CA1117732A - Method of dehydrating carnallite - Google Patents
Method of dehydrating carnalliteInfo
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- CA1117732A CA1117732A CA000297735A CA297735A CA1117732A CA 1117732 A CA1117732 A CA 1117732A CA 000297735 A CA000297735 A CA 000297735A CA 297735 A CA297735 A CA 297735A CA 1117732 A CA1117732 A CA 1117732A
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- carnallite
- reaction zone
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- water
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Abstract
Abstract of the Disclosure A method of dehydrating carnallite, in which preliminarily enriched carnallite with 39-41 wt.% water is heated up to 205-230°C by fuel combustion products having a temperature of 500-600°C, and a partially dehydrated carnallite with 3-8 wt.% water is obtained.
Said dehydrated carnallite is melted in a reaction zone and the melt is subjected to the action of HCl is a chlorinating agent.
Thereafter the melted carnallite is allowed to settle from solid impurities and, as a result, dehydrated carnallite is obtained with water content less than 0.5 wt.%. The melting of partially dehydrated carnallite with 3-8 wt.% water is performed with the aid of fuel combustion products containing air and water vapour having a temperature of 1050°C-1150°C. These products are introduced tangently to the surface defining the reaction zone at a rate ensuring the formation of an intensive eddy flow of gases, which occupies the whole volume of the reaction zone. The partially dehydrated carnal-lite is thrown on the side surface of the reaction zone by the eddy flow due to the action of centrifugal forces, a continuous film of the melt being formed on the side surface of the reaction zone.
Gases containing the products of fuel combustion and the gases liberating upon interaction of the chlorinating agent with the carnallite melt being removed from the reaction zone. The present invention can be successfully used in titanium industry as well as in magnesium industry in which dehydrated carnallite is one of the types of stock material for electrolytic production of magnesium and chlorine.
Said dehydrated carnallite is melted in a reaction zone and the melt is subjected to the action of HCl is a chlorinating agent.
Thereafter the melted carnallite is allowed to settle from solid impurities and, as a result, dehydrated carnallite is obtained with water content less than 0.5 wt.%. The melting of partially dehydrated carnallite with 3-8 wt.% water is performed with the aid of fuel combustion products containing air and water vapour having a temperature of 1050°C-1150°C. These products are introduced tangently to the surface defining the reaction zone at a rate ensuring the formation of an intensive eddy flow of gases, which occupies the whole volume of the reaction zone. The partially dehydrated carnal-lite is thrown on the side surface of the reaction zone by the eddy flow due to the action of centrifugal forces, a continuous film of the melt being formed on the side surface of the reaction zone.
Gases containing the products of fuel combustion and the gases liberating upon interaction of the chlorinating agent with the carnallite melt being removed from the reaction zone. The present invention can be successfully used in titanium industry as well as in magnesium industry in which dehydrated carnallite is one of the types of stock material for electrolytic production of magnesium and chlorine.
Description
1~17732 The present invention relates to a method of dehydrating carnallite.
The present invention can be used in the magnesium ~ndustry, where dehydrated carnallite is one of the types of stock material for the electrolytic production of magnesium and chlorine, and in the titanium industry.
It is widely known that enriched carnallit~, obtained by recrystallization from carnallite rock, is a stock material for the electrolytic production of magnesium. The enriched carnallite contains 31-33% of MgC12 and 39-41~ of H2O, of which 2-4% is hygro-scopic water and 35-39% is crystallization water. The main struc-tural components of the enriched carnallite are hexahydrous carnal-lite KCl.MgC12.6H20 (85-90 wt.%), parent solution of bischofite MgC12 in water (5-10 wt.%), and sodium NaC1 ~4-5 wt.~).
Prior to electrolysis, it is necessary to remove the water. ~therwise electrolytic decomposition of water takes place, which greatly reduces the current yield of magnesium. The process of crystallization water removal from carnallite is called dehydration.
Carnallite dehydration is performed in two stages.
At the first stage the enriched carnallite is heated in a solid state up to 205-230C by the heat of fuel combustion products. l~his process is performed in a counterflow or cross flow of the combustion products and the ~ - 2 -`` 111773Z
carnallite being heated. The duration of the proce~
1~5-2 hour~.
In the temperature range from 90 ~o 130-1 40C hydro-~copic ~ater is removed and hexahydrous c~rnallite is transformed into dihydrous one according to the reaction:
KCl.MgC12.6H20 ~ KCl.M~C12.2H20 + 4H20~
In t~e temperature range from 150 to ~05-230C di~yd-rous carnallite i8 partially trans~ormed into de~ydrated carnallite according to the reaction:
KCl.lllgC12.2H2Q ~ KCl.MgC}2 ~ 2X20~
~ hi3 reaction is accompanied by hydrolysis of magnes-ium chloride with t~e ~ormation oi magnesium hydroxychlor-ide, and can be ~c~ematically presented as.
