Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D45/00—Separating dispersed particles from gases or vapours by gravity, inertia, or centrifugal forces
  • B01D45/12—Separating dispersed particles from gases or vapours by gravity, inertia, or centrifugal forces by centrifugal forces
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/75—Multi-step processes

Definitions

• the present invention relates to a process and an installation for purifying cement fumes.
• cement in particular Portland cement
• Portland cement is widely used in sectors as varied as bridges and pavements, the construction or realization of large pipes.
• Several varieties of cements and several processes aimed at their manufacture are used, each with its own specificities.
• the cement manufacturing process begins with the preparation of a mixture made from raw materials such as clay, limestone, lime. These elements provide silicon, calcium, aluminum and iron which are the essential elements in a cement.
• a grinding of these various elements is then carried out, either wet or dry. This grinding can generate a huge amount of dust and it is necessary to use smoke treatment devices, such as bag filters, cyclones or sometimes electrostatic precipitators.
• the ground material dry or wet
• the ground material is calcined in ovens, where the product is brought to a maximum temperature of about 1450 ° C.
• ovens Several types of ovens exist and one can quote in particular the ovens of the type "LEPOL", as well as the long rotary ovens. Preheaters are often used.
• a selective, non-catalytic process for the reduction of nitrogen oxides can be used.
• a reducing agent such as ammonia NH 3 or urea NH 2 -C0-NH 2
• ammonia NH 3 or urea NH 2 -C0-NH 2 is injected and reacts with the oxides to transform them into nitrogen. This process, if it makes it possible to reduce nitrogen oxides by 50 to 70%, imposes particular constraints and cannot always be put into service.
• the reagent namely ammonia or urea
• the reagent must be introduced in a narrow window of temperatures. This, which is between 950 and 1150 ° C, is not always accessible.
• these methods generate a certain amount of nitrous oxide N 2 0, a pronounced greenhouse gas.
• US Pat. No. 5,137,704 presents an improved variant of this technology.
• Another known method consists in using burners of a particular type, called low NO x burners, or "Low NO x ".
• the reduction of the NO and NO 2 contents is limited, and the quality of the clinker obtained can be reduced by the use of these burners, due to the alteration of the speciation of sulfur. '
• SCR Selective Catalytical Reduction
• the catalyst used is sensitive to dust and must be protected. If a filter is used, the temperature should generally drop below 200 ° C. However, most catalysts must work above 250 ° C.
• the exchangers that are used represent additional equipment and therefore corresponding investments.
• the cyclones, which are also used, have a too low yield to be able to guarantee a dust content compatible both with the input contents imposed by the process, and those necessary for a reliable and economical use of the SCR catalysts. These must have a lifespan of several years, and therefore be protected.
• the present invention aims to propose a process for purifying cement fumes, making it possible to overcome the various drawbacks explained above.
• the fumes to be purified are extracted from the oven, these extracted fumes having a temperature between 250 and
• the extracted fumes have a temperature between 280 and 350 ° C;
• the marginal fraction of fumes is between 2 and 4%, in particular 3%, of the fumes admitted to the dedusting unit;
• the denitrified fumes and the marginal fraction are mixed, then the mixture of denitrified fumes and of said marginal fraction is directed towards the drying chamber of the oven.
• the invention also relates to a plant for purifying fumes from a cement plant, comprising an oven belonging to a cement manufacturing installation, this oven comprising a drying chamber and a calcination chamber in which the fumes to be purified circulate, in service, characterized in that it includes:
• these extraction means extending from an intermediate zone of said oven having, in service, a temperature between 250 and 400 ° C., preferably between 280 and 350 ° C;
• first means of evacuation making it possible to extract from the dusting unit the dusted fumes
• second exhaust means making it possible to extract from the dedusting unit a marginal fraction of the fumes admitted into this unit, this marginal fraction being collected at the same time as dust
