CN105793473B - The apparatus and method for flexibly using electric power - Google Patents

Abstract

This invention provides an apparatus for chlor-alkali electrolysis, comprising a cathode half-cell, an oxygen-consuming electrode disposed therein, a conduit for supplying gaseous oxygen to the cathode half-cell, and a conduit for purging the cathode half-cell with an inert gas. The apparatus achieves flexible use of electricity through the following method: chlorine is generated in the apparatus by chlor-alkali electrolysis; when the power supply is low, gaseous oxygen is supplied to the oxygen-consuming electrode, and oxygen is reduced at the oxygen-consuming electrode at a first cell voltage; when the power supply is high, no oxygen is supplied to the oxygen-consuming electrode, and hydrogen is generated at the cathode at a second cell voltage higher than the first cell voltage.

Description

Apparatus and method for utilizing electric power flexibly

technical field

The present invention relates to an apparatus and method for the flexible use of electric power by which excess electric energy can be used for the production of hydrogen.

Background technique

Harnessing renewable energy sources, such as wind and solar power, is of increasing importance for power generation. Typically, electrical energy is supplied to many users through long-distance, cross-regional and transnationally connected power supply networks (referred to simply as power networks). Since electrical energy cannot be stored in large quantities within the power network itself, it is necessary to match the power supplied to the power network with the power demand on the customer side, which is called load. As is known, the load fluctuates over time, in particular according to the time of day, day of the week or time of year. A continuous balance of power generation and power consumption is necessary for a stable and reliable power supply. Possible short-term deviations are balanced out by what is known as forward or reverse control energy or control power. In the case of r For example time of day and weather related fluctuations, which are only predictable under certain circumstances and generally do not coincide with the energy demand at that particular moment.

The difference between the generation and consumption of fluctuating renewable energy sources at a given time is usually smoothed out by other power plants, such as gas-fired, coal-fired and nuclear power plants. As fluctuating renewable energy sources are expanding and taking up a larger and larger share of the electricity supply, greater fluctuations in their output and consumption at any given time must be balanced out. Therefore, even today, not only gas-fired power plants, but also increasingly bituminous coal-fired power plants are operating at part load or being shut down completely in order to balance out these fluctuations. Due to the considerable additional costs involved in such variable operation of power plants, studies to develop alternative measures have been underway for some time.

As an alternative or in addition to changing the output of the power plant in the case of excess electrical energy, it is known to use the excess electrical energy to produce hydrogen by electrolytic cracking of water. This method has the disadvantage that a separate device for the electrolytic splitting of water has to be constructed, which only operates with excess electrical energy and is not used most of the time.

The production of chlorine by chlor-alkali electrolysis of sodium chloride solution is one of the industrial processes with the highest power consumption. For chlor-alkali electrolysis, plants with a relatively large number of electrolytic cells operating in parallel are used in industry. In addition to chlorine, the usual by-products are sodium hydroxide solution and hydrogen. In order to reduce the power consumption of chlor-alkali electrolysis, a method has been developed in which there is no reduction of protons to molecular hydrogen at the cathode of the electrolytic cell, but the reduction of molecular oxygen to water at the oxygen-consuming electrode. Chlor-alkali electrolysis plants with oxygen-consuming electrodes known from the prior art are not designed for the production of molecular hydrogen.

It has been proposed to operate chlor-alkali electrolysis in such a way that a different number of electrolytic cells is operated as a function of the power supply, in order to make flexible use of electricity. This method has the disadvantage that the amount of chlorine produced varies with the electricity supply and does not correspond to the current demand for chlorine, so for this operation of chlor-alkali electrolysis, either a large buffer store of chlorine is necessary, or downstream consumption of chlorine The device must be operated under loads that vary according to the power supply. However, intermediate storage of large quantities of the hazardous substance chlorine is not advisable for safety reasons, and frequent operation of chlorine consumers at low loads is uneconomical.

