Solid oxide water electrolysis system

Abstract

A solid oxide water electrolysis system is disclosed. The disclosed system comprises: a stack including a fuel electrode, an electrolyte, and an air electrode; a fuel electrode recuperator configured to exchange heat between a product discharged from the fuel electrode and water vapor supplied to the fuel electrode; a recycle blower configured to recirculate a portion of the product discharged from the fuel electrode recuperator to the fuel electrode recuperator; a product cooler configured to cool the remainder of the product discharged from the fuel electrode recuperator; a separator configured to separate the product discharged at least from the product cooler into hydrogen and water; an air blower configured to supply outside air to the air electrode; and an air electrode recuperator configured to exchange heat between exhaust discharged from the air electrode and the outside air supplied to the air electrode.

Description

Solid oxide water electrolysis system

[0001] A solid oxide electrolysis system is disclosed. More specifically, a solid oxide electrolysis system with improved energy efficiency through reduced parasitic load is disclosed.

[0002] Existing high-temperature water electrolysis systems have the problem that waste heat recovery from the product is limited and a lot of energy is required for cooling to separate water and hydrogen.

[0003] Additionally, cooling through the air cooler, energy consumption due to the water and hydrogen separation process, and waste heat generation due to high-temperature exhaust air (since the waste heat of the exhaust air is recovered through the already heated feed water as it passes through the product / water exchanger, the exhaust air discharged to the outside of the system inevitably becomes high temperature) all reduce energy efficiency.

[0004] Additionally, irreversible energy loss occurs during the process of cooling the product and then recirculating and reheating it.

[0005] Additionally, the separation of the separator and the buffer vessel incurs additional CAPEX (Capital Expenditures), and additional costs are incurred due to the structural limitation that the separator must be positioned on top of the buffer vessel for fluid flow from the separator to the buffer vessel.

[0006] In addition, in the case of the existing solid oxide electrolysis system, the parasitic load reaches approximately 18.5% based on computer simulation, and when the actual heat loss in the high temperature section is taken into account, an even higher parasitic load occurs.

[0007] One embodiment of the present invention provides a solid oxide electrolysis system with improved energy efficiency through reduction of parasitic load.

[0008] One aspect of the present invention is:

[0009] A stack comprising a fuel electrode, an electrolyte and an air electrode;

[0010] A fuel electrode recuperator configured to heat-exchange products discharged from the fuel electrode and steam supplied to the fuel electrode;

[0011] A recycle blower configured to recirculate a portion of the products discharged from the fuel electrode recuperator to the fuel electrode recuperator;

[0012] A product cooler configured to cool the remainder of the product discharged from the above fuel electrode recuperator;

[0013] A separator configured to separate at least the product discharged from the product cooler into hydrogen and water;

[0014] An air blower configured to supply outside air to the air electrode; and

[0015] A solid oxide electrolysis system is provided, which includes an air electrode recuperator configured to heat-exchange exhaust gas discharged from the air electrode and outside air supplied to the air electrode.

[0016] The above solid oxide electrolysis system can be configured to directly mix the feed water, which is a source of water vapor supplied to the fuel electrode, with the product discharged from the product cooler and supply it to the separator.

[0017] The above solid oxide electrolysis system may further include a preheater configured to heat-exchange water discharged from the separator and exhaust discharged from the air electrode recuperator.

[0018] The above solid oxide electrolysis system further includes an expander that shares a rotational axis with the air blower, and the expander can be configured to obtain rotational force from the rotational axis by expanding exhaust gas discharged from the preheater to supplement the rotational force of the air blower.

[0019] The above solid oxide electrolysis system may further include a first evaporator configured to secondarily heat water primarily heated in the preheater.

[0020] The above first evaporator may be configured to heat exchange water primarily heated in the preheater and a refrigerant carrying heat recovered in the product cooler.

[0021] The above product cooler may be configured to heat-exchange the remaining portion of the product discharged from the fuel electrode recuperator with the refrigerant.

[0022] The above solid oxide electrolysis system may further include a compressor configured to compress the refrigerant discharged from the product cooler and supply it to the first evaporator.

