PRODUCTION METHOD FOR PRODUCING CEMENT AND CO-PRODUCING SULFURIC ACID FROM PHOSPHOGYPSUM

Abstract

The disclosure discloses a production method for producing cement and co-producing sulfuric acid from phosphogypsum. The method includes: pretreating and purifying the phosphogypsum to reduce insoluble phosphorus, water-soluble phosphorus impurities, and most free water in the phosphogypsum, directly feeding the materials kneaded and granulated with a reducing agent into a reduction and decomposition integrated rotary kiln with a fluidized preheating function, and controlling to carry out step-by-step heating, drying, dehydration, reduction and decomposition in a gas phase atmosphere under pulverized coal combustion; using sulfur dioxide gas generated after reduction and decomposition to produce the sulfuric acid after dust removal and purification; making the materials after reduction and decomposition enter an oxidation calcining kiln for sintering a cement clinker, and controlling to heat, mineralize and sinter the cement clinker in the gas phase atmosphere under the pulverized coal combustion.

Claims

1. A production method for producing cement and co-producing sulfuric acid from phosphogypsum, comprising: pretreating and purifying the phosphogypsum to reduce contents of non-gypsum ingredients and most free water, then granulating with a reducing agent carbon powder and an auxiliary material, feeding the granulated materials into an integrated rotary kiln formed by preheating, drying, dehydration, reduction and decomposition for reduction and decomposition of the phosphogypsum to generate sulfur oxide gas, and making the decomposed material enter a cement clinker sintering kiln for mineralizing and sintering, wherein: the pretreating refers to pulping with water, and then carrying out gravity separation and pressure filtration separation to remove most of the non-gypsum impurity ingredients and free water, and mechanically granulating a phosphogypsum filter cake with most impurities removed with the reducing agent carbon powder and the auxiliary material; the mechanically granulated phosphogypsum materials are fed to an integrated reduction and decomposition kiln provided with a shoveling plate for fluidized heating, drying and dehydration, heating, reduction and decomposition are controlled to be carried out in a gas phase atmosphere under pulverized coal combustion, the materials are dehydrated and dried by reverse flow of the reduced and decomposed gas, heated and self-cooled, and then purified, converted and absorbed to produce the sulfuric acid; and the integrally reduced and decomposed materials enter the cement clinker sintering kiln, and are controlled to be heated and sintered into a cement clinker in the gas phase atmosphere under the pulverized coal combustion.

2. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 1, wherein the pretreating refers to pulping with water, separating the non-gypsum impurity ingredients by a gravity and reducing the free water of the phosphogypsum filter cake by pressure filtration extrusion, and then mechanically granulating the ingredients.

3. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 1, wherein the integrated reduction and decomposition rotary kiln is composed of two parts, a high-temperature part is lined with a heat-resisting high-temperature material as a reduction and decomposition reaction section; and a low-temperature part is provided with different models of shoveling plates for lifting along a periphery as a fluidized heating, drying and dehydration section.

4. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 1, wherein the pulping ratio of the phosphogypsum to the water in the pretreating and purifying is 1:2 to 4, and preferably 1:2.5; after the phosphogypsum slurry is subjected to the gravity separation, a total amount of separated coarse particles is 2% to 8%, and preferably 5%; the free water of the phosphogypsum filter cake subjected to the pressure dehydration is 8% to 15%, and preferably 10% to 12%; the filter cake of the dehydrated phosphogypsum is mechanically granulated with reducing pulverized coal and clay, and a stirring and kneading granulator is preferably used as a granulator.

5. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 2, wherein the pulping ratio of the phosphogypsum to the water in the pretreating and purifying is 1:2 to 4, and preferably 1:2.5; after the phosphogypsum slurry is subjected to the gravity separation, a total amount of separated coarse particles is 2% to 8%, and preferably 5%; the free water of the phosphogypsum filter cake subjected to the pressure dehydration is 8% to 15%, and preferably 10% to 12%; the filter cake of the dehydrated phosphogypsum is mechanically granulated with reducing pulverized coal and clay, and a stirring and kneading granulator is preferably used as a granulator.

6. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 1, wherein the reduction and decomposition integrated rotary kiln with fluidized preheating, drying and dehydration is an integral cylindrical steel-shell rotary kiln, the fluidized preheating, drying and dehydration section is provided with a special-type shoveling plate for lifting, so that the materials are shoveled when the rotary kiln rotates, and the materials are lifted from low to high along with the rotation, and after reaching a certain rotation angle, the materials start to be scattered gradually; the fluidized materials are heated by contacting with high-temperature gas reversely flowing in the kiln, dried and dehydrated, and meanwhile, the high-temperature gas is cooled by heat exchange; a setting area of the special-type shoveling plate for lifting is 0.2 L to 0.5 L, preferably 0.3 L to 0.4 L of a total length of the kiln; the special-type shoveling plates for lifting are capable of being respectively arranged at intervals of an a-type shoveling plate, a b-type shoveling plate, and a c-type shoveling plate, and preferably, the b-type shoveling plate and the c-type shoveling plate are arranged at an interval on a circumference; and refractory bricks are laid in the high-temperature reduction and decomposition section, and a setting area of the refractory bricks is 0.8 L to 0.5 L, and preferably 0.7 L to 0.6 L of the total length of the kiln.

7. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 2, wherein the reduction and decomposition integrated rotary kiln with fluidized preheating, drying and dehydration is an integral cylindrical steel-shell rotary kiln, the fluidized preheating, drying and dehydration section is provided with a special-type shoveling plate for lifting, so that the materials are shoveled when the rotary kiln rotates, and the materials are lifted from low to high along with the rotation, and after reaching a certain rotation angle, the materials start to be scattered gradually; the fluidized materials are heated by contacting with high-temperature gas reversely flowing in the kiln, dried and dehydrated, and meanwhile, the high-temperature gas is cooled by heat exchange; a setting area of the special-type shoveling plate for lifting is 0.2 L to 0.5 L, preferably 0.3 L to 0.4 L of a total length of the kiln; the special-type shoveling plates for lifting are capable of being respectively arranged at intervals of an a-type shoveling plate, a b-type shoveling plate, and a c-type shoveling plate, and preferably, the b-type shoveling plate and the c-type shoveling plate are arranged at an interval on a circumference; and refractory bricks are laid in the high-temperature reduction and decomposition section, and a setting area of the refractory bricks is 0.8 L to 0.5 L, and preferably 0.7 L to 0.6 L of the total length of the kiln.

8. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 3, wherein the reduction and decomposition integrated rotary kiln with fluidized preheating, drying and dehydration is an integral cylindrical steel-shell rotary kiln, the fluidized preheating, drying and dehydration section is provided with a special-type shoveling plate for lifting, so that the materials are shoveled when the rotary kiln rotates, and the materials are lifted from low to high along with the rotation, and after reaching a certain rotation angle, the materials start to be scattered gradually; the fluidized materials are heated by contacting with high-temperature gas reversely flowing in the kiln, dried and dehydrated, and meanwhile, the high-temperature gas is cooled by heat exchange; a setting area of the special-type shoveling plate for lifting is 0.2 L to 0.5 L, preferably 0.3 L to 0.4 L of a total length of the kiln; the special-type shoveling plates for lifting are capable of being respectively arranged at intervals of an a-type shoveling plate, a b-type shoveling plate, and a c-type shoveling plate, and preferably, the b-type shoveling plate and the c-type shoveling plate are arranged at an interval on a circumference; and refractory bricks are laid in the high-temperature reduction and decomposition section, and a setting area of the refractory bricks is 0.8 L to 0.5 L, and preferably 0.7 L to 0.6 L of the total length of the kiln.

9. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 1, wherein a temperature of the sulfur oxide gas discharged from a kiln tail of the reduction and decomposition rotary kiln after reduction and decomposition, fluidized preheating, drying, and dehydration is 320° C. to 400° C., and preferably 330° C. to 350° C.; a content of O.sub.2 in the sulfur oxide gas is 0 to 1.0%, and preferably 0.2% to 0.6%; and a temperature of the high-temperature decomposition section of the reduction and decomposition rotary kiln is 1,000° C. to 1,300° C., and preferably 1,100° C. to 1,200° C.

10. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 3, wherein a temperature of the sulfur oxide gas discharged from a kiln tail of the reduction and decomposition rotary kiln after reduction and decomposition, fluidized preheating, drying, and dehydration is 320° C. to 400° C., and preferably 330° C. to 350° C.; a content of O.sub.2 in the sulfur oxide gas is 0 to 1.0%, and preferably 0.2% to 0.6%; and a temperature of the high-temperature decomposition section of the reduction and decomposition rotary kiln is 1,000° C. to 1,300° C., and preferably 1,100° C. to 1,200° C.

11. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 5, wherein a temperature of the sulfur oxide gas discharged from a kiln tail of the reduction and decomposition rotary kiln after reduction and decomposition, fluidized preheating, drying, and dehydration is 320° C. to 400° C., and preferably 330° C. to 350° C.; a content of O.sub.2 in the sulfur oxide gas is 0 to 1.0%, and preferably 0.2% to 0.6%; and a temperature of the high-temperature decomposition section of the reduction and decomposition rotary kiln is 1,000° C. to 1,300° C., and preferably 1,100° C. to 1,200° C.

12. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 1, wherein the material from a kiln head of the reduction and decomposition kiln directly enters the cement clinker sintering rotary kiln, a diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times a diameter ϕ of the reduction and decomposition rotary kiln; a temperature of the high-temperature section of the cement clinker sintering kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C.; and a content of O.sub.2 in outlet gas of the kiln tail of the cement clinker sintering kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%.

13. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 2, wherein the material from a kiln head of the reduction and decomposition kiln directly enters the cement clinker sintering rotary kiln, a diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times a diameter ϕ of the reduction and decomposition rotary kiln; a temperature of the high-temperature section of the cement clinker sintering kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C.; and a content of O.sub.2 in outlet gas of the kiln tail of the cement clinker sintering kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%.

14. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 3, wherein the material from a kiln head of the reduction and decomposition kiln directly enters the cement clinker sintering rotary kiln, a diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times a diameter ϕ of the reduction and decomposition rotary kiln; a temperature of the high-temperature section of the cement clinker sintering kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C.; and a content of O.sub.2 in outlet gas of the kiln tail of the cement clinker sintering kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%.

15. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 4, wherein the material from a kiln head of the reduction and decomposition kiln directly enters the cement clinker sintering rotary kiln, a diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times a diameter ϕ of the reduction and decomposition rotary kiln; a temperature of the high-temperature section of the cement clinker sintering kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C.; and a content of O.sub.2 in outlet gas of the kiln tail of the cement clinker sintering kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%.

16. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 5, wherein the material from a kiln head of the reduction and decomposition kiln directly enters the cement clinker sintering rotary kiln, a diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times a diameter ϕ of the reduction and decomposition rotary kiln; a temperature of the high-temperature section of the cement clinker sintering kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C.; and a content of O.sub.2 in outlet gas of the kiln tail of the cement clinker sintering kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%.

17. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 6, wherein the material from a kiln head of the reduction and decomposition kiln directly enters the cement clinker sintering rotary kiln, a diameter of the sintering rotary kiln is 0.5 to 0.7 times, and preferably 0.4 to 0.6 times a diameter ϕ of the reduction and decomposition rotary kiln; a temperature of the high-temperature section of the cement clinker sintering kiln is 1,250° C. to 1,450° C., and preferably 1,300° C. to 1,350° C.; and a content of O.sub.2 in outlet gas of the kiln tail of the cement clinker sintering kiln is 1.0% to 4.0%, and preferably 2.0% to 3.0%.

18. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 7, wherein the cement clinker of the cement clinker sintering rotary kiln enters a cooler to be cooled from 1,150° C. to 110° C.-160° C., and preferably to 110° C.-130° C.

19. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 1, wherein hot air cooling the cement clinker from the cooler flows reversely to enter the cement clinker sintering rotary kiln, and hot air tail gas from the cement clinker sintering rotary kiln enters the integrated reduction and decomposition kiln, and is adjusted according to a system gas phase atmosphere.

20. The production method for producing the cement and co-producing the sulfuric acid from the phosphogypsum according to claim 3, wherein hot air cooling the cement clinker from the cooler flows reversely to enter the cement clinker sintering rotary kiln, and hot air tail gas from the cement clinker sintering rotary kiln enters the integrated reduction and decomposition kiln, and is adjusted according to a system gas phase atmosphere.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 is a diagram showing a relationship between a decomposition temperature of phosphogypsum and gas composition of a gas phase.

[0041] FIG. 2 is a schematic diagram of an integrated rotary kiln for fluidized preheating, drying, dehydration, reduction and decomposition of phosphogypsum according to the disclosure.

[0042] In FIG. 2, L refers to a total length of a decomposition integrated rotary kiln; L1 refers to a length of a fluidized shoveling plate for lifting; L2 refers to a set length of refractory bricks; and A, B and C-type shoveling plates refer to cross-sectional diagrams of fluidized shoveling plates for lifting arranged in the rotary kiln.

[0043] FIG. 3 is a flow chart of a technology for producing cement and co-producing sulfuric acid from phosphogypsum according to the disclosure.

[0044] In FIG. 3, A refers to a kneading granulator; C1 refers to a separator; C2 refers to a cyclone dust collector; D refers to a bucket elevator; F refers to a filter press; J refers to a tail gas purification system; K1 refers to a reduction and decomposition integrated rotary kiln; K2 refers to a cement mineralization and sintering kiln; K3 refers to a cement cooler; P1 refers to a slurry transfer pump; P2 refers to a filter pressing feeding pump; T1 refers to a pulping tank; T2 refers to a separation storage tank; V1 refers to a reducing coal injection fan; V2 refers to a sintering coal injection fan; V3 refers to a cooling blower; V4 refers to a tail gas induced draft fan; X refers to a sulfuric acid absorption system; and Z refers to a sulfuric acid conversion system.

DETAILED DESCRIPTION

[0045] The disclosure is further described hereinafter with reference to the accompanying drawings.

Embodiment 1

[0046] As shown in FIG. 3, a phosphogypsum filter cake from a phosphoric acid production filter and production process water were continuously fed into a pulping tank T1 for pulping according to a ratio of 1:2.5, a pulped slurry was continuously fed into a C1 separator for separation through a pump P1, and separated coarse-particle materials were returned to a phosphorite ore grinding process of a phosphoric acid production process; a separated fine slurry entered a slurry storage tank T2, and then was fed into a filter press F through a pump P2 for filtering. A filtrate was phosphorus-containing water, and was returned to washing of the phosphogypsum filtered with phosphoric acid produced by a phosphoric acid plant. The filter cake was squeezed by a diaphragm and dried in air to obtain purified and dehydrated phosphogypsum. Compositions before and after purification refer to Table 1. After determining a ratio according to a quality requirement for producing cement and co-producing sulfuric acid, a purified phosphogypsum filter cake was fed into a kneading granulator A with a reducing agent coke and other grinded auxiliary materials for continuous kneading and granulation. After granulation, materials with an input amount of 43,500 kg per hour were lifted by an elevator D and fed into an integrated rotary K1 kiln for fluidized preheating, drying, dehydration, reduction and decomposition. Combusting pulverized coal was fed into a pulverized coal injection combustor of the integrated rotary kiln K1 by using a pulverized coal injection combustion fan V1, and a maximum temperature of materials in a decomposition section in the integrated rotary kiln K1 was controlled at 1,150° C. High-temperature gas generated by combustion and reduction and decomposition gas were jointly contacted with an overflow of the materials in the integrated kiln K1, cooled to 800° C. after gradually passing through the decomposition section, cooled to 680° C. after entering a fluidized dehydration section provided with a shoveling plate for lifting, cooled to 550° C. in a drying section, and cooled to 340° C. in a preheating section. The reduction and decomposition gas of 99,319 Nm.sup.3 was produced ever hour. Composition thereof refers to Table 2. Meanwhile, a concentration of O.sub.2 in the decomposed gas was controlled at 0.36% with matching secondary air and high-temperature hot air tail gas discharged from a cement mineralization and sintering kiln K2. The reduction and decomposition gas was returned to a granulator A after most dust was separated by a cyclone dust collector C2, and separated gas was fed for sulfuric acid production by a fan V4, which was purified by a purification system J, converted by a conversion system Z, and prepared into the sulfuric acid by an absorption system X.

