Apparatus and Method for Producing Cement Through Flue Gas Desulfurization

Abstract

The present invention provides an apparatus and a method for producing cement through flue gas desulfurization, and specifically provides an apparatus and a method for simultaneously producing magnesium sulfate cement during a magnesium oxide based flue gas desulfurization process. The apparatus of the present invention includes a flue gas desulfurization equipment, a concentration equipment, a crystallization equipment, a centrifugation equipment, a drying equipment, a waste ash supplying equipment, a slag material supplying equipment, a mixing equipment, etc. By adopting the apparatus and method of the present invention, the problems in the present conventional cement production such as high energy cost, severe damage to the environment and so on can be solved, and the problems like high production cost of ordinary magnesium sulfate cement and high transportation cost of supplies thereby causing incapability in a large scale market spreading and application can also be solved.

Claims

1. An apparatus for producing cement through flue gas desulfurization, comprising: a flue gas desulfurization equipment, configured to remove sulfur dioxide from a flue gas in a magnesium oxide based manner, and form an absorption product containing magnesium sulfate; a concentration equipment, configured to concentrate the absorption product containing magnesium sulfate from the flue gas desulfurization equipment to form a concentration product; a crystallization equipment, configured to receive the concentration product formed in the concentration equipment, and generate crystal particles in the concentration product, so as to acquire a concentration product containing magnesium sulfate crystals; a centrifugation equipment, configured to centrifugally separate the concentration product containing the magnesium sulfate crystals from the crystallization equipment to form a precipitate containing the magnesium sulfate crystals; a drying equipment, configured to dry the precipitate containing the magnesium sulfate crystals from the centrifugation equipment to form a dried precipitate; a waste ash supplying equipment, configured to provide waste ash; a slag material supplying equipment, configured to provide a slag material used for cement; an additive supplying equipment, configured to provide an additive used for cement; a mixing equipment, configured to mix the dried precipitate from the drying equipment, the waste ash from the waste ash supplying equipment, the slag material used for cement from the slag material supplying equipment and the additive used for cement from the additive supplying equipment to form cement.

2. The apparatus for producing cement through flue gas desulfurization according to claim 1, wherein, an upper portion of an interior of the flue gas desulfurization equipment is provided with a sulfur dioxide absorbing and spraying region, configured to remove sulfur dioxide in the flue gas in a magnesium oxide based manner, and form the absorption product containing magnesium sulfate.

3. The apparatus for producing cement through flue gas desulfurization according to claim 1, wherein, the concentration equipment is: 1) a cycling and precipitating tank provided inside the flue gas desulfurization equipment, and the cycling and precipitating tank is arranged at a lower portion of the flue gas desulfurization equipment, or 2) an evaporation and concentration equipment provided outside the flue gas desulfurization equipment.

4. The apparatus for producing cement through flue gas desulfurization according to claim 1, wherein, further comprising a slag material grinding equipment, configured to grind the slag material used for cement into a powder, and transport the powder to the slag material supplying equipment.

5. The apparatus for producing cement through flue gas desulfurization according to claim 1, wherein, the flue gas satisfies one of following conditions: 1) the flue gas is a flue gas that comes from a coal fired boiler, a sintering machine, a pellet or a furnace; 2) a content of sulfur dioxide in the flue gas is 300 mg/Nm340000 mg/Nm3, and a content of oxygen is 318 vt %.

6. A method for producing cement with the apparatus for producing cement through flue gas desulfurization according to claim 1, wherein, comprising steps of: 1) a flue gas desulfurization step: removing sulfur dioxide from a flue gas in a magnesium oxide based manner in a flue gas desulfurization equipment, and forming an absorption product containing magnesium sulfate; 2) a concentration step: concentrating the absorption product containing magnesium sulfate from the flue gas desulfurization equipment in a concentration equipment, so as to form a concentration product; 3) a crystallization step: receiving, by a crystallization equipment, the concentration product formed in the concentration equipment, and generating crystal particles in the concentration product, so as to acquire a concentration product containing magnesium sulfate crystals; 4) a centrifugation step: separating centrifugally the concentration product containing the magnesium sulfate crystals from the crystallization equipment in a centrifugation equipment, so as to form a precipitate containing the magnesium sulfate crystals; 5) a drying step: drying the precipitate containing the magnesium sulfate crystals from the centrifugation equipment in a drying equipment, so as to form a dried precipitate; 6) a mixing step: mixing the dried precipitate from the drying equipment, waste ash from a waste ash supplying equipment, slag material from a slag material supplying equipment and an additive from an additive supplying equipment in a mixing equipment, so as to form cement.

