Product category:
Industrial Drives/Controls
News Release from: Emotron | Subject: Variable speed drives and soft starters
Edited by the Engineeringtalk Editorial
Team on 21 November 2006
Variable speed drives cut the cost of
sewage
When the sewage treatment plant in Svenljunga was renovated in the summer of 2005, investments were made in order to increase operational efficiency and reliability.
When the sewage treatment plant in Svenljunga, 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 Emotron variable speed drives and soft starters to control pumps, blowers and mixers, and Emotron shaft power monitors to protect equipment
This article was originally published on Engineeringtalk on 1 May 2006 at 8.00am (UK)
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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 time has been freed up 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.
In a sewage treatment plant, the objective is to keep a constant flow despite the large variation in load during the day and night.
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In Svenljunga, Emotron products ensure efficient operation continuously adjusted to demand.
Variable speed drives and soft starters regulate pumps, blowers and mixers, and shaft power monitors protect screw conveyors.
"One advantage of Emotron products is that they can withstand harsh environments and be located within the plant", says Arvidsson.
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"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.
The operator can take action quickly in order to prevent damage and downtime.
Common and costly problems such as cavitation and dry-running can be avoided.
The stop sequence is a critical moment in pump operation, often causing stress on pipes, valves and other equipment.
The Emotron solution offers soft stops by gradually reducing the pump speed, thereby avoiding water hammer and other potential damage.
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, ie 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 220m3/h 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 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".
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.
Equipment wear and downtime are minimised.
The monitors are connected to the motor cable.
No sensors are required.
Emotron FDU variable speed drives control the sludge pumps that pump out surplus sludge from the basins.
The FDU units are located in cabinets out by 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.
Mixers placed down in the basins are regulated by Emotron FDUs, as are the sludge pumps that pump sludge to centrifuges where it is dewatered.
Seven Emotron MSF softstarters control the screw conveyors for the centrifuges.
The sludge is used as fertiliser or sent for final disposal.
As Svenljunga sewage treatment plant was being renovated, the largest local industry, Elmo Leather, built their own plant next to the municipal plant.
The sewage water from the tannery had been putting high demands on its capacity.
"Now our plant is rated at 3000pe, compared with the 100,000pe required to treat the sewage from Elmo Leather", says Johan Arvidsson.
Elmo Leather's new wastewater treatment plant is the first of its kind.
A fully biological process is used that has never been tested before in an operation that uses such large quantities of chemicals.
The EU's environmental fund contributed to the financing and the good results mean that the company will lead the way for other tanneries in Europe.
The new technique reduces nitrogen emissions by 80%, compared with 30% in the old plant.
Emotron variable speed drives control, among other things, the blowers that oxygenate the waste water.
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