Integrated method for producing sulphur dioxide quality suitable for a sulphuric acid process from calcium sulphate/phosphogypsum from phosphoric acid production

Patent metadata

Field	Value
Publication number	US-11845657-B2
Application number	US-202117791869-A
Country	US
Kind code	B2
Filing date	Jan 5, 2021
Priority date	Jan 8, 2020
Publication date	Dec 19, 2023
Grant date	Dec 19, 2023

Abstract

A process for producing sulfuric acid and cement clinker may use calcium sulfate that is formed as a solid by-product and separated off in phosphoric acid production in a reaction of raw phosphate with sulfuric acid to form phosphoric acid. The process comprises treating calcium sulfate separated from the phosphoric acid with an acid to obtain a suspension comprising purified calcium sulfate, separating the purified calcium sulfate in solid form from the liquid phase of the suspension, mixing the purified calcium sulfate with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production, burning the raw meal mixture to obtain the cement clinker, with formation of sulfur dioxide as offgas, and subjecting the sulfur dioxide formed to offgas purification and feeding the sulfur dioxide as raw material to sulfuric acid production to produce the sulfuric acid. The sulfuric acid produced may be used as starting material in phosphoric acid production.

First claim

What is claimed is:

1. A process for producing sulfuric acid and cement clinker using calcium sulfate that is formed as a solid by-product and separated off in phosphoric acid production in a reaction of raw phosphate with sulfuric acid to form phosphoric acid, wherein the process comprises:
(a) treating the calcium sulfate that is separated off from the phosphoric acid with an acid to obtain a suspension comprising purified calcium sulfate;
(b) separating the purified calcium sulfate in solid form from a liquid phase of the suspension, wherein the purified calcium sulfate that is separated off contains at least 50% by weight of anhydrite based on dry calcium sulfate;
(c) mixing the purified calcium sulfate that is separated off with admixtures and reducing agents to obtain a raw meal mixture for cement clinker production;
(d) burning the raw meal mixture to obtain the cement clinker, forming sulfur dioxide as an offgas;
(e) subjecting the sulfur dioxide to offgas purification, wherein the offgas purification comprises:
(e1) dry depositioning particles having a size greater than 100 μm,
(e2) wet depositioning particles having a size of 20 to 100 μm,
(e3) removing particles having a size less than 20 μm, and
(e4) removing nitrogen oxides; and

(f) feeding the sulfur dioxide as raw material to a sulfuric acid production to produce the sulfuric acid.

2. The process of claim 1 being an integrated process.

3. The process of claim 1 wherein the phosphoric acid production is executed by a process selected from a dihydrate (DH) process, a hemihydrate (HH) process, a dihydrate-hemihydrate (DHH) process, a hemihydrate-dihydrate (HDH) process, and a dihydrate attack-hemihydrate filtration (DA-HF) process.

4. The process of claim 1 wherein the calcium sulfate used in step (a) is obtained from a separation unit in the phosphoric acid production, obtained after a first separation from the phosphoric acid.

5. The process of claim 1 wherein the calcium sulfate used in step (a):
is calcium sulfate filtercake;
is from the phosphoric acid production directly or after one or more washes with water; and/or
is stockpiled calcium sulfate from the phosphoric acid production.

6. The process of claim 1 comprising at least one of:
wherein in step (a) the acid is added in such an amount that a weight ratio of solids to liquid in the suspension is in a range from 1/10 to 1/1;
wherein the acid resulting from the treatment after step (a) is a 1 to 12 molar acid;
wherein the acid is hydrochloric acid, nitric acid, sulfurous acid, and/or sulfuric acid;
wherein the treating in step (a) is conducted at a temperature in a range from 15 to 100° C.; or
wherein a duration of the treating in step (a) is in a range from 5 to 120 minutes.

7. The process of claim 1 wherein a D v (50) of a grain size distribution of the calcium sulfate obtained in step (b) is in a range of 0.5-100 μm.

8. The process of claim 1 comprising using the liquid phase obtained in step (b) as feedstock in the phosphoric acid production as a portion of sulfuric acid required to digest raw phosphate.

