as adsorbent coal, lime or coal-lime mixtures. A method according to claim 1, characterized in that the mercury adsorption takes place in the air flow method. A method according to claim 1, characterized in that the mercury adsorption takes place in a solid. A method according to claim 1, characterized in that the adsorption process is used only at high mercury emissions, such as occur in direct operation. A method according to claim 1, characterized in that the SCR catalyst is preceded by a SNCR. A method according to claim 1, characterized in that at the same time a desulfurization of the exhaust gas takes place in the mercury removal in scrubbers or the adsorption device. Plant for carrying out the method according to one or more of the preceding claims with a. a preheater ( 1 ) for preheating cement raw meal with hot exhaust gases, b. at least one furnace ( 2 ) for calcining and / or sintering the preheated material into cement clinker, c. a cooler ( 3 ) for cooling the cement clinker, d. an SCR catalyst ( 6 ) for the denitrification of the exhaust gas of the preheater, for the adsorption of metallic mercury (Hg °) and for the desorption of ionic mercury (Hg _ion ) and e. a the SCR catalyst ( 6 ) downstream device for the separation of mercury containing a mercury scrubber ( 9 ) or an adsorption device ( 11 ) for separating the mercury.

Images