It has been found that in an electrolytic cell for chlor-alkali electrolysis with an oxygen-consuming electrode as cathode, when the cathode half-cell is provided with a conduit for purging the cathode half-cell, the cathode can be operated as a function of the power supply, either for the production of hydrogen or When reducing oxygen, the disadvantages of the devices and methods described above can be avoided.

Contents of the invention

The present invention provides a device for flexible use of electricity comprising an electrolytic cell for chlor-alkali electrolysis having an anode half-cell, a cathode half-cell and a cation exchange membrane separating the anode and cathode half-cells from each other, an anode disposed in the anode half-cell for the gradual generation of chlorine, an oxygen-consuming electrode disposed in the cathode half-cell as a cathode, and a conduit for supplying gaseous oxygen to the cathode half-cell, wherein the device has at least one conduit for The cathode half-cell is purged with an inert gas.

The present invention also provides a method for flexible use of electricity, wherein, in the device of the present invention, chlorine is produced by chlor-alkali electrolysis, wherein:

a) when the power supply is low, gaseous oxygen is supplied to the oxygen-consuming electrode and oxygen is reduced at the oxygen-consuming electrode at the first cell voltage, and

b) When the power supply is high, no oxygen is supplied to the oxygen consuming electrodes and hydrogen is produced at the cathode at a second cell voltage higher than the first cell voltage.

The device according to the invention comprises an electrolytic cell for chlor-alkali electrolysis having an anode half-cell, a cathode half-cell and a cation exchange membrane separating the anode and cathode half-cells from one another. The device of the invention may comprise a plurality of such electrolytic cells, which may be connected to form a monopolar or bipolar electrolyser, preferably a bipolar electrolyser.

The anode for the gradual generation of chlorine is arranged within the anode half-cell of the device of the invention. The anode used may be any anode of membrane chlor-alkali electrolysis known in the prior art. Preference is given to using dimensionally stable electrodes with a support of metallic titanium and a mixed oxide coating of titanium oxide and ruthenium oxide or iridium oxide.

The anode and cathode half-cells of the device of the invention are separated from each other by a cation exchange membrane. The cation exchange membrane used may be any known cation exchange membrane suitable for membrane chlor-alkali electrolysis. Suitable cation exchange membranes can be Aciplex ^(TM) and Flemion ^(TM) are available under the tradenames from Du Pont, Asahi Kasei and Asahi Glass.

An oxygen-consuming electrode is provided as cathode in the cathode half-cell of the device of the invention. The device of the invention also has a conduit for supplying gaseous oxygen to the cathode half-cell and at least one conduit for purging the cathode half-cell with an inert gas.

Preferably, the device of the invention also has a gas separator separating the hydrogen formed at the cathode, and a conduit connected to said gas separator for purging the gas separator with an inert gas. The gas separator may take the form of a gas collector at the upper end of the cathode half-cell. Alternatively, the gas separator may be connected to the cathode half-cell via a conduit with which the mixture of electrolyte and hydrogen is drawn from the cathode half-cell.

In a preferred embodiment, the apparatus of the invention comprises electrolyzers arranged in parallel. Each electrolyzer in turn comprises a plurality of electrolytic cells with cathode half-cells, and a common conduit for supplying gaseous oxygen to the cathode half-cells of the electrolyzers and for purging the cathode half-cells of the electrolyzers with an inert gas. Furthermore, the device comprises a separate conduit for supplying oxygen to the electrolyzer and a separate conduit for supplying inert gas to the electrolyzer. Preferably, each electrolyser comprises a gas separator supplied with a mixture of electrolyte and hydrogen from the cathode half-cell of the electrolyser via a collecting conduit. In this embodiment, the device preferably comprises one or more conduits for supplying the inert gas to the gas separator of the electrolyzer. At a low level of instrumental complexity, the arrangement of the device in which the electrolyzers are arranged in parallel enables the device to operate different proportions of the electrolytic cells in which hydrogen is produced.

