Method for oxidation of flue gas desulfurization absorbent and the product produced thereby

Claim 3

The method of claim 1 wherein the amount of calcium chloride present is less than about 1%, by weight.

Claim 4

The method of claim 2 wherein the bed temperature is over 800° C.

Claim 5

The method of claim 3 wherein the particulate fine-grained calcium sulfite material has an average particle size in the range from about 50μ to 100μ.

Claim 6

The method of claim 4 wherein the oxidized pellets have an average diameter of from 0.5 mm to 5 mm.

Claim 7

The method of claim 4 wherein the oxidized pellets have an average diameter of several millimeters.

Claim 8

The method of claim 3 wherein said low-melting constituents are selected from the group consisting of Na 2 CO 3 , K 2 SO 4 , K 2 CO 3 , Na 2 SiO 3 , (NH 4 ) 2 SO 4 and CaCl 2 .

Claim 9

The method of claim 1 wherein the amount of low-melting constituents in said calcium sulfite material is brought within the desired range of from about 1% to about 3%, by weight, by the addition of one or more low-melting constituents selected from the group consisting of Na 2 CO 3 , K 2 SO 4 , K 2 CO 3 , Na 2 SiO 3 , (NH 4 ) 2 SO 4 and CaCl 2 , with the CaCl 2 component, if present, amounting to less than 1%, by weight; the addition of said low-melting constituents being carried out prior to introduction of the calcium sulfite material into said fluidized bed reactor.

Claim 10

The method of claim 1 wherein the amount of low-melting constituents being in excess of the desired range of from about 1% to about 3%, a step of washing the calcium sulfite material in water to dissolve and thus remove excess quantities of low-melting constituents is carried out on at least a portion of the calcium sulfite material prior to its introduction into said fluidized bed reactor.

Claim 11

The method of claim 2 wherein a portion of the pellets formed in step (c) of claim 1 are ground to a size intermediate said particulate fine grained calcium sulfite material and said pellets and the ground pellets are returned to the fluidized bed as nuclei for pellet growth.

Claim 12

Pellets having a diameter in the range from 0.5 mm to 5 mm composed of agglomerated particles having an average size range of from about 50μ to about 100μ and having binder components therein in an amount from about 1% to about 3%, by weight, with small amounts of impurities and inerts, the balance being essentially calcium sulfate.

Claim 13

Pellets having a diameter in the range from 0.5 mm to 5 mm composed of agglomerated particles having an average size range of from about 50μ to about 100μ and having binder components therein in an amount from about 1% to about 3%, by weight, with small amounts of impurities and inerts, the balance being essentially calcium sulfate.

Claim 14

The pellets of claim 11 wherein the binder components are selected from the group consisting of Na 2 CO 3 , K 2 SO 4 , K 2 CO 3 , Na 2 SiO 3 , (NH 4 ) 2 SO 4 and CaCl 2 .

Claim 15

The pellets of claim 12 wherein the CaCl 2 component, if present, is in an amount less than 1%, by weight.

Claim 16

The pellets of claim 12 wherein the binder component is Na 2 CO 3 .

Claim 17

In the dry flue gas desulfurization process wherein the gas is first dedusted to remove fly ash and thereafter is passed through a spray drier in which the gas is subjected to a spray of an absorbent liquid comprising milk of lime, the absorbent reacting with the sulfur dioxide in said gas while the liquid component thereof evaporates, thereby yielding a fine-grained dry spent absorbent composed primarily of calcium sulfite and calcium sulfate, the improvement whereby a useful product is obtained by treating the spent absorbent to produce pellets composed primarily of calcium sulfate, comprising providing the dry spent absorbent with relatively low-melting binder constituents in controlled amounts in the range from about 1% to about 3%, by weight, and oxidizing the absorbent in a fluidized bed reactor at a temperature of from about 700° C. to about 1000° C. at which temperature said binder constituents are in the liquid phase to form oxidized pellets having an average diameter of from about 0.5 mm to about 5 mm composed primarily of calcium sulfate particles having an average diameter of from about 50μ to about 100μ bound to each other by said binder constituents.

Claim 18

In the dry flue gas desulfurization process wherein the gas is first dedusted to remove fly ash and thereafter is passed through a spray drier in which the gas is subjected to a spray of an absorbent liquid comprising milk of lime, the absorbent reacting with the sulfur dioxide in said gas while the liquid component thereof evaporates, thereby yielding a fine-grained dry spent absorbent composed primarily of calcium sulfite and calcium sulfate, the improvement whereby a useful product is obtained by treating the spent absorbent to produce pellets composed primarily of calcium sulfate, comprising providing the dry spent absorbent with relatively low-melting binder constituents in controlled amounts in the range from about 1% to about 3%, by weight, and oxidizing the absorbent in a fluidized bed reactor at a temperature of from about 700° C. to about 1000° C. at which temperature said binder constituents are in the liquid phase to form oxidized pellets having an average diameter of from about 0.5 mm to about 5 mm composed primarily of calcium sulfate particles having an average diameter of from about 50μ to about 100μ bound to each other by said binder constituents.

Claim 19

The process of claim 15 in which said binder constituents are added to the absorbent liquid before said liquid is sprayed in said spray drier.

Claim 20

The process of claim 15 in which said binder constituents are added to said fine-grained dry spent absorbent before said absorbent is introduced into said fluidized bed reactor.

Claim 21

The process of claim 15 in which the amount of binder constituents is controlled by removing excess binder by washing at least part of said absorbent with water before introducing said absorbent into said spray drier, whereby binder constituents go into solution and can be removed from the process in that form.

Claim 22

The process of claim 15 in which the size of pellets produced in said fluidized bed reactor is controlled by providing nuclei of predetermined size on which the particles of calcium sulfate can agglomerate, said nuclei produced by grinding a portion of the pellets formed in the fluidized bed reactor to a size intermediate that of said pellets and said particles of calcium sulfate and recycling said nuclei to said fluidized bed reactor.