A CO2 capture method in which CO2 is separated and captured by heating a CO2 absorption solution

Abstract

To provide a method for recovering CO2 at a reduced total cost by using slag granulating water, which is an extremely low-grade waste heat source, and by making it possible to heat a CO2 absorption liquid in a chemical absorption method.SOLUTION: Provided is a method for recovering CO2 in which a CO2 absorption liquid, in which CO2 in a CO2-containing gas is absorbed by chemical absorption method, is heated to separate and recover CO2. In the method, heat is recovered using a heat pump device from a slag granulating water arising when spraying a molten blast furnace slag with cooling water for crushing / quenching to obtain a blast furnace water granulated slag, and steam is generated to heat the CO2 absorption liquid, and the slag granulating water that has been temperature-lowered through the heat recovery using the heat pump device is circulated and used as at least a part of a cooling water for the molten blast furnace slag.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a CO2 recovery method for separating and recovering CO2 by heating a CO2 absorption liquid that has absorbed CO2 from a CO2-containing gas. More specifically, this invention relates to a CO2 recovery method in which heat is recovered from granulated slag water generated when granulated blast furnace slag is obtained from molten blast furnace slag using a heat pump device, and the granulated slag water, which has been cooled after the heat recovery, is recycled and reused as cooling water for the molten blast furnace slag. [Background technology]

[0002] As carbon dioxide (CO2) reduction is required, in addition to drastic measures such as CO2 emission control and development of energy-saving technologies, various technologies for separating and capturing emitted CO2 are being considered. In particular, measures to deal with CO2 released into the atmosphere in the steelmaking process are becoming increasingly important. In this specification, the separation and capture of CO2 may be referred to as "separation and capture" or "separation and capture."

[0003] For example, as described in Patent Document 1, technological development is underway to separate and capture CO2 emitted from steel mills using a chemical absorption method in which by-product gases generated in the steel mills are dissolved in an amine liquid to absorb them, and the amine liquid is then heated.

[0004] Among the by-product gases generated in steelworks, for example, blast furnace gas (BFG) has a carbon dioxide ratio of more than 20%. Therefore, according to the method described in Patent Document 1, it is possible to reduce CO2 emissions from steelworks, which are one of the large-scale sources of carbon dioxide.

[0005] The chemical absorption method uses a chemical absorption solution containing amines and the like, and brings CO2-containing gas containing carbon dioxide (CO2) into contact with the chemical absorption solution at room temperature in a carbon dioxide absorption facility called an absorption tower, allowing the CO2 to be absorbed by the chemical absorption solution. The CO2 absorbing solution that has absorbed the CO2 is then sent to a regeneration tower, which is an absorption solution regeneration facility, and heated to separate and recover the CO2 from the CO2 absorbing solution. The regenerated chemical absorption solution is returned to the absorption tower, allowing it to be recycled between the absorption tower and the regeneration tower.

[0006] Here, the aforementioned Patent Document 1 states that waste heat generated in steelworks can be used when separating and capturing CO2 using chemical absorption, and gives examples of usable waste heat such as 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 relatively low-temperature, low-grade waste heat (500°C or less), but higher-grade waste heat with temperatures exceeding 500°C is already being used for power generation, heating, etc., and high-grade waste heat has too much thermal energy for the CO2 separation and capture process using chemical absorption as described above. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-292298 Summary of the Invention [Problem to be solved by the invention]

[0008] Currently, in the CO2 capture and separation project under the Development of Environmentally Friendly Process Technologies / Development of Hydrogen Reduction and Other Process Technologies (COURSE50), targets for the amount of CO2 emitted from an integrated steelworks with a specified crude steel production capacity are being set as needed. For CO2 capture by chemical absorption, research and development has reduced the heating temperature required for CO2 capture, and saturated steam at 115°C can now be used. While the amount of thermal energy required has also been reduced, a large amount of heat energy is still required to separate and capture large amounts of CO2. While one possible method for providing this large amount of heat is to burn city gas, this not only incurs high fuel costs but also generates CO2 during combustion. Therefore, one solution to this problem is the need for more utilization of unused waste heat and a method for achieving this at low cost.

