Quantitative Estimation of Biomass Energy and Evaluation of Biomass Utilization-A Case Study of Jilin Province , China

Jilin Province, as a large agricultural province, has abundant reserve of biomass resources. At the same time Jilin Province is currently suffering from energy shortage. Besides, consumption of conventional fossil fuels has resulted in the exacerbation of global warming and air pollution. Biomass energy as a renewable and substitutive energy, can mitigate the energy crisis and global warming, and improve environmental quality once it is fully utilized. This paper estimated the supply potential of biomass energy and integrated LCA and environmental cost analysis to make evaluation on biomass utilization taking biomass power generation system as example. Acquirable and utilizable amount of biomass energy in Jilin Province is equivalent to 21.26 tce, which can be accounted for 25.6% of total energy consumption in Jilin Province in 2011. Among all biomass energy, 59.1% comes from straw and agricultural residues, followed by 33.8% from livestock manure. According to the LCA results, total environmental impact of biomass power generation system is 0.721, much smaller than 25.321 of thermal power generation system. General cost of biomass power generation is higher, however its environmental cost is much lower than thermal power generation system (396 yuan/10kWh < 1819 yuan/10kWh). The results showed that biomass utilization has better environmental advantages and has the potential for the mitigation of energy crisis in Jilin Province.


Introduction
With the increasingly depletion of conventional and non-renewable energy sources, research on biomass energy, which is a kind of renewable, abundant and environmentally friendly substitutive energy has been a hot issue around the world.Biomass energy is a kind of energy form that converts from solar energy to chemical energy through photosynthesis of green plants directly or indirectly and stored inside biomass (Wang & Ai, 2006).
Jilin Province, located in the northeast of China, is important industrial base and commodity grain base of China.Along with the acceleration of industrialization and urbanization, energy consumption of Jilin Province is increasing rapidly.Shortage of primary energy, low energy self-sufficiency rate and unreasonable energy structure are urgent problems for Jilin Province to solve.Besides, consumption of conventional fossil fuels has resulted in the exacerbation of global warming and air pollution.Reserve of primary energy of Jilin Province only accounts for 0.3% of China and its energy self-sufficiency rate is less than 50% (Zhao, 2011).Energy consumption is increasing continuously and there is large disparity between energy production and consumption.Figure 1 shows energy production and energy consumption of Jilin Province from 2000 to 2010.In 2010, conventional fossil energy accounted for 94.1% of the total energy consumption and new and renewable energy only accounted for 5.9%.Figure 2 shows the consumption ratio of different kinds of energy.

Quantitative Estimation of Biomass Energy Potential
There are different indexes for the availability evaluation of biomass energy and the amount calculation of organic biomass resources in corresponding to different criterion (Li, Ren, & Zhuang, 2001).Here three definitions including physical reserve, acquirable and utilizable amount, and equivalent of standard energy are introduced (Liu & Shen, 2007).The amount of major biomass resources is evaluated step by step according to these three definitions.

Physical Reserve
Physical reserve is the total amount of theoretically physical production of major biomass resources from four sources including straw and agricultural residues, firewood and forestry residues, livestock manure and municipal waste.
(1) Straw and agricultural residues Straw and other agricultural residues mainly come from food crops, cotton, hemp and sugar.Straw-grain ratio method is widely adopted to calculate the amount of crop straw.Straw-grain ratio is the ratio of the amount of stems above the ground and the amount of economic yield of crops.The yield of straw can be calculated by: (1) CR: physical amount of straw, Qc i : yield of Crop i, r i : straw-grain ratio of Crop i. Straw-grain ratios of different crops are shown in Table 1 (Liu, Na, & Wang, 2010;Bi, 2010).(2) Firewood and forestry residues Forestry biomass resources mainly derive from clearing, cutting and processing residues of forestry production, firewood forests and forest tending and thinning.The amount of forestry biomass resources can be calculated either with index as area of forests, firewood coefficient and production of per unit area (Yuan, Wu, & Huang, 2002) or by respectively calculating the amount of firewood forests, residues of forestry production and other forestry biomass (Research Group of Chinese Forest Bio-energy [RGCFB], 2006).This article mainly calculates the amount of forestry residues, firewood forests, forest tending and thinning and the adjacent small trees by: FR: physical amount of forestry biomass, Qf i : amount of Forestry biomass i, r i : conversion coefficient.Some related conversion coefficients are shown in Table 2 (Yuan et al., 2002;RGCFB, 2006;Shi, 2008).(3) Livestock manure The amount of manure is related to species, breeds, genders, growing season and so on (Ding, 2000).Here the livestock is assumed as mature and the breeding cycle is assumed as fixed.The amount of manure can be calculated with daily yields and breeding cycle by: (3) D: physical amount of manure, Qd i : the number of Livestock i, d i : daily yield of dry manure of Livestock manure i, m i : breeding cycle, M i : manure yield of Livestock i within the whole breeding cycle.Breeding cycle and manure yield of different livestock and poultry are shown in table 3 (Liu & Shen, 2007;Ding, 2000;Wang, 1998;Peng & Wang, 2004).Municipal waste consists of municipal solid waste and municipal waste water.Municipal solid waste can be divided into organic waste and inorganic waste according to the composition.The organic waste can be utilized as biomass resources.Municipal waste water is divided into domestic sewage and industrial wastewater, both can be treated to produce biogas.The amount of total municipal waste can be calculated by: (4) SW: the amount of municipal solid waste, r 1 : the percentage of organic waste from municipal solid waste, Qw: the amount of waste water, r 2 : the percentage of COD in waste water.

