METHOD FOR PREPARING INORGANIC COMPOUND BY USING RECYCLABLE RESOURCES TO REDUCE GREENHOUSE GAS EMISSIONS

Abstract

The present invention relates to a method for preparing an inorganic compound by using recyclable resources to reduce greenhouse gas emissions and, more specifically, to a method for preparing an inorganic compound, wherein a carbonated inorganic compound can be prepared in a continuous pattern by capturing carbon dioxide generated at industrial sites, with a desulfurization byproduct, which is an industrial waste, serving as a medium, although not using a separate drying process and an additive for pH adjustment for promoting carbonation, thereby significantly reducing greenhouse gas and process costs compared with existing processes.

Claims

1. A method for producing inorganic compounds using circulating resources comprising: a slurry preparation step of preparing a desulfurized gypsum slurry by mixing desulfurized gypsum with water; and an inorganic compound preparation step of supplying a carbon dioxide-containing gas to the desulfurized gypsum slurry and capturing carbon dioxide through a carbonation reaction to prepare an inorganic compound, wherein the prepared inorganic compound is in the form of a dried solid powder.

2. The method for producing inorganic compounds using circulating resources according to claim 1, wherein the desulfurized gypsum is produced in a CFBC boiler, and comprises 40 to 80% by weight of CaO and 15 to 35% by weight of SO.sub.3.

3. The method for producing inorganic compounds using circulating resources according to claim 1, wherein the desulfurized gypsum and water in the slurry preparation step are mixed in a weight ratio of 25-45:55-75.

4. The method for producing inorganic compounds using circulating resources according to claim 1, wherein no additives for pH control are used in the slurry preparation step.

5. The method for producing inorganic compounds using circulating resources according to claim 1, wherein the carbon dioxide-containing gas is an exhaust gas of a circulating fluidized bed combustion boiler.

6. The method for producing inorganic compounds using circulating resources according to claim 1, wherein a process temperature is maintained at 100 to 150° C. using a carbon dioxide-containing gas as a heat source in the inorganic compound preparation step.

7. The method for producing inorganic compounds using circulating resources according to claim 1, wherein the carbonation reaction occurs by contacting the carbon dioxide-containing gas and the desulfurized gypsum slurry in a cross-flow in the inorganic compound preparation step.

8. The method for producing inorganic compounds using circulating resources according to claim 1, wherein the carbonation reaction is performed by contacting the carbon dioxide-containing gas and the desulfurized gypsum slurry in a co-directional flow in the inorganic compound production step.

9. The method for producing inorganic compounds using circulating resources according to claim 1, wherein the inorganic compound includes gypsum and calcium carbonate.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0015] FIG. 1 is a schematic view of a carbonation reactor of Example 1 in which the method for producing an inorganic compound according to the present invention is applied on a laboratory-scale.

[0016] FIG. 2 is a schematic view of a carbonation reactor of Example 2 in which the method for producing an inorganic compound according to the present invention is applied on a commercial-scale.

[0017] FIG. 3 is a schematic diagram of a wet carbonation reactor of Comparative Example 1 applied on a laboratory scale.

[0018] FIG. 4 is a result of X-ray diffraction analysis of desulfurized gypsum.

[0019] FIG. 5 is a result of SEM/EDS analysis of desulfurized gypsum.

[0020] FIG. 6 is a result of SEM/EDS analysis of inorganic compounds obtained after the carbonation reaction of Example 1.

[0021] FIG. 7 is a result of X-ray diffraction analysis of the inorganic compound obtained after the carbonation reaction of Example 1.

[0022] FIG. 8 is a result of X-ray diffraction analysis of the inorganic compound obtained after the carbonation reaction of Example 2.

[0023] FIG. 9 is a result of X-ray diffraction analysis of the inorganic compound obtained after the carbonation reaction of Comparative Example 1.

CONCRETE MODE FOR CARRYING OUT THE INVENTION

[0024] The present invention is explained in more detail below.

[0025] The method for producing inorganic compounds using circulating resources according to the present invention comprises: a slurry preparation step of preparing a desulfurized gypsum slurry by mixing desulfurized gypsum with water; and an inorganic compound preparation step of supplying a carbon dioxide-containing gas to the desulfurized gypsum slurry and capturing carbon dioxide through a carbonation reaction to prepare an inorganic compound, wherein the prepared inorganic compound is in the form of a dried solid powder.

[0026] The method for producing inorganic compounds according to the present invention comprises a slurry preparation step of preparing a desulfurized gypsum slurry by mixing desulfurized gypsum with water.

[0027] The desulfurized gypsum used in the slurry preparation step is an industrial by-product, and in one embodiment, desulfurized gypsum produced in a CFBC (circulating fluidized bed combustion) boiler may be used.

