CN114865014A - Purging method for fuel cell - Google Patents

Abstract

The invention discloses a fuel cell purging method, which purges water in a cell stack after the cell stack is shut down, and monitors the impedance of the stack in the purging process: in the first blowing stage, air flow is introduced into the cell stack for blowing in a constant-pressure constant-flow mode until the monitored resistance of the cell stack reaches a first resistance threshold value, and the set range is a target resistance valueR _dry 50% to 70%; in the second purging stage, gas flow is introduced into the cell stack for purging in a mode of boosting pressure and increasing flow until the monitored resistance of the cell stack reaches a second resistance threshold value, wherein the set range isR _dry 85% to 100%; in the third purging stage, the air flow is introduced into the battery in a mode of increasing the pressure and increasing the flow, then decreasing the pressure and decreasing the flow and then increasing the pressure and increasing the flowPurging the stack until the monitored resistance of the stack reaches a third resistance threshold, wherein the set range isR _dry 98% to 100%. Tests prove that the battery purging method has the advantages of low gas consumption and short purging time.

Description

A kind of fuel cell purging method

technical field

The invention relates to the field of fuel cell control, in particular to a fuel cell purging method.

Background technique

During the operation of the fuel cell stack, the cathode and anode need to pass gas with a certain humidity, and the cathode will produce a large amount of water. The stack failed to start cold or flooded when the stack started.

The focus of the relevant patents is on the detection methods for controlling the start and stop of purging, such as the use of high-frequency impedance detection methods to determine whether the remaining water content in the stack reaches the standard: continuous ventilation and purging of the stack with constant current and constant pressure, when the real-time high-frequency impedance Above the set threshold, the purging is stopped.

For example, in the Chinese patent application with the publication number CN111029623A, the disclosed purging strategy takes a long time, and the required purging air flow is large, resulting in low purging efficiency and waste gas, which is not economical; and the patent application does not consider the influence of the steady-state process , that is, the internal resistance value meets the requirements after one purging is completed, but after standing for a period of time, the internal resistance value shows a slow decline until it becomes stable. This is mainly because the local residual water does not really discharge the membrane under the purging of atmospheric air. In the electrode, but in the porous capillary structure of the gas diffusion layer, after a period of steady-state process (due to the influence of the concentration gradient, the local residual water diffuses from the high-concentration area to the low-concentration area until equilibrium), the local residual water is regenerated. The distribution remains in the membrane electrode, the purging is incomplete, and the purging requirements are not actually met.

Another example is the Chinese patent application with publication number CN113839068A, which discloses a strategy of intermittent multiple purging, but the system is too complicated, and the purging efficiency of the constant current and constant pressure strategy is still low, which is not economical.

The disclosure of the above background technology content is only used to assist the understanding of the inventive concept and technical solution of the present invention, and it does not necessarily belong to the prior art of the present patent application, nor does it necessarily give technical teaching; The above background art should not be used to evaluate the novelty and inventive step of the present application if it has been disclosed before the filing date of the present patent application.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a fuel cell purging method that implements different purging strategies in stages, so as to improve the purging efficiency and improve the purging effect.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

A fuel cell purging method, after the fuel cell stack is shut down, the water in the stack is purged, and the impedance of the stack is monitored during the purging process, the purging method includes purging according to three purging stages sweep:

In the first purging stage, the air flow is flowed into the battery stack in a constant pressure and constant flow manner for purging until it is detected that the impedance of the battery stack reaches a preset first impedance threshold, wherein the set range of the first impedance threshold is 50% to 70% of the target impedance value;

In the second purging stage, the air flow is pumped into the battery stack in the manner of increasing the pressure and increasing the flow rate for purging until the impedance of the stack is monitored to reach a preset second impedance threshold, wherein the set range of the second impedance threshold 85% to 100% of the target impedance value;

In the third purging stage, the air flow is injected into the battery stack for purging by first boosting the pressure and increasing the flow rate and then decreasing the flow rate until the monitored impedance of the battery stack reaches a preset third impedance threshold, wherein the third The impedance threshold can be set from 98% to 100% of the target impedance value.

Further, in the third purging stage, after first boosting the pressure and increasing the flow rate, then decreasing the pressure and decreasing the flow rate, the air flow is injected into the battery stack for purging by increasing the pressure and increasing the flow rate until the impedance of the stack is monitored to reach a preset value. The third impedance threshold, wherein the airflow back pressure value of the second rise is greater than the airflow back pressure value of the first rise, and the airflow flow value of the second rise is greater than the airflow flow value of the first rise.

Further, controlling the volume flow of the purging gas flow in the first purging stage is the volume flow value of the gas required for the anode corresponding to a current density of 0.1 to 0.3 ^A /cm when the stack is operating; The volume flow of the purge gas flow in the second purge stage is increased from the volume flow rate of the gas required by the anode corresponding to the first current density value when the stack is operating to the volume flow rate of the gas required by the anode corresponding to the second current density value value, wherein the setting range of the first current density value is 0.1 to 0.3 A/cm ² , and the setting range of the second current density value is 0.3 to 0.7 A/cm ² .

