Preparation method and production equipment of urea-coated slow-release fertilizer

The invention discloses a preparation method of a coated urea slow-release fertilizer, the coated urea slow-release fertilizer comprises bentonite, biogas residue, plant ash, water, a urea agricultural fertilizer, a dissolution inhibitor, a urease inhibitor and the like, the plant ash and the biogas residue are crushed, the plant ash of 80 +/-5 meshes and the biogas residue of 50 +/-5 meshes are selected, the water is added into the bentonite, the mixture is stirred according to the proportion of 1: 2, then the mixture is stirred uniformly, and the coated urea slow-release fertilizer is obtained. The preparation method comprises the following steps: uniformly mixing plant ash, biogas residue, bentonite, a dissolution inhibitor and a urease inhibitor, carrying out secondary granulation on the uniformly mixed mixture, and drying the granules by adopting an air drying or low-temperature drying mode to obtain the coated urea slow release fertilizer. Through cooperative use of the extrusion conveying pipe, the dis