Systems and methods for reducing fuel consumed in combustion facilities and recovering generated co2

Abstract

The present invention relates to a system for reducing fuel consumption and recovering CO2, comprising: a water electrolysis facility system for producing hydrogen and oxygen from water or steam; a combustion facility for combusting fuel by using the produced oxygen; and a CO2 recovery facility for recovering CO2 from an exhaust gas discharged from the combustion facility.

Description

System and method for reducing fuel consumption in combustion facilities and recovering generated CO2

[0001] The present invention relates to a method for reducing fuel consumed in a combustion facility and recovering CO2 generated, and more specifically, to a method for reducing fuel consumed in a combustion facility and recovering CO2 generated by using oxygen obtained through electrolysis.

[0002] Technologies for producing hydrogen at low cost are being proposed to achieve carbon neutrality, and among them, technologies for producing hydrogen through water electrolysis using electricity generated by solar energy and other sources are gaining significant attention.

[0003] Water electrolysis methods can be broadly categorized into high-temperature and low-temperature methods. Low-temperature electrolysis involves placing water in an electrolyte solution and electrolyzing it to separate hydrogen and oxygen. High-temperature electrolysis involves placing high-temperature steam in a solid oxide electrolysis cell (SOEC) to electrolyze it into hydrogen and oxygen.

[0004] Meanwhile, conventional technologies focus on producing hydrogen through electrolysis, without paying much attention to the use of oxygen produced in the process. Therefore, there is a need to develop technologies that utilize oxygen produced through electrolysis.

[0005] One aspect of the invention is to provide a method for reducing fuel consumption in a combustion facility and recovering CO2 generated by using oxygen obtained from electrolysis.

[0006] Another aspect of the present invention is to provide a facility system that reduces fuel consumption and recovers CO2 produced by using oxygen obtained from electrolysis.

[0007] According to one embodiment of the present invention, a fuel saving and CO2 recovery system is provided, which includes a water electrolysis facility that produces hydrogen and oxygen from water or steam; a combustion facility that burns fuel using the oxygen produced; and a CO2 recovery facility that recovers CO2 from exhaust gas discharged from the combustion facility.

[0008] According to another embodiment of the present invention, a method for reducing fuel consumed in a combustion facility and recovering CO2 generated is provided, the method comprising: a water electrolysis step of producing hydrogen and oxygen from water or steam; a combustion step of combusting fuel using the oxygen produced; and a CO2 recovery step of recovering CO2 from exhaust gas discharged after the combustion step.

[0009] According to the present invention, oxygen, a byproduct of electrolysis equipment, can be used as an oxidizer to increase the thermal efficiency of the equipment. Furthermore, since the recovered oxygen and CO2 are used for combustion, the CO2 concentration in the combustion exhaust gas can be increased compared to when cooling with air, resulting in higher concentrations of high-purity CO2.

[0010] Figures 1 to 3 are schematic diagrams illustrating a fuel consumption reduction and CO2 recovery system according to one embodiment of the present invention.

[0011] Figures 1 to 3 are schematic diagrams illustrating a fuel consumption reduction and CO2 recovery system according to one embodiment of the present invention.

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 1 to 3. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0013] According to one embodiment of the present invention, a fuel saving and CO2 recovery system (10) may be provided, which includes a water electrolysis facility (100) that produces hydrogen and oxygen from water or steam; a combustion facility (200) that burns fuel using the oxygen produced; and a CO2 recovery facility (300) that recovers CO2 from the exhaust gas from which H2O has been removed.

[0014] The above-mentioned electrolysis facility (100) may be a facility that produces hydrogen and oxygen by electrolyzing water using electricity generated from solar energy, etc.

[0015] The above-mentioned water electrolysis facility (100) may be a low-temperature water electrolysis facility that electrolyzes water containing electrolyte to produce hydrogen and oxygen, or a high-temperature water electrolysis facility that electrolyzes steam at 700 to 800°C by putting it into a water electrolysis cell called SOEC (solid oxide electrolysis cell) to produce hydrogen and oxygen.

