Method for production of ammonium phosphate from phosphate rock slurry

Abstract

A method for production of ammonium phosphate from phosphate rock slurry. The method includes: introducing flue gas containing SO.sub.2 into a phosphate rock slurry, to yield an absorption solution; evaporating waste ammonia water containing 10-20 wt. % ammonia to yield ammonia gas; introducing the ammonia gas into the absorption solution at a temperature of 110-135° C. until a neutralization degree of the absorption solution reaches 1.5-1.6, thus yielding an ammonium phosphate solution and calcium sulfate; separating the calcium sulfate from the ammonium phosphate solution; and introducing the ammonium phosphate solution to a granulator for granulation to yield ammonium phosphate granules; drying and sieving the ammonium phosphate granules, thereby yielding ammonium phosphate.

Claims

1. A method, comprising: 1) introducing flue gas containing SO.sub.2 and oxygen into an absorption tower, and pumping a phosphate rock slurry comprising Ca.sub.10(PO.sub.4).sub.6F.sub.2 into the absorption tower to contact the flue gas, whereby a first absorption solution comprising sulfuric acid and 20-25 wt. % of water is yielded; 2) transferring the absorption solution obtained in 1) into a neutralization tank, and reacting phosphate rock with sulfuric acid in the first absorption solution to obtain a second absorption solution comprising phosphoric acid and calcium sulfate; 3) evaporating waste ammonia water containing 10-20 wt. % ammonia to yield ammonia gas; 4) introducing the ammonia gas into the second absorption solution at a temperature of 110-135° C. until a neutralization degree of the second absorption solution reaches 1.5-1.6, thus yielding an ammonium phosphate solution and calcium sulfate; 5) separating the calcium sulfate from the ammonium phosphate solution; and 6) introducing the ammonium phosphate solution to a granulator for granulation to yield ammonium phosphate granules; drying and sieving the ammonium phosphate granules, thereby yielding ammonium phosphate.

2. The method of claim 1, wherein the phosphate rock slurry has a solid content of 35-55 wt. %, and is prepared by: grinding a phosphate rock using a ball mill until more than 90% of phosphate rock powders pass through a 100-mesh sieve; and mixing the phosphate rock powders with water in a surge tank.

3. The method of claim 2, wherein the flue gas comprises 10-25% (v/v) of O.sub.2 and less than or equal to 3% (v/v) of SO.sub.2; the phosphate rock slurry has a pH value of 4-6; the phosphate rock slurry and the flue gas are introduced to an absorption tower in a liquid-gas ratio of 8-12 L/m.sup.3, and a temperature in the absorption tower is 25-60° C.

Description

DETAILED DESCRIPTION

(1) To further illustrate, embodiments detailing a method for production of ammonium phosphate from phosphate rock slurry are described below. It should be noted that the following embodiments are intended to describe and not to limit the disclosure.

Example 1

(2) 1) A phosphate rock was ground by a ball mill until 95% of the produced phosphate rock powders passed through a 100-mesh sieve (0.15 mm). The phosphate rock powders were mixed with distilled water in a surge tank to yield phosphate rock slurry; the solid content of the phosphate rock slurry was 35%. The pH value of the phosphate rock slurry was 4. The phosphate rock slurry was guided out of the surge tank and transferred through a slurry pump to a circulation pump. A flue gas containing 10% (v/v) of O.sub.2 and 3% (v/v) of SO.sub.2 was introduced to an absorption tower. The liquid-gas ratio was 8 L/m.sup.3. The phosphate rock slurry was pumped into the absorption tower through the circulation pump and contacted the flue gas to yield an absorption solution. The concentration of SO.sub.2 at the outlet of the absorption tower was measured. The temperature in the absorption tower was 30° C.

(3) 2) The absorption solution obtained in 1) was buffered in an oxidation buffer tank, and then transferred to a neutralization tank of a wet process phosphoric acid workshop through an output pump, where the mass concentration of phosphoric acid in the absorption solution rose to 5%. The concentration of SO.sub.2 at the outlet reduced to 250 mg/m.sup.3, and the pH value of the phosphate slurry was ≤1.5.

(4) 3) The waste ammonia water containing 10% ammonia was introduced to an evaporator at normal temperature. The evaporator condensed the low-pressure saturated water steam to release the latent heat to heat and evaporate the waste ammonia water.

(5) 4) The low-pressure saturated steam entered the shell side of the evaporator through a pipeline and was condensed to release heat and exchanged heat with ammonia water in the shell side. The ammonia water absorbed the heat and was heated up and evaporated to produce ammonia gas. The temperature of ammonia gas/water steam was 130° C.

(6) 5) The ammonia gas was guided out of the evaporator and flowed to the neutralization tank, and the steam condensate was drained and discharged.