Further, the flow rate of the purging gas flow in the third purging stage is controlled to increase from the volume flow value of the gas required by the anode corresponding to the first current density value during the operation of the stack to the anode corresponding to the third current density value. The volume flow value of the required gas decreases to the volume flow value of the gas required for the anode corresponding to the first current density value, and then increases to the volume flow value of the gas required for the anode corresponding to the fourth current density value, wherein the first current The setting range of the density value is 0.1 to 0.3 A/cm ² , the setting range of the third current density value is 0.4 to 0.5 A/cm ² , and the setting range of the fourth current density value is 0.5 to 0.8 A/cm ² ;

The flow rate of the initial purge gas flow in the second purge stage is the same or different from the flow rate of the initial purge gas flow in the third purge stage.

Further, the flow rate of the airflow is calculated by the following formula:

，其中，v为电堆运行时阳极所需气体的体积流量，j为电堆电流密度，A为反应面积，a为电堆所含单电池节数，S为化学计量比，V _m 为气体摩尔体积，n为反应转移电子数；F为法拉第常数，单位为C/mol。

, where v is the volume flow of gas required by the anode when the stack is running, j is the stack current density, A is the reaction area, a is the number of cells contained in the stack, S is the stoichiometric ratio, and V _m is the gas Molar volume, n is the number of electrons transferred in the reaction; F is the Faraday constant, in C/mol .

Further, the airflow back pressure in the first purge stage is controlled to be less than 0.2 kPa, and the airflow back pressure in the second purge stage is controlled to increase from a first pressure value to a second pressure value, wherein the first pressure The setting range of the value is 2 to 20 kPa, the setting range of the second pressure value is 15 to 40 kPa, and the first pressure value is smaller than the second pressure value.

Further, the airflow back pressure in the third purge stage is controlled to increase from the first pressure value to the third pressure value, drop to the first pressure value, and then increase to the fourth pressure value, wherein the first pressure value is The setting range is 2 to 20 kPa, the setting range of the third pressure value is 20 to 40 kPa, the setting range of the fourth pressure value is 20 to 40 kPa, and the third pressure value is smaller than the third pressure value. Four pressure values.

Further, the first pressure value of the second purging stage is the same as or different from the first pressure value of the third purging stage; or, the back pressure of the purging gas flow in the first purging stage is 0.

Further, after the first purging stage is completed, the second purging stage is started after waiting for a first time period, and the setting range of the first time period is 1 to 5 min;

After the second purging stage is completed, the third purging stage is started after waiting for a second time period, and the setting range of the second time period is 1 to 5 min;

The set values of the first time period and the second time period are the same or different.

Further, the target impedance value is a qualified impedance value of the stack under the condition of water content that meets the shutdown requirement of the fuel cell stack product.

Further, the fuel cell purging method further includes: formulating multiple purging schemes, at least one purging parameter is different between each purging scheme, and comparing the purging effects of different purging schemes to determine a better purging scheme. Program;

Among them, the purging effect is evaluated in the following ways:

The airflow consumption of the first purging stage, the second purging stage and the third purging stage is counted, and/or the purging time from the beginning of the first purging stage to the end of the third purging stage is counted.

Further, the optimal purging scheme is determined as:

The back pressure of the gas flow in the first purge stage is controlled to be less than 0.1 kPa, and the flow rate of the purge gas flow in the first purge stage is controlled to correspond to a current density between 0.15 and 0.25 A/cm ² during the operation of the stack. the volume flow value of the gas required by the anode until the impedance of the stack reaches a preset first impedance threshold, wherein the setting range of the first impedance threshold is 58% to 62% of the target impedance value;

Controlling the back pressure of the gas flow in the second purging stage to increase from a first pressure value to a second pressure value, and controlling the flow rate of the purging gas flow in the second purging stage from a first current density when the stack operates The volume flow value of the gas required for the anode corresponding to the value increases to the volume flow value of the gas required for the anode corresponding to the second current density value, until the monitored impedance of the stack reaches the preset second impedance threshold, wherein the first The setting range of the second impedance threshold is 92% to 98% of the target impedance value, wherein the setting range of the first pressure value is 8 to 12 kPa, and the setting range of the second pressure value is 20 to 35 kPa , the setting range of the first current density value is 0.15 to 0.25 A/cm ² , and the setting range of the second current density value is 0.4 to 0.6 A/cm ² ;

Control the airflow back pressure of the third purge stage to increase from the first pressure value to the third pressure value, decrease to the first pressure value and then increase to the fourth pressure value, and control the purge of the third purge stage The flow rate of the gas flow increases from the volume flow value of the gas required by the anode corresponding to the first current density value to the volume flow value of the gas required for the anode corresponding to the third current density value when the stack is running, and then decreases to the first current density value. The corresponding volume flow value of the gas required by the anode is increased to the volume flow value of the gas required by the anode corresponding to the fourth current density value, until it is monitored that the impedance of the stack reaches a preset third impedance threshold, wherein the first The setting range of the three impedance thresholds is 99% to 100% of the target impedance value, wherein the setting range of the first pressure value is 8 to 12 kPa, and the setting range of the third pressure value is 22 to 28 kPa kPa, the setting range of the fourth pressure value is 32 to 40 kPa, the setting range of the first current density value is 0.15 to 0.25 A/cm ² , and the setting range of the third current density value is 0.42 A/cm ² to 0.48 A/cm ² , the setting range of the fourth current density value is 0.55 to 0.65 A/cm ² .

