Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B11/00—Calcium sulfate cements
  • C04B11/02—Methods and apparatus for dehydrating gypsum
  • C04B11/028—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained
  • C04B11/0283—Fluidised beds

Definitions

• the present invention relates to a method for the thermal treatment of gypsum, in which the material in the fluidized bed with built-in heat exchange surfaces is dewatered in a continuous process.
• the invention also relates to an apparatus for performing this method.
• Moist gypsum that is, calcium sulfate dihydrate, including Feucht ⁇ gypsum from flue gas desulphurisation plants, so-called.
• FGD gypsum listening ge ⁇ can at temperatures up to about 6 ⁇ to 70 ° C devis ⁇ be surface-dried without the water of crystallization to entfer ⁇ NEN. At temperatures up to about 150 ° C, the crystal water is extracted primarily with the formation of the hemihydrate. Of this there is the alpha or beta modification, with the beta modification mostly occurring.
• DE kl 09 7 ⁇ 3 describes a two-stage process for producing calcined gypsum with an adjustable phase composition.
• the drying of moist gypsum in a fluid bed apparatus is built in in the first stage Heat exchange surfaces leads to a low temperature level Runaway ⁇ .
• the dried gypsum is treated in a second fluidized bed apparatus with built-in heat exchange surfaces at a low temperature level in order to remove the water of crystallization.
• the heat to be used is entered with the fluidizing gas and the heat exchange surfaces, the majority of the heat being introduced via the heat exchange surfaces.
• each particle contains the following phases: external anhydride (e.g. A III), internal dihydrate and intermediate ⁇ -hemihydrate.
• external anhydride e.g. A III
• internal dihydrate e.g. A III
• intermediate ⁇ -hemihydrate e.g. A III
• the proportions of these phases, i.e. the degree of calcimerization depends on the particle size. Small particles have a low dihydrate content under the same conditions. i.e. a higher degree of calcimerization than large particles.
• the object of the present invention is to provide a method of the type mentioned, in which a calcined Gypsum with high purity and consistency in the phase composition is obtained. Furthermore, a process is to be created in which both dried and moist gypsum can be used as the starting material. Furthermore, an apparatus for carrying out the method is to be proposed.
• this object is achieved in that the material is passed through at least one fluidized bed zone and in this zone both the water vapor partial pressure and the material temperature are set in order to form phase-pure beta hemihydrate at the outlet of the at least one zone.
• Preferred embodiments of the method result from claims 2 to 9.
• a preferred device for carrying out the method is given in claim 10.
• Particularly preferred embodiments of the device are contained in claims 11 to 15.
• anhydrite e.g. the reactive Alll phase
• the suppression of anhydrite formation is more energetically advantageous than conventional subsequent conversion back to the hemihydrate, since the heat of dehydration does not have to be used.
• Anhydrite III which in the starting material that is fed to the calcination due to a pretreatment can already be partially present, is also returned in the at least one zone in the hemihydra phase in the process according to the invention.
• a fluidized bed zone is sufficient to produce phase-pure beta hemihydrate.
• zu ⁇ sharmlichen Wasserdampfpar ⁇ partial pressure and the Materla1temperatur is also adjusted in each case.
• a anhydrite is zones by adjusting the Wasserdampfpart1al horrs and the material temperature separately in each of the additional F passedbett ⁇ in each of these zones permeable prevented reli ⁇ .
• a cooling zone can be connected to the at least one fluidized bed zone for the hemihydrate formation, in which a cooling medium is supplied to the heat exchange surfaces in the fluidate layer and into the slightly tempered, i.e. with a temperature substantially below the product temperature, fluidizing gas is introduced.
• a further fluidized bed zone for anhydride formation is to be provided between the at least one fluidized bed zone for hemihydrate formation and the cooling zone, water vapor partial pressure also being present in this further zone and material temperature can be set.
• water vapor partial pressure and material temperature are set in the further flow zone to values at which no anhydrite forms. If the end product is the anhydrite or a hemihydrate / anhydride mixture If a certain composition is desired, the water vapor pressure and material temperature in this further fluidized bed zone are set to values at which the hemihydrate is wholly or partly converted into anhydrite.
