JPS62186472A - Fuel system controller for fuel cell power generation plant - Google Patents

Abstract

PURPOSE:To make fuel gas flow rate quickly follow its target value while keeping a reformer reaction tube temperature constant by controlling the quantity of fuel supplied to a reformer auxiliary burner in accordance to the difference between the balance energy and the compensating energy of the reformer. CONSTITUTION:Balance energy in a reformer 15 is obtained by a heat balance computer 35 by introducing therein such data as combustion energy signal E, row fuel flow rate signal F2, exhaust gas flow rate signal F3, exhaust gas temperature signal T2 and reforming rate x. The heat balance computer 35 also takes in a signal representing the difference between target temperature signal RTT of a reformer reaction tube 16 and actual temperature signal T1 obtained with a thermometer 28 to obtain the compensating energy required to maintain the reaction tube 16 at the target temperature by means of a compensating energy computer 34. Then the quantity of fuel supplied to a reformer auxiliary burner 23 is controlled in accordance to the difference between the compensating energy and balance energy through an auxiliary burner output computer 33.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel system control device for a fuel cell (hereinafter referred to as FC) power plant, and more particularly.

A fuel reformer (reformer) reacts raw fuel containing hydrocarbons with water to reform it into fuel gas containing hydrogen as a main component, and supplies this fuel gas to the fuel cell as a reducing agent, as well as the above. The present invention relates to a control m+ device that is capable of always stably maintaining a refoher temperature in a fuel system in which fuel exhaust gas discharged from a fuel cell is combusted as a heat source necessary for reforming in a refohmer.

(Technical background of the invention and its problems) As is well known, an FC power plant consists of a power section that generates electricity, and a fuel section that produces hydrogen-rich fuel gas.
and an air system that pressurizes air and supplies it to the FC.

It consists of a thermal management system that controls the temperature of the FC.

By the way, what about the fuel system of an FC power plant?

Normally, as shown in Figure 6, there is a re-former 1 that adds water vapor to raw fuel gas containing hydrocarbons as its main component to convert it into hydrogen-rich fuel gas, and a re-former 1 that adds water vapor to carbon monoxide produced in this re-former 1. and a shift converter 2 that generates hydrogen. Since the reforming reaction that changes hydrocarbons into hydrogen is an endothermic reaction, the fuel gas after passing through the FC 4 via the flow control valve 3 (
Hereinafter, it will be referred to as FC fuel exhaust gas. ) to refill the burner 5
By combusting the hydrogen in this FC fuel exhaust gas, the amount of heat required for the reaction in the reformer 1 is reduced by 1q. Further, the temperature of the re-former 1 is controlled by adjusting the flow control valve 3.

However, the conventional fuel system configured as described above has the following problems.

In other words, it takes a long time for the temperature of the re-former 1 to stabilize after operating the flow control valve 3, and even if the fuel gas flow layer is the same, the hydrogen concentration and residual hydrocarbon concentration in the FC fuel exhaust gas may Since the combustion energy differs greatly, it is extremely difficult to control the temperature of the refoamer 1 to keep it constant. - For example, the tube temperature fluctuates greatly and it is not easy to stabilize it. Such vibrations not only cause unnecessary thermal fatigue to the reformer reaction tube and shorten its lifespan, but also make the reforming reaction rate unstable, inhibiting the supply of fuel gas to the FC4, and making quick load response difficult. was.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to provide a fuel cell that can quickly make the fuel gas flow rate follow a target value while keeping the temperature of the re-former reaction tube constant. An object of the present invention is to provide a fuel system control device for a power plant.

[Summary of the invention]

The control device according to the present invention reformes raw fuel containing hydrocarbons as a main component with water in a reformer to reform it into a fuel gas containing hydrogen as a main component, and supplies this fuel gas to a fuel cell as a reducing agent. At the same time, the fuel system of a fuel cell power generation plant is controlled, in which the fuel exhaust gas discharged from the fuel cell is combusted as a heat source necessary for reforming in the reformer. In order to control such a system, a control device according to the present invention includes a reheater main burner that burns fuel exhaust gas discharged from a fuel cell in a reheater, a reheater auxiliary burner connected to a fuel supply source, Means for calculating correction energy for maintaining the temperature of the refohmer reaction tube at the target temperature from the difference between the target temperature of the refohmer reaction tube and the actual temperature; the combustion energy of the fuel exhaust gas supplied to the refoamer main burner from the reforming rate determined by this means, the load current of the fuel $1 cell, and the flow rate of the fuel gas supplied to the fuel cell; means for calculating, from the flow rate of the raw fuel flowing into the reformer, the flow rate and temperature of the combustion exhaust gas discharged from the reformer, and the reforming rate; Means for determining the balance energy in the re-boomer from the difference between the energy and the balance energy, and means for controlling the amount of fuel supplied to the ref-o-mer auxiliary burner in accordance with the difference between the correction energy and the balance energy are provided.