[0016] Meanwhile, since the purity of hydrogen or oxygen may be somewhat low in low-temperature electrolysis, the electrolysis equipment (100) may preferably be a high-temperature electrolysis equipment.

[0017] The above electrolysis facility (100) electrolyzes water or steam (H2O), and thus can produce high-purity oxygen, i.e., pure oxygen. For example, the oxygen produced by the above electrolysis facility (100) may have a purity of 90% or more, 95% or more, 99% or more, or 100% on a molar % basis.

[0018] The oxygen produced in the above electrolysis facility (100) can be fed into the combustion facility (200) and used to burn fuel.

[0019] It is known that fuel savings of up to 50% are possible when pure oxygen is used as an oxidizer.

[0020] Therefore, the fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention can increase energy efficiency by using oxygen obtained from the electrolysis facility (100) as an oxidizing agent.

[0021] The above combustion equipment (200) may be a combustion furnace or a boiler. More specifically, the combustion furnace may be equipment selected from the group consisting of a drying furnace for drying and removing moisture from raw materials such as coal, an incinerator for incinerating waste, a heating furnace for heating steel slabs, and a forging furnace for heating materials for forging, but is not limited thereto.

[0022] Fuel can be injected into the above combustion equipment (200) together with oxygen for combustion. The fuel used in the above combustion equipment (200) is not particularly limited, and any conventionally known fuel can be used without limitation. For example, natural gas, hydrogen, etc. can be used as the fuel.

[0023] The oxygen supplied to the above combustion equipment (200) may be oxygen produced from the above water electrolysis equipment (100).

[0024] The above combustion equipment (200) can discharge exhaust gas generated after combustion. The exhaust gas may be a gas containing CO2.

[0025] More specifically, exhaust gas discharged from a conventional combustion facility (200) that burns fuel by injecting air as an oxidizer may contain CO2, H2O, O2, and a small amount of unburned gas and NOx (nitrogen oxides).

[0026] Meanwhile, the fuel saving and CO2 recovery system (10) according to one embodiment of the present invention uses oxygen obtained from the electrolysis facility (100) as an oxidizing agent, thereby reducing the NOx content contained in the exhaust gas. Accordingly, the exhaust gas discharged from the combustion facility (200) may contain a high content of CO2, H2O, and some O2 that did not participate in the oxidation reaction.

[0027] A fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention may include a CO2 recovery facility (300) that recovers CO2 from the exhaust gas.

[0028] The above CO2 recovery facility (300) can be used without limitation as long as it is a facility capable of separating CO2 from exhaust gas containing CO2. For example, the above CO2 recovery facility (300) may be a facility selected from the group consisting of a PSA facility, a deep-freezing facility that obtains liquid CO2 by lowering the temperature below the CO2 liquefaction temperature, and a compression facility that liquefies CO2 by applying high pressure.

[0029] The above CO2 recovery facility (300) can recover 80% or more, 90% or more, 95% or more, 99% or more, or 100% of CO2 from exhaust gas based on mole %.

[0030] The fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention may further include a condenser (400).

[0031] The above condenser (400) may be configured to cool the exhaust gas discharged from the combustion equipment (200) and thereby condense and separate H2O contained in the exhaust gas.

[0032] The above condenser (400) can cool the exhaust gas discharged from the combustion equipment (200) to -20 to 100°C, more specifically, to 0 to 50°C. If the temperature of the cooled exhaust gas is below -20°C, excessive energy may be consumed for cooling, which may be uneconomical, and if it exceeds 100°C, H2O in a vapor state may not be sufficiently condensed and removed.

[0033] That is, since the H2O in the vapor state contained in the exhaust gas is condensed and removed, the exhaust gas passing through the condenser (400) may contain a higher content of CO2.

[0034] Meanwhile, the condenser (400) can cool the exhaust gas discharged from the combustion equipment (200) by removing the residual heat through heat exchange with the cooling water.

[0035] In addition, the cooling water, i.e., water, that is heated while the condenser (400) cools the exhaust gas through heat exchange can be supplied to the water electrolysis facility (100) in the form of heated water or steam to produce oxygen.

