Membrane filter and filtering method

A method for filtering a liquid in a membrane filter,

• wherein the membrane filter includes a base element, a circumferentially closed tube, and a gas inlet,
• wherein the base element includes a tubular shell and one membrane carrier arranged in the tubular shell and connected by at least one anchor location with the tubular shell,
• wherein hollow fiber membranes are attached at a top of the membrane carrier,
• wherein the circumferentially closed tube adjoins the tubular shell at a top of the tubular shell,
• wherein the base element includes at least one downward open flow cavity between the tubular shell and the membrane carrier,
• wherein the at least one downward open flow cavity includes an outlet at a top of the base element leading out of the base element into the circumferentially closed tube,
• wherein the at least one downward open flow cavity is in contact with and adjacent to the tubular shell and also in contact with and adjacent to the one membrane carrier in each horizontal section through the one membrane carrier,
• wherein the at least one downward open flow cavity envelops the one membrane carrier and forms an annular gap,
• wherein the annular gap is only interrupted by the at least one anchor location,
• wherein a height of the at least one downward open flow cavity equals an overlap portion of a height of the one membrane carrier and a height of the tubular shell,
• wherein the one membrane carrier closes the base element completely for a flow of the liquid from a bottom of the base element to a top of the base element with an exception of the at least one downward open flow cavity, and
• wherein the circumferentially closed tube extends beyond an upper end of the hollow fiber membranes,
• the method comprising the steps:
• flowing the liquid into the base element, flowing the liquid through the at least one downward open flow cavity and thus flowing the liquid around the one membrane carrier;
• flowing a gas through a gas inlet into the base element by initially letting the gas into a tub which then flows out openings in the tub into the at least one downward open flow cavity;
• flowing the liquid only through the outlet at the top of the base element out of the base element and flowing the liquid from the outlet at the top of the base element only into the circumferentially closed tube,
• flowing the gas out of the outlet at the top of the base element into the circumferentially closed tube and generating a rising gas flow in the circumferentially closed tube and thus generating a rising liquid flow in the membrane filter;
• flushing the hollow fiber membranes on an outside of the hollow membranes with the rising liquid flow and the rising gas flow;
• providing a pressure differential between an outside of the hollow fiber membranes and lumens of the hollow fiber membranes, wherein the pressure differential causes a liquid permeate to be filtered out of the liquid and to flow into the lumens of the hollow fiber membranes;
• and
• collecting the liquid permeate from the lumens and flowing the liquid permeate out of the membrane filter;
• flowing the gas through the gas inlet into the at least one flow cavity;
• and subsequently,
• flowing the gas together with the liquid through the base element in the at least one downward open flow cavity between the tubular shell and the one membrane carrier and flowing the liquid and the gas through the outlet at the top of the base element into the circumferentially closed tube,
• wherein the at least one downward open flow cavity includes bulges extending into the one membrane carrier.