Electrochemical systems

Abstract

This provides an electrochemical system that reduces constraints on the placement of equipment connected to a pump. [Solution] The electrochemical system comprises a pump that transfers water from a suction pipe to a discharge pipe, and a cell to which the discharge pipe is connected and to which the water supplied from the pump is used in a chemical reaction. The inner diameter and length of the discharge pipe are set such that, within the flow rate range of the water supplied from the pump, the water pressure P2 acting on the discharge pipe is greater than the water pressure P1 acting on the suction pipe.

Description

Technical Field

[0001] The present invention relates to an electrochemical system including a pump for transferring water.

Background Art

[0002] Regarding an electrochemical system including a pump, the prior art disclosed in Patent Document 1 stores water used in a chemical reaction occurring in a cell in a tank and transfers it to the cell by a pump.

Prior Art Documents

Patent Documents

[0003] [[ID=-23]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, since the atmospheric pressure acting on the water surface in the tank is used to suck water into the pump, there are restrictions on the arrangement of the devices connected to the pump, such as the need to arrange the device on the discharge side of the pump at a position higher than the water surface in the tank.

[0005] The present invention has been made to solve this problem, and an object thereof is to provide an electrochemical system capable of reducing the restrictions on the arrangement of the devices connected to the pump.

Means for Solving the Problems

[0006] A first embodiment for achieving this objective is an electrochemical system comprising a pump for transferring water from a suction pipe to a discharge pipe, and a cell to which the discharge pipe is connected and to which the water supplied from the pump is used in a chemical reaction, wherein the inner diameter and length of the discharge pipe are set such that, within the flow rate range of the water supplied from the pump, the water pressure P2 acting on the discharge pipe is greater than the water pressure P1 acting on the suction pipe. Setting the inner diameter and length of the discharge pipe such that the pressure P2 in the discharge pipe is greater than the pressure P1 in the suction pipe is equivalent to setting the inner diameter and length of the suction pipe, which is relative to the discharge pipe.

[0007] In a second embodiment, the suction pipe is a closed system, as in the first embodiment.

[0008] In the third embodiment, a water supply pipe is connected to the suction pipe in the second embodiment.

[0009] The fourth aspect is that in any of the first to third aspects, the pressure P2 is less than the rated pressure of the pump.

[0010] The fifth embodiment is a configuration in which, in any of the first to fourth embodiments, a connecting pipe is provided between the discharge pipe and the cell, wherein the inner diameter of the connecting pipe is greater than the inner diameter of the discharge pipe. [Effects of the Invention]

[0011] According to the present invention, the inner diameter and length of the discharge pipe are set such that the water pressure P2 acting on the discharge pipe is greater than the water pressure P1 acting on the suction pipe within the flow rate range of the water supplied by the pump. This reduces the constraints on the arrangement of devices connected to the discharge and suction sides of the pump. [Brief explanation of the drawing]

[0012] [Figure 1] This is a piping diagram of the electrochemical system in the first embodiment. [Figure 2] This is a schematic diagram of a stack. [Figure 3] This is a schematic diagram of an electrochemical system. [Figure 4]This is a piping diagram of the electrochemical system in the second embodiment. [Modes for carrying out the invention]

[0013] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a piping diagram of the electrochemical system 10 in the first embodiment. The electrochemical system 10 is a system that electrolyzes water in a stack 11. There are no restrictions on the cell design or material of the stack 11. Examples of cell designs for the stack 11 include flat plate type, cylindrical vertical stripe type, cylindrical flat plate type, cylindrical horizontal stripe type, and metal-supported flat plate type. Examples of cells include solid polymer type, molten carbonate type, and solid oxide type.

[0014] The electrochemical system 10 includes a pump 12 that supplies water, the raw material for the hydrogen produced by the stack 11, to the stack 11. A suction pipe 13 and a discharge pipe 14 are connected to the pump 12, and the stack 11 is connected downstream of the discharge pipe 14. The hydrogen produced by the electrolysis of water in the stack 11 flows out into a hydrogen tube 15 connected to the stack 11. If the stack 11 is a solid polymer type with a cell operating temperature of 100°C or less, a gas-liquid separator 16 is connected to the hydrogen tube 15. The hydrogen separated from water by the gas-liquid separator 16 is extracted at a pressure set by the control valve 17.