〔Effect of the invention〕

With the above configuration, the heat balance of the refoamer is constantly calculated and the amount of fuel supplied to the auxiliary refoamer burner is controlled accordingly, so it is stable without being affected by changes in the composition of the FC fuel exhaust gas. It becomes possible to control the temperature of the re-former, making it significantly easier to control the temperature of the re-former. In addition, since a refohmer auxiliary burner is installed in the refohmer combustion chamber as a control end for the refohmer temperature, unlike the conventional 1I11 control using a valve installed on the upstream side of the FC, the operating end is operated. This can shorten the time it takes for a change in temperature to appear. For this reason.

Fast tracking performance and high disturbance suppression performance can be achieved.

[Embodiments of the invention]

Two embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the main parts of a fuel cell power plant incorporating a control device according to an embodiment of the present invention.

That is, in FIG. 2, numeral 41 indicates a supply end for raw fuel containing hydrocarbon as a main component, and numeral 12 indicates a supply end for water vapor. The raw fuel and steam supplied to each supply end 11.12 are
After being led and joined by pipes 13 and 14, the gas is led to the re-former reaction tube 16 of the re-former 15 and reformed into a fuel gas containing hydrogen as a main component. Refoma reaction tube 16
The fuel gas sent out is sent to the FCI 8 as a reducing agent via a shift converter and a flow control valve 17 (not shown). Then, the fuel exhaust gas discharged from the FCI 8 is supplied to the reheater main burner 20 via the pipe 19. On the other hand, a part of the raw fuel supplied to the supply end 11 is transferred to the pipe 2). It is supplied to the reheater auxiliary burner 23 via the flow control valve 22.

In the figure, 24 indicates a flow meter for measuring the flow rate of fuel gas supplied to the FCI 8, 25 indicates a flow meter for measuring the flow rate of raw fuel flowing into the re-former reaction tube 16, and 26 indicates a flow meter for measuring the flow rate of the fuel gas supplied to the FCI 8. 27 is a flow meter for measuring the flow rate of combustion exhaust gas in the refoamer 15, 27 is a flowmeter for measuring the flow rate of raw fuel supplied to the refoamer auxiliary burner 23, and 28 is a flowmeter for measuring the humidity of the refoamer reaction tube 16. A thermometer for measuring the temperature is shown, and 29 is a concentration meter for measuring the temperature of the combustion exhaust gas. Also.

In the figure, numeral 30 indicates a fuel flow calculator that calculates a fuel flow rate corresponding to the load request command LP and outputs a fuel flow signal as shown in FIG. given to. The controller 31 is
The output of the calculator 30 and the flow rate signal F1 obtained by the flow meter 24
The opening degree of the flow regulating valve 17 is controlled so that the flow rate signal F1 matches the output of the computing unit 30. In addition, 32 in Figure 2 indicates a controller, and this controller 32 compares the flow rate signal F4 obtained by the flow meter 27 and the output M of an auxiliary burner output calculator 33, which will be described later.
The opening degree of the flow regulating valve 22 is controlled so that the flow rate signal F4 matches the output M.

Therefore, the flow rate signals Fl, F2, F! obtained by the flow meters 24, 25, 26 are obtained. The temperature signals Ti and T2 obtained by the thermometers 28 and 29 are introduced into the auxiliary burner output calculator 33. This auxiliary burner output calculator 33 is for calculating the heat balance of the ref. It is configured as shown in the figure. That is, the main parts of this calculator 33 are roughly divided into a correction energy calculator 34 and a heat balance calculator 35.
, a burner output calculator 36 for estimating the output of the re-former main burner 20, a reforming rate calculator 37, and a divider 38.

The correction energy calculator 34 introduces a difference signal between the target temperature signal RTT of the re-homer reaction tube 16 and the actual temperature signal T1 obtained by the thermometer 28 via the subtracter 39, and calculates the PI.
It is used to perform calculations and calculate correction energy for maintaining the reformer reaction tube 16 at the target concentration. and.