Acquirable and Utilizable Amount
Physical reserve of biomass resources is the amount representing the theoretically richest developing potential (LIU & SHEN, 2007).Not all the reserve can be acquired and utilized to produce energy.There is availability coefficient and utilization coefficient of biomass resources for energy generation.The acquirable and utilizable amount refers to the amount of biomass resources that can be acquired and utilized to produce energy under theoretical conditions.It can be calculated from the amount of physical reserve.
CR': acquirable and utilizable amount of straw, λ i : availability coefficient of Crop i. δ i : utilization coefficient.Acquirable and utilizable amount of forestry residues (FR'), livestock manure (D') and municipal waste (MW') can be calculated with corresponding λ i and δ i .Availability coefficient of all kinds of biomass resources is the collection ratio and determined according to local conditions and the average value will be adopted.The ratio of straw amount utilized as household fuel and discarded or combusted can be considered as energy production and is determined as 80%.About 1/3 of forestry residues and livestock manure can be utilized to produce energy.About 60% of municipal solid waste can be utilized through combustion and compost.About 50% of municipal waste water can be utilized to produce biogas.Table 4 concludes the availability coefficient and utilization coefficient of different biomass resources (Liu & Shen, 2007;Liu et al., 2010;RGCFB, 2006;Yuan, Wu & Ma, 2005;National Development and Reform Commission-Energy Research Institute [NDRCERI], 2010;Milbrandt, 2005).
*The data of the amount of municipal waste water collected from statistical year book can be considered as the acquirable amount, therefore the availability coefficient is determined as 100%.

Equivalent of Standard Energy
When put into unified and practical studies, biomass energy is usually accounted to the equivalent of standard energy, which is generally standard coal equivalent.In terms of the calculation of straw standard energy (ECR), conversion coefficient η i is introduced into the calculation as: As for the calculation of forestry residues standard energy equivalent (EFR), livestock manure standard energy equivalent (ED) and municipal waste standard energy equivalent (EMW), corresponding η i should be introduced.When waste water is converted to standard energy equivalent, it is firstly converted to biogas (0.907 m 3 biogas can be generated from 1 kg COD) (Milbrandt, 2005).Table 5 concludes conversion coefficient of different types of biomass resources (Liu & Shen, 2007).

Life Cycle Environmental Impact Assessment of Biomass Power Generation System
Life Cycle Assessment (LCA) is a tool used to assess the impacts on environment brought by products or conduct during the life cycle.LCA can identify and quantify the utilization of energy and materials and the emission of wastes; assess the impact extent of the utilization and emission and strive to seek the chance to improve the environmental quality (Liu & Wang, 2008).
This part is a case study that associates LCA and cost analysis to make comprehensive evaluation on biomass utilization taking a biomass power generation system in Jilin Province as example.

