System Performance: Resistivity > 18 megohms, On-line TOCs < 5 parts per billion |
 Prior to system start-up, a 50 psi pressure test was conducted for a period of two hours to validate the system's integrity. During this process, two leaks were identified at improperly assembled solvent-cemented connections in the distribution loop. Each leak was visually identified with a light source and repaired quickly with minimal downtime. A secondary analysis of the failures revealed that insufficient cement had been applied, and the pipe was not inserted completely during assembly, which created a dry joint.
After a secondary pressure test to validate repairs, the system was filled with a 1 percent solution of Minncare® cold sterilant in DI water, allowed to soak for approximately 45 minutes, and then rinsed to drain prior to bringing the system on-line. From a cold start, both resistivity and TOC levels were continually monitored at system startup to evaluate water quality over time. Resistivity is measured at the DI system prior to introduction of the water into the distribution loop, as well as on the return side of the distribution loop where process water is returned to the RO tanks. On-line TOC is measured continuously on the return side of the loop utilizing an Anatel Corporation A-1000 S20P Organics Analyzer.
So effective was the combination of purifying systems and Harvel LXT® UPW piping that on-line TOC levels in Ebara's process water fell nearly to the E-2 spec of 50 ppb within five hours of system activation. After just 28 days, on-line TOC had dropped to 5.51 ppb - a little more than one-tenth of the allowable maximum (refer to chart 1).
Resistivity measured on the return side of the distribution loop continued to increase over time as the water was continually polished (refer to chart 2).
After approximately one month of being on-line, a portion of the DI system was modified and reconfigured to relocate a UV light sterilization unit. This modification provided a second opportunity to evaluate the rinse-down time of a newly installed piping network. This change required the installation of approximately 30 feet of 11/2-inch Harvel LXT® piping, and involved approximately 116 new solvent-welded connections. |
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On-line TOC is measured continuously on the return side of the loop. |
Due to the fast joining techniques of the Harvel LXT® system, the modifications were made in one day, and the system was brought back on-line the following day, minimizing critical downtime. Water quality was closely monitored during modification, confirming the fast clean-up of the piping system. Chart 3 reveals TOC, generated as a result of the newly assembled connections, quickly dropped to acceptable limits. And, as chart 4 indicates, resistivity climbed above 18 megohms shortly after the modifications were made.
Ebara's water system continues to produce and maintain UPW having a resistivity greater than 18 megohms, and on-line TOC averaging less than 5 ppb, exceeding their initial E-2 water quality specification per ASTM D5127.
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Silicon growth furnace controls at Ebara Solar are highly automated. |
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