Simultaneous Optimization Of Barley Straw To Oil Processes And Utility Systems

With the shortage of oil resources, the rise of crude oil price, the influence of green house effect and so on, it is necessary to strengthen the development and application of biofuels. According to our national conditions, developing biomass liquid fuels is inevitable.The biomass into oil (BTO) processes consist of biomass collection, biomass fast pyrolysis, bio-oil gasification, water gas shift, acid gas removal and CO2capture, Fischer-Tropsch (FT) synthesis, syncrude refining and tail gas treating. The process tail gas include FT synthesis tail gas and syncrude refining tail gas containing CO, H2, CH4, C2H6and so on. The process tail gas can be used as utility system fuel for energy and power generation to satisfy process heating, cooling, electricity, and shaft power demands. It also can be recycled with CO and H2recovery for process synthesis by reverse-flow autothermal reforming (RFAR), the coupling of membrane separation and pressure swing adsorption (PSA), or cryogenic separation recovery method. Utility systems comprise gas turbines, heat recovery steam generators, boilers, steam turbines etc.Different process tail gas treating methods will change the process products, steam, water, electricity, power demands, etc and the design of utility system structure. So the simultaneous optimization of BTO processes and utility systems can improve the whole system productions and energy efficiency.In this paper, taking barley straw as biomass feed, based on the Aspen Plus simulation of BTO processes, a MILP model of the simultaneous optimization of BTO processes and utility systems has be formulated to make the gross profit maximum. And obtain the optimal design of the BTO processes and utility systems by GAMS.By the economic benefits, CO2emissions comparison of three tail gas recovery methods including RFAR, membrane and PSA coupling, and cryogenic separationit, it is found that the optimal process operation parameters are all the same, and the H2/CO mole ratio of FT synthesis feed, FT synthesis reaction temperature and FT synthesis recovery percentage are2.06,200℃,100%, respectively. When FT tail gas is recovered by RFAR, the maximum gross profit is113.68M$/a, which increases41.69%by the non-optimal condition, the productions increase22.30%, and the utility systems operation cost increases35.99%. Therefore, it is necessary for the simultaneous optimization of BTO processes and utility systems. It also finds that the maximum gross profit of RFAR is more than cryogenic separation, and the membrane and PSA coupling is the least. The CO2emission cost of cryogenic separation is more than membrane and PSA coupling, and the RFAR is the least.