Method for processing dust containing organic residues in a cement production plant

Description

[0001] The invention relates to a method for processing dust containing organic residues in a cement production plant.

[0002] To reduce the use of fossil fuels in cement production, alternative fuels such as dried sewage sludge, industrial waste, or non-recyclable plastics are increasingly being used. When large quantities of alternative fuels are used in a cement plant, organic residues and heavy metals can accumulate in the cement production plant as an indirect consequence. The natural and alternative raw materials used in clinker production can also contribute to organic residues and pollutants.

[0003] These organic residues typically accumulate in cement kiln dust, making it impossible to simply add the cement kiln dust to the cement mill after it has been separated from the exhaust stream, unlike usual, because the unburned organic residues in the cement represent undesirable contaminants. For example, organic residues in cement lead to dark spots in the final concrete product, which is aesthetically detrimental. Furthermore, organic residues negatively impact the control of air entrainment in concrete compositions and the rheology of concrete compositions before setting.

[0004] The accumulation of heavy metals in kiln exhaust gas leads to environmental pollution if appropriate measures are not taken to remove them. One particularly problematic heavy metal, for example, is mercury, which is present in the kiln exhaust gas in a gaseous state.

[0005] JP2022129625 describes a chlorine bypass plant and its operating method, a cement clinker manufacturing apparatus and a cement clinker manufacturing method.

[0006] The present invention therefore aims to enable the use of alternative fuels and organically contaminated raw materials for the production of cement clinker without having to accept the disadvantages described above.

[0007] To achieve this object, the invention provides a method for processing dust containing organic residues in a cement production plant, comprising introducing the dust into the chlorine bypass of the cement production plant, contacting the introduced dust with kiln exhaust gas laden with kiln dust introduced into the chlorine bypass from a rotary kiln of the cement production plant, and combusting the organic residues in a reaction zone of the chlorine bypass at a temperature of > 580°C. The dust is then cooled downstream of the reaction zone, separated from the kiln exhaust gas, and discharged from the chlorine bypass. The invention is thus based on the idea of utilizing the thermal energy present in the chlorine bypass to eliminate the organic residues of the dust by combustion.A chlorine bypass is a partial gas extraction system for the kiln exhaust gas of a rotary kiln in a cement production plant near the kiln inlet to limit chlorine, alkali, and sulfur cycles. In many cement production plants, such a chlorine bypass is installed between the rotary kiln and the preheater to subject a partial flow of the kiln gas to separate treatment. This reduces the chlorine content near the kiln inlet, resulting in less accumulation of this element and fewer caking and blockages.

[0008] The kiln exhaust gas diverted at the kiln inlet and entering the chlorine bypass has a temperature of approximately 1,000 to 1,100°C. Upon contact with the dust laden with organic residues introduced into the chlorine bypass, it causes the organic residues to be burned. The reaction zone of the chlorine bypass, into which the dust is introduced and where combustion takes place, is located as close as possible to the kiln inlet, with the temperature in the reaction zone being > 580°C, preferably > 650°C.

[0009] The dust containing organic residues to be processed according to the invention is not the kiln dust that enters the chlorine bypass directly along with the kiln exhaust gas from the rotary kiln. Rather, the dust to be processed according to the invention is dust that is introduced into the chlorine bypass from the outside, for example, from a dust silo. For the introduction of the dust, a feed pipe is provided, for example, which opens into the chlorine bypass transversely, in particular perpendicularly or obliquely, to the pipe axis of the chlorine bypass.

[0010] Preferably, the dust loaded with the organic residues is introduced, in particular injected, into a riser shaft of the chlorine bypass connected to the furnace inlet.

[0011] To ensure the most complete combustion of the organic residues possible, a minimum residence time of the dust in the hot reaction zone of the chlorine bypass is desirable. A preferred embodiment of the process according to the invention therefore provides that the dust is kept in the chlorine bypass, in particular in the reaction zone, for a period of time that ensures complete combustion of the organic residues. The residence time of the dust in the reaction zone, which has a temperature of > 580°C, is preferably at least 1 second, preferably at least 2 seconds.

[0012] However, it is not mandatory that the complete combustion of the organic residues takes place in the reaction zone itself. It is also possible that the combustion process of the organic residues continues downstream of the reaction zone after a residence time of > 1 second, preferably > 2 seconds, at a temperature of > 580°C, preferably > 650°C.

[0013] In order to ensure a sufficient residence time of the dust in the reaction zone, it is preferably provided that a flow rotating around a pipe axis of the chlorine bypass is generated and / or maintained in the reaction zone.

[0014] Preferably, a carrier gas, preferably air, is introduced into the chlorine bypass with a swirl to create the rotating flow. This is achieved, for example, by blowing the carrier gas tangentially into the chlorine bypass. The carrier gas, introduced at ambient temperature, forms a cold protective layer on the pipe wall of the chlorine bypass, which surrounds the dust and imparts a component of motion to the dust in the direction of rotation. The carrier gas thus reduces contact between the dust and the pipe wall and cools the pipe wall, thereby reducing the sticking of the pipe wall due to deposits of components such as sulfur and chlorine.

[0015] After the organic contaminants have been burned off, the dust is cooled, separated from the furnace exhaust gas, and discharged from the chlorine bypass. Cooling of the dust is preferably achieved by blowing in air, for example, in a quench chamber, as is conventionally done with a chlorine bypass.