Introduction of Biomass Power Generation System
(1) Introduction of the study object Songyuan City is a new petrochemical city located in the west of Jilin Province.It is large commodity grain base and oil base of China whose yield of corn is 4 million ton, accounting for 1/4 of Jilin Province's total yield.The government deployed the overall route of straw power generation to construct Datang Songyuan biomass power generation project in Songyuan City to develop and promote biomass utilization.
The study object of this research is 15MW (2 sets) straw direct-fired power generation system, whose annual electricity generation time is 6000 h and rated annual generating capacity is 1.8×10 8 kWh.Environmental impacts brought by 10000 kWh of power generation will be calculated and analyzed, which means the functional unit of the system is 10000 kWh.Main processes of the system include feedstock collection, straw combustion, water recycling and purification, and power generation.
(2) Sources of straw There are 0.76 million hm 2 of farmlands in Songyuan City.Total yield of corn in normal year is 5 million ton.Within the scope of 25 km radius, yield of corn straw is 0.691 million t/a, of which 65% is discarded.Calculated by this proportion, corn straw that can be used as fuel for power generation is 0.449 million t/a.6 shows straw consumption of the plant.Fuel demand of the plant is 0.204 million t/a.So the supply amount can satisfy the fuel demand of the power generation system.

Assessment Scope and Boundary Demarcation
When determining the assessment boundary, some points should be considered: (1) In order to form a closed loop system, the coal, oil, electricity, steel and water consumed during construction period of the plant are not involved into the boundary; (2) Because biomass power generation system is a new system that has not reached the scrapping age, equipment recovery unit is not considered.(Liu, 2010) Based on the assumptions above, biomass power generation system can be divided into three parts: (1) Agricultural production period; (2) Transportation period; (3) Plant operational period.Figure 3 shows the life cycle boundary and frame of the power generation system.
Figure 3. Life cycle boundary and frame of the power generation system

Inventory Analysis
Inventory analysis is to quantify and assess the processes of energy and resources consumption and environmental release during life cycle of the system.The raw materials and energy consumed is determined as input inventory and the substances (including waste gases, waste water and solid waste etc.) emitted into environment from all processes of the system is determined as output inventory.
(1) Agricultural production period Emissions from agricultural production has three sources: (1) Pollutant emission from mechanical use; (2) Pollutant emission from fertilizer use; (3) Emission of nitrogen fertilizer loss due to inefficient use of fertilizers.
In life cycle inventory analysis, there should be distribution of energy flow and pollutant emission for the system that has various kinds of output.During planting process of corn, straw is by-product.According to the economic value, energy consumption and pollutant emission of corn straw account for 10% of the whole energy flow and pollutant emission of the planting process of corn.Calculated by this proportion, emission amount of pollutants from corn straw consumed by the plant in one year can be obtained and shown in (2) Transportation period The transportation radius is within 25km.9 collection stations will be established around the power generation plant.Because the binding of straw is mostly done manually, consumption of this period is mainly fuel consumption of transportation tools.Pollutant emission is mainly from exhaust of diesel vehicles.According to the distances between collection stations and the plant, average transportation radius can be determined as 25 km and the transportation tool is determined as agricultural diesel vehicle whose load is 5 ton.Emission amount of pollutants during transportation period can be calculated with diesel consumption and emission coefficient.The results are shown in Types of waste gases and emission amount are shown in Table 10.Waste water from all discharge links is either reused or discharged into municipal pipe network after treatment.The discharge concentration can reach the standard and has little impact on environment.So when calculating environmental impact potential, water environmental impacts can be neglected.Wangsheng Fertilizer Company will purchase all the straw ashes to produce organic fertilizers.So all the ashes will be reused and their environmental impacts can be neglected.
(4) Inventory summary Considering the close carbon cycle, here is a crucial premise that the amount of CO 2 generated during plant operational period is equivalent to that absorbed by corn during growing process (Zhang, 2002).What brings impacts to environment is mainly air pollutants.According to the annual emission amount of pollutants and the annual amount of electricity generation, emission amount of pollutants of 1 functional unit can be calculated as is shown in Table 11.This part will quantify environmental impacts brought by energy consumption and pollutant emission of the power generation system to lay the foundation of evaluation and improvement of the system.According to the life cycle inventory, five environmental impacts caused by the pollutant emission including Global Warming, Acidification, Photochemical Ozone Creation, Health Toxicity and Solid Waste will be analyzed.
(1) Environmental impact potential Environmental impact potential refers to the sum of all the impacts of similar pollutant emission within the system.Similar pollutants can be converted to reference's environmental impact potential with equivalent coefficient.Calculation formula of environmental impact potential is: (

2) Standardization
Standardization of data is to make environmental impact potential dimensionless.The standardized data can intuitively and exactly reflect the environmental impacts of the biomass power generation system.This article chooses the environmental impact potential per capita of the whole society in 1990 as the norm of the standardization.According to the concept of standard human equivalent (the environmental impact potential caused by per capita annually) established by Yang Jianxin (Yang, Xu, & Wang, 2002), the unit of normalized environmental impact potential is standard human equivalent (PE China , 1990).The calculation formula is:  12.This paper mainly analyzes five environmental impacts and adopts Analytic Hierarchy Process (AHP) to analyze the relative importance of the five environmental impacts to determine the weights of them.The judging matrix of nine-scale analysis is adopted as is shown in Table 13.
The Consistency Index, CI can be calculated as 0.056.The Random index, RI is 1.13 according to random index table.The Consistency Rate, CR=CI/RI=0.0459<0.1 (according to average random consistent index, when m>=3, CR<0.1, consistency can meet the requirement), so the consistency can be accepted.

