Water Technologies & Solutions technical bulletin

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low level deoxygenation using gas transfer membranes

figure 1: Gas Transfer System

application objective Reduce makeup water dissolved oxygen to less than 15 ppb at ambient temperatures using Gas Transfer Membrane (GTM*) process.

application discussion This system consists of two 1x1x1 (3 in series) arrays producing a combined effluent of 200 gpm (0.8 m3/h). Dissolved oxygen levels less than 15 ppb are easily obtained.

The system utilizes a hydrophobic, hollow fiber, polypropylene membrane. A low volume of nitrogen, utilized as a strip gas, is pulled through the hollow fiber’s lumen by vacuum, creating a concentration gradient. This causes the dissolved oxygen to pass through the membrane wall from the liquid phase to the gas phase.

The hydrophobic nature of the membrane prevents water transport through the membrane. The removal mechanism is based on Ideal Gas Laws and is similar to how a vacuum deaerator operates. However, the hollow fiber design offers much more surface area in a smaller footprint than a conventional deaerator.

figure 2: Effluent Dissolved Oxygen and Temperature

figure 3: Dissolved Oxygen by Stage

Page 2 TB1105EN.docx

technology advantage Gas transfer membrane technology offers many advantages over conventional dissolved gas removal methods:

Flexibility - GTM contactors can be configured in series to achieve dissolved oxygen levels below 5 ppb.

Size - GTM contactors have a remarkably small footprint. In a space occupying less than 330 ft3 (9.3 m3), up to 160 gpm (0.6 m3/h) of product can be produced by a skid containing the contactors, vacuum pumps, controls, and instrumentation.

Reliability - The low level deoxygenation processes have demonstrated a documented 99% operational availability.

Process Control - The system requires only the continuous flow of process water and small amount of 99.9% nitrogen gas in addition to an applied vacuum.

table 1: Operating Parameters for (2) 1x1x1 GTM

Flow Rate 200 gpm (100 gpm per Array) 0.8 m3/h (0.4 m3/h per Array)

Influent Pressure 26 psi, 90 psi Maximum @ -29” Hg

Pressure Drop 15 psi

Influent Dissolved Oxygen

3.5 to 14 ppm

Effluent Dissolved Oxygen

< 15 ppb (99.9% Reduction)

Nitrogen Requirement 99.9% Pure, 1.4 scfm

Vacuum -24” to – 27” Hg

Vacuum Pumps 2) 26 HP/ 38 Amps / 480 VAC (total), Liquid Ring Seal

Temperature Range 33° to 100°F (1° to 38°C)

Materials of Construction

316L Housings, PVC Piping, Polypropylene Tubing

Service Connections 3” 150 psi ANSI Raised Face Flange

Pretreatment Requirements

5 Micron Cartridge Filter (Minimum)

System Guarantees:

With Nitrogen (1 pass / 2 pass / 3 pass)

<800 ppb / <200 ppb / <50 ppb (Typical <20 ppb)

Vacuum Only (1 pass / 2 pass / 3 pass)

<1000 ppb / <500 ppb / <200 ppb

figure 4: Typical Low Level Deoxygenation

GTM Application

figure 5: Transfer Diagram

figure 6: Transfer System Diagram