A Study on Methane and Nitrous Oxide Emissions Characteristics from Anthracite Circulating Fluidized Bed Power Plant in Korea

In order to tackle climate change effectively, the greenhouse gas emissions produced in Korea should be assessed precisely. To do so, the nation needs to accumulate country-specific data reflecting the specific circumstances surrounding Korea's emissions. This paper analyzed element contents of domestic anthracite, calorific value, and concentration of methane (CH4) and nitrous oxide (N2O) in the exhaust gases from circulating fluidized bed plant. The findings showed the concentration of CH4 and N2O in the flue gas to be 1.85 and 3.25 ppm, respectively, and emission factors were 0.486 and 2.198 kg/TJ, respectively. The CH4 emission factor in this paper was 52% lower than default emission factor presented by the IPCC. The N2O emission factor was estimated to be 46% higher than default emission factor presented by the IPCC. This discrepancy can be attributable to the different methods and conditions of combustion because the default emission factors suggested by IPCC take only fuel characteristics into consideration without combustion technologies. Therefore, Korea needs to facilitate research on a legion of fuel and energy consumption facilities to develop country-specific emission factors so that the nation can have a competitive edge in the international climate change convention in the years to come.


Introduction
The Kyoto Protocol, which was adopted in 1997 at the third Conference of Parties, specified the GHG reduction targets and action plans for Annex I countries. The Bali Road Map was agreed upon at the 13th session of the Conference of Parties, held in December 2007, which encourage developing nations with making voluntary efforts to reduce GHG emissions. Accordingly, Korea established "Comprehensive Plans on Combating Climate Change" (2008∼2012), to capitalize on the crisis of climate change to create new opportunities to further advance our nation. The nation will be proactive in joining international efforts to reduce GHG emissions, and at the same time will take an early response to climate change at home to minimize the burden of GHG emission reduction [1].
Burden sharing, with regard to GHG emission reduction, includes technology transfer and GHG emission trade, as well as the reduction of the absolute quantity of emissions. In this context, it is vital to have precise information on the amount of emissions produced and the emission sources to seek methods of reducing GHG emissions. In other words, only if we can quantitatively estimate the spatial distribution and time variance of emissions in different emission sources can we establish a concrete strategy to reduce emissions. First and foremost, we must establish an inventory of emissions based on credible data in order to achieve the goal of mandatory emission reduction [2].
In this regard, it is essential for Korea to secure statistics on basic greenhouse gases that reflect the nation's circumstances and reality. GHG emissions will vary depending on intrinsic factors including fuel type, fuel property, different types of boiler and control facilities, and the amount of fuel consumption. In particular, CH 4 and N 2 O emissions are influenced by numerous additional factors, some of which are hidden, such as conditions of consumption and operation as well as technical elements [3]. Accordingly, IPCC recommends that nations apply country-specific or technology-specific emission factors rather than default emission factors of IPCC when assessing national GHG emissions [3]. However, Korea has used the default emission factors due to the lack of relevant research within the nation.  Therefore, it is fundamental to assess the emission factors befitting national circumstances in order to predict and estimate GHG emissions and establish emission reduction plans.
Although the anthracite coal-fired power plants in Korea consume a significant amount of domestic anthracite coal, there is virtually no research to assess emission factors on these power plants [4]. In particular, designated power plants in this study are one of the world's largest scaled anthracite coal-fired fluidized bed power plants [5].
Therefore, it should be categorized as a major GHG emission source in mapping out Korean GHG inventory as the plant uses anthracite produced in Korea and is exclusively a domestic technology. To this end, we need to develop Korean country-specific emission factors on fluidized power plants. ). An electric precipitator is installed as the first air pollution control facility, and a filter dust collector is installed as the second control facility. The designated power plants are the only anthracitefired power plants in Korea, which are run in the manner of circulating fluidized combustion, but not in the mixture combustion of pulverized coal and heavy oil. Annually, anthracite is consumed approximately 1.1 million tons, it means 25% of total domestic anthracite production, and 40% of total consumption from domestic anthracite-fired power plants. The combustion temperature of a fluidized bed is 900 • C, significantly lower than pulverized coal combustion (1,200∼1,500 • C). The concentration of NO x is 60 ppm, a figure much lower than 350 ppm, the effluent quality standard of NO x .

