TB 50: Taiwan o2 co2 removal case study

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A semiconductor plant in Taiwan is using Liqui-Cel® Membrane Contactors to remove dissolved gas from their ultra pure water (UPW) system. The UPW system is used to purify water used in the chemical mechanical polishing
process (CMP) at the fab. The water system was designed and built by United Purification Technologies in Taichung Taiwan.

The water system has two degasification stages. The first stage removes both carbon dioxide and oxygen from the water and the second stage is in the final polishing loop where additional oxygen is removed to <5 ppb. (See system flow illustration 1)

The UPW system uses CEDI (Ionpure) technology as the primary system to remove ions and charged particles from the water.

The feed water to the system is first treated by Reverse Osmosis (RO). RO membranes are designed to remove ions but gasses will freely pass through them. Analysis of the RO water found that about 7.5 ppm of carbon dioxide was
present in the water. Outlet water quality cannot be achieved if CO2 loading is high on the CEDI system. In order to lower the ionic load into the CEDI system, UPT installed a membrane contactor system.

Membrane contactors are widely used to remove dissolved gasses from water. They utilize micro porous hollow fiber membranes to bring a liquid and gas phase in direct contact with each other. The membranes are hydrophobic so that water will not flow through the pores. Water flows on the outside of the membrane and gasses flow on the inside of the hollow fiber membrane. Controlling the partial pressure of gasses on the inside of the membrane creates a driving force to remove dissolved gasses from the water.

The first stage membrane contactor system operates at 29 m3/hr (128 gpm). It consists of four 10 inch X-IND membrane contactors configured two in parallel with two in series. This system is designed to remove 85% of the carbon dioxide in the water. It also lowers the dissolved oxygen to 6 ppb.

The conductivity measurement after the membrane contactor system is 8-10 μs/cm. This allows the CEDI system to continuously produce water with an outlet resistivity of 16 mega ohm-cm or higher.

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