An LCA Study of an Electricity Coal Supply Chain

Purpose: The aim of this paper is to provide methods to find the emission source and estimate the amount of waste gas emissions in the electricity coal supply chain, establish the model of the environmental impact (burden) in the electricity coal supply chain, detect the critical factor which causes significant environmental impact, and then identify the key control direction and reduce amount of environmental pollution in the electricity coal supply chain. Design/methodology/approach: In this context, life cycle inventory and life cycle assessment of China’s electricity coal were established in three difference stages: coal mining, coal transportation, and coal burning. Then the outcomes were analyzed with the aim to reduce waste gases emissions’ environmental impact in the electricity coal supply chain from the perspective of sensitivity analysis. Findings: The results and conclusion are as follow: (1) In terms of total waste gas emissions in electricity coal supply chain, CO2 is emitted in the greatest quantity, accounting for 98-99 wt% of the total waste gas emissions. The vast majority of the CO2, greater than 93%, is emitted from the power plant when the coal is combusted. (2) Other than CO2, the main waste gas is CH4, SO2 and so on. CH4 is mainly emitted from Coal Bed Methane (CBM), so the option is to consider capturing some of the CH4 from underground mines for an alternative use. SO2 is mainly emitted from power plant when the coal is combusted. (3) The environmental burden of coal burning subsystem is greatest, followed by the coal mining subsystem, and finally the coal transportation subsystem. Improving the coal-burning efficiency of coal-fired power plant


Introduction
According to the official data from the National Bureau of Statistic (CSY, 2013), in 2012, the velocity of national electric power grows overwhelmingly in the recent years in China. And 81% of the electricity was produced from the coal-fired power plant (IEA, 2010). Therefore, coal plays a dominant role in China economic growth. Coal accounts for almost 90% of China's primary energy storage (Qiu, 2013) and accounts for about 70% of China's primary energy production and consumption (Yan, 2006). Because of its abundance in proven reserves and its stability in supply, coal will continue to be a key component of primary energy mix in China at least over the next few decades (Li & Leung, 2012). However, coal also accounts for a large share of CO2 emissions generated by anthropogenic activities, and based on Miao (2009) over 70% of total SP, 90% of SO2, 67% of NOx, 85% of CO2 produced by fossil fuels come from coal now. Therefore, in this carbon-constrained global world, understanding the environmental implications of producing electricity from coal life cycle is an important component of any policy to reduce total pollutants emissions.
Electricity coal life cycle involves coal-mining, transportation and coal-burning process (Liu & Zhao, 2011) which is also called electricity coal supply chain. It has seriously adverse effects on natural environment and human society. Main waste gas emissions includes CO2, SO2, NOx and smoke dust, which could cause acid rain, ozonosphere damage and global warming after emission. Coal-mining process can result in overburden waste and slag heaps, mine fires (Mann & Spath, 2001). The combustion of fuel for the coal transportation can result in air pollution, water pollution, traffic hazards etc. SO2, NOx and particulate matters are released from the power plant in coal-burning process. However most researchers only give rise to the growing concern of the discharges and control methods of pollutants in coal burning process, not from the perspective of coal lifecycle, because of the high consumption of coal and high levels of waste emissions. Therefore, various measures have been taken to achieve better use of resources and energy as well as implement more sustainable practices in the coal-electricity system. Bates (1995), Uchiyama (1996), Restrepo, Miyake, Kleveston and Bazzo (2012) and Liang, Wang, Zhou, Huang, Zhou and Cen (2012) aimed at power plants in U.K, Japan, Brail and China respectively, studied the power plants' influence on environment with a Life Cycle Assessment (LCA) method. Pacca and Horvath (2002) calculated Global Warming Potential (GWP) of coal, gas, solar power and wind energy power plants. Hondo (2005) calculated greenhouse gas emission in eight power plants' construction, operation and retirement processes in Japan, using LCA method, process analysis and input-output analysis method. Kannan, Leong, Osman and Ho (2007) studied on five power plants and their influence on environment in Singapore from the point of power generation technology with LCA and LCC methods. Lave and Freeburg (1973) found that comparison with petroleum and gas, coal has the most significant impact on environment in mining process, transportation process, as well as coalburning process. Hence, it is necessary to study the environmental influence of electricity coal from cycle life point. However, the literature on this aspect is rare. Pan and Mu (2011) compared the influence of nuclear power supply chain and electricity coal supply chain on health, environment and climate in China, with radiation effect from natural radioactive nuclides in coals as a indicator. Some researchers studies the environmental performance from natural gas (Korre, Nie & Durucan, 2012), forestry (Björk, Erlandsson, Häkli, Jaakkola, Nilsson, Nummila et al., 2011), biofuel (You, Tao, Graziano & Snyder, 2012). This paper studies an electricity coal supply chain by employing a LCA approach. The remainder of the present paper is organized as follows. Section 2 gives a brief introduction of a specific electricity coal supply chain in China. Section 3 studies this electricity coal supply chain with LCA. Methods of sensitivity analysis are presented in Section 4. Finally, conclusions are drawn in Section 5.

