JPH0377122B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell power generation plant, and particularly to a control device thereof.

[Technical background of the invention and its problems]

The transformer in a fuel cell power plant removes the carbon monoxide CO produced by the reforming reaction in the reformer installed before it, and generates the hydrogen H ₂ required by the battery itself. . The reaction in the reformer is shown by equation (1) below, and the reaction in the shift converter is shown by equation (2) below.

CH ₄ +H ₂ O→CO+3H ₂ …(1) CO+H ₂ O→CO ₂ +H ₂ …(2) Here, CH ₄ is methane, which is a typical component of fuel gas, H ₂ O is water vapor, and CO ₂ is carbon dioxide. It is.

Usually, in this type of reactor, the internal reaction rate is an important condition for performance evaluation, and it is required to accelerate the reaction rate and improve the reaction rate. The reaction rate is determined by the reaction temperature and the temperature-dependent equilibrium characteristics of the reaction, in addition to the properties of the catalyst used. This can be understood by considering Arrhenius' reaction rate equation (3), which generally gives the reaction rate.

Ω=Aexp(-Ea/RT)(x-xe)...(3) In this equation (3), Ω is the reaction rate, R is the gas constant, and A and Ea are determined by the reactants and catalyst used. where T is the reaction temperature, x is the reactant concentration, and xe is the equilibrium concentration at the time when an equilibrium state is reached, which changes depending on the temperature.

From this equation (3), at a certain initial concentration x, xe
When is constant, the reaction rate increases as the reaction temperature increases. On the other hand, in the metamorphism reaction of equation (2), when the temperature rises, the equilibrium reaction rate decreases and xe increases, which acts to slow down the reaction rate. Therefore,
The reaction rate is determined by the synergistic effect of the above two, and there is an optimal reaction temperature.

Although there is an optimal reaction temperature, conventionally this was represented by the fuel gas temperature at the inlet of the transformer, and the first
The temperature was controlled at a constant rate, as shown in the figure below. In this figure, 1 is a transformer, 2 is a heat exchanger for cooling or heating the fuel gas by exchanging heat between the fuel gas and the secondary fluid, 3 is a temperature detector,
4 is a regulator, and 5 is a control valve. A reformer 10 generates hydrogen gas (fuel gas) required by the fuel cell main body from natural gas. 11 is a detector that detects the flow rate of natural gas (reformed raw fuel).
In addition, signal a is the fuel gas set temperature at the transformer inlet,
The signal b is the process temperature, the signal c is a difference signal between the two temperatures, and the signal d is an operation signal to the control valve 5. In this control method, the inlet temperature is controlled to be constant by changing the flow rate of the secondary fluid of the heat exchanger 2 according to the temperature deviation c.

By the way, since the shift reaction represented by equation (2) is an exothermic reaction, the gas temperature increases as the reaction progresses within the shift converter. Therefore, if the fuel gas flow rate changes and the internal reaction rate changes, the internal temperature distribution will also change as shown in FIG. In this figure, T ₁ is the fuel gas inlet temperature of the transformer,
T ₂ is the outlet temperature, and if the fuel flow rate increases now, the calorific value decreases as the reaction rate decreases, and the outlet temperature becomes T ₃ . Note that the horizontal axis L is the dimensionless length of the reaction section in the flow direction.

In this way, if the reaction is an exothermic reaction and the internal temperature distribution changes as the flow rate changes, the optimum inlet temperature also changes and increases as the flow rate increases. Furthermore, since fuel cell power plants are small-scale power plants by their nature and have good partial load efficiency, when considering that they are operated under a wide range of flow conditions in actual operation, it is difficult to compare conventional Constant fuel gas inlet temperature control cannot necessarily be said to perform control that should fully utilize the functions of the transformer.

[Purpose of the invention]

The present invention sets an optimum temperature corresponding to changes in the flow rate of fuel gas required by the nature of the plant for temperature control of a transformer in a fuel cell power generation plant. The present invention aims to provide a control device for a fuel cell power generation plant that can perform optimal control to always fully demonstrate the performance of a transformer by controlling the transformer based on the control method.

[Summary of the invention]

The present invention improves the reaction rate in the shift converter by considering changes in the optimum operating temperature due to fluctuations in the fuel gas flow rate while controlling the fuel gas temperature at the inlet of the shift converter to be constant.

