Dynamic life-cycle carbon analysis for fast pyrolysis biofuel produced from pine residues: implications of carbon temporal effects

Abstract

Background Woody biomass has been considered as a promising feedstock for biofuel production via thermochemical conversion technologies such as fast pyrolysis. Extensive Life Cycle Assessment studies have been completed to evaluate the carbon intensity of woody biomass-derived biofuels via fast pyrolysis. However, most studies assumed that woody biomass such as forest residues is a carbon–neutral feedstock like annual crops, despite a distinctive timeframe it takes to grow woody biomass. Besides, few studies have investigated the impacts of forest dynamics and the temporal effects of carbon on the overall carbon intensity of woody-derived biofuels. This study addressed such gaps by developing a life-cycle carbon analysis framework integrating dynamic modeling for forest and biorefinery systems with a time-based discounted Global Warming Potential (GWP) method developed in this work. The framework analyzed dynamic carbon and energy flows of a supply chain for biofuel production from pine residues via fast pyrolysis. Results The mean carbon intensity of biofuel given by Monte Carlo simulation across three pine growth cases ranges from 40.8–41.2 g CO2e MJ−1 (static method) to 51.0–65.2 g CO2e MJ−1 (using the time-based discounted GWP method) when combusting biochar for energy recovery. If biochar is utilized as soil amendment, the carbon intensity reduces to 19.0–19.7 g CO2e MJ−1 (static method) and 29.6–43.4 g CO2e MJ−1 in the time-based method. Forest growth and yields (controlled by forest management strategies) show more significant impacts on biofuel carbon intensity when the temporal effect of carbon is taken into consideration. Variation in forest operations and management (e.g., energy consumption of thinning and harvesting), on the other hand, has little impact on the biofuel carbon intensity. Conclusions The carbon temporal effect, particularly the time lag of carbon sequestration during pine growth, has direct impacts on the carbon intensity of biofuels produced from pine residues from a stand-level pine growth and management point of view. The carbon implications are also significantly impacted by the assumptions of biochar end-of-life cases and forest management strategies.

Circular utilization of urban tree waste contributes to the mitigation of climate change and eutrophication

“…31 It has been widely used in LCAs to quantify the climate change implications of different greenhouse gas (GHG) emissions. 17,18,32 Eutrophication is a phenomenon of nutrient enrichment in aquatic ecosystems and eutrophication potential is a common impact category in different life-cycle impact assessment methods (e.g., Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts [TRACI], ReCiPe). 31,33,34 The urban tree wastes in this study are categorized into three groups based on their sizes, including leaf waste, merchantable logs, and residues.…”

“…For example, more than 80% of carbon can be retained in biochar from medium temperature pyrolysis even after 100 years for cropland or grassland applications. 18,41 Hence, biochar can be a potential stable long-term carbon pool. 42 Urban-tree-waste-derived biochar can substitute traditional charcoal, which is included in this analysis as substitution effects.…”

“…The potential substitution benefits are commonly considered in LCAs for biobased products. 11,18,79,83,126 Compost can replace mineral fertilizers that contain nitrogen, phosphorus, and potassium. The lumber made from urban tree waste can replace lumber and chips sold in the market, including both hardwood and softwood products.…”

“…They were selected based on their potential economic and environmental benefits discussed in the previous literature. 7,[17][18][19][20][21] LCA is a standardized and widely accepted tool to evaluate the environmental impacts of a product or a service throughout its life cycle. 17,[22][23][24][25][26] To explore the potential environmental benefits, counterfactual systems for alternative end-of-life cases were considered.…”

Feasibility of gasifying mixed plastic waste for hydrogen production and carbon capture and storage

“…Techno-economic analysis (TEA) is one of the most widely used tools to assess the economic and technical feasibility of emerging technologies [19][20][21][22][23][24] ; Life Cycle Assessment (LCA) is a standardized tool to quantify life-cycle environmental impacts [25][26][27][28][29][30][31] . Several studies have used TEA to evaluate the economic feasibility or LCA to assess the environmental implications of plastic wastes to energy products (see Supplementary Note 1 for literature review).…”