Optimization of sewage pumping stations

Power of pumps in pump cells are projected in relation to the worst scenarios that may occur in this area and with a certain additional redundancy. Therefore, pumps are placed in the crate station, which are predetermined for operation in standard conditions, which is present in most of the time. By optimizing the speed of the pump, it is possible to achieve significant savings in the electricity consumption spent on  the pump work. Optimum operation is based on pump speed management and the use of smart optimization algorithms.

The pump solution proposed is based on measuring the pressure in the pipeline immediately after the pump and regulating pump speed (Image 1).

Image 1: Illustration of optimum pump management
using a pressure sensor (PT) located behind pumps

Liquid drainage involves overcoming the following pressures:

  • hydrostatic pressure due to the weight of the fluid column above the pump and the consequence of the height difference between the starting and the destination (in image 1, denoted by h),
  • dynamic flow resistance of the fluid flow rate,
  • output pressure at the end of the pipeline.

Optimum pump speed control

Increase of the pump efficiency is achieved by reducing the speed, which reduces the dynamic flow resistance of the pipeline and reduces the outlet pressure to the minimum. By pumping the fluid too fast, the dynamic resistance of the pipeline increases and the output pressure is generated at the end of the pipeline which has no practical application.

Upon receipt of the pump start request, the engine speed of the piston is gradually increasing. By achieving optimum speed and flow rate, the measured pressure increases due to the increase in hydrostatic pressure due to the lifting of the fluid column. When the flow is established, the measured pressure ceases to exist, indicating that the optimum pump speed has been reached.

An additional advantage of this solution is the elimination of the classic sensor elements, including a level meter and switch level, whose functionality has been replaced by the pressure sensor and the in-built telemetry functions of the frequency converter. The frequency inverters intended for
installation in the pump cells contain integrated pump break detection functions and dry running protection based on pump momentum metering.

Manage multiple pumps using one frequency converter

Additional savings are also achieved with Duplico d.o.o’s newly developed solution to control multiple pumps using one frequency converter. With this innovative solution, the frequency inverter is responsible for the sequential start and stop of all pumps and the precise regulation of the speed of the current pump.

Q-H feature of pump

The Q-H characteristics of the centrifugal pump are shown in Figure 2 for two running speeds of the pump motor drive (full and intermittent line).

Image 2: Q-H ump characteristics for two speeds

Hcn: pump height with nominal flow,
Qcn: nominal flow,
The cross section Qcn and Hcn is a working point,
The power with which the pump operates is determined by the differential pressure and pressure:
It is worth noting that pump height H is proportional to the flow square:

The above two terms show that the power that the pump takes from the supply network is proportional to the third flow potency:

Iz gornja dva izraza proizlazi da je snaga koju crpka uzima iz napojne mreže proporcionalna trećoj potenciji protoka:

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