Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – By impinging or atomizing with gaseous jet or blast
Reexamination Certificate
1999-04-09
2001-10-02
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
By impinging or atomizing with gaseous jet or blast
C264S014000, C423S498000
Reexamination Certificate
active
06296790
ABSTRACT:
The present invention relates to production of magnesium metal, and more particularly to production of anhydrous magnesium chloride particles from magnesium chloride brines, the particles being used as feed in an energy demanding process of electrolysis.
Several processes for producing anhydrous magnesium chloride prills are known, e.g. the process described in U.S. Pat. No. 3,742,100, comprising steps of:
a) Evaporation of brine to a concentration of 55% MgCl
2
b) Prilling the concentrated brine to form prills of MgCl
2
×4-6 H
2
O with a particle size ranging from 0.5-1 mm
c) Two stage fluidized bed dehydration with air
d) Multistage fluidized bed dehydration with anhydrous HCl gas to give anhydrous magnesium chloride particles
Such production of anhydrous magnesium chloride is, however, presently a capital intensive process, and consequently the object for the present invention is to reduce the investment and operating costs of the above steps b) and c), requiring a large amount of energy.
It is also known that similar granulation processes have been patented for different applications and described in the literature, but not specifically covering the present granulation of MgCl
2
.
The above and other object(s) of the present invention are achieved by provision of a new, improved method of dehydration and granulation of MgCl
2
as claimed in claim
1
.
Thus, the present invention provides a method of producing magnesium chloride granules with a particle size in the range from 0.4 to 3.0 mm suitable for fluidization, air drying and chlorinating to anhydrous state, the method comprising the steps of: preparing a feed solution of MgCl
2
having a 30-55% by weight of MgCl
2
, feeding the solution and keeping it at high temperatures from the feeding tank to the nozzles, atomisation of the feed solution into the bed of already dried particles by pressure or compressed air, passing preheated air upwardly through the bed, maintaining the particles in a fluidizing state and a bed temperature between 100-170° C., continuously recovering entrained particles in a cyclone, discharging magnesium chloride particles continuously, classifying discharged material and recycling of any undersized fraction and crushed oversize fraction together with fines from the cyclone to the fluid bed for further granulation.
The feed solution is preferably at a temperature of the range of 120-200° C., and feed supply equipment is preferably heated with steam at temperatures in the range of 120-200° C.
The fluidized bed preferably comprises magnesium chloride particles with water content ranging from 1.5-4 mole H
2
O/mole MgCl
2
and MgOHCl values in the range 1-5%.
The fluidizing air preferably has a velocity of 1-2 m/s and is, together with panels in the fluidized bed, preferably heated sufficiently to maintain the bed at a temperature within the range of 100-170° C., by indirect heating or electrical calorifiers in order to keep the humidity as low as possible.
Drying air is preferably used at as low humidity as possible.
The temperature of the feed is preferably controlled by using saturated steam with a saturation pressure that gives the desired steam temperature.
Heating panels are preferably installed inside the fluidizing layer.
According to the present invention a bed of hydrous magnesium chloride particles is fluidized at a temperature between 100° C. to 150° C., preferably between 120-130° C. The bed particles contain 1.5 to 4 moles H
2
O per mole MgCl
2
. Preferably the particles should have a water content ranging from 2.7-2.9 moles H
2
O per mole MgCl
2
. A feed solution of magnesium chloride is prepared in a concentration of 30-55%, and preferably in a concentration of 45-55%, weight % anhydrous magnesium chloride. It is more complicated to granulate MgCl
2
brine at higher concentrations, but the overall energy comsumption is reduced. The solution is delivered at its boiling point, which is in the range of 120-190° C. from the upstream equipment. The solution is injected into the fluidizing zone which can be done by nozzles from the bottom, top or side of the granulation bed in the fluidized zone. The last one is preferable. The nozzles are spraying downwards or upwards, downwards from the bed height level is preferable, but any height in the bed can be used. The solution may be dispersed by employing compressed air, preferably air at a pressure of 1-6 bar, and preferably at the same temperature as the feed, but preferably it is dispersed under pressure. Pressurised nozzles without air for dispersion at pressures as high as 60 bar (preferably 20-30 bar) can also be used here. Heat tracing of feed supply equipment such as pipes, valves and pumps to avoid solidification or freezing of brine due to temperature gradients, is required at high brine concentrations. The heat tracing can be done electrically, but preferably it is done by steam tracing. The bed is fluidized by preheated air passing through the bed and at sufficiently high temperature to maintain the bed between about 100-170° C., preferably between about 120-130° C. The fluidization inlet temperature is in the range between 180-400° C. but preferably 230-240° C. The exhaust gas passes through a fines-separator such as a cyclone dust collector, which removes entrained fines, and return them back into the granulation bed. Granules are continuously withdrawn from the fluid bed and the particles or the granules, with a range of particle size, are then subjected to screening or other classification means. Undersized particles or fines are returned to the bed for further granulation. Oversized particles are crushed and returned to the fluid bed or to the screen to thus provide a means of product control and a means of stabilising the performance of the fluid bed operation. Seed particles are continuously fed or recycled to the fluidized bed. The seed particles are a combination of fines collected in the dust collector, undersized and crushed oversized particles separated from the screen. Within the bed the seed particles, and any other formed particles in the bed, grow both by agglomeration and layering as a result of the of the incoming feed solution and the particular conditions existing in the bed. The particles grow and the size increases with the retention time in the bed. The process of this invention will produce free-flowing and dustfree granules. The particles also seem to be stronger and more resistant to attrition and breakage in downstream equipment making transportation and further processing easier. Particles produced by this process are also easier to dry further and the chlorinating properties are also better than for prills. The operating conditions may be varied in accordance with the present invention to obtain the desired result with respect to quality of the granules and energy requirement.
The invention will now be described in more details with reference to the drawing (
FIG. 1
) illustrating schematically a process line (circuit) suitable for production of anhydrous MgCl
2
according to the present invention. A feed tank
1
contains a heated solution of magnesium chloride brine which is transported by a pump
2
to the spray nozzles
3
where the solution is atomised into the fluidized zone
4
, preferably by pressure nozzles. Two phase nozzles using compressed air with approximately the same temperature as the feed entering at 5 may also be used. The air is heated, e.g. by electrical calorifiers or indirect gas burner, in order to avoid humid air. Fluidizing air
6
is transported by a centrifugal fan
7
and electrically heated or indirect by heat exchangers if gas burners B are used to ensure that the bed of particles
4
is maintained in a temperature range of 100-170° C. The air enters a predistribution chamber
9
before a perforated plate
10
distributes the air uniformly through the fluid bed
11
. The distance from the atomising nozzles
3
to the perforated plate
10
is adjustable, and the nozzles are positioned right above the fluidized layer or other suitable locations. From the fluid bed unit
Frigstad Arne Bent
Grønstad Leif K{dot over (a)}re
Langseth Birger
Norsk Hydro ASA
Theisen Mary Lynn
Wenderoth , Lind & Ponack, L.L.P.
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