WO2002096821A1 - Method and device for calcination - Google Patents

Method and device for calcination Download PDF

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Publication number
WO2002096821A1
WO2002096821A1 PCT/SE2002/000909 SE0200909W WO02096821A1 WO 2002096821 A1 WO2002096821 A1 WO 2002096821A1 SE 0200909 W SE0200909 W SE 0200909W WO 02096821 A1 WO02096821 A1 WO 02096821A1
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WO
WIPO (PCT)
Prior art keywords
raw material
gas
lime
calcination
carbon dioxide
Prior art date
Application number
PCT/SE2002/000909
Other languages
French (fr)
Inventor
Roland Lundqvist
Torsten Ekdahl
Mats Westermark
Original Assignee
Vattenfall Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Vattenfall Ab filed Critical Vattenfall Ab
Publication of WO2002096821A1 publication Critical patent/WO2002096821A1/en

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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
    • C04B2/00—Lime, magnesia or dolomite
    • C04B2/10—Preheating, burning calcining or cooling
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00—Technologies relating to the processing of minerals
    • Y02P40/40—Production or processing of lime, e.g. limestone regeneration of lime in pulp and sugar mills

Definitions

  • the present invention concerns a method and a device for calcination of lime raw material such as lime sludge (CaC0 3 ) , or other materials that can be calcined.
  • Green liquor contains i.a. sodium carbonate in a water solution, which is converted to sodium hydroxide through the addition of slaked lime:
  • a lime sludge oven which is formed as a long (usually 70-100 m) tubular masonry oven which is slightly inclined and slowly rotating. Inside the oven there are different temperature zones where drying, preheating, calcination and sintering take place. Heat is usually supplied through burning of oil. The hot fumes are led in counter-flow against the solid material through the oven. Calcination occurs at about 900 °C. After the calcination zone, the temperature is raised to against or above 1100 where the quick lime sinters. The quick lime is then slaked with green liqueur in a slaking vessel, whereby hydration heat (q r ) is emitted:
  • the slaked lime is subsequently used for the above described causisicing process, where the green liqueur is recovered as white liqueur.
  • the lime cycle there are further several filtering and washing steps which are not described here.
  • the lime sludge ovens are not only space demanding, because the flows to pass through them are considerable and the dwelling time is long, but they are also energy demanding. Relatively great losses of heat to the surroundings result in poor use of energy at calcination.
  • the use of fossil fuels also results in considerable discharges of fumes containing i.a. carbon dioxide and sulphur dioxide, and considerable amounts of the supplied energy dwell in the exhaust gases.
  • Many ovens are today overloaded leading to inferior specific efficiency and thereby increased fuel consumption and greater discharges. A possible production increase by extension of buildings or renewal of machinery is difficult because the lime sludge ovens are very space demanding and require a great investment .
  • An aim of the present invention is to provide a method and a device for calcination of the kind mentioned above wherein the drawbacks of the prior art are avoided, resulting in a smaller investment and to obtain a faster, better controllable and less energy requiring method for calcination and thus a lower production cost .
  • the calicination plant may be made more compact than in previously known methods .
  • the cost for new investment or increase of capacity may be held relatively low.
  • the present invention thus concerns using plasma technology for calcination of lime raw material.
  • lime raw material is intended calcium carbonate containing minerals or substances such as limestone, lime sludge, dolomite, calcium containing sludge.
  • the lime raw material often also contains other elements than sodium as natural constituents or as additives.
  • a plasma generator functions such that a gas is supplied with electrical energy from a kind of electric arc which is formed between electrodes, whereby the gas is ionized to a certain degree and forms an energetic gas plasma.
  • the gas plasma has a temperature of 3000-4000 °C at the- discharge of the plasma generator.
  • the lime raw material is mixed with the hot gas from the plasma generator.
  • Calcination normally takes place at 900-1100 °C.
  • the reaction is reversible which means that the temperature must be held above a calcination temperature in order for reformulation of calcium carbonate not to occur in- the presence of carbon dioxide.
  • Higher calcination temperatures than 1200 °C should be avoided since there is a risk for inactivating the lime.