[0023] The above solid oxide electrolysis system may further include an expansion valve or a second additional expander configured to expand the refrigerant discharged from the first evaporator and supply it to the product cooler.

[0024] The above solid oxide electrolysis system may further include a second evaporator configured to further evaporate water secondarily heated in the first evaporator and supply the evaporated water to the fuel electrode recuperator.

[0025] The above solid oxide electrolysis system may further include a fuel electrode heater configured to heat water vapor discharged from the fuel electrode recuperator and supply the heated water vapor to the fuel electrode.

[0026] The above solid oxide electrolysis system may further include an air electrode heater configured to heat the outside air discharged from the air electrode recuperator and supply it to the air electrode.

[0027] A solid oxide electrolysis system according to one embodiment of the present invention can improve both OPEX (Operational Expenditures) and CAPEX (Capital Expenditures) by improving energy efficiency through reduction of parasitic load.

[0028] FIG. 1 is a schematic diagram of a solid oxide electrolysis system according to one embodiment of the present invention.

[0029] Hereinafter, a solid oxide electrolysis system according to one embodiment of the present invention will be described in detail with reference to the drawings.

[0030] In this specification, “outside air” means all air present at the front of the stack (i.e., the air blower side end), and “exhaust air” means all air present at the back of the stack (i.e., the expander side end).

[0031] Also, in this specification, "product" means hydrogen, steam, water or a combination thereof.

[0032] FIG. 1 is a schematic diagram illustrating a solid oxide electrolysis system (SOEC) according to one embodiment of the present invention.

[0033] Referring to FIG. 1, a solid oxide electrolysis system (SOEC) according to one embodiment of the present invention includes a stack (ST), a fuel electrode recuperator (FR), a recycle blower (RB), a product cooler (PC), a separator (SP), an air blower (AB), and an air electrode recuperator (AR).

[0034] A stack (ST) may include a fuel electrode (FE), an electrolyte (EL), and an air electrode (AE).

[0035] At the fuel electrode (FE), the reaction of the following reaction formula 1 occurs, and at the air electrode (AE), the reaction of the following reaction formula 2 occurs, and the overall reaction can be expressed as in the following reaction formula 3.

[0036] [Reaction Formula 1]

[0037] H2O + 2e - → H2+ O 2-

[0038] [Reaction Formula 2]

[0039] 2O 2- → O2+ 4e -

[0040] [Reaction Formula 3]

[0041] 2H2O → 2H2+ O2

[0042] Additionally, the fuel electrode (FE) may include Ni-doped yttrium-stabilized zirconia (YSZ), perovskite lanthanum strontium manganese (LSM), lanthanum strontium manganese chromate (LSCM), scandium-doped LCSM, or a combination thereof.

[0043] The electrolyte (EL) may include 8 mol% Y2O3 doped ZrO2 (YSZ), scandia stabilized zirconia (ScSZ), a ceria-based electrolyte, a lanthanum gallate material, or a combination thereof.

[0044] The air electrode (AE) may include a material obtained by impregnating LSM, Gd-doped CeO2 (GDC) nanoparticles into LSM, or a combination thereof.

[0045] Additionally, the stack (ST) can be operated at high temperatures of 600 to 850°C.

[0046] The fuel electrode recuperator (FR) may be configured to heat-exchange the product discharged from the fuel electrode (FE) with the steam supplied to the fuel electrode (FE). Specifically, the fuel electrode recuperator (FR) may be configured to heat-exchange the product discharged from the fuel electrode (FE) with the steam supplied to the fuel electrode (FE), thereby cooling the product and heating the steam. At this time, the waste heat in the product may be transferred to the steam and recovered (primary recovery of product waste heat).

[0047] In addition, the fuel electrode recuperator (FR), stack (ST) and air electrode recuperator (AR) described below are devices that constitute a high-temperature section that operates at 300°C or higher, and can be packaged with a high-temperature insulating material (not shown) to minimize heat loss.

[0048] Additionally, the fuel electrode recuperator (FR) can be configured to transfer as much waste heat from the product as possible to the feed water (FW) to minimize the temperature of hydrogen (H2) discharged to the outside of the solid oxide electrolysis system (SOEC) and to minimize heat loss in the piping.

