Carbon dioxide separation and recovery method and carbon dioxide separation and recovery apparatus

Abstract

To provide a method and an apparatus for separating and recovering carbon dioxide capable of recovering carbon dioxide by using atmospheric pressure steam which is exhaust heat of extremely low quality.SOLUTION: In the method for separating and recovering carbon dioxide according to the present invention, when carbon dioxide is separated and recovered by heating, with a regenerative heat source, a carbon dioxide absorbing solution in which carbon dioxide in a carbon dioxide-containing gas is absorbed by a chemical absorbing solution, saturated steam at 150 °C or less, which is pressurized and heated by a steam compressor from atmospheric pressure steam generated in a factory, is used for at least a part of the regenerative heat source. A carbon dioxide separation and recovery apparatus of the present invention includes a carbon dioxide absorption tower in which carbon dioxide is absorbed by a chemical absorption liquid, a chemical absorption liquid regeneration tower in which a regeneration heat source is received by a reboiler to desorb carbon dioxide, and a steam compressor that generates saturated steam from atmospheric pressure steam.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for separating and capturing carbon dioxide and an apparatus for separating and capturing carbon dioxide. [Background technology]

[0002] As carbon dioxide (CO2) reduction is required, various technologies for separating and capturing emitted carbon dioxide are being considered, in addition to drastic measures such as curbing carbon dioxide emissions and developing energy-saving technologies. In particular, there is growing importance in taking measures to deal with the large amounts of carbon dioxide released into the atmosphere from various factories such as chemical complexes, steel mills, thermal power plants, and cement factories.

[0003] For example, as described in Patent Document 1, technological development is underway to separate and capture carbon dioxide using a chemical absorption method in which carbon dioxide is dissolved in an amine liquid from by-product gases generated at steelworks, absorbed, and then recovered by heating the amine liquid. Of the by-product gases generated at steelworks, for example, blast furnace gas (BFG) is generated in large quantities and has a carbon dioxide ratio of over 20%. Therefore, the method described in Patent Document 1 can reduce carbon dioxide emissions at steelworks, which are one of the large-scale sources of carbon dioxide.

[0004] As shown in Figure 1, the chemical absorption method uses a chemical absorption solution (also simply referred to as absorption solution) containing amines and the like, and brings a carbon dioxide-containing gas containing carbon dioxide into contact with the chemical absorption solution at about room temperature in a carbon dioxide absorption tower (also simply referred to as absorption tower) to absorb the carbon dioxide into the chemical absorption solution. Next, the carbon dioxide absorption solution that has absorbed the carbon dioxide (rich amine solution) is sent to a chemical absorption solution regeneration tower (also simply referred to as regeneration tower), which is equipment for regenerating the chemical absorption solution, and is heated in a reboiler to separate and recover the carbon dioxide from the carbon dioxide absorption solution. The regenerated chemical absorption solution (lean amine solution) is returned to the absorption tower, and is recycled between the absorption tower and regeneration tower.

[0005] In the aforementioned Patent Document 1, waste heat generated in steelworks is utilized when separating and capturing carbon dioxide using a chemical absorption method. Examples of usable waste heat include waste heat from sinter product coolers (approximately 350°C), main sintering exhaust gas (approximately 280°C), hot stove exhaust gas (approximately 230°C), main sintering exhaust gas (approximately 180°C), and wastewater used in the granulation of molten blast furnace slag (approximately 90°C). These are low-grade waste heat with a relatively low temperature of 500°C or less, but high-grade waste heat with a higher temperature of over 500°C is already being utilized for power generation, heating, etc.

[0006] Meanwhile, Patent Document 2 discloses an invention that uses granulated slag water (approximately 80–90°C), a type of extremely low-grade waste heat, to separate and capture carbon dioxide from a carbon dioxide absorbing solution in a chemical absorption process and to recycle the granulated slag water. The invention described in this document employs a heat pump capable of generating steam as a means for specifically recovering heat from the granulated slag water, which is an extremely low-grade waste heat. In this invention, as shown in Figure 5, the heat pump cools the 80°C granulated slag water recovered from the granulated slag process to 62°C (heat recovery), and this recovered heat is used to produce 115°C saturated steam at a rate of 4 t / h for every 100 t / h of granulated slag water. The resulting 115°C saturated steam is used to heat the CO2 absorbing solution in the chemical absorption CO2 recovery process. Meanwhile, the 62°C granulated slag water cooled by the heat pump is replenished with 5 t / h of fresh 25°C make-up water to make 100 t / h of 60°C granulated slag water, just like in existing processes, and is reused to cool the next batch of molten blast furnace slag. According to the same document, an integrated model steelworks with an annual crude steel production capacity of 8 million t uses more than 1,000 t / h of granulated slag water, which shows that the effects of the invention described in the document have a wide range.

