Process Integration of a Polygeneration Plant with Biomass/Coal Co-pyrolysis

The concept of co-pyrolysis of biomass and conventional fossil fuel offers various advantages such as higher liquid product yield and higher char conversion than if the coal and biomass particles were processed individually. In the case of added value fuel production such as diesel and gasoline, the maximization of the fraction of pyrolysis oil is the foremost objective. At the same time, the produced char and permanent gases should be properly used for the isothermal and stable operation of the pyrolysis process. This study presents an integrated model of co-pyrolysis in ASPEN Plus for the production of advanced hydrocarbons aiming to determine the conditions under which the process performance is maximized. The methodology for the design and modeling of each main unit of the system (i.e., the pyrolysis plant, the oil upgrading unit, and char exploitation plant) is described in detail. Simulation runs were performed for various blending ratios from 0% to 100% of coal to biomass, aiming for the optimum design and operation scheme regarding (a) maximization of the yields of the desired products and (b) exploitation of the retrieved char. Simulation results revealed that high yields of hydrocarbons (up to 0.179 kg(HCs)/kg(feed)) can be produced due to the synergetic effects of co-pyrolysis of coal and biomass. Moreover, the total process efficiency when the rest of char is utilized for electricity and methanol production can reach at 55.5% and 61.9%, respectively. Finally, the energy balance calculations for the case of 60% coal blending ratio showed that almost 30% of the initial heat input is used as heat for pyrolysis and allothermal gasification of the char. Possible use of alternative heat sources, e.g., from solar energy for these two processes would further improve the system performance in terms of advanced fuels productivity.