[0036] If the above electrolysis facility (100) is a high-temperature electrolysis facility, steam can be supplied using the residual heat of the exhaust gas recovered from the condenser (400), so the energy required to heat water with electricity to create steam can be saved, thereby increasing thermal efficiency.

[0037] Referring to FIG. 2, the fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention may further include an exhaust gas recirculation path (500).

[0038] The above exhaust gas recirculation path (500) can separate at least a portion of the exhaust gas as recirculated exhaust gas, and supply the recirculated exhaust gas to the combustion equipment (200) by mixing it with oxygen produced in the electrolysis equipment (100).

[0039] The above recirculated exhaust gas may be a gas containing 80% or more, 90% or more, 95% or more, 99% or more or 100% CO2 by mole %.

[0040] Accordingly, the exhaust gas recirculation path (500) can lower the concentration of oxygen fed into the combustion equipment (200) by mixing the recirculated exhaust gas with the oxygen produced in the electrolysis step. Accordingly, the flame temperature within the combustion equipment (200), which has become excessively high, can be lowered, thereby preventing deterioration of the combustion equipment (200) and reducing the amount of NOx generated.

[0041] The fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention may further include a flow rate control valve that controls the flow rate of the recirculated exhaust gas flowing through the exhaust gas recirculation path (500).

[0042] The fuel saving and CO2 recovery system (10) according to one embodiment of the present invention can achieve a fuel saving effect by controlling the flow rate of recirculated exhaust gas through the flow rate control valve, while at the same time preventing deterioration of the combustion equipment (200) and reducing NOx generation.

[0043] In addition, the fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention may further include a temperature measuring device that measures the temperature of the exhaust gas discharged from the combustion facility (200), i.e., the outlet temperature of the combustion facility.

[0044] A fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention can measure the outlet temperature of a combustion facility (200) and control the flow rate of exhaust gas flowing through an exhaust gas recirculation path (500) according to the measured outlet temperature of the combustion facility (200).

[0045] Referring to FIG. 3, the fuel consumption reduction and CO2 recovery system (10) according to one embodiment of the present invention may further include a recirculating exhaust gas preheater (600) for preheating the recirculating exhaust gas.

[0046] The above-mentioned recirculating flue gas preheater (600) may be a heat exchanger that preheats the recirculating flue gas by heat-exchanging the flue gas discharged from the combustion equipment (200) and the recirculating flue gas flowing through the flue gas recirculation path (500).

[0047] Through heat exchange in the recirculating exhaust gas preheater (600), the recirculating exhaust gas can be heated to 300 to 700°C, and the exhaust gas discharged from the combustion equipment (200) can be cooled to 200 to 600°C.

[0048] That is, the recirculating flue gas preheater (600) reduces the cooling burden of the condenser (400) by primarily cooling the flue gas discharged from the combustion equipment (200), and at the same time, by recycling the sensible heat to increase the temperature of the recirculating flue gas supplied to the combustion equipment (200), thereby improving the thermal efficiency of the entire process.

[0049] According to another embodiment of the present invention, a method for reducing fuel consumed in a combustion facility and recovering CO2 generated is provided, the method comprising: a water electrolysis step of producing hydrogen and oxygen from water or steam; a combustion step of combusting fuel using the oxygen produced; and a CO2 recovery step of recovering CO2 from exhaust gas discharged after the combustion step.

[0050] The above water electrolysis step can be performed by a low-temperature water electrolysis method in which water containing an electrolyte is electrolyzed to produce hydrogen and oxygen, or a high-temperature water electrolysis method in which steam at 700 to 800°C is put into a water electrolysis cell called SOEC (solid oxide electrolysis cell) and electrolyzed to produce hydrogen and oxygen.

[0051] The above electrolysis step can produce high-purity oxygen, i.e., pure oxygen. For example, the oxygen produced in the electrolysis step can have a purity of 90% or more, 95% or more, 99% or more, or 100% on a molar % basis.

[0052] The oxygen produced in the above electrolysis step can be input into the combustion step and used to combust fuel.