[0015] Figure 2 is a schematic diagram of stack 11. Figure 2 shows an example of stack 11, which is a flat plate type or a metal-supported flat plate type solid oxide type stack 11. Examples of stack 11 include electrolytic devices that generate hydrogen by electrolyzing water (water vapor), and electrolytic devices that generate hydrogen and CO by electrolyzing water vapor together with CO2 (co-electrolysis). Stack 11 includes those that allow reversible operation as a fuel cell and electrolytic device, generating electricity from fuel gases such as hydrogen, carbon monoxide, and hydrocarbons.

[0016] Stack 11 has a plurality of cells 20. Each cell 20 includes a fuel electrode 21, an air electrode 22, and an electrolyte 23 that separates the fuel electrode 21 and the air electrode 22. Stack 11 is heated by a heater (not shown). The heater is not limited as long as it can heat Stack 11, and examples include a heat exchanger that heats Stack 11 with high-temperature gas and a heating element.

[0017] Stack 11 is heated by a heater to the operating temperature of cell 20 (about 600°C to 1000°C). In the case of electrolysis of water (steam), when the positive electrode of a power source (not shown) is connected to the air electrode 22 of cell 20 and the negative electrode of the power source is connected to the fuel electrode 21, electrons flow out toward the fuel electrode 21. Since the steam supplied to cell 20 is reduced at the fuel electrode 21, hydrogen is generated at the fuel electrode 21. At the air electrode 22, electrons are taken away, so the oxide ions that have moved to the air electrode 22 through the electrolyte 23 are oxidized at the air electrode 22, and oxygen is generated at the air electrode 22. Separators 24, 25 isolate the fuel electrode 21 and the air electrode 22 to prevent the hydrogen generated at the fuel electrode 21 and the oxygen generated at the air electrode 22 from mixing.

[0018] Figure 3 is a schematic diagram of an electrochemical system 10 showing the inner diameter and length of the pipes connected to stack 11 and pump 12. In the electrochemical system 10, a water supply pipe 26 is connected upstream of the suction pipe 13, and a pure water production device 27 is provided between the water supply pipe 26 and the suction pipe 13. A connecting pipe 29 connected via a joint 28 (flange) is provided downstream of the discharge pipe 14 between the discharge pipe 14 and stack 11. In Figure 3, the illustration of devices such as a vaporizer provided between the discharge pipe 14 and stack 11 is omitted.

[0019] The inner diameter D and length L of the discharge pipe 14 are set such that the pressure P2 of the water acting on the discharge pipe 14 is greater than the pressure P1 of the water acting on the suction pipe 13 within the flow rate range of the water supplied from the pump 12 to the stack 11. The length L of the discharge pipe 14 refers to the length from the discharge port 12a of the pump 12 to the joint 28 provided at the end of the discharge pipe 14.

[0020] When the pump 12 transfers water from the suction pipe 13 and the water flows into the discharge pipe 14, a pressure loss ΔP occurs inside the discharge pipe 14, corresponding to the flow velocity. The water pressure P2 acting on the discharge pipe 14 is equal to the pressure loss ΔP. ​​The pressure loss ΔP (Pa) is expressed by the following Darcy-Weisbach equation (Equation 1): ΔP = f·L / D·(ρv 2 / 2)···(Equation 1) f: coefficient of friction, L: length of discharge pipe 14 (m), D: inner diameter of discharge pipe 14 (m), ρ: density of water (kg / m³) 3 ), where v is the flow velocity (m / s).

[0021] The friction coefficient f can be calculated from the respective empirical formulas for laminar or turbulent flow, after calculating the Reynolds number Re using the following (Equation 2): Re = ρvd / μ···(Equation 2) where d is the inner surface dimension of the discharge pipe 14 and μ is the viscosity of water. For laminar flow (Re < 2100), the Hagen-Poiseuille formula f = 64 / Re is an example of the empirical formula, and for turbulent flow, the empirical formula is 3 × 10⁻⁶ 3 ≤Re < 1 × 10 5 In this case, Prasius's formula f = 0.3164Re -1 / 4 An example is given, 1 × 10 5 ≤Re < 3 × 10 6 In this case, Nicrase's formula f = 0.0032 + 0.221Re -0.237 Examples are given.

[0022] The flow velocity v is the value obtained by dividing the flow rate of water transported by the pump 12 through the discharge pipe 14 by the cross-sectional area of ​​the discharge pipe 14, and the density ρ and viscosity μ of water depend on the temperature of the environment in which the discharge pipe 14 is located. The lower limit of the flow rate range of water transported by the pump 12 through the discharge pipe 14 is determined by considering the performance of the pump 12 and ensuring that the water supply does not become the rate-limiting factor in the chemical reaction occurring in the cell 20. The upper limit of the water flow rate range is determined by considering the rate of the chemical reaction occurring in the cell 20, the pressure resistance of the cell 20, and the performance of the pump 12. Therefore, once the pump 12 is determined, the flow velocity v and the friction coefficient f are values ​​that can be derived from the operating conditions for each operating condition of the cell 20. Thus, (Equation 1) can be expressed as ΔP = C·L / D for each operating condition, where C is a constant.