The corrected energy signal G calculated by the corrected energy calculator 34 is introduced into one input terminal of the subtracter 40.

The reforming rate calculator 37 estimates the rate of progress of the first-order reaction expressed by equation (1) in the refohmer 15 and the shift converter from the temperature of the refohmer reaction tube 16, that is, the temperature signal T1 obtained from the thermometer 28. It is for the purpose of

CH4+2H20→4H2+CO2...(1) The rate of progress of this reaction, that is, the reforming rate, is actually determined by temperature and other factors.
Although it varies depending on the pressure and the flow rate of raw fuel (the above equation is for methane), in an FC power plant, all conditions except temperature can be considered to be almost constant, and as shown in Figure 4, the higher the temperature, the higher the reforming rate. approach.

Therefore, in this embodiment, the reforming rate is calculated based on the temperature signal T1.

The burner output calculator 36 is for estimating the combustion energy in the refoamer main burner 20 using the reforming rate X calculated by the reforming rate calculator 37. That is, this calculator 36 calculates the flow rate signal F1 of the flow meter 24, the reforming rate X, and the load? [Introducing the wave signal l oad and using the 9th order Equation (2) and (3), calculate the FC fuel exhaust gas 111F,x flowing into the refoamer main burner 20 and its energy density EM
The combustion energy is calculated from this.

F,, -Fand -kl x Load
-(2) 2 to E□- (3 to A-, 4 to Fand-, Eg2, L Oad) / F xx
-(3 However.

F, : FC fuel exhaust gas flow m (kgmol/hr)
E, X: Combustion energy per unit volume of FC fuel exhaust gas (
kcai/kgIol) Fand: Fuel gas flow rate (ki
Load: FC load current (A>A:C/DC:(1-x)E+4xE,.

m4 D: 1+4X EcR4; (-'T(, combustion energy (-22), 8
kcal/101. 1at125℃) E! ! 2 ; Combustion energy of H2 (-57.8kcal
/ 1 dol.

1at12S℃) X: Modification rate! 4; Constant *The combustion energy signal E obtained by multiplying *Fxx and Emx in this way is sent to the heat balance calculator 35.
will be introduced to

The heat balance calculator 35 receives the combustion energy signal @E.

Raw fuel flow rate signal F2 and exhaust gas flow rate signal F3.

An exhaust gas temperature signal T2 and a reforming rate X are introduced.

This is for calculating the heat balance in the re-former 15 using the following equations (4) to (7).

Qb = Qy - Qtux - Qnp ・
...(4) Qy = Flr-E-z
...(5) QRF -ks -Fo -
T5...(6)QRF-Exy
"Fz"X"・(7)
however.

Qb ; heat balance (kcal/hr) QF ; reheater main burner output (kcal/hr) Q
*x: Exhaust gas heat removal fi (kcal/hr) Ql; Reformed gas heat absorption m (kc'al/hr) Fo: Exhaust gas flow 1 (knot/hr) Ta; Exhaust gas temperature ('
C) EFIF; amount of endotherm due to reforming reaction (kca
l/.

kgmoi) Fx; Raw fuel supply 1 (koiol/hr)ks
;Constant (kcal/kga+ol-"C) In this way, the heat balance signal T (calculated by the heat balance calculator 35) is introduced into the other input terminal of the subtractor 840. The output is introduced into a divider 38. This divider 38 divides the output signal Y of the reduction unit 40 by the combustion energy J in unit *m of raw fuel known in advance. This signal M is then given to the controller 32 as a flow control signal.Therefore, the reheater auxiliary burner 23 is always supplied with the following signal M.

The amount of fuel necessary to maintain the temperature of the reformer reaction tube 16 constant will be supplied.

In this way, the refoamer auxiliary burner 23 is provided, the heat balance of the refoamer 15 is determined, and the fuel supply to the refoamer auxiliary burner 23 is controlled by taking this heat balance into account. For this reason.

This fuel system can quickly respond to sudden load demands, and can also suppress disturbances in the temperature of the re-former 15 to a small extent. Figure 5 is.

This shows the actual control using this control device. As can be seen from this figure, a fast fuel flow response can be achieved. Moreover, the temperature of the re-former reaction tube 16 can be stabilized.

Thermal fatigue of the reformer reaction tube 16 can also be prevented.

Since the lifespan can be significantly extended, the above-mentioned effects can be achieved after all.

FIG. 6 shows in block form another embodiment of the present invention.