  • the reaction may be conducted in a compact reactor with great energy transfer per volume unit. This is possible because of the solid material in powder form having a large surface and getting good contact with the plasma.
  • inactivation sin called "dead burning" of the lime is avoided to a great extent in spite of the very high temperature of the plasma gas .
  • the method according to the invention has proved superior compared to calcination using fumes obtained from burning fossil fuels, since traditional technology results in calcination of agglomerates of lime raw material, resulting in a smaller contact surface and thereby ineffective and slow burning.
  • the time used for calcination in traditional lime sludge ovens is counted in hours.
  • Calcination according to the present invention is also achieved much faster than in methods based on resistive technology, radio waves or microwaves.
  • the efficiency for energy transformation between electricity and plasma is about 85-90%, whereas the efficiency for energy transformation between electricity and microwaves is only about 50-60%.
  • Using electric coils for transfer of heat at calcination also results in a high efficiency (about 90%) , but subsequently results in totally lower efficiency because of losses of energy in the ' very large oven which is required for using this technology.
  • the range of utilisation of supplied energy in the device according to the present invention is very good because of the use of plasma technology in calcination and heat exchange of all flows.
  • the present invention is advantageous also from an environmental point of view. Firstly, a great amount of fumes is avoided since no combustion is necessary at calcination or in any other step of the present method. This gives the advantage of minimising discharge of impurities otherwise being generated during combustion, such as for example sulphuric compounds .
  • generated gas mainly including carbon dioxide instead of carbon dioxide diluted in fumes
  • discharge of carbon dioxide to the atmosphere may be essentially avoided.
  • cleaning of great amounts of exhaust gases is also avoided.
  • Diverted carbon dioxide may be used as raw material, for example in the production of carbon dioxide gas.
  • figure 1 diagrammatically a device for calcination using plasma technology according to the invention.
  • FIG 2 diagrammatically an alternative device for calcination using plasma technology according to the invention.
  • Figure 1 shows a device for calcination using plasma technology including a drying apparatus 2 into which moist lime raw material is supplied in any suitable way for drying.
  • drying is carried out using the drying apparatus 2, heated with for example steam.
  • Steam may be supplied externally of internally, for example taken from steam generated in the slaking step in a heat exchanger 20.
  • a possible excess of steam or steam-gas mix from the slaker may be used as drying medium when drying the lime raw material.
  • drying media such as for example carbon dioxide may also be used. Steam emitted at the drying may be used for slaking the quick lime .
  • a step follows wherein the dried lime raw material is led by a conveyor 3 from the drying apparatus 2 to a pulverising apparatus 4 for pulverising. It is also possible that the lime raw material is already sufficiently disintegrated so that the pulverising step may be avoided.
  • the particle size may be in the range 1 - lOO ' O ⁇ m. The size-may be adjusted to - the requirements on the reactor.
  • the' conveyor 5 leads the ' dried and pulverised' lime raw material over a -gas sluice 6, through -an inlet 7 into ' the calcination reactor 8.
  • a gas conduit 23a leads initial gas (re-cycled carbon dioxide) into the plasma generator 9 for forming the gas plasma.
  • a tube conduit 23b leads, over a second inlet 11, auxiliary gas which is comprised of re-cycled carbon dioxide into the calcination reactor 8.
  • the auxiliary gas is used for feeding and distribution of incoming lime raw material and, if necessary, for lowering the temperature.
  • the temperature at the point where the lime is in contact with the plasma is controlled over the energy supply to the plasma reactor and the flow of lime raw material .
  • the incoming lime raw material is then calcinated during a part of one or a few seconds in contact with the gas plasma.
  • Calcination may be carried out pressurised, but preferably atmospheric pressure or a minor overpressure or underpressure is used.
  • gas essentially carbon dioxide
  • solid material are separated.
  • the solid material is brought to a slaking apparatus 16, wherein the quick lime is slaked with steam (water vapour) for producing the end product slaked lime.
  • steam-gas mixtures or water in liquid form may be used for slaking.
  • steam gas mixtures are intended dry water vapour mixed with air or other gases. Water vapour is generated in the heat exchanger 20 with the energy generated at the slaking step.