(7) 6) The ammonia gas was introduced to the neutralization tank to neutralize the absorption solution. The water content of the absorption solution was 20%, and the temperature was 120° C. The neutralization degree of the absorption solution was 1.5-1.6.

(8) 7) The neutralized absorption solution was sent into a granulator by the slurry pump and mixed with a circulating material of dried ammonium phosphate for granulation; the excess water in the absorption solution was absorbed by the circulating material of dried ammonium phosphate, and the neutralized absorption solution was coated on the surface of the circulating material of dried ammonium phosphate and solidified into granules; the ammonia gas was further added into the granulator to ammoniate the neutralized absorption solution to a neutralization degree of 1.8-1.9 (subject to the actual content of impurities in phosphoric acid). The ammonization reaction evaporated part of water, promoted the solidification of the slurry, and the water content of the ammonium phosphate at the outlet was 5%; the ammonium phosphate prepared by the granulator was further dried to less than 2.0% of water content by a dryer.

(9) 8) The dried ammonium phosphate granules were screened, and the granules with a particle size of 2-4 mm were cooled and packaged as a final product. The granules with a particle size larger than 4 mm were crushed. The crushed granules, granules with a particle size less than 2 mm, and part of granules with a particle size of 2-4 mm were mixed as a circulating material returning back to the granulator for continuous production.

Example 2

(10) 1) A phosphate rock was ground by a ball mill until 93% of the produced phosphate rock powders passed through a 100-mesh sieve (0.15 mm). The phosphate rock powders were mixed with distilled water in a surge tank to yield phosphate rock slurry; the solid content of the phosphate rock slurry was 40%. The pH value of the phosphate rock slurry was 5. The phosphate rock slurry was guided out of the surge tank and transferred through a slurry pump to a circulation pump. A flue gas containing 12% (v/v) of O.sub.2 and 2% (v/v) of SO.sub.2 was introduced to an absorption tower. The liquid-gas ratio was 10 L/m.sup.3. The phosphate rock slurry was pumped into the absorption tower through the circulation pump and contacted the flue gas to yield an absorption solution. The concentration of SO.sub.2 at the outlet of the absorption tower was measured. The temperature in the absorption tower was 35° C.

(11) 2) The absorption solution obtained in 1) was buffered in an oxidation buffer tank, and then transferred to a neutralization tank of a wet process phosphoric acid workshop through an output pump, where the mass concentration of phosphoric acid in the absorption solution rose to 5%. The concentration of SO.sub.2 at the outlet reduced to 200 mg/m.sup.3, and the pH value of the phosphate slurry was ≤1.5.

(12) 3) The waste ammonia water containing 12% ammonia was introduced to an evaporator at normal temperature. The evaporator condensed the low-pressure saturated water steam to release the latent heat to heat and evaporate the waste ammonia water.

(13) 4) The low-pressure saturated steam entered the shell side of the evaporator through a pipeline and was condensed to release heat and exchanged heat with ammonia water in the shell side. The ammonia water absorbed the heat and was heated up and evaporated to produce ammonia gas. The temperature of ammonia gas/water steam was 160° C.

(14) 5) The ammonia gas was guided out of the evaporator and flowed to the neutralization tank, and the steam condensate was drained and discharged.

(15) 6) The ammonia gas was introduced to the neutralization tank to neutralize the absorption solution. The water content of the absorption solution was 22%, and the temperature was 125° C. The neutralization degree of the absorption solution was 1.5-1.6.

(16) 7) The neutralized absorption solution was sent into a granulator by the slurry pump and mixed with a circulating material of dried ammonium phosphate for granulation; the excess water in the absorption solution was absorbed by the circulating material of dried ammonium phosphate, and the neutralized absorption solution was coated on the surface of the circulating material of dried ammonium phosphate and solidified into granules; the ammonia gas was further added into the granulator to ammoniate the neutralized absorption solution to a neutralization degree of 1.8-1.9 (subject to the actual content of impurities in phosphoric acid). The ammonization reaction evaporated part of water, promoted the solidification of the slurry, and the water content of the ammonium phosphate at the outlet was 3.7%; the ammonium phosphate prepared by the granulator was further dried to less than 2.0% of water content by a dryer.

(17) 8) The dried ammonium phosphate granules were screened, and the granules with a particle size of 2-4 mm were cooled and packaged as a final product. The granules with a particle size larger than 4 mm were crushed. The crushed granules, granules with a particle size less than 2 mm, and part of granules with a particle size of 2-4 mm were mixed as a circulating material returning back to the granulator for continuous production.