In the same figure, reference numeral 101 is a re-former, in which methane as a raw fuel mixed with water vapor is introduced into the inside of a re-former reaction tube in which a reforming catalyst layer is provided, and combustion fuel is introduced outside the re-former reaction tube. and combustion air to the combustion chamber and former main burner 107. By circulating high-temperature combustion gas obtained by combustion in the reformer auxiliary burner 108, reformed gas containing a large amount of hydrogen is generated. Further, 103 is a transformer having the same function as described above, and 104 is a transformer that uses the gas obtained by this transformer 103 as a fuel gas to be introduced into the fuel electrode, and an oxidizing gas such as air is introduced into the oxidizing electrode. This is a fuel cell that extracts electrical energy from both 11fl181 through an electrochemical reaction. The fuel cell 104 is connected to a main burner 107 in the combustion chamber of the reformer 101.
The fuel gas discharged from the l pole and methane as a fuel gas separately supplied from the outside are introduced into the refoamer auxiliary burner 108 as fuel for combustion.

On the other hand, 109 is a flow rate control valve provided on the line for supplying fuel gas to the re-boomer auxiliary burner 108;
0A is a first flow rate detector installed on a line through which methane, which is a raw fuel, flows, and detects its flow rate; 110B is a second flow rate detector installed on a line through which methane mixed with water vapor flows, and detects its flow rate. A third flow rate detector 110G is provided on the line immediately after the outlet of the re-homer 101 to detect the flow rate, and 110D is a third flow rate detector installed on the line that supplies fuel gas to the re-homer auxiliary burner 108. a fourth flow rate detector for detecting flow rate, 11
Reference numeral 1 denotes a current detector serving as an output electricity quantity detector that detects current as an output electricity quantity from the fuel cell 104.

Also.

Reference numerals 112 indicate detection signals FA to Fo output from the above-mentioned 8 flow detectors 110A to 110D and the current detector 111, respectively.
and ■ as input, and uses these to calculate the combustion energy ff1Q in the combustion chamber of the re-former 101, taking into account changes in the composition of fuel gas based on scientific knowledge such as reforming reactions and combustion reactions. A device 113 compares the amount of combustion energy according to the detection signal I output from the current detector 111 and the combustion energy index Q calculated by the first arithmetic device 112, and based on the comparison result. This is a second computing device that outputs a control signal Vc that adjusts the opening degree of the flow rate control valve 109.

Here, the first arithmetic unit M112 includes an adder/subtractor 114, an adder/subtractor 115 . Adder/subtractor 116. Adder/subtractor 117. Adder/subtractor 118. Coefficient unit 119. Coefficient unit 120. Coefficient unit 12)
．． Coefficient unit 122. The second arithmetic unit 113 is composed of a coefficient unit 123A, a coefficient unit 123B, and a coefficient unit 124 as shown in the figure, and a function generator 125. Limiter 126. Coefficient unit 1
27 and an adder/subtractor 128 as shown in the figure.

Next, a fuel cell power generation system configured as described above will be described. The combustion control function of the combustion chamber of the re-former 101 will be described.

First, the fuel reforming reaction in the reformer 101 can be generally regarded as a chemical reaction represented by the above formula (1).

Although this reaction is reversible, the shift of the equilibrium point to the right can be seen as a change in the molar flow rate of the reaction flow rate. That is, an increment of 2 moles of fuel gas occurs for every 1 mole of methane reaction. From this, it can be seen that half of the difference in the flow rate of the fuel gas before and after the reforming reaction is equal to the flow rate of methane that caused the reforming reaction.

Now, the first flow rate detector 110A, the second flow rate detector 11
If the flow rate signals detected by 0B and the third flow rate detector 110C are FA, FB, and FC, then the methane flow rate FR that has undergone one reaction is calculated by the adder/subtractor 114 in the first arithmetic unit 112.
．． By the coefficient unit 119.

FR= (Fc-FB)/2...-(8)
becomes.

On the other hand, the hydrogen flow l F generated by the reforming reaction
H and the methane flow 41 F M remaining after reforming repulsion are:
By the coefficient unit 120 and the adder/subtractor 115.

FH-4・FR...(9) FM-FA-FR....(10). Therefore, the energy flow rate as a combustible component of the fuel gas after the reforming reaction is determined by the coefficient unit 12), the coefficient unit 122. By the adder/subtractor 116.