  • Water vapour for slaking is supplied for example over a tube conduit 22 from the drying apparatus 2.
  • the energy in the vapour which is not used for slaking may preferably be used in other heat/steam requiring processes, for example for drying lime raw material.
  • the separated gas from the separator 14 is led over a gas conduit 23 whereto is coupled a separating device 24, for example a filter, which filters away possible dust passing the separator 14.
  • a separating device 24 for example a filter, which filters away possible dust passing the separator 14.
  • the incoming gas in this case has a high temperature which means that it is required to use a filter that can withstand high temperatures.
  • the separating device 24 follows a heat exchanger 25, which is also connected to the gas conduit 23. Inside the heat exchanger 25, steam is generated from the heat of the gas. After the heat exchange 25 the gas conduit 23 branches into the two gas conduits 23a and 23b.
  • the plasma generator 9 requires pressurised initial gas so as to overcome the pressure drop over the generator, this gas firstly has to be compressed in a compressor. Cooling is suitable regarding the gas is to be compressed. Since compressors are sensitive to dust and particles it may also be necessary to filter the incoming gas to the compressor.
  • the gas conduit 23a leads initial gas (re-cycled carbon dioxide) for the plasma over a cooler/heat exchanger 26 which cools the gas to a suitable temperature for compressing. After the cooler there may follow a filtering device 27, if there is a requirement for further filtering. After the cooler/heat exchanger 26 and the filtering device 27 follows a compressor 28 which compresses the gas which is led into the plasma generator 9 where it is used for producing the carbon oxide plasma.
  • the hot gas may be heat exchanged against the gas after the compressor 28 before the cooler 26 in order to raise gas temperature before the plasma generator and this way reduce the energy consumption of the process.
  • the gas conduit 23b leads auxiliary gas (carbon oxide) over a compressor 29, which compresses the gas which is led into the calcination reactor 8, where it is used as auxiliary gas for feeding and distributing incoming lime raw material, and if needed, for lowing the temperature.
  • auxiliary gas carbon oxide
  • the highly concentrated carbon dioxide gas is discharged over a gas discharge valve which is not shown here at a suitable position after the separator 14.
  • the generated carbon dioxide may be used for any optional, commercial use, be let out into the atmosphere or be recovered.
  • the hot carbon dioxide rich gas may, before or after discharge, be used for preheating the lime raw material before the calcination reactor 8.
  • Figure 2 shows an alternative device for calcination using plasma technology according to the invention. It is generally arranged in the same way as the device 1, and where this is not the case it is marked with further reference numbers .
  • the embodiment in figure 2 differs from the first embodiment by the dried lime raw material after the pulverisation apparatus 4 is admixed with hot carbon dioxide diverted after the separator 14 over a tube conduit 30 for heating the dry lime raw material going into the calcinations reactor 8 in a preheating step 31.
  • the preheated lime raw material is thereafter led over the conveyor 32 into a separator 33 where lime raw material and carbon dioxide are separated.
  • the lime raw material continues as in embodiment 1 into the calcination reactor 8 over a conveyor 34.
  • the separated carbon dioxide from the separator 33 is diverted over a tube conduit 35 to the filtering device 24.
  • the hot carbon dioxide for drying the lime raw material, either as drying medium in the drying apparatus or with heat exchange with moist lime raw material.
  • the invention may of course be modified within the scope of the claims and may as an example be provided with or without pressurising or without at least one of the separating devices and with a varying number and positions of the heat exchangers .

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

A device for calcination of lime raw material is distinguished in that it includes: a plasma generator (9) for generating a gas plasma of carbon dioxide, and a calcination reactor (8), wherein the lime raw material is arranged to be brought into contact with said gas plasma of carbon dioxide for the formation of quick lime. The invention also concerns a method for calcinations.

Description

METHOD AND DEVICE FOR CALCINATION
Field of the invention
The present invention concerns a method and a device for calcination of lime raw material such as lime sludge (CaC03) , or other materials that can be calcined.
