Mixed nitrate salt heat transfer medium and process for providing the same
First Claim
1. A process for preparing particles of a non-friable, eutectic mixture of sodium nitrate and potassium nitrate for use as a heat transfer and thermal storage medium for solar power stations comprising steps of:
- (a) preparing a fluid mixture of between about 70% and about 30% by weight sodium nitrate and about 30% and about 70% by weight potassium nitrate, wherein said fluid mixture has a combined level of sulfates, oxides, carbonates and chlorides of no more than about 0.7% by weight and with the chloride being no more than about 0.2% by weight;
(b) granulating said fluid mixture by a process selected from the group consisting of shock chilling and spray graining to form substantially homogeneous particles of said mixture; and
(c) recovering a salt product comprised of particles having a predetermined mesh size.
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Accused Products
Abstract
A process for producing particles of a non-friable eutectic mixture of sodium nitrate and potassium nitrate for solar power station use is disclosed. In one embodiment of the invention, the particles are produced by shock chilling a molten stream of mixed nitrate material and crushing the resulting flakes to a size range of between about -5 mesh and about +30 mesh. In a second embodiment, particles of this size are produced by spray granulation of a concentrated solution of mixed nitrate salts onto a fluidized bed to produce dry, free-flowing, solid spheres. In both embodiments, the particles are extremely hard, resistant to moisture pickup and adaptable to being readily shipped by bulk containers.
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Citations
25 Claims
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1. A process for preparing particles of a non-friable, eutectic mixture of sodium nitrate and potassium nitrate for use as a heat transfer and thermal storage medium for solar power stations comprising steps of:
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(a) preparing a fluid mixture of between about 70% and about 30% by weight sodium nitrate and about 30% and about 70% by weight potassium nitrate, wherein said fluid mixture has a combined level of sulfates, oxides, carbonates and chlorides of no more than about 0.7% by weight and with the chloride being no more than about 0.2% by weight; (b) granulating said fluid mixture by a process selected from the group consisting of shock chilling and spray graining to form substantially homogeneous particles of said mixture; and (c) recovering a salt product comprised of particles having a predetermined mesh size. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A process for making non-friable, dried salt particles for use as a heat transfer medium for solar power stations, said salt particles being a eutectic mixture of between about 70% and about 30% by weight sodium nitrate and between about 30% and about 70% by weight potassium nitrate, said particles being further characterized by having a maximum combined chloride, sulfate, oxide and carbonate content of about 0.7% by weight with the maximum chloride content being about 0.2%, said salt particles having been produced by a method comprising the steps of:
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(a) admixing granular NaNO3 and granular KNO3 to produce a dry blended substantially homogeneous salt mix; (b) heating said salt mix to a temperature in the range of about 220°
C. to about 300°
C. while agitating it until it fuses to form a molten mass;(c) pouring said molten mass onto a chilled surface at a rate sufficient to form a solid, amorphous homogeneous sheet of between about 0.20" and about 1.25" thick; (d) breaking up said sheet to form said particles; and (e) classifying said particles to recover a final product. - View Dependent Claims (20, 21, 22)
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19. A process for making non-friable, dried salt particles for use as a heat transfer medium for solar power stations, said salt particles being a eutectic mixture of between about 70% and about 30% by weight sodium nitrate and between about 30% and about 70% by weight potassium nitrate, said particles being further characterized by having a maximum combined chloride, sulfate, oxide and carbonate content of about 0.7% by weight with the maximum chloride content being about 0.2%, said salt particles having been produced by a method comprising the steps of:
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(a) forming an aqueous solution of sodium nitrate and potassium nitrate, said solution having a total salt content of between about 60% and about 75% combined salt by weight at a temperature of between about 95°
C. and about 120°
C.;(b) spraying said aqueous solution into a drying chamber and contacting said sprayed solution with a heated gas flowing through said chamber to form a dried fine particulate product, said fine particulate product being fluidized by said flowing gas; (c) agglomerating said fluidized fine particulate product by contacting it with additional aqueous solution which is being sprayed into said drying chamber for a time sufficient to form said particles; and (d) classifying said particles to recover a final product.
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- 23. Non-friable, dried salt particles for use as a heat transfer medium for solar power stations, said salt particles being a eutectic mixture of between about 70% and about 30% by weight sodium nitrate and between about 30% and about 70% by weight potassium nitrate, said particles being further characterized by having a maximum combined chloride, sulfate, oxide and carbonate content of about 0.7% by weight with the maximum chloride content being about 0.2%.
Specification