When a Tennessee water treatment facility needed to change its neutralization system, plant administrators decided to seize the opportunity to implement a number of cost-saving and environmental benefits as well.
The treatment facility switched from a manual system that utilized granular hydrated lime to an automated, instrumented system that uses a 25 percent sodium hydroxide solution for neutralization. The system maintains an alkaline pH level in a treatment plant that handles approximately 24 mgd.
According to the plant superintendent, a decision was made to invest in a new liquid caustic neutralization system. The installation was completed in less than 12 months and has been operating trouble-free ever since. A critical part of the system involves the installation of two sealless, magnetically-driven thermoplastic pumps that handle corrosive and caustic fluids from the 12,500 gallon, double-wall storage tanks to a 500 gallon, double-wall day tank.
The use of double-wall tanks and double-wall piping has eliminated concerns about chemical leakage and has made it unnecessary to build and maintain concrete containment basins normally required as protection against such leakage.
A key decision that needed to be made in the changeover from the hydrated lime system that had been used to neutralize the clarified water involved the choice of the pumps that would be required to transfer the caustic liquid from the main storage tanks to the day-tank, and to accomplish it without concern for leakage or system interruption.
A review of commercial pumps available led to specifying that the pumps be of sealless design, be magnetically coupled, have no metal components in contact with the fluid and be constructed to withstand the adverse conditions with minimum maintenance. After an extensive study of available products, the consulting engineers specified a thermoplastic design that would meet ANSI process pump specification B73.1. The utility chose the magnetically coupled, polypropylene Chem-Gard model CGM-PY3x2x6 by Vanton Pump and Equipment Corporation, featuring 3” x 2” polypropylene flanged pumps with 6” keyed impellers, dual non-metallic containment can assembly; high-performance, permanent, rare earth magnets; and no metal-to-fluid contact. Additional specifications included:
Materials of Construction: Casing, casing cover and impeller are precision-injection molded from homogeneous polypropylene; the inner can (in contact with the fluid) is polypropylene and the outer can is fiberglass reinforced plastic. A polypropylene shaft sleeve and cap isolate the stainless steel shaft from the fluid.
Bearings: Extra-large stationary bearing made from silicon carbide and rotating sleeve/thrust bearings of ultrapure alumina ceramic are locked in place with anti-rotation keys.
Impeller: Dynamically balanced, key-driven thermoplastic impeller, injection molded with stainless steel insert to assure positive drive.
Motors: 3 HP, 460/3/60/1800 RPM, TEFC, chemical duty.
Service Conditions: 55 GPM at 30’ total dynamic head.
The installation has been so successful that plans are underway to expand the system from 24 to 36 mgd. Not only has the operation more than met expectations but the noticeable improvements in environmental conditions brought about by switching from powdered lime to liquid caustic have resulted in cleaner air and happier employees and neighbors.
Vanton Pump & Equipment Corp. is exhibiting at WEFTEC.16, Booth 3545. For more information, visit www.vanton.com.