[Embodiments of the invention]

The present invention will be explained below with reference to Examples. First, a first embodiment is shown in FIG. In the figure, 1 is a transformer, 2 is a heat exchanger, 3 is a temperature detector, 4 is a regulator, 5 is a control valve, 6 is a flow rate detector, 10 is a reformer, and 11 is a detection of the reformed raw fuel flow rate. vessel, the first
The configuration is similar to that shown in the figure. Further, 7 is a computing unit that generates an optimum inlet set temperature according to the flow rate. For example, maximum and minimum flow rate during operation as shown in equation (4)
Optimal inlet temperature Tmax at Fmax and Fmin,
Based on Tmin, perform functional calculations that directly change the optimum temperature.

f=Tmax-Tmin/Fmax-Fmine+Tmin (4) In the above equation, f is the optimum inlet setting temperature and e is the detected flow rate value.

In this control configuration, the computing unit 7
The optimum inlet set temperature f is calculated by
This method controls the transformer inlet temperature to this optimum temperature f.

In this embodiment, the fuel gas flow rate detection position is set at the transformer inlet, but it may be at least a point where the transformer flow rate can be detected, such as at the transformer outlet. In addition, since the fuel gas flow rate flowing into the transformer 1 corresponds to the flow rate of natural gas (reformed raw fuel), the current of the fuel cell, the power generation output, etc., the reformed gas raw fuel flow rate detector 11 detects The value may be used instead of the detected value of the fuel gas flow rate detector 6, or the current and power generation output of the fuel cell main body (not shown) may be detected and used instead of the detected value of the fuel gas flow rate detector 6. May be used for. In short, it may be the detected value of the fuel gas flow rate itself or a physical quantity that corresponds to this.

Now, as shown in Figure 4, the inlet temperature to transformer 1 is
It is assumed that the fuel gas flows in at T ₁ and the exit temperature reaches T ₂ due to the heat generated by the reaction. Here, when the gas flow rate increases and the reaction rate in the transformer decreases, the outlet temperature will decrease as mentioned above.
Go down from T ₂ to T ₃ . This means that the temperature distribution in the reaction section is the same at the inlet, but falls overall.

In the embodiment of the present invention, when the flow rate increases, the arithmetic unit 7 calculates the set value of the inlet temperature based on equation (4). Now, if this is T ₄ , the set value of the inlet temperature will be T ₄ . In this case the outlet temperature will be T ₅ . Therefore, by increasing the set value of the inlet temperature in response to an increase in flow rate and controlling the temperature distribution to T ₄ - _{T 5} , the internal fuel gas temperature distribution can be improved overall compared to the conventional constant inlet temperature control. act in the direction of raising the

〔Effect of the invention〕

A fuel cell power generation plant is a type of small-scale power generation equipment, and due to its nature, its operating status changes significantly in response to load fluctuations. Therefore, even in the fuel processing equipment of this plant, the fuel gas flow rate will fluctuate widely, and it is necessary to optimize the transformer and fully demonstrate its performance in response to these fluctuations. .

In the conventional constant inlet temperature control of a transformer, the internal temperature distribution drops overall when the flow rate increases, and conversely increases when the flow rate decreases, resulting in deviation from the optimal operating temperature. In contrast, according to the present invention, control is performed to raise the inlet temperature when the flow rate increases, so the average or overall operating temperature inside the transformer is kept constant and always optimal for any flow rate. It is possible to operate at a certain temperature.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional temperature control configuration of a transformer, FIG. 2 is a schematic diagram of fuel gas temperature distribution of a transformer, and FIG. 3 is a first diagram of a transformer control configuration according to the present invention.
FIG. 4 is an explanatory diagram of the fuel gas temperature distribution inside the transformer according to the present invention. DESCRIPTION OF SYMBOLS 1... Transformer, 2... Heat exchanger, 3... Temperature detector, 4... Regulator, 5... Control valve, 6... Flow rate detector, 7... Optimum inlet temperature calculator, 8... ...Temperature detector, 9...Average value calculator.

Claims (1)

[Claims] 1 A reformer that generates the fuel gas required by the fuel cell main body from natural gas, and a monoxide gas generated in the reforming reaction in this reformer that is installed between this reformer and the fuel cell main body. In a fuel cell power generation plant that has a transformer that converts carbon to carbon dioxide and a heat exchanger that is provided upstream of the transformer and maintains an appropriate operating temperature of the transformer, the transformer is used. a detection means for detecting a flowing fuel gas flow rate or a physical quantity corresponding thereto; a computing unit for calculating an optimum inlet temperature setting value of the transformer from this detected value; and a temperature detecting means for detecting the actual temperature at the inlet of the transformer. A detector and a regulator for controlling the fuel gas transformer inlet temperature based on the deviation between the inlet temperature set value and the actual temperature are provided, and the operating temperature of the transformer is maintained appropriately according to the flow rate of the fuel gas. A control device for a fuel cell power generation plant.