• the various zones, ie at least dratzone a Halbhy ⁇ further Anhydritzone and ⁇ ie Kuhlzone kön ⁇ NEN be arranged in ge t rennten fluidized bed apparatus with F ö r d ereinrich t Ungen to the to behan ⁇ elnde material from a Flie SSB et t shakers in next to transport. It is, however, are Appara t iv simpler and therefore preferable to set the zones in a F1 1 eßbet t apoara t to arrange, in the crushed them by Trenn ⁇ vo n separated from one another, with openings for the Materialflu ß from one zone to the next provided are. Innerhal bj e d he zone may be additional separating weirs net angeord ⁇ to a narrower retention to achieve the delnden to behan ⁇ material.
• Wet or dried gypsum can be used as the starting material.
• the Ver ⁇ will ride with reference to a preferred embodiment described, are used in the two zones of beta-Halbhydrat Anlagen, pressure the following information to adjust the 'Wasserdampfpartial- and temperature are in the first zone entspre ⁇ accordingly even if only a zone for hemihydrate formation is used.
• moist gypsum is used, a relatively large amount of water vapor is released in the first zone, so that the risk is lower that the water vapor partial pressure drops below the target value and anhydrite forms on the particle surfaces.
• the water vapor partial pressure is set in the first zone. This setting can be made by measuring the water vapor partial pressure, preferably above the fluidized bed. If the setpoint is undershot, water vapor is supplied to the first zone. The water vapor partial pressure can also be set by measuring the moisture of the starting material, the amount of the starting material and the amount of the fluidizing gas introduced into the flow zone. The water vapor partial pressure of the exhaust air from the fluidized bed during the production of the hemihydrate can be calculated from these values. If this calculated value is too low, a corresponding amount of water vapor is introduced into the fluidized bed zone, so that the target value is reached. With this setting of the water vapor partial pressure, a measuring device for determining the water vapor partial pressure in the device is not necessary. The feed for the fluidizing gas is then to be provided with a flow meter.
• the formation of anhydrite on the surface of the Prevents particles and possibly converts anhydrite contained in the starting material into gypsum hemihydrate.
• the water vapor is preferably fed to the fluidized bed of the first zone with the fluidizing gas, generally air.
• the water vapor partial pressure in the at least one zone for beta hemihydrate formation is generally set to a value in the range from 0.1 to 1.1 bar, preferably 0.5 to 1 bar.
• the gew ä hlte value also depends on the set in the jeweili ⁇ gen zone material temperature.
• vorge partial pressure adjustment of the material temperature in addition to the adjustment of the water vapor ⁇ .
• the temperature in the fluidized bed is measured, the measured value is compared with a desired value and the heat supply is correspondingly reduced, increased or left unchanged.
• the heat supply to the fluidized bed takes place for the most part via the warm listening surfaces and to a small extent via the Fluidi s ⁇ erunc; sj; as.
• the setting of the desired material temperature is preferably based on the temperature and / or temperature of the heating medium flowing through the heat exchange surfaces? made, usually steam or Thermool. In principle, if the actual value deviates from the boli value, it is also possible to change the temperature of the fluidizing gas or to change the throughput of the material.
• the set material temperature ie the setpoint, depends on the residence time of the material in the zone. In general, the material temperature is chosen to be lower with a long residence time than with a short residence time. In the at least one zone in which the hemihydrate is formed, the material temperature can be in the range from about 100 to 150 ° C., depending on the residence time. The selected temperature within this range also depends on the set water vapor partial pressure. As a rule, that a higher product temperature can be set at higher water vapor partial pressures.
• the water vapor partial pressure and the product temperature are adjusted separately from the first zone.
• the calcination takes place to the phase-pure hemihydrate.
• the height of the water vapor partial pressure and the product temperature in the second zone need not deviate from the values in the first zone.