[0049] The feed water (FW) may be demineralized water.

[0050] Additionally, the fuel electrode recuperator (FR), stack (ST), and air electrode recuperator (AR) described below can be configured to minimize volume and weight and maximize high-temperature durability.

[0051] A recycle blower (RB) may be configured to recirculate a portion (the first portion) of the product discharged from the anode recuperator (FR) to the anode recuperator (FR). At this time, waste heat in the product (i.e., the first portion) may be transferred to the anode recuperator (FR) and recovered (secondary recovery of product waste heat). The recycle blower (RB) may be configured to withstand a high temperature of 200°C or higher based on the discharge temperature, and accordingly, due to the product (i.e., the first portion) recycled to the anode recuperator (FR), the fluid heat capacity of the anode recuperator (FR) and the stack (ST), which constitute the high temperature section, increases, thereby increasing temperature homeostasis, which may help extend the life of the stack (ST).

[0052] The product cooler (PC) may be configured to cool the residue (second portion) of the product discharged from the fuel electrode recuperator (FR). Specifically, the product cooler (PC) may be configured to heat-exchange the residue (second portion) of the product discharged from the fuel electrode recuperator (FR) with a refrigerant, which will be described later. More specifically, the product cooler (PC) may be configured to heat-exchange the residue (second portion) of the product discharged from the fuel electrode recuperator (FR) with a refrigerant, which will be described later, to cool the residue (second portion) of the product and heat the refrigerant. At this time, the waste heat of the residue of the product may be transferred to the refrigerant and recovered (3-1 recovery of product waste heat).

[0053] The separator (SP) can be configured to separate at least the product discharged from the product cooler (PC) into hydrogen and water. Conventional solid oxide electrolysis systems include a buffer vessel arranged at the rear end of the separator, and since the flow of water from the separator to the buffer vessel is based on the action of gravity, the separator had to be installed on top of the buffer vessel, which resulted in additional costs such as the installation of a two-stage structure. However, in the solid oxide electrolysis system (100) according to one embodiment of the present invention, the lower end of the separator (SP) can function as a buffer vessel, so the buffer vessel can be omitted, thereby reducing installation costs.

[0054] The air blower (AB) can be configured to supply outside air (AA) to the air electrode (AE) of the stack (ST).

[0055] An air electrode recuperator (AR) may be configured to heat-exchange exhaust air (EA) discharged from an air electrode (AE) of a stack (ST) and outside air (AA) supplied to the air electrode (AE). Specifically, the air electrode recuperator (AR) may be configured to heat-exchange exhaust air (EA) discharged from an air electrode (AE) of a stack (ST) and outside air (AA) supplied to the air electrode (AE) to cool the exhaust air (EA) and heat the outside air (AA) (primary recovery of exhaust air (EA) waste heat).

[0056] Additionally, the air electrode recuperator (AR) can be configured to transfer as much waste heat as possible in the exhaust (EA) to the outside air (AA) to minimize the temperature of the exhaust (EA) discharged to the outside of the solid oxide electrolysis system (SOEC), and also to minimize heat loss in the piping.

[0057] In addition, the solid oxide electrolysis system (SOEC) can be configured to directly mix the feed water (FW), which is the source of water vapor supplied to the fuel electrode (FE) of the stack (ST), with the product discharged from the product cooler (PC) and supply it to the separator (SP). At this time, the waste heat in the product discharged from the product cooler (PC) is transferred to the feed water (FW), so that the feed water (FW) is heated and the product can be cooled (quaternary recovery of the product waste heat). Under the conditions of the cooling unit for separating water from the product, heat exchange occurs in the phase equilibrium temperature range (around 60°C). Therefore, when recovering waste heat through a general heat exchanger, the maximum temperature rise of the feed water (FW) is limited to around 50℃ due to the heat exchange approach limit (exceeding 10℃) and the phase change of the product (the amount of water vapor condensation of the product increases, but the temperature of the feed water (FW) does not rise as the temperature is maintained), and considering this, there is a limit to using the entire cooling capacity of the feed water (FW). In order to solve the above-mentioned problem, the solid oxide electrolysis system (SOEC) was configured to maximize the cooling efficiency by directly introducing and mixing the feed water (FW), which is both a cooling source and fuel, into the product, taking into account that the product is composed only of water vapor and hydrogen and that the gas-liquid separation is performed under saturated conditions in the separator (SP) located at the rear end of the product cooler (PC).

