In the production process of polyethylene terephthalate P (PET) by terephthalic acid and ethylene glycol acetylation, the following reasons often cause the material anomalies: (1) the condensation time is too long, the material flow is not smooth, resulting in the dead angle resulting in yellow and black pot scale; (2) because of the leakage of the system, the temperature control is relatively high, which causes the thermal oxidation to increase the gel content; (3) careless operation, the produ