[0028] Although not particularly limited, the desulfurized gypsum may comprise 40 wt % or more of CaO—for example, 40 to 80 wt % (where CaO also includes CaSO.sub.4), and 15 to 35 wt % of SO.sub.3. Calcium compounds including SO.sub.3 do not participate in the carbonation reaction in a stable state, and only the quicklime component participates in the carbonation reaction.

[0029] The desulfurized gypsum and water in the slurry preparation step may be mixed at a weight ratio of 25-45: 55-75—for example, 28-42:58-72, 30-40:60-70 or 32-38:62-68. In the method for producing the inorganic compound of the present invention, an additive for adjusting pH is not used in the slurry preparation step because carbon dioxide capture efficiency is high when the desulfurized gypsum slurry is prepared at the above weight ratio. If the weight ratio is out of the above range, the carbonation reaction between carbon dioxide and the desulfurized gypsum slurry does not occur smoothly, resulting in poor production of inorganic compounds and poor greenhouse gas reduction effects.

[0030] The method for producing an inorganic compound of the present invention comprises an inorganic compound preparation step of supplying a carbon dioxide-containing gas to the desulfurized gypsum slurry and capturing carbon dioxide through a carbonation reaction to prepare an inorganic compound.

[0031] In the inorganic compound preparation step, the carbon dioxide-containing gas may be an exhaust gas of a circulating fluidized bed combustion boiler. Greenhouse gas can be reduced by using exhaust gas from a circulating fluidized bed combustion boiler, which is an industrial by-product, as a carbon dioxide-containing gas, and process costs can be minimized by utilizing the thermal energy of the gas in the process, as will be described later.

[0032] In one embodiment, the boiler exhaust gas composition is as follows. Carbon dioxide is produced from limestone for combustion of fuel and desulfurization reactions, and is about 15 to 20 vol % of the exhaust gas. Nitrogen is 70 to 75 vol %, and moisture and oxygen are 3 to 6 vol % and 2 to 5 vol %, respectively. SO.sub.x and NO.sub.x are managed by TMS in accordance with environmental regulations.

[0033] In one embodiment, in the inorganic compound preparation step, a process temperature may be maintained at 100 to 150° C. using a carbon dioxide-containing gas as a heat source. In addition, in the inorganic compound preparation step, a carbonation reaction may occur by contacting the carbon dioxide-containing gas and the desulfurized gypsum slurry in cross-flow or co-directional flow.

[0034] In the method for producing inorganic compounds according to the present invention, the carbonation reactor where the inorganic compound preparation step is performed is in the form of a flue-gas desulfurization (FGD) reactor, with a cross-flow or co-directional flow structure of the injection method, and the boiler exhaust gas flows from bottom to top (see FIG. 2). The reaction temperature is maintained at 100 to 150° C. by carbon dioxide-containing gas—i.e., the exhaust gas. The desulfurized gypsum slurry is mixed in a storage tank equipped with an agitator and can be heated before being introduced into the carbonation reactor. The desulfurized gypsum slurry is injected into the carbonation reactor through injection nozzles, and atomizing air can also be injected into the nozzle to enable good atomization and formation of small droplets.

[0035] In the inorganic compound preparation step, under the above conditions the slaked lime contained in the desulfurized gypsum slurry reacts with the carbon dioxide contained in the carbon dioxide-containing gas to be converted into calcium carbonate, and the injected water is vaporized due to the heat generated during the carbonation reaction and the heat of the carbon dioxide-containing gas (boiler exhaust gas) and is discharged in the form of steam. Therefore, the inorganic compound produced in the present invention is in the form of a dried solid powder and does not require a separate drying process, thereby reducing process costs compared to prior art. The converted inorganic compound can be stored in the bag house in the form of a solid powder from which moisture has been removed. The inorganic compound comprises gypsum and calcium carbonate.

[0036] The present invention is explained in more detail through the following Examples and Comparative Examples. However, the scope of the present invention is not limited thereby in any manner.

EXAMPLES

Example 1

[0037] In laboratory-scale, a cylindrical carbonation reactor with cross-flow nozzle injection was used to capture carbon dioxide, and desulfurized gypsum slurry and gas were injected into the reactor (see FIG. 1).

[0038] The desulfurized gypsum slurry was prepared by mixing desulfurized gypsum and water in a slurry tank (1) with a weight ratio of 25-45:55-75 for desulfurized gypsum and water, respectively. A magnetic stirrer (2) was used to ensure that the quicklime particles were well mixed with the water, promoting hydration reaction. Prior to injection, the slurry tank was pressurized (6) with nitrogen at 1.5-2.0 bar.Math.g and preheated to 95° C. to suppress the temperature drop caused by the injection of the slurry into the reactor. The slurry was injected from the side of the cylindrical reactor (4) in a spray form.

[0039] The carbon dioxide gas (7) was preheated (3) to 110-120° C. and injected into the cylindrical reactor from the top under a pressure of 3 bar.Math.g.