~gC12 f ~0 ~ MgO~Cl + HCl~
Carnallite semi-product obtained in t~e process of dehydration in a solid state contains 45-50 wt.% of ~gC12 and 3-8 wt.% of ~2- ~e main structural components oi the carnallite semi-product are dehydrated and dihydrous car-nallite ~83-88 wt.%)`, magnes~um hydroxychloride (7-11.~t.%
or, as calculated ~or ~gO, 2-3 wt.% of MgO), and ~ h~
chloride (5-6 ~t~%). ~he second stage oi dehydrating carnal lite, i.e. the stage of ¢omplete dehydration oi carnallite semi-product ~it~ the formation o~ debydrated carnallite, i9 performed by melting the carnallite semi-product, treat-ing the re~ulting carnallite melt with a chlorinsting age3t, and settling the melt ~rom the solid impuritie~. In the known method electric ener~y ~s used as a heat sour~e for melting carnallite se~i~product. The process lasts for 2-2.5 hours.
The melting of carnallite semi product is performed at 500-550C. Under these conditions-water is almost completely re-moved from the melt and magnes~um hydroxychloride decomposes with the formation of solid magnesium oxide according to the reaction:
MgOHCl ~ MgO + HCl~
Additional hydrolysls of magnesium chloride also takes place, due to which the content of MgO in the me-lt increases up to 3.5-5 wt.%.
Then the obtained melt is heated up to 700-800C and treated with a chlorinated agent, gaseous chlorine being used as the chlorinating agent which bubbles through the melt. As a de-oxidizing agent use is made of petroleum coke (1 wt.% in a mixture with the carnallite semi-product). Upon treatment of the melt with chlorine, partial chlorination of magnesium oxide takes place by the reaction:
The present invention can be used in the magnesium ~ndustry, where dehydrated carnallite is one of the types of stock material for the electrolytic production of magnesium and chlorine, and in the titanium industry.
It is widely known that enriched carnallit~, obtained by recrystallization from carnallite rock, is a stock material for the electrolytic production of magnesium. The enriched carnallite contains 31-33% of MgC12 and 39-41~ of H2O, of which 2-4% is hygro-scopic water and 35-39% is crystallization water. The main struc-tural components of the enriched carnallite are hexahydrous carnal-lite KCl.MgC12.6H20 (85-90 wt.%), parent solution of bischofite MgC12 in water (5-10 wt.%), and sodium NaC1 ~4-5 wt.~).
Prior to electrolysis, it is necessary to remove the water. ~therwise electrolytic decomposition of water takes place, which greatly reduces the current yield of magnesium. The process of crystallization water removal from carnallite is called dehydration.
Carnallite dehydration is performed in two stages.
At the first stage the enriched carnallite is heated in a solid state up to 205-230C by the heat of fuel combustion products. l~his process is performed in a counterflow or cross flow of the combustion products and the ~ - 2 -`` 111773Z
carnallite being heated. The duration of the proce~
1~5-2 hour~.
In the temperature range from 90 ~o 130-1 40C hydro-~copic ~ater is removed and hexahydrous c~rnallite is transformed into dihydrous one according to the reaction:
KCl.MgC12.6H20 ~ KCl.M~C12.2H20 + 4H20~
In t~e temperature range from 150 to ~05-230C di~yd-rous carnallite i8 partially trans~ormed into de~ydrated carnallite according to the reaction:
KCl.lllgC12.2H2Q ~ KCl.MgC}2 ~ 2X20~
~ hi3 reaction is accompanied by hydrolysis of magnes-ium chloride with t~e ~ormation oi magnesium hydroxychlor-ide, and can be ~c~ematically presented as.
~gC12 f ~0 ~ MgO~Cl + HCl~
Carnallite semi-product obtained in t~e process of dehydration in a solid state contains 45-50 wt.% of ~gC12 and 3-8 wt.% of ~2- ~e main structural components oi the carnallite semi-product are dehydrated and dihydrous car-nallite ~83-88 wt.%)`, magnes~um hydroxychloride (7-11.~t.%
or, as calculated ~or ~gO, 2-3 wt.% of MgO), and ~ h~
chloride (5-6 ~t~%). ~he second stage oi dehydrating carnal lite, i.e. the stage of ¢omplete dehydration oi carnallite semi-product ~it~ the formation o~ debydrated carnallite, i9 performed by melting the carnallite semi-product, treat-ing the re~ulting carnallite melt with a chlorinsting age3t, and settling the melt ~rom the solid impuritie~. In the known method electric ener~y ~s used as a heat sour~e for melting carnallite se~i~product. The process lasts for 2-2.5 hours.
The melting of carnallite semi product is performed at 500-550C. Under these conditions-water is almost completely re-moved from the melt and magnes~um hydroxychloride decomposes with the formation of solid magnesium oxide according to the reaction:
MgOHCl ~ MgO + HCl~
Additional hydrolysls of magnesium chloride also takes place, due to which the content of MgO in the me-lt increases up to 3.5-5 wt.%.