Description of prior art
In sulphate pulp plant digester chemicals such as white liquor, which essentially comprises sodium sulphide and sodium hydroxide, are recovered through causticising of green liquor. Green liquor contains i.a. sodium carbonate in a water solution, which is converted to sodium hydroxide through the addition of slaked lime:
Na2C03 (aq) + Ca (OH) 2 (s) → 2NaOH (aq) + CaC03 (s)
At causticising a residual product is obtained of lime sludge and including calcium carbonate, which after dewatering
(mechanical and possibly thermal) is heated whereby carbon dioxide escapes and calcium oxide is formed (calcination) :
CaC03 (s) + heat → <- CaO (s) + C02 (g)
At calcination is usually employed a lime sludge oven, which is formed as a long (usually 70-100 m) tubular masonry oven which is slightly inclined and slowly rotating. Inside the oven there are different temperature zones where drying, preheating, calcination and sintering take place. Heat is usually supplied through burning of oil. The hot fumes are led in counter-flow against the solid material through the oven. Calcination occurs at about 900 °C. After the calcination zone, the temperature is raised to against or above 1100 where the quick lime sinters. The quick lime is then slaked with green liqueur in a slaking vessel, whereby hydration heat (qr) is emitted:
Cao (s) + H20 (liq) → Ca (OH) 2 (s) + qr
The slaked lime is subsequently used for the above described causisicing process, where the green liqueur is recovered as white liqueur. In the lime cycle there are further several filtering and washing steps which are not described here.
The lime sludge ovens are not only space demanding, because the flows to pass through them are considerable and the dwelling time is long, but they are also energy demanding. Relatively great losses of heat to the surroundings result in poor use of energy at calcination. The use of fossil fuels also results in considerable discharges of fumes containing i.a. carbon dioxide and sulphur dioxide, and considerable amounts of the supplied energy dwell in the exhaust gases. Many ovens are today overloaded leading to inferior specific efficiency and thereby increased fuel consumption and greater discharges. A possible production increase by extension of buildings or renewal of machinery is difficult because the lime sludge ovens are very space demanding and require a great investment .
There are also alternative methods for calcination. In for example US-4 707 350 there is shown calcination using resistive technology. Hereby some of the traditional drawbacks of lime sludge ovens are avoided, but the method remains more energy demanding as a whole than in respect of the present invention because of energy losses in the very large oven which is required using this technology. During the last years, i.a. microwave or radio wave technology has been suggested for supply of energy at calcination. In US- 5 378 319 is shown calcination methods using microwave technology. The method allows calcination to be made in a few minutes. Microwaves are used for drying as well as calcination of the lime sludge.
Even if these newer technologies provide an improvement of economy and environmental impact compared to older technology, they are still linked with high energy consumption and technical difficulties.
Using plasma technology in combustion/burning of different substances is also described. In US-4 152 169 there is shown using plasma technology for producing cement . The described method, however, has a different purpose than the present invention.
Aim and most important features of the invention
An aim of the present invention is to provide a method and a device for calcination of the kind mentioned above wherein the drawbacks of the prior art are avoided, resulting in a smaller investment and to obtain a faster, better controllable and less energy requiring method for calcination and thus a lower production cost .
This aim is obtained through the features of the characterizing portions of the respective claims 1 and 16.
Because of the high efficiency resulting hereof, the calicination plant may be made more compact than in previously known methods . The cost for new investment or increase of capacity may be held relatively low. The present invention thus concerns using plasma technology for calcination of lime raw material. With lime raw material is intended calcium carbonate containing minerals or substances such as limestone, lime sludge, dolomite, calcium containing sludge. The lime raw material often also contains other elements than sodium as natural constituents or as additives. A plasma generator functions such that a gas is supplied with electrical energy from a kind of electric arc which is formed between electrodes, whereby the gas is ionized to a certain degree and forms an energetic gas plasma. The gas plasma has a temperature of 3000-4000 °C at the- discharge of the plasma generator. The lime raw material is mixed with the hot gas from the plasma generator.
Calcination normally takes place at 900-1100 °C. The reaction is reversible which means that the temperature must be held above a calcination temperature in order for reformulation of calcium carbonate not to occur in- the presence of carbon dioxide. Higher calcination temperatures than 1200 °C should be avoided since there is a risk for inactivating the lime.