[0058] Additionally, the solid oxide electrolysis system (SOEC) may further include a preheater (PH).

[0059] The preheater (PH) may be configured to heat-exchange water discharged from the separator (SP) and exhaust (EA) discharged from the air cathode recuperator (AR). Specifically, the preheater (PH) may be configured to heat-exchange water discharged from the separator (SP) and exhaust (EA) discharged from the air cathode recuperator (AR), thereby heating the water discharged from the separator (SP) and cooling the exhaust (EA) discharged from the air cathode recuperator (AR). At this time, waste heat in the exhaust (EA) discharged from the air cathode recuperator (AR) may be transferred to the water discharged from the separator (SP) and recovered (secondary recovery of exhaust (EA) waste heat).

[0060] Additionally, the solid oxide electrolysis system (SOEC) may further include an expander (EP).

[0061] The expander (EP) can share a rotational axis with the air blower (AB). That is, the rotational axis of the expander (EP) and the rotational axis of the air blower (AB) are formed integrally, so that when the rotational axis of the expander (EP) rotates, the rotational axis of the air blower (AB) rotates. Therefore, when the rotational axis of the expander (EP) rotates, the power required to rotate the rotational axis of the air blower (AB) can be reduced. That is, the expander (EP) can be configured so that the rotational axis obtains rotational power by expanding the exhaust (EA) discharged from the preheater (PH), thereby supplementing the rotational power of the air blower (AB). In this way, the expander (EP) can recover the remaining waste heat and increase the power efficiency of the solid oxide electrolysis system (SOEC) (tertiary recovery of exhaust (EA) waste heat). Due to the nature of the solid oxide electrolysis system (SOEC), in order to maintain the oxygen partial pressure on the cathode (AE) side, the outside air (AA) introduced into the stack (ST) and the oxygen produced in the stack (ST) are combined to produce a large amount of exhaust air (EA) that is discharged to the outside of the SOEC (the discharged outside air flow rate increases by more than 100% compared to the initial inflow outside air flow rate). Therefore, waste heat recovery is impossible with the cathode recuperator (AR) alone, so the exhaust air (EA) at the rear end of the cathode recuperator (AR) must be utilized to heat the feedwater (FW). However, the cooling capacity of the feedwater (FW), whose temperature has already risen due to the direct cooling of the product (i.e., the fourth recovery of the waste heat from the product described above), is limited in cooling the exhaust air (EA) at the rear end to the level of the outside air, and therefore, an expander (EP) is required.

[0062] Additionally, the solid oxide electrolysis system (SOEC) may further include a first evaporator (EVP1).

[0063] The first evaporator (EVP1) may be configured to secondarily heat water that has been primarily heated in the preheater (PH). Specifically, the first evaporator (EVP1) may be configured to heat-exchange water that has been primarily heated in the preheater (PH) with a refrigerant that carries heat recovered from the product cooler (PC). More specifically, the first evaporator (EVP1) may be configured to secondarily heat the primarily heated water and cool the refrigerant by heat-exchanging the primarily heated water and the refrigerant. At this time, the waste heat of the refrigerant may be transferred to the primarily heated water and recovered (3-2 recovery of product waste heat).

[0064] The above refrigerant may include at least one refrigerant having a boiling point at the level of n-pentane (a boiling point of 41.5° C. at a pressure of 0.2 barg).

[0065] Additionally, the solid oxide electrolysis system (SOEC) may further include a compressor (CP).

