JPH04171669A - Fuel cell - Google Patents

Abstract

PURPOSE:To avoid the reduction of the life characteristic due to gas deficiency worried when a load is abruptly increased without reducing the plant efficiency or increasing the installation area by providing a control means increasing/ decreasing the inlet pressure of the reaction gas according to the fuel cell operation mode. CONSTITUTION:The pressure of a pressure transmitter 7 connected to a fuel gas inlet manifold is controlled by a pressure adjusting valve 11 installed on a discharge side pipe 4. The pressure signal, load signal and linkage/single operation mode transfer signal are concurrently inputted to a sequencer controlling the inlet pressure, and the inlet pressure is controlled based on the preset load/pressure relational expression. The feed delay of the reformed gas against the abrupt increase of the load is compensated. The excess auxiliary machine power and pipe parts of a buffer tank and the like are not required, the reduction of the life characteristic due to the fuel gas deficiency when the load is abruptly increased is prevented, the reduction of efficiency is prevented, and a fuel cell can be made compact.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel cell, and particularly to a fuel cell that focuses on the deterioration of the characteristics of the cell main body due to sudden changes in load.

[Conventional technology] Fuel cells have been introduced into the market as a clean and highly efficient power generation system for distributed power generation plans in the suburbs of cities and on-site power generation systems for individual installation at consumers. has begun.

The specifications required for a power generation system include not only cost, but also long-term stable life characteristics, high followability to fluctuations in the user's power load, and compact installation space and volume. is necessary.

Conventional power generation systems, especially on-site competing gas turbines and diesel power plants, are designed to respond instantaneously to these load fluctuations, and of course fuel cells are also designed to respond instantaneously to these load fluctuations. response is required.

However, fuel cells differ from other power generation plans I.
Because the reformer simultaneously performs a reforming reaction using raw materials such as natural gas and methanol, there was a delay in response comparable to that of a chemical plant.

For this reason, the supply response of reformed gas as fuel waste is delayed in response to sudden load fluctuations, and especially when the load increases rapidly, the utilization rate of fuel gas increases for the fuel cell, resulting in fuel starvation. In particular, in phosphoric acid fuel cells, there was a high possibility that the life characteristics would deteriorate due to damage to the cell electrodes.

This situation is shown in FIG. That is, since the increase in the supply of reactant gas is delayed in response to the increase in load, the reactant gas utilization rate of the battery body increases beyond OO% per month, and as a result, the voltage of the battery drops rapidly. This voltage drop is likely to damage the battery and reduce its life characteristics.

′ When operating in conjunction with grid power in power generation mode, if a sudden load rises, the grid power is switched off to compensate for the delay in the supply of reactant gas. The increased amount can be supplied in parallel, and gas starvation can be avoided. However, in the case of independent operation, all the increase in load is applied as a load to the battery, and some kind of workaround is required to prevent this gas shortage condition.

Therefore, as a countermeasure for this problem, Japanese Patent Application Laid-Open No. 1-3159
As disclosed in Publication No. 57, in order to prevent gas shortage due to sudden load increase, a reformer (
Fuel supply piping (3) from 2) to fuel cell body 1)
A method has been proposed in which a pipe is provided connecting the battery body (1) and a discharge pipe (4) from the battery body (1), and a buffer tank (5) and a blower (6) are further provided in the pipe.

With this configuration, the exhaust gas is always recycled by the blower (6) and unconsumed fuel gas is accumulated in the buffer tank (5), thereby reducing the delay in increasing the supply of reformed gas when the load increases. Even in the event of a fuel gas shortage, the unconsumed fuel gas stored in the buffer tank (5) compensates, thereby avoiding a fuel gas shortage situation.