• - a denitrification reactor put in communication with the first means of evacuation
• third means of evacuation making it possible to extract the denitrified fumes from the denitrification reactor
• the dedusting unit is of the cyclonic type, and it is constituted by a cyclone or a battery of cyclones;
• the additional dust collector is a bag filter or an electrostatic precipitator.
• FIGS. 1 and 2 are schematic representations of two plants for purifying fumes from cement works, in accordance with the invention .
• FIG 1 shows a furnace 2, belonging to a cement manufacturing installation.
• This oven which is of the "LEPOL” type, usually comprises a drying chamber 4, as well as a calcination chamber 6.
• a material intended for the manufacture of clinker is admitted by line 8, then passes through the drying chamber 4, as well as the calcination chamber 6, along a conveyor belt 10.
• the clinker thus obtained is then removed from the furnace 2 at an outlet orifice 12.
• This furnace is also provided a safety chimney 14.
• the fumes generated inside the furnace are collected via cyclones 16, then directed into a line 18, extending from an intermediate zone 20 of the furnace 2.
• the fumes are loaded with dust, at a concentration of between 20 and 300 g / Nm 3 , and have a temperature between 250 and 400 ° C, especially between 280 and 350 ° C.
• the latter which is provided with a fan 22, is placed in communication, at its end opposite the oven, with a unit dust removal 24, consisting of a cyclone or a battery of cyclones.
• a line 26 puts this unit 24 in communication with a denitrification reactor 28.
• a pipe 30, intended for the outlet of the dust also extends from the unit 24.
• a small, or marginal fraction of the fumes initially admitted through the pipe 18 is voluntarily allowed to leave, with the underflow of each cyclone, this fraction mixed with the dust, which is evacuated via the pipe 30 with the solids collected by the dedusting unit 24 is between 1 and 6% of the gas flow admitted into this unit 24, preferably between 2 and 4%.
• line 26 carries dusted fumes, which contain between 100 mg / Nm 3 and 5 g / Nm 3 of dust, preferably between 200 mg and 1 g / Nm 3 .
• the pipes 30 and 34 are then placed in mutual communication, at a junction 36. This ensures mixing between, on the one hand, the fumes collected with the dust, outside of the unit 24 and, on the other hand , the dust and denitrified fumes discharged from the reactor 28, via the drying chamber 4.
• FIG. 2 illustrates an alternative embodiment of the invention, in which the marginal fraction of fumes mixed with the dust is extracted, via a pipe 31. Furthermore, the dust dedusted, then denitrified, is evacuated from the reactor 28, by the intermediate of a line 33. This pipe 31 and this line 33 are placed in mutual communication, at a junction 37. A line 39, which extends from this junction 37, returns to the drying chamber 4 of the oven 2.
• the denitrified fumes, leaving the reactor 28, and the fumes collected with the dust, outside of the unit 24, are mixed at the junction 37, then returned to the oven 2.
• This mixture of fumes is then extracted from the oven, via a line 41, and is admitted into the final dust collector 40.
• the invention takes advantage of the extraction of the fumes, outside the oven, at an intermediate zone of the latter.
• Such a zone is, on the one hand, of easy access and has, on the other hand, a temperature favorable to the treatment of fumes by means of a denitrification reactor.
• Such a measure therefore makes it possible to dispense with the use of heat exchangers, which are expensive and of delicate use, taking into account the high dust content of the fumes.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Treating Waste Gases (AREA)
• Cyclones (AREA)

Applications Claiming Priority (3)

Publications (1)

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ID=8857215

Family Applications (1)

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• 2000
  • 2000-12-04 FR FR0015697A patent/FR2817487B1/fr not_active Expired - Fee Related
• 2001
  • 2001-12-03 WO PCT/FR2001/003811 patent/WO2002045824A1/fr not_active Application Discontinuation
  • 2001-12-03 CA CA002436315A patent/CA2436315A1/fr not_active Abandoned
  • 2001-12-03 US US10/433,367 patent/US20040042946A1/en not_active Abandoned
  • 2001-12-03 AU AU2002216158A patent/AU2002216158A1/en not_active Abandoned
  • 2001-12-03 PL PL36205501A patent/PL362055A1/xx not_active Application Discontinuation
  • 2001-12-03 EP EP01999416A patent/EP1355722A1/de not_active Withdrawn

Non-Patent Citations (1)

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