Previous situation
A freshwater pumping system in a paper industry was analyzed. It consisted of three centrifugal pumps operating in a 2+1 configuration at full load, requiring 380 kWe of power. The pumps were activated by a control logic system based on the pressure in the discharge manifold. During the installation, an operational recirculation system was identified between the manifold and the water tank, used to maintain a safe pressure of 6.5 barg. When the pressure drops below 6 barg, recirculation is automatically deactivated, and upon reaching a minimum pressure, the system activates one of the remaining pumps. However, when demand decreases (and pressure increases), the pumps do not automatically shut off, requiring manual intervention by plant personnel.
As a result, a large part of the pumped flow returns to the tank, reducing the overall efficiency of the system for different process water demands.
💡This overconsumption of electricity, going unnoticed, leads to higher costs not only in energy but also in preventive and corrective maintenance.
The solutions
To increase overall pumping efficiency, ENEF coordinated the installation of a variable frequency drive (VFD) on one of the pumps and a new pressure sensor on the delivery manifold. The pressure signal was integrated into the controller that incorporates the VFD itself. This controller is capable of turning the remaining pumps on and off and simultaneously modifying their frequency according to the delivery pressure. By performing various tests on the system, a new delivery pressure of 5 barg was determined, demonstrating that it can be operated with a single pump at 48 HZ.
The result was an increase in the overall efficiency of the system from 29% to 51%.
By installing the VFD on a pump, it is possible to supply the different demands at a lower delivery pressure without requiring the use of recirculation to control the pressure.
It should be noted that the optimal operating point will depend on the characteristic curves of the pump and the system 📑.
This intervention increases the reliability of the pumping system by operating with one less piece of equipment, reduces emissions of polluting gases by consuming less electricity, and supports the plant’s environmental policies 🌎.
Results
8 months
Return on investment
120.000 USD
Annual financial savings
