Abstract
A life-cycle analysis (LCA) of greenhouse gas (GHG) emissions and energy use was performed to study bio-jet fuel (BJF) production from micro-algae grown in open ponds under Chinese conditions using the Tsinghua University LCA Model (TLCAM). Attention was paid to energy recovery through biogas production and cogeneration of heat and power (CHP) from the residual biomass after oil extraction, including fugitive methane (CH4) emissions during the production of biogas and nitrous oxide (N2O) emissions during the use of digestate (solid residue from anaerobic digestion) as agricultural fertilizer. Analyses were performed based on examination of process parameters, mass balance conditions, material requirement, energy consumptions and the realities of energy supply and transport in China (i.e., electricity generation and heat supply primarily based on coal, multiple transport modes). Our LCA result of the BJF pathway showed that, compared with the traditional petrochemical pathway, this new pathway will increase the overall fossil energy use and carbon emission by 39% and 70%, respectively, while decrease petroleum consumption by about 84%, based on the same units of energy service. Moreover, the energy conservation and emission reduction benefit of this new pathway may be accomplished by two sets of approaches: wider adoption of low-carbon process fuels and optimization of algae cultivation and harvest, and oil extraction processes.
Highlights
Water movement occurs when the ponds are mixed to keep the algae in suspension, when culture is moved for settling, when the supernatant is recycled to the pond, and when water lost due to evaporation and soil leakage is replaced
Our analyses showed that this hypothetical bio-jet fuel (BJF) pathway can increase total fossil energy use and greenhouse gas (GHG) emission by 39% and 70%, respectively, while reducing petroleum consumption by 84%, compared with the conventional jet fuel (CJF) pathway
Our life-cycle study suggests that compared with the traditional petrochemical pathway, the algae jet fuel pathway will increase overall fossil energy use and GHG emission by 39% and 70%, respectively, while decreasing petroleum consumption by 84%
Summary
China is Facing Rapidly Increasing Energy Demand and Oil Imports. With global primary energy demand expected to grow at a compound annual growth rate of. 1.6% from 2009 to 2035 driven by future global population and economic growth [1], mitigation of greenhouse gas (GHG) emissions is imperative. 5.82% annually, underpinning the 10% average annual growth of the national economy during the. China is the largest energy producer and consumer in the World [2]. In 2011, China consumed 1839 million tons of oil equivalents (Mtoe) of coal, 461.8 Mtoe of oil and. 117.6 Mtoe of natural gas (NG), representing 49.4%, 11.4% and 4.0% of the World total, respectively [3]. Its per capita reserves of coal, petroleum and NG are 67.0%, 5.4%, and 7.5% of World averages, respectively [4]
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