Due to the high cost of energy, a chemical plant in Southern Texas had to find ways to increase its energy efficiency to lower its total operational cost.
The plant had two cooling water towers (CWT), a main unit responsible for approximately 80% of the total water cooling capacity, and a smaller CWT unit required for the remainder.
Shutting down the smaller CWT was an attractive idea, but required careful accounting of the energy consumed to demonstrate viability. Careful monitoring indicated that a significant efficiency improvement in the main CWT, if feasible, would require a combination of measures to increase water flow and better monitoring and control of water temperature.
Increasing water flow in the five (horizontally split between bearings) pumps of the main CWT unit was a critical component of the solution. That has been achieved by an overhaul which included installation of Vespel® CR-6100 stationary wear rings, under-filing of impeller vanes and slight
enlargement of the volute radii.
With smaller clearances made possible by Vespel® CR-6100, water recirculation and turbulence has been reduced, increasing flow and discharge pressure. The combined result of pump overhaul resulted in an improvement in pump efficiency of about 8%.
The full decommissioning of the smaller CWT led to savings in electricity and maintenance that were estimated to be over $400,000 per year (at $0.06 per kWh). The cost to overhaul five pumps and one spare pump has been fully paid with the energy savings of just one year. If avoidance of yearly maintenance costs of the smaller CWT unit were included, the savings figures would be even larger.
Because total water flow in the main CWT increased by more than needed to compensate for the decommissioning of the smaller CWT unit, additional savings in energy (in electricity and steam) of over $200,000 per year were achieved.