Ql ・FM+Q2 ・FH (11). Here, Ql and Q2 are the combustion heat of methane and hydrogen, respectively. This is then determined by an appropriate transmission delay (coefficient unit 123
A) passes through the fuel cell 104. On the other hand, the hydrogen flow rate consumed by the fuel cell 104 is equal to the output current I of the fuel cell 104, and this can be determined by multiplying the detection signal from the current detector 111 by a physical constant in the coefficient unit 124. can be determined. In addition, this fuel cell 10
The combustion gas energy obtained by subtracting the hydrogen energy consumed in step 4 by adder/subtracter 117 is further delayed in transmission (coefficient device 1
23B) and is finally converted into combustion heat by the refoamer main burner 107. Then, by adding the detection signal FD from the fourth flow rate detector 110D to this at the adder/subtractor 118, the heat IQ generated in the reheater auxiliary burner 108 is calculated.

On the other hand, in the second arithmetic unit 113, the current detector 11
Combustion energy day Q re according to the detection signal I from 1
f is determined by the function generator 125.

Further, using this value Q ref as a target value, an adder/subtractor 128 obtains a deviation signal from the amount of combustion energy Q calculated by the first computing unit [112], and this is sent to the second computing unit 11.
3. By converting it into a control signal Vc through the counter 127 and applying it to the flow layer control valve 109, the flow rate of methane, which is the fuel gas, supplied to the flow rate control valve 109 is controlled.

Note that the present invention is not limited to the embodiments described above. For example, the auxiliary burner output calculator may be implemented as software on a computer. Also, other 1
Of course, various modifications can be made without departing from the gist of the invention.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the main parts of a fuel cell power generation plant incorporating a control device according to an embodiment of the present invention, Fig. 2 is a diagram showing the output characteristics of a fuel flow rate calculator in the same plant, and Fig. Configuration diagram of the auxiliary burner output calculator in the plant,
FIG. 4 is a diagram for explaining the relationship between the reformer reaction tube temperature and the reforming rate. FIG. 5 is a diagram showing changes in each process amount when the load current is changed under conditions using the control device according to the present invention;
FIG. 6 is a block diagram of main parts of a fuel cell power generation plant incorporating a control device according to another embodiment of the present invention, and FIG. 7 is a block diagram of a conventional fuel system. FIGS. 8 and 9 are diagrams for explaining problems in the conventional system. 11... Raw fuel supply end, 12... Water vapor supply end. 15.101...Reformer, 16...Reformer reaction tube, 17.22...Flow control valve, 18.104...
Fuel cell (FC), 20.107=・7t-v main burner, 23,108...Refoma auxiliary burner, 30・
...Fuel flow rate calculator, 31.32...Controller. 33... Auxiliary burner output calculator, 34... Correction energy calculator, 35... Heat balance calculator, 36... Burner output calculator, 37... Reforming rate calculator, 38...・Divider. 112...first arithmetic device, 113 second arithmetic device. Applicant's representative Patent attorney Takehiko Suzue jj

Claims (2)

[Claims] (1) A reformer reacts raw fuel containing hydrocarbons with water to reform it into a fuel gas containing hydrogen as a main component, and supplies this fuel gas as a reducing agent to the fuel cell, and from the above fuel cell. This is for controlling a fuel system of a fuel cell power generation plant in which the discharged fuel exhaust gas is combusted as a heat source necessary for reforming in the reformer, and the fuel exhaust gas discharged from the fuel cell is A reformer main burner for combustion in the reformer, a reformer auxiliary burner connected to a fuel supply source, and a method for maintaining the temperature of the reformer reaction tube at the target temperature based on the difference between the target temperature and the actual temperature of the reformer reaction tube. means for calculating correction energy; means for determining the reformer's reforming rate from the temperature of the reformer reaction tube; and the reforming rate determined by this means, the load current of the fuel cell, and the load current supplied to the fuel cell. means for calculating the combustion energy of the fuel exhaust gas supplied to the reformer main burner from the flow rate of the fuel gas, the flow rate of the raw fuel flowing into the reformer, the flow rate of combustion exhaust gas discharged from the reformer, its temperature, and means for calculating the consumed energy in the reformer from the quality factor; means for determining the balance energy in the reformer from the difference between the combustion energy and the consumed energy; 1. A fuel system control device for a fuel cell power generation plant, comprising means for controlling the amount of fuel supplied to a reformer auxiliary burner. (2) The fuel system control device for a fuel cell power plant according to claim 1, wherein the fuel supply source to which the reformer auxiliary burner is connected is the same as the raw fuel supply source. .