EWT Water Technology – Water Treatment

EWT Water Technology

Membrane Degasser

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Membrane degassing or membrane gas transfer is a membrane separation process for removal of dissolved gases from liquids, in water treatment especially for removal of carbon dioxide(CO2) and oxygen (O2) from water.

A membrane contactor is a device for membrane degassing, mainly consisting of an outer pressure vessel with inside hollow fibre membranes. Liquids flows through the pressure vessel and around the outside of the hollow fibre membranes. Depending upon the operating mode, there is either sweep gas flowing through the inside of the hollow fibre membranes, or they are being evacuated by vacuum pumps. Both will result in the gas diffusing from the liquid and through the hollow fibre membranes, to be either removed with the sweep gas or evacuated by the vacuum pumps.

Membrane gas transfer a continuous process. During operation, a small amount of waste water will need to be periodically discharged from the gas side, in addition to any cooling water requirements for the vacuum pumps.

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Design Example:

membrane gas transfer plant

Membrane gas transfer plant for removal of CO2 from water, combined air sweep and vacuum mode, two lines, with two membrane contactors arranged in series for each line.

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Technical Data:

degassed water volume flow available from approx. 0.5 up to 150 m³/h for each line
amount of lines usually 1x 100% or 2x 50%
degassed water quality free carbon dioxide < 5 ... 10 mg/L CO2, depending upon the process conditions
oxygen depending upon the plant design and process conditions
differential pressure at nominal load approx. 0.2 ... 0.5 bar
operating pressure, absolute ≤ 7 bar on the liquid side
approx. 75 mbar on the gas side, for CO2-removal
operating temperature 5 ... 30 °C
sweep gas • ambient air or compressed air, for CO2-removal
• nitrogen, for oxygen-removal
sweep gas consumption depending upon the plant design and the process conditions
waste water discharge approx. 0.5 ... 2.5 L/day, plus any required cooling water for the vacuum pumps
recommended raw water quality turbidity < 0.5 NTU
total suspended solids (TSS) < 1 mg/L
Silt Density Index (SDI15 min) < 3 %/min
total alkaline earths (hardness) < 0.1 mmol/L
iron < 0.3 mg/L Fe
free chlorine < 0.5 mg/L Cl2
surfactants not detectable
total organic carbon (TOC) < 1 ... 3 mg/L C
oil, grease < 0.5 mg/L
total service life of the membrane contactors usually approx. 3 ... 5 years
material options membrane contactor • polypropylene (PP)
• stainless steel (1.4404)
vacuum pump • stainless steel (e.g. 1.4301, 1.4408)
pipelines • polyvinyl chloride (PVC)
• polypropylene (PP)
• polyvinylidene fluoride (PVDF)
• stainless steel (e.g. 1.4541, 1.4571)
valves • polyvinyl chloride (PVC)
• polypropylene (PP)
• polyvinylidene fluoride (PVDF)
• stainless steel (e.g. 1.4541, 1.4571)
gaskets • etyhlene propylene diene monomer rubber (EPDM)
• polytetrafluorethylene (PTFE)
control options start-up, service, and shut-down • fully automated, via control circuitry
• fully automated, via PLC

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2018-05-05 • water treatment made in GermanyCompany InformationPrivacy