Heat integrated distillation apparatus

A distillation apparatus of the present invention includes high-pressure column 1 corresponding to a region above a heat exchanging section located at a lowermost part of a region including a trayed section or a packed bed section, which is used as a rectifying section; and low-pressure column 2 that is located above as seen from high-pressure column 1, which integrates a region including a trayed section or a packed bed section which is used as a stripping section, with rectifying section corresponding portion 2g that corresponds to a region locating below the heat exchanging section located at the lowermost part in the rectifying section. Rectifying section corresponding portion 2g is located on top 2c of the stripping section in low-pressure column 2 so that rectifying section corresponding portion 2g continues to the stripping section. The distillation apparatus further includes first pipe 26 that connects column bottom 1a of high-pressure column 1 with rectifying section corresponding portion 2g via means 6 that pressure-feeds liquid that remains in column bottom 1a of high-pressure column 1 to rectifying section corresponding portion 2g, heat exchanger 8 located at a stage in a lower part of low-pressure column 2, a second pipe (23, 4a) that connects rectifying section corresponding portion 2g with heat exchanger 8 in a lower part of low-pressure column 2, compressor 4 installed in the first pipe (23, 4a) and configured to compress vapor from rectifying section corresponding portion 2g and then feed the compressed vapor to heat exchanger 8 in the lower part of low-pressure column 2, and third pipe 30 that introduces fluids flowing out from heat exchanger 8 in the lower part of low-pressure column 2 to column bottom 1a of high-pressure column 1. According to the apparatus configuration, further energy saving can be achieved.