6. Task6 Development of PEFC Utilizing Pure Hydrogen

6.1 Targets for Research and Development

Element technology for the fuel cell power generation system which meets the utilization of pure hydrogen and achieves about 45% electrical efficiency at the AC sending terminal (higher heating value basis), shall be established and a stationary type 30kW class generation system shall be demonstrated. The above-mentioned research and development shall achieve the following targets.

(1) Higher electrical efficiency at the sending terminal of the power plant shall be about 45%. (higher heating value basis)

(2) Verification of performance and reliability by carrying out field test of the proton exchange fuel cell 30kW power generation plant using the pure hydrogen.

Resulting from the investigation carried out since fiscal 1994, development of element technologies to achieve above targets, was started from fiscal 1999. During 1999, by using pure hydrogen, the problems on cell voltage characteristics in the hydrogen high utilization plant were picked up and measures against such problems on the high utilization rate operation were studied.

6.2 Result of Investigation and Development in Fiscal 1999

6.2.1 Study of the cell voltage characteristics in the utilization operation.

In the proton exchange fuel cell power generation plant using the pure hydrogen, the hydrogen utilization rate is above 90%. Then at the multiple layer cells, when not homogeneous flow occurs, degradation of the characteristics caused by the short supply of hydrogen, was predicted.

Therefore degradation caused by short supply of hydrogen was investigated. The test using a single cell, was conducted to find out the reverse polarization caused by the short supply of hydrogen and the corrosion caused by the reverse polarization phenomenon. As the result, it was found out that at the reverse polarization of -0.3V, influence was small, but at the reverse polarization of -0.7V, the cell characteristic goes down and corrosion appears in the short periods. By the analysis of the reverse polarized cell, peeling was found out between membrane and hydrogen pole.

By using the actual size cell to be used for the 30kW class plant, hydrogen high utilization rate operation was conducted. At the conventional high utilization rate operation, humidification of the membrane are carried out at the anode side, but it was made clear that at the hydrogen high utilization operation, it is more effective to make wetting of the cell on the air side.

6.2.2 Development of Hydrogen High Utilization Operation

The following three operating methods were examined, as the suitable operating method for the high hydrogen utilization operation. At the same time, following conditions were considered. The method can operate by using the recycle system even if the hydrogen utilization rate is near 100%, and energy loss to recycle the exhaust hydrogen is small, and equipment used for recycle is simple.

(1) Hydrogen recovery and recycle operation

(2) Anode outlet line closed operation

(3) Anode recycle operation

(1) Hydrogen recovery and recycle operation

Illustration and typical data of this recycle method are shown in Figure 6.2.2-1.

In this method, exhaust hydrogen is introduced in the vessel etc. and is recovered to the prescribed pressure. Then after the inlet of the vessel is closed, recovered hydrogen is introduced to the fuel cell by the gas pressure and consumed.

The data in Figure 1 are data at the 100% hydrogen utilization rate. Cell voltage are not stable under the low recovery pressure but it became stable when the recovery pressure in the vessel is about 0.19MPa.

(2) Anode outlet line closing operation

Illustration and typical data at the anode outlet line closing operation are shown in Figure 6.2.2-2.In this operation, outlet of the exhaust hydrogen is closed and only the amount of the hydrogen that can be consumed in the fuel cell is supplied. In this system, since only the reduced pressure hydrogen is supplied to the fuel cell, the control system is very simple.

As shown in Figure 6.2.2-2, at the initial stage of the fuel cell operation, the cell voltage goes down due to short of the hydrogen caused by the existent of impurity, especially the accumulated steam, but afterward operation became stable.

(3) Anode recycle operation

Anode recycle operation is illustrated in Figure 6.2.2-3.

At the anode side, not consumed and exhausted hydrogen is recycled by means of the devices such as compressor and or ejector. This method was used for the phosphoric fuel cell using pure hydrogen and for the fuel cell for cosmic use. But in this method, there are problems regarding the amount of recycle hydrogen and control of driving power of the circulation equipment. As it was impossible to confirm through the single cell test this year about the amount of recycle hydrogen, it will be tested at the short stack (app.100 cell) next year.

6.2.3 Investigation of fuel cell auxiliary facilities

(1) Investigation of the specification for the auxiliary facilities

Situation of the existing auxiliary devices which are needed for the operation of fuel cell power plant, such as supply device of hydrogen, nitrogen, pure water etc., electric distribution and disaster prevention facilities etc. and troubles experienced during the previous operation were investigated. So that the field tests can be performed smoothly in the coming fiscal year. The equipments that to be improved were picked up and effective improvement plans were discussed.

As the result, it was made clear that measures for the drainage in the existing feed fuel line (by-product hydrogen) are required and 3 drain traps are additionally installed.

(2) Safety Measures

Considering the history of the existing devices, safety measures that are applicable at present were examined and proposed to the factory where the field test is performed.

The proposals were accepted under the conditions that ventilation in the fuel cell power generation package and the installation of the partition wall between inverter and fuel cell should be considered.

(3) Humidity control in the supplied hydrogen.

Through the operating experiences, it was made clear that in the existing feed gas piping system, water seal tank is provided and wet hydrogen containing steam vaporized at the water surface or carried-over, is supplied to the fuel cell power generation system.

Especially in summer season, temperature and humidity of the gas in the water seal tank are high, and steam is contained at over saturation state.

On the other hand, it was made clear that at polymer electrolyte memberane fuel cell, moisture control of the gas is one of the important factors on its characteristics and humidified anode gas (hydrogen gas) gives the influence to the voltage drop.

Therefore, so that feed gas supplied from the water seal tank does not give any bad influence to fuel cell characteristics, de-humidification of the feed gas have been investigated. Definite degree of de-humidification has not been decided, but brine chilling unit which produces about 0℃ refrigerant shall be considered as one of the suitable candidates, considering the outdoor temperature in winter.

6.3 Schedule and Problem in Future

(1) Development of polymer electrolyte membrane fuel cell system supplied pure hydrogen

In order to realize the high efficiency of polymer electrolyte membrane fuel cell supplied pure hydrogen, a lot of basic data have been obtained on the pure hydrogen high utilization operation in fiscal 1999. However, at the commercial plant, 0.75V cell voltage, 40,000 hours life are required. Based on the data obtained up to fiscal 1999 and technologies on the anode recycle operation, short stack consisting of 100 cells will be manufactured and 0.75V cell voltage and stable long life shall be confirmed during fiscal 2000.

(2) Investigation and examination of fuel cell auxiliary system

To prevent hydrogen explosion, the water seal tank are installed in the feed gas piping line. But it was known by the previous operation, steam is splashed from the tank and a lot of steam is contaminated in the gas to be supplied to fuel cell.

On the other hand, it was experimentally made clear that the humidity of anode gas (hydrogen) to be supplied to polymer electrolyte membrane fuel cell, becomes one of the factors to drop cell voltage.

For de-humidification in raw feed gas to improve the characteristics of 30kW class fuel cell, consumption of large amount of electric energy should be avoided from the viewpoint of construction of high efficiency plant.

Therefore, it is scheduled to construct a raw feed gas de-humidification system to perform the fuel cell capability up to 100%, under the close tie-up with the designers and manufacturers of the fuel cell.