TABLE-US-00001 TABLE 1 Indexes of phosphogypsum before and after purification and dehydration Ingredient CaO SO.sub.3 SiO.sub.2 P.sub.2O.sub.5 insoluble P.sub.2O.sub.5 water-soluble Free water Before purification 22.55 32.10 4.56 0.37 0.64 24.40 After purification 26.45 38.36 5.45 0.25 0.03 12.06

TABLE-US-00002 TABLE 2 Composition table of reduction and decomposition gas Ingredient CO.sub.2 SO.sub.2 N.sub.2 O.sub.2 H.sub.2O Density Composition % 15.37 9.16 61.18 0.36 13.82 1.463 Remark Kg/Nm.sup.3

[0047] Reduced and decomposed high-temperature materials from the integrated rotary kiln K1 continuously entered the cement clinker sintering rotary kiln K2, and pulverized coal was fed into a pulverized coal injection combustor in the cement clinker sintering rotary kiln K2 by using a pulverized coal injection combustion fan V2 for combustion. A maximum temperature of materials in the cement clinker sintering rotary kiln K2 was controlled at 1,300° C., an excess air coefficient was controlled at 1.06 with matching secondary air of the pulverized coal injection combustion fan V2, and a concentration of O.sub.2 in a gas phase was 3.0%. The sintered clinker from the cement clinker sintering rotary kiln K2 continuously entered a cooler K3 and was cooled to 160° C. by using a cooling blower V3. 20,000 kg of cement clinker was obtained every hour, and fed for a cement grinding process to produce finished cement. Composition thereof refers to Table 3.

TABLE-US-00003 TABLE 3 Composition table of cement clinker Ingredient fCaO CaS SO.sub.3 C.sub.3S C.sub.2S C.sub.3A C.sub.4AF Composition % 0.80 0.60 0.92 43.90 36.92 7.36 9.25 Remark