[0016] Preferably, the cooling takes place in two stages, whereby the dust is subjected to a first cooling step to a temperature of 580-680°C. The partially cooled dust is fed to a separation device in which a coarse fraction of the dust is separated and discharged and, if necessary, introduced into the rotary kiln. The dust is then subjected to a second cooling step to a temperature of <140°C, during which heavy metals contained in the kiln exhaust gas condense and are deposited on a fine fraction of the dust. The first and / or second cooling step is preferably carried out by blowing in air, in particular ambient air.

[0017] By feeding the partially cooled dust to a separation device, in particular a cyclone separator, in which a coarse fraction of the dust is separated and discharged and fed into or returned to the rotary kiln, the amount of dust produced by the cement production plant can be further reduced.

[0018] In principle, dusts containing organic residues of any origin can be treated with the method according to the invention. In particular, these dusts contain both organic residues and heavy metals such as As, Pb, Cd, Cr, Co, Ni, Tl, Zn, and Hg.

[0019] Particular preference is given to treating dust originating from the cement production plant itself, namely cement kiln dust separated from the kiln exhaust gas after the kiln exhaust gas has passed through a raw meal preheater and has then been cooled.

[0020] Since the process according to the invention ensures that the dust treated in the chlorine bypass and separated from it no longer contains any organic contaminants, it can be easily added to cement clinker and ground with it in a cement mill.

[0021] The invention will be explained in more detail below with reference to an embodiment shown schematically in the drawing. Fig. 1 a layout of a cement production plant designed to carry out the process according to the invention.

[0022] The cement production plant comprises a rotary kiln 1, in which preheated and, if necessary, precalcined raw meal is burned to produce cement clinker. The raw meal is stored in a silo 2 and fed to a raw meal preheater 3, in which the raw meal is passed through several cyclone or vortex chamber stages arranged one behind the other in countercurrent to the hot exhaust gas coming from the rotary kiln 1. The preheated raw meal enters the rotary kiln 1 via the kiln inlet 4, while the exhaust gas is discharged from the raw meal preheater 3 via line 5. The heat from the exhaust gas can be utilized in a waste heat recovery unit 6, after which the exhaust gas is quenched in a conditioning tower 7 with the addition of water 8. The residual heat from the exhaust gas can be used in a raw meal mill and / or a raw meal preheater 9 to preheat the raw meal.The dust components contained in the exhaust gas, including cement kiln dust and raw meal dust, are separated in the main filter 10 so that the dust-free exhaust gas can be discharged via the chimney 11.

[0023] The dust 13 containing organic residues separated in the main filter 10 is now fed, according to the invention, to the chlorine bypass 12 of the cement kiln plant. The chlorine bypass 12 is connected to the kiln inlet 4 and serves to withdraw a portion of the kiln exhaust gas from the rotary kiln 1 to limit chlorine, alkali, and sulfur cycles. In the reaction zone 14 of the chlorine bypass 12, the organic components of the fed dust 13 are at least partially combusted at a suitable temperature. Further combustion can also take place in a further downstream region 22 of the chlorine bypass. A cooling chamber 23 and an optional separation cyclone 15 are arranged between them, via which coarse components of the dust can be separated and returned to the rotary kiln 1. Subsequently, the exhaust gas is cooled in another quench chamber 16 by the addition of air 21, and the dust is separated in a filter 17.The dust is stored in a silo 18, with the purified exhaust gas being fed to the chimney 11 via line 19. The dust 20 can subsequently be added to a cement mill as an additive to the cement.

Claims

1. A method for processing dust containing organic residues in a cement manufacturing plant, comprising the introduction of the dust into the chlorine bypass (12) of the cement manufacturing plant, contacting the introduced dust with kiln exhaust gas loaded with kiln dust and introduced into the chlorine bypass (12) from a rotary kiln (1) of the cement manufacturing plant, and burning the organic residues in a reaction zone (14) of the chlorine bypass (12) at a temperature of > 580°C, whereupon the dust is cooled downstream of the reaction zone (14) and separated from the kiln exhaust gas and discharged from the chlorine bypass (12).

2. The method according to claim 1, characterized in that the dust is kept in the chlorine bypass (12), in particular in the reaction zone (14), for a period of time that causes complete combustion of the organic residues.

3. The method according to claim 1 or 2, characterized in that a flow rotating about a pipe axis of the chlorine bypass (12) is generated and / or maintained in the reaction zone (14).

4. The method according to claim 3, characterized in that a carrier gas, preferably air, is introduced into the chlorine bypass (12) with an angular momentum to generate the rotating flow.

5. The method according to any one of claims 1 to 4, characterized in that the cooling of the dust is carried out by blowing in air (21,24).

6. The method according to any one of claims 1 to 5, characterized in that the dust is subjected to a first cooling (23) to a temperature of 580-680°C, the partially cooled dust is fed to a separation device (15), in which a coarse fraction of the dust is separated and discharged and optionally introduced into the rotary kiln (1), and in that the dust is subjected to a second cooling (16) to a temperature of < 140°C, at which heavy metals contained in the kiln exhaust gas condense and are deposited on a fine fraction of the dust.

7. The method according to any one of claims 1 to 6, characterized in that the dust is separated from the kiln exhaust gas, which has passed through a raw meal preheater (9) and has then been cooled, and is introduced into the chlorine bypass (12).

8. The method according to any one of claims 1 to 7, characterized in that the dust discharged from the chlorine bypass (12) is added to a cement clinker and ground therewith in a cement mill.