The case study
The electricity coal supply chain involves the coal mining process, coal transportation process and coal burning process, all based in China. The goal of coal mining is to remove coal from the ground. After coal preparation/cleaning, coal is moved to the coal-fired power plant by barge, rail or truck. This paper presents a thorough case study of the environmental impact of waste gas emissions in an electricity coal supply chain, where the coal is mined by an underground colliery-Jiangzhuang Coal Mine (JZCM) of Zaozhuang Coal Mining Group Co.,Ltd. and is transported 93 Km by heavy-truck and then burned at Shiliquan Plant (SLQP) of Zaozhuang which is a coal-fired power plant.

Coal mining process
Underground mining operations include: cutting, drilling, blasting, loading, and hauling.
Auxiliary operations include ventilation, drainage, power, communications, and lighting. Roof support is another task which is considered to be a unit operation. The raw coal output of JZCM  Table 1 gives the underground mining equipment fuel and material requirement, and Table 2 gives a breakdown of the electrical details.
The research result of Clean Production Standard in Coal Washing and Processing Industry (2010) shows that electricity consumption of raw coal production in state-owned key coal mines usually ranges between 15 kWh/t and 25 kWh/t, and the rock bottom electricity consumption reaches 4.4 kWh/t. In this case, coal preparation/cleaning is a part of coal mining process in JZCM. Coal preparation normally involves size reduction of the mined coal, the removal of ash-forming materials and rocks, as well as the removal of very fine coal. Coal preparation methods include the gravity method, floatation, magnetic separation and electro-separation. The JZCM uses the gravity method. The coal and detrimental impurities can be separated by weight differences of the coal and the waste in both water and air. In this process, the coal floats on the surface and the detrimental impurities submerge to the bottom. And then coal is shipped to coal-fired power plants, while the waste are used for filling. The coal preparation process includes screening, crushing, separating, dewatering, storing and loading. Screening is to identify the constitution of different raw coal particles. Crushing is to grind the mined coal blocks into coal power. Separating is to classify coal particles according to their size, and to separate mineral particles from the coal. Dewatering is to remove water from the coal. Storing and loading is to store the cleaned coal, load it and then ship it to the coal-consuming enterprises. The preparation process and coal preparation equipment requirements are shown in Table 3, and the coal preparation fuel and material requirements are presented in Table 4. According to Clean Production Standard in Coal Washing and Processing Industry (2010), energy demand for washing 1 ton of coal in large coal preparation plant is less than 10 kWh, and the lowest energy consumption is less than 5 kWh.