7. The method according to claim 6, wherein, a granularity of the crystal particles in step 3) is larger than 0.2 mm.

8. The method according to claim 6, wherein, a water content of the dried precipitate in step 5) is less than 1 wt %.

9. The method according to claim 6, wherein, the slag material of step 6) is one or more selected from a group consisting of furnace slag, mineral waste residue, steel slag, iron slag and pulverized fuel ash; and/or the additive of step 7) is one or more selected from a group consisting of silicone rubber, polyester fiber, glass fiber, phosphate acid, dihydrogen phosphate salt, hydrogen phosphate salt, tartaric acid, tartrate, magnesium oxide or Nitrilotri(methylphosphonic acid).

10. The method according to claim 6, wherein, the cement is magnesium sulfate cement.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0046] FIG. 1 is a diagram of an apparatus of Embodiment 1 of the present invention.

[0047] FIG. 2 is a diagram of an apparatus of Embodiment 2 of the present invention.

[0048] Reference signs: 1desulfurization tower, 2sulfur dioxide absorbing and spraying region, 3discharging pump, 41cycling and precipitating tank, 42three-effect evaporator, 6crystallizer, 7centrifuge, 8dryer, 9mixer, 10slag material grinder, 11slag material feeder, 12pulverized fuel ash feeder, 13additive feeder, 14magnesium oxide feeder, 15packaging machine.

DESCRIPTION OF EMBODIMENTS

[0049] The expressions % described in the present invention, unless otherwise specified, all refer to volume percentage. The expressions vt % described in the present invention refer to volume percentage.

[0050] In the present invention, the magnesium oxide based flue gas desulfurization is a flue gas desulfurization process in which magnesium oxide is the main ingredient of the desulfurization agent, and the addition of other ingredients (e.g. calcium oxide, calcium hydroxide) is not limited. The structure and composition of the desulfurization agent varies according to differences of product categories, product types and quality of the magnesium sulfate cement to be produced later, and the composition or variation is well known for the person in the art.

[0051] According to an embodiment of the present invention, the flue gas of the present invention can be a flue gas from a coal fired boiler, a sintering machine, a pellet or a furnace, preferably from the coal fired boiler, the sintering machine or the furnace, further preferably from the coal fired boiler or the sintering machine. The purity of the magnesium sulfate product can be improved, since a certain amount of oxygen and an appropriate content of sulfur dioxide exist in the flue gas. According to another embodiment of the present invention, the content of sulfur dioxide in the flue gas can be 300 mg/Nm.sup.340000 mg/Nm.sup.3, preferably 500 mg/Nm.sup.330000 mg/Nm.sup.3, and further preferably 1000 mg/Nm.sup.35000 mg/Nm.sup.3. The content of oxygen in the flue gas of the present invention can be 318 vt %, preferably 918 vt %, and further preferably 1218 vt %. Thus the output and product purity of the magnesium sulfate product can be improved.

[0052] The cement of the present invention is cement containing magnesium sulfate, including magnesium sulfate cement, magnesium oxysulfate cement or magnesia cement. The magnesia cement is meant to include magnesium oxychloride cement, Sorel cement, and the mixture thereof. The cement of the present invention is preferably magnesium sulfate cement.

[0053] <Apparatus for Producing Cement Through Flue Gas Desulfurization>

[0054] The apparatus for producing cement through flue gas desulfurization of the present invention includes following equipment: a flue gas desulfurization equipment, a concentration equipment, a crystallization equipment, a centrifugation equipment, a drying equipment, a waste ash supplying equipment, a slag material supplying equipment, a magnesium oxide supplying equipment and a mixing equipment. Preferably, the apparatus for producing cement through flue gas desulfurization of the present invention can further include a discharging equipment. Preferably, the apparatus for producing cement through flue gas desulfurization of the present invention can further include a packaging equipment.

[0055] The flue gas desulfurization equipment of the present invention is configured to remove sulfur dioxide from the flue gas in a magnesium oxide based manner, and form an absorption product containing magnesium sulfate. The flue gas desulfurization equipment of the present invention can be a flue gas desulfurizer or a flue gas desulfurization tower. In view of industrial application, the flue gas desulfurization tower is preferably selected.