Then the obtained melt is heated up to 700-800C and treated with a chlorinated agent, gaseous chlorine being used as the chlorinating agent which bubbles through the melt. As a de-oxidizing agent use is made of petroleum coke (1 wt.% in a mixture with the carnallite semi-product). Upon treatment of the melt with chlorine, partial chlorination of magnesium oxide takes place by the reaction:
2 MgO + 2 C12 + C----~2 MgC12 + C02 as a result of which the MgO content in the melt decreases down to 2-3 wt.%.
~fter treating with chlor~ne, the melt is allowed to settle from solid-impurities, mainly from magnesium oxide, at 700-750C. The melt of dehydrated carnallite obtained after sedi-mentation contains 50-52 wt.~ of MgC12, no more than 0.5~ of H2O, and no more than 0.8~ of MgO. The melt of dehydrated carnallite is subjected to electrolysis with the formation of magnesium and chlorine. Chlorine obtained durino electrolysis is partially ; used as ~ chlorinating agent for treating the carnallite melt.
In the known method the second stage of carnallite dehy-. . .
dration is characterized, f~rstly, by low intensity of heat and massexchan~e and by the specific efficiency less th~n 1 t/m3.hr.
~1773Z
which is typical for the processes performed in bath furnaces;
secondly, by the use of such expensiye heat source as electric energy; thirdly, by difficulties in controlling the process, since it is practically i~mpossible to automatize it completely; and, finally, by the necess;ty to purify the process exhaust gases from chlorine, since only 40-50~ of chlorine is used in the process, the rest of it being entrained by the exhaust gases.
It is difficult to control the process of dehydrating carnallite semi-product since the process is complex consisting of melting, chlorination and settling.
The complexity and long duration of the process do not allow its complete automation It is an object of the invention to intensify the process of dehydrating carnallite at the second stage, namely, at the stage of complete dehydration.
Another object of the invention is to decrease energy consumption at the second state of carnallite dehydration.
~117732 It is also an object of the invention to provide an easily controllable process of dehydrating carnallite at the second stage, which can be completelv automated, and thus to reduce considerably labour inputs required for the process.
Among other objects of the present invention note should be made of a decrease in expenditures on purification of the exhaust gases from noxious substances.
Finally, it is an object of the invention to reduce power inputs at the first stage of dehydrating carnallite.
According to the present invention there is provided a method for the final dehydration of carnallite in which carnallite pre-dehydrated in a solid state, with a water content of 3 to 8%, is treated with a gaseous mixture containing air, water vapor and ~Cl, which gaseous mixture is introduced tangentially into a reaction zone, the gaseous mixture having a temperature of between 1,050C
and 1,150C being introduced into the reaction zone at a rate sufficient for a solid film of continuously flowing molten carnallite, with a moisture content of not more than 0.5~ to be formed on the surface of the reaction zone.
In a particular aspect thereof the present invention pro-vides a method of dehydrating carnallite preliminarily enriched carnallite with water content 39-41 wt.% is heated up to 205-230C
by fuel combustion products having a temperature of 500-600C
and partially dehydrated carnallite is obtained containing 3-8 wt.%
of water; then the partially dehydrated carnallite is fed into a reaction zone where it is melted and the melt is subjected to the action of HCl as a chlorinating agent, after which the melted carnallite is allowed to settle from solid impurities and, as a result, dehydrated carnallite is obtained with water content less than 0.5 wt.%; in which method according to the invention, the melting of partially dehydrated carnallite is performed by fuel combustion products containina air and water vapour having a temperature of 1050C to 1150C, said products being introduced tangentially to the surface defining the reaction zone, at a rate ensuring the formation of an intensive gaseous eddy flow; said flow occupies the whole volume of the reaction zone and throws - 6a -111~73Z
partially deh~drated carnallite on the side surface of the reaction zone due to centrifugal forces; as a result, a continuous film of the carnallite melt is formed on the side surface of the reac-tion zone, the gases comprising the fuel combustion products and the gases liberating upon the interaction of the chlorinating agentwith the carnallite melt being removed from the reaction zone.
The processes of heat and mass exchange are extremely intensified due to high relative rates (usually about 100 m/sec) between the fuel combustion pro-ducts and the melt film. As a re-sult, the process of carnallite melting and dehydration becomeshighly intensive and cyclone-type.
The method of the present invention of dehydrating car-nallite semi-product reduces considerably energy consumption, since 70-80~ of electric energy is replaced with heat releasing upon fuel combustion.
On of the most important characteristics of high inten-sity of dehydrating carnallite semi-product is extremely short duration of the process: half of a second for medium lot product-ion and 2-3 seconds for large-lot production. Low inertia of the process makes possible its complete automation, considerable reduction of labour intensity, and stabilization of the quantity of the obtained dehydrated carnallite.