[Problems to be Solved by the Invention] =4= In the conventional fuel cell as described in 2 below, a buffer tank and a blower are provided in the piping in order to prevent a shortage of scum due to a delay in increasing the supply of fuel gas. However, in such a configuration, electric power is required for the blower, resulting in a decrease in power generation efficiency, and the installation of a buffer tank and blower, which require a large capacity, significantly increases the normally required installation space. In particular, this becomes an obstacle to meeting the compact specifications required by on-site type I users.

This invention was made to solve the above problems, and by compensating for delays in reformed gas supply due to sudden increases in load, it eliminates the need for extra auxiliary power and piping parts such as buffer tanks. The object of the present invention is to provide a fuel cell that can prevent a decrease in life characteristics due to a lack of fuel gas when the load is suddenly increased, prevent a decrease in efficiency, and achieve compactness.

Means for Solving 1 Problem] The fuel cell according to the first aspect of the present invention is equipped with means for increasing or decreasing the inlet pressure of the reactant gas depending on the operation mode.

Further, in the fuel cell according to the second invention, the volume of the inlet manifold for the reaction scum is larger than the volume of the outflow manifold.

Furthermore, in the fuel cell according to the third aspect of the invention, the horizontal cross-sectional area of the inlet manifold for the reaction gas is greater than or equal to the effective reaction area of the cell body.

[Function] The reaction gas supply amount Qs of the fuel cell is the gas consumption amount Q due to the cell reaction. The amount divided by a certain usage rate is set. That is, -F QB=Qc/UxlOO (2 formulas) Qc: Gas consumption [m3/hr] No.: Number of cells in the battery body
[-] ■: Battery current [A] n 5 reaction order [-] F: Faraday constant [8 s/mol] Vo:
Volume per mol [m37mol]QB gas supply M [m3/hr]U ・Gas utilization rate
[%].

Since an increase in load means an increase in battery current (2), QC increases, and in order to keep the utilization factor U constant, an increase in Q5 is required.

However, as described above, the supply increase in the reformed waste supply amount Q□ is delayed in response to a sudden increase in load.

Therefore, the inlet manifold volume ■. Therefore, we are considering the use of the reactant gas inside.

Normally, in the artificial manifold of the fuel cell main body, the pressure loss in the cell flow path and the pressure loss in the discharge piping are added to 100.
It has a pressure of about ~200 mmAq.

Q due to sudden increase in load. In other words, an increase in the amount of exhaust gas is accompanied by a decrease in the amount of exhaust gas, so the inlet pressure decreases due to the decrease in pressure drop on the exhaust side, and when this pressure decreases, the pressure bone reaction gas that was previously in the inlet manifold is supplied to the battery. will be done.

This amount is expressed by the following three formulas.

9.81 PM x VN Vp -X Vo (3 formulas) VP: Accumulated gas amount in the inlet manifold [m3] PM: Pressure in the inlet manifold [to mm8] VM: Inlet manifold volume [m3] R: Gas constant
[J/ni/mol]T: Gas? quality
[K] This accumulated gas amount V9 is supplied as a reaction gas to the battery for t seconds until it runs out of gas due to the supply delay time, so the reformed reaction mass flow rate Q during this period is
R and reaction gas consumption Q in the battery. 1° is expressed as in equation 4.

In order to compensate for the delay in increasing the supply of reaction gas to the reformer by increasing the length of the reaction gas, it is effective to increase (2).

That is, in order to increase ■2, as expressed by equation 3, 1) Increase the inlet Mayubold internal pressure P (first invention) 2) Inlet Romanifold volume ■. There are two possible ways to increase this (second and third inventions).

[Example] Hereinafter, an example of the first invention will be described with reference to FIGS. 1 to 3. In FIG. 1, a pressure signal device (7) is connected to a fuel gas-filled Romanibold to which a fuel gas supply pipe (3) to a fuel cell main body (1) is connected. A pressure signal device (10) is also connected to the air inlet manifold to which the air supply pipe (9) from the blower (8) is connected. Pressure signal (7).

