Fangwei Cheng

Carbon emissions accounting with forest-derived biomass energy is more complex than for waste or crop-residue biomass because carbon emissions and uptake occur over more heterogeneous landscapes and longer timeframes. To better understand climate impacts of forest bioenergy use, we develop a comprehensive framework for assessing the dynamic lifecycle greenhouse gas emissions for bioenergy projects using pine pulpwood feedstocks from managed forests in the U.S. South. We apply it in eight different forest basins to determine the carbon payback period and cumulative carbon storage for hypothetical bioenergy projects with 30-year plant operating lives (2030-2060). Variations in local forest types, age class distributions, and traditional wood product market demands result in large differences in carbon payback times between basins. In general, carbon debt repayment is faster for biofuel or bioelectricity projects that employ CCS than those that do not. We find that facilities employing CCS and consuming 3 million green tons of feedstock annually yield carbon payback periods below 10 years if located within pine-dominated coastal plain or gulf coast regions. In a hardwood-dominated basin such as in Virginia, carbon payback is not achieved.

The Inflation Reduction Act (IRA) in the United States provides unprecedented incentives for deploying low-carbon hydrogen and liquid fuels, among other low-greenhouse gas (GHG) emissions technologies. To better understand the prospective competitiveness of low-carbon or negative-carbon hydrogen and liquid fuels under the IRA in the early 2030s, we examined the impacts of the IRA provisions on the costs of producing hydrogen and synthetic liquid fuel made from natural gas, electricity, short-cycle biomass (agricultural residues), and corn-derived ethanol. We determined that, with IRA credits (45V or 45Q) but excluding the incentives provided by other national or state policies, hydrogen produced by electrolysis using carbon-free electricity (green H₂) and by natural gas reforming with carbon capture and storage (CCS) (blue H₂) is cost-competitive with the carbon-intensive benchmark gray H₂, which is produced by steam methane reforming. Biomass-derived H₂ with or without CCS is not cost-competitive under the current IRA provisions. However, if the IRA allowed biomass gasification with CCS to claim a 45V credit for carbon-neutral H₂ and a 45Q credit for negative biogenic CO₂ emissions, this pathway would be less costly than gray H₂. The IRA credit for clean fuels (45Z), currently stipulated to end in 2027, would need to be extended or similar policy support would need to be provided by other national or state policies in order for clean synthetic liquid fuel to be cost-competitive with petroleum-derived liquid fuels. The levelized IRA subsidies per unit of CO₂ mitigated for all of the hydrogen and synthetic liquid fuel production pathways, except for electricity-derived synthetic liquid fuel, range from $65-$384/t of CO₂. These values are within or below the range of the U.S. federal government's estimates of the social cost of carbon (SCC) in the 2030-2040 time frame.

The Inflation Reduction Act (IRA) in the United States provides unprecedented incentives for deploying low-carbon hydrogen and liquid fuels, among other low greenhouse gas (GHG) emissions technologies. To better understand the prospective competitiveness of low-carbon or negative-carbon hydrogen and liquid fuels under the IRA in the early 2030s, we examine the impacts of IRA provisions on costs of producing hydrogen and synthetic liquid fuel made from natural gas, electricity, short-cycle biomass (agricultural residues), and corn-ethanol. With IRA credits (45V or 45Q), but excluding incentives provided by other national or state policies, hydrogen produced by electrolysis using carbon-free electricity (green H2) and natural gas reforming with carbon capture and storage (CCS) (blue H2) are cost-competitive with the carbon-intensive benchmark gray H2 from steam methane reforming. Biomass-derived H2 with or without CCS is not cost-completive under current IRA provisions. However, if IRA allowed biomass gasification with CCS to claim a 45V credit for carbon-neutral H2 and a 45Q credit for negative biogenic-CO2 emissions, this pathway would be less costly than gray H2. The IRA credit for clean fuels (45Z), currently stipulated to end in 2027, would need to be extended, or similar policy support provided by other national or state policies, for clean synthetic liquid fuel to be cost-competitive with petroleum-derived liquid fuels. Levelized IRA subsidies per unit of CO2 mitigated for all hydrogen and synthetic liquid fuel production pathways, except electricity-derived synthetic liquid fuel, range from 65 to 384 $/t CO2, which is within or below the range in U.S. federal government estimates of the Social Cost of Carbon (SCC) in the 2030 to 2040 timeframe.

The increasing amount of municipal sludge in China requires safe and effective management to protect human health and ensure environmental sustainability. Pyrolysis is a thermochemical process that that decompose organic matter at elevated temperature and under anaerobic conditions, and it has attracted an increasing attention in sludge treatment in the recent years. However, comprehensive environmental and economic assessment of sludge pyrolysis in China's context is rare, due to the small quantities of full-scale sludge pyrolysis plant. In this paper, we applied our design and operation parameters of full-scale sludge pyrolysis plants to generate the material and energy consumptions of the pyrolysis system under various of conditions, including sludge organic content and moisture content, system size, system energy distribution, and whether or not heat substitution is applied. Life cycle assessment and techno-economic assessment were then applied to investigate the environmental and economic performance of the system Our results demonstrate the significant environmental and economic impacts associated with sludge properties and system size. Generally, sludge with higher organic content and lower moisture content requires less natural gas consumption, which leads to a simultaneous improvement of the system environmental and economic performance. The system economic performance is more sensitive to the system size, and centralized sludge handling using a larger pyrolysis is more economic favorable. In the most ideal case, the average global warming potential and minimum sludge handling price of sludge pyrolysis could be as low as -32.5 kg CO2-Eq/t DS and 188.8 $/t DS, respectively. Based on these results, we discussed the pathways that could be taken to further optimize the environmental and economic performances of the pyrolysis system.

Metal-organic frameworks (MOFs) are a new class of materials that has shown great potential in catalysis, sensing, separations, and carbon capture and storage. Conventionally, MOFs are synthesized at lab-scale using organic solvent-based systems, leading to high environmental burdens and high operating costs, which ultimately hinders the large-scale production and application of MOFs. Aqueous synthesis of MOFs overcomes such difficulty by eliminating the organic solvent, which makes it an environmentalfriendlier and economically-favorable alternative to the current production method. However, further quantitative analysis is required to compare the environmental and economic performances of the two methods. Here, we used life cycle assessment (LCA) coupled with techno-economic analysis (TEA) to evaluate the environmental and economic performances of different UiO-66-NH2 production methods. When the solvothermal method was replaced by the aqueous solution-based method, the LCA and TEA results suggest the environmental burdens and cost of UiO-66-NH2 production were reduced by up to 91% and 84%, respectively. By using aqueous solution-based method, the cradle to gate carbon footprint and production cost of UiO-66-NH2 were estimated to be 43 kg CO2 eq/kg and $15.8/kg, respectively. We further applied our LCA results to reassess the role of UiO-66-NH2 in carbon capture and storage (CCS) and compare its environmental performance with current benchmark (amine-based solvent). Our results show that UiO-66-NH2 could potentially have better environmental performance than the amine-based solvent if the number of regeneration cycles is greater than 1513. This work is the first comprehensive LCA-TEA study that quantifies the substantial environmental and economic benefits of using the aqueous solution-based systems to produce UiO-66-NH2, and the analysis in this work is intended to be a starting point for further systematic studies on the full life-cycle impacts of MOFs.