[0009] The aforementioned Patent Document 1 discloses, with several examples, the use of low-grade waste heat when separating and capturing CO2 by chemical absorption, but steam exceeding 100°C is required to heat the CO2 absorbing solution that has absorbed CO2 to separate and capture CO2. In other words, among the low-grade waste heat exemplified in the aforementioned Patent Document 1, the wastewater (approximately 90°C) used in the granulation of molten blast furnace slag, i.e., the granulated slag water generated when molten blast furnace slag is pulverized and rapidly cooled by spraying cooling water onto it to obtain granulated blast furnace slag, has been able to be used to preheat the chemical absorption solution, but has not been able to be used when heating the CO2 absorbing solution to capture CO2 (regenerating the amine solution).

[0010] Therefore, the inventors have conducted extensive research into means for utilizing the above-mentioned granulated slag water as the thermal energy required to heat the CO2 absorption liquid in the chemical absorption method. As a result, they have completed the present invention, which involves recovering heat from the granulated slag water using a heat pump device capable of generating steam, and using the granulated slag water after heat recovery as cooling water for molten blast furnace slag. This makes it possible to use the granulated slag water to recover CO2 (regenerate the amine liquid), and also makes it possible to recycle it when obtaining granulated blast furnace slag.

[0011] Therefore, the object of the present invention is to provide a method for recovering CO2 using a chemical absorption method that can recover CO2 from a CO2 absorption solution using granulated slag water, which is an extremely low-quality waste heat that does not reach 100°C, and that can be recycled to obtain granulated blast furnace slag, thereby reducing total costs. [Means for solving the problem]

[0012] That is, the gist of the present invention is as follows. (1) A CO2 recovery method for separating and recovering CO2 by heating a CO2 absorbing solution that has absorbed CO2 from a CO2-containing gas, A CO2 recovery method for separating and recovering CO2 by heating a CO2 absorbing liquid, characterized in that heat is recovered using a heat pump device from granulated slag water generated when molten blast furnace slag is sprayed with cooling water to pulverize and rapidly cool it to obtain granulated blast furnace slag, and the steam is used to heat the CO2 absorbing liquid, and the granulated slag water that has been cooled by heat recovery using the heat pump device is recycled and reused as at least a part of the cooling water for the molten blast furnace slag. (2) A CO2 recovery method according to (1), wherein the CO2-containing gas is a CO2-containing gas generated in a steelworks. (3) The CO2 recovery method according to (2), wherein the CO2-containing gas is blast furnace gas. [Effects of the Invention]

[0013] The CO2 capture method of the present invention can provide a portion of the thermal energy required to heat the CO2 absorption solution in the chemical absorption process using granulated slag water, which is an extremely low-quality waste heat. In particular, large amounts of heat are required for large-scale capture of CO2 emitted from steelworks, but this invention makes it possible to supply this heat inexpensively. Furthermore, the granulated slag water after heat recovery can be used as at least a portion of the cooling water for molten blast furnace slag, enabling recycling in the production of granulated blast furnace slag, which also leads to total cost reductions. In addition, because the granulated slag water is generated in the same place as the blast furnace gas (BFG), which is the primary target for CO2 capture in steelworks (both from blast furnaces), there is no need for large-scale transportation of the recovered heat, making this an extremely useful method that can be industrially implemented. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating a method according to a first embodiment of the present invention, which combines a slag granulation process for obtaining granulated blast furnace slag with a CO2 capture process for heating a CO2 absorbing liquid to separate and capture CO2, based on the heat balance and material balance of the granulated slag water. [Figure 2] FIG. 2 is a schematic diagram illustrating a method according to a second embodiment of the present invention in which a cooling tower and a heat pump device are installed in parallel. [Figure 3] FIG. 3 is a schematic diagram illustrating a method according to a third embodiment of the present invention in which a cooling tower and a heat pump device (in the case of a compression type heat pump device) are installed in series. [Figure 4] FIG. 4 is a schematic diagram illustrating a method according to a third embodiment of the present invention in which a cooling tower and a heat pump device (in the case of an absorption heat pump device) are installed in series. [Figure 5] FIG. 5 is a schematic diagram illustrating a method according to a fourth embodiment of the present invention in which a cooling tower and a heat pump device are installed in series and in parallel. [Figure 6]FIG. 6(a) is a schematic diagram showing a conventional CO2 separation and capture process using a chemical absorption method, and FIG. 6(b) is a schematic diagram showing a CO2 separation and capture process using a chemical absorption method according to the present invention. [Figure 7] FIG. 7 is a schematic diagram showing a conventional method (existing process) for obtaining granulated blast furnace slag, explained based on the heat balance and material balance of the granulated slag water. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below with reference to the drawings. In this invention, when CO2 absorbing liquid that has absorbed CO2 from CO2-containing gas by chemical absorption is heated to separate and recover CO2, the granulated slag water generated when molten blast furnace slag is pulverized and rapidly cooled by spraying cooling water onto it to obtain granulated blast furnace slag is used. That is, heat is recovered from this granulated slag water using a heat pump device to generate steam that is used to heat the CO2 absorbing liquid in the chemical absorption method, and the granulated slag water that has been cooled by heat recovery using the heat pump device is recycled and reused as at least a part of the cooling water for the molten blast furnace slag.