Through the use of plasma technology in calcination according to the invention, the reaction may be conducted in a compact reactor with great energy transfer per volume unit. This is possible because of the solid material in powder form having a large surface and getting good contact with the plasma. By the reaction according to the invention taking place during this short period, inactivation (so called "dead burning") of the lime is avoided to a great extent in spite of the very high temperature of the plasma gas .
As concerns productivity, the method according to the invention has proved superior compared to calcination using fumes obtained from burning fossil fuels, since traditional technology results in calcination of agglomerates of lime raw material, resulting in a smaller contact surface and thereby ineffective and slow burning. The time used for calcination in traditional lime sludge ovens is counted in hours.
Calcination according to the present invention is also achieved much faster than in methods based on resistive technology, radio waves or microwaves. The efficiency for energy transformation between electricity and plasma is about 85-90%, whereas the efficiency for energy transformation between electricity and microwaves is only about 50-60%. Using electric coils for transfer of heat at calcination also results in a high efficiency (about 90%) , but subsequently results in totally lower efficiency because of losses of energy in the' very large oven which is required for using this technology.
The range of utilisation of supplied energy in the device according to the present invention is very good because of the use of plasma technology in calcination and heat exchange of all flows.
The present invention is advantageous also from an environmental point of view. Firstly, a great amount of fumes is avoided since no combustion is necessary at calcination or in any other step of the present method. This gives the advantage of minimising discharge of impurities otherwise being generated during combustion, such as for example sulphuric compounds .
By generated gas mainly including carbon dioxide instead of carbon dioxide diluted in fumes, it will be more economically advantageous to divert the carbon dioxide. Hereby discharge of carbon dioxide to the atmosphere may be essentially avoided. Hereby cleaning of great amounts of exhaust gases is also avoided. Diverted carbon dioxide may be used as raw material, for example in the production of carbon dioxide gas.
Since, according to the invention, there is a possibility of having essentially carbon dioxide atmosphere in the reactor, this reduces formation of unwanted nitrogen compounds such as nitrogen oxides (NOx) .
Many conventional lime sludge ovens of today are overloaded because of the high costs required for building new or extending lime sludge ovens. The overload makes the oil • consμmption unnecessary great. By in stead extending with plasma . calcination in parallel with' the old lime .sludge oven, ■ the production capacity may be raised at the same time- as- increased flume flows may be avoided.
Since the calcination reaction occurs faster using plasma technology than in -traditional lime sludge ovens, it. is. possible to make the calcination oven smaller with maintained, capacity.
In a further embodiment of the present invention it is also envisaged after completed calcination to produce slaked lime through slaking with water, vapour, water-vapour gas mixes or water in liquid form, supplied in such an amount that it corresponds to what is required for slaking. Emitted energy at slaking is recovered through heat exchange. This contributes to making the process energy effective.
Brief description of drawing
Further advantages that are obtained through using the present invention will come clear from the following detailed description wherein reference is made to the annexed drawings . The drawings show:
figure 1, diagrammatically a device for calcination using plasma technology according to the invention, and
figure 2, diagrammatically an alternative device for calcination using plasma technology according to the invention.
Description of embodiments
Figure 1 shows a device for calcination using plasma technology including a drying apparatus 2 into which moist lime raw material is supplied in any suitable way for drying.
For energy economy and environmental reasons it is suitable' to remove water in the lime raw material before calcination. Since the lime raw material is dewatered mechanically and possibly dried, the amount of emitted sulphur compounds are reduced since the sodium sulphide possibly being present in the lime raw material cannot react with the carbon dioxide and water so as to form hydrogen sulphide.
Na2S (s) + C02 (g) + H20 → NA2C03 (s) + H2S (g)
In the present embodiment drying is carried out using the drying apparatus 2, heated with for example steam. Steam may be supplied externally of internally, for example taken from steam generated in the slaking step in a heat exchanger 20. A possible excess of steam or steam-gas mix from the slaker may be used as drying medium when drying the lime raw material.