[0023] The electrochemical system 10 is connected to a water supply pipe 26 via a pure water production device 27 through a suction pipe 13. The water pressure acting on the water supply pipe 26 is generally a maximum of 0.4 MPa. Therefore, when a suction pipe 13 with the same inner diameter as the water supply pipe 26 is connected, the water pressure P1 acting on the suction pipe 13 is a maximum of 0.4 MPa, taking into account the pressure loss in the pure water production device 27.

[0024] The length L and inner diameter D of the discharge pipe 14 are set so that the water pressure P2 acting on the discharge pipe 14 is greater than the pressure P1 (0.4 MPa) over the entire flow rate range of the water transferred by the pump 12 through the discharge pipe 14. This prevents water from leaking out of the suction pipe 13 into the discharge pipe 14 through the pump 12, thus preventing the discharge rate of the pump 12 from changing. This prevents changes in the discharge rate of the pump 12 from becoming the rate-limiting factor in the chemical reaction occurring in cell 20, thus ensuring the production amount of the chemical reaction products in cell 20.

[0025] Furthermore, since water cannot leak from the suction pipe 13 to the discharge pipe 14 through the pump 12, it is possible to reduce the height constraints on the placement of equipment, such as having to place devices like vaporizers (not shown) and stacks 11 connected downstream of the discharge pipe 14 at a higher position than the suction pipe 13. This greatly increases the degree of freedom in placing devices such as stacks 11, allowing the devices constituting the electrochemical system 10 to be placed in relatively free positions.

[0026] The pressure loss ΔP of the discharge pipe 14 can be increased by setting the shape of the discharge pipe 14, such as by making the section between the outlet 12a of the pump 12 and the joint 28 of the discharge pipe 14 a bend, providing a section where the inner diameter of the discharge pipe 14 abruptly narrows, providing a partition in the section where the inner diameter of the discharge pipe 14 narrows, or branching the discharge pipe 14. When the shape of the discharge pipe 14 is set, the pressure loss ΔP (pressure P2) of the discharge pipe 14 is the sum of the pressure losses between the outlet 12a of the pump 12 and the joint 28 of the discharge pipe 14. The setting of the length L and inner diameter D of the discharge pipe 14 also includes setting the shape of the discharge pipe 14. If a valve (not shown) is connected to the discharge pipe 14, the pressure loss is variable because the flow rate can be changed by the valve opening. Therefore, when considering the pressure loss (pressure P2) of the discharge pipe 14, the pressure loss of the valve is excluded. When a valve is connected to the fitting 28 of the discharge pipe 14 (flange connection), the length L of the discharge pipe 14 is the length from the discharge port 12a to the fitting 28. When the discharge pipe 14 is screwed into the valve (threaded connection), the length L of the discharge pipe 14 is the length from the discharge port 12a to the valve inlet.

[0027] The water pressure P2 acting on the discharge pipe 14 is preferably lower than the rated pressure of the pump 12 within the flow rate range of the water transported by the pump 12 through the discharge pipe 14. This is because if the pressure P2 is higher than the rated pressure of the pump 12, the load on the pump 12 increases, making the pump 12 more susceptible to damage. By making the pressure P2 lower than the rated pressure of the pump 12, the occurrence of damage to the pump 12 can be reduced.

[0028] The suction pipe 13 of the electrochemical system 10 is a sealed system in which an open-air tank is not connected downstream of the suction pipe 13. Therefore, a tank can be omitted, and the electrochemical system 10 can be made smaller by eliminating the tank. In addition, since the suction pipe 13 is a sealed system to which the water supply pipe 26 is connected, the piping on the suction side of the pump 12 can be simplified.

[0029] Instead of connecting the water supply pipe 26 upstream of the suction pipe 13, an open-air tank (not shown) may be connected upstream of the suction pipe 13. It is possible to connect the water supply pipe 26 to the tank and supply water from the water supply pipe 26 to the tank. The water pressure P1 acting on the suction pipe 13 to which the open-air tank is connected is atmospheric pressure. In this case, the length L and inner diameter D of the discharge pipe 14 are set such that the pressure P2 is greater than the pressure P1 (atmospheric pressure) over the entire flow rate range of the water transported by the pump 12 through the discharge pipe 14. This reduces the height constraints on the placement of equipment such as the stack 11, such as placing the discharge-side equipment of the pump at a position higher than the water level in the tank.