[0066] The compressor (CP) may be configured to compress the refrigerant discharged from the product cooler (PC) and supply it to the first evaporator (EVP1). In this way, the refrigerant discharged from the product cooler (PC) may be compressed in the compressor (CP) to increase its temperature and pressure. In addition, the refrigerant discharged from the product cooler (PC) may be used as a heat source for the first evaporator (EVP1). In addition, when the refrigerant discharged from the product cooler (PC) is compressed in the compressor (CP), the target temperature may be set to be 10 to 15°C higher than the saturation temperature at the operating pressure of water in the first evaporator (EVP1) to provide an appropriate level of heat supply for evaporating water. In this case, if all the water is not evaporated in the first evaporator (EVP1), the insufficient heat may be supplemented in the subsequent second evaporator (EVP2) to produce superheated steam and supply it to the stack (ST).

[0067] Additionally, the solid oxide electrolysis system (SOEC) may further include an expansion valve (EV).

[0068] The expansion valve (EV) may be configured to expand the refrigerant discharged from the first evaporator (EVP1) and supply it to the product cooler (PC). In addition, the refrigerant discharged from the expansion valve (EV) and then supplied to the product cooler (PC) may be in the form of a gas-liquid mixture having a lower temperature than the refrigerant discharged from the first evaporator (EVP1) and then supplied to the expansion valve (EV).

[0069] Additionally, the solid oxide electrolysis system (SOEC) may further include a second additional expander (not shown) instead of an expansion valve (EV).

[0070] The second additional expander may be configured to expand the refrigerant discharged from the first evaporator (EVP1) and supply it to the product cooler (PC), similar to the expansion valve (EV) described above. In addition, the refrigerant discharged from the second additional expander and then supplied to the product cooler (PC) may be in the form of a gas-liquid mixture having a lower temperature than the refrigerant discharged from the first evaporator (EVP1) and then supplied to the second additional expander.

[0071] In addition, the solid oxide electrolysis system (SOEC) may further include a turbine (not shown) disposed at a rear end of the second additional expander and sharing a rotational axis with the second additional expander. That is, the rotational axis of the second additional expander and the rotational axis of the turbine are formed integrally, so that the rotational axis of the second additional expander rotates, which means that the rotational axis of the turbine rotates. Therefore, when the rotational axis of the second additional expander rotates, the rotational axis of the turbine rotates, thereby generating electricity. The generated electricity may be used for a compressor (CP) of the solid oxide electrolysis system (SOEC), etc.

[0072] A technology for secondarily heating water that has been primarily heated in a preheater (PH) by additionally recovering waste heat of the remainder of the product (i.e., the second portion) by utilizing a series of refrigerant circulation loops including the above-described product cooler (PC), compressor (CP), first evaporator (EVP1) and expansion valve (EV) or the second additional expander can be a very effective hydrogen cost reduction method because it can reduce the electric energy required for cooling the product and heating the feed water (FW) due to the nature of the green hydrogen production process that must utilize only renewable energy, and can additionally recover waste heat discarded by cooling the product.

[0073] Additionally, the solid oxide electrolysis system (SOEC) may further include a second evaporator (EVP2).

[0074] The second evaporator (EVP2) can be configured to further evaporate the remaining water that has been secondarily heated but not evaporated in the first evaporator (EVP1) and supply it to the fuel electrode recuperator (FR) in the form of water vapor.

[0075] Additionally, the solid oxide electrolysis system (SOEC) may further include a fuel electrode heater (FH).

[0076] The fuel electrode heater (FH) may be configured to additionally heat water vapor and / or unevaporated residual water discharged from the fuel electrode recuperator (FR) and supply it to the fuel electrode (FE) of the stack (ST).

[0077] Additionally, the solid oxide electrolysis system (SOEC) may further include an air electrode heater (AH).

[0078] The air electrode heater (AH) can be configured to heat the outside air (AA) discharged from the air electrode recuperator (AR) and supply it to the air electrode (AE) of the stack (ST).