(10), the fuel exhaust gas pressure regulating valve (11), and the air exhaust gas pressure regulating valve (12) are each operated by an arithmetic controller (13).
It is connected to the. The detection signal of the load detector (14) is input to the arithmetic controller (13).

With the above configuration, the pressure of the pressure transmitter (7) connected to the fuel gas manifold is controlled by the pressure control valve (11) installed in the discharge side pipe (4).

This pressure signal and a load signal and cooperative/independent operation mode switching signal are simultaneously input to a sequencer that controls the inlet pressure, and the inlet pressure is controlled based on a preset load-pressure relational expression.

The relationship in this setting is shown in FIG. As shown in this figure, as the load increases, the difference between working and independent becomes smaller, but this is because the leakage of reactant gas to the outside from the manifold seal increases as the pressure increases, so This is because we want to keep the number small, and as the load increases, the rate of increase in the utilization rate due to a sudden increase in load becomes smaller.

In other words, when the load increases by 20%, the utilization rate doubles from 20 to 40%, but only 1.25 times from 80 to 100%.

Figure 3 shows how the characteristics change when the load suddenly increases when these measures are taken.

By optimally controlling the inlet manifold as described above, reactive gas is sufficiently accumulated in the inlet manifold iz, and as a result, as shown in Fig. 3, an excessive increase in the utilization factor can be avoided, and the battery voltage can be reduced. The decrease in the battery voltage is also minimal, and the battery can be avoided from damage.

FIG. 4 shows another embodiment of the first invention, in which (15) is a fuel exhaust gas heat exchanger, (16) is an air exhaust gas heat exchanger, and the same reference numerals as in FIG. This is a considerable portion.

With the above configuration, the heat exchanger (15) of the exhaust gas system piping, which is usually installed for exhaust heat recovery and residual heat of raw material gas, etc.
A bypass is provided for the bypass, and a cutoff valve (11
) are controlled to open and close by the sequencer.

That is, in independent operation, since it is desirable that the inlet pressure be high, the bypass cutoff valve is closed, and in coordinated operation, the cutoff valve is opened to prevent passage of the bypass pipe.

Although this control method is the simplest, it is necessary to carefully design the pressure drop of this heat exchanger in order to ensure compensation for the sudden increase in load at light loads.

Next, an embodiment of the second invention, in which the volume of the inlet manifold is made larger than the volume of the outlet manifold, will be described.

10 where the electrode area per cell is 3500cm3 class
The manifold, which was designed to uniformly supply reactant gas to each cell in a one-scale fuel cell stack based on airflow analysis, was 0.64 m'. At this time, the number of cells per stack is 300 cells, and the fuel utilization rate is 75.
%Met.

The procedure for designing the required volume of the inlet manifold when the increase in the amount of reformed fuel follows the load increase from 100A to 200A within 5 seconds is as follows.

In the first set, PM is 200 mmAq, and the T of the third set is
is 200°C.

Q from this. , QI] are each;, Q 8= 16.7 [No+'/
hr], and ■2 is also calculated as 8.314×463, so if you substitute this into equation 4 and rearrange it, you get 0.0115V.

5 < -x3600 25.1-16.7 °, V, > 1.01 [m']
(Equation 5) % Equation % Since the result of the airflow analysis is the design volume of the outlet manifold, the volume 8 obtained here has a volume that is approximately 1.6 times that volume. This situation is shown in Figure 5.

Of course, it is preferable to make the design volume approximately twice as large as possible, taking into account the margin.

Furthermore, if the pressure control described above is performed at the same time, the pressure setting can be made smaller and the manifold volume can also be made smaller.

However, the outlet manifold volume could be as large as the inlet manifold, but this would result in wasted space throughout the blunt.

As another configuration, the same effect can be obtained even if the diameter of the inlet pipe is made larger.

Furthermore, an embodiment of the third invention will be described.

Since the effective reaction area of the cell is 3500 cm2,
The inlet manifold was designed to have a cross-sectional area larger than this reaction area.