Life Cycle Cost Analysis
In order to stress the environmental advantages of biomass power generation system, this article calculates the external environmental cost of biomass power generation system and involves it into life cycle cost analysis.
(1) General cost analysis General cost mainly consists of the consumption cost of raw materials and energy, operational cost, transportation cost, investment cost, depreciation cost and tax cost.Table 14 shows the economic evaluation of biomass power generation system.The calculation formula is:

Results of Biomass Energy Potential in Jilin Province
With the calculation analysis and data summary (collected from Statistical Yearbook of Jilin Province 2011), results of physical reserves, acquirable and utilizable amount and equivalent of standard energy are obtained and shown in Table 16.
www.ccsen    Cost structure of biomass power generation system shows that its general cost is 4240 yuan/10 4 kWh.Average general cost of thermal power generation system is 3250 yuan/10 4 kWh (Chinese Energy, 2012).Compared with thermal power generation system, the cost of biomass power generation system is higher.And among all the costs, fuel cost accounts for more than 50%.Several reasons are responsible for the high cost of biomass power generation system: (1) Higher investment in advanced equipments; (2) Lower electricity generation efficiency and high demand of fuels; (3) Higher transportation cost of fuels due to corn straw's large volume.The results show that environmental cost of biomass power generation system is 395.7 yuan/10 4 kWh and environmental cost of thermal power generation system is 1818.6 yuan/10 4 kWh, which is much larger.Due to high amount of pollutants emission in transportation process of coal and the emission of high concentrations of SO 2 and NOx in operational process of plant, thermal power generation system produces more serious impacts to environment that generates higher environmental cost.

Environmental Cost Analysis
Figure 2. Ener ) EP(m): Environmental impact potential m, EP(m)n: Environmental impact potential m of Pollutant n, Q(m)n: emission amount of Pollutant n, EF(m)n: coefficient of Environmental impact potential m of Pollutant n.
8) NP(m): Standardized environmental impact potential m, EP(m): Environmental impact potential m of the system, ER(m): standardization norm.Standardization norm of environmental impacts is shown in Table 9) WP(m): Weighted environmental impact potential m, WF(m): weight of Environmental impact potential m, NP(m): Standardized environmental impact potential m.
) LCEC: Life cycle environmental cost, Q(n): emission amount of Pollutant n, EV(n): Environmental value of Pollutant n.

Figure
Figure 4.A Figure

Table 1 .
Straw-grain ratio of different crops

Table 4 .
Availability coefficient and utilization coefficient of different biomass resources (λ i and δ i )

Table 6 .
Straw consumption of the plant

Table 8 (
Hu, 2006).During plant operational period, diesel is the major combustion accelerant and electricity is consumed.Pollutants including waste gases, waste water and solid waste are from the following production links:

Table 9 .
Pollutant generation links of plant operation

Table 10 .
Types and emission amount of the waste gases during plant operational period

Table 11 .
Inventory of life cycle emission of biomass power generation system per functional unit Unit:

Table 12 .
Standardization norm of environmental impactsStandardization cannot compare the relative seriousness of different environmental impacts.It is necessary to make the sequence of the seriousness of different environmental impact potential by endowing different weights to the extent of environmental damage.The calculation formula is:

Table 13 .
The judging matrix of nine-scale analysis

Table 14 .
Economic evaluation of biomass power generation systemExternal environmental cost of biomass power generation system refers to the value converts from the impacts caused by pollutants during the whole life cycle.The conversion is according to current environmental costs of all kinds of pollutants.Taking reference of the Pollution Charge Standard (PSC) of China and the Environmental Value Standard of the USA (U.S.EVS)(Huang, 2008), the standard measurement of environmental value of different pollutants can be shown in Table15.

Table 17 .
Results of life cycle environmental impact potential

Table 18 .
Standardized results of life cycle environmental impact potential

Table 23 .
Environmental cost account of biomass power generation system