[0053] The above combustion step may be a step in which fuel is injected together with oxygen and combusted. The fuel used in the combustion step is not particularly limited, and any conventionally known fuel may be used without limitation. For example, natural gas, hydrogen, etc. may be used as the fuel.

[0054] The oxygen injected into the above combustion step may be oxygen produced in the above water electrolysis step.

[0055] The above combustion step can discharge exhaust gas generated after combustion, and the exhaust gas can be a gas containing CO2.

[0056] A method according to one embodiment of the present invention may include a CO2 recovery step of recovering CO2 from the exhaust gas.

[0057] As for the CO2 recovery method used in the above CO2 recovery step, any method capable of separating CO2 from exhaust gas containing CO2 can be used without limitation.

[0058] The above CO2 recovery step can recover 80% or more, 90% or more, 95% or more, 99% or more, or 100% of CO2 from the exhaust gas based on mole %.

[0059] The method according to one embodiment of the present invention may further include a dehydration step for separating H2O contained in the exhaust gas discharged after the combustion step.

[0060] The above dehydration step may be a step of condensing and separating H2O contained in the exhaust gas by cooling the exhaust gas discharged after the combustion step.

[0061] In the above dehydration step, the exhaust gas discharged after the combustion step can be cooled to -20 to 100°C, more specifically, to 0 to 50°C. If the temperature of the cooled exhaust gas is below -20°C, excessive energy may be consumed for cooling, which may be uneconomical, and if it exceeds 100°C, H2O in a vapor state may not be sufficiently condensed and removed.

[0062] The exhaust gas that has gone through the above dehydration step can contain a higher content of CO2 because the H2O in the vapor state contained in the exhaust gas is condensed and removed.

[0063] In the above dehydration step, the residual heat of the exhaust gas can be removed and cooled through heat exchange with the cooling water.

[0064] The cooling water, i.e., water, which is heated while cooling the exhaust gas in the above dehydration step can be supplied to the water electrolysis step in the form of heated water or steam and used to produce oxygen.

[0065] When the above electrolysis step is performed using a high-temperature electrolysis facility, steam can be supplied using the residual heat of the exhaust gas, thereby saving the energy required to heat water with electricity to create steam, thereby increasing thermal efficiency.

[0066] The method according to one embodiment of the present invention may further include an exhaust gas recirculation step.

[0067] The above exhaust gas recirculation step may be a step of separating at least a portion of the exhaust gas as recirculated exhaust gas, mixing the recirculated exhaust gas with oxygen produced in the water electrolysis step, and supplying the mixture to a combustion facility.

[0068] The above recirculated exhaust gas may be a gas containing 80% or more, 90% or more, 95% or more, 99% or more or 100% CO2 by mole %.

[0069] Accordingly, the exhaust gas recirculation step can lower the concentration of oxygen fed into the combustion equipment (200) by mixing the recycled exhaust gas with the oxygen produced in the water electrolysis step. Accordingly, the flame temperature within the combustion equipment (200), which has become excessively high, can be lowered, thereby preventing deterioration of the combustion equipment (200) and reducing the amount of NOx generated.

[0070] In the above exhaust gas recirculation step, the flow rate of the recirculated exhaust gas can be controlled.

[0071] For example, the above exhaust gas recirculation step:

[0072] (i) a step of measuring the outlet temperature of the combustion equipment; and

[0073] (ii) It may include a step of controlling the flow rate of recirculated exhaust gas mixed with oxygen through the exhaust gas recirculation path when the outlet temperature of the combustion facility is outside a predetermined temperature range.

[0074] More specifically, step (ii) above:

[0075] (ii-a) a step of reducing the flow rate of recirculated exhaust gas mixed with oxygen through the exhaust gas recirculation path when the outlet temperature of the combustion facility exceeds the upper threshold value; and

[0076] (ii-b) may include a step of increasing the flow rate of recirculated exhaust gas mixed with oxygen through the exhaust gas recirculation path when the outlet temperature of the combustion facility is below the lower threshold value.