Preferably, the oxygen-consuming electrode is arranged in the cathode half-cell such that the cathode half-cell has an electrolyte space between the cation exchange membrane and the oxygen-consuming electrode through which electrolyte flows, and a gas space between the oxygen-consuming electrode The oxygen-consuming electrode is adjoined on the surface facing away from the electrolyte space and can be supplied with oxygen via a conduit supplying gaseous oxygen. Preferably, the cathode half-cell has at least one conduit for purging the gas space with an inert gas. The gas space may be continuous over the entire height of the cathode half-cell, or may be divided into a plurality of gas pockets arranged vertically one above the other, in which case each pocket has a gas pocket for A hole that equalizes the pressure with the electrolyte space. Suitable embodiments of such air pockets are known to the person skilled in the art, for example from DE 44 44 114 A1.

In this embodiment, the electrolyte space is preferably configured such that gas bubbles can rise between the cation exchange membrane and the oxygen-consuming electrode. For this purpose, the electrolyte space may take the form of a gap between the flat cation exchange membrane and the flat oxygen consuming electrode, and the oxygen consuming electrode may have elevations adjoining the cation exchange membrane. Alternatively, the oxygen-consuming electrode may take the form of a corrugated or folded sheet adjoining a flat cation-exchange membrane so as to form an electrolyte space in the form of a channel in the corrugations or folds between the oxygen-consuming electrode and the cation-exchange membrane Extends upwards from the bottom so that air bubbles can rise through it. Suitable oxygen-consuming electrodes are known from WO 2010/078952. The device preferably has a hydrogen collector at the upper end of the electrolyte space.

The oxygen-consuming electrodes used may be noble metal-containing gas diffusion electrodes. Preference is given to using silver-containing gas diffusion electrodes, more preferably gas diffusion electrodes having a porous hydrophobic gas diffusion layer comprising metallic silver and a hydrophobic polymer. The hydrophobic polymer is preferably a fluorinated polymer, more preferably polytetrafluoroethylene. More preferably, the gas diffusion layer consists essentially of polytetrafluoroethylene sintered silver particles. The gas diffusion electrode may additionally contain a support structure in the form of a mesh or grid, which is preferably electrically conductive and more preferably consists of nickel. A particularly suitable multilayer oxygen-consuming electrode is known from EP 2 397 578 A2. Oxygen-consuming electrodes with polymer-bound silver particles exhibit high stability in both oxygen reduction and hydrogen evolution operations. The multilayer oxygen-consuming electrode known from EP 2397 578 A2 is capable of being operated with high pressure differences and can thus be used in a cathode half-cell with a continuous gas space over its entire height.

The device of the invention preferably comprises at least one conduit operable to supply inert gas to the cathode half-cell, and at least one conduit operable to withdraw inert gas from the cathode half-cell. The conduit for supplying an inert gas to the cathode half-cell is connected to the cathode half-cell separately from the conduit for supplying gaseous oxygen, or it may be connected upstream of the cathode half-cell to the conduit for supplying gaseous oxygen so that the connection is separate from the conduit for supplying gaseous oxygen to the cathode half-cell. The section of conduit between the cells can be purged with an inert gas. The conduit available for drawing inert gas from the cathode half-cell may be connected to a gas collector at the upper end of the electrolyte space, or may be connected to a separation device which is arranged outside the cathode half-cell and in which the gas is separated from the cathode half-cell The effluent electrolyte is separated. Preferably, the sensor capable of measuring the oxygen and hydrogen content in the extracted gas is arranged in the conduit capable of extracting the inert gas from the cathode half-cell.

The gas space adjacent to the oxygen-consuming electrode, any gas pockets present, any gas collectors present, and conduits for supplying and withdrawing gas connected to the cathode half-cell are preferably configured such that the cathode is purged with an inert gas Little gas backmixing occurs in half cells. Thus, the gas space, any air pockets present, and any gas collector present are configured with a minimum gas volume.

