Spectrally Efficient Frequency Division Multiplexing (SEFDM) is a non-orthogonal multicarrier communication technique that can pack more sub-carriers than Orthogonal Frequency Division Multiplexing (OFDM) in a given bandwidth. In this work, we propose a multi-band architecture named Block-Spectrally Efficient Frequency Division Multiplexing (B-SEFDM) for a large non-orthogonal system. Furthermore, a Block Efficient Detector (BED) is presented in this work and computer simulations show that the performance is improved by at most 4.5 dB while the complexity is decreased by one order of magnitude. Finally, a butterfly structure, which is reconfigurable according to required complexity/throughput, is proposed here for the detection.