[0056] In an embodiment of the present invention, the upper portion of the interior of the flue gas desulfurization equipment is provided with a sulfur dioxide absorbing and spraying region, in which the sulfur dioxide in the flue gas is removed in a magnesium oxide based manner, and an absorption product containing magnesium sulfate is formed. The flue gas enter the interior of the flue gas desulfurization equipment from the lower portion of the equipment, and goes through the sulfur dioxide absorbing and spraying region during ascending and the sulfur dioxide in the flue gas is absorbed, and the purified flue gas is discharged from the top of the flue gas desulfurization equipment. Agents used in the sulfur dioxide absorbing and spraying region can be the frequently adopted desulfurization agent slurry used for the magnesium oxide based flue gas desulfurization in the art. Preferably, the desulfurization agent of the present invention can be those desulfurization agents disclosed in Chinese patent application with publication No. CN102745726A, CN102745725A and CN102836636A. For example, the desulfurization agents disclosed in Embodiment 1 or 2 of CN102745726 A. The contents of all the above patent applications are incorporated herein by reference in their entireties. These desulfurization agent slurries can be acquired by evenly dispersing the desulfurization agents in water.

[0057] The concentration equipment of the present invention is configured to concentrate the absorption product containing magnesium sulfate from the flue gas desulfurization equipment to form a concentration product. According to an embodiment of the present application, the concentration equipment is a cycling and precipitating tank provided inside the flue gas desulfurization equipment, and the cycling and precipitating tank is arranged at the lower portion of the flue gas desulfurization equipment. The cycling and precipitating tank can be configured to be singer layer precipitating or double-layer precipitating or multiple-layer precipitating. The material of the cycling and precipitating tank can be glass fiber reinforced plastics, special steel, or ordinary steel material after anti-corrosion treatment.

[0058] According to another embodiment of the present application, the concentration equipment can be a one-effect, two-effect or three-effect evaporation and crystallization equipment. The material of the evaporation and concentration equipment is mainly a titanium material. Preferably, the concentration equipment of the present invention is a three-effect evaporation and concentration equipment arranged outside the flue gas desulfurization equipment.

[0059] In the present application, the concentration equipment is preferably configured to evaporate water in the absorption product containing magnesium sulfate (sometimes called magnesium sulfate solution) to form a saturated magnesium sulfate solution. The concentration equipment of the present invention is preferably a three-effect evaporation and concentration equipment (e.g. three-effect evaporator): a secondary steam produced by a first effect enter a second effect as a heat source, a secondary steam produced by evaporation of the second effect is used as a heat source of a third effect, so as to save the live steam. The second effect and the third effect of the equipment adopt a manner of forced cycle and concentration, such that the heat transfer efficiency is improved, the cycle is intensive, the evaporation rate is fast, the heating time is short, and the scaling will not readily occur. The temperature of the feed magnesium sulfate solution of the three-effect evaporation and concentration is 3040 C. and the density is 1.11.26 t/m.sup.3; the temperature of the magnesium sulfate solution after evaporation is 6070 C. and the density is 1.321.46 t/m.sup.3.

[0060] The crystallization equipment of the present invention is configured to receive the concentration product formed from the concentration equipment, and generate crystal particles in the concentration product, so as to acquire a concentration product containing magnesium sulfate crystals. Preferably, the crystallization equipment of the present invention is configured for cooling crystallization of the concentration product, so as to precipitate magnesium sulfate from the solution. The crystallization equipment is preferably a continuous cooling crystallizer, further preferably DTB continuous cooling crystallizer, most preferably three-stage recrystallization flash tank, where the magnesium sulfate waste solution goes from a first effect concentration, through a second effect concentration and to a third effect concentration with a concentration degree reaching 38%, which is already a saturated solution; and then the crystal solution is pumped out by a discharging pump and delivered to a three-stage recrystallization flash tank to precipitate for crystallization. The DTB crystallizer is consisted of a crystallization tank, a condenser, a forced cycling pump, a discharging pump and a vacuum pump, etc. DTB (Drabt Tube Babbled) crystallizer is a crystallizer with a draft tube and a baffle plate, and is a circulating crystallizer for a fine crystal slurry. With a draft tube and a tube-shaped baffle plate arranged in the crystallizer and a propelled stirring system configured therein, a hot saturated feed liquid is added into the lower portion of a cycling pipe, and is delivered to a heater after mixing with the mother liquid entrained with small crystals in the cycling pipe. The heated solution flows into the crystallizer from a position near the bottom of the draft tube, and is delivered to the liquid surface along the draft tube by a slowly rotating propeller. The solution is cooled and evaporated at the surface of the solution and reaches an over-saturated state, in which part of the solute is precipitated on the surface of suspended particles, so as to make the crystal grow. A precipitation area is provided on the periphery of the annular baffle plate. Big particles are precipitated in the precipitation area, while small particles enter the cycling pipe with the mother liquid and are heated to dissolve. The crystals sink into the elutriation column from the bottom of the crystallizer. In order to make the granularity of the crystalline product as uniform as possible, part of the mother liquid from the precipitation area is added to the bottom of the elutriation column, so that small particles flow back to the crystallizer with the solution due to the effect of hydraulic classification, and the crystalline product is discharged from the lower portion of the elutriation column. The temperature for the cooling crystallization is generally controlled at 2535 C., and preferably 2530 C.