It is recommended to maintain the rate of feeding the fuel combustion prod~cts having a temperature of 1050C -1150C
into the reaction zone within the range of 40-200 m/sec. At a rate less than 40 m/sec the value of the tangential component of the gaseous eddy flow, which is responsible for an intensive heat and mass exchange, is not high enough along the whole height of the reaction zone and the cyclone character of the process disap-pears. At a Xate above 200 m~-sec the pressure at which the com-- bustion p~oducts aFe fed into the reaction zone, increases sharply and, as ~ reslut, the economic efficiency of the method decreases as com~ared with the known one, It is expedient to use as a chlorinating agent hydrogen chloride which i.s generated by deliveriny gaseous chlorine into the fuel com~ustion torch into the zone having a temperature of 1050-1150~C. Gaseous chlorine, interacting with water vapours of the fuel combustion products, transforms into hydrogen chloride according to the reaction:
C12 + H2O ~ 2 HCl + 1/2 2 Melting of carnallite in an atmosphere containing HCl inhibits MgC12 hydrolysis and, if the process is performed properly, leads to chlorination of MgO according to the reaction:
MgO + 2 HCl ~ MgC12 + H2O
This reaction does not require introduction of an addi-tional deoxidizing agent as in the case of chlorinating with gas-eous chlorine. In addition, purification of the exhaust gases from HCl is much cheaper than from C12, since it is performed with water and the solution of HCl thus obtained can be used, for example, for producingofsuch a valuable chemical as FeC13, which finds wide appl~cation in purification of waste waters.
To increase thermal efficiency of the process of carna-llite dehydration and reduce energy consumption at the first stage of dehydration, it is desirable to feed the gases removed from the reaction zone ~or heating the enriched carnallite up to 205-230C.
The gases removed from the reaction zone have a temper-ature no less t~an 500C and contain fuel combustion products as well as steam and hydrogen chloride in an amount of up to 10 vol.%.
Such utilization of the process exhaust gases decreases hydroly-sis of magnesium chloride MgC12 at the first stage of dehydration.
-~r a better understandlng of other objects and advan-taaes of the present ;nvention a specific example of realizing the method of dehydrating carnallite and a drawing with a schematic representat~on of the process are given hereinbelow by way of 1~1773Z
illustration.
Enriched carnallite obtained by recrystallization from carnallite rock and containing 31.5-32.0 ~`t.% of MgC12 and 39.5-40.0 wt.~ of H2O, of which 1.5-2.0 wt.% is hygroscopic water and 38.0-38.5 wt.~ is crystallization water, is a stock material for electrolytic productionofmagnesium.The main structural com-ponents of enriched carnallite are hexahydrous carnallite KCl.MgC12-.6H2O (87-88 wt.%~, mother solution of bischofite MgC12 in water (7-8 wt.%~, and sodium chloride NaCl (4-S wt.%). Prior to use in electrolysis, carnallite is dehydrated in two stages. The first stage of partial dehydration of carnallite is carried out in an apparatus 1 in which preliminarily enriched carnallite in a solid state is heated up to 220C by the heat of the products of combus-tion of natural gas, the temperature of the products being 550-600C. In the process of heat exchange with carnallite the tem-perature decreases to 105-110C. Natural gas is burnt in a furnace 2 of the apparatus 1, the process being performed in the counter-~low of the com~ustlon products and the carnallite for 2 hours. In the temperature range of 90-140C hygroscopic water is removed from solid carnalllte and crystallization water is partly removed due to transformation of the hexahydrous carnallite to the dihydrous one by the reaction:
KCl.MgC12.6 H2O , g 2' 2 2 In the temperature range of 150-220C partial transfor-mation o~ the dihydrous carnallite into dehydrated one takes place accordin~ to the reaction:
KCl.MgC12.2 H20 ~ KCl.~gC12 + 2 H20~
This is accompanied by hydrolysis of magnesium chloride with the formation of magnesium hydroxychloride which can be presented schematically as:
MgC12 + H2O ~ - ~ ~gOHCl + HCl~
Hy~rolysis of magnesium chloride is the main cause for magnesium losses during electrolytic production of magnesium from carnallite, since the products of magnesium chloride hydroly-sis do not decompose upon electrolysis but form slime in the reaction zone of magnesium electrolyzers.
Partially dehydrated carnallite, obtained at the first stage of dehydrating carnallite in a solid state, contains 47-48 wt.% of MgC12 and 5.0-5.5 wt.~ of H2O. The main structural components of the ~artially dehydrated carnallite is dehydrated and dihydrous carnallite (86-87 wt.%); magnesium hydroxychloride (8-8.5 wt.% or, as calculated for MgO, 2.4-2.6 wt.~ of MgO) and sodium chloride (5-6 wt.%). Then partially dehydrated carnallite (carnallite semi-product) is treated at the second stage, the stage of complete dehydratingcarnallite. The carnallite semi-product is fed into an apparatus 3 where it is melted in the reaction zone and is subjected to the action of the chlorinating agent, thereafter the obtained melt is allowed to settle from solid impurities in a sedimentation tank 4. The melting of the carnallite semi-product and treatment of the obtained melt with the chlorinating agent are preformed simultaneously in the same reaction zone. The reac-tion zone 5 of the apparatus 3 is defined by a vertical rotation surface. Into the upper part of the zone 5 the natural gas combus-tion products are fed tangentially to the surface thereof through a slot. The products are introduced at a rate of 140-150 m/sec at a temperature 700-1150C sufficent for melting the carnallite.