Example 3

(18) 1) A phosphate rock was ground by a ball mill until 98% of the produced phosphate rock powders passed through a 100-mesh sieve (0.15 mm). The phosphate rock powders were mixed with distilled water in a surge tank to yield phosphate rock slurry; the solid content of the phosphate rock slurry was 45%. The pH value of the phosphate rock slurry was 5. The phosphate rock slurry was guided out of the surge tank and transferred through a slurry pump to a circulation pump. A flue gas containing 15% (v/v) of O.sub.2 and 2% (v/v) of SO.sub.2 was introduced to an absorption tower. The liquid-gas ratio was 10 L/m.sup.3. The phosphate rock slurry was pumped into the absorption tower through the circulation pump and contacted the flue gas to yield an absorption solution. The concentration of SO.sub.2 at the outlet of the absorption tower was measured. The temperature in the absorption tower was 40° C.

(19) 2) The absorption solution obtained in 1) was buffered in an oxidation buffer tank, and then transferred to a neutralization tank of a wet process phosphoric acid workshop through an output pump, where the mass concentration of phosphoric acid in the absorption solution rose to 8%. The concentration of SO.sub.2 at the outlet reduced to 150 mg/m.sup.3, and the pH value of the phosphate slurry was ≤1.5.

(20) 3) The waste ammonia water containing 14% ammonia was introduced to an evaporator at normal temperature. The evaporator condensed the low-pressure saturated water steam to release the latent heat to heat and evaporate the waste ammonia water.

(21) 4) The low-pressure saturated steam entered the shell side of the evaporator through a pipeline and was condensed to release heat and exchanged heat with ammonia water in the shell side. The ammonia water absorbed the heat and was heated up and evaporated to produce ammonia gas. The temperature of ammonia gas/water steam was 150° C.

(22) 5) The ammonia gas was guided out of the evaporator and flowed to the neutralization tank, and the steam condensate was drained and discharged.

(23) 6) The ammonia gas was introduced to the neutralization tank to neutralize the absorption solution. The water content of the absorption solution was 23%, and the temperature was 128° C. The neutralization degree of the absorption solution was 1.5-1.6.

(24) 7) The neutralized absorption solution was sent into a granulator by the slurry pump and mixed with a circulating material of dried ammonium phosphate for granulation; the excess water in the absorption solution was absorbed by the circulating material of dried ammonium phosphate, and the neutralized absorption solution was coated on the surface of the circulating material of dried ammonium phosphate and solidified into granules; the ammonia gas was further added into the granulator to ammoniate the neutralized absorption solution to a neutralization degree of 1.8-1.9 (subject to the actual content of impurities in phosphoric acid). The ammonization reaction evaporated part of water, promoted the solidification of the slurry, and the water content of the ammonium phosphate at the outlet was 4%; the ammonium phosphate prepared by the granulator was further dried to less than 2.0% of water content by a dryer.

(25) 8) The dried ammonium phosphate granules were screened, and the granules with a particle size of 2-4 mm were cooled and packaged as a final product. The granules with a particle size larger than 4 mm were crushed. The crushed granules, granules with a particle size less than 2 mm, and part of granules with a particle size of 2-4 mm were mixed as a circulating material returning back to the granulator for continuous production.

Example 4

(26) 1) A phosphate rock was ground by a ball mill until 96% of the produced phosphate rock powders passed through a 100-mesh sieve (0.15 mm). The phosphate rock powders were mixed with distilled water in a surge tank to yield phosphate rock slurry; the solid content of the phosphate rock slurry was 50%. The pH value of the phosphate rock slurry was 5.5. The phosphate rock slurry was guided out of the surge tank and transferred through a slurry pump to a circulation pump. A flue gas containing 20% (v/v) of O.sub.2 and 2% (v/v) of SO.sub.2 was introduced to an absorption tower. The liquid-gas ratio was 9 L/m.sup.3. The phosphate rock slurry was pumped into the absorption tower through the circulation pump and contacted the flue gas to yield an absorption solution. The concentration of SO.sub.2 at the outlet of the absorption tower was measured. The temperature in the absorption tower was 45° C.

(27) 2) The absorption solution obtained in 1) was buffered in an oxidation buffer tank, and then transferred to a neutralization tank of a wet process phosphoric acid workshop through an output pump, where the mass concentration of phosphoric acid in the absorption solution rose to 3%. The concentration of SO.sub.2 at the outlet reduced to 300 mg/m.sup.3, and the pH value of the phosphate slurry was ≤1.5.

(28) 3) The waste ammonia water containing 16% ammonia was introduced to an evaporator at normal temperature. The evaporator condensed the low-pressure saturated water steam to release the latent heat to heat and evaporate the waste ammonia water.

(29) 4) The low-pressure saturated steam entered the shell side of the evaporator through a pipeline and was condensed to release heat and exchanged heat with ammonia water in the shell side. The ammonia water absorbed the heat and was heated up and evaporated to produce ammonia gas. The temperature of ammonia gas/water steam was 180° C.