Method of Sample Extraction.
In this paper, EPA Method 18 ( Figure 1) was applied when extracting GHG samples to assess the emission factor from GHG emitted from the plants [6]. A variety of tests were conducted to assess the temperature of flue gas, the amount of moisture, flow velocity, pressure, temperature, and others during sample extraction [7]. In order to reduce the margin of error, a one-liter Tedlar bag (SKC, US) was used for GHG sample extraction. Fuel samples were extracted from the sample extractor installed at a coal conveyor, which provides coal from the coal center to a boiler when replacing fuel. The samples for moisture measurement were extracted through two stages on each level in a swift manner. The rest of the samples were reduced through quartering, and then final samples were extracted. The fuel extraction was conducted at each power plant, and the extracted anthracite was the fuel used as the exhaust gases were extracted.

Element Contents Analysis
Method. The contents of carbon and hydrogen are highly important in order to assess GHG emissions in the consumption of fossil fuel. It is essential to analyze elements of coal, because the fuel properties vary greatly depending on the origin. The same anthracite that is used for sample extraction in the research was analyzed by Thermo Finnigan-Flash EA 1112, USA, at a laboratory for analysis of Carbon, Nitrogen, Sulfur, Hydrogen, and other elements. A two-meter ParaQX column was used in the process. The reproducibility result of elemental analysis showed that the absolute difference of Carbon and Hydrogen was between 0.10%∼0.37% and between 0.15%∼ 0.25%, respectively, as shown in Table 2 when using BBOT (2,5-bis (5-tert-butyl-benzoxazolyl) thiophene) as samples.  samples were quantified from an electronic scale (Mettler Toledo-AB204S, Switzerland) with 0.1 mg sensitivity. The water temperature of the analyzer was set at 25 • C using a temperature control device (KV-500, Germany) to analyze calorific values in Isoperibolic Mode. Cooling water used for the analyzer was created with a pure water apparatus (Duplex-150H, Korea). The reproducibility of anthracite was analyzed five times. The reproducibility was exceptional, with relative standard error (RSE) standing at 0.008%, as shown in Table 3.  Figures 2 and 3, respectively.

Exhausted Gas Analysis
In order to confirm the reproducibility of CH 4 analysis, standard gas (RIGAS, KOREA) with a concentration of 1.1 µmol/mol was analyzed ten times repeatedly. A standard gas (RIGAS, KOREA) with a concentration of 1.0 µmol/mol was analyzed ten times repetitively for reproducibility confirmation of N 2 O analysis. The result of reproducibility analysis was presented in Tables 4 and 5. The Relative Standard Error (RSE) of CH 4 and N 2 O stood at 0.19340% and 0.57101%, respectively, displaying excellent reproducibility.

Moisture Content of Exhaust Gas Analysis Method.
Moisture in the exhaust gas emitted from the power plants was measured from a moisture sampling apparatus (M-5, Astek Korea) and an electronic scale (Ohaus adventurer, USA). Heat rays were installed inside the tubes of the moisture sampling apparatus so that moisture in the exhaust gas can condense inside the tubes, maintaining a temperature at 120 • C to extract moisture. In order to measure the amount of moisture, a certain amount of granular anhydrous calcium chloride was filled into a roundshape absorption bottle as a moisture absorbent connected to sampling tubes for GHG. The gases were measured down to two decimal places (EPA method 4) on an integrated  flow meter installed to a moisture sampling apparatus. After extracting the samples, the absorption bottle was weighed with a cap on it. The amount of moisture in the exhaust gases was measured, taking numerous factors into consideration including the differences of the bottle weight before and after extracting the samples, the flow rate of the samples, and the temperature of the gases.

Estimated Method of Emission
Factor. The elemental analysis of fuel enables a reliable assessment of emission factors for CO 2 . However, the emission factors for CH 4 and N 2 O are susceptible to numerous variables of combustion conditions, such as combustion technology and its management. Therefore, it is hard to use the emission factors based on fuel analysis itself as a representative value [3]. Accordingly, emission factors for CH 4 and N 2 O were assessed after precise measurement of the exhaust gas concentration from the power plants used in this research. There are four stages of work sheets for emission factor assessment through measurement. The measured concentration and flow rate of CH 4 and N 2 O are inputted, and the unit is converted for the emission factor assessment in the first stage. The energy unit for fuel consumption is standardized in the second stage, and the amount of fuel consumption, power generation, and heat production are inputted in the third stage. In the fourth stage, the analysis for the calorific value of fuel is conducted, and the calorific value is inputted to assess CH 4 and N 2 O emissions, and the same for CH 4 and N 2 O emission factors in the fifth stage.