Other drying media such as for example carbon dioxide may also be used. Steam emitted at the drying may be used for slaking the quick lime .
After the drying step a step follows wherein the dried lime raw material is led by a conveyor 3 from the drying apparatus 2 to a pulverising apparatus 4 for pulverising. It is also possible that the lime raw material is already sufficiently disintegrated so that the pulverising step may be avoided.
Providing the lime as a powder results in that the contact surface of the lime with the plasma will become- very large, whereby the contact time can-be minimized. The particle size may be in the range 1 - lOO'O μm. The size-may be adjusted to - the requirements on the reactor.
After the pulverising step the' conveyor 5 leads the' dried and pulverised' lime raw material over a -gas sluice 6, through -an inlet 7 into 'the calcination reactor 8.
Because of the presence of the carbon dioxide atmosphere with low oxygen and nitrogen contents inside the calcination reactor only insignificant amounts of nitrogen oxides will be formed .
Into the calcination reactor 8 there also debouches a plasma generator 9 over en inlet 10. A gas conduit 23a leads initial gas (re-cycled carbon dioxide) into the plasma generator 9 for forming the gas plasma.
A tube conduit 23b leads, over a second inlet 11, auxiliary gas which is comprised of re-cycled carbon dioxide into the calcination reactor 8. The auxiliary gas is used for feeding and distribution of incoming lime raw material and, if necessary, for lowering the temperature. The temperature at the point where the lime is in contact with the plasma is controlled over the energy supply to the plasma reactor and the flow of lime raw material .
The incoming lime raw material is then calcinated during a part of one or a few seconds in contact with the gas plasma.
Calcination may be carried out pressurised, but preferably atmospheric pressure or a minor overpressure or underpressure is used.
A quick lime then swirls in the gas flow out through an outlet 12 in the calcination reactor 8 and is brought through a conduit 13 to a separator 14, e.g. cyclone, whereas the temperature still exceeds 900 C. Here gas (essentially carbon dioxide) and solid material are separated.
The solid material is brought to a slaking apparatus 16, wherein the quick lime is slaked with steam (water vapour) for producing the end product slaked lime. Also steam-gas mixtures or water in liquid form may be used for slaking. With steam gas mixtures are intended dry water vapour mixed with air or other gases. Water vapour is generated in the heat exchanger 20 with the energy generated at the slaking step.
Water vapour for slaking is supplied for example over a tube conduit 22 from the drying apparatus 2. The energy in the vapour which is not used for slaking may preferably be used in other heat/steam requiring processes, for example for drying lime raw material.
The separated gas from the separator 14 is led over a gas conduit 23 whereto is coupled a separating device 24, for example a filter, which filters away possible dust passing the separator 14. The incoming gas in this case has a high temperature which means that it is required to use a filter that can withstand high temperatures.
After the separating device 24 follows a heat exchanger 25, which is also connected to the gas conduit 23. Inside the heat exchanger 25, steam is generated from the heat of the gas. After the heat exchange 25 the gas conduit 23 branches into the two gas conduits 23a and 23b.
Since the plasma generator 9 requires pressurised initial gas so as to overcome the pressure drop over the generator, this gas firstly has to be compressed in a compressor. Cooling is suitable regarding the gas is to be compressed. Since compressors are sensitive to dust and particles it may also be necessary to filter the incoming gas to the compressor.
The gas conduit 23a leads initial gas (re-cycled carbon dioxide) for the plasma over a cooler/heat exchanger 26 which cools the gas to a suitable temperature for compressing. After the cooler there may follow a filtering device 27, if there is a requirement for further filtering. After the cooler/heat exchanger 26 and the filtering device 27 follows a compressor 28 which compresses the gas which is led into the plasma generator 9 where it is used for producing the carbon oxide plasma.
It is also within the scope of the invention that the hot gas may be heat exchanged against the gas after the compressor 28 before the cooler 26 in order to raise gas temperature before the plasma generator and this way reduce the energy consumption of the process.
The gas conduit 23b leads auxiliary gas (carbon oxide) over a compressor 29, which compresses the gas which is led into the calcination reactor 8, where it is used as auxiliary gas for feeding and distributing incoming lime raw material, and if needed, for lowing the temperature.
