초록 ▼

An energy-efficient water evaporation process uses a falling film evaporator having a plurality of substantially vertical and equidistant heat exchange elements made of a synthetic polymeric material. Each evaporating surface is in contact with a liquid spreading means, and each heat exchange elemen

An energy-efficient water evaporation process uses a falling film evaporator having a plurality of substantially vertical and equidistant heat exchange elements made of a synthetic polymeric material. Each evaporating surface is in contact with a liquid spreading means, and each heat exchange element is heated by steam having a condensation temperature slightly higher than the boiling point of the aqueous solution from which water is being evaporated. Steam formed by evaporation of water either is recompressed and reintroduced as heating steam in a single-stage process or is used as heating steam for another stage, operating at a lower temperature and pressure, in a multistage process. Heating steam condenses to fresh water, which is recovered. This process is operated at a low feed rate, preferably below 45 Kg of incoming aqueous solution per linear meter of horizontal width of each evaporating surface, and is capable of providing a 50% fresh water recovery per pass from sea water. Higher recoveries are possible in the case of brackish waters and various industrial waters. The process is useful in water desalination and purification.

대표청구항 ▼

In a process for the evaporation of water from an aqueous solution, wherein (1) The aqueous solution is preheated substantially by means of heat from hot fresh water, and when the volume of liquid concentrate produced downstream is means of heat of liquid concentrate, and is deaerated; (2) the prehe

In a process for the evaporation of water from an aqueous solution, wherein (1) The aqueous solution is preheated substantially by means of heat from hot fresh water, and when the volume of liquid concentrate produced downstream is means of heat of liquid concentrate, and is deaerated; (2) the preheated aqueous solution is introduced at or near the top of a single- or multiple-stage falling film evaporator having a plurality of substantially vertical and equidistant heat exchange elements made of a film of a synthetic polymeric material, each such element having two outer heat exchange surfaces and two inner heat exchange surfaces, said outer surfaces communicating with a feed means for the aqueous solution at or near the top of the evaporator and with a liquid concentrate collection means at the bottom of the evaporator; and said inner surfaces being heated by steam having a temperature higher than the boiling point of the aqueous solution at the operating pressure, the average temperature difference, D0.1°-3.5°C.; (3) the aqueous solution is distributed among the several heat exchange elements and is allowed to fall as a film down their outer heat exchange surfaces, and a portion of the water evaporates from the aqueous solution at its boiling point, evaporation heat being supplied by steam in contact with the inner heat exchange surfaces of the heat exchange elements, whereby steam condenses to hot fresh water; hot fresh water being removed from the falling film evaporator and recovered, its heat being used to preheat the incoming aqueous solution; liquid concentrate, which collects at the bottom of heat exchange elements being removed from the falling film evaporator and disposed of, but if the volume of liquid concentrate is sufficient for an economically attractive operation, its heat being used to preheat the incoming aqueous solution; and steam formed by water evaporating from the outer surfaces of the heat exchange elements being either compressed and recirculated as the heating steam for the same stage of the falling film evaporator or introduced without compression to a second stage of the falling film evaporator operating in the same manner as the first stage but at a lower steam pressure and lower water boiling temperature; the improvement of: (a) providing liquid spreading means being made of fibers or particles which are wettable or made wettable by water, said liquid spreading means having a free area of at least 20%, and the spacing and dimensioning of the individual fibers or particles being such that the descending aqueous solution forms droplets which completely fill the voids, such that each liquid spreading means coacts with its closest outer heat exchange surface and with the flowing aqueous solution to form a stable, thin film over said outer heat exchange surface, thereby permitting even evaporation of water from each said surface without formation of either dry spots or rivulets, said liquid spreading means having a horizontal spreading means component; (b) maintaining the feed rate of the aqueous solution to be evaporated at less than 300 kg per linear horizontal meter of each outer heat exchange surface per hour, said feed rate always being higher than the evaporation rate of said solution; and (c) forming said stable, thin film over the entire area of each of said outer heat exchange surfaces.