NOVELTY - Energy-saving bio-gas plant comprises an anaerobic fermentor (12) for producing bio-gas by anaerobically fermenting the organic waste, a fermentation liquid conveying tank (13) for storing fermentation broth from the anaerobic fermentor, a conveying pipe (14) for conveying fermentation broth in the anaerobic fermentor from the fermentation liquid conveying tank, a flow rate adjustment tank (15) for conveying fermentation broth in the conveying pipe and supplying the raw water in the anaerobic fermentor, and a double jacket pipe (16) for heat exchanging with the fermentation broth.    USE - Used as energy-saving bio-gas plant (claimed).    ADVANTAGE - The bio-gas plant improves bio gas production efficiency in cost effective manner.    DETAILED DESCRIPTION - Energy-saving bio-gas plant comprises an anaerobic fermentor (12) for producing bio-gas by anaerobically fermenting the organic waste, a fermentation liquid conveying tank (13) for storing fermentation broth from the anaerobic fermentor, a conveying pipe (14) for conveying fermentation broth in the anaerobic fermentor from the fermentation liquid conveying tank, a flow rate adjustment tank (15) for conveying fermentation broth in the conveying pipe and supplying the raw water in the anaerobic fermentor, and a double jacket pipe (16) for heat exchanging with the fermentation broth. The double-jacket pipe includes a heat exchange pipe for passing raw water, and a jacket for heat exchanging with raw water within the heat exchange pipe during passing the fermentation broth in the outer side. The jacket is provided with single channel connected to each other by a connection part to avoid bending area of the heat exchange pipe which is provided with multiple heat exchange pipes.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic representation of the energy-saving bio-gas plant.    Anaerobic fermentor (12)    Fermentation liquid conveying tank (13)    Conveying pipe (14)    Flow rate adjusting tank (15)    Double jacket pipe (16)