The highly concentrated carbon dioxide gas is discharged over a gas discharge valve which is not shown here at a suitable position after the separator 14. The generated carbon dioxide may be used for any optional, commercial use, be let out into the atmosphere or be recovered. The hot carbon dioxide rich gas may, before or after discharge, be used for preheating the lime raw material before the calcination reactor 8.
Figure 2 shows an alternative device for calcination using plasma technology according to the invention. It is generally arranged in the same way as the device 1, and where this is not the case it is marked with further reference numbers .
The embodiment in figure 2 differs from the first embodiment by the dried lime raw material after the pulverisation apparatus 4 is admixed with hot carbon dioxide diverted after the separator 14 over a tube conduit 30 for heating the dry lime raw material going into the calcinations reactor 8 in a preheating step 31.
The preheated lime raw material is thereafter led over the conveyor 32 into a separator 33 where lime raw material and carbon dioxide are separated. The lime raw material continues as in embodiment 1 into the calcination reactor 8 over a conveyor 34. The separated carbon dioxide from the separator 33 is diverted over a tube conduit 35 to the filtering device 24.
It is also within the scope of the invention to be able to use the hot carbon dioxide for drying the lime raw material, either as drying medium in the drying apparatus or with heat exchange with moist lime raw material. The invention may of course be modified within the scope of the claims and may as an example be provided with or without pressurising or without at least one of the separating devices and with a varying number and positions of the heat exchangers .

Claims

1. Method for calcination lime raw material, characterized in that lime raw material is brought into contact with a plasma of carbon dioxide in a calcination reactor (8) , whereby quick lime is produced.
2. Method according to claim 1, characterized in that lime sludge is calcined.
3. Method according to claim 1 or 2 , characterized in that the incoming wet lime raw material is dried in a drying apparatus (2) .
4. Method according to any of the previous claims characterized in that the lime raw material is pulverised.
5. Method according to any of the previous claims characterized in that carbon dioxide is re-cycled from the calcination reactor (8) to a plasma generator (9) for forming the gas plasma.
6. Method according to any of the claims 1-5, characterized in that carbon dioxide is re-cycled from the calcination reactor back to the calcination reactor (8) where it is used as auxiliary gas for feeding and distributing incoming lime raw material and if necessary for lowering the temperature .
7. Method according to claim 6, characterized in that the auxiliary gas is used as gas medium for sluicing the lime raw material in to the calcination reactor.
Method according to any of the previous claims, characterized in that the quick lime is separated from gaseous substances in one or plural separators (14) , operative at a temperature near or over the calcination temperature .
Method according to any of the previous claims characterized in that the quick lime is slaked with water vapour, water vapour-gas mixtures or with liquid water.
Method according to claim 9, characterized in that water vapour generated in the drying step is used for slaking.
Method according to claim 9 or.10, characterized in that the energy generated in the slaking reaction is recovered for for example generating steam or heating water.
Method according to any of the claims 9 - .11, characterized in that water vapour or water vapour-gas mixture not required for slaking is used as drying medium when drying lime raw material.
Method according to any of the previous claims, characterized in that at least part of hot carbon dioxide discharged from the calcination reactor is used for heat exchange with either moist or dry lime raw material, is used as drying medium in a drying apparatus (2) , or is used for preheating dried lime raw material.
Method according to any of the previous claims, characterized in that at least part of carbon dioxide which is formed at the calcination reaction and is recycled to the calcination reactor (8) is used for steam production.
15. Method according to any of the previous claims, characterized in that a carbon dioxide rich process gas is discharged from the process.
16. Device for calcination of lime raw material, characterized in that it includes :
- a plasma generator (9) for generating a gas plasma of carbon dioxide, and
- a calcination reactor (8) , wherein the lime raw material is arranged to be brought into contact with said gas plasma of carbon dioxide for the formation of quick lime.
17. Device according to claim 16, characterized in that it includes a drying apparatus (2) for drying lime raw material before calcination.
18. Device according to claim 17, characterized in that the drying apparatus (2) is preheated with re-cycled carbon dioxide .