[0077] The upper limit threshold value of the outlet temperature of the above combustion equipment may be a pre-selected value in the range of 800 to 1200°C.

[0078] The lower limit threshold value of the outlet temperature of the above combustion equipment may be a pre-selected value in the range of 300 to 700°C.

[0079] The flow rate of the exhaust gas that is increased or decreased above can be adjusted within a range of 0% to 10% based on the flow rate before adjusting the flow rate of the exhaust gas, but is not limited thereto.

[0080] The method according to one embodiment of the present invention may further include a step of preheating the recirculated exhaust gas.

[0081] The above-mentioned recirculated exhaust gas preheating step may be a heat exchange step that preheats the recirculated exhaust gas by heat-exchanging the exhaust gas discharged from the combustion equipment (200) and the recirculated exhaust gas flowing through the exhaust gas recirculation path (500).

[0082] Through the heat exchange performed in the above recirculated exhaust gas preheating step, the recirculated exhaust gas can be heated to 300 to 700°C, and the exhaust gas discharged from the combustion equipment (200) can be cooled to 200 to 600°C.

[0083] [Explanation of symbols]

[0084] 10: Fuel consumption reduction and CO2 recovery system

[0085] 100: Water electrolysis equipment

[0086] 200: Combustion equipment

[0087] 300: CO2 recovery facility

[0088] 400: Condenser

[0089] 500: Exhaust gas recirculation path

[0090] 600: Recirculating flue gas preheater

Claims

1. Water electrolysis equipment that produces hydrogen and oxygen from water or steam; A combustion facility that burns fuel using the oxygen produced above; and A fuel saving and CO2 recovery system including a CO2 recovery facility that recovers CO2 from exhaust gas emitted from the above combustion facility.

2. A fuel saving and CO2 recovery system further comprising a condenser for condensing and separating H2O contained in exhaust gas discharged from the combustion facility in the first paragraph.

3. In paragraph 1, an exhaust gas recirculation path is further included, The above exhaust gas recirculation path is a fuel saving and CO2 recovery system that separates at least a portion of the exhaust gas as recirculated exhaust gas, mixes the recirculated exhaust gas with oxygen produced in the water electrolysis facility, and supplies it to a combustion facility.

4. A fuel saving and CO2 recovery system further comprising a flow rate control valve for controlling the flow rate of recirculated exhaust gas flowing through the exhaust gas recirculation path in the third paragraph.

5. In the third paragraph, a recirculating exhaust gas preheater is further included, The above-mentioned recirculating flue gas preheater is a fuel saving and CO2 recovery system that heat-exchanges the flue gas discharged from the combustion facility and the recirculated flue gas flowing through the flue gas recirculation path.

6. A method for reducing fuel consumption in combustion equipment and recovering CO2 generated. A water electrolysis step for producing hydrogen and oxygen from water or steam; A combustion step for burning fuel using the oxygen produced above; and A method comprising a CO2 recovery step for recovering CO2 from exhaust gas discharged after the combustion step.

7. A method according to claim 6, further comprising a dehydration step for separating H2O contained in exhaust gas discharged after the combustion step.

8. In paragraph 6, an exhaust gas recirculation step is further included, A method wherein the above exhaust gas recirculation step is a step of separating at least a portion of the exhaust gas, mixing the separated at least a portion of the exhaust gas with oxygen produced in the water electrolysis step, and supplying the mixture to a combustion facility.

9. In paragraph 8, the exhaust gas recirculation step: (i) a step of measuring the outlet temperature of the combustion equipment; and (ii) a step for controlling the flow rate of exhaust gas mixed with oxygen through the exhaust gas recirculation path when the measured outlet temperature of the combustion facility is outside a predetermined temperature range; Step (ii) above: (ii-a) a step of reducing the flow rate of exhaust gas mixed with oxygen through the exhaust gas recirculation path when the outlet temperature of the combustion facility exceeds the upper threshold value; and (ii-b) A method comprising the step of increasing the flow rate of flue gas mixed with oxygen through the flue gas recirculation path when the outlet temperature of the combustion facility is below the lower threshold value.

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