Coal transportation process
In China, the main transportation methods are railways, highways and waterways. In the coal transportation process, this paper only considers coal that is transported from the coal mine to the power plant. Ammonium nitrate and other blasting materials which are transported to the coal mine, and ammonia (NH3), hydrogen chloride (HCl), sodium hydroxide (NaOH), calcium carbonate (CaCO3), etc, which are transported to the power plant are not included in the LCA.
According to the investigation, from JZCM to SLQP, the coal is shipped by steyr-king heavy duty trucks which have a loading capacity of 24 tons. The distance is 93 Km, the total diesel fuel consumption is 36L, and the transportation routing is presented in Figure 1.

Coal burning process
The burning process occurred in coal-fired power plants, and data collected from SLQP are as show below. The total installed capacity is 1225 MW, and the power generation is 8.39 billion kW. In 2012, SLQP consumed 1.91 million tons of raw coal, 1.62 million tons of coal gangue, 2.76 million tons of coal slurry, and 58.30 million tons of fresh water. The power plant inventory includes energy and non-energy (material) demand (See Table 5).

Life cycle analysis of the electricity coal supply chain
An LCA approach is adopted to investigate the cumulative environmental burden produced by the supply chain generating 1 kWh of electricity (reference flow).

Goal and scope definition
The overall objectives of the LCA study are to: • Demonstrate the usefulness of the LCA method in measuring the environmental impacts of a defined electricity coal supply chain system.
• Provide an overall understanding of an electricity coal supply chain and the associated environmental burden involved in the main processes of the supply chain.
• Seek quantitatively the most effective way to reduce the environmental burden of waste gas emissions.
• Highlight important areas for future research (further LCA studies concerning coal cinder utilization and the cost factor).
The scope of the LCA study (system boundary) is defined as follows: The system starts with the mining of coal and ends with electricity as the product. The main processes are the coal mining process, coal transportation process and coal burning process. The power plant which supplies energy to the supply chain is included in the system. Based on the scope of the LCA, the supply chain model is displayed in Figure 2. The model represents a "Mining to Products (MTP)" system as distinct from a "Cradle to Grave" system.
This means that coal's end of life (recycling) is not included in the study.

Main processes
The LCI of the waste gas emissions released by the system are shown in Appendix A. All the results are based on the reference flow of 1 kWh of electricity.

Coal mining process
In the coal mining process, a lot of waste gases will be released. For example, greenhouse gases like CO2 and CH4 will be released during the coal mining process, and gases like CO2, SO2, CO and H2S will be spontaneously released from coal gangues. The mining process has great effects on the regional ecological environment, with the major sources of waste gases being the mine ventilation process, coal gangue, and the coal preparation process. All emissions of waste gases in the mining process are listed in Appendix A.

Coal transportation process
The atmospheric environmental problems arising in the coal transportation process are mainly caused by the burning of transport fuels, spontaneous combustion of coal in the process of transportation and coal dust pollution near the transport route. Main waste gases consist of HC, CO, NOx, SO2 and H2S. Considering the coal transport from JZCM to SLQP by heavy duty trucks, all emissions of waste gases in the coal transportation process are listed in Appendix A.

Coal burning process
The coal-fired power plants in coal burning process often burn large quantities of low grade coal with high sulfur and high ash, even coal gangues, and are adjudged as the greatest sources of waste gases in China. Waste gases from burning mainly contain CO2, SO2, CO and NOx. The direct consequence is that smoke dust and SO2 emissions are dominant among emissions from industrial various sectors in China (Zhao, Wang, Nielsen, Li & Hao, 2010). In fact, the emissions of SO2 from coal and electricity account for more than 59% of the emissions in Controlled Zones for Acid rain and Sulfur Dioxide (Lu, Streets, Zhang, Wang, Carmichael, Cheng et al., 2010). All emissions of waste gases in the coal burning process are listed in Appendix A.