[0016] Steelworks have a wide variety of waste heat sources, but one of the major sources is the granulated slag water produced when granulated blast furnace slag is obtained. Blast furnace slag is generated when pig iron is produced in a blast furnace and is discharged in a molten state similar to lava. To use this molten blast furnace slag as a by-product, it must be rapidly cooled by spraying a large amount of water (cooling water) onto the molten blast furnace slag and granulated, which produces granulated slag water. The resulting granulated blast furnace slag is sandy and has a composition similar to cement. It exhibits latent hydraulic properties over time, and is therefore widely used, for example by being further pulverized and used as a cement raw material.

[0017] Figure 7 shows a schematic diagram of the existing process for obtaining granulated blast furnace slag, explained based on the heat and material balances of the granulated slag water. The figures are based on 100 t / h of granulated slag water. Note that an integrated steelworks with a crude steel production capacity of 8 million t / y uses more than 1,000 t / h of granulated slag water.

[0018] First, 95 t / h of 80°C granulated slag water (simply referred to as granulated water in the diagram, and the same applies below) is recovered from the slag granulation process, in which 60°C water (cooling water) is sprayed onto molten blast furnace slag to obtain granulated blast furnace slag. During this process, the water vapor evaporated by cooling the molten blast furnace slag is released outside the system at a rate of 5 t / h. Next, the 95 t / h of recovered 80°C granulated slag water is sent to a cooling tower, where it is cooled to 62°C. Then, fresh water is replenished at 25°C at 8 t / h to the 62°C granulated slag water cooled in the cooling tower, to make 100 t / h of 60°C granulated slag water, which is reused to cool the molten blast furnace slag.

[0019] Figure 7 also shows the water loss that occurs when the granulated slag water is cooled in the cooling tower. 95 t / h of 80°C granulated slag water recovered from the previous granulation process is cooled to 63°C in the cooling tower. At this time, 3 t / h is released outside the system as steam (part of the granulated slag water is evaporated and released outside the system to lower its own temperature), so 8 t / h of new make-up water at 25°C is added to make up 100 t / h of 60°C granulated slag water, which is then reused to cool the next batch of molten blast furnace slag.

[0020] Granulated slag water, recovered (discharged) when producing granulated blast furnace slag, is a waste heat unique to integrated steelworks. As mentioned above, its temperature is low, at around 80-90°C, but it contains a huge amount of heat. In addition, because it is generated in the same place as blast furnace gas (BFG), the primary target for CO2 capture in steelworks (both blast furnaces), there is no need for large-scale transportation of the recovered heat. This makes granulated slag water ideal for CO2 capture. However, because saturated steam at 115°C is required to heat the CO2 absorption liquid and separate and capture CO2, granulated slag water, which has a lower temperature than this, has not been used until now.

[0021] Therefore, in this invention, a heat pump device capable of generating steam from granulated slag water is used to heat the CO2 absorbing solution used in the chemical absorption process to separate and capture CO2. Specifically, referring to the existing process described above (Fig. 7), in a first embodiment of the invention, as shown in Fig. 1, a heat pump device capable of generating steam is used to cool the 80°C granulated slag water recovered from the granulated slag process to 62°C (heat recovery), and the recovered heat is used to produce 4 t / h of 115°C saturated steam. The resulting 115°C saturated steam is used to heat the CO2 absorbing solution in the chemical absorption CO2 capture process. Meanwhile, as in the existing process, the 62°C granulated slag water cooled by the heat pump device is replenished with 5 t / h of new 25°C make-up water to produce 100 t / h of 60°C granulated slag water, which is then reused to cool the next batch of molten blast furnace slag.