Due to high rates of the combustion products, an intensive gaseous eddy flow is formed in the reaction zone 5, which occupies the whole volume of the reaction zone. The carnallite semi-product is introduced from the top of the reaction zone 5. Hydrogen chloride is used as a chlorinating agent. Gaseous chlorine is delivered into the natural gas combustion torch into the zone of 1050-1150~C in an amount of 80 Nm3 per 100 Nm of the natural gas.
Chlorine, interacting with water vapours of the prbducts of~the na-'~ _ ln _ 11~7732 ~ural gascom~ustion,transforms intohydrogen chlorideby the reaction:
2 2 -~- 2HC1 ~ 1~2 2 The carnallite product, charged into the reaction zone, is invol-ved by a gaseous eddy flow, containing HCl, into an intensive ro-tation and is tllrown by the flow on the side surface of the re-action zone 5 due to the action of centrifugal forces. The car-nallite partlcles melt in the volume and form a continous film of the melt on the side surface of the reaction zone 5. The melt flows do~m into the sedimentation tank 4.
The high relative rates between the melt film and the products of natural gas combustion, amounting to 100-120 m/sec, extremely intensify the processes of heat and mass exchange.
In the reaction zone 5, as. a result of melting of the carnallite semi-product and the action of the chlorinating agent HCl on the melt obtained, almost complete removal. of water from carnallite takes place, partial chlorination of MgOHCl by the reaction:
MgOHCl + HCl ~ MgC12 H2O
and decomposition of MgOHCl, remaining after chlorination with isolation of solid magnesium oxide according to the reaction:
MgOHCl -- ~ MgO + HCl~.
Comsumption of the natural gas with a calorific value of 8100-8150 kcal/Nm3iS 75-.80 Nm per tonof the melt obtained.
The melt flowing f~om the reaction zone S contains 1.8-2.0% of MgQ and has a temperature of 500-520C. In the sedi-mentation tank 4 the melt is heated up to 700-750~C and allowed to settle from sol~d impurities, mainly, from MgO. The melt of dehydrated carnall~te obtained after sedimentation contains 51-52 wt.% o~ MgC12, no more than 0.5 wt.% of H2O, and 0.6-0.8 wt. %
of M~O; the melt IS` used for eIectrolytic production of magnesium and chlor~.ne, Exhaust gases conta~ning the products of combustion of 11~7732 natural fuel, stea~ and hydxo,gen chloride are removed from the reaction zone 5 at 600-650C and delivered through a gas duct 7 into the apparatus l to the first stage of dehydrating carnallite.
The gases introduce 40-50 wt.% of the heat necessary for dehydrating carnallite at this stage, thus increasiny the total heat efficien-cy of the process of carnallite'dehydrating up to 75-80~.
The melt of dehydrated carnallite is periodically re-moved from the sedimentation tank 4 through a hole 8, by opening a locking device 9, and the melt is delivered for electrolysis.
Example A melt of dehydrated carnallite, obtained by the method according to the invention, contains:
MgC12 - 51-52 wt.~;
H2O - no more than 0.5 wt.~;
MgO - 0.6-0.8 wt.%;
KCl and NaCl - the balance.
It is to be understood that the present invention is not limited to the given specific example of realizing the method of dehydrating carnallite.
The method of dehydrating carnallite, according to the invention, ensures specific capacity of 13-15 t/hr of dehydrated carnallite per m3 of the reaction zone, the mean capacity being 10 t of dehydrated carnallite per hour, and complete automation of the process. The residence time of the material in the reaction zone is 1.0-1.5 sec, and the total heat efficiency of the carnal-lite dehydrating process is 75-80%. Hydrochloric acid obtained upon water purification of the exhaust gases from hydrogen chloride can be used, for example, for producing such a valuable chemical as ferric chloride.
~fter treating with chlor~ne, the melt is allowed to settle from solid-impurities, mainly from magnesium oxide, at 700-750C. The melt of dehydrated carnallite obtained after sedi-mentation contains 50-52 wt.~ of MgC12, no more than 0.5~ of H2O, and no more than 0.8~ of MgO. The melt of dehydrated carnallite is subjected to electrolysis with the formation of magnesium and chlorine. Chlorine obtained durino electrolysis is partially ; used as ~ chlorinating agent for treating the carnallite melt.
In the known method the second stage of carnallite dehy-. . .
dration is characterized, f~rstly, by low intensity of heat and massexchan~e and by the specific efficiency less th~n 1 t/m3.hr.
