Ventilation System
Safety Because construction took place underground, higher standards were placed on safety. The aeration and deaeration ventilators were designed for an air exchange of one to six times per hour. The ventilators are divided into three control loops (side gallery 1, central gallery and side gallery 3). Gas sensors for explosive agents, butane-propane, benzene, methane and a petroleum-derived hydrocarbon measuring instrument are installed at the entrance of the mountain. The same gases are measured where the 960 m long inlet gallery meets the plant and also before the coarse screen. The explosive materials, methane, H2S, CO and O2, the temperature and the moisture content are measured in the air outlet pipe.
| Ventilation System of the Galleries |
| Air exchange: |
| Preliminary treatment area: |
1 - 6 times1 |
| Side galleries area: |
1 - 3 times1 |
| Technical chambers area: |
1 - 15 times1 |
| Maximum amount of air: |
approx. 150.000 m3/h |
Alarm When the level of the above mentioned gases reaches 20 % of the lower explosion limit, the warning alarm is activated through the process control system. Then the fresh air and the exhaust air ventilators automatically operate with the maximum quantity of air. When 40 % of the lower explosion limit are reached, the main alarm is activated. The inlet valve is closed manually and everything in the central gallery is operated without electricity in order to prevent an explosion in the mountain. If neither the warning alarm or the main alarm go off, the ventilators are regulated according to an adjustable temperature and/or moisture level. The ventilators can be regulated between 12,000 m3/h to 48,000 m3/h, as required.
Exhaust Air
The exhaust air is treated biologically and chemically with a three-stage crosscurrent washer. CO, O2, the temperature and the moisture level are measured in the side galleries' exhaust air pipes. The ventilators are regulated according to an adjustable temperature and/or moisture level. Oxygen and carbon monoxide have no regulation functions, but they represent important indicators for the work safety. During two years of operation, there have been three minor petroleum accidents which ran their course without great difficulties.
Operational Costs
The operational costs of the plant are approx. 10 % higher than those of a sewage purification plant with an open building method. This is due to the regular calibration of the gas sensors in three months, the comparatively short life-time of the measuring heads (about one to two years) and the high current demand of the ventilators, which have to be run constantly because of safety reasons.