[0079] A solid oxide electrolysis system (SOEC) according to an embodiment of the present invention having the above configuration can reduce parasitic load by about 16%, and about 2.5% on a system basis, which can be a great benefit from a long-term operation perspective. Here, the expression "parasitic load" refers to the power consumed in the remaining portion excluding the stack (ST) among the power supplied to the actual solid oxide electrolysis system (SOEC). In other words, the expression "parasitic load" is used because it is not used for actual hydrogen production but is used for the operation of the stack (ST). Therefore, a 16% reduction in parasitic load means that 16% of the power used in the remaining portion excluding the stack (ST) is reduced, and this means about 2.5% on the basis of the entire solid oxide electrolysis system (SOEC) including the stack (ST). The above-mentioned reduction standard is a figure considering the operating load of the compressor (CP) generated by adding a series of refrigerant circulation loops including the above-mentioned product cooler (PC), compressor (CP), first evaporator (EVP1), air blower (AB) and expansion valve (EV) or the second additional expander.

[0080] While the present invention has been described with reference to the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent implementations are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

[0081] [Explanation of symbols]

[0082] SOEC: Solid Oxide Electrolysis System FW: Feedwater

[0083] SP: Separator PH: Preheater

[0084] EVP1, EVP2: Evaporator EV: Expansion valve

[0085] PC: Product Cooler CP: Compressor

[0086] RB: Recycle Blower FR: Fuel Anode Recuperator

[0087] FH: Fuel electrode heater ST: Stack

[0088] FE: fuel electrode EL: electrolyte

[0089] AE: Air electrode AA: Outside air

[0090] AB: Air blower AR: Air electrode recuperator

[0091] AH: Air electrode heater EP: Expander

[0092] EA: Exhaust

Claims

1. A stack including a fuel electrode, an electrolyte and an air electrode; A fuel electrode recuperator configured to heat-exchange products discharged from the fuel electrode and steam supplied to the fuel electrode; A recycle blower configured to recirculate a portion of the products discharged from the fuel electrode recuperator to the fuel electrode recuperator; A product cooler configured to cool the remainder of the product discharged from the above fuel electrode recuperator; A separator configured to separate at least the product discharged from the product cooler into hydrogen and water; An air blower configured to supply outside air to the air electrode; and A solid oxide water electrolysis system including an air electrode recuperator configured to heat-exchange exhaust air discharged from the air electrode and outside air supplied to the air electrode.

2. In paragraph 1, A solid oxide electrolysis system configured to directly mix feed water, which is a source of water vapor supplied to the fuel electrode, with the product discharged from the product cooler and supply it to the separator.

3. In paragraph 1, A solid oxide water electrolysis system further comprising a preheater configured to heat-exchange water discharged from the separator and exhaust discharged from the air electrode recuperator.

4. In paragraph 3, A solid oxide electrolysis system further comprising an expander sharing a rotational axis with the air blower, wherein the expander is configured to obtain rotational force from the rotational axis by expanding exhaust gas discharged from the preheater, thereby supplementing the rotational force of the air blower.

5. In paragraph 3, A solid oxide water electrolysis system further comprising a first evaporator configured to secondarily heat water primarily heated in the above preheater.

6. In paragraph 5, A solid oxide water electrolysis system in which the first evaporator is configured to heat-exchange water primarily heated in the preheater and a refrigerant carrying heat recovered in the product cooler.

7. In paragraph 6, The above product cooler is a solid oxide electrolysis system configured to heat-exchange the remaining portion of the product discharged from the fuel electrode recuperator and the refrigerant.

8. In paragraph 7, A solid oxide electrolysis system further comprising a compressor configured to compress the refrigerant discharged from the product cooler and supply it to the first evaporator.

9. In paragraph 8, A solid oxide electrolysis system further comprising an expansion valve or a second additional expander configured to expand the refrigerant discharged from the first evaporator and supply it to the product cooler.

10. In paragraph 5, A solid oxide water electrolysis system further comprising a second evaporator configured to further evaporate water secondarily heated in the first evaporator and supply the evaporated water to the fuel electrode recuperator.

11. In paragraph 1, A solid oxide water electrolysis system further comprising a fuel electrode heater configured to heat water vapor discharged from the fuel electrode recuperator and supply the heated water vapor to the fuel electrode.

12. In paragraph 1, A solid oxide water electrolysis system further comprising an air electrode heater configured to heat the outside air discharged from the air electrode recuperator and supply it to the air electrode.

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