Water gap membrane distillation module with a circulating line

A membrane distillation module, comprising:

• a vessel with an internal cavity;
• a hydrophobic membrane that divides the internal cavity into a feed zone and a distillate zone;
• a thermally conductive divider disposed in the distillate zone to separate a coolant zone from the distillate zone such that the distillate zone is sandwiched between the feed zone and the coolant zone;
• a feed inlet fluidly connected to the feed zone for delivering a feed stream to the feed zone, and a feed outlet fluidly connected to the feed zone for discharging the feed stream from the feed zone;
• a coolant inlet fluidly connected to the coolant zone for delivering a coolant stream to the coolant zone, and a coolant outlet fluidly connected to the coolant zone for discharging the coolant stream from the coolant zone;
• at least one distillate inlet and at least one distillate outlet fluidly connected to the distillate zone;
• a circulating line disposed outside of the distillate zone that fluidly connects the at least one distillate outlet to the at least one distillate inlet;
• and
• a pump fluidly connected to the circulating line,
• wherein the feed stream comprises water and water vapor, and a portion of the water vapor permeates through the hydrophobic membrane and condenses in the distillate zone in the form of distilled water,
• wherein the pump circulates at least a portion of the distilled water in the circulating line, and
• wherein at least a portion of the circulating line is disposed in the coolant zone with a coil shape such that the distilled water of the circulating line heat exchanges with the coolant stream.