Analysis Results of Fuel Properties.
The results from proximate analysis and elemental analysis for domestic anthracite used in the power plants are presented in Table 6. The carbon contents in the anthracite on dry basis stood at 65.35%, while hydrogen stood at 1.46%. The proximate analysis of volatile components, fixed carbon, and inherent moisture stood at 7.16%, 57.94%, and 4.42%, respectively. When comparing the results of proximate analysis and elemental analysis with the results of a previous anthracite analysis from different anthracite-fired plants, the carbon contents were similar at 62.26%. The hydrogen contents were nearly identical at 1.12% [8].

Analysis Results of Methane and Nitrous Oxide Emissions.
The numerous analysis results, which include the concentration of CH 4 and N 2 O emissions, the temperature of exhaust gas, and the moisture and emissions measured from research-designated power plants, are shown in Table 7. The average CH 4 concentration from the first exhaust pipe of the power plant was measured at 2.22 ppm, and the second exhaust pipe at 1.41 ppm. The average concentration of total emissions stood at 1.85 ppm. The average N 2 O concentrations from each exhaust pipe were measured at a value between 2.78∼3.72 ppm, and the average concentration of emissions from all facilities stood at 3.25 ppm. The research found that there were slight differences in the concentrations of CH 4 and N 2 O emissions from some exhaust pipes, even though they used the same energy source. The disparities are likely attested to the concentrations of CH 4 and N 2 O, which are more susceptible to circumstantial factors such as combustion conditions, fuel amount, and flow rate.

Estimated Results of Emission Factors of Methane and
Nitrous Oxide Emissions. In order to assess the CH 4 and N 2 O emission factors of fluidized bed power plants that consume anthracite as their energy source, the low calorific values were calculated through fuel analysis. CH 4 and N 2 O emission factors were assessed using the element's concentration out of exhaust gases extracted from exhaust pipes, the emission flow rate of Tele-monitoring system (TMS), and the amount of power generation. The assessed emission factors are presented in Table 8

Conclusion
We selected circulating fluidized bed power plants as research facilities, which consume 25% of domestically produced anthracite. In order to analyze GHG emission factors of anthracite-fired circulating fluidized bed power plants, we assessed the calorific values and carbon contents for domestic low-grade anthracite through fuel analysis for domestic coal. We conducted an analysis on CH 4 and N 2 O emission concentration from the stack of the plants. With the analysis results, we assessed GHG emission factors for CH 4 and N 2 O. The fuel analysis showed that the low calorific value for coal used at the research-designated facility was at 19.1 TJ/ Gg. The analysis of CH 4 and N 2 O concentration from exhausted gas showed that the average emission concentrations for CH 4 and N 2 O from research-designated facilities were at 1.82 ppm and 3.25 ppm, respectively. The emission factors for CH 4 and N 2 O from the same analysis stood at 0.486 kg/TJ and 2.198 kg/TJ, respectively. The assessed emission factors for CH 4 from anthracite-fired circulating fluidized bed power plants were 52% lower than 1 kg/TJ, the default emission factors for anthracite presented by the IPCC. The disparities were due to differences in the method for and the conditions of combustion. The emission factors for N 2 O were assessed 46% higher than 1.5 kg/TJ, the emission factors presented by the IPCC. This disparity is attributable to the variance in method for combustion and other conditions because the default emission factors suggested by IPCC do not take combustion technologies into consideration. When calculate the national GHG emissions from these power plants using the emission factors in this study, CH 4 emissions could be 52% lower than emissions calculated by IPCC emission factor. But N 2 O emissions should be 46% higher than emissions estimated used by emission factor of IPCC.
Therefore, it is vital to proactively promote research for developing country-specific emission factors on a wide variety of fuel and energy consumption facilities in order to secure a dominant position in future international negotiation on climate change convention.