Study On Calculation Model And Method Of Carbon Dioxide Emissions For Coal-fired Power Plant

In the constitution of energy consumption in China, coal is the main energy. CO₂ emissions from coal combustion significantly lead to the enhancement of greenhouse effect. Coal-fired power plant is an important source of carbon dioxide emissions. CO₂ produced by coal-fired power plants account for 50% of the total emissions of CO₂, and the number shows a rising trend. At present, most countries are based on the 2006 IPCC guidelines for National Greenhouse Gas Inventories with appropriate adjustments according to self-condition to calculate CO₂ emissions. But these calculation methods do not form a recognized method. They only consider CO₂ emissions in generating process and wet desulfurization by simple algorithm. The consideration for many factors influencing CO₂ emissions is not quite comprehensive. Meanwhile, there are also large differences between the calculated results and actual emissions due to the fixed emission factors. Therefore, accurate CO₂ emissions computing model and method are conducive to set higher targets for reduction of CO₂ scientifically and rationally.In this study, the calculating boundary of CO₂ emissions based on the life cycle of coal and the actual operation of the coal-fired power plant was identified. Also, considering the process of coal mining, washing and selecting, transportation as well as the process of coal combustion, desulfurization, denitration, decarburization, dedusting and purchased electricity, a more accurate calculation method to compute CO₂ emissions for coal-fired power plant has been creatively put forward. At the same time, a prediction method for CO₂ emissions was also applied by using the RBF（Radial Basis Function） neural network algorithm which can compensate the lack of some parameters needed by the accurate calculation method. Meanwhile, cases were studied according to three coal-fired power plants of different installed capacities. In contrast, the accurate calculation results were compared with the values which were gotten by GHG Protocol Calculation Tool for Chinese Coal-fired Power Plants provided by World Resource Institute. At the same time, a computing platform based on Web development for CO₂ calculation was designed. Those research results are as follow:（1）By analyzing the CO₂ emissions boundary, we found that there were CO₂ direct emissions in coal combustion and desulfurization process, while CO₂ indirect emissions were produced in coal mining, coal selecting and washing, coal transportation, decarburization, dedusting and purchased electricity processes and the rate can reach 5.5%. By analyzing the influencing factors for CO₂ emissions in coal-fired power plant, we found that there was a close relationship between the net coal consumption rate and load rate. Generally, the higher the load rate was and the smaller the coal consumption was, and the emissions per unit quantity of electricity reduced correspondingly. And we also found that the increasing of desulfurizer consumption will increase the carbon dioxide emissions; the increasing of station service power consumption rate will add the carbon dioxide emissions as well; the increasing of volatile matter of coal and the fixed carbon will increase the carbon dioxide emissions.（2） Based on the CO₂ emissions boundary and the consideration of the characteristics of CO₂ emissions in China’s power plant, the precise computation model of CO₂ emissions for coal-fired power plant was established. Modified mass conservation method was used in coal combustion and desulfuration. At the same time, modified emission factor method was used in other processes with considering the power consumption. The calculation results of the modle can provide a reference for the formulation of the development strategy of energy conservation and emissions reduction.（3）By taking the development tendency of CO₂ emissions and influencing factors into consideration, six influencing factors was confirmed. And the prediction computing modle was establelished based on RBF neural network. Users can predict the CO₂ emissions by entering related parameters through the optimized prediction computing modle. After the debugging of programs repeatedly, the RBF neural network training network was eventually determined as: net = newrb（input_train,output_train,0,4,20,500）. This modle has strong ability of linear fitting and it can make up the shortfall that this modle cannot do some calculation sometimes because of the poor data.（4）Based on the calculation of three typical power plants in different capacity, we found that the CO₂ emissions from coal combustion accounted for 94.5% in total emissions and the CO₂ emissions orders in 2010, 2012 and 2014 were: coal combustion > coal transportation > desulfurization > denitration ≈ coal selecting and washing > purchased electricity > dust removal. By comparing the results of our precise computation model with the results of the GHG Protocol Calculation Tool for Chinese Coal-fired Power Plants, we found that the former calculated CO₂ emissions earn 2.7 percent more than the latter CO₂ emissions.