The low temperature coal pyrolysis technology and the atmospheric and vacuum tar distillation were combined to establish a low-rank coal based process system, which can co-produce semicoke, syngas and light oil. And then the simulation models of key units and whole system were also developed. As the calculation results, the lignite with 41.0% moisture can be converted to semicoke, syngas and light oil. Their yields are 42.31%, 8.47% and 4.10%, respectively. The distribution shows that the energy consumption and the exergy loss of drying unit are all the largest with 323.1 kW and 300.1 kW, and those of pyrolysis unit rank the second with 196.2 kW and 131.4 kW. Based on a graphic illustration of energy analysis, the reasons of energy consumption and depreciation were explained. The energy grades of products are increased or decreased at the cost of energy consumption and depreciation. A heat integrated co-production system was proposed to assess the energy saving potential of the original system. The energy consumption and the exergy loss for the whole system have been reduced by 14.9% and 10.9%, and the heat integration effect of drying unit has a relatively larger influence on that of the whole system. (C) 2013 Elsevier Ltd. All rights reserved.