9. The process of claim 1 wherein at least one of:
the admixtures of step (c) are raw materials or compounds comprising one or more oxides of Si, Al, Fe, Ca, or precursors thereof;
carbon and/or hydrocarbons are mixed into the calcium sulfate as reducing agents; or
the cement clinker produced in step (d) is used for cement production.

10. The process of claim 1 wherein the dry depositioning of particles from the sulfur dioxide in steps (e1) and/or (e3) is undertaken by means of a cyclone, settling separator, rotational flow separator, and/or electrofilter.

11. The process of claim 10 wherein step (e2) is undertaken by means of a Venturi scrubber, rotary scrubber, and/or jet scrubber, wherein residual moisture in the sulfur dioxide is removed by condensation and/or a wet electrofilter.

12. The process of claim 1 comprising separating nitrogen oxides from the sulfur dioxide in step (e4) by way of a breakdown of the nitrogen oxides to N 2 and H 2 O.

13. The process of claim 1 wherein the purified calcium sulfate obtained in step (b), before being fed to step (c), is subjected to an additional purification step for removal of rare earths in which the purified calcium sulfate obtained in step (b) is treated with a liquid and the further-purified calcium sulfate is separated in solid form from the liquid phase in the suspension that is obtained, wherein the further-purified calcium sulfate is sent to step (c), with one or more rare earths being present in the liquid phase.

14. The process of claim 1 wherein an extent of purification of the calcium sulfate in step (a) is established taking into account impurities present in the admixtures used for the raw meal, wherein guide values for phosphorus and fluorine are observed for the cement clinker, which are not more than 1.0% by weight of P 2 O 5 and/or not more than 0.5% by weight F, wherein a liquid budget of the phosphoric acid production is altered only insignificantly, if at all, by an integrated process because an input of liquid for purification of the calcium sulfate in the integrated process is coupled to the liquid budget of the phosphoric acid production.

15. A plant for production of sulfuric acid and cement clinker using calcium sulfate by the process of claim 1 , wherein the calcium sulfate is formed and separated off as a solid by-product in phosphoric acid production in a reaction of raw phosphate with sulfuric acid to form phosphoric acid, wherein the plant comprises:
a calcium sulfate reaction unit for treating the calcium sulfate separated from the phosphoric acid therein with an acid to obtain a suspension comprising purified calcium sulfate;
a calcium sulfate separation unit for separating the purified calcium sulfate in solid form from a liquid phase of the suspension;
a raw meal mixing unit suitable for mixing the purified calcium sulfate separated off with admixtures and reducing agents therein to obtain a raw meal mixture for cement clinker production;
a cement clinker production unit comprising a preheater, at least one burner device, and a cooler that are suitable for preheating, burning, and cooling the raw meal mixture to obtain the cement clinker, forming sulfur dioxide as offgas;
a sulfur dioxide offgas purification plant that is suitable for removing impurities from the sulfur dioxide offgas, wherein the sulfur dioxide offgas purification plant is suitable for removing impurities from the sulfur dioxide offgas and includes:
a cyclone, rotational flow separator and/or dry electrofilter configured to dry deposit particles having a size greater than 100 μm and remove particles having a size less than 20 μm;
and a Venturi scrubber, quench/column scrubber and/or wet electrofilter to wet deposit particles having a size of 20 to 100 μm; and
a sulfuric acid production plant configured to be supplied with the sulfur dioxide offgas that has been formed in the cement clinker production unit to produce sulfuric acid.

Assignees

• Thyssenkrupp Ind Solutions Ag
• Thyssenkrupp Ag

Inventors

• Stockhoff Peter
• Guetta Zion

Classifications

• C01B17/745 Primary

  from sulfates · CPC title

• C01B17/506

  of calcium sulfates · CPC title

• C01B17/56

  Separation; Purification · CPC title

• C01B25/232

  Preparation by reacting phosphate containing material with concentrated sulfuric acid and subsequently lixiviating the obtained mass, e.g. clinker process · CPC title

• C01F11/468

  Purification of calcium sulfates · CPC title