An evaporator adapted for a counter-current flow of at least one liquid and one vapor therein, comprising: a first inlet for a first liquid feed stream, a first outlet for a first liquid output stream, a second outlet for a first vapor stream, an evaporator sub-unit comprising an evaporating means for evaporation of a liquid to produce a vapor, an internal sub-unit having a surface embodied such that a contact is provided between a vapor and a liquid and a mass transfer is provided between the vapor and the liquid, a heat exchanger sub-unit comprising a heat exchanging means embodied such that a heat exchange is provided between a liquid stream, preferably the feed stream or a cooling or heating stream, and a liquid or vapor contained within the evaporator, and a condenser sub-unit comprising a condensing means for condensing the vapor to a condensate, characterized in that the first inlet, the first outlet, second outlet, the evaporator sub-unit, the internal sub-unit, the heat exchanger sub-unit, and the condenser sub-unit are all in fluid and/or vapor communication with one another and are contained within one common vessel, wherein the internal sub-unit is located above the evaporator sub-unit, the heat exchanger sub-unit is located above the evaporator sub-unit, preferably above the internal sub-unit, and the condenser sub-unit is located above the heat exchanger sub-unit and the internal sub-unit, wherein the first inlet is located in a lower portion of the vessel, preferably above the evaporator sub-unit, the first outlet is located below the evaporator sub-unit, and the second outlet is located above the evaporator sub-unit and the first inlet, and wherein the evaporator additionally comprises a first collector, preferably having a jacket for providing thermal isolation, located in an upper portion of the vessel and below the heat exchanger sub-unit, and above the evaporator sub-unit, and embodied such that a condensate is collected and the collected condensate is partially or fully withdrawn from or refluxed within the common vessel.. a first inlet for a first liquid feed stream, a first outlet for a first liquid output stream, a second outlet for a first vapor stream, an evaporator sub-unit comprising an evaporating means for evaporation of a liquid to produce a vapor, an internal sub-unit having a surface embodied such that a contact is provided between a vapor and a liquid and a mass transfer is provided between the vapor and the liquid, a heat exchanger sub-unit comprising a heat exchanging means embodied such that a heat exchange is provided between a liquid stream, preferably the feed stream or a cooling or heating stream, and a liquid or vapor contained within the evaporator, and a condenser sub-unit comprising a condensing means for condensing the vapor to a condensate, characterized in that the first inlet, the first outlet, second outlet, the evaporator sub-unit, the internal sub-unit, the heat exchanger sub-unit, and the condenser sub-unit are all in fluid and/or vapor communication with one another and are contained within one common vessel, wherein the internal sub-unit is located above the evaporator sub-unit, the heat exchanger sub-unit is located above the evaporator sub-unit, preferably above the internal sub-unit, and the condenser sub-unit is located above the heat exchanger sub-unit and the internal sub-unit, wherein the first inlet is located in a lower portion of the vessel, preferably above the evaporator sub-unit, the first outlet is located below the evaporator sub-unit, and the second outlet is located above the evaporator sub-unit and the first inlet, and wherein the evaporator additionally comprises a first collector, preferably having a jacket for providing thermal isolation, located in an upper portion of the vessel and below the heat exchanger sub-unit, and above the evaporator sub-unit, and embodied such that a condensate is collected and the collected condensate is partially or fully withdrawn from or refluxed within the common vessel..