Embodiment 2

[0048] As shown in FIG. 3, a phosphogypsum filter cake from a phosphoric acid production filter and production process water were continuously fed into a pulping tank T1 for pulping by 1:2.0, a pulped slurry was continuously fed into a C1 separator for separation through a pump P1, and separated coarse-particle materials were returned to a phosphorite ore grinding process of a phosphoric acid production process; a separated fine slurry entered a slurry storage tank T2, and then was fed into a filter press F through a pump P2 for filtering. A filtrate was phosphorus-containing water, and was returned to washing of the phosphogypsum filtered with phosphoric acid produced by a phosphoric acid plant and supplementation of wet-grinding ore pulp. The filter cake was squeezed by a diaphragm and dried in air to obtain purified and dehydrated phosphogypsum. Compositions before and after purification refer to Table 4. After determining a ratio according to a quality requirement for producing cement and co-producing sulfuric acid, a purified phosphogypsum filter cake was fed into a kneading granulator A with a reducing agent coke and other grinded auxiliary materials for continuous kneading and granulation. After granulation, materials with an input amount of 87,000 kg per hour were lifted by an elevator D and fed into an integrated rotary kiln K1 for fluidized preheating, drying, dehydration, reduction and decomposition. Combusting pulverized coal was fed into a pulverized coal injection combustor of the integrated rotary kiln K1 by using a pulverized coal injection combustion fan V1 for injection and combustion, and a maximum temperature of materials in a decomposition section in the integrated rotary kiln K1 was controlled at 1,150° C. High-temperature gas generated by combustion and reduction and decomposition gas were jointly contacted with an overflow of the materials in the integrated kiln K1, cooled to 800° C. after gradually passing through the decomposition section, cooled to 680° C. after entering a fluidized dehydration section provided with a shoveling plate for lifting, cooled to 550° C. in a drying section, and cooled to 340° C. in a preheating section. The reduction and decomposition gas of 1,180,153 Nm.sup.3 was produced ever hour. Composition thereof refers to Table 5. Meanwhile, a concentration of O.sub.2 in the decomposed gas was controlled at 0.50% with matching secondary air and high-temperature hot air tail gas discharged from a cement mineralization and sintering kiln K2.

[0049] Reduced and decomposed high-temperature materials from the integrated rotary kiln K1 continuously entered the cement clinker sintering rotary kiln K2, and pulverized coal was fed into a pulverized coal injection combustor in the cement clinker sintering rotary kiln K2 by using a pulverized coal injection combustion fan V2 for injection and combustion. A maximum temperature of materials in the cement clinker sintering rotary kiln K2 was controlled at 1,300° C., an excess air coefficient was controlled at 1.08 with matching secondary air of the pulverized coal injection combustion fan V2, and a concentration of O.sub.2 in a gas phase was 3.5%. The sintered clinker from the cement clinker sintering rotary kiln K2 continuously entered a cooler K3 and was cooled to 160° C. by using a cooling blower V3. 20,000 kg of cement clinker was obtained every hour. Composition thereof refers to Table 6.

TABLE-US-00004 TABLE 4 Indexes of phosphogypsum before and after purification and dehydration Ingredient CaO SO.sub.3 SiO.sub.2 P.sub.2O.sub.5 insoluble P.sub.2O.sub.5 water-soluble Free water Before purification 22.55 32.10 4.56 0.37 0.64 24.40 After purification 26.35 38.32 5.84 0.28 0.04 11.06

TABLE-US-00005 TABLE 5 Composition table of reduction and decomposition gas Ingredient CO.sub.2 SO.sub.2 N.sub.2 O.sub.2 H.sub.2O Density Composition % 16.34 10.10 61.58 0.5 11.48 1.463 Remark Kg/Nm.sup.3

[0050] Reduced and decomposed high-temperature materials from the integrated rotary kiln K1 continuously entered the cement clinker sintering rotary kiln K2, and pulverized coal was fed into a pulverized coal injection combustor in the cement clinker sintering rotary kiln K2 by using a pulverized coal injection combustion fan V2. A maximum temperature of materials in the cement clinker sintering rotary kiln K2 was controlled at 1250° C., an excess air coefficient was controlled at 1.08 with matching secondary air of the pulverized coal injection combustion fan V2, and a concentration of O.sub.2 in a gas phase was 3.5%. The sintered clinker from the cement clinker sintering rotary kiln K2 continuously entered a cooler K3 and was cooled to 160° C. by using a cooling blower V3. 40,000 kg of cement clinker was obtained every hour. Composition of the cement clinker refers to Table 6.

TABLE-US-00006 TABLE 6 Composition table of cement clinker Ingredient fCaO CaS SO.sub.3 C.sub.3S C.sub.2S C.sub.3A C.sub.4AF Composition % 0.80 0.42 1.10 43.8 36.92 7.36 9.25 Remark