Lift stations are pump stations that move wastewater from lower to higher elevations. Wastewater lift stations help to save a lot of money in terms of sewerage collection systems’ excavation costs.
When lift stations are installed at strategic points in gravity pipeline systems, they save on construction and excavation costs without sacrificing the efficiency and functionality of the sewage collection system.
Since they play such a crucial role in sewage collection, they must run efficiently. Below are a few tips
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Using Variable Speed
You can change the operating mode of pumps through process considerations. Use variable speed pumping at the headwork to minimize slug loading. Variable speed pumping also reduces energy costs.
Apply the affinity laws to the pump characteristic curves to create curves at varying speeds. Next, superimpose the system curve to determine the new operating point. Remember not to determine the new operating point by applying affinity laws directly to old operating points, as it can cause errors.
Small stations with a flat system curve will have a small energy bill when they use variable speed pumping. Additionally, variable speed pumping lowers the flow rate and the pump power, lowering the peak demand for the larger stations. This significantly lowers the cost.
Control considerations
Most lift stations are controlled using across-the-line motor starters and float switches. Pumps are operated to maintain constant wet well levels, which matches the influent flow rate to the pump flow rate. This means pump speeds will rise when wet-well levels rise as they need to maintain that level.
You can use various devices to measure the level. This ensures that you can adjust the pump speed to control power consumption. Use affordable devices such as submersible pressure transducers, or you can use a non-contact device like an ultrasonic level transmitter.
Motor controls
All lift stations have motor control. Most of the motors use three-phase power. They are more reliable and more efficient. The motors have varying voltages of 208V to 4160V. The most common motors are 480V motors.
Motors are started and protected using different means, depending on the pump’s power and its control method.
In smaller stations, VFDs should be preferred when using variable-speed pump controls, though various designs have magnetic couplings. This is because VFDs remove the need for starters and have motor protection. Bypass contactors can also be used.
Instrumentation and enclosure selection for motors can significantly impact reliability and cost. While small stations have the VFDs wall mounted, large stations should install motor control centers. This saves on space and simplifies wiring.
Additionally, wet wells produce explosive and corrosive gases, which require appropriate precaution measures. The station should therefore locate an enclosure in a ventilated location. The enclosures should be waterproof.
Methane in wet wells also necessitates intrinsically safe instrumentation, entry permits, and the necessary safety precautions. Consult professional experts for further advice.
Generators
Your lift station should operate regardless of the weather. This necessitates using generators to provide standby power in cases of insufficient power. However, you can also use two power sources, but ensure that nothing can interrupt both power sources at the same time.
Generators can be used to provide power in emergencies as electrical safety is of utmost importance. Interlocks must be appropriately installed to prevent back-feeding of power into the grid. Also, ensure that the installations are reviewed.
Maintain the emergency power system periodically and adequately test it to prevent accidents. Generator sizing, the influence of VFDs, miscellaneous loads, ambient temperature, and altitude must be analyzed before the installation of the generator.
Scum Handling and Screening
The wastewater system needs to cope with the entry of solids into the conveyance system. Such solids include grit, logs, and non-putrescible materials. These solids can accumulate in the station’s wet wells and cause damage to the pumps and accumulation of odors.
You can use screens before the wet well to remove solids or trash racks to prevent pump damage. Some chemicals can also be used to minimize the accumulation of scum.
Regardless of how you prevent a lift station alarm, ensure that the wet well is periodically cleaned.
Bottom Line
There are many things to consider regarding the proper running of lift stations to ensure efficiency and minimize costs.
However, the most crucial factors are to ensure safety for people working at the station by following all the necessary regulations. Read through this article to understand more ways to enhance efficiency in a lift station.