Table 1 Performance of 5MW plant

Table 1 Performance of 5MW plant replaced to the improved type to restore the performance, as well as the reformer packed material was increased to prevent a catalyst powdering. Plant operation was restarted in October 1995, a periodic inspection was executed from February to March 1996. Plant operation has been continuing since April 1996.

A summary of performance test carried out at .around 1800hours operation was shown in Table 1. The maximum load was stayed in 94% of rated load, because of cell stack performance unbalance. Gross generating efficiency was decreased approximately 1% as compared with planned efficiency. For FPS efficiency and inverter efficiency were almost satisfied the designed rate, cell stacks voltage time decay supposed to be a major factor of plant efficiency decrease. In particular, 18 times starts/stops conducted in the adjusting test

I A Ho. / Stack g Ho. 3 Stack o Ho.4 Stack a Ho. 7 Stick □ No. 8 Stack v Ho. 9 Stack |

Fig. 2 Cell voltage time deterioration

I A Ho. / Stack g Ho. 3 Stack o Ho.4 Stack a Ho. 7 Stick □ No. 8 Stack v Ho. 9 Stack |

Fig. 2 Cell voltage time deterioration made the cell voltage deterioration accelerated. Regarding the parasite power increase, the air compressotfgas turbine internal efficiencies were shorten and mechanical loss were unexpectedly larger. NOx emmision was 3ppmv, indicated the environmental advantage of PAFC power plant Heat recovery, load change characteristics and special operation tests such as low SIC operation will be conducted in the second half of 1996.

The cell voltage time deterioration was illustrated in Fig. 2. Cell voltages shown in this Fig. were modified to the rated load state, that is the current density is as of 300mA/cm2. Average cell voltage decay in 2500hours operation was around 50mV. Although, a gradual voltage deterioration was shown in ordinary operation after the initial frequent start/stop, the voltage decay was larger than expected. On the other hand, only a little cell voltage decrease was confirmed in more than 8000hours short stack test operation. Observing the further transition of cell voltage deterioration in the hereafter operation, the improvement of cell stack strength against the start/stop will be studied.

Cause of plant shutdown were shown in Table 2. Increase of differential pressure between anode and cathode or auxiliary machineries trips which triggered the emergency shutdown, and growth of pressure drop in the reforming process or exhaust gas blockade that caused the normal shutdown, were major factors of plant shutdown, excluding the result with operational plan and adjusting test As the whole operation hours are inadequate, hereafter continueing the plant operation, extracting and overcoming the subjects, plant overall technologies will be established.

Cumulative start and stop 50

Normal shutdown 18

Operational plan 6

Increase of A p in reforming process 4

Blockade in exhaust gas 4

Cell voltage decay 3

Auxiliary machinery failure 1

Emergency shutdown 32

Adjusting test 18

Increase of A p between anode and cathode 5

Auxiliary machineries trips 3

Transmission system failure 3

Direct current ground fault 2

Increase of A p in reforming process 1

Table 2 Cause of plant shutdown


5MW plant operation and testing will be continued untill March 1997, short stack test and evaluation studies will be kept going in parallel. The reliability, durability, maintenance and economy of PAFC plants and components will be grasped in these studies, so that the R&D on urban energy center-type PAFC power plants for practical use will be promoted.


Masabiro Watanabe1', Hideaki Miyoshi2*, Hiroyuki Uchida1', Noriyuki Nakajima3>, Takashi KitaiJ), and Kunihiro Nishizaki5' Cooperative Research & Development Center, Yamanashi University, Takeda 4-3, Kofii 400, Japan 1; Yamanashi University, 2; Mitsubishi Electric Co., 3; Fuji Electric Co., 4; Toshiba Co., 5; Tokyo Gas Co. Ltd.

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