Further, the optimal purging scheme is determined as:

The back pressure of the airflow in the first purge stage is controlled to be 0, and the flow rate of the purge airflow in the first purge stage is controlled to be an anode corresponding to a current density of 0.2±0.01 A/cm ² during operation of the stack The volume flow value of the required gas until the impedance of the stack reaches 60% of the target impedance value;

Wait 2±0.3 min;

Control the airflow back pressure of the second purge stage to increase from 10±0.1 kPa to 30±0.1 kPa, and control the flow rate of the purge airflow in the second purge stage to be 0.2±0.2± The volume flow value of the gas required for the anode corresponding to 0.01 A/cm ² is increased to the volume flow value of the gas required for the anode corresponding to the current density of 0.5±0.01 A/cm ² until the monitored impedance of the stack reaches 95% of the target impedance value. %;

Wait 3±0.5 min;

Control the airflow back pressure of the third purging stage to increase from 10±0.1 kPa to 25±0.1 kPa, decrease to 10±0.1 kPa and then increase to 35±0.1 kPa, and control the purging of the third purging stage The flow rate of the gas flow is increased from the volume flow value of the gas required by the anode corresponding to the current density of 0.2 ± 0.01 A/cm ² when the stack is running to the value of the volume flow rate of the gas required by the anode corresponding to the current density of 0.45 ± 0.01 A/cm ² , decrease to the volume flow value of the gas required for the anode corresponding to the current density of 0.2 ± 0.01 A/cm ² and then increase to the volume flow value of the gas required for the anode corresponding to the current density of 0.6 ± 0.01 A/cm ² until the stack is monitored. The impedance reaches 100% of the target impedance value.

The beneficial effects brought by the technical scheme provided by the invention are as follows:

a. Use different purging strategies in stages to purge the stack after shutdown. The three stages are reasonable: use lower flow and lower air pressure in the early stage for preliminary purging until the R _dry reaches 60 %, in the mid-term, the air flow with gradually increasing flow and back pressure is used to further purge to reach about 95% of R _dry , and in the later stage, the flow and back pressure are first increased, then decreased, and then increased to a higher air flow to be purged to R _dry ;

b. The purging strategies at each stage have their own emphasis: before reaching 60% R _dry , use a gentle airflow to take into account both air consumption and purging time; in the stage between 60% R _dry and 95% R _dry , gradually increase the atmospheric air flow , focusing on the purging efficiency; in the stage from 95% R _dry to 100% R _dry , the mode of first rise, then fall and then rise is used to prevent or reduce the phenomenon that the internal resistance value shows a slow decline after the purging is completed.

Description of drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only These are some embodiments described in this application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

FIG. 1 is a schematic schematic diagram of a basic flow of a fuel cell purging method provided by an exemplary embodiment of the present invention;

FIG. 2 is a schematic flow chart of a preferred purging scheme provided by an exemplary embodiment of the present invention.

Detailed ways

In order to make those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only Embodiments are part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "first", "second" and the like in the description and claims of the present invention and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used may be interchanged under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having", and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, apparatus, product or device comprising a series of steps or units is not necessarily limited to those expressly listed Rather, those steps or units may include other steps or units not expressly listed or inherent to these processes, methods, products or devices.

The gas diffusion layer in the membrane electrode of the fuel cell has a porous capillary structure, and the water in it is not easy to blow out of the stack. The phenomenon of slow decline until smooth, mainly because the local residual water does not really discharge the membrane electrode under the purging of the atmospheric flow, but in the porous capillary structure of the gas diffusion layer, after a period of steady state process (due to the concentration Due to the influence of the gradient, the local residual water diffuses from the high-concentration area to the low-concentration area until equilibrium), and the local residual water is re-distributed evenly in the membrane electrode, resulting in the actual purging not meeting the purging requirements, that is, the stack The internal water content does not meet the shutdown requirements. Specifically, the shutdown requirements of the fuel cell stack product have an index requirement for the water content in the stack. If the purging does not meet the standard, the water content in the stack is higher than the index requirement. The present invention seeks to provide a fuel cell purging method capable of addressing the above-identified deficiencies.

In one embodiment of the present invention, a fuel cell purging method is provided. After the fuel cell stack is shut down, the water in the stack is purged according to three purging stages. The impedance of the stack is used to determine the completion of the three purge stages, as shown in Figure 1. The purge method includes the following steps:

In the first purging stage, the air flow is flowed into the battery stack in a constant pressure and constant flow manner for purging until it is detected that the impedance of the battery stack reaches a preset first impedance threshold, wherein the set range of the first impedance threshold is is 50% to 70% of the target impedance value; the target impedance value is the qualified impedance value of the stack under the condition of water content that meets the shutdown requirements of the fuel cell stack product, hereinafter referred to as R _dry .

