NOVELTY - A multifunctional reaction kettle for producing biodiesel comprises kettle body (1), jacket (2), baffle (3), methanol charging tube (4), overhauling hole (5), raw oil charging tube (6), main stirring shaft (7), main speed reducer (8), main electromotor (9), sub-electromotor (10), sub-speed reducer (11), exhaust tube (12), sub-stirring shaft (13), catalyst charger (14), hot medium exit (15), turbine paddle (16), shaft flow paddle (17), discharge hole (18), and hot medium entrance (19).    USE - The multifunctional reaction kettle is used for producing biodiesel (claimed).    ADVANTAGE - The main stirring device and the sub-stirring device of the multifunctional reaction kettle are composed of a high-low-configured double-paddle device to achieve a whole strong loop and a local high cut.    DETAILED DESCRIPTION - A multifunctional reaction kettle for producing biodiesel comprises kettle body (1), jacket (2), baffle (3), methanol charging tube (4), overhauling hole (5), raw oil charging tube (6), main stirring shaft (7), main speed reducer (8), main electromotor (9), sub-electromotor (10), sub-speed reducer (11), exhaust tube (12), sub-stirring shaft (13), catalyst charger (14), hot medium exit (15), turbine paddle (16), shaft flow paddle (17), discharge hole (18), and hot medium entrance (19), where the kettle body (1) is set with a main stirring device and a sub-stirring device, the main stirring device is set with the main electromotor (9), the main speed reducer (8), the main stirring shaft (7), the shaft flow paddle (17), the main electromotor (9) outside the kettle is connected with the shaft flow paddle (17) inside the kettle to drive through the main stirring shaft (7), the sub-stirring device is set with the sub-electromotor (10), the sub-speed reducer (11), the sub-stirring shaft (13), the turbine paddle (16), the sub-electromotor (10) outside the kettle is connected with the turbine paddle (16) inside the kettle to drive through a sub-stirring shaft (13), the turbine paddle (16) is started when charging the catalyst, at this time, a charging jet flow and a radial discharge flow compose a crash jet flow to achieve to disperse the catalyst quickly; the upper part of the kettle body (1) is set with the methanol charging tube (4), the overhauling hole (5), the raw oil charging tube (6), the exhaust tube (12), the catalyst charger (14), the hot medium exit (15), the bottom of the kettle body (1) is set with the discharge hole (18), the hot medium entrance (19), the kettle is set with the baffle (3), the boundary of the kettle body (1) is set with the jacket (2), a reaction temperature is controlled by heating the jacket. An INDEPENDENT CLAIM is an operation method for multifunctional reaction kettle for producing biodiesel comprising: (1) adding raw oils based on a process ability of the reaction kettle, constantly heating in the jacket (2) of the reaction kettle and by means of inletting the hot medium from the hot medium entrance (19), only starting the main stirring device with the rotating speed of 80-120 rotation/minute, evacuating and dehydrating the kettle body through the exhaust tube (12) connected with the vacuum pump, the constant temperature is 70-75 degrees C, the heating time is 30-60 minutes, the vacuum degree is 0.01-0.02 Mpa; (2) after dehydrating in vacuum, continuously starting the main stirring device, firstly adding methanol having the quality ratio which is 3-10% of the raw oil in the reaction kettle based on an acid value of the raw oil, starting the sub-stirring device with the rotating speed 180-240 rotation/minute, slowly adding concentrated acid having the quality ratio which is 0.2-0.5% of the raw oil through the catalyst charger (14), performing pre-esterification reaction, controlling the reaction temperature by heating the jacket, the reaction temperature is 60-80 degrees C, the reaction time is 1.5 hours, etherifying the free fatty acid in the raw oil into the fatty acid methyl ester; after the reaction time of 1.5 hours, if the acid value of the raw oil has not been lowered under 2 mg potassium hydroxide (KOH)/g, consciously starting the main stirring device, closing the sub-stirring device, continuously and constantly heating the kettle body for 30 minutes in the evacuating situation to perform dehydration and de-methanol, reusing methanol through rectification and after separating from the water, performing the acid catalysis pre-esterification reaction for 1 hour; (3) after ending the pre-esterification reaction, stopping heating, computing the amount of just completely neutralizing the needed strong base, matching the saturated solution of the strong base, slowly adding into the reaction kettle through the catalyst charger (14) in the condition of the main stirring device, the sub-stirring device continuously stirring, performing the neutralization reaction for 5-10 minutes; (4) after ending the neutralization reaction, starting the main stirring device, closing the sub-stirring device, performing evacuation, dehydration, de-methanol in the condition of continuously and constantly heating the kettle body, reusing methanol through rectification and separating from the water, the constant temperature is 70-75 degrees C, the heating time is 30-60 degrees C, the vacuum degree is 0.01-0.02 MPa; (5) after vacuum dehydration and de-methanol, continuously starting the main stirring device, first adding methanol having the quality ratio which is 16-22% of the raw oil in the reaction kettle, starting the sub-stirring device with the rotating speed 80-120 rotation/minute, slowing adding strong base having the quality ratio which is 0.8-1.2% of the raw oil through the catalyst charger to perform the ester exchange reaction, controlling the reaction temperature by heating the jacket, the reaction temperature is 55-75 degrees C, the reaction time is 30-50 minutes, reacting the fatty acid glyceride in the raw oil to generate the fatty acid methyl ester; (6) after ending the ester exchange reaction, continuously starting the main stirring device, closing the sub-stirring device, performing the evacuation and de-methanol in the condition of continuously and constantly heating the kettle, directly using after condensing methanol, the constant temperature is 65-70 degrees C, the heating time is 30-60 minutes, the vacuum degree is 0.01-0.02 MPa; and (7) after de-methanol in vacuum, exhausting the mixture of the product fatty acid methyl ester and glycerol from the reaction kettle, after the static delamination and or centrifugation, respectively refining fatty acid methyl ester and glycerol.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of the multifunctional reaction kettle for producing biodiesel.    Kettle body (1)    Jacket (2)    Baffle (3)    Methanol charging tube (4)    Overhauling hole (5)    Raw oil charging tube (6)    Main stirring shaft (7)    Main speed reducer (8)