Interpretation of LCI
Appendix A represents waste gas emissions in the coal mining process, coal transportation process and coal burning process in the electricity coal supply chain. It is seen that: • In terms of total air emissions, CO2 is emitted in the greatest quality, accounting for 98.8% wt% of the total air emissions for all processes examined. The vast majority of CO2, about 93.6%, is emitted from the power plant when the coal is combusted. (See Table   6) • Excluding the CO2, the main waste gases emissions in the electricity coal supply chain are displayed in Table 6. The largest proportion of the main waste gases is CH4, because JZCM is a high gas mine which releases 200m 3 CH4 from CBM in producing one ton of coal. SO2 mainly comes from the coal burning process. Because there is no denitrification process in SLQP, the percentage of NOx in the burning process, mining process and transportation process is 66.5%, 28% and 5.56% respectively.

Process in electricity supply chain CO2
Other mainly waste gas Coal mining process ( Note: (a) Mining process is the underground mining process of JZCM; (b) Transportation process is that coal is transported 93Km by truck from JZCM to SHQP; (c) Burning process is that coal is burned by SHQP.  characterization, normalization and final weighted scores.

Characterization
In this step, the LCI data are sorted into ''classes'' or environmental impact categories according to the effect they have on the environment. For example, CO2 will be classified under Global Warming Potential. Within each ''class'', the emissions are aggregated to produce an effect score.

Eutrophication Potential
Eutrophication Potential (EP) is defined as the potential of nutrients to cause over-fertilization of water and soil which in turn can result in increased growth of biomass. EP in the electricity coal supply chain is calculated in

Normalization
A normalization step is performed to provide the relative size of each environmental impact.
Each of the total characterized scores is benchmarked against the known total effect (usually  (Yang, Cheng & Wang, 2002). Table 13 illustrates that in the electricity coal supply chain, the biggest environmental impact of waste gas emissions is GWP, followed by EP, POCP, AP and ODP.

Final weighted scores
It is assumed that the relative importance of various impacts is the same. However, in fact, the relative importance of various impacts is different, which on the one hand depends on the characteristics of the environment itself, while on the other hand this reflects the current understanding of human society and its degree of concern. In the final stage, the normalized scores are multiplied by a weighting factor representing the relative importance of the total environmental impact. The environmental impacts of GWP, EP, POCP, AP and ODP after weighting are shown in Table 13. It is seen that the coal burning process has the biggest environmental impact, followed by the coal mining process and the coal transportation process. Table 13 presents that the biggest environmental impact in the electricity coal supply chain is GWP, then followed by EP, AP, POCP and ODP. The global environmental burden of the electricity coal supply chain is 1.03E-04 man·a, and the regional environmental burden of the electricity coal supply chain is 1.58E-04 man·a., so the regional impact is greater than the global impact. The environmental burden of the electricity coal supply chain is 2.61E-04 man·a.

Classification
Step Mining process

Sensitivity analysis
A sensitivity analysis was conducted to determine the parameters that had the largest effect on the results and to determine the impact of estimated data as well as variations in data on the conclusions. One variable may affect several factors and thus several process steps, or it may affect only one process in the overall life cycle assessment. For instance, changing the coal-burning efficiency can affect the amount of coal required at the plant, which in turn affects the coal mining and transportation requirements. However, varying the transportation distance affects only the emissions associated with the coal transportation process. These effects were taken into account automatically in the LCA model. The base case assumed transportation to the average user (QLQP) by truck. The following are abbreviations used in the different sensitivity analyses: A means base case; B means CH4 utilization ratio is 30%; C means nearest user; D means farthest user; E means increase coal-burning efficiency by 5 points; F means decrease coal-burning efficiency by 5 points.