In the second purging stage, the air flow is pumped into the battery stack in the manner of increasing the pressure and increasing the flow rate for purging until the impedance of the stack is monitored to reach a preset second impedance threshold, wherein the set range of the second impedance threshold 85% to 100% of the target impedance value;

In the third purging stage, the air flow is injected into the battery stack for purging by first boosting the pressure and increasing the flow rate and then decreasing the flow rate until the monitored impedance of the battery stack reaches a preset third impedance threshold, wherein the third The impedance threshold can be set from 98% to 100% of the target impedance value.

As shown in FIG. 1 , in the third purging stage, after first boosting the pressure and increasing the flow rate, then decreasing the pressure and decreasing the flow rate, the airflow is injected into the battery stack for purging by increasing the pressure and increasing the flow rate until the impedance of the stack is monitored. The preset third impedance threshold value is reached, wherein the airflow back pressure value of the second rise is greater than the airflow back pressure value of the first rise, and the airflow flow value of the second rise is greater than the airflow value of the first rise flow value.

The following takes a fuel cell stack product with a power of 80 kW as an example, combined with the specific pressure value and flow value of constant pressure and constant flow, boosting and increasing flow, first boosting and increasing flow, then reducing and decreasing flow, and then boosting and increasing flow. To illustrate the scheme of this embodiment:

The first purge stage: constant pressure and constant flow:

The flow rate of the purge gas flow in the first purge stage is controlled to be the volume flow value of the gas required for the anode corresponding to a current density of 0.1 to 0.3 A/cm ² when the stack is operating;

，其中，v为电堆运行时阳极所需气体的体积流量，j为电堆电流密度，A为反应面积，a为电堆所含单电池节数，S为化学计量比，V _m 为气体摩尔体积，n为反应转移电子数；F为法拉第常数，单位为C/ mol；对于本实施例中80 kW的燃料电池电堆产品，计算0.1至0.3 A/cm²的电流密度对应的阳极所需气体的体积流量值范围为70至230 NLPM，下面根据电流密度换算气流流量同理于此。Specifically, the flow rate of the airflow is calculated by the following formula:

, where v is the volume flow of gas required by the anode when the stack is running, j is the stack current density, A is the reaction area, a is the number of cells contained in the stack, S is the stoichiometric ratio, and V _m is the gas Molar volume, n is the number of electrons transferred in the reaction; F is the Faraday constant, in C/ mol ; for the fuel cell stack product of 80 kW in this example, calculate the current density of 0.1 to 0.3 A/cm ² corresponding to the anode The volume flow value of the required gas ranges from 70 to 230 NLPM, and the same is true for the following conversion of the gas flow according to the current density.

In addition, the airflow back pressure in the first purge stage is controlled to be less than 0.2 kPa.

Until the impedance of the stack is monitored to reach a certain set value between 50% R _dry and 70% R _dry , the purging action of the first purging stage can be stopped.

The second purge stage: boost pressure boost flow:

The flow rate of the purge gas flow in the second purge stage is controlled to be increased from the volume flow value of the gas required by the anode corresponding to the first current density value when the stack is running to the volume flow rate of the gas required by the anode corresponding to the second current density value. The volume flow rate value, wherein the setting range of the first current density value is 0.1 to 0.3 A/cm ² , which is converted into an airflow flow rate range of 70 to 230 NLPM, and the setting range of the second current density value is 0.3 to 0.3 A/cm 2 . 0.7 A/cm ² , which translates to a flow rate range of 230 to 530 NLPM.

And control the airflow back pressure in the second purging stage to increase from a first pressure value to a second pressure value, wherein the setting range of the first pressure value is 2 to 20 kPa, and the second pressure value is in the range of 2 to 20 kPa. The setting range is 15 to 40 kPa, and the first pressure value is smaller than the second pressure value.

The purging action of the second purging stage can be stopped until the monitored impedance of the stack reaches a certain set value between 85% R _dry and 100% R _dry .

The third purging stage: first increase the pressure and increase the flow, then reduce the pressure and reduce the flow, and then increase the pressure and increase the flow:

The flow rate of the purge gas flow in the third purge stage is controlled to be increased from the volume flow value of the gas required by the anode corresponding to the first current density value when the stack is running to the volume flow rate of the gas required by the anode corresponding to the third current density value. The volume flow value decreases to the volume flow value of the gas required for the anode corresponding to the first current density value, and then increases to the volume flow value of the gas required for the anode corresponding to the fourth current density value, wherein the value of the first current density value is The setting range is 0.1 to 0.3 A/cm ² , and the range of the air flow rate is 70 to 230 NLPM, and the setting range of the third current density value is 0.4 A/cm ² to 0.5 A/cm ² , which is converted to the air flow The flow range is 300 to 380 NLPM, and the setting range of the fourth current density value is 0.5 to 0.8 A/cm ² , which is converted into an airflow flow range of 380 to 610 NLPM;

And control the airflow back pressure in the third purge stage to increase from the first pressure value to the third pressure value, drop to the first pressure value and then increase to the fourth pressure value, wherein the setting of the first pressure value The range is 2 to 20 kPa, the setting range of the third pressure value is 20 to 40 kPa, the setting range of the fourth pressure value is 20 to 40 kPa, and the third pressure value is smaller than the fourth pressure value.

