Environmental Impact Assessment Of The Life Cycle Of Black Locust(Robinia Pseudoacacia L.)-Wood Pellets

Biomass energy is an important part of renewable energy,the development of renewable biomass energy has become a consensus of globalization.China is rich in forestry resources,the development of forestry non-food biomass energy has a broad prospect.Woody energy has become the main component of non-grain biomass energy due to its relatively high energy density,low environmental pollution and convenient use of local materials.As an alternative energy source of fossil fuels,wood pellets is not only clean in the use stage,but also clean in the transportation and production of raw materials.In order to promote the sustainable development of wood energy industry,it is necessary to establish an environmental impact assessment index system in the life cycle of wood pellets.Therefore,FAHP and a wide range of expert questionnaire scores were used to establish an environmental impact assessment index system of the life cycle of wood pellets in this paper.In addition,three locust energy forests（Shanxi,Henan,Shandong provinc）were selected as research objects,to studied the environmental sustainable development The paper draws the following conclusions:（1）The environmental impact assessment index system of the life cycle of wood pellets industry was established by using FAHP method.The index system includes five grade-one indicators（greenhouse gas soil quality,water quality,other gas and biodiversity indicators）and 17 standard-layer indicators.The greenhouse gas index has the highest weight（0.33）,the weight of other indicators from high to low is:Soil quality index（0.26）other gas index（0.25）water quality index（0.10）and biodiversity index（0.08）.（2）Application of the established evaluation index system,Locust forest in Luning county,Henan province,Fangshan county,Shanxi province,Ju county,shandong province,3333 plant/hm² and without water fertilizer measures management were taken as the research object.Based on the case analysis of the index system,Henan province scored 0.12 points,Shandong province 0.15 points,and Shanxi Province 0.06 points,all of which were in the middle and upper level（0-0.5 points）,far from 1（fully sustainable）.It indicates that the development of wood pellets industry in three regions has no adverse impact on the current environment,with the potential for sustainable development,there is great room for future improvement.（3）According to the calculation results of the scores of the three regions’secondary indicators,CO₂emission reduction（0.03,0.09）and soil erosion intensity（0.02,0.04）are the two indexes with high scores,which are the most important environmental impact types.The indexes with low scores mainly focus on soil quality（-0.06,0.01）,NO_X emission（-0.03,-0.02）and shannon diversity index（-0.03,-0.02）.（4）Among the three regional index layers,the indexes with single score less than 0 were concentrated in soil nutrient and biodiversity.Analysis of soil element content in the three regions shows that the content of nitrogen is low in Luning county,Henan province,whereas phosphorus is deficient in,Fangshan county,Shanxi province and Ju county,shandong province,and the content of soil elements in different regions will indirectly affect the content of other elements.This in turn affects soil quality.At the same time,this study assumes that Locust forest serves as a long-term raw material supply base,under which the overall soil quality tends to decrease,which may lead to the decrease of raw material yield.The low Shannon diversity index is due to the fact that the energy forest is mainly for the purpose of producing biomass energy and pays little attention to the ecological benefits of the stand.（5）According to the life cycle inventory data,the wood pellets gas emissions from the three regions are from the largest to the smallest:processing stage emissions（47%）,combustion use stage（29%）,cultivation stage（13%）,wood harvesting stage（1%）.Combined with domestic and foreign investigations on the transportation distance of biomass energy,20 km is selected as the transportation distance of the molding fuel in this study.Since transportation emission is related to the transportation radius,the transportation radius is affected by the transportation rate,raw material collection cost,terrain conditions,etc.Therefore,the greenhouse gas emission in the transportation stage needs to be calculated according to the actual situation of the future development of locust wood pellets fuel industry.High emission in processing and use stage are mainly due to indirect emission caused by power energy input.Meanwhile,incomplete combustion of molding fuel will produce a large number of CO emissions.The lack of dust removal device in current combustion equipment makes PM₁₀ emission higher.（6）According to the results of the evaluation,to achieve environmental sustainability in the robinia pseudoacacia wood pellets industry,soil quality maintenance and process emission reduction must be taken into account.At the same time,the emission of pollution gas and combustion dust particles during combustion need to be concerned.Therefore,the improvement measures of industrial development include:First,the principle of suitable soil and suitable seed should be followed to ensure high and stable yield of raw materials and heat selection in temperate continental monsoon climate zone.The soil type is brown soil and loam,a 1.5m×2m cultivation mode should be selected to cultivate black locust energy forest.Second,nitrogen fertilizer is applied to Luoning area of Henan province,while Phosphorus is applied to Juxian County of Shandong and Fangshan County of Shanxi Province to increase the content of soil elements and thus improve soil fertility.Third,improve the production efficiency of production and use equipment,promote energy conservation,emission reduction,increase air flow rate,promote complete combustion of fuel,increase secondary combustion equipment,high temperature polymerization of dust particles,and reduce emissions of various gases.Fourth,establish a complete standard system and technical specifications to promote long-term scientific management.