[0040] The carbonation reactor was maintained at 110-120° C. by the heat jacket (5) and the preheated carbon dioxide gas. After injecting the desulfurized gypsum slurry and carbon dioxide gas into the reactor, the generated material was collected at the bottom of the reactor (9). The carbon dioxide gas and evaporated water were discharged from the top of the carbonation reactor (8).

[0041] To confirm whether the desulfurized gypsum captures carbon dioxide through the carbonation reaction, SEM/EDS and X-ray diffraction analysis were performed (see FIGS. 6 and 7). By comparing the X-ray diffraction and SEM/EDS analysis results of the desulfurized gypsum (see FIGS. 4 and 5), it was confirmed that the quicklime in the desulfurized gypsum captures carbon dioxide to produce calcium carbonate (crystalline form: calcite).

Example 2

[0042] In a commercial-scale operation for capturing carbon dioxide, a co-directional flow nozzle injection type carbonate reactor was used, and desulfurized gypsum slurry was injected into the reactor along with gas (see FIG. 2).

[0043] The desulfurized gypsum and water were added to the desulfurized gypsum slurry tank (11) at a weight ratio of 25-45:55-75, and the quicklime in the desulfurized gypsum was well contacted with water using an agitator (12) to cause a hydration reaction. The desulfurized gypsum slurry including the resulting slaked lime by the hydration reaction, was transported to the carbonate reactor (15) through a nozzle (14) by a pump (13) at a pressure of 3-5 bar.Math.g, with an injection angle of 40-60°. To ensure uniform injection of the slurry into the carbonate reactor, atomizing air (18) was injected into the nozzle at a pressure of 2.5-4.5 bar.Math.g.

[0044] The reaction temperature was maintained at 130 to 150° C. by the flow of the CFBC boiler exhaust gas (17). Carbon dioxide contained in the exhaust gas from the CFBC boiler was converted into calcium carbonate through a carbonation reaction with slaked lime contained in the desulfurized gypsum slurry injected through the nozzle.

[0045] Inorganic compounds including the converted calcium carbonate were discharged to the upper part of the carbonation reactor along the boiler discharge gas flow (19) and transported to the bag house (16). Among them, solids containing inorganic compounds are discharged to the lower part (20) of the bag house, and after reaction, the exhaust gas is discharged to the upper part (21) and discharged to the atmosphere through the chimney. At this time, the water used in the production of slaked lime was vaporized by the temperature of the reactor during the carbonation reaction and was included in the exhaust gas after the reaction and released into the atmosphere. The inorganic compound thus produced could be obtained as a dried solid powder containing no moisture.

[0046] X-ray diffraction analysis was performed to confirm whether the quicklime in the desulfurized gypsum captured carbon dioxide through the carbonation reactor (see FIG. 8). After the carbonation reaction, the peak corresponding to quicklime was reduced, and the calcium carbonate peak was greatly enhanced, confirming that the carbonation reaction proceeded.

Comparative Example 1

[0047] A laboratory-scale carbon dioxide capture experiment was conducted by applying a wet process, which is already a common process (see FIG. 3). Into the desulfurized gypsum slurry tank (36), the desulfurized gypsum and water is added at a weight ratio of 25-45:55-75, stirred at room temperature using a magnetic stirrer (35), and gas injection nozzle (34) into the desulfurized gypsum slurry was placed to inject carbon dioxide (37). At this time, the wet carbonation reactor was pressurized (31, 33) at 0.8 to 1.2 bar.Math.g to promote the carbonation reaction, and carbon dioxide was injected, but the gas outlet was blocked to immediately inject as much carbon dioxide as consumed by the carbonation reaction. The reaction was terminated when the injection of carbon dioxide no longer occurred, and the degree of injection was determined using the ball flow meter (32). After completion of the reaction, the product was obtained as a solid powder through filtration and drying processes.

[0048] X-ray diffraction analysis was performed to confirm whether the desulfurized gypsum captured carbon dioxide through the carbonation reaction (see FIG. 9). After the carbonation reaction, the peak corresponding to quicklime was removed, and the calcium carbonate peak was greatly enhanced, confirming that the carbonation reaction proceeded.

[0049] As can be seen from the above experiment, since the inorganic compound in the form of a dried solid can be prepared in the method for producing the inorganic compound of the present invention, a continuous process can be performed without using a separate drying process and an additive for adjusting pH to promote carbonation. It was confirmed that the inorganic compound can be prepared with the method, and the process cost can be drastically reduced compared to the existing process.

[0050] However, in the case of manufacturing inorganic compounds through a conventional wet process performed in Comparative Example 1, since carbonation occurs in the carbon dioxide injector and the injection nozzle was clogged, the operation was unstable. And a separate filtration and drying process is required. Thus, it was confirmed that the economics and efficiency of the process are relatively lowered.