Method and system for preparing fuel by using high acid value biological oil and fat

A method for preparing fuel using high-acid-value biological grease, comprising:

• (a) subjecting the high-acid-value biological grease to thermal cracking and deoxidization under a first set of heating conditions;
• (b) subjecting a product of step (a) to vacuum distillation to separate water, a high-acid-value fraction, a low-acid-value fraction and a heavy component;
• (c) catalytically cracking and deoxidizing the high-acid-value fraction obtained in the step (b) to separate water and non-condensable gas in the presence of a catalytic cracking deoxidization catalyst under a second set of heating conditions;
• and
• (d) catalytically hydrodeoxygenating a mixture of a product obtained in the step (c) and the low-acid-value fraction obtained in the step (b) with hydrogen in the presence of a hydrodeoxygenation catalyst under a third set of heating conditions.