In this case, since the cell thickness per cell including the thickness of the cooling plate is approximately 1 CITl, first, the inlet manifold volume per cell is V. seek.

V, = 3500X1/1000=3.4 [
1/cell] Since the stack is composed of 300 cells, the total volume of the inlet manifold VM is calculated as follows: V, = 3.4x300/1000 =], 05
[m3].

This value is the Mayuhole 1~volume that is sufficient to compensate for the delay in fuel gas supply when the load suddenly increases, as determined by Equation 5.
This is a value larger than 1.01m3.

That is, from this relationship, the necessary inlet manifold volume can be achieved by making the horizontal cross-sectional area of the manifold equal to or larger than the effective reaction area of the cell.

In this way, by increasing the pressure or volume of the inlet manifold, it is possible to avoid a gas shortage situation due to a sudden increase in load, and the associated changes in equipment specifications include the outlet pressure regulating valve and its control. This is done by installing equipment.

In addition, when designing a manifold, the size and shape are usually designed based on the results of airflow analysis to prevent uneven gas flow in the vertical and horizontal directions.
A sufficient effect can be obtained by increasing the manifold volume to increase the gas storage charge by increasing the manifold thickness designed by air flow analysis by several tens of centimeters.

Therefore, as a result of the design changes made by the present invention, the overall installation area and plant incidental equipment costs will increase.
It is so small that it can be ignored.

In addition, when increasing the pressure and volume of the inlet manifold, consider not only the fuel-side inlet manifold but also the air-side inlet manifold if the blower for supplying oxidizing gas such as air is slow to follow the load increase. There is a need.

[Effects of the Invention] As described above, according to the present invention, by increasing the pressure of the reaction gas in the inlet manifold and/or increasing the volume of the inlet manifold, sudden loads can be reduced. Sufficient reactant gas has been accumulated to compensate for the delay in increasing the reactant gas supply to the reformer during the rise.

As a result, the plant efficiency decreases and the installation area increases.
It was possible to completely avoid the deterioration in life characteristics due to lack of gas, which was a concern when the load suddenly increased.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an embodiment of the first invention, Fig. 2 is a load-population pressure characteristic diagram, Fig. 3 is a diagram of each characteristic change, and Fig. 4 is a diagram of the characteristic changes of the first invention. A system diagram of another embodiment, FIG. 5 is a schematic diagram of main parts for explaining an embodiment of the second invention, FIG. 6 is a line diagram of each characteristic change of a conventional fuel cell, and FIG.
The figure is also a system diagram. (1)・Fuel cell main body, (2)・Reformer, (3)・
Fuel gas supply piping, (4)...Fuel exhaust gas piping, (7)
- Fuel stone input pressure transmitter, (11)...Fuel exhaust gas pressure regulating valve (heat exchanger bypass valve), (13)...Arithmetic controller, (14)-Load detector, (15)...Fuel Exhaust gas heat exchanger. In each figure, the same reference numerals indicate the same or corresponding parts. Representative Person Zeng I Teru 81 [secl

Claims (3)

[Claims] (1) A fuel cell that generates electricity by supplying fuel gas and oxidant gas as reaction gases, characterized in that the fuel cell comprises a control means for increasing or decreasing the inlet pressure of the reaction gas depending on the fuel cell operation mode. (2) In a fuel cell in which fuel gas and oxidizing gas are used as reaction gases, and this reaction gas is supplied to the cell through an inlet manifold and discharged from an outlet manifold, the inlet manifold has a volume larger than the volume of the outlet manifold. A fuel cell characterized by comprising: (3) In a fuel cell in which fuel gas and oxidant gas are used as reaction gases, and this reaction gas is supplied to the cell via an inlet manifold and discharged from an outlet manifold, the horizontal cross-sectional area is larger than the effective reaction area of the cell body. A fuel cell comprising: the inlet manifold having the inlet manifold.