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Screw blower ZS VSD brings efficiency to sewage treatment works
In the seepage water treatment installation at the Münster waste management center, the ZS VSD oil-free screw blower from Atlas Copco supplies aerobic bacteria with air.
ZS VSD screw blower supplies bacteria with oil-free air
The low-maintenance technology and the integrated frequency inverter were the deciding factors to use the energy-efficient ZS 55+ VSD.
The installation has been treating the seepage water from the 2 central waste dumps, one of which is still in operation, for 15 years.
"One of two wastedumps has already been closed,” operating manager Christian Lüke explained. “But water will still seep through for a long time, which we will need to treat in the main waste water treatment plant before final cleaning.”
Household garbage deposited there contains decades-worth of medicines, half empty containers of home oil changes, or paint leftovers, despite waste separation.
"Certain ingredients eventually find their way in, in spite of the best waste separation efforts," Lüke said.
I can't smell anything at all here,” the visitor comments as he enters the seepage water treatment installation at the Münster waste management center.
Excess operating pressure up to 1.2 bar
The oil-free ZS screw blower range is designed for volume flows from around 250 to just under 4600 m3/h and excess operating pressures up to 1.2 bar. The integrated speed regulation (variable speed drive, VSD) installed in the machine in Münster automatically adjusts to the precise current air requirement. The speeds of the old blowers could only be regulated with external frequency inverters.
The ZS 55+ produces, volume flows of up to 1680 m3/h and is suitable for pressure increases between 0.3 and 1.2 bar. You can see the muddy brown water from the bridges over the basins. The clarifier basins where the seepage water is pumped in first are six to seven meters deep.
Münster uses the energy-saving process of upstream denitrification; this is done in the first fifth of the basin where anaerobic bacteria are active and do not need any oxygen. The sewage water flows over an overflow into the aerated nitrification. The nominal pressure for aeration is about 0.86 bar.
“We need 0.6 to 0.7 bar just to compensate for the pressure of the water column,” Rasch explains, “and an additional 0.2 bar to inflate the membranes of the aeration pipes.”
In the meantime, the Atlas Copco ZS VSD screw blower operates permanently in the installation; one of the two rotary lobe blowers is switched on if there is a large air requirement. The third blower is used as a reserve and is operated alternately with the second old device.
The advantages of Variable Speed Drive
The direct drive and the integrated frequency inverter were the the deciding factors, Christian Lüke said about the decision to acquire the ZS 55+ VSD when one of the three old rotary piston blowers had expensive motor damage.
These older machines require more maintenance due to the v-belt drive between motor and gear than the Atlas Copco screw blower where the motor and compressor element form one unit, Lüke said. The variable speed motor and the screw element are flange-mounted directly on the gear housing.
“The bacteria can survive for a maximum of half a day without aeration,” the engineer stressed, “so we need to be sure that he blower will operate absolutely reliably.”
The new compressor fulfills this requirement, ensuring an uninterrupted supply of oil-free compressed air.
