The invention relates to a process for carrying out strengthening circulation, stage
grinding and quality improvement on lignite by utilizing
superheated steam and a
system thereof. The method comprises the following steps: (1) carrying out
grinding on the
raw material lignite; (2) burning one part of
coal blocks /
powder to produce high-temperature
flue gas serving as a heat source and carrying out
air separation and dring on the other part of
coal blocks /
powder requiring to be subjected to quality improvement; (3) in the process of
air separation, adopting the high-temperature
flue gas from the step (2), carrying out
drying, separation and dust removal on the qualified
coal blocks /
powder conforming to the standard grain
diameter after
air separation, collecting the qualified coal blocks / powder, sending the qualified coal blocks / powder to the forming process, making the unqualified coal blocks / powder drop in a
grinding ventilating device to carry out grinding and
drying, then continuously completing deep
drying by air separation and repeating the steps, wherein the
oxygen content in the
flue gas is less than 8 percent; and (4) sending one path of
waste gas subjected to air separation and drying to the washing process and returning the other path of
waste gas serving as a return
tail gas part to the step (2) so as to prepare the high-temperature
flue gas and carry out air separation. The process has the advantages of safety, energy saving, environment protection, high efficiency, stability and the like.