[0022] This allows the granulated slag water, which has a huge calorific value, to be used as the thermal energy needed to heat the CO2 absorption liquid. Furthermore, since the loss that previously occurred when the granulated slag water was cooled in a cooling tower and released outside the system as water vapor is eliminated, this leads to total cost reductions, including the granulated blast furnace slag manufacturing process, making CO2 capture at steelworks sustainable. Furthermore, because granulated slag water is generated in the same place as blast furnace gas, the primary target for CO2 capture, it is extremely suitable from the perspectives of heat transport efficiency and facility construction when separating and capturing CO2 from blast furnace gas.

[0023] In the example shown in Figure 1, a compression heat pump device is used as a heat pump device capable of generating steam. Compression heat pump devices transfer heat by utilizing the property that a refrigerant's temperature rises when compressed and drops when expanded. A suitable example is a waste hot water heat recovery steam generation heat pump manufactured by Fuji Electric Co., Ltd. (https: / / www.fujielectric.co.jp / products / heat_pump / ). This heat pump device recovers waste heat from waste hot water at a temperature of 60 to 80°C and an average flow rate of approximately 500 to 2000 kg / h, and uses that heat to generate saturated steam at 120°C. In this process, the water is heated in a two-phase gas-liquid state in the condenser, where the water is heated with a high-temperature refrigerant, with some of the water becoming steam. Furthermore, a thermosiphon system is employed, in which steam rises and water flows down, to circulate water from a gas-liquid separator to an evaporator (heat exchanger) to generate steam (Publication No. 2015 / 064347). Incidentally, if granulated slag water (80°C, 95 t / h) is supplied to this heat pump device and the temperature of the granulated slag water is lowered to 62°C, the amount of 115°C steam that can be produced is 4 t / h, which is equivalent to a CO2 recovery rate of 5 t / h.

[0024] The heat pump device in the present invention may be any device capable of producing steam from hot water (wastewater). In addition to the compression heat pump device described above, an absorption heat pump device or an adsorption heat pump device can also be used. Among these, an absorption heat pump device utilizes the heat of vaporization of water in a cycle consisting of evaporation, absorption, regeneration, and condensation. Generally, a heat pump device uses an evaporator that converts a refrigerant (water) into water vapor by removing heat from a heat source; an absorber that absorbs the water vapor into an absorbing liquid; a regenerator that heats the absorbing liquid to evaporate the water and concentrate the absorbing liquid; and a condenser that converts the water vapor generated in the regenerator back into water. These processes are repeated to generate steam using the heat generated in the absorber and condenser. A suitable example of such an absorption heat pump device is a Type 2 absorption heat pump manufactured by Hitachi Johnson Controls Air Conditioning Co., Ltd.

[0025] Adsorption heat pumps convert the adsorption and desorption of an adsorbent, such as activated carbon or silica gel, and a working medium, such as water vapor, into thermal energy. They generally consist of an adsorber, an evaporator, and a condenser, and the adsorber is filled with an adsorbent, which generates steam by utilizing the exothermic and endothermic reactions that occur when the adsorbent adsorbs and desorbs the refrigerant.

[0026] Since granulated slag water is directly injected onto molten blast furnace slag, it contains contaminants such as slag powder. To recover heat from such wastewater, it is desirable for the heat pump device to exchange heat with the wastewater indirectly via a heat exchanger, as in the compression heat pump device described above. For example, an adsorption heat pump device (Patent Publication No. 2015-64192), which directly injects wastewater hot water into an adsorbent, is not suitable (cannot be used) for the use of contaminated wastewater such as granulated slag water.

[0027] In the present invention, a cooling tower used in an existing process may be used in combination with a heat pump device capable of generating steam. That is, as a second embodiment of the present invention, for example, as shown in Fig. 2, a cooling tower and a heat pump device may be installed in parallel, and the scale of use of the heat pump device may be freely set according to the required amount of steam production (required amount of CO2 recovery). When a cooling tower and a heat pump device are used in combination, the slag granulation process and CO2 recovery process may be the same as those described in the first embodiment of the present invention and the existing process, and the same applies to the following third and fourth embodiments.

[0028] As a third embodiment of the present invention, a cooling tower and a heat pump unit may be installed in series, as shown in Figure 3. In this case, as with Figure 2, the scale of use of the heat pump unit can be freely set according to the required amount of steam production (required amount of CO2 recovery). In addition, by installing the cooling tower and the heat pump unit directly, it becomes possible to increase the coefficient of performance (COP) of the heat pump unit, and the amount of CO2 recovered per unit of electricity used can be increased.

[0029] FIG. 4 shows an example of a third embodiment of the present invention in which an absorption heat pump device is used instead of the compression heat pump shown in FIG.

