This invention relates to temperature control of a vaporizer in a fuel cell power plant which uses reformate gas.
Tokkai 2000-178001 and Tokkai 2000-185903 published by the Japanese Patent Office in 2000 disclose a temperature control of a vaporizer of a fuel cell power plant which uses reformate gas.
The fuel cell power plant is provided with a fuel cell stack which generates electricity by a reaction of reformate gas, a reformer which reforms vaporized fuel and generates reformate gas, a vaporizer which vaporizes liquid fuel, and a combustor which heats the vaporizer. The combustor burns anode effluent discharged from the anode of the fuel cell stack, and heats the vaporizer by combustion gas.
The temperature of the vaporizer depends on the combustion gas supplied from the combustor and the amount of liquid fuel to be vaporized. If there is a large amount of liquid fuel, i.e., if the load of the vaporizer is large, the temperature of the vaporizer will fall. In this case, if the supply amount of liquid fuel to the vaporizer is further increased in order to increase the anode effluent burnt by the combustor, the temperature of the vaporizer will decrease still further.
Hence, the above-mentioned prior art supplies supplementary fuel in addition to anode effluent to the combustor such that the temperature and amount of combustion gas supplied to the vaporizer can be controlled irrespective of the discharge amount of anode effluent.
Even in this case, after increasing the fuel amount supplied to the combustor, it will take time until the temperature of the vaporizer actually rises, and during this interval, the temperature of the vaporizer may fall below the temperature required to vaporize the fuel.
If the electric power generated by the fuel cell stack is insufficient due to the temperature decrease of the vaporizer, a secondary battery will discharge to compensate and the load of the secondary battery will increase.
Moreover, if the temperature of the vaporizer falls, part of the liquid fuel may flow into the reformer without vaporizing. The inflow of liquid fuel to the reformer reduces the reforming performance of the reformer, and increases generation of carbon monoxide in the reformer. Carbon monoxide poisons the fuel cell stack, and reduces the power generation performance of the fuel cell stack.
Thus, the temperature decrease of the vaporizer has an undesirable influence on the overall performance of the fuel cell power plant.
It is therefore an object of this invention to prevent the temperature of the vaporizer of a fuel cell power plant from falling below the temperature required to vaporize the fuel.
In order to achieve the above object, this invention provides a fuel cell power plant, comprising a vaporizer which applies heat to a liquid source material and generates a vaporized source material, a fuel cell stack which generates power using hydrogen-rich gas obtained from the vaporized source material, a device which supplies the liquid source material to the vaporizer, a sensor which detects a power generation requirement of the fuel cell stack, and a programmable controller programmed to calculate a liquid source material supply amount to the vaporizer based on the power generation requirement, calculate a prediction temperature of the vaporizer based on the supply amount of the liquid source material, and control the liquid source material supply amount supplied by the supply device so as to prevent the prediction temperature from falling below a predetermined temperature.
This invention also provides a method for controlling a liquid source material supply to a vaporizer of a fuel cell power plant. The fuel cell power plant comprises a fuel cell stack which generates power using hydrogen-rich gas obtained from a vaporized source material generated by the vaporizer. The vaporizer generates the vaporized source material by applying heat to the liquid source material. The fuel cell power plant further comprises a device which supplies the liquid source material to the vaporizer. The control method for controlling the liquid source material supply to the vaporizer comprises detecting a power generation requirement of the fuel cell stack, calculating a liquid source material supply amount to the vaporizer based on the power generation requirement, calculating a prediction temperature of the vaporizer based on the supply amount of the liquid source material, and controlling the liquid source material supply amount supplied by the supply device so as to prevent the prediction temperature from falling below a predetermined temperature.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.