NOVELTY - The biogas digesters comprise a tank body, a feeding hole, a discharging hole, an air outlet (7), a feeding hole sleeve and a discharging pipe (5). The feeding hole is sleeved above the tank body via the feeding hole sleeve. The discharging hole is connected with the bottom of the tank body via the discharging pipe. The air outlet is arranged at a top of the tank body. The feeding hole sleeve is a tubular.    USE - The biogas digesters are useful for discharging small-scale thermoplastic composite materials.    ADVANTAGE - The biogas digesters are capable of conveniently discharging small-scale thermoplastic composite materials with less energy consumption and good air tightness in a simple and an economical manner    DETAILED DESCRIPTION - The biogas digesters comprise a tank body, a feeding hole, a discharging hole, an air outlet (7), a feeding hole sleeve and a discharging pipe (5). The feeding hole is sleeved above the tank body via the feeding hole sleeve. The discharging hole is connected with the bottom of the tank body via the discharging pipe. The air outlet is arranged at a top of the tank body. The feeding hole sleeve is a tubular. The feeding hole sleeve, tank body and feeding hole are connected in a seamless sealing way and then are locked and fixed via a bolt (11) or a clamp. The discharging pipe and the bottom of the tank body are linked via a plastic flange and then are sealed via a high sticky polyurethane. The discharging pipe is directly inserted into the discharging hole, and a connection is welded by a plastic welding bar and is hermetically connected in the seamless sealing way. The tank body is a combined structure, which is assembled by an upper semispherical sheet (1) and a lower semispherical sheet (2). The upper semispherical sheet and the lower semispherical sheet are formed via a rotational molding technology at a time. The upper semispherical sheet and the lower semispherical sheet are sealed in the seamless sealing way and then are locked and fixed via the bolt or the clamp. The feeding hole sleeve and the upper semispherical sheet are connected and extended to the connection between the upper semispherical sheet and the lower semispherical sheet to increase a gas storage chamber. The feeding hole sleeve and the upper semispherical sheet are connected in the seamless sealing way and then are locked and fixed via the bolt or the clamp. The upper semispherical sheet and the lower semispherical sheet are provided with reinforced ribs. The tank body is a sphere, near sphere, a spheroid, and a paraboloid or a polyhedron.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a biogas digesters.    Upper semispherical sheet (1)    Lower semispherical sheet (2)    Discharging pipe (5)    Air inlet (7)    Bolt. (11)