[0061] According to the apparatus of the present invention, the crystallization equipment can also be a crystallization tank which can adopt natural cooling or can be an automatic cooling system with a water cooling ring device. The cold source can be natural wind, normal temperature water or chilled water. An independent cooling device such as cooling tower can be provided.

[0062] The centrifugation equipment of the present invention is configured to centrifugally separate the concentration product containing magnesium sulfate crystals from the crystallization equipment to form a precipitate containing the magnesium sulfate crystals. The centrifugation equipment includes those well-known in the art, which will not be repeated herein.

[0063] The drying equipment of the present invention is configured to dry the precipitate containing the magnesium sulfate crystals from the centrifugation equipment to form a dried precipitate. The drying equipment of the present invention is preferably a vibrated fluidized bed drying equipment, which is especially suitable for the drying process of the magnesium sulfate crystals. The present invention preferably adopts a vibrated fluidized bed drying equipment configured with a hot air device. The ventilator inputs filtered air into an air heater, the heated air enters the lower box body of the host, and then goes through the air distribution plate of the fluidized bed and is vertically blew from down to up into the dried supplies, so as to make the supplies to be in a boiling state. The supplies get in from an feed inlet, the host generates symmetrical vibration under an exciting force of a vibrating motor, such that the supplies are horizontally threw, so as to form a fluidization state due to the comprehensive effect of the heated air flow and the vibration of the machine, which therefore achieves a long contact time of the supplies with the hot air and a large area, thereby obtaining highly efficient drying effect. The apparatus of the present invention can adopt saturated steam with a low calorific value at a temperature of 120433 C. and a pressure of 0.20.3 MPa to heat and deliver the air into the vibrated fluidized bed, and to realize fully drying of the magnesium sulfate crystals to form magnesium sulfate supplies. The steam output from the fluidized bed can be used for the evaporation and concentration equipment, which not only saves energy but also reduces the operating cost.

[0064] The magnesium oxide supplying equipment of the present equipment is configured to provide magnesium oxide used for the magnesium oxysulfate cement.

[0065] The waste ash supplying equipment of the present invention is configured to provide waste ash. The supplying equipment includes those well-known in the art, which will not be repeated herein.

[0066] The slag material supplying equipment of the present invention is configured to provide slag material. Since the granularity of the slag materials from different sources is large and heterogeneous, which needs to be powdered and uniformed, therefore, the flue gas desulfurization apparatus of the present invention can also include a slag material grinding equipment, configured to grind the slag material used for the cement into a powder, and to be transported to the slag material supplying equipment. The slag material grinding equipment mainly refers to a ball grinder in the field of the cement production. The ball grinder can grind waste slags such as mineral waste slag, steel slag, pulverized fuel ash, industrial waste and so on, the ground product can reach a specific surface area of 400 m.sup.2/kg600 m.sup.2/kg.

[0067] The additive supplying equipment of the present invention is configured to provide an additive used for cement. The supplying equipment includes those well-known in the art, which will not be repeated herein.

[0068] The waste ash supplying equipment, the slag material supplying equipment, the additive supplying equipment are preferably arranged in parallel, so as to respectively provide raw material for the mixing equipment.

[0069] The mixing equipment of the present invention is configured to mix the dried precipitate from the drying equipment, the waste ash from the waste ash supplying equipment, the slag material used for cement from the slag material supplying equipment and the additive used for cement from the additive supplying equipment, so as to form cement. The mixing equipment of the present invention can be a single-shaft mixer, a double-shaft mixer or a blender. Preferably, the mixing equipment of the present invention is a blender.

[0070] The apparatus for producing cement through flue gas desulfurization can also include a discharging equipment, configured to discharge the absorption product containing magnesium sulfate from the flue gas desulfurization equipment and transport the same to the concentration equipment. According to a specific embodiment of the present invention, the discharging equipment is a discharging pump.

