Development of emission reduction measures of trace gas emissions from coal-fired power plants in Indonesia

Most of Indonesia’s electricity demand is supplied by coal fired power plants (CFPPs) which can potentially emit huge amounts of air pollutant gases such as NOx and SO2 gas. The country has committed to reduce Greenhouse Gases (GHGs) emission by 2030 through Nationally Determined Contributions but some emission reduction measures may also reduce air pollutant gases. Flue Gas Desulfurization (FGD) and Atmospheric Fluidized Bed Combustion (AFBC) are the leading control technologies for reducing SO2 and NOx emissions that can be installed in the CFPPs. This study aims to determine the pollution load of SO2 and NOx gases in 2030 generated from CFPPs operation with (reduction scenario) and without FGD and AFCB control technology (business as usual (BAU)). The gas pollution load was calculated using the Atmospheric Brown Clouds- Emissions Inventory Manual (ABC-EIM) procedure. Based on the BAU scenario, the emission load accounted of 1,440,192 tons/year for NOx and 613,121 tons/year for SO2 in 2030. After implementing the control technology scenarios in 2030, the NOx emission load is projected to decrease to 579,610 tons/year, and the SO2 emission load decrease to 77,920 tons/year. The application of AFBC and FGD control technologies can potentially reduce NOx and SO2 emissions load from CFPPs operation in 2030 thus it can help to improve air quality in the future.


Introduction
As technology develops more advanced, the electrical energy demand is increasing.Steam Power Plants supply Indonesia's electricity demand by 47%.The dominant fuel used by those power plants is coal.Coal is a fuel commonly used by industry due to its calorific content, readily available, and relatively cheap price [1].Coal consists of 4 types with different qualities: lignite, sub-bituminous, bituminous, and anthracite [2].Burning coal produces sulfur dioxide (SO2) and nitrogen oxide (NOx) gases, which harm human health, such as respiratory disorders, headaches, and nervous disorders.At the same time, it will lead to cause acid rain due to acidification occurred in the atmosphere [3].Indonesia's efforts to reduce Greenhouse Gases (GHGs) emissions by 2030 is expressed through Nationally Determined Contributions (NDC) and under the national blue-sky program the efforts are more focusing on air pollutants emission reduction [4].The emission reduction scenario in this study assumed implementation of air pollution control technology.Due to existing regulations related to emission standards for power generation in Indonesia, air pollution control devices need to be installed to reduce emissions.[5].Flue Gas Desulfurization (FGD) and Atmospheric Fluidized Bed Combustion (AFCB) are control technologies that are able to reduce SO2 and NOx emissions.In FGD, a binder in the form of 1239 (2023) 012013 IOP Publishing doi:10.1088/1755-1315/1239/1/012013 2 lime will bind gas emissions containing sulfur so that the sulfur content in gas emissions is low [6], while in AFCB combustion occurs at low temperatures resulting in lower NOx [3].This study aims to determine the load of SO2 and NOx gas pollutants in 2030 produced by coal-fired power plants with and without FGD and AFCB control technology.Therefore, emission reductions of NOx and SO2 were analyzed under the emission reduction scenario as compared to the Business as Usual (BAU) scenario in 2030.

Study Location
This study was conducted for all coal-fired steam power plants in Indonesia.In total, there were-147 coal-fired power plants in Indonesia which comprise of 45 plants using lignite coal types, 94 plants using sub-bituminous coal types, 6 plants using bituminous coal types and 2 plants using anthracite coal types.The spatial distribution of the plants location can be seen in Figure 1.

Figure 1. Location of coal-fired power plants in Indonesia
Source: Koplitz, 2017

Projected coal fuel consumption
This study used the baseline year of 2011 to calculate coal consumption for all coal-fired power plants in Indonesia.The data were then projected to the year of 2030, following the NDC target to reduce the emission load in 2030.The projection was conducted in two scenarios: (i) business as usual (BaU) and, (ii) emission reduction scenario by assuming installation of gas control technology.
The projection of coal fuel consumption was carried out by determining the ratio between fuel consumption in 2011 (baseline) and 2030 (BaU).Total fuel consumption data in 2011 was obtained from previous studies results and fuel consumption data in 2030 was obtained from the Rencana Usaha Penyediaan Tenaga Listrik (RUPTL) or Electricity Supply Business Plan 2021-2030.The ratio obtained is used to project fuel consumption per coal-fired power plant unit in 2030.The equation used for projecting coal fuel consumption per unit of coal-fired power plant is: Where, EM = emission load (Ton/year) EF = emission factor (g/kg) AR = activity data (coal fuel consumption, Ton/year) EC = control efