NOVELTY - Producing bio-diesel, comprises (i) pre-treating waste oil; (ii) performing esterification reaction; (iii) performing transesterification reaction in an alkaline methanol preparation machine; (iv) performing dealcoholization by circulating the mixture once from the mixed crude methyl ester temporary storage tank into a soft water heater; (v) washing the crude methyl ester by adding water, stirring under washing conditions, and performing centrifugal separation; (vi) distilling, and deodorizing aqueous crude methyl ester; (vii) recycling methanol; and (viii) purifying and recycling.    USE - The method is useful for producing bio-diesel oil (claimed).    ADVANTAGE - The method has high utilization rate of crude oil, less amount of esterification catalyst, produces product with high catalytic activity, shortens the esterification reaction time, effectively controls the heating medium temperature, can effectively reduce generation of saponified products, reduces the energy consumption, has lower production costs, The bio-diesel oil has acid value not less than 0.5 mg potassium hydroxide/g, production yield can reach up to more than 92%, ensures the quality of the product according to BD100, and is suitable for industrial production.    DETAILED DESCRIPTION - Producing bio-diesel oil, comprises (i) pre-treating waste oil in a crude oil pre-treating kettle (13), adding 10-15% water into waste oil, heating at 60-80 degrees C under stirring condition, stirring at constant temperature for 20-40 minutes, adding 0.1-0.5% methanesulfonic acid into waste oil, continuously stirring for 30-60 minutes, adding 0.01-0.03% polyacrylamide into waste oil, then stirring for 30-60 minutes, performing centrifugal separation in a butterfly-type centrifuge (12), transferring the pre-treated waste oil into a crude oil temporary storage tank (11); (ii) performing esterification reaction by transferring pre-treated waste oil from crude oil temporary storage tank into a crude oil heat exchanger (10), and preheating to 50-60 degrees C, and heating waste oil in a crude oil steam heater (9), and heating the waste oil at 100-110 degrees C in an esterification reaction kettle, adding an 0.1-0.5% esterification catalyst into waste oil added into esterification reaction kettle, preheating the waste oil at 50-60 degrees C by adding refined methanol into a methanol heat exchanger of a refined methanol storage tank, heating in a methanol steam heater, heating the gasification methanol at 70-90 degrees C having flow rate of 0.7-0.8 m3/hour in esterification reaction kettle, passing gaseous-phase methanol into the bottom portion of the tube set with esterification reaction kettle, turning on a stirring device and a temperature control device of the esterification reaction kettle, controlling the temperature of the esterification reaction kettle at 100-110 degrees C, performing esterification reaction for 2-3 hours at constant temperature, degreasing the steam generated during esterification reaction and unreacted gasification methanol generated in the esterification reaction kettle located on top of a demister, successively transferring the mixture into methanol heat exchanger, a waste methanol cooler and a waste methanol temporary storage tank, and allowing esterified oil to outflow into the lower portion of the esterification reaction kettle, then transferring into the crude oil heat exchanger and a first circulating water cooler provided with a transesterification reaction kettle; (iii) performing transesterification reaction; (iv) performing dealcoholization by circulating the mixture once from the mixed crude methyl ester temporary storage tank into a soft water heater, heating at 65-70 degrees C, dealcoholizing the mixture into a flash evaporation dealcoholization tower under vacuum conditions, allowing the methanol to overflow from the flash evaporation dealcoholization tower, and removing alcohol and transferring into an ice brine cooler, cooling the recycled alcohol in a vacuum system, and circulating the other portion of methanol and ester exchange product for second time into the soft water heater, heating to 65-70 degrees C, dealcoholizing in a falling film dealcoholation tower, collecting the overflowing methanol from the top of the falling film dealcoholation tower into a collecting groove, transferring the second time dealcoholized product into the ice brine cooler, and cooling the recycled alcohol in vacuum system, and allowing the falling film dealcoholated crude methyl ester mixture to flow into a crude methyl ester washing tank; (v) washing the crude methyl ester by adding 5-10% water, stirring at 40-60 degrees C for 2-15 minutes under washing conditions, performing centrifugal separation of the washed coarse methyl ester mixture in a second disc-type centrifuge, adding crude glycerin into a crude glycerin tank, adding water into aqueous crude methyl ester placed in a crude ester temporary storage tank; (vi) distilling, and deodorizing aqueous crude methyl ester placed in a crude ester temporary storage tank, transferring aqueous crude methyl ester into a steam heater, heating at 100-110 degrees C, and removing residual moisture by transferring the mixture into a falling film dehydration tower, cooling moisture in a second circulation water cooler, circulating into a water jet vacuum system, dehydrating crude methyl ester, and transferring into crude ester temporary storage tank, and successively adding crude ester into heat exchanger and a second crude ester heat exchanger, and heating the crude methyl ester in a heat transfer fluid (HTF) heat exchangers backward, and distilling in a distillation tower; (vii) recycling methanol by methanol rectification process in the waste methanol temporary storage tank, and successively adding crude methanol into waste methanol preheater, and waste methanol steam heater of the methanol distillation column, heating the distillation product, allowing the methanol to flow from the top of the methanol distillation column, and then transferring into the waste methanol preheater, transferring the mixture into a fifth circulating water cooler and a second ice brine cooler, and flowing into refined methanol temporary storage tank, allowing the a portion of refined methanol to inflow from refined methanol temporary storage tank into refined methanol storage tank, re-entering into methanol distillation column, concentrating aqueous methanol extract from methanol distillation column into bottom port of waste methanol extraction concentration tower, boiling, and continuously distilling in methanol distillation column; and (viii) purifying and recycling glycerin.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the a device used in the above mentioned method.    Crude oil steam heater (9)    Crude oil heat exchanger (10)    Crude oil temporary storage tank (11)    Butterfly-type centrifuge (12)    Crude oil pre-treating kettle (13)