Coal mining process -utilization ratio of CH4 sensitivity analysis
CH4 emissions in the electricity coal supply chain is mainly caused by the emissions of CBM in the coal mining process, which accounts for 94% of the total CH4 emissions in the electricity coal supply chain. So the reduction of CH4 emissions mainly focuses on the coal mining process, and the utilization of CH4 as an alternative mode of power generation. At present, the utilization of mine gas is mainly based on civil and industrial use; this percentage has already reached 80% (Zhuo, Lin & Wang, 2008). The gas chemical industry also has wide market prospects, and gas power generation is a leading direction of development. Methane-power generation (heat supply) is used in many large industries. Methane power generation is a mature technology, with the main technologies being gas turbine power generation, steam turbine power generation, gas-fired generator power generation, combined cycle system power generation and CHER power generation.
The coal seam in JZCM has low air permeability and the coal bed is soft, so recovery and utilization of CBM is quite difficult. In addition, without data about power consumption of CH4 recovery equipment, the waste gas emissions from the equipment is ignored. Thus, this paper considers the environmental impacts caused by waste gas emissions in the electricity coal supply chain based on the assumption that the utilization ratio of CH4 can reach 30%. The results are shown in Table 14 and a comparative analysis of impact assessment is made in   Under the assumption that the utilization ratio of CH4 is 30% in the coal mining process, Table   15 gives the global environmental burden, regional environmental burden and total environmental burden of waste gas emissions in the electricity coal supply chain change as 2.91%, 1.9% and 2.3%, respectively. So the environmental burden caused by waste gases emissions is not sensitive to the change of CH4 in the coal mining process and utilization of CH4 is not an effective method to reduce the environmental burden in the electricity coal supply chain.

Coal transportation process -transportation distance sensitivity analysis
This section analyzes sensitivity of transportation distance and studies the environmental impact of transportation distance on waste gas emissions in the electricity coal supply chain.
According to the investigation of JZCM, the fastest user is Yangzhou power plant, and the nearest user is JZ plant, mine mouth power plant. Detailed data are shown in Table 16.

Scenario Vehicles Path Distance
Base case Truck Jiangzhuang coal mine--->Shiliquan power plant Highway 93Km Nearest user Truck JZ power plant Highway 2Km Farthest user Barge and truck Jiangzhuang coal mine--->Zaozhuang port--->Jinghang canal --->Yangzhou port--->Yangzhou power plant Highway 89Km, Waterway 427Km  Table 17 gives the change of input index (standard coal, diesel, electricity consumption and non-coal energy) and Table 18 presents the change of output index (GWP, EP, POCP, AP and ODP), in order to assess the environmental impact of three different of transportation distances. And it shows that change of transportation distance has a great influence on diesel and non-coal energy.  Table 17. Impact of electricity coal supply chain on transportation distance (Input index) Table 18 illustrates POCP is most sensitive to fluctuations of transportation distance compared with GWP, ODP, AP, EP, because large amounts of CO are released in the coal transportation process. Therefore an oxidation catalyst on the vehicles is recommended to oxidize the carbon monoxide into carbon dioxide.  Table 18. Impact of electricity coal supply chain on transportation distance (Output index)

Coal burning process -coal-burning efficiency sensitivity analysis
Both a decrease and an increase in the coal-burning efficiency were examined. The base case efficiency for the average is 37%. The coal-burning efficiency is changed by plus or minus five percentage points for each system, i.e., 32% and 42% for the Average system. Changing the coal-burning efficiency had a large effect on the energy efficiency and energy ratios defined in Table 19.  Table 19. Impact of electricity coal supply chain on coal boiler efficiency (Input index) Table 20 shows the base case as well as the results for increasing and decreasing the coalburning efficiency. So improving the coal-burning efficiency of a coal-fired power plant in the electricity coal supply chain is the most effective way to reduce the environmental burden of waste gas emissions.  Table 20. Impact of electricity coal supply chain on coal boiler efficiency (Output index)

Conclusion
LCA results help to pinpoint several tangible strategies to decrease the environmental impact in the coal life cycle, from coal mine to coal-fired power plant. The results show that the environmental burden of the coal burning process is greatest, followed by the coal mining process, and finally the coal transportation process. In the electricity coal supply chain, the biggest environmental impact of waste gas emissions is GWP, followed by EP, AP, POCP and ODP, and the regional impact is greater than the global impact. Improving the coal-burning efficiency of a coal-fired power plant is the most effective way to reduce the environmental burden of waste gas emissions in the electricity coal supply chain.
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