~1773Z
which is typical for the processes performed in bath furnaces;
secondly, by the use of such expensiye heat source as electric energy; thirdly, by difficulties in controlling the process, since it is practically i~mpossible to automatize it completely; and, finally, by the necess;ty to purify the process exhaust gases from chlorine, since only 40-50~ of chlorine is used in the process, the rest of it being entrained by the exhaust gases.
It is difficult to control the process of dehydrating carnallite semi-product since the process is complex consisting of melting, chlorination and settling.
The complexity and long duration of the process do not allow its complete automation It is an object of the invention to intensify the process of dehydrating carnallite at the second stage, namely, at the stage of complete dehydration.
Another object of the invention is to decrease energy consumption at the second state of carnallite dehydration.
~117732 It is also an object of the invention to provide an easily controllable process of dehydrating carnallite at the second stage, which can be completelv automated, and thus to reduce considerably labour inputs required for the process.
Among other objects of the present invention note should be made of a decrease in expenditures on purification of the exhaust gases from noxious substances.
Finally, it is an object of the invention to reduce power inputs at the first stage of dehydrating carnallite.
According to the present invention there is provided a method for the final dehydration of carnallite in which carnallite pre-dehydrated in a solid state, with a water content of 3 to 8%, is treated with a gaseous mixture containing air, water vapor and ~Cl, which gaseous mixture is introduced tangentially into a reaction zone, the gaseous mixture having a temperature of between 1,050C
and 1,150C being introduced into the reaction zone at a rate sufficient for a solid film of continuously flowing molten carnallite, with a moisture content of not more than 0.5~ to be formed on the surface of the reaction zone.
In a particular aspect thereof the present invention pro-vides a method of dehydrating carnallite preliminarily enriched carnallite with water content 39-41 wt.% is heated up to 205-230C
by fuel combustion products having a temperature of 500-600C
and partially dehydrated carnallite is obtained containing 3-8 wt.%
of water; then the partially dehydrated carnallite is fed into a reaction zone where it is melted and the melt is subjected to the action of HCl as a chlorinating agent, after which the melted carnallite is allowed to settle from solid impurities and, as a result, dehydrated carnallite is obtained with water content less than 0.5 wt.%; in which method according to the invention, the melting of partially dehydrated carnallite is performed by fuel combustion products containina air and water vapour having a temperature of 1050C to 1150C, said products being introduced tangentially to the surface defining the reaction zone, at a rate ensuring the formation of an intensive gaseous eddy flow; said flow occupies the whole volume of the reaction zone and throws - 6a -111~73Z
partially deh~drated carnallite on the side surface of the reaction zone due to centrifugal forces; as a result, a continuous film of the carnallite melt is formed on the side surface of the reac-tion zone, the gases comprising the fuel combustion products and the gases liberating upon the interaction of the chlorinating agentwith the carnallite melt being removed from the reaction zone.
The processes of heat and mass exchange are extremely intensified due to high relative rates (usually about 100 m/sec) between the fuel combustion pro-ducts and the melt film. As a re-sult, the process of carnallite melting and dehydration becomeshighly intensive and cyclone-type.
The method of the present invention of dehydrating car-nallite semi-product reduces considerably energy consumption, since 70-80~ of electric energy is replaced with heat releasing upon fuel combustion.
On of the most important characteristics of high inten-sity of dehydrating carnallite semi-product is extremely short duration of the process: half of a second for medium lot product-ion and 2-3 seconds for large-lot production. Low inertia of the process makes possible its complete automation, considerable reduction of labour intensity, and stabilization of the quantity of the obtained dehydrated carnallite.
It is recommended to maintain the rate of feeding the fuel combustion prod~cts having a temperature of 1050C -1150C
into the reaction zone within the range of 40-200 m/sec. At a rate less than 40 m/sec the value of the tangential component of the gaseous eddy flow, which is responsible for an intensive heat and mass exchange, is not high enough along the whole height of the reaction zone and the cyclone character of the process disap-pears. At a Xate above 200 m~-sec the pressure at which the com-- bustion p~oducts aFe fed into the reaction zone, increases sharply and, as ~ reslut, the economic efficiency of the method decreases as com~ared with the known one, It is expedient to use as a chlorinating agent hydrogen chloride which i.s generated by deliveriny gaseous chlorine into the fuel com~ustion torch into the zone having a temperature of 1050-1150~C. Gaseous chlorine, interacting with water vapours of the fuel combustion products, transforms into hydrogen chloride according to the reaction:
C12 + H2O ~ 2 HCl + 1/2 2 Melting of carnallite in an atmosphere containing HCl inhibits MgC12 hydrolysis and, if the process is performed properly, leads to chlorination of MgO according to the reaction:
MgO + 2 HCl ~ MgC12 + H2O
This reaction does not require introduction of an addi-tional deoxidizing agent as in the case of chlorinating with gas-eous chlorine. In addition, purification of the exhaust gases from HCl is much cheaper than from C12, since it is performed with water and the solution of HCl thus obtained can be used, for example, for producingofsuch a valuable chemical as FeC13, which finds wide appl~cation in purification of waste waters.
