The BioCap® is designed to store the waste bio gas produced in the digesters. The cover is also designed to impart a pressure to the bio gas to enable reticulation of the bio gas to the appliances which will utilise the bio gas.
The cover is typically fitted with:
- Sample hatches
- Pressure / vacuum relief valves whose purpose is to protect the digester cover from excessive gas pressure or vacuum conditions
- Flame arrester with weather hood and isolating valve
- Access manholes which allow ingress into the cover gas space during digester maintenance
- Cover height indicator which gives a visual measure of the cover’s position in respect of its vertical travel
- Seal pipes for mounting of sludge mixing lances (not required if external mixing is used)
- Cover movement is detected by ultrasonic level detector
- Bio gas pressure under the cover is monitored by a pressure sensor with high and low adjustable set points
The stored bio gas is prevented from escaping to the atmosphere by a cover water seal system. The cover skirt is permanently immersed in a water bath of sufficient depth to prevent the bio gas pressure exceeding the water depth and thus escaping from under the cover up to a maximum pressure of 500 mm WC. The water seal water is maintained at a set level at all times by constant make up from a header tank fed by a permanent water supply through a ball float valve.