[0071] The apparatus for producing cement through flue gas desulfurization can also include a packaging equipment, e.g. those packaging equipment well known in the art, which will not be repeated herein.

[0072] <Method for Producing Cement>

[0073] The apparatus for producing cement through flue gas desulfurization can be used to produce cement. The method for producing cement of the present invention can include following steps: 1) a flue gas desulfurization step, 2) a concentration step, 3) a crystallization step, 4) a centrifugation step, 5) a drying step, 6) a mixing step. The method for producing cement of the present invention can also include a discharging step. Preferably, the method for producing cement of the present invention can also include a packaging step.

[0074] The fuel gas desulfurization step includes: removing sulfur dioxide from a flue gas in a magnesium oxide based manner in a flue gas desulfurization equipment, and forming an absorption product containing magnesium sulfate. According to an embodiment of the present invention, the upper portion of the interior of the flue gas desulfurization equipment is provided with a sulfur dioxide absorbing and spraying region. The flue gas enter the interior of the flue gas desulfurization equipment from the lower portion of the equipment, and goes through the sulfur dioxide absorbing and spraying region during ascending and the sulfur dioxide in the flue gas is herein absorbed, and the purified flue gas is then discharged from the top of the flue gas desulfurization equipment. The agent used for the sulfur dioxide absorbing and spraying region is described above, which will not be repeated herein.

[0075] The concentration step of the present invention includes: concentrating the absorption product containing magnesium sulfate from the flue gas desulfurization equipment in a concentration equipment, so as to form a concentration product. According to an embodiment of the present application, the absorption product containing magnesium sulfate from the flue gas desulfurization equipment is concentrated in a cycling and precipitating tank provided inside the flue gas desulfurization equipment (the cycling and precipitating tank is arranged at the lower portion of the flue gas desulfurization equipment), such that the absorption product containing magnesium sulfate is introduced into the cycling and precipitating tank by gravity.

[0076] According to another embodiment of the present application, the absorption product containing magnesium sulfate from the flue gas desulfurization equipment is concentrated in a three-effect evaporation and concentration equipment provided outside the flue gas desulfurization equipment. For example, a discharging equipment can be used to introduce the above-mentioned absorption product into the three-effect evaporation and concentration equipment to be concentrated.

[0077] The crystallization step includes: receiving, by a crystallization equipment, the concentration product formed from the concentration equipment, and generating crystal particles in the concentration product, so as to acquire a concentration product containing magnesium sulfate crystals. The concentration product of the present invention is mainly a saturated magnesium sulfate solution, from which a magnesium sulfate crystal slurry is obtained by cooling. The temperature for the cooling crystallization is controlled at 2535 C., preferably 2830 C. The granularity of the magnesium sulfate crystal particles obtained from the crystallization step of the present invention is larger than 0.2 mm, preferably larger than 0.3 mm. The granularity of the present invention is measured by a sieving manner (see GB/T21524-2008).

[0078] The centrifugation step of the present invention includes: centrifugally separating the concentration product containing the magnesium sulfate crystals from the crystallization equipment in a centrifugation equipment, so as to form a precipitate containing the magnesium sulfate crystals. In order to guarantee sufficient centrifugation, the speed of centrifugation is controlled at 15002000 rpm, preferably 16001800 rpm. For a batch operation, the centrifugation time for each batch of supplies is controlled at 530 minutes, preferably at 510 minutes. For a continuous operation, the centrifugation time for each batch of supplies is controlled at 1030 minutes, preferably at 1015 minutes.

[0079] The drying step of the present invention includes: drying the precipitate containing the magnesium sulfate crystals from the centrifugation equipment in a drying equipment, so as to form a dried precipitate. The drying step of the present invention can be operated in a way of vacuum drying or introducing heated air. The drying temperature is 90150 C., preferably 100130 C., further preferably 110120 C.; the drying pressure is 0.010.5 MPa, preferably 0.050.2 MPa. Through the drying step, the water content of the dried precipitate is less than 1 wt %, preferably less than 0.5 wt %, further preferably less than 0.1 wt %.