To increase thermal efficiency of the process of carna-llite dehydration and reduce energy consumption at the first stage of dehydration, it is desirable to feed the gases removed from the reaction zone ~or heating the enriched carnallite up to 205-230C.
The gases removed from the reaction zone have a temper-ature no less t~an 500C and contain fuel combustion products as well as steam and hydrogen chloride in an amount of up to 10 vol.%.
Such utilization of the process exhaust gases decreases hydroly-sis of magnesium chloride MgC12 at the first stage of dehydration.
-~r a better understandlng of other objects and advan-taaes of the present ;nvention a specific example of realizing the method of dehydrating carnallite and a drawing with a schematic representat~on of the process are given hereinbelow by way of 1~1773Z
illustration.
Enriched carnallite obtained by recrystallization from carnallite rock and containing 31.5-32.0 ~`t.% of MgC12 and 39.5-40.0 wt.~ of H2O, of which 1.5-2.0 wt.% is hygroscopic water and 38.0-38.5 wt.~ is crystallization water, is a stock material for electrolytic productionofmagnesium.The main structural com-ponents of enriched carnallite are hexahydrous carnallite KCl.MgC12-.6H2O (87-88 wt.%~, mother solution of bischofite MgC12 in water (7-8 wt.%~, and sodium chloride NaCl (4-S wt.%). Prior to use in electrolysis, carnallite is dehydrated in two stages. The first stage of partial dehydration of carnallite is carried out in an apparatus 1 in which preliminarily enriched carnallite in a solid state is heated up to 220C by the heat of the products of combus-tion of natural gas, the temperature of the products being 550-600C. In the process of heat exchange with carnallite the tem-perature decreases to 105-110C. Natural gas is burnt in a furnace 2 of the apparatus 1, the process being performed in the counter-~low of the com~ustlon products and the carnallite for 2 hours. In the temperature range of 90-140C hygroscopic water is removed from solid carnalllte and crystallization water is partly removed due to transformation of the hexahydrous carnallite to the dihydrous one by the reaction:
KCl.MgC12.6 H2O , g 2' 2 2 In the temperature range of 150-220C partial transfor-mation o~ the dihydrous carnallite into dehydrated one takes place accordin~ to the reaction:
KCl.MgC12.2 H20 ~ KCl.~gC12 + 2 H20~
This is accompanied by hydrolysis of magnesium chloride with the formation of magnesium hydroxychloride which can be presented schematically as:
MgC12 + H2O ~ - ~ ~gOHCl + HCl~
Hy~rolysis of magnesium chloride is the main cause for magnesium losses during electrolytic production of magnesium from carnallite, since the products of magnesium chloride hydroly-sis do not decompose upon electrolysis but form slime in the reaction zone of magnesium electrolyzers.
Partially dehydrated carnallite, obtained at the first stage of dehydrating carnallite in a solid state, contains 47-48 wt.% of MgC12 and 5.0-5.5 wt.~ of H2O. The main structural components of the ~artially dehydrated carnallite is dehydrated and dihydrous carnallite (86-87 wt.%); magnesium hydroxychloride (8-8.5 wt.% or, as calculated for MgO, 2.4-2.6 wt.~ of MgO) and sodium chloride (5-6 wt.%). Then partially dehydrated carnallite (carnallite semi-product) is treated at the second stage, the stage of complete dehydratingcarnallite. The carnallite semi-product is fed into an apparatus 3 where it is melted in the reaction zone and is subjected to the action of the chlorinating agent, thereafter the obtained melt is allowed to settle from solid impurities in a sedimentation tank 4. The melting of the carnallite semi-product and treatment of the obtained melt with the chlorinating agent are preformed simultaneously in the same reaction zone. The reac-tion zone 5 of the apparatus 3 is defined by a vertical rotation surface. Into the upper part of the zone 5 the natural gas combus-tion products are fed tangentially to the surface thereof through a slot. The products are introduced at a rate of 140-150 m/sec at a temperature 700-1150C sufficent for melting the carnallite.
Due to high rates of the combustion products, an intensive gaseous eddy flow is formed in the reaction zone 5, which occupies the whole volume of the reaction zone. The carnallite semi-product is introduced from the top of the reaction zone 5. Hydrogen chloride is used as a chlorinating agent. Gaseous chlorine is delivered into the natural gas combustion torch into the zone of 1050-1150~C in an amount of 80 Nm3 per 100 Nm of the natural gas.
Chlorine, interacting with water vapours of the prbducts of~the na-'~ _ ln _ 11~7732 ~ural gascom~ustion,transforms intohydrogen chlorideby the reaction:
2 2 -~- 2HC1 ~ 1~2 2 The carnallite product, charged into the reaction zone, is invol-ved by a gaseous eddy flow, containing HCl, into an intensive ro-tation and is tllrown by the flow on the side surface of the re-action zone 5 due to the action of centrifugal forces. The car-nallite partlcles melt in the volume and form a continous film of the melt on the side surface of the reaction zone 5. The melt flows do~m into the sedimentation tank 4.