The device according to the invention can also additionally have a buffer store for the chlorine generated in the anode half-cell, which is able to store an amount of chlorine capable of compensating for the anodic half-cell caused by purging the cathode half-cell with an inert gas. interruption of chlorine production.

In the method of the invention with flexible use of electricity, chlorine is produced by chlor-alkali electrolysis in the device according to the invention, and at least one electrolytic cell in the device is operated with different cell voltages as a function of the power supply. When the power supply is low, gaseous oxygen is supplied to the oxygen-consuming electrodes of the electrolysis cell, and oxygen is reduced at the oxygen-consuming electrodes at the first cell voltage. When the power supply is high, no oxygen is supplied to the oxygen consuming electrodes and hydrogen is produced at the cathode at a second cell voltage higher than the first cell voltage.

A high power supply may be caused by a surplus of power, while a low power supply may be caused by a shortage of power. A power surplus occurs when, at a certain moment, more electricity is supplied from renewable sources than is consumed in total at that moment. Power surpluses also arise when large amounts of electricity are supplied by fluctuating renewable energy sources, and the scaling back or closing of power plants is associated with high costs. When relatively small amounts of renewable energy are available, power shortages occur and inefficient or costly power plants must be operated. A power surplus can also exist when operators of power generating plants, such as windfarms, generate more power than predicted and sold. Similarly, power shortages may also exist when less power is generated than expected. Alternatively, the distinction between high and low electricity supply can also be divided on the basis of the price of electricity transactions, in which case low electricity prices correspond to high electricity supplies and high electricity prices correspond to low electricity prices. electricity supply. In this case, in order to distinguish between high and low power supply, a fixed or time-varying threshold of power prices for power trading may be used.

In a preferred embodiment, a threshold value for the power supply is defined for the method of the invention. In this case, the current power supply is determined at regular or irregular intervals, and when the power supply is below a threshold, the electrolytic cell is operated at the first battery voltage and gaseous oxygen is supplied to the oxygen-consuming electrodes, and when the power supply When the supply is above the threshold, the second cell voltage is operated and no oxygen is supplied to the oxygen consuming electrodes. As described above, the threshold value of the power supply and the current power supply may be defined or determined on the basis of the difference between the power generation and consumption, the current output of the power plant, or the power price of the power transaction.

By changing between the two modes of operation at different cell voltages, in the method of the present invention it is possible to flexibly match the electricity consumption of chlor-alkali electrolysis with the electricity supply without requiring any change in the output of chlorine production or for this purpose Intermediate storage of chlorine. The electrical energy otherwise consumed as a result of the higher second battery voltage is used to generate hydrogen and enables storage of surplus electricity in the form of chemical energy without the construction and operation of additional electrical storage devices. In this way, more hydrogen is produced per kilowatt-hour (kWh) consumed than in the case of water electrolysis.

Suitable values for the first cell voltage for oxygen reduction at the oxygen-consuming electrode and for the second cell voltage for hydrogen production at the electrode depend on the design of the oxygen-consuming electrode used and the envisioned current density for the chlor-alkali electrolysis, and can be obtained with The known mode is determined by the measurement of the current-voltage curve in the two operating modes.

Gaseous oxygen can be supplied as substantially pure oxygen or as an oxygen-enriched gas, in which case the oxygen-enriched gas preferably contains more than 50% by volume oxygen, more preferably more than 80% by volume oxygen. Preferably, the oxygen-enriched gas consists essentially of oxygen and nitrogen, and may optionally additionally contain argon. Suitable oxygen-enriched gases can be obtained from air by known methods, for example by pressure swing adsorption or membrane separation.