Until the impedance of the stack reaches 100% R _dry , the purging action of the third purging stage can be stopped to complete the purging. The purge gas flow in the three purge stages mentioned above is simultaneously applied to the cathode and anode of the stack. The usual flow rate of the purge airflow is usually based on empirical values (the higher the power of the stack, the larger the flow rate of the purge airflow needs to be) or the corresponding setting results obtained by relying on experiments. The flow rate of the gas flow is different from the conventional method. In this embodiment, the volume flow value of the gas required by the anode corresponding to the preset target current density value during operation of the stack is used as the set reference. The advantage of such a control strategy is that it is applicable to various For fuel cell stack products with power specifications, only the above flow calculation formula can be used to determine the flow rate of purge airflow corresponding to stacks with different power and different structures, without the need for a new power specification as in conventional practice. The stack needs to be retested to match the purge gas flow settings.

Wherein, the flow rate of the initial purging gas flow in the second purging stage and the flow rate of the initial purging gas flow in the third purging stage are both in the range of 70 to 230 NLPM, but the specific set values may be the same, or may be different; the first pressure value of the second purging stage and the first pressure value of the third purging stage are both in the range of 2 to 20 kPa, but the specific set values may be the same or different.

As mentioned at the beginning of the example, under the purging of the gas stream, the water is not completely discharged from the membrane electrode, but in the porous capillary structure of the gas diffusion layer, and after a period of steady-state process, the residual water is re-distributed evenly In the membrane electrode, therefore, in a possible embodiment of the present invention, after the first purge stage is completed, the second purge stage is started after a first period of time, the first period of time The setting range is 1 to 5 min; after the second purging stage is completed, the third purging stage is started after waiting for the second time period, and the setting range of the second time period is 1 to 5 min; the set values of the first time period and the second time period are the same or different.

On the basis of the above framework, formulate multiple purging schemes, at least one purging parameter is different between each purging scheme, compare the purging effects of different purging schemes, and determine the optimal purging scheme;

Among them, the purging effect is evaluated in the following ways:

The airflow consumption of the first purging stage, the second purging stage and the third purging stage is counted, and/or the purging time from the beginning of the first purging stage to the end of the third purging stage is counted. Among them, the smaller the airflow consumption and the shorter the purging time, the better the purging effect, otherwise the worse the purging effect. Specifically, the corresponding weight values can be set for the airflow consumption and the purging time. For example, if the weight coefficients of the two are 0.85 and 0.15, respectively, then calculate: airflow consumption * 0.85 + purging time * 0.15 to obtain the evaluation score of the purging effect. , the higher the score, the worse the purging effect.

The following examples and comparative examples are provided below by taking a fuel cell stack product with a power of 80 kW as an example:

Example 1

The stack impedance dropped to 99.3% R _dry 0.5h after the purging ended, and the stack impedance dropped to 98.9% R _dry 12h after the purging ended.

Example 2

The stack impedance dropped to 99.9% R _dry 0.5h after the purging ended, and the stack impedance dropped to 99.6% R _dry 12h after the purging ended.

Example 3

The stack impedance dropped to 99.5% R _dry 0.5h after the purging, and 98.7% R _dry 12h after the purging.

Comparative Example 1

The stack impedance dropped to 99.1% R _dry 0.5h after the purging, and 98.2% R _dry 12h after the purging.

Comparative Example 2

The stack impedance dropped to 98.7% R _dry 0.5h after the purging ended, and the stack impedance dropped to 98.1% R _dry 12h after the purging ended.

Comparative Example 3

According to the usual purging strategy, that is, constant current purging until 100% of the preset impedance threshold is reached, the purging data are as follows:

The stack impedance dropped to 97.1% R _dry 0.5h after the purging, and 95.4% R _dry 12h after the purging.

Comparing Examples 1 to 3, it can be seen that Example 2 has less gas consumption, shorter purging time, and lower value of stack impedance drop after purging, so a better purging scheme is established.

In the solutions of Comparative Examples 1 to 3, the air consumption is greater than that of Example 1, the purge time is greater than that of Example 1, and the stack impedance decline trend is more obvious for a period of time after the purge is completed. Therefore, it can be verified that the setting range given in this embodiment is an optimal parameter range, and within this range, the setting value applied in Embodiment 2 establishes an optimal purging scheme.