19. Device according to claim 17, characterized in that the drying apparatus (2) is heated with water vapour, water- vapour-gas mixture or any other drying medium such as fumes .
20. Device according to any of the claims 16 - 19, characterized in that it includes a pulverising apparatus (4) for pulverising lime raw material before calcination.
21. Device according to any of the claims 16 - 20, characterized in that it includes a slaking device (16) for slaking a quick lime with water vapour and/or water- vapour-gas mixtures, or with liquid water.
22. Device according to claim 21, characterized in that it includes a heat exchanger (20) for recovering energy generated at the slaking reaction.
23. Device according to any of the claims 16 - 22, characterized in that it includes a heat exchanger/cooler (26) for cooling the initial gas for the plasma before the plasma generator (9) .
24. Device according to any of the claims 16 - 23, characterized in that it includes one or several filters (27) for filtering the initial gas for the plasma before the plasma generator (9) .
25. Device according to any of the claims 16 - 24, characterized in that it includes a compressor (28) for pressurising the carbon dioxide gas before the plasma generator (9) .
26. Device according to any of the claims 16 - 25, characterized in that it includes means for supply of auxiliary gas to the calcination reactor (8) for feeding and distributing lime raw material.
27. Device according to claim 26, characterized in that it includes a compressor 29 for pressurising auxiliary gas before it is led into the calcination reactor (8) .
28. Device according to any of the claims 16 - 27, characterized in that it includes at least one separator (14) for separating quick lime and gaseous substances before the calcination reactor.
29. Device according to claim 28, characterized in, that it includes one or plural heat exchangers (25) which is/are positioned after the separator (14) , for recovering energy through heat exchange with gas discharged from the calcination reactor.
30. Device according to any of the claims 16 - 29, characterized in that it includes a gas sluice (6) for lime raw material for obtaining a carbon dioxide atmosphere inside a calcination reactor.
31.Device according to any of the claims 28 - 30, characterized by one or plural filters (24) which is/are positioned after the,separator (14) for filtering the gas from the calcination reactor.
32.Device according to any of the claims 28 - 31, characterized by means (30, 31) for preheating lime, raw material with hot carbon dioxide ■ discharged from the separator (14) .
33.Device according to any of the claims 28 - 32, characterized by means for using at least part of hot carbon dioxide discharged from the calcination reactor for heat exchange with lime raw material.
34. Device according to any of the claims 28 - 32, characterized by means for providing use of hot carbon dioxide as drying medium in a drying apparatus (2) .
PCT/SE2002/000909 2001-05-30 2002-05-13 Method and device for calcination WO2002096821A1 (en)

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WO2023234847A1 (en) * 2022-06-03 2023-12-07 Limearc Process Ab Injection arrangements in a calcination system
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WO2022229192A1 (en) 2021-04-28 2022-11-03 Saltx Technology Ab Plasma cyclone reactor
SE545800C2 (en) * 2022-06-03 2024-02-06 Limearc Process Ab Heat recovery in a calcination system
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SE2250679A1 (en) * 2022-06-03 2023-12-04 Limearc Process Ab System and method for calcination
SE2250682A1 (en) * 2022-06-03 2023-12-04 Limearc Process Ab Heat recovery in a calcination system
WO2023234847A1 (en) * 2022-06-03 2023-12-07 Limearc Process Ab Injection arrangements in a calcination system
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SE2250680A1 (en) * 2022-06-03 2023-12-04 Limearc Process Ab Injection arrangement in a calcination system
WO2023234845A1 (en) * 2022-06-03 2023-12-07 Limearc Process Ab System and method for calcination
SE545798C2 (en) * 2022-06-03 2024-02-06 Limearc Process Ab System and method for calcination
WO2024089134A1 (en) 2022-10-27 2024-05-02 Saltx Technology Ab Plasma cyclone calcination reactor design
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SE545972C2 (en) * 2023-03-01 2024-04-02 Limearc Process Ab A calcination method and system comprising a particle separator
SE546005C2 (en) * 2023-03-01 2024-04-09 Limearc Process Ab System and method for calcination
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SE0101896D0 (en) 2001-05-30
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