[0080] The mixing step of the present invention includes mixing the dried precipitate from the drying equipment, the magnesium oxide from the magnesium oxide supplying equipment, the waste ash from the waste ash supplying equipment, the slag material from the slag material supplying equipment and the additive from the additive supplying equipment in a mixing equipment, so as to form cement. The slag material of the present invention is one or more selected from a group consisting of furnace slag, mineral waste residue, steel slag and iron slag. Preferably, the slag material of the present invention is selected from furnace slag and/or mineral waste residue. The additive of the present invention is one or more selected from a group consisting of silicone rubber, polyester fiber, glass fiber, phosphate acid, dihydrogen phosphate salt, hydrogen phosphate salt, tartaric acid, tartrate, magnesium oxide and Nitrilotri(methylphosphonic acid), and preferably form a group consisting of phosphate acid, dihydrogen phosphate salt, hydrogen phosphate salt, tartaric acid, tartrate and Nitrilotri(methylphosphonic acid). The waste ash of the present invention can be one or more selected from a group consisting of pulverized fuel ash, gypsum powder, dolomite powder and shale powder, and preferably from pulverized fuel ash.

[0081] During production, varieties of slags like furnace slag, mineral waste residue, steel slag and iron slag produced in power plant, steel plant and chemical plant can be collected, and then ground into powders of desired specifications by a slag material grinding equipment to be delivered to a warehouse for reserve; the ash (e.g. pulverized fuel ash) discharged from the lower portion of the dust collector behind the coal fired boiler, sintering machine, shaft furnace or pellet of the power plant or steel plant can all be collected to a waste ash warehouse for reserve.

[0082] Unless otherwise noted, the raw materials, process conditions used in the following embodiments and examples are as follows:

[0083] 1. The Operating Conditions of the Flue Gas Desulfurization are Shown in the Following Tables.

Operating Condition Parameters of a Flue Gas Desulfurization Project of a Sintering Machine in a Steel Plant

[0084]

TABLE-US-00001 No. Project Number Unit 1 Inlet flue gas volume of the 1590000 m.sup.3/h desulfurization tower (operating condition) 2 Flue gas volume in a standard 1104504 Nm.sup.3/h state 3 Inlet temperature of the 120 C. desulfurization tower 4 Inlet concentration of sulfur 2000 mg/Nm.sup.3 dioxide 5 Desulfurization efficiency 98 % mass percentage 6 Ratio of magnesium to sulfur 1.02 7 Purity of magnesium oxide 85 % mass percentage 8 Moisture content of the flue 9 % mass percentage gas

Discharging Condition of the Desulfurization Project

[0085]

TABLE-US-00002 No. Project Number Unit 1 Outlet flue gas volume of the 1374117 m.sup.3/h desulfurization tower (operating condition) 2 Flus gas discharge temperature 50 C. 3 Discharge concentration of <50 mg/Nm.sup.3 sulfur dioxide 4 Output of magnesium sulfate 4.3 t/h 5 Quality of magnesium sulfate >98 % mass percentage

[0086] 2. Other Specifications

[0087] The composition and ratio of the desulfurization agent are as follows: magnesium oxide powder.

[0088] The ratio of the desulfurization agent slurry is as follows: the weight ratio of the desulfurization agent to water is 1:3.

[0089] The temperature of the cycling and precipitating tank is 60 C., the residence time of the supplies is 30 minutes;

[0090] With respect to the temperature of the three-effect evaporator, the temperature of the first effect, the second effect and the third effect is respectively 120 C., 90 C. and 60 C.; the residence time of the supplies is respectively 30 minutes, 20 minutes and 20 minutes.

[0091] The cooling temperature of the crystallizer is 30 C., the crystallization time is 10 minutes;

[0092] The rotation speed of the centrifuge is 2000 rpm, the centrifugation time is 5 minutes;

[0093] The drying temperature is 120 C., the drying time is 30 minutes.

[0094] In the complex additive, the weight ratio of sodium dihydrogen phosphate to magnesium oxide is 0.5:9.5.

[0095] The present invention is further described in detail by combining the following accompanying drawings.

Embodiment 1

[0096] FIG. 1 is a diagram of an apparatus of Embodiment 1. Industrial tap water is added into the desulfurization agent magnesium oxide powder to form desulfurization agent slurry-magnesium hydroxide slurry which then is pumped to a desulfurization tower 1, configured to absorb sulfur dioxide in the flue gas in the sulfur dioxide absorbing and spraying region.

[0097] The flue gas from a coal fired boiler (the content of sulfur dioxide is 2000 mg/Nm.sup.3, the content of oxygen is 18 vt %) enter the desulfurization tower 1 from the lower portion of the desulfurization tower 1. The flue gas contacts with the sulfur dioxide absorbing and spraying region 2 during ascending, and is discharged from the top of the desulfurization tower 1. The sulfur dioxide absorbing and spraying region 2 sprays the desulfurization agent slurry so as to absorb sulfur dioxide in the flue gas.