The purging scheme for the optimal parameter range was determined as:

The back pressure of the gas flow in the first purge stage is controlled to be less than 0.1 kPa, and the flow rate of the purge gas flow in the first purge stage is controlled to correspond to a current density between 0.15 and 0.25 A/cm ² during the operation of the stack. the volume flow value of the gas required by the anode until the impedance of the stack reaches a preset first impedance threshold, wherein the setting range of the first impedance threshold is 58% to 62% of the target impedance value;

Controlling the back pressure of the gas flow in the second purging stage to increase from a first pressure value to a second pressure value, and controlling the flow rate of the purging gas flow in the second purging stage from the first current when the stack operates The volume flow value of the gas required by the anode corresponding to the density value is increased to the volume flow value of the gas required by the anode corresponding to the second current density value, until it is monitored that the impedance of the stack reaches a preset second impedance threshold, wherein the said The setting range of the second impedance threshold is 92% to 98% of the target impedance value, wherein the setting range of the first pressure value is 8 to 12 kPa, and the setting range of the second pressure value is 20 to 20 kPa. 35kPa, the setting range of the first current density value is 0.15 to 0.25 A/cm ² , and the setting range of the second current density value is 0.4 to 0.6 A/cm ² ;

Control the airflow back pressure of the third purge stage to increase from the first pressure value to the third pressure value, decrease to the first pressure value and then increase to the fourth pressure value, and control the purge of the third purge stage The flow rate of the gas flow increases from the volume flow value of the gas required by the anode corresponding to the first current density value to the volume flow value of the gas required for the anode corresponding to the third current density value when the stack is running, and then decreases to the first current density value. The corresponding volume flow value of the gas required by the anode is increased to the volume flow value of the gas required by the anode corresponding to the fourth current density value, until it is monitored that the impedance of the stack reaches a preset third impedance threshold, wherein the first The setting range of the three impedance thresholds is 99% to 100% of the target impedance value, wherein the setting range of the first pressure value is 8 to 12 kPa, and the setting range of the third pressure value is 22 to 28 kPa kPa, the setting range of the fourth pressure value is 32 to 40 kPa, the setting range of the first current density value is 0.15 to 0.25 A/cm ² , and the setting range of the third current density value is 0.42 A/cm ² to 0.48 A/cm ² , the setting range of the fourth current density value is 0.55 to 0.65 A/cm ² .

Wherein, the preferred purging scheme corresponding to Example 2 is determined as shown in Figure 2:

Control the airflow back pressure of the first purge stage to be 0, and control the flow rate of the purge airflow in the first purge stage to be the anode corresponding to the current density of 0.2±0.01 A/cm ² when the stack is operating. The volume flow value of the required gas, until the impedance of the stack reaches 60% of the target impedance value;

Wait 2±0.3 min;

Control the airflow back pressure of the second purge stage to increase from 10±0.1 kPa to 30±0.1 kPa, and control the flow rate of the purge airflow in the second purge stage to be 0.2±0.2± The volume flow value of the gas required for the anode corresponding to 0.01 A/cm ² is increased to the volume flow value of the gas required for the anode corresponding to the current density of 0.5±0.01 A/cm ² until the monitored impedance of the stack reaches 95% of the target impedance value. %; in this process, the growth rate of airflow back pressure and airflow flow can be adjusted. On the premise that airflow back pressure and airflow can be increased to the above-mentioned endpoint values before the end of this stage, the slower or the slowest growth can be selected. speed, try to use a uniform growth method to reach the end point, in order to achieve a better purging effect.

Wait 3±0.5 min;

Control the airflow back pressure of the third purging stage to increase from 10±0.1 kPa to 25±0.1 kPa, decrease to 10±0.1 kPa and then increase to 35±0.1 kPa, and control the purging of the third purging stage The flow rate of the gas flow is increased from the volume flow value of the gas required by the anode corresponding to the current density of 0.2 ± 0.01 A/cm ² when the stack is running to the value of the volume flow rate of the gas required by the anode corresponding to the current density of 0.45 ± 0.01 A/cm ² , decrease to the volume flow value of the gas required for the anode corresponding to the current density of 0.2 ± 0.01 A/cm ² and then increase to the volume flow value of the gas required for the anode corresponding to the current density of 0.6 ± 0.01 A/cm ² until the stack is monitored. The impedance reaches 100% of the target impedance value; in this process, the increase/decrease/re-increase speed of the airflow back pressure and airflow flow rate can be adjusted, and the airflow back pressure and airflow flow rate can be increased to the above-mentioned endpoint values before the end of this stage Under the premise of , you can choose the slowest or slowest growth/decline/re-increase speed, and try to use the method of uniform growth/decline/re-increase to reach the end point to achieve better purging effect.

The present invention aims to provide a fuel cell purging method that is reasonably divided into three stages, each of which has a core strategy: in the early stage, a moderate air flow is used to blow out most of the liquid in the stack, and in the middle stage, a gradually increased air flow is used to blow out the remaining liquid. The vast majority of the liquid in the pump, taking into account the air consumption and the purging efficiency, the later stage uses the air flow that gradually strengthens, weakens and gradually strengthens to blow to the end point, and uses the waiting time period between each stage to weaken the internal resistance value after the purging is completed. phenomenon of slow decline.