[0007] Furthermore, Patent Document 2 provides a schematic explanation of the heat and material balances of 100 t / h of granulated slag water in a slag granulation process according to prior art at the time of the invention, which does not use a heat pump, as shown in Figure 6. In other words, in the conventional slag granulation process, when 100 t / h of cooling water at 60°C is injected onto molten blast furnace slag, 5 t / h of atmospheric steam is released, and at the same time, 95 t / h of granulated slag water at 80°C is recovered. Furthermore, the high-temperature granulated slag water is sent to a cooling tower, where a portion of it is released as steam to lower its own temperature. The amount of steam released is 3 t / h. Here, the steam generated by contacting a high-temperature object with cooling water at atmospheric pressure is called atmospheric pressure steam. Steam generated at atmospheric pressure is 100°C if there is no air or if there is very little air mixed in, and its pressure is about atmospheric pressure. In places where large amounts of atmospheric pressure steam are generated, chimneys or other devices are usually built to actively remove the generated atmospheric pressure steam, and natural suction is used. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-292298 [Patent Document 2] Japanese Patent Application Publication No. 2023-133742 Summary of the Invention [Problem to be solved by the invention]

[0009] In carbon dioxide capture by chemical absorption, research and development has reduced the heating temperature required for carbon dioxide capture. While some methods have been shown to be possible at temperatures below 100°C, the preferred heating temperature range is generally around 100–120°C. The amount of thermal energy required has also been reduced. However, the separation and capture of large amounts of carbon dioxide is expected as a means to achieve carbon neutrality, and a large amount of thermal energy is required to separate and capture such large amounts of carbon dioxide. One possible way to supply such large amounts of heat is to burn city gas, but this not only requires high fuel costs, but also produces carbon dioxide during combustion. Therefore, as a solution to these problems, there is a need for further utilization of unused waste heat and an affordable way to do so.

[0010] The aforementioned Patent Document 1 discloses, with several examples, the use of low-grade waste heat when separating and recovering carbon dioxide by chemical absorption, but steam exceeding 100°C is required to heat the carbon dioxide absorbing solution that has absorbed carbon dioxide to separate and recover the carbon dioxide. Therefore, among the low-grade waste heat examples given in the aforementioned Patent Document 1, the granulated slag water (approximately 90°C) generated when obtaining granulated blast furnace slag could not be used as is when heating the carbon dioxide absorbing solution in the chemical absorption method to recover carbon dioxide (regenerate the amine solution).

[0011] In contrast to this, as mentioned above, Patent Document 2 focuses on granulated slag water as a heat source for heating and regenerating a carbon dioxide absorption liquid (amine liquid) in a chemical absorption method, and discloses an invention in which steam for heating is generated from this granulated slag water using a heat pump. As the inventors continued their research, they discovered that, as shown in Figures 5 and 6, unused steam was still released in the slag granulation process of the invention described in the document, and that there was potential for further utilization of unused waste heat. Incidentally, the steam generated in the slag granulation process is atmospheric pressure steam as explained above, and if there is no air or other contamination, or if there is a sufficiently small amount of air, it is at 100°C. However, as mentioned above, atmospheric pressure steam at 100°C cannot be used to separate and capture carbon dioxide using the chemical absorption method. In response to this, the inventors came up with the idea that if a steam compressor is used to increase the temperature and pressure of the steam by sucking in and compressing it, the waste heat, which had previously been unusable, could be used to regenerate the amine liquid.

[0012] Therefore, an object of the present invention is to provide a method for separating and capturing carbon dioxide and an apparatus for separating and capturing carbon dioxide, which are capable of capturing carbon dioxide using atmospheric pressure steam, which is an extremely low-quality waste heat. [Means for solving the problem]

[0013] [1] A method for separating and recovering carbon dioxide, in which carbon dioxide in a carbon dioxide-containing gas is absorbed into a chemical absorption solution, is heated with a regenerative heat source to separate and recover carbon dioxide, A method for separating and recovering carbon dioxide, wherein at least a portion of the regenerative heat source is saturated steam of 150°C or less that is adjusted from superheated steam obtained by compressing and heating atmospheric pressure steam generated during water cooling of high-temperature materials in a factory using a steam compressor. [2] The high-temperature material is molten blast furnace slag; The carbon dioxide separation and recovery method according to [1], wherein the atmospheric pressure steam is atmospheric pressure steam generated when cooling water is sprayed onto the molten blast furnace slag to pulverize and rapidly cool it to obtain granulated blast furnace slag. [3] A method for separating and recovering carbon dioxide according to [1] or [2], further comprising, as part of the regenerative heat source, saturated steam of 150°C or less obtained by using a heat pump from the granulated slag water generated when obtaining the granulated blast furnace slag.

[0014] [4] A method for separating and recovering carbon dioxide according to any one of [1] to [3], wherein the carbon dioxide-containing gas is a carbon dioxide-containing gas generated within a steelworks. [5] The carbon dioxide separation and recovery method according to [4], wherein the carbon dioxide-containing gas generated in the steelworks is blast furnace gas. [6] The method for separating and recovering carbon dioxide according to any one of [1] to [5], wherein dust is removed from the atmospheric pressure steam by a dust removal device before being introduced into the steam compressor.

[0015] [7] A method for separating and recovering carbon dioxide described in any one of [1] to [6], wherein the saturated steam is water vapor adjusted by injecting water into the superheated steam. [8] A method for separating and recovering carbon dioxide described in any one of [1] to [6], wherein the saturated steam is water vapor adjusted by cooling the superheated steam through heat exchange. [9] A method for separating and recovering carbon dioxide according to any one of [1] to [6], wherein the saturated steam is water vapor prepared from water by heat exchange with the superheated steam.

[0016]

[10] A carbon dioxide separation and capture device that separates and captures carbon dioxide by heating a carbon dioxide absorption liquid obtained by absorbing carbon dioxide in a carbon dioxide-containing gas into a chemical absorption liquid with a regenerative heat source, a carbon dioxide absorption tower that absorbs carbon dioxide from the carbon dioxide-containing gas with the chemical absorption solution; a chemical absorption solution regeneration tower that receives the regeneration heat source from an associated reboiler and separates carbon dioxide from the carbon dioxide absorbing solution; A steam compressor that increases the pressure and temperature of atmospheric pressure steam generated when water-cooling high-temperature objects in a factory to turn it into superheated steam; a steam adjusting means for converting the superheated steam into saturated steam of 150°C or less, The saturated steam having a temperature of 150°C or lower is supplied to the reboiler as at least a part of the regenerative heat source.

