Like in any other sealed environment, the processing of waste (human, food, or other types) is a serious consideration for ship designers and operators. It must be collected, stored and processed in order to be safely disposed of into the ocean. The International Maritime Organisation (IMO) lays down strict guidelines on the discharge of sewage into the sea. Raw sewage must be suitably treated using on-board compact effluent process systems. These typically generate foam as part of the treatment. The whole process is operated by a vacuum to move effluent around the ship and foam in the system can prevent it from working efficiently.
Hycontrol sensors have been used in such systems to detect foam and keep effluent foam under control for customers including the Australian Navy. It is here that 42 Hycontrol SmartFoam probes were selected for foam control for new packaged sewerage systems fore and aft on seven frigates. This came after completing a successful 3-month trial on board another ship.
The SmartFoam is a unique product, designed to measure and control foam in a single unit which is easy and quick to install. The sensor contains its own transmitter located inside the probe head so it can connect directly to a process controller or a pump. The SmartFoam can be used to create an effective foam control system without the need for any additional transmitter and is designed to be robust for industrial use. The sensor is designed using the unique patented IMA Sensing™ technology which enables foam to be measured reliably even when it is covered with a build-up of sticky material which frequently happens during foam measurement.
SmartFoam operates by passing a small alternating current through the foam being detected, and uses this to measure impedance. The impedance of the material being sensed is used to determine when foam is present. The SmartFoam is designed with two electrodes. One is used to sense foam while the other is designed to supply any leakage currents which pass along the body of the sensor. If the sensor is covered with a fouling layer deposited on it, then a leakage current must pass through that layer and down to earth. This leakage may be measure as part of the sensing current and consequently cause false readings. In the case of serious fouling this could cause a false alarm and an unnecessary intervention to the process. In the Hycontrol design, the guard electrode supplies all the leakage current leaving the sense electrode to sense only foam. The guard electrode effectively isolates the sensor from the interference caused by fouling. This gives the sensor the unique ability to continue working reliably even in conditions of extreme fouling.