Preferably, when changing from hydrogen production at the second cell voltage to oxygen reduction at the first cell voltage, the cell voltage is reduced until substantially no current flows anymore and gaseous oxygen is supplied to the consumer Before the oxygen electrode, the cathode half-cell is purged with an inert gas. Similarly and preferably, when changing from oxygen reduction at a first cell voltage to hydrogen production at a second cell voltage, the cell voltage is reduced until substantially no current flows anymore and hydrogen is produced at the cathode Before, the cathode half-cell was purged with an inert gas. Suitable inert gases are all gases which do not form flammable mixtures with oxygen or hydrogen and which do not react with aqueous sodium hydroxide solution. The inert gas used is preferably nitrogen. Preferably, the purging with the inert gas is continued and the reduced cell voltage is maintained until the hydrogen or oxygen content in the gas leaving the cathode half-cell due to purging falls below a defined limit. Preferably, the limit for hydrogen is chosen such that a mixture of a hydrogen-containing gas with pure oxygen cannot produce a flammable mixture, and preferably the limit for oxygen is chosen such that a mixture of an oxygen-containing gas with pure hydrogen cannot produce a flammable mixture . Suitable limit values can be taken from known diagrams of the flammability of gas mixtures or determined by methods known to those skilled in the art for determining flammability. When changing between the two operating modes of the method according to the invention, the reduction of the cell voltage and the purging with an inert gas can reliably avoid the formation of combustible gas mixtures.

When changing from hydrogen production at the second cell voltage to oxygen reduction at the first cell voltage, after purging with an inert gas, preferably also with an oxygen-containing gas, to avoid gas diffusion as an oxygen-consuming electrode Inhibition of mass transport in oxygen reduction as a result of the high inert gas content within the layer.

Preferably, a prediction of the expected power supply is performed on the method of the invention, a minimum duration of operation at the first and second battery voltages is set, and operation at the first battery voltage with gaseous oxygen supply is compared to operation at the second battery voltage without oxygen supply. Switching between operation at battery voltage occurs only when the predicted duration of low or high power supply is longer than a set minimum duration. By this mode of operation, loss of chlorine production capacity as a result of too many cell voltage variations and the associated interruption of chlorine production during purging with inert gas can be avoided.

In a preferred embodiment of the method of the invention, after the change from oxygen reduction at the first cell voltage to hydrogen production at the second cell voltage, a gas mixture comprising hydrogen and an inert gas is drawn from the cathode half-cell, and Hydrogen is separated from the gas mixture, preferably by a membrane. Through such separation, substantially all of the hydrogen produced can be obtained in high purity and stable quality.

Preferably, the method of the invention is carried out in a device according to the invention with a plurality of electrolytic cells and the proportion of electrolytic cells to which oxygen is not supplied and in which hydrogen is produced at the cathode is varied as a function of the power supply. More preferably, for this purpose, the above-mentioned arrangement with a plurality of electrolyzers arranged in parallel is used. This enables regulation of the power consumption of the chlor-alkali electrolysis over a wide range with essentially constant chlorine production. In this embodiment, the method of the invention can be used to provide negative control energy to the operation of the distribution network without any adverse effect on chlorine production.

Claims (15)

1. flexibly use electric power device, its include for chloric alkali electrolysis electrolytic cell, the electrolytic cell have anodic half-cell, Cathode half-cell and the cation-exchange membrane that anodic half-cell and cathode half-cell are separated, it is arranged on anodic half-cell Interior anode gradually to produce chlorine, it is arranged on as the oxygen-consuming electrode of negative electrode in cathode half-cell and is supplied to cathode half-cell The conduit of gaseous oxygen, it is characterised in that described device has an at least conduit with the electricity of negative electrode half described in inert gas purge Pond, the gas separator for separating the hydrogen formed in negative electrode and the conduit for being connected to the gas separator, for using inertia Gas purges the gas separator.

2. device as claimed in claim 1, it is characterised in that：

A) cathode half-cell has electrolyte space, and electrolyte is by the electrolyte space in the cation-exchange membrane Flowed between the oxygen-consuming electrode；

B) gas compartment, oxygen, and the gas compartment are supplied to the gas compartment by the conduit for supplying gaseous oxygen Abutted on the surface backwards to electrolyte of the oxygen-consuming electrode with the oxygen-consuming electrode；And

C) cathode half-cell has an at least conduit, for the gas compartment described in inert gas purge.