[11] The high-temperature material is molten blast furnace slag; The carbon dioxide separation and recovery apparatus according to

[10] , wherein the atmospheric pressure steam is atmospheric pressure steam generated when cooling water is sprayed onto the molten blast furnace slag to pulverize and rapidly cool it to obtain granulated blast furnace slag.

[12] A heat pump for producing saturated steam from granulated slag water generated when obtaining the granulated blast furnace slag, The carbon dioxide separation and recovery apparatus according to

[10] or

[11] , wherein saturated steam of 150°C or less produced by the heat pump is further supplied to the reboiler as part of the regenerative heat source.

[0017]

[13] A carbon dioxide separation and capture device according to any one of

[10] to

[12] , wherein the carbon dioxide-containing gas is a carbon dioxide-containing gas generated within a steelworks.

[14] The carbon dioxide separation and recovery apparatus according to

[13] , wherein the carbon dioxide-containing gas generated in the steelworks is blast furnace gas.

[15] A carbon dioxide separation and capture device according to any one of

[10] to

[14] , which has a dust removal device that removes dust in a process before the atmospheric pressure steam is introduced into the steam compressor.

[0018]

[16] The carbon dioxide separation and capture device according to any one of

[10] to

[15] , wherein the steam adjustment means is a water-reducing device that adjusts the steam by injecting water into the superheated steam.

[17] A carbon dioxide separation and capture device according to any one of

[10] to

[15] , wherein the steam adjustment means is a heat exchanger that adjusts the superheated steam by cooling it through heat exchange.

[18] The carbon dioxide separation and capture device according to any one of

[10] to

[15] , wherein the steam adjustment means is a steam generator that adjusts the steam from water by heat exchange with the superheated steam. [Effects of the Invention]

[0019] According to the present invention, a portion of the thermal energy required to desorb carbon dioxide from a carbon dioxide absorbing solution that has absorbed carbon dioxide can be provided by atmospheric pressure steam, which is extremely low-quality waste heat. In particular, when the present invention is implemented in a steelworks, a large amount of heat is required to recover the large amount of carbon dioxide emitted from the steelworks on a large scale. This heat can be supplied inexpensively by the present invention. Moreover, the steam used to heat the reboiler is condensed into return water, which can be reused as granulated slag water, thereby reducing the amount of makeup water required and reducing overall costs. In addition, most of the carbon dioxide-containing gas emitted from a steelworks is generally generated in locations close to the blast furnace, where blast furnace slag is generated. In other words, the location where the carbon dioxide-containing gas is generated and the heat source required for separation and recovery are close to each other. Therefore, this is an extremely useful invention that can be industrially implemented, including the fact that there is no need for large-scale transportation of the carbon dioxide-containing gas and / or steam as a regenerative heat source. As described above, according to the present invention, it is possible to provide a carbon dioxide separation and capture method and a carbon dioxide separation and capture apparatus that can separate and capture carbon dioxide using atmospheric pressure steam, which is extremely low-quality waste heat. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating the principle of a carbon dioxide separation and capture process by chemical absorption according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram illustrating a process for supplying saturated steam obtained by pressurizing and heating atmospheric pressure steam generated in a slag granulation process in a steam compressor to produce superheated steam, which is a key part of a carbon dioxide separation and capture device according to an embodiment of the present invention, to a reboiler. [Figure 3] FIG. 3 is a diagram showing the main part of a carbon dioxide separation and capture device according to another embodiment of the present invention, and is a diagram for schematically explaining a process in which a heat pump is added to the carbon dioxide separation and capture device shown in FIG. 2. [Figure 4]FIG. 10 is a diagram showing a main part of a carbon dioxide separation and capture device according to still another embodiment of the present invention, which diagrammatically explains a process in which a saturated steam circulation system and an atmospheric pressure steam circulation system are made independent of each other by using a steam generator as the steam adjustment means instead of the reduced temperature water injection device shown in FIG. [Figure 5] FIG. 1 is a diagram illustrating a carbon dioxide recovery method according to the prior art based on the heat balance and material balance of granulated slag water. [Figure 6] FIG. 1 is a diagram illustrating a slag granulation process for obtaining granulated blast furnace slag according to the prior art, based on the heat balance and material balance of the granulated slag water. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, a carbon dioxide separation and capture method and a carbon dioxide separation and capture device according to an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiment.

[0022] Fig. 1 is a diagram illustrating the principle of a carbon dioxide separation and capture process using a chemical absorption method according to an embodiment of the present invention. Fig. 2 is a diagram illustrating a main part of a carbon dioxide separation and capture apparatus according to an embodiment of the present invention, which illustrates a process in which atmospheric-pressure steam generated in a slag granulation process is pressurized and heated in a steam compressor to produce superheated steam, and the saturated steam obtained by adjusting the superheated steam using a reduced-temperature water injector is supplied to a reboiler. Fig. 3 is a diagram illustrating a main part of a carbon dioxide separation and capture apparatus according to another embodiment of the present invention, which illustrates a process in which a heat pump is added to the carbon dioxide separation and capture apparatus shown in Fig. 2. Fig. 4 is a diagram illustrating a main part of a carbon dioxide separation and capture apparatus according to yet another embodiment of the present invention, which illustrates a process in which the saturated steam circulation system and the atmospheric-pressure steam circulation system are separated from each other by using a steam generator as the steam adjustment means instead of the reduced-temperature water injector shown in Fig. 3. Hereinafter, a carbon dioxide separation and capture method and a carbon dioxide separation and capture apparatus according to an embodiment of the present invention will be described with reference to FIGS. 2 to 4, taking into account the carbon dioxide separation and capture apparatus using a chemical absorption method shown in FIG. 1, which is common to the background art of the present invention.