• the set values depend on the material to be calcined, e.g. the Partike.llarge, from the zone size u. hence the dwell time and the mutual influence of water vapor partial pressure and material temperature already mentioned. The optimal values can be determined by simple tests.
• the at least one fluidized bed zone is preferably followed by a further fluidized bed zone which can be used for the partial or complete formation of anhydrides. However, as already explained above, it can also be used as a conveying section of the hemihydrate into the cooling zone if the desired end product is the hemihydrate. In this case, water vapor partial pressure and product temperature in this fluidized bed zone are kept at values at which the hemihydrate is not changed.
• the flow zone for the formation of anhydrite is preferably followed by at least one cooling zone for the end product.
• This cooling zone is also a fluidized bed with heat exchange surfaces.
• the cooling zone can also be provided with a temperature and water vapor partial pressure setting.
• a fluidized bed device is designated.
• weirs 2 to -i are provided, which divide the device into the chambers (zones) 5 to 8, through which the material supplied through the inlet 9 into the fluidized bed device flows in succession.
• the separating weirs 2 to -4 are provided with openings (not shown) for the material flow.
• the chambers 5 and 6 are for gypsum hemihydrate formation, the chamber 7 for gypsum anhydrite formation and the chamber 8 is for cooling the product before it leaves the device via the product outlet 10.
• there are additional dividing weirs 12 provided with openings in order to achieve a narrow residence time spectrum for the material to be calcined.
• heat exchangers 13 to 16 are arranged.
• the heat exchangers 13 to 15 are supplied via lines 17 to 19 heating medium, which via lines 20 to 22nd flows out of the heat exchangers again. Cooling medium is fed to the heat exchanger l6 via the line 23 and flows off again via the line 2k.
• the guides to ⁇ 25 to 28 for the fluidizing gas At about the ⁇ guides 25 to 27 is passed through a register 29 heated fluidizing gas in the chambers 5 to 7. Via the feed 28 30 tempered Fluidisie ⁇ approximately gas is passed into the cooling chamber 8 through a register.
• the amount of the fluidization gas which is supplied to the chambers 5 to 7 can be regulated via the flow regulator 31.
• the quantity of the heating medium or cooling medium and thus the temperature of the heat exchangers 13 to 16 can be set via valves k 1 to k k in the supply lines 17-19 and 23.
• Exhaust air channels 32 to 34 are provided above the chambers 5 to 8.
• a thermal sensor is arranged in the fluidized bed, which are designated 35 to 37.
• 5 to 7 measuring devices 38-40 for the water vapor partial pressure are in the chambers above the fluidized bed.
• the water vapor partial pressure and the material temperature can be measured in each of the chambers 5 to 7 and can be set to different values from chamber to chamber. If the measured value deviates from the target value, the temperature or the water vapor partial pressure in the relevant chamber can be set via control loops (not shown). At the temperature, the setting is made via the respective heat exchanger, 13, lk or 15, by the amount of heating medium supplied to it via the relevant valve kl. k 2 or 43 in the feed line 17, 18 or 19 is changed. At the water vapor partial pressure, the adjustment is made by feeding water vapor through the lines provided with valves 45 to kl. lines 48, 49 or 50 in the feeds 25, 26 or 27 of the fluidizing gas. Live steam can be fed in via lines 48 to 50. It is also possible, for example, the water vapor rich of the exhaust duct 32 to the exhaust feed-solution into the conduit 49 or 50 to be used, provided that the water vapor in the chamber 6 or 7 is too low t
• a fan and a register can also be used for each of the feeds.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Catalysts (AREA)
• Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)

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• 1996
  • 1996-02-19 DE DE19606075A patent/DE19606075C2/de not_active Expired - Fee Related
• 1997
  • 1997-02-17 EP EP97905035A patent/EP0881996A1/de not_active Withdrawn
  • 1997-02-17 HU HU9900997A patent/HUP9900997A3/hu unknown
  • 1997-02-17 CZ CZ982631A patent/CZ263198A3/cs unknown
  • 1997-02-17 US US09/125,407 patent/US6054101A/en not_active Expired - Fee Related
  • 1997-02-17 WO PCT/EP1997/000743 patent/WO1997030004A1/de not_active Ceased
  • 1997-02-17 PL PL97328347A patent/PL328347A1/xx unknown

Non-Patent Citations (1)

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