[0098] The absorption product (the temperature is 30 C., the density is 1.2 t/m.sup.3) formed after the desulfurization agent slurry absorbs the sulfur dioxide is introduced into a cycling and precipitating tank 41 located at the lower portion of the interior of the desulfurization tower 1 by gravity, a concentration product (a saturated magnesium sulfate solution, the temperature is 70 C., the density is 1.4 t/m.sup.3) is obtained by concentration.

[0099] The above-mentioned concentration product enter a crystallizer 6, generates crystal particles with a granularity of larger than 0.2 mm in the crystallizer, and then most of water therein is removed by a centrifuge 7, and then is delivered to a dryer 8 for drying. The dryer 8 is a vibrated fluidized bed. Air at 120 C., 0.2 MPa is introduced into the vibrated fluidized bed and a fully drying of the magnesium sulfate crystals is realized under the effect of the mechanical vibration, and the magnesium sulfate supplies are introduced into a blender 9 when the water content is less than 1 wt %.

[0100] The furnace slag collected from a steel plant is ground by a grinder 10 into a powdered material with a specific surface area of approximately 500 m.sup.2/kg, which then is delivered into a slag material suppler 11; the pulverized flue ash from the coal fired boiler of the steel plant is added into a pulverized flue ash suppler 12; the complex additive is added into an additive supplier 13. The above-mentioned slag material, pulverized flue ash, magnesium oxide and complex additive are then delivered into the bender 9 by a pneumatic conveying equipment.

[0101] In the bender 9, the above-mentioned slag material, pulverized flue ash, magnesium oxide, complex additive and the magnesium sulfate product produced in the above-mentioned flue gas desulfurization process are evenly mixed by stirring, and the stirring time is 30 minutes, so as to obtain magnesium sulfate cement. Finished magnesium sulfate cement is delivered to a warehouse after being packaged by a packaging machine 15.

Embodiment 2

[0102] FIG. 2 is a diagram of an apparatus of Embodiment 2. Industrial tap water is added into the desulfurization agent magnesium oxide powder to form a desulfurization agent slurry-magnesium hydroxide slurry, which then is delivered to a desulfurization tower 1, configured to absorb sulfur dioxide in the flue gas in the sulfur dioxide absorbing and spraying region.

[0103] The flue gas from a coal fired boiler (the content of sulfur dioxide is 2000 mg/Nm.sup.3, the content of oxygen is 18 vt %) enter the desulfurization tower 1 from the lower portion of the desulfurization tower 1. The flue gas contacts with the sulfur dioxide absorbing and spraying region 2 during ascending, and is discharged from the top of the desulfurization tower 1. The sulfur dioxide absorbing and spraying region 2 sprays the desulfurization agent slurry so as to absorb sulfur dioxide in the flue gas.

[0104] The absorption product (the temperature is 30 C., the density is 1.2 t/m.sup.3) formed after the desulfurization agent slurry absorbs the sulfur dioxide is discharged by a discharging pump 3 and introduced into a three-effect evaporator 42 outside the desulfurization tower 1, and a concentration product (a saturated magnesium sulfate solution, the temperature is 70 C., the density is 1.4 t/m.sup.3) is obtained by concentration.

[0105] The above-mentioned concentration product enter a crystallizer 6, generates crystal particles with a granularity of larger than 0.2 mm in the crystallizer, and then most of water therein is removed by a centrifuge 7, and then is delivered to a dryer 8 for drying. The dryer 8 is a vibrated fluidized bed. Air at 120 C., 0.2 MPa is introduced into the vibrated fluidized bed and a fully drying of the magnesium sulfate crystals is realized under the effect of the mechanical vibration, and the magnesium sulfate supplies are introduced into a blender 9 when the water content is less than 1 wt %.

[0106] The furnace slag collected from a steel plant is ground by a grinder 10 into a powdered material with a specific surface area of approximately 400 m.sup.2/kg which then is delivered into a slag material suppler 11; the pulverized flue ash from the coal fired boiler of the steel plant is added into a pulverized flue ash suppler 12; the complex additive is added into an additive supplier 13. The above-mentioned slag material, pulverized flue ash, magnesium oxide and complex additive are then delivered into the bender 9 by a pneumatic conveying equipment.

