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Short path type molecular evaporator for used lubricating oil recycling

2014-05-03
1.General description Many fluids such as heavy petroleum oil, chemical medicine, drugs, natural food, health products, fatty acid, etc. are heat sensitive, viscous, and high flash point materials. Separating these materials from other fractions, at same time maintaining properties, can only be distilled under a low boiling temperature or lower than boiling point, in addition, it need to be within a very short duration to reduce thermolysis or polymerization to minimal, so as to avoid deterioration of products. When vacuum degree at 500pa, it can be distilled through thin film evaporator or falling film evaporator. But it doesn’t work if distillation must under high vacuum( for example pressure 0.001-100pa). It must use evaporator that fluid’s vapor pressure not exceeding falling pressure between heating surface and cooling surface, so evaporators with external condenser are excluded from high vacuum evaporation processes. By contrast, SPE short path evaporator is very suitable to this condition, condenser is fitted in evaporator, directly located at the opposite side of evaporation occurring. Short path evaporator is a new kind of evaporator not yet widely used in industrial manufacturing, it is a new form of separation technology able to solve a lot of problems that common evaporation technologies can’t do. 2. Operation procedure Short path evaporator consists of one jacketed cylinder body, built-in condenser and rotor, etc. built-in condenser in the center of evaporator, rotor with scraping system rotating between evaporator and condenser. Evaporation process: feed stock is coming from the top of evaporator, it is averagely distributed to the heating surface by the fluid distributor on rotor, scraper makes feedstock in to a extremely thin, turbulence type liquid film. In this procedure, light molecules evaporated from the heating surface are formed in to liquid by condenser almost free of collisions, flow down through condenser pipe, discharged through discharge tubes at the bottom of evaporator. Fluid residue is the heavy molecules collected in the bottom of heating zone, it flows out from the lateral discharge tubes. 3. Basic principle Distillation is a kind of method for separating of mixture liquid in chemical industrial unit. It is divided in to atmospheric distillation and vacuum distillation, by utilizing volatility difference of mixture liquid to make separation. In other words, the separated light fraction of fluid has saturated vapor pressure higher than system pressure, the fluid can be separated, so the lower system pressure(higher vacuum), the easier separation. Molecular evaporation is based on common evaporation and introduced idea of saturated vapor pressure and molecular average free path, the fastest speed capturing and accumulating light fraction molecules which separated away from liquid fluid, means the distance between heating surface to condenser surface equal or lower than light fraction molecular free path, but must be higher than molecular free path of heavy fraction, to reach good capture performance, condenser surface area shall larger than evaporation surface area, to reach the target of molecular evaporation. But due to it is affected by the equipment structure, practical equipment can’t reach ideal molecular evaporation condition, only approach or simulate molecular evaporation, so we call it short path evaporator, the factors decide separation ability of short path evaporator as below: 1)The dispersing speed of light fraction evaporating from mixture fluid to heating surface. 2)The saturated steam pressure of light fraction and vacuum degree of system. 3)The speed of light fraction from separation to being captured and condensed (distance between heating surface and condensing surface). In view of the above working principle, to enhance the speed of light fraction separating from fluid to evaporating surface, using wiped-film method, scraping fluid on to heating surface as a thin film, makes the dispersing speed of light fraction from fluid to evaporating surface reach the maximum, dispersing time very short. Condenser is precisely built in, makes the distance between heating surface and cooling surface shorter or equal to the molecular average free path, evaporated molecules from evaporating surface are vaporing and collected on to the cooling surface, makes the speed of light fraction collection reach to the ultimate. Instant condensate of light fraction almost free of pressure changes, ensures high vacuum of inner equipment. Molecule’s average free path λ=8.589  n/p  (T/M)1/2  N        Viscosity of fluid  P        Absolute pressure T        Absolute temperature M        Molecular weight   So the factors determine molecular average free path are vacuum degree, heating temperature, viscosity, molecular weight. The higher vacuum degree(the lower absolute pressure) and higher temperature, the higher molecular average free path. So adjusting vacuum degree is the most effective measure to change molecular average free path, it can be decided as per operation expenses. Increasing temperature can also increase molecular average free path, at the same time improve saturated steam pressure of light fraction, help separation ability a lot, but it has negative effect on product quality. 4. Features The features of short path evaporator comparing to common evaporator 1) The separation can be implemented blow boiling point temperature, only if system pressure lower than saturated steam pressure of light fraction and the distance between heating surface and condensation surface lower or equal to molecular average free path of light fraction. 2) Common distillation is operated above boiling point, so evaporation and condensation is a reversible process, short path evaporator is operated below boiling point, so evaporation and condensation of short path evaporator is an irreversible process. 3) Common distillation has bubble, boiling phenomenon, separation operation of short path evaporator is below boiling point, so it is without bubble, boiling phenomenon, which is helpful to maintain high vacuum degree of system. 5. The short path evaporator from our company is combined of international advanced technologies and our technicians'innovations, using different wiping methods for different fluids to meet processing requirement, and different forms built-in condensers to suit fluids of different molecular average free path, proper configuration and precise processing to ensure distance between evaporation surface and condensation surface, boring and polishing processing make the evaporation surface very smooth for fluid flows. 6. System equipment assembly Proper system assembly is not only able to ensure normal running, avoid wasting of investment. Generally speaking, short path evaporator needs high operating vacuum, so before entering in to short path evaporator, it is required to remove light fraction of fluid (non-condensable gas, low boiling point parts). 7. Applicable area A: Petrochemical industry: the regeneration of waste oil, amide, amine, quinoline derivatives, epoxy resins, resin acids, isocyanates, iso-butyl ketone, peroxides, LCD, polyethylene glycol, silicone oil, softener etc. ; B: The pharmaceutical industry: amino acid ester, polymer intermediate, vitamin E, vitamin, etc.; C: Oil Industry: lubricants, diglycerides, dimer fatty acid, fatty acid, fatty acid derivatives, glycerides, acids, lanolin alcohol, etc.; D: Food industry: monoglyceride, bay acid, propylene glycol fat, L-lactic acid, cod liver oil, rice bran oil, wheat germ oil primary three, cinnamon oil, rose oil; E: the molecules produced by the light component extraction equipment for bleaching and then go smell the fragrance of the product to achieve perfect purification process. F: the used extraction extracts were extracted repeatedly used.