The high relative rates between the melt film and the products of natural gas combustion, amounting to 100-120 m/sec, extremely intensify the processes of heat and mass exchange.
In the reaction zone 5, as. a result of melting of the carnallite semi-product and the action of the chlorinating agent HCl on the melt obtained, almost complete removal. of water from carnallite takes place, partial chlorination of MgOHCl by the reaction:
MgOHCl + HCl ~ MgC12 H2O
and decomposition of MgOHCl, remaining after chlorination with isolation of solid magnesium oxide according to the reaction:
MgOHCl -- ~ MgO + HCl~.
Comsumption of the natural gas with a calorific value of 8100-8150 kcal/Nm3iS 75-.80 Nm per tonof the melt obtained.
The melt flowing f~om the reaction zone S contains 1.8-2.0% of MgQ and has a temperature of 500-520C. In the sedi-mentation tank 4 the melt is heated up to 700-750~C and allowed to settle from sol~d impurities, mainly, from MgO. The melt of dehydrated carnall~te obtained after sedimentation contains 51-52 wt.% o~ MgC12, no more than 0.5 wt.% of H2O, and 0.6-0.8 wt. %
of M~O; the melt IS` used for eIectrolytic production of magnesium and chlor~.ne, Exhaust gases conta~ning the products of combustion of 11~7732 natural fuel, stea~ and hydxo,gen chloride are removed from the reaction zone 5 at 600-650C and delivered through a gas duct 7 into the apparatus l to the first stage of dehydrating carnallite.
The gases introduce 40-50 wt.% of the heat necessary for dehydrating carnallite at this stage, thus increasiny the total heat efficien-cy of the process of carnallite'dehydrating up to 75-80~.
The melt of dehydrated carnallite is periodically re-moved from the sedimentation tank 4 through a hole 8, by opening a locking device 9, and the melt is delivered for electrolysis.
Example A melt of dehydrated carnallite, obtained by the method according to the invention, contains:
MgC12 - 51-52 wt.~;
H2O - no more than 0.5 wt.~;
MgO - 0.6-0.8 wt.%;
KCl and NaCl - the balance.
It is to be understood that the present invention is not limited to the given specific example of realizing the method of dehydrating carnallite.
The method of dehydrating carnallite, according to the invention, ensures specific capacity of 13-15 t/hr of dehydrated carnallite per m3 of the reaction zone, the mean capacity being 10 t of dehydrated carnallite per hour, and complete automation of the process. The residence time of the material in the reaction zone is 1.0-1.5 sec, and the total heat efficiency of the carnal-lite dehydrating process is 75-80%. Hydrochloric acid obtained upon water purification of the exhaust gases from hydrogen chloride can be used, for example, for producing such a valuable chemical as ferric chloride.
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for the final dehydration of carnallite in which carnallite pre-dehydrated in a solid state, with a water content of 3 to 8%, is treated with a gaseous mixture containing air, water vapor and HCl, which gaseous mixture is introduced tangentially into a reaction zone, the gaseous mixture -having a temperature of between 1,050° and 1,150°C being intro-duced into the reaction zone at a rate which ensures the forma-tion of a continuously flowing molten carnallite film having a water content of not more than 0.5% on the surface of the reaction zone.
2. A method as claimed in claim 1, in which the gaseous mixture is introduced into the reaction zone at a rate of 40 to 200 m/sec.
3. A method as claimed in claim 1 or 2, in which the gases escaping from the reaction zone are used for the pre-dehydrating of the carnallite.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000297735A CA1117732A (en) | 1978-02-27 | 1978-02-27 | Method of dehydrating carnallite |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000297735A CA1117732A (en) | 1978-02-27 | 1978-02-27 | Method of dehydrating carnallite |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1117732A true CA1117732A (en) | 1982-02-09 |
Family
ID=4110858
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000297735A Expired CA1117732A (en) | 1978-02-27 | 1978-02-27 | Method of dehydrating carnallite |
Country Status (1)
| Country | Link |
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| CA (1) | CA1117732A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113044862A (en) * | 2021-04-09 | 2021-06-29 | 河北大有镁业有限责任公司 | Method for dehydrating different ammonium carnallite materials by utilizing synergistic coupling effect of different ammonium carnallite materials |
-
1978
- 1978-02-27 CA CA000297735A patent/CA1117732A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113044862A (en) * | 2021-04-09 | 2021-06-29 | 河北大有镁业有限责任公司 | Method for dehydrating different ammonium carnallite materials by utilizing synergistic coupling effect of different ammonium carnallite materials |
| CN113044862B (en) * | 2021-04-09 | 2022-07-08 | 河北大有镁业有限责任公司 | Method for dehydrating different ammonium carnallite materials by utilizing synergistic coupling effect of different ammonium carnallite materials |
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