Simulation Of China's Straw Use To Conserving Energy And Carbon Reduction:Climate Change Mitigation

Straw conversion for feed,fuel and fertilizer by replacing commercial product contributes to energy conservation and greenhouse gasses emission reduction in China.However,completion among multiple users for the limited straw resources attracts great attention.China as a huge agricultural country,produces about 800 million tons of straw annually,and most of those straw was comprehensively used for various purposes.However,a large amount of straw is still burned,leading to resource waste in addition to emission of greenhouse gases(GHGs)emissions.Therefore,it is of great significance to optimize the policy of straw utilizations and to maximize the potential of energy conservation and GHGs emission reduction.Based on the current situation of straw utilization in China,this paper applied the method of life cycle assessment to quantify the efficiency of energy conservation and GHGs emission reduction of 14 kinds of straw conversion technologies.Competitive utilization system and reference system of multiple straw uses were established.Based on the predefined scenarios of straw use policies,this study conducted the uncertainty optimization to find out the optimal policy,so that the national scale straw use system is capable of conserving energy and reduce GHGs emission to the largest extent.The results are as follows:(1)Different straw conversion technology generate different capacity in energy-conservation and GHGs emission reduction.Feeding livestock straw-based forage produced by the Fsilage method unexpectedly maximized the rate of climate-change mitigation among all conversion technologies.Hgasification and Pgasification,as alternatives to fossil energy,had the highest rates of energy conserving of 5.23 and 2.48 GJ t-1 on average,respectively.They were inferior to Pco-firing and HL-digestion in reducing GHGs.Techonologies of Hstove(TSC),Hstove(ISC)and Hboiler were comparable to each other in reducing GHGs reduction with similar rates of 260 kg CO2e t-1,but differed slightly in energy conservation ranging from 0.18 to 0.76 GJt-1.(2)In all competitive uses,straw uses for feeding livestocks has the greatest environmental benefit,followed by alternative nutrient purpose and finally by fossil fuels,with energy conservation rates of 2.79,0.46 and 1.15 GJ t-1,and GHG reduction of 834,319 and 583 kg CO2e t-1,respectively.Sensitivity analysis shows that mechanary paramter of straw returning to fields and SOC increasing contributes the most to the uncertainty of climate-change mitigation for straw uses as a substitute for commercial fertilizers.When straw is used as livestock forage,uncertaities mainly resulted from ammonia synthesis,urea synthesis and straw chopping processes.Moreover,Hstove(Isc)functions significantly in the generation of uncertainty when straw was used for energy purposes by both a traditional stove()and an anaerobic digester.(3)Comprehensive straw use in China benefits considerably in climate change mitigation.The average(95%confidence intervals)annual amount of reduced GHGs and conserved energy reaches up to 271(228-297)Mt yr-1 and 0.75(0.52-1.05)EJ yr-1,respectively.Substituting straw for commercial forage contributes the most,followed by the use of straw as farmland nutrients by adding straw to fields.In contrast,energy use of straw contributes the least based on the currently surveyed and estimated pattern of straw uses.Simulations on scenarios of competitive straw use policy suggest that cooperative decision-making among China's multi-administrations is critical to maximizee the potential of climate change mitigation(i.e.1.84-2.26 EJ yr-1 of energy conserving,or GHGs reductions of 465-569 Mt CO2e yr-1).China's straw uses for forage,farm nutrients and energy are managed by different departments,and competition on the limited straw resource is unavoidable in practice.Analysis of this study shows that cooperation among agricultural,environmental,animal-husbandry and energy departments is critical to achieve the dual goals to ban straw burning and maximize climate change mitigation,which is of great significance for China to mitigate climate change.