[0023] In an embodiment of the present invention, carbon dioxide is separated and recovered from a carbon dioxide-containing gas using a chemical absorption method. Figure 1 is a principle diagram of a process for separating and recovering carbon dioxide from a carbon dioxide-containing gas containing carbon dioxide by a chemical absorption method. As shown in Figure 1, the chemical absorption method uses a chemical absorption liquid (absorption liquid) containing amines and the like, and brings a carbon dioxide-containing gas into contact with the chemical absorption liquid at room temperature (for example, around 50°C) in a carbon dioxide absorption tower (absorption tower) to absorb the carbon dioxide into the chemical absorption liquid. Next, the carbon dioxide absorption liquid (rich amine liquid) is sent to a chemical absorption liquid regeneration tower (regeneration tower), where it is heated to around 100 to 120°C in a reboiler using a heating medium (steam, etc.) that serves as a regeneration heat source, thereby separating and recovering carbon dioxide from the carbon dioxide absorption liquid and regenerating the chemical absorption liquid. The regenerated chemical absorption liquid (lean amine liquid) is returned to the absorption tower and circulated between the absorption tower and the regeneration tower. Such a chemical absorption liquid is not particularly limited, and any conventionally known liquid may be used as appropriate, such as an aqueous solution containing amines.

[0024] In a carbon dioxide separation and capture method according to an embodiment of the present invention, a carbon dioxide absorbing solution obtained by absorbing carbon dioxide in a carbon dioxide-containing gas into a chemical absorption solution is heated with a regenerative heat source to separate and capture carbon dioxide. At least a portion of the regenerative heat source used here is atmospheric pressure steam generated in a factory, which is pressurized and heated by a steam compressor and adjusted as necessary to become saturated steam at 150°C or less. The upper limit of 150°C is set because this is the temperature required to satisfy the heating temperature (120°C) of the rich amine solution described above. In other words, the temperature of the heating medium (steam) needs to be higher than the temperature of the object to be heated (rich amine solution), and this temperature range is generally set to about +10 to +20°C, or at most about +30°C.

[0025] The steam used is saturated steam because it is common in heating devices that primarily utilize the latent heat of steam. Because saturated steam has a uniquely defined temperature and pressure, maintaining the target heating temperature simply requires controlling the pressure of the heating device to a constant level. This convenience makes saturated steam widely used. When atmospheric-pressure steam is pressurized and heated by a steam compressor, it typically becomes superheated steam rather than saturated steam. To obtain saturated steam suitable for use in a reboiler, the superheated steam pressurized and heated by the steam compressor can be cooled in a heat exchanger or injected with a de-superheated water injector. Alternatively, superheated steam pressurized and heated by the steam compressor can be used as a heat source, and saturated steam for the reboiler can be prepared from water in a separate system from the atmospheric-pressure steam. Furthermore, to remove large amounts of atmospheric-pressure steam from its source and transport it to the reboiler, it is preferable to suction it using a steam compressor and pump it through piping or ducts.

[0026] Furthermore, in this embodiment, it is not necessary for the entire heat source for regenerating the chemical absorption solution to be atmospheric pressure steam, which is extremely low-quality waste heat at 100° C. Within the scope of the object of the present invention, low-quality waste heat above 100° C. to high-quality waste heat above 500° C., and even combustion heat of fossil fuels or the like can be simultaneously used in addition to atmospheric pressure steam. The steam compressor is not particularly limited and may be a large turbo steam compressor capable of compressing steam on the order of several hundred t / h, or a smaller screw steam compressor or reciprocating steam compressor, either alone or in combination.

[0027] In this embodiment, examples of the carbon dioxide-containing gas to be separated and recovered include carbon dioxide-containing gases released into the atmosphere in large quantities from various factories such as chemical complexes, steel mills, thermal power plants, cement factories, etc. At least a part of the heat source for regenerating the carbon dioxide absorbing solution can be atmospheric pressure steam generated in various cooling processes in each factory, which is pressurized and heated by a steam compressor and adjusted as necessary to become saturated steam at 150°C or less. In the following description of this embodiment, separation and recovery of carbon dioxide in a steelworks will be mainly described as an example.

[0028] Suitable carbon dioxide-containing gases that can be separated and captured in steelworks include by-product gases (unburned gases) such as blast furnace gas (BFG), coke oven gas (COG), and converter furnace gas (LDG), which are generated in large quantities. The combustion exhaust gas from the use of these by-product gases or other fuels as heating fuel in a heating furnace or the like may also be used as a carbon dioxide-containing gas. Furthermore, gases (process gases) produced during the process of reforming by-product gases such as coke oven gas and converter furnace gas for the purpose of hydrogen production may also be used as carbon dioxide-containing gases. These by-product gases may be used alone or in a mixture of two or more.

