When a sewage treatment plant in Svenljunga, Sweden, with a community of 10,000 inhabitants, was renovated in the summer of 2005, investments were made in order to increase operational efficiency and reliability. One measure taken was to install equipment from Emotron, a Swedish company offering solutions for managing machines and processes driven by electric motors. Emotron installed its variable speed drives and softstarters to control pumps, blowers and mixers, and shaft power monitors to protect equipment. As a result the Svenljungaplant now has more reliable control, lower energy consumption and reduced wear.
The whole plant is now managed by one operator, instead of the two or three that used to be required for daily control and supervision. The increased efficiency means, among other things, that there is more time for preventive measures and maintenance. “We used to regulate most of the equipment manually, but today everything is controlled by Emotron products,” says electrician Johan Arvidsson.
Constant flow demand
In a sewage treatment plant, the objective is to keep a constant flow despite the large variation in load during the day and night. In Svenljunga,Emotron products ensure efficient operation continuously adjusted to demand. Variable speed drives and softstarters regulate pumps, blowers and mixers, and shaft power monitors protect screw conveyors.
“Emotron products can withstand harsh environments and be located within the plant,” says Johan Arvidsson. “No costly cabling or cabinets are required. We also minimise the risk of damage and downtime, since we are warned in good time in case of process disturbances.” The Emotron products react immediately to deviations and send a warning or stop the process if operation is not optimal, for example if a pipe is blocked or a valve is not fully opened then the operator can take action quickly in order to prevent damage and downtime.
Minimised energy consumption
A total of 17 Emotron FDU variable speed drives are installed in the plant. They control, among other things, three inlet pumps that pump in untreated sewage water. Two of the pumps are normally used to handle overflow water, i.e. water that is allowed to pass the plant after only limited treatment, for example in the case of heavy rainfall. The flow must not exceed 220 m3/hour in order for the particles that are to be removed to have time to settle to the bottom and not run out with the water. If the flow is too high, the system regulates this by starting the third pump to pump water past so that the particles can settle.
The operation of the blowers supplying oxygen to the sewage water was also made more efficient by installing Emotron FDU variable speed drives.
“Until now the blowers were either running at maximum speed or standing still,” says Johan Arvidsson. “That was wasting energy. The Emotron FDU now continuously adjusts to demand, ensuring that the water maintains the correct oxygen content. In this way we minimise our energy consumption and equipment wear.”
More efficient sludge treatment
The sludge scrapers in the sedimentation basins are monitored by Emotron M20 shaft power monitors. The monitors send a warning or stop the process if operation is not optimal, for example if a scraper is blocked, a blade is worn or a chain is broken. This means that equipment wear and downtime are minimised.
Emotron FDU variable speed drives control the sludge pumps that pump out surplus sludge from the basins. An excentre screw pump that pumps sludge to a thickener is also controlled by an Emotron FDU. An Emotron M20 shaft power monitor monitors the screw conveyor and sends a warning or stops the process if a blockage occurs.