[0107] In the bender 9, the above-mentioned slag material, pulverized flue ash, magnesium oxide, complex additive and the magnesium sulfate product produced in the above-mentioned flue gas desulfurization process are evenly mixed by stirring, and the stirring rate is 1600 rpm, the stirring time is 30 minutes, so as to obtain magnesium sulfate cement. Finished magnesium sulfate cement is delivered to a warehouse after being packaged by a packaging machine 15.

APPLICATION EXAMPLE 1

[0108] The apparatus and process of Embodiment 1 are adopted to produce cement, the formula of the mixing step is as follows:

TABLE-US-00003 Magnesium Magnesium Pulverized Complex Specification sulfate supplies oxide flue ash additive kg 30 30 35 5

[0109] 100 kg of the above-mentioned magnesium sulfate cement and 30 kg of water are mixed to obtain a cement slurry, the cement slurry is poured into a 4040160 mm mould for casting, and then the casted cement is tested according to the GB177-1999 standard, the testing results are shown in the following table.

TABLE-US-00004 Number of days Compressive strength Rupture strength (d) (MPa) (MPa) 3 22 3.9 7 56 8.5 28 76 14.6

APPLICATION EXAMPLE 2

[0110] The apparatus and process of Embodiment 2 are adopted to produce cement, the formula of the mixing step is as follows:

TABLE-US-00005 Magnesium Pulverized Magnesium Complex Specification sulfate supplies flue ash oxide additive kg 30 25 30 15

[0111] 100 kg of the above-mentioned magnesium sulfate cement and 30 kg of water are mixed to obtain a cement slurry, the cement slurry is poured into a 4040160 mm mould for casting, and then the casted cement is tested according to the GB177-1999 standard, the testing results are shown in the following table.

TABLE-US-00006 Number of days Compressive strength Rupture strength (d) (MPa) (MPa) 3 26 4.1 7 59 8.8 28 81 15.0

APPLICATION EXAMPLE 3

[0112] The apparatus and process of Embodiment 2 are adopted to produce cement, the formula of the mixing step is as follows:

TABLE-US-00007 Magnesium Pulverized Magnesium Complex Specification sulfate supplies flue ash oxide additive kg 35 35 25 5

[0113] 100 kg of the above-mentioned magnesium sulfate cement and 30 kg of water are mixed to obtain a cement slurry, the cement slurry is poured into a 4040160 mm mould for casting, and then the casted cement is tested according to the GB177-1999 standard, the testing results are shown in the following table.

TABLE-US-00008 Number of days Strength Bending strength (d) (MPa) (MPa) 3 21 2.9 7 52 7.6 21 72 12.8

APPLICATION EXAMPLE 4

[0114] The apparatus and process of Embodiment 2 are adopted to produce cement, the formula of the mixing step is as follows:

TABLE-US-00009 Magnesium Slag Magnesium Complex Specification sulfate supplies material oxide additive kg 45 25 25 5

[0115] 100 kg of the above-mentioned magnesium sulfate cement and 30 kg of water are mixed to obtain a cement slurry, the cement slurry is poured into a 4040160 mm mould for casting, and then the casted cement is tested according to GB177-1999 standard, the testing results are shown in the following table.

TABLE-US-00010 Number of days Strength Bending strength (d) (MPa) (MPa) 3 19 2.2 7 48 6.6 28 66 10.8

APPLICATION EXAMPLE 5

[0116] The apparatus and process of Embodiment 2 are adopted to produce cement, the formula of the mixing step is as follows:

TABLE-US-00011 Magnesium Magnesium Pulverized Complex Specification sulfate supplies oxide flue ash additive kg 25 25 45 5

[0117] 100 kg of the above-mentioned magnesium sulfate cement and 30 kg of water are mixed to obtain a cement slurry, the cement slurry is poured into a 4040160 mm mould for casting, and then the casted cement is tested according to GB177-1999 standard, the testing results are shown in the following table.

TABLE-US-00012 Number of days Strength Bending strength (d) (MPa) (MPa) 3 21 3.2 7 54 7.9 28 72 12.8

[0118] It can be seen from the above data that, the performances of the cement are better when the content of magnesium sulfate in the cement is between 2545 wt %; the strength and bending strength of the cement is reduced when the content of magnesium sulfate exceeds 45%. Besides, in order to maintain the performances of the cement, the content of the complex additive in the cement is preferably maintained between 515 wt %.

[0119] The present invention is not limited to the above-mentioned embodiments, any variation, modification or replacement that can be conceived by the person skilled in the art without departing from the substantial content of the present invention shall fall into the scope of the present invention.