NOVELTY - Making glycerol involves delivering trans-esterification by-product from bio-diesel fuel processing process to blending tank (101); guiding clean water from tank (103) to blending tank and phosphoric acid from tank (102) to homogenizer (104) at pre-setting ratio for blending; operating pump (107) to deliver blended by-product to homogenizer; delivering homogenized by-product mixture to feedstock tank and then to three-phase stack disc separator to separate into free fatty acid, crushed crystalloid potassium phosphoric acid and crude glycerol mixture of glycerol, water and methanol.    USE - For preparing glycerol, particularly a medical grade glycerol, from a by-product of a bio-diesel process, where the by-product comprises ethylene glycol (claimed).    ADVANTAGE - The efficient and automatic glycerol manufacturing process prepares medical grade glycerol having purity over 99.75%. In the process methanol obtained is evaporated at 58 degrees C when under the working pressure 100 mBar. This design avoids exposure of glycerol composition to a high temperature environment to affect its quality, and eliminates the risk of approaching of methanol steam to flash point. Also water is evaporated at 95 degrees C when under the working pressure 100 mBar. This design avoids exposure of glycerol composition to a high temperature environment and emulsification of glycerol by steam, thus maintaining the product quality. Moreover, the free fatty acid obtained from the process as a by-product is useful as an animal feed additive and as a fuel and the crushed crystalloid potassium phosphoric acid obtained is useful for making potassium phosphoric acid fertilizer.    DETAILED DESCRIPTION - Preparation of glycerol using a system comprising a trans-esterification by-product blending tank (101), a phosphoric acid tank (102), a clean water tank (103), a homogenizer (104), a feedstock tank, a three-phase stack disc separator and several delivery pumps (105-108), involves: putting phosphoric acid in the phosphoric acid tank; delivering a trans-esterification by-product obtained from a bio-diesel fuel processing process to the blending tank; guiding clean water from clean water tank to blending tank and guiding phosphoric acid from phosphoric acid tank to the homogenizer at a pre-setting ratio for blending; operating one delivery pump (107) to deliver the blended by-product from blending tank to homogenizer for homogenizing into a homogenized by-product mixture; delivering homogenized by-product mixture to feedstock tank; and delivering homogenized by-product mixture from feedstock tank to three-phase stack disc separator and then operating three-phase stack disc separator to separate homogenized by-product mixture into free fatty acid, crushed crystalloid potassium phosphoric acid, and a crude glycerol mixture of crude glycerol, water and methanol. The glycerol preparation system further comprises a thin film evaporator unit and a crude glycerol mixture dehydrator unit. The glycerol preparation method further involves a methanol recycling procedure used with thin film evaporator unit; and a crude glycerol mixture dehydrating procedure.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic drawing showing the arrangement of a pre-treatment unit.    Trans-esterification by-product blending tank (101)    Phosphoric acid tank (102)    Clean water tank (103)    Homogenizer (104)    Delivery pumps (105-108)