[0029] Of these by-product gases, blast furnace gas has a high carbon dioxide ratio of over 20%, and also contains a few percent of hydrogen, which is a fuel component, and over 20% carbon monoxide. The carbon dioxide concentration in the exhaust gas (also called combustion exhaust gas) after combustion is also over 20%. Converter gas contains around 70% carbon monoxide along with over 10% carbon dioxide, and the carbon dioxide concentration in the exhaust gas (combustion exhaust gas) after combustion is very high, over 20%, just like blast furnace gas. Coke oven gas is rich in hydrogen and methane, which are suitable as fuel gas, but the carbon dioxide concentration in the exhaust gas (combustion exhaust gas) after combustion is less than 10%.

[0030] In this embodiment, in addition to the by-product gases described above, carbon dioxide-containing gases such as hot stove exhaust gases that are generated within the steelworks and contain a relatively large amount of carbon dioxide, exhaust gases from various heating furnaces, and exhaust gases from thermal power plants installed within the steelworks may be supplied. Furthermore, if a lime calcination plant that produces lime products used in steelmaking plants, sintering plants, etc. is located within the steelworks, a large amount of carbon dioxide, which is a pyrolysis gas of limestone, is also emitted in addition to the exhaust gas from the heating fuel for limestone, and these gases may be supplied as the carbon dioxide-containing gas.

[0031] On the other hand, in the chemical absorption method, the thermal energy required for heating in the regeneration tower is the dominant factor in the operating cost. Therefore, in this embodiment, atmospheric pressure steam (100°C) of extremely low-quality waste heat generated in steelworks and the like is pressurized and heated by a steam compressor, and adjusted as necessary to become saturated steam of 150°C or less, which is used as at least a part of the regeneration heat source for regenerating the chemical absorption solution. In this embodiment, atmospheric pressure steam is preferably used as atmospheric pressure steam, typically generated when water-cooling a high-temperature material. Water-cooling here includes not only direct water-cooling but also indirect cooling via a heat exchanger or the like. The use of a heat exchanger advantageously prevents corrosive components, dust, and the like from being contained in the atmospheric pressure steam. In the case of direct water-cooling, if corrosive components, dust, and the like contained in the original heat source are contained in the atmospheric pressure steam, this can interfere with the operation of the steam compressor. Therefore, it is preferable to remove these by installing a dry dust removal device such as a cyclone between the atmospheric pressure steam generation point and the steam compressor, i.e., before the steam is fed to the steam compressor.

[0032] Although wet dust removal devices such as venturi scrubbers are available, wet dust removal devices are not preferred because they cool atmospheric steam and condense it. Dry dust removal devices include cyclones, bag filters, dust removal plates, and electrostatic precipitators. All of these devices are applicable, and they may be used alone or in combination. Dust removal plates remove dust by causing dust particles to collide with a plate installed opposite the gas flow. While their performance is not as high as other dust removal methods, they are inexpensive. Bag filters are not preferred because the high humidity of atmospheric steam can cause sticky dust layers to form on the filter cloth surface, resulting in increased pressure loss, poor dust removal, and a shortened service life. For these reasons, cyclones and electrostatic precipitators are preferred. In this embodiment, it is preferable to avoid mixing of outside air into the atmospheric pressure steam as much as possible, because mixing of outside air into the atmospheric pressure steam reduces the efficiency of the steam compressor in generating saturated steam at 150°C or less.

[0033] In this embodiment, molten blast furnace slag is the most preferable high-temperature material that generates atmospheric steam when cooled, even in steelworks where a wide variety of waste heat sources exist. Blast furnace slag is generated as a by-product when producing pig iron in a blast furnace. It is discharged from the blast furnace in a molten state similar to lava. The amount of slag is about 0.3 t per ton of molten pig iron, and its temperature is about 1500°C, containing a huge amount of heat. To be used as a by-product, the molten blast furnace slag is crushed and rapidly cooled in a blast furnace slag granulation facility installed near the blast furnace. This process generates a large amount of atmospheric steam, but in the past, this waste heat was dissipated into the atmosphere without effective utilization. As shown in Figures 5 and 6, the amount of atmospheric steam generated during slag granulation is estimated at 5 t / h per 100 t / h of granulated slag water. Since the waste heat recovery from atmospheric steam is close to the main source of carbon dioxide-containing gases emitted from steelworks, large-scale transportation of the recovered heat is not required. Therefore, waste heat recovery from a blast furnace slag granulation facility is advantageous for carbon dioxide capture. The granulated blast furnace slag obtained here is sandy and has a cement-like composition. It exhibits latent hydraulic properties over time, and is therefore widely used, such as being further crushed into cement raw material.

[0034] Other examples of high-temperature materials that generate atmospheric pressure steam include atmospheric pressure steam generated during wet quenching of red-hot coke discharged from a coke oven (see, for example, JP 2011-074225 A), but a detailed description thereof will be omitted here.

[0035] In a first embodiment of the present invention, as shown in FIG. 2, atmospheric-pressure steam generated in the slag granulation process is utilized as at least a portion of the regenerative heat source in the chemical absorption process. Specifically, atmospheric-pressure steam generated in the slag granulation process is pressurized and heated by a steam compressor to produce superheated steam, which is then conditioned by a temperature-reducing water injector to produce saturated steam at 150°C or less. This saturated steam is then supplied to a reboiler for chemical absorption solution regeneration. The steam used to heat the reboiler is condensed into return water, which is reused as granulated slag water. While FIG. 2 partially omits the conventional carbon dioxide separation and capture process using chemical absorption as shown in FIG. 1, this embodiment also employs a carbon dioxide separation and capture process using chemical absorption similar to that used in the conventional technology. Furthermore, the same effects can be achieved by using a heat exchanger instead of the temperature-reducing water injector shown in FIG. 2 to convert superheated steam into saturated steam. As described above, a known steam compressor can be used in this embodiment. The electric power input to the steam compressor required to raise the pressure and temperature of atmospheric pressure steam at 100°C to, for example, about 140°C is about 20% of the thermal energy of the latent heat of the steam, and the usable thermal energy is far greater.

