Abstract
Sorption-enhanced chemical looping gasification (SECLG) of biomass is a promising process for H2 and transportation fuel (TF) production at reduced CO2 emissions and energy penalties. This work developed a comprehensive process simulation model for the SECLG of waste bagasse to produce H2 and TFs. The model compares the efficiency of high-performance Nickel Oxide (NiO) and Ferric oxide (Fe2O3) oxygen carriers. The effect of parameters such as the fuel reactor (FR) temperature, pressure, equivalence ratio, and solid recirculation is examined. Transitory-state pathways of solid carriers during various redox loops are evaluated. The model is additionally further assessed using techno-economic analysis (TEA) and life cycle assessment (LCA) sustainability tools. The results indicate that SECLG can produce syngas with a molar H2 concentration of 68% at the lowest FR temperature and pressure of 6000C and 5 bar. CO2 in the syngas is significantly limited to substantially less than 10% of the producer’s gas. The overall tar yield in the syngas is attainable at low yields within 2×10-5 g/kg dry bagasse. The TF yield is promising owing to a tunable H2/CO ratio obtained post a reverse water gas shift phase. Regarding the oxygen carrier performance, NiO is more efficient in delivering high-purity H2 syngas with increased CO2 sequestration, while Fe2O3 gains superiority in delivering a producer gas blend with elevated combustibility potential and a higher TF yield.
According to the economic analysis, the biomass-to-gas (BTG) and biomass-to-liquid (BTL) plants require investment costs of 22.81 and 58.26 M$US, payable within non-discounted periods of 4.7 and 7.1 years, separately. These costs are compatible with those of unenhanced gasification plants reported to be within 399M$US given higher processing scales of 1900 ton/day. Levelized costs of syngas and petroleum of 1.08 $US/kg and 2.11 $US/gal were essential in delivering these estimates. These economic options are, however, most sensitive to changes in the selling costs of syngas/petroleum and CAPEX margins of 15%. Nevertheless, a global change in the oxygen carriers and CaO sorbent material has less impact on the economic viability of these plants. Furthermore, the LCA using midpoint impacts on ecosystem quality, terrestrial and human health toxicity, and residual matter formation was evaluated for both process plants - BTG and BTL. In these instances, quantified SO2 and CO2 within 0.009 kg and 91 kg were reported as the major concerns. These globally translated to within 3.3E-2 and 3.3E-6 DALY per unit production of BTG and BTL plants, respectively. However, these were attributed to the linked supply chains, e.g., coal electricity production and harvesting, and were asserted to be less significant compared to impacts from conventional gasification plants. The chemical energy demand (CED) within its derivatives revealed non-renewable energy consumption of 0.0037 and 0.00502 MJ-Eq for the BTG and BTL plants, respectively. Due to minimal deviation in the data within 10000 Montecarlo uncertainty runs, these LCA results were considered valid.