[0030] The inner diameter of the connecting pipe 29, which is connected between the discharge pipe 14 and the stack 11, is larger than the inner diameter D of the discharge pipe 14. This makes the water pressure acting on the connecting pipe 29 smaller than the water pressure P2 acting on the discharge pipe 14. This reduces the force applied to the cells 20 of the stack 11 to which water (water vapor) is supplied, thus reducing the occurrence of cell 20 failure. This is particularly effective in the case of a solid oxide type stack 11, which is prone to fracture starting from cracks when mechanical load is applied to the electrolyte 23. The connecting pipe 29, which has an inner diameter larger than the inner diameter D of the discharge pipe 14, only needs to be present in at least a portion of the pipe connecting the discharge pipe 14 and the stack 11.

[0031] A second embodiment will be described with reference to Figure 4. In the first embodiment, an electrochemical system 10 was described when the stack 11 is an electrolytic device. In the second embodiment, an electrochemical system 30 was described when the stack 11 is a fuel cell. Parts identical to those described in the first embodiment are denoted by the same reference numerals as in the first embodiment, and some of the descriptions in the second embodiment are omitted.

[0032] Figure 4 is a piping diagram of the electrochemical system 30 in the second embodiment. The electrochemical system 30 comprises a stack 11 consisting of fuel cells and a pump 12 that transfers water from the suction pipe 13 to the discharge pipe 14. The suction pipe 13 is connected to a water supply pipe 26 via a pure water production device 27.

[0033] The electrochemical system 30 includes a desulfurizer 32 to which a gas pipe 31 supplying city gas is connected, a vaporizer 33 to which a discharge pipe 14 is connected, and a reformer 34 adjacent to the vaporizer 33 and filled with a catalyst. The desulfurizer 32 removes odorants contained in the city gas. The vaporizer 33 vaporizes water supplied by the pump 12 to generate steam.

[0034] The city gas, from which the odorant has been removed in the desulfurizer 32, is mixed with steam in the vaporizer 33 and then steam reformed in the reformer 34 to become reformed gas. The stack 11 consumes the methane and carbon monoxide contained in the reformed gas through a chemical reaction between the hydrogen and oxygen contained in the reformed gas, accompanied by reforming and shifting reactions, respectively, to generate electricity.

[0035] The inner diameter D and length L of the discharge pipe 14 are set such that, within the flow rate range of water supplied from the pump 12 to the vaporizer 33, the water pressure P2 acting on the discharge pipe 14 is greater than the water pressure P1 acting on the suction pipe 13. This reduces the height constraints on the placement of equipment, such as the requirement to place equipment like the vaporizer 33 connected downstream of the discharge pipe 14 at a higher position than the suction pipe 13, similar to the first embodiment. Consequently, the degree of freedom in arranging the equipment constituting the electrochemical system 30 is greatly increased.

[0036] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0037] In the embodiment (see Figure 2), the shape of cell 20 and separators 24 and 25 when viewed from the thickness direction is shown to be rectangular, but this is not necessarily the only option. The shape of cell 20 and separators 24 and 25 can be arbitrarily set to a circle, ellipse, polygon other than a rectangle, etc. [Explanation of symbols]

[0038] 10,30 Electrochemical Systems 12 pumps 13 Suction pipe 14 Discharge pipe 20 cells 26. Water supply pipes 29 connecting pipes

Claims

1. A pump that transfers water from the suction pipe to the discharge pipe, An electrochemical system comprising a cell to which the discharge pipe is connected and which is used in a chemical reaction by water supplied from the pump, An electrochemical system in which the inner diameter and length of the discharge pipe are set such that, within the flow rate range of the water supplied from the pump, the water pressure P2 acting on the discharge pipe is greater than the water pressure P1 acting on the suction pipe.

2. The electrochemical system according to claim 1, wherein the suction pipe is a sealed system.

3. The electrochemical system according to claim 2, wherein a water supply pipe is connected to the suction pipe.

4. The electrochemical system according to any one of claims 1 to 3, wherein the pressure P2 is less than the rated pressure of the pump.

5. A connecting pipe is provided between the discharge pipe and the cell, The electrochemical system according to any one of claims 1 to 3, wherein the inner diameter of the connecting pipe is larger than the inner diameter of the discharge pipe.

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