[0036] The following shows the results of a trial calculation of the effect of utilizing waste heat in this embodiment when the equipment is configured as shown in Figure 2, assuming that the atmospheric pressure steam generated in the slag granulation process is estimated at 5 t / h per 100 t / h of granulated slag water, as in Figures 5 and 6. Note that the energy required to operate the equipment, such as the power input to the steam compressor, has been omitted here for simplicity.

[0037] (a) 5 t / h of atmospheric steam is drawn in by the steam compressor and passes through a cyclone to remove dust particles. (b) The purified atmospheric pressure steam is pressurized and heated by a steam compressor to produce 5 t / h of superheated steam at 240°C and 360 kPaA (A stands for absolute pressure). (c) To adjust the superheated steam to saturated steam, the superheated steam is introduced into a de-superheating water injector, and water at 25°C is supplied (injected) at 0.5 t / h by spraying. As a result, the water evaporates, lowering the temperature of the superheated steam, and a total of 140°C and 5.5 t / h of saturated steam is obtained.

[0038] (d) The saturated steam at 140°C and 5.5 t / h obtained here is supplied to the reboiler as at least a part of the regenerative heat source. Assuming that this saturated steam of 5.5 t / h releases 2.2 GJ / t-steam as latent heat of steam when condensing in the reboiler, 2.2 x 5.5 = 12.1 GJ / h is the amount of heat that can be used as atmospheric pressure steam to heat the carbon dioxide absorption liquid.

[0039] (e) The amount of carbon dioxide separated and recovered per 100 t / h of granulated slag water using this exhaust heat is 12.1 / 2.0 = 6.1 t-CO2 / h, assuming that the carbon dioxide recovery heat intensity is, for example, 2.0 GJ / t-CO2. This amount is per 100 t / h of granulated slag water, and when converted into the annual amount of carbon dioxide captured, assuming an operating time of 11 months, it comes to approximately 48,000 t-CO2 / year. Furthermore, this amount amounts to a massive 480,000 t-CO2 per year or more, since an integrated steelworks with an annual crude steel production capacity of 8 million t uses more than 1,000 t / h of granulated slag water.

[0040] (f) The 5.5 t / h of return water condensed in the reboiler is combined with 95 t / h of granulated slag water to become 100.5 t / h, which is recycled. The amount of cooling water injected into the granulated slag process is 100 t / h, but the difference of 0.5 t / h is purged or evaporated when the circulating water is cooled, and is discharged outside the system.

[0041] Incidentally, the production of granulated blast furnace slag also generates granulated slag water (at about 80 to 90°C). Therefore, as disclosed in Patent Document 2 by the present inventors (see FIG. 5), the waste heat of this granulated slag water can also be used as a heat source for regenerating the chemical absorption solution, and so it may be used together with atmospheric pressure steam. That is, as a second embodiment of the present invention, for example, as shown in FIG. 3, an embodiment in which a heat pump is provided in addition to the carbon dioxide separation and capture apparatus according to the first embodiment (see FIG. 2) is also possible.

[0042] The second embodiment can be similar to the first embodiment of the present invention, except for the use of a heat pump. In detail, in the first embodiment, the return water from the reboiler is saturated steam condensate adjusted by a de-heating water injector from superheated steam obtained by increasing the pressure and temperature of atmospheric pressure steam in a steam compressor. Meanwhile, in the second embodiment, the return water from the reboiler is saturated steam condensate adjusted by a de-heating water injector from superheated steam obtained by increasing the pressure and temperature of atmospheric pressure steam in a steam compressor, and saturated steam condensate produced by a heat pump. However, there is no significant difference between the two, since both types of return water are recycled in the slag granulation and the heat pump.

[0043] The steam obtained from atmospheric pressure steam and the steam obtained from the heat pump may be mixed and used in the reboiler, or they may be used in the reboiler without being mixed. When using them in the reboiler without mixing, the reboiler should have separate inlet and outlet for the steam obtained from atmospheric pressure steam and the inlet and outlet for the steam obtained from the heat pump. This makes it possible to keep the circulating water for the heat pump cleaner, thereby extending the maintenance cycle and lifespan of the heat exchanger in the heat pump. The heat pump used here may be any known type, such as a compression heat pump, an absorption heat pump, or an adsorption heat pump, and is not particularly limited.

[0044] In the second embodiment, the waste heat of the granulated slag water is utilized by using a heat pump in addition to the atmospheric pressure steam in the granulated slag process, but other waste hot waters that are generated in the steelworks and have a relatively large calorific value may also be utilized, similar to the granulated slag water. For example, ammonia water (aqueous ammonia) generated when separating tar in the refining process of high-temperature coke oven gas (COG), and LDG cooling water generated when water-cooling high-temperature converter gas (LDG) are waste hot waters with a temperature of approximately 60 to 90°C, and can be used in the same way as the granulated slag water.

[0045] The waste heat utilization effect of the second embodiment is calculated as follows, in addition to the effect of the first embodiment, assuming that saturated steam is generated at 4 t / h from 100 t / h of granulated slag water by a heat pump, as in the case of Figure 5. The temperature of the saturated steam here is set to 115°C.

