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T. Yamaguchi
The cooling tower at the top of the building is a feature of this new plant, and
the fan of the cooling tower also serves as ventilation inside the plant. Its operation
started in September 2011. Although the construction work and the test operation
were interrupted by the Great East Japan Earthquake, some thorough tests in advance
and the newly introduced monitoring system worked well, and the start-up operation
was so smooth for a while. However, we experienced two major troubles some months
later.
Troubles in the Start-up Stage
Electrolyte Temperature Drop and Piping Blockage
The first trouble is an extreme electrolyte temperature drop in winter.
Electrolyte temperature is one of the important factors in electrolytic operation.
When the electrolyte temperature drops, the electrolyte resistance and the power
cost rise in the meantime. Therefore, it is important to manage it in the appropriate
temperature range. The Annaka refinery adjusts the electrolyte temperature to 40–
41 °C when the maximum current is used.
The average outside temperature of Annaka drop to around 3 °C in winter evening.
In the new plant, piping which bypasses the cooling tower is prepared not to get the
electrolyte too cold by circulating in winter. However, since this bypass pipe is a path
that goes over the upper part of the cooling tower, the distance is so long, and even if
the cooling tower is bypassed, the electrolyte temperature often falls. On weekdays
from 8:00 to 22:00, the current is kept to the minimum low level, so the heat generated
in the electrolytic cell is so low. As a result, the electrolyte temperature dropped to
around 20 °C around 22:00 when a large current was available.
Firstly, in order to keep the electrolyte temperature, its circulation was stopped
during the daytime on weekdays, and only purified solution was supplied to the electrolytic cell. This treatment had some effects but was inadequate. After several days,
ZnSO 4 in the purified solution crystallized, and the supply piping to the electrolytic
cell was blocked.
Secondary, new bypass piping was added in the middle of the electrolyte circulation route. As shown in Fig. 5, since this new pipe bypasses the cooling tower through
the shortest route, the drop of the electrolyte temperature was greatly suppressed. As
a result, as shown in Fig. 6, the electrolyte temperature can be kept over 30 °C.
ZnSO 4 Crystal Adhesion to Cooling Fan Casing
This trouble also occurred in the first winter. During the year-end and New Year
holidays, electricity prices are cheap all day, so the operation was continued using the
T. Yamaguchi
The cooling tower at the top of the building is a feature of this new plant, and
the fan of the cooling tower also serves as ventilation inside the plant. Its operation
started in September 2011. Although the construction work and the test operation
were interrupted by the Great East Japan Earthquake, some thorough tests in advance
and the newly introduced monitoring system worked well, and the start-up operation
was so smooth for a while. However, we experienced two major troubles some months
later.
Troubles in the Start-up Stage
Electrolyte Temperature Drop and Piping Blockage
The first trouble is an extreme electrolyte temperature drop in winter.
Electrolyte temperature is one of the important factors in electrolytic operation.
When the electrolyte temperature drops, the electrolyte resistance and the power
cost rise in the meantime. Therefore, it is important to manage it in the appropriate
temperature range. The Annaka refinery adjusts the electrolyte temperature to 40–
41 °C when the maximum current is used.
The average outside temperature of Annaka drop to around 3 °C in winter evening.
In the new plant, piping which bypasses the cooling tower is prepared not to get the
electrolyte too cold by circulating in winter. However, since this bypass pipe is a path
that goes over the upper part of the cooling tower, the distance is so long, and even if
the cooling tower is bypassed, the electrolyte temperature often falls. On weekdays
from 8:00 to 22:00, the current is kept to the minimum low level, so the heat generated
in the electrolytic cell is so low. As a result, the electrolyte temperature dropped to
around 20 °C around 22:00 when a large current was available.
Firstly, in order to keep the electrolyte temperature, its circulation was stopped
during the daytime on weekdays, and only purified solution was supplied to the electrolytic cell. This treatment had some effects but was inadequate. After several days,
ZnSO 4 in the purified solution crystallized, and the supply piping to the electrolytic
cell was blocked.
Secondary, new bypass piping was added in the middle of the electrolyte circulation route. As shown in Fig. 5, since this new pipe bypasses the cooling tower through
the shortest route, the drop of the electrolyte temperature was greatly suppressed. As
a result, as shown in Fig. 6, the electrolyte temperature can be kept over 30 °C.
ZnSO 4 Crystal Adhesion to Cooling Fan Casing
This trouble also occurred in the first winter. During the year-end and New Year
holidays, electricity prices are cheap all day, so the operation was continued using the