(30) 5) The ammonia gas was guided out of the evaporator and flowed to the neutralization tank, and the steam condensate was drained and discharged.

(31) 6) The ammonia gas was introduced to the neutralization tank to neutralize the absorption solution. The water content of the absorption solution was 25%, and the temperature was 130° C. The neutralization degree of the absorption solution was 1.5-1.6.

(32) 7) The neutralized absorption solution was sent into a granulator by the slurry pump and mixed with a circulating material of dried ammonium phosphate for granulation; the excess water in the absorption solution was absorbed by the circulating material of dried ammonium phosphate, and the neutralized absorption solution was coated on the surface of the circulating material of dried ammonium phosphate and solidified into granules; the ammonia gas was further added into the granulator to ammoniate the neutralized absorption solution to a neutralization degree of 1.8-1.9 (subject to the actual content of impurities in phosphoric acid). The ammonization reaction evaporated part of water, promoted the solidification of the slurry, and the water content of the ammonium phosphate at the outlet was 4%; the ammonium phosphate prepared by the granulator was further dried to less than 2.0% of water content by a dryer.

(33) 8) The dried ammonium phosphate granules were screened, and the granules with a particle size of 2-4 mm were cooled and packaged as a final product. The granules with a particle size larger than 4 mm were crushed. The crushed granules, granules with a particle size less than 2 mm, and part of granules with a particle size of 2-4 mm were mixed as a circulating material returning back to the granulator for continuous production.

Example 5

(34) 1) A phosphate rock was ground by a ball mill until 91% of the produced phosphate rock powders passed through a 100-mesh sieve (0.15 mm). The phosphate rock powders were mixed with distilled water in a surge tank to yield phosphate rock slurry; the solid content of the phosphate rock slurry was 55%. The pH value of the phosphate rock slurry was 5.8. The phosphate rock slurry was guided out of the surge tank and transferred through a slurry pump to a circulation pump. A flue gas containing 23% (v/v) of O.sub.2 and 3% (v/v) of SO.sub.2 was introduced to an absorption tower. The liquid-gas ratio was 11 L/m.sup.3. The phosphate rock slurry was pumped into the absorption tower through the circulation pump and contacted the flue gas to yield an absorption solution. The concentration of SO.sub.2 at the outlet of the absorption tower was measured. The temperature in the absorption tower was 55° C.

(35) 2) The absorption solution obtained in 1) was buffered in an oxidation buffer tank, and then transferred to a neutralization tank of a wet process phosphoric acid workshop through an output pump, where the mass concentration of phosphoric acid in the absorption solution rose to 5%. The concentration of SO.sub.2 at the outlet reduced to 250 mg/m.sup.3, and the pH value of the phosphate slurry was ≤1.5.

(36) 3) The waste ammonia water containing 14% ammonia was introduced to an evaporator at normal temperature. The evaporator condensed the low-pressure saturated water steam to release the latent heat to heat and evaporate the waste ammonia water.

(37) 4) The low-pressure saturated steam entered the shell side of the evaporator through a pipeline and was condensed to release heat and exchanged heat with ammonia water in the shell side. The ammonia water absorbed the heat and was heated up and evaporated to produce ammonia gas. The temperature of ammonia gas/water steam was 130° C.

(38) 5) The ammonia gas was guided out of the evaporator and flowed to the neutralization tank, and the steam condensate was drained and discharged.

(39) 6) The ammonia gas was introduced to the neutralization tank to neutralize the absorption solution. The water content of the absorption solution was 25%, and the temperature was 133° C. The neutralization degree of the absorption solution was 1.5-1.6.

(40) 7) The neutralized absorption solution was sent into a granulator by the slurry pump and mixed with a circulating material of dried ammonium phosphate for granulation; the excess water in the absorption solution was absorbed by the circulating material of dried ammonium phosphate, and the neutralized absorption solution was coated on the surface of the circulating material of dried ammonium phosphate and solidified into granules; the ammonia gas was further added into the granulator to ammoniate the neutralized absorption solution to a neutralization degree of 1.8-1.9 (subject to the actual content of impurities in phosphoric acid). The ammonization reaction evaporated part of water, promoted the solidification of the slurry, and the water content of the ammonium phosphate at the outlet was 4%; the ammonium phosphate prepared by the granulator was further dried to less than 2.0% of water content by a dryer.

(41) 8) The dried ammonium phosphate granules were screened, and the granules with a particle size of 2-4 mm were cooled and packaged as a final product. The granules with a particle size larger than 4 mm were crushed. The crushed granules, granules with a particle size less than 2 mm, and part of granules with a particle size of 2-4 mm were mixed as a circulating material returning back to the granulator for continuous production.

(42) It will be obvious to those skilled in the art that changes and modifications may be made, and therefore, the aim in the appended claims is to cover all such changes and modifications.