[0046] (a') 5 t / h of atmospheric steam is drawn in by the steam compressor and passes through a cyclone to remove any dust it contains. (b') The purified atmospheric pressure steam is pressurized and heated by a steam compressor to produce 5 t / h of superheated steam at 153°C and 170 kPaA (A means absolute pressure). (c') To adjust the superheated steam to saturated steam, the superheated steam is introduced into a de-superheating water injector, and water at 25°C is supplied (injected) at 0.2 t / h by spraying. As a result, the water evaporates, lowering the temperature of the superheated steam, and a total of 115°C and 5.2 t / h of saturated steam is obtained.

[0047] (d') When 5.2 t / h of saturated steam at 115°C from this steam compressor is added to 4 t / h of saturated steam at 115°C from the heat pump, a total of 9.2 t / h of saturated steam at 115°C is supplied to the reboiler as at least a part of the regenerative heat source. Note that this saturated steam may be supplied to the reboiler either mixed as described above or without being mixed. Assuming that this 9.2 t / h of saturated steam releases 2.2 GJ / t-steam as latent heat of steam when condensed in the reboiler, 2.2 x 9.2 = 20.2 GJ / h of the 9.2 t / h of saturated steam per 100 t / h of granulated slag water can be used to heat the carbon dioxide absorption liquid.

[0048] (e') The amount of carbon dioxide separated and recovered per 100 t / h of granulated slag water using this exhaust heat is 20.2 / 2.0 = 10.1 t-CO2 / h, using 2.0 GJ / t-CO2 as the carbon dioxide recovery heat consumption rate as mentioned above. This amount is per 100 t / h of granulated slag water, and when converted into the annual amount of carbon dioxide captured, assuming an operating time of 11 months, it comes to approximately 80,000 t-CO2 / year. Furthermore, this amount amounts to a massive 800,000 t-CO2 or more per year, since an integrated steelworks with an annual crude steel production capacity of 8 million t uses more than 1,000 t / h of granulated slag water.

[0049] (f') Of the 9.2 t / h of return water condensed in the reboiler, 4 t / h is returned to the heat pump, and the remaining 5.2 t / h is combined with 95 t / h of granulated slag water to become 100.2 t / h, which is recycled. The amount of cooling water injected into the granulated slag process is 100 t / h, but the difference of 0.2 t / h is purged or evaporated when the circulating water is cooled, and is discharged outside the system.

[0050] In the third embodiment, as shown in FIG. 4 , atmospheric-pressure steam from the slag granulation process is compressed and heated by a steam compressor to produce superheated steam, as in the other embodiments. However, this superheated steam is supplied to a steam generator to produce saturated steam, which is then used in a reboiler. Although the use of a steam generator inevitably reduces overall thermal efficiency, this method provides cleaner saturated steam to the reboiler, thereby extending the reboiler's maintenance cycle and lifespan. Furthermore, when saturated steam is supplied using a heat pump, as in the second embodiment, it is easy to mix the saturated steam from the heat pump and the saturated steam from the steam generator. This is because the same water can be used as the saturated steam source for both the steam generator and the heat pump.

[0051] The results of trial calculations performed on the exhaust heat utilization effect in the third embodiment in the same manner as in the second embodiment are shown below. (a") 5 t / h of atmospheric steam is drawn in by the steam compressor and passes through a cyclone to remove dust particles. (b) The purified atmospheric pressure steam is pressurized and heated by a steam compressor to produce 5 t / h of superheated steam at 135°C and 143 kPaA (A stands for absolute pressure). (c") Superheated steam is supplied to the steam generator as a heat medium. 4.5 t / h of hot water (return water from the reboiler) is supplied as the steam source to be used as the saturated steam source, and 4.5 t / h of saturated steam at 115°C is obtained. Here, the thermal efficiency of the steam generator is assumed to be 90%. The temperature of the superheated steam supplied as the heat medium is set to 135°C, while the temperature of the saturated steam is 115°C, because, as mentioned above, the temperature of the heating medium needs to be higher than the temperature of the saturated steam that is generated.

[0052] (d") If 4.5 t / h of saturated steam at 115°C from this steam generator is added to 4 t / h of saturated steam at 115°C from the heat pump, a total of 8.5 t / h of saturated steam at 115°C is supplied to the reboiler as at least a part of the regenerative heat source. Note that this saturated steam can be mixed and supplied to the reboiler as described above. Assuming that this 8.5 t / h of saturated steam releases 2.2 GJ / t-steam as latent heat of steam when condensing in the reboiler, 2.2 x 8.5 = 18.7 GJ / h of the 8.5 t / h of saturated steam per 100 t / h of granulated slag water can be used to heat the carbon dioxide absorption liquid.

[0053] (e") The amount of carbon dioxide separated and recovered per 100 t / h of granulated slag water using this exhaust heat is 18.7 / 2.0 = 9.4 t-CO2 / h, using 2.0 GJ / t-CO2 as the carbon dioxide recovery heat intensity as before. This amount is per 100 t / h of granulated slag water, and when converted into the annual amount of carbon dioxide captured, assuming an operating time of 11 months, it comes to approximately 74,000 t-CO2 / year. Furthermore, this amount amounts to a massive 740,000 t-CO2 or more per year, since an integrated steelworks with an annual crude steel production capacity of 8 million t uses more than 1,000 t / h of granulated slag water.

[0054] (f") Of the 8.5 t / h of return water condensed in the reboiler, 4 t / h is returned to the heat pump and the remaining 4.5 t / h is returned to the steam generator. The 5 t / h of superheated steam used as a heat transfer medium in the steam generator is condensed in the steam generator and recycled in the slag granulation process. This reduces the amount of wastewater discharged outside the system. This also reduces the need for makeup water, which is effective in improving costs.

