78    DESIGN AND CONSTRUCTION OF A 200-GALLON PER
MINUTE ULTRAHIGH PURITY WATER SYSTEM
James D. Edwards, Associate
John W. Cammarn, Senior Chemical Engineer
Burgess & Niple, Limited
Columbus, Ohio 43220
INTRODUCTION
When a large Midwestern manufacturing company decided to integrate forward to produce finished electronic computer components, it needed a new treatment system for ultrahigh purity, sterile
water. The minimum water quality standard was 18 megohm which contains less than 30 fig/L of total
dissolved solids. Due to the extremely short deadline, the company retained Burgess & Niple Service
Corp. (B&NSC) to act as Construction Manager. Burgess & Niple, Limited was retained to complete
the technical design. The project included design and construction of both the ultrahigh purity water
system and an associated heavy metal wastewater treatment system. Two major equipment suppliers
were used, along with general/civil, mechanical, and electrical subcontractors. Design specifications,
fabrication, and installation of the systems were completed in less than 6 months with a total cost
below the original project estimate.
The process engineering evaluation of the main line production system determined that approximately 200 gpm of finished water would be required. The recommended system involved three stages:
treating incoming municipal water, treating recycle effluent, and polishing both streams to produce
finished water of the required volume and purity. The available city water was a combination of
surface and well water which is treated using the soda/lime softening process.
PROCESS DESIGN
The process design began in July of 1984 for both the water and wastewater treatment systems.
Both systems required a great deal of background development. The basic design parameters for the
system were developed and discussed with a number of equipment suppliers and some electronic
components manufacturers.
One item was universally expressed —when there is a problem in product quality, the probable cause
is water quality. Early electronics applications specified 4 megohm, then 9 megohm, and now the
standard appears to be 18 megohm quality water. As an example, a certified U.S. Environmental
Protection Agency (U.S. EPA) or Department of Health laboratory does not require even 1 megohm
water. There is limited information on the corrosion properties of water purer than 1 megohm. Above
1 megohm water becomes very aggressive and can lose its "purity" quickly.
The primary key to obtaining of high purity water is the reverse osmosis (RO) membrane. There are
three basic types: the original cellulose acetate, tubular membrane; the Arimid hollow fiber membrane; and the spiral wound composite membrane. The cellulose acetate membranes require the most
pressure and are seldom used in the new larger RO systems. Hollow fiber membrane units allow the
maximum passage per square foot of floor space, but since the fiber is only about 42 microns (0.0016
inches) in diameter, they require the most careful pretreatment. A new, spiral wound composite
membrane manufactured by Dow Chemical was selected.
An RO membrane typically has a 0.1 to 1.0 micron (0.000004 to 0.000039 inches) thick "skin" on a
porous substructure. In a spiral wound cartridge, the membrane is formed into an envelope over a
support backing. The open end of the envelope is attached to the center product tube. The membrane
envelopes are alternated with plastic feed-channel spacers and wrapped in a spiral 8 inches OD by 40
inches long. The feed water stream passes between the spirals parallel to the product tube. The
product water (permeate) which passes through the membrane passes to the center product tube and
flows out countercurrent to the feed flow. The membrane itself is selectively permeable to water and
the feed side is maintained at a pressure above the osmotic pressure of water in the system. Less than
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