It should be noted that, in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any relationship between these entities or operations. any such actual relationship or sequence exists. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device that includes a list of elements includes not only those elements, but also includes not explicitly listed or other elements inherent to such a process, method, article or apparatus. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in a process, method, article or apparatus that includes the element.

The above are only specific embodiments of the present application. It should be pointed out that for those skilled in the art, without departing from the principles of the present application, several improvements and modifications can also be made. It should be regarded as the protection scope of this application.

Claims (13)

1. A fuel cell purge method of purging water from a fuel cell stack after shutdown of the stack, wherein the impedance of the stack is monitored during the purge, the purge method comprising purging in three purge stages:

in the first blowing stage, air flow is introduced into the cell stack for blowing in a constant-pressure constant-flow mode until the impedance of the cell stack is monitored to reach a preset first impedance threshold, wherein the set range of the first impedance threshold is 50-70% of a target impedance value;

in the second purging stage, gas flow is introduced into the cell stack for purging in a pressure-boosting and flow-boosting mode until the monitored impedance of the cell stack reaches a preset second impedance threshold value, wherein the set range of the second impedance threshold value is 85% -100% of the target impedance value;

and in the third purging stage, the gas flow is introduced into the cell stack for purging in a mode of increasing the pressure and increasing the flow rate and then decreasing the pressure and decreasing the flow rate until the impedance of the cell stack is monitored to reach a preset third impedance threshold, wherein the set range of the third impedance threshold is 98-100% of the target impedance value.

2. A fuel cell purge method according to claim 1, wherein the third purge stage is configured to purge the stack by raising the pressure and raising the flow rate before lowering the pressure and lowering the flow rate, until the stack impedance is monitored to reach a preset third impedance threshold, wherein the second raised flow back pressure value is greater than the first raised flow back pressure value, and the second raised flow rate value is greater than the first raised flow rate value.

3. A fuel cell purge method according to claim 1 or 2, wherein the volume flow rate of the purge gas flow of the first purge stage is controlled so that the current density is between 0.1 and 0.3A/cm when the stack is in operation ² The volume flow value of the gas required by the corresponding anode; controlling the volume flow of the purge gas flow of the second purge stage from the volume flow value of the anode required gas corresponding to the first current density value to the volume flow value of the anode required gas corresponding to the second current density value when the galvanic pile is operated, wherein the first current density value is set to be in the range of 0.1 to 0.3A/cm ² Setting of the second current density valueIn the range of 0.3 to 0.7A/cm ² 。

4. The fuel cell purge method according to claim 3, wherein the flow rate of the purge gas in the third purge stage is controlled by increasing the volume flow rate of the anode required gas corresponding to the first current density value to the volume flow rate of the anode required gas corresponding to the third current density value, decreasing the volume flow rate of the anode required gas corresponding to the first current density value, and increasing the volume flow rate of the anode required gas corresponding to the fourth current density value, wherein the first current density value is set in a range of 0.1 to 0.3A/cm ² The third current density value is set within the range of 0.4 to 0.5A/cm ² The fourth current density value is set within the range of 0.5 to 0.8A/cm ² ；

The flow rate of the initial purge gas flow of the second purge stage is the same as or different from the flow rate of the initial purge gas flow of the third purge stage.

5. A fuel cell purge method according to claim 1, 2 or 4, wherein the flow rate of the gas flow is calculated by the following formula:

wherein, in the step (A),vthe volumetric flow of the gas required by the anode for the operation of the stack,jis the current density of the electric pile,Athe reaction area is the area of reaction,athe number of single cell sections contained in the electric pile,Sin the form of a stoichiometric ratio,V _m is the molar volume of the gas,ntransferring the number of electrons for the reaction;Fis the Faraday constant inC/mol。

6. A fuel cell purge method according to claim 1 or 2, wherein the gas flow back pressure of the first purge stage is controlled to be less than 0.2kPa, the gas flow back pressure of the second purge stage is controlled to be increased from a first pressure value to a second pressure value, wherein the first pressure value is set to range from 2 to 20 kPa, the second pressure value is set to range from 15 to 40 kPa, and the first pressure value is smaller than the second pressure value.

7. The fuel cell purge method according to claim 6, wherein the gas flow back pressure in the third purge stage is controlled to increase from a first pressure value to a third pressure value, decrease to the first pressure value and then increase to a fourth pressure value, wherein the first pressure value is set within a range of 2 to 20 kPa, the third pressure value is set within a range of 20 to 40 kPa, the fourth pressure value is set within a range of 20 to 40 kPa, and the third pressure value is smaller than the fourth pressure value.

8. The fuel cell purge method of claim 7, wherein the first pressure value of the second purge stage is the same as or different from the first pressure value of the third purge stage; alternatively, the back pressure of the purge gas flow of the first purge stage is 0.

9. A fuel cell purge method according to claim 2, wherein the second purge stage is started after waiting a first period of time set in a range of 1 to 5 min after the first purge stage is completed;

after the second purging stage is finished, starting the third purging stage after waiting for a second time period, wherein the set range of the second time period is 1-5 min;

the set value of the first time period is the same as or different from that of the second time period.