[0055] As described above, in this embodiment, atmospheric pressure steam, which is extremely low-quality waste heat at 100°C that has traditionally been difficult to use in steelmaking processes, is used, thereby reducing the amount of fossil fuels that have traditionally been used and significantly reducing the cost of carbon dioxide separation and capture using chemical absorption. In addition, this embodiment also has the effect of making it possible to reallocate low-quality waste heat of 500°C or less, as disclosed in Patent Document 1, for other uses. Additionally, in this embodiment, most of the carbon dioxide-containing gas to be treated and the atmospheric pressure steam used as a regenerative heat source are generated in close proximity to each other within factories such as steelworks. Furthermore, much of the carbon dioxide-containing gas generated at steelworks is supplied in a state of high carbon dioxide concentration. Therefore, the carbon dioxide separation and capture device according to this embodiment not only allows the entire facility to be made compact, but also reduces the consumption of utilities such as electricity and water required for the facility, thereby further reducing operating costs.

Claims

1. A method for separating and recovering carbon dioxide, comprising heating a carbon dioxide absorbing solution obtained by absorbing carbon dioxide in a carbon dioxide-containing gas into a chemical absorption solution with a regenerative heat source to separate and recover carbon dioxide, A method for separating and recovering carbon dioxide, wherein at least a portion of the regenerative heat source is saturated steam of 150°C or less that is adjusted from superheated steam obtained by pressurizing and heating atmospheric pressure steam generated during water cooling of high-temperature materials in a factory using a steam compressor.

2. The high-temperature object is molten blast furnace slag, 2. The method for separating and capturing carbon dioxide according to claim 1, wherein the atmospheric pressure steam is atmospheric pressure steam generated when cooling water is sprayed onto the molten blast furnace slag to pulverize and rapidly cool it, thereby obtaining granulated blast furnace slag.

3. 3. The carbon dioxide separation and recovery method according to claim 1 or claim 2, further comprising saturated steam at 150°C or less obtained by using a heat pump from granulated slag water generated when obtaining the granulated blast furnace slag, as part of the regenerative heat source.

4. 3. The method for separating and capturing carbon dioxide according to claim 1, wherein the carbon dioxide-containing gas is generated in a steelworks.

5. 5. The method for separating and capturing carbon dioxide according to claim 4, wherein the carbon dioxide-containing gas generated in the steelworks is blast furnace gas.

6. 3. The method for separating and capturing carbon dioxide according to claim 1, wherein dust is removed from the atmospheric pressure steam by a dust remover before the atmospheric pressure steam is introduced into the steam compressor.

7. 3. The method for separating and capturing carbon dioxide according to claim 1, wherein the saturated steam is water vapor adjusted by injecting water into the superheated steam.

8. 3. The method for separating and capturing carbon dioxide according to claim 1, wherein the saturated steam is water vapor adjusted by cooling the superheated steam through heat exchange.

9. 3. The method for separating and recovering carbon dioxide according to claim 1, wherein the saturated steam is water vapor prepared from water by heat exchange with the superheated steam.

10. A carbon dioxide separation and capture device that separates and captures carbon dioxide by heating a carbon dioxide absorbing solution obtained by absorbing carbon dioxide in a carbon dioxide-containing gas into a chemical absorption solution with a regenerative heat source, a carbon dioxide absorption tower that absorbs carbon dioxide from the carbon dioxide-containing gas with the chemical absorption solution; a chemical absorption solution regeneration tower that receives the regeneration heat source from an associated reboiler and separates carbon dioxide from the carbon dioxide absorbing solution; A steam compressor that increases the pressure and temperature of atmospheric pressure steam generated when water-cooling high-temperature objects in a factory to turn it into superheated steam; a steam adjusting means for converting the superheated steam into saturated steam of 150°C or less, The saturated steam having a temperature of 150°C or less is supplied to the reboiler as at least a part of the regenerative heat source.

11. The high-temperature object is molten blast furnace slag, 11. The carbon dioxide separation and capture apparatus according to claim 10, wherein the atmospheric pressure steam is atmospheric pressure steam generated when cooling water is sprayed onto the molten blast furnace slag to pulverize and rapidly cool it, thereby obtaining granulated blast furnace slag.

12. a heat pump for producing saturated steam from granulated slag water generated when obtaining the granulated blast furnace slag; 12. The carbon dioxide separation and capture apparatus according to claim 10 or 11, wherein saturated steam at 150°C or less produced by the heat pump is further supplied to the reboiler as part of the regenerative heat source.

13. The carbon dioxide separation and capture apparatus according to claim 10 or 11, wherein the carbon dioxide-containing gas is generated in a steelworks.

14. 14. The carbon dioxide separation and capture system according to claim 13, wherein the carbon dioxide-containing gas generated in the steelworks is blast furnace gas.

15. The carbon dioxide separation and capture system according to claim 10 or 11, further comprising a dust removal device for removing dust from the atmospheric pressure steam before the atmospheric pressure steam is introduced into the steam compressor.

16. 12. The carbon dioxide separation and capture apparatus according to claim 10, wherein the steam adjustment means is a water-reducing / water-injecting device that adjusts the superheated steam by injecting water into the superheated steam.

17. 12. The carbon dioxide separation and capture apparatus according to claim 10, wherein the steam adjustment means is a heat exchanger that adjusts the superheated steam by cooling it through heat exchange.

18. 12. The carbon dioxide separation and capture apparatus according to claim 10, wherein the steam adjusting means is a steam generator that adjusts the steam from water by heat exchange with the superheated steam.

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