3. device as claimed in claim 2, it is characterised in that the gas compartment is divided into one and hung down on the other side The multiple air pockets directly set, and each air pocket has for making its hole balanced with electrolyte space pressure.

4. device as claimed in claim 2 or claim 3, it is characterised in that it has the gas collector in the hydrogen of electrolyte space upper end.

5. such as the device any one of claim 1-3, it is characterised in that the oxygen-consuming electrode, which has, contains argent and fluorine The porous hydrophobic gas diffusion layers of fluidized polymer.

6. such as the device any one of claim 1-3, it is characterised in that it includes conduit, will be lazy by the conduit Property gas from cathode half-cell extract out, and at the conduit set sensor, inertia can be measured by the sensor The content of oxygen and hydrogen in gas.

7. such as the device any one of claim 1-3, it is characterised in that it includes more electrolyzers being arranged in parallel, often Platform electrolyzer includes multiple electrolytic cells with cathode half-cell, and gaseous oxygen is supplied to the cathode half-cell of electrolyzer The common conduit of common conduit and cathode half-cell with inert gas purge electrolyzer, and described device includes and supplies oxygen The independent conduit of electrolyzer should be supplied to the independent conduit of electrolyzer and by inert gas.

8. flexibly use the method for electric power, it is characterised in that in the device as any one of claim 1-7, chlorine is As caused by chloric alkali electrolysis, wherein：

A) when supply of electric power is low, gaseous oxygen is supplied to the oxygen-consuming electrode, and oxygen under the first cell voltage in oxygen consumption Electrode is reduced, and

B) when supply of electric power is high, no oxygen is supplied to the oxygen-consuming electrode, and higher than the first cell voltage second Under cell voltage hydrogen is produced in negative electrode.

9. method as claimed in claim 8, it is characterised in that change when from the production hydrogen under the second cell voltage to first When hydrogen reduction under cell voltage, cell voltage is lowered, until there is no that electric current flows through, and in gaseous oxygen quilt It is supplied to before the oxygen-consuming electrode, with inert gas purge cathode half-cell.

10. method as claimed in claim 8 or 9, it is characterised in that when from the hydrogen reduction under the first cell voltage change to When production hydrogen under the second cell voltage, cell voltage is lowered, until there is no that electric current flows through, and in negative electrode Before producing hydrogen, with inert gas purge cathode half-cell.

11. method as claimed in claim 8 or 9, it includes step：

A) threshold value of supply of electric power is limited,

B) supply of electric power is determined,

C) when supply of electric power is less than threshold value, electrolytic cell is operated with the first cell voltage and gaseous oxygen is supplied to oxygen-consuming electrode, And when supply of electric power is higher than threshold value, electrolytic cell is operated with the second cell voltage, and oxygen is not supplied to oxygen-consuming electrode, and

D) repeat step b) and c).

12. method as claimed in claim 8 or 9, it is characterised in that nitrogen is used as the inert gas.

13. method as claimed in claim 8 or 9, it is characterised in that be switched to from the hydrogen reduction under the first cell voltage After production hydrogen under second cell voltage, the admixture of gas comprising hydrogen and inert gas is extracted out from cathode half-cell, and Hydrogen is separated with the admixture of gas by film.

14. method as claimed in claim 8 or 9, it is characterised in that described device has multiple as appointed in claim 1-6 Electrolytic cell described in one, and not to its supply oxygen and wherein at negative electrode produce hydrogen electrolytic cell ratio as electric power The function of supply and change.

15. method as claimed in claim 8 or 9, it is characterised in that be expected the prediction of supply of electric power, the first He is set The minimum length in time operated under second cell voltage, and and if only if the Duration Ratio of the low or high supply of electric power of prediction is set Minimum length in time it is long when, just carry out having the operation under the first cell voltage that gaseous oxygen is supplied with being supplied without oxygen Switching between the operation under the second cell voltage answered.