10. A fuel cell purge method as claimed in claim 1, wherein the target impedance value is a qualified impedance value of the stack at a moisture content condition that meets a fuel cell stack product shutdown requirement.

11. A fuel cell purge method according to any one of claims 2, 4, 7, 8, 9, further comprising: a plurality of blowing schemes are formulated, at least one blowing parameter is different among the blowing schemes, and the blowing effect of different blowing schemes is compared to determine a better blowing scheme;

wherein the purging effect is evaluated in the following manner:

and counting the gas flow consumption of the first purging stage, the second purging stage and the third purging stage, and/or counting the purging time from the beginning of the first purging stage to the end of the third purging stage.

12. A fuel cell purge method as claimed in claim 11, wherein the preferred purge strategy is determined as:

controlling the gas flow back pressure of the first blowing stage to be less than 0.1 kPa, and controlling the flow of the blowing gas flow of the first blowing stage to ensure that the current density is between 0.15 and 0.25A/cm when the galvanic pile operates ² The volume flow value of the gas required by the corresponding anode is calculated until the impedance of the galvanic pile reaches a preset first impedance threshold value, wherein the set range of the first impedance threshold value is 58-62% of the target impedance value;

controlling the gas flow back pressure of the second purging stage to be increased from a first pressure value to a second pressure value, and controlling the flow of the purging gas flow of the second purging stage to be increased from the volume flow value of the anode required gas corresponding to the first current density value to the volume flow value of the anode required gas corresponding to the second current density value when the galvanic pile operates until the impedance of the galvanic pile is monitored to reach a preset second impedance threshold value, wherein the set range of the second impedance threshold value is 92% -98% of the target impedance value, the set range of the first pressure value is 8-12 kPa, the set range of the second pressure value is 20-35 kPa, and the set range of the first current density value is 0.15-0.25A/cm ² The second current density value is set within the range of 0.4 to 0.6A/cm ² ；

Controlling the gas flow back pressure of the third purging stage to increase from a first pressure value to a third pressure value, decrease to the first pressure value and increase to a fourth pressure value, and controlling the flow of the purging gas flow of the third purging stage to be controlled by the electricityWhen the reactor is operated, the volume flow value of the anode required gas corresponding to the first current density value is increased to the volume flow value of the anode required gas corresponding to the third current density value, the volume flow value of the anode required gas corresponding to the first current density value is reduced to the volume flow value of the anode required gas corresponding to the first current density value, and the volume flow value of the anode required gas corresponding to the fourth current density value is increased to the volume flow value of the anode required gas corresponding to the fourth current density value until the impedance of the galvanic pile is monitored to reach a preset third impedance threshold value, wherein the set range of the third impedance threshold value is 99% -100% of the target impedance value, the set range of the first pressure value is 8-12 kPa, the set range of the third pressure value is 22-28 kPa, the set range of the fourth pressure value is 32-40 kPa, and the set range of the first current density value is 0.15-0.25A/cm ² The third current density value is set within the range of 0.42A/cm ² To 0.48A/cm ² The fourth current density value is set within the range of 0.55 to 0.65A/cm ² 。

13. A fuel cell purge method as claimed in claim 11, wherein the preferred purge strategy is determined as:

controlling the airflow backpressure of the first blowing stage to be 0, and controlling the flow of the blowing airflow of the first blowing stage to be 0.2 +/-0.01A/cm of current density when the galvanic pile operates ² The volume flow value of the gas required by the corresponding anode is up to 60% of the target impedance value;

waiting for 2 +/-0.3 min;

controlling the gas flow back pressure of the second purging stage to be increased from 10 +/-0.1 kPa to 30 +/-0.1 kPa, and controlling the flow of the purging gas flow of the second purging stage to be increased from the current density of 0.2 +/-0.01A/cm when the galvanic pile runs ² The volume flow value of the gas required by the corresponding anode is increased to the current density of 0.5 +/-0.01A/cm ² The volume flow value of the gas required by the corresponding anode is detected until the impedance of the galvanic pile reaches 95% of the target impedance value;

waiting for 3 +/-0.5 min;

controlling the gas flow back pressure of the third purging stage to increase from 10 +/-0.1 kPa to 25 +/-0.1 kPa, decrease to 10 +/-0.1 kPa and increase to35 +/-0.1 kPa, and the flow of the purge gas flow of the third purge stage is controlled by the current density of 0.2 +/-0.01A/cm when the galvanic pile operates ² The volume flow value of the gas required by the corresponding anode is increased to 0.45 +/-0.01A/cm of current density ² The volume flow value of the gas required by the anode is reduced to 0.2 +/-0.01A/cm of current density ² The volume flow value of the gas required by the corresponding anode is increased to 0.6 +/-0.01A/cm of current density ² And the volume flow value of the gas required by the corresponding anode is detected until the impedance of the galvanic pile reaches 100 percent of the target impedance value.

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