Replacing the technical water pumps with fresh water pumps in Kakolanmäki WWTP
The original technical water pumps were wastewater pumps that were designed for a large quantity of solids. The life cycle of the pumps was short in spite of regular maintenance. Also the energy consumption was particularly high compared to other same size pumps in the plant.
Why has the life cycle been so short? Is the type of the pumps right for the technical water? Are the two large pumps the best solution for small flows? Technical water is clean with solids, so could you use clean water pumps?
Water content was analyzed from technical water samples. The solids were mostly sand, and the content was so small that the pumps for clean water were suitable for pumping it.
The actual flow curves were examined to find out the required yields for the pumps. Needs were presented to the pump supplier.
Components installed in the solution
Two non-self-priming, single-stage, centrifugal volute pumps of 30 kW and one non-self-priming, single-stage, centrifugal volute pump of 11 kW Grundfos NB 65-200 / 217 A-F2-A-BAQE were chosen as pumps for replacing original 2 x 122 kW dry-type wastewater pumps.
New pumps were installed inside the cave of Kakolanmäki WWTP. Technical water is stored in two 500 m3 tanks. The demanded flowrate for the technical water is 15-300 m3/h with a pressure of 3,5 bar.
Original pumps were operated with a constant pressure control (i.e. one pump adjusts according to the pressure at a time). This was changed to the mode where operation of the three pumps is automatically alternated to meet the flow requirements.
When it comes to the maintenance, it is important to check the needs for and use of the equipment to determine if better technology is available. Good metering, such as purchase price, life cycle, energy and maintenance costs, makes the evaluation easier.
It is advisable to carry out trial runs as far as possible before the changes, and it is very important to take into account the opinions of the use and maintenance professionals in the design. It is good to use a designer with experience in similar projects. Appliance vendors have templates for web sites that help in designing.
Before the change, energy consumption of the technical water pumps was 530,000 kWh / year
After the installation energy consumption was 170,000 kWh / year
Savings were 360,000 kWh / year
Purchasing cost of 3 new pumps was less than 1 old one