[0030] Furthermore, as a fourth embodiment of the present invention, a bypass line may be provided to the heat pump device, and the cooling tower and the heat pump device may be installed in series and in parallel, as shown in Figure 5. This makes it possible to supply an appropriate amount of granulated slag water depending on the size of the heat pump device.

[0031] The present invention is a method for separating and capturing CO2 by heating a CO2-absorbing solution in a chemical absorption process using granulated slag water recovered during the production of granulated blast furnace slag. However, similar to the granulated slag water, other waste hot waters generated within steelworks and having a relatively large calorific value can also be used to heat the CO2-absorbing solution. Examples of such waste hot waters include ammonia water (ammonia water) generated during the separation of tar in the refining process of high-temperature coke oven gas (COG) and LDG cooling water generated during the water cooling of high-temperature LDG (LDG). These waste hot waters, like the granulated slag water, contain impurities and are generally hot waste waters at temperatures of approximately 60 to 90°C.

[0032] In the present invention, blast furnace gas has been used as a suitable example of a CO2-containing gas from which CO2 can be separated and recovered. However, like blast furnace gas, CO2 can also be separated and recovered from CO2-containing gases such as hot stove exhaust gas, coke oven exhaust gas, and various other heating furnace exhaust gases that are generated within steelworks and contain relatively large amounts of CO2, as well as exhaust gas from thermal power plants installed within steelworks.

[0033] In the present invention, the CO2 absorbing solution that has absorbed CO2 in the CO2-containing gas can be heated to separate and recover CO2 in the same manner as in known chemical absorption methods.

[0034] Specifically, in a CO2 separation and capture process using chemical absorption, an absorbent (lean absorbent (amine liquid)) such as an amine solution containing almost no CO2 is generally sprayed from the top of an absorption tower. The absorbent comes into contact with a CO2-containing gas, and absorbs CO2 from the CO2-containing gas. The resulting absorbent (rich absorbent (amine liquid)) is discharged from the bottom of the absorption tower. The rich absorbent is then sent to a regeneration tower, where it is sprayed from the top of the tower and heated by steam or the like in a reboiler installed at the bottom of the regeneration tower, releasing CO2. The released CO2 is captured, and the lean absorbent, with a reduced amount of absorbed CO2, is discharged from the bottom of the regeneration tower and used again for CO2 absorption. In other words, the present invention can be applied to the heating with steam in a reboiler installed at the bottom of the regeneration tower. As shown in Figure 6, a heat pump device is used instead of the conventional steam production process (Figure 6(a)) (Figure 6(b)).

[0035] Although the preferred embodiments of the present invention have been described above, the CO2 recovery method according to the present invention is not limited to these, and can include any combination of these to the extent possible.

[0036] According to the present invention, it is possible to provide a portion of the thermal energy required to heat the CO2 absorbing solution in the chemical absorption method using granulated slag water, which is an extremely low-quality waste heat. In particular, a large amount of heat is required to capture CO2 emitted from steelworks on a large scale, and this invention makes it possible to supply this heat inexpensively. Moreover, the granulated slag water after heat recovery can be used as at least a portion of the cooling water for molten blast furnace slag, making it possible to recycle it in obtaining granulated blast furnace slag. Furthermore, because granulated slag water is generated in the same place as blast furnace gas, which is the main target for capturing CO2 emitted from steelworks, it is extremely advantageous from the standpoints of heat transport and thermal efficiency.

Claims

【Request Item 1】 CO ２ CO in the gas ２ CO absorbed ２ The absorption liquid is heated to ２ CO is separated and recovered ２ A recovery method comprising: The granulated slag is obtained by spraying cooling water onto molten blast furnace slag to crush and rapidly cool it, and heat is recovered from the granulated slag water generated by the granulated slag water using a heat pump device to generate steam and to use the CO ２ The granulated slag water is used to heat the absorption liquid, and the heat is recovered by a heat pump device to reduce the temperature of the granulated slag water, and the granulated slag water is recycled and used as at least a part of the cooling water for the molten blast furnace slag. ２ The absorption liquid is heated to ２ CO is separated and recovered ２ Recovery method. 【Request Item 2】 The CO ２ The contained gas is CO generated in the steelworks. ２ 2. The CO gas according to claim 1 ２ Recovery method. 【Request Item 3】 The CO ２ 3. The CO2-containing gas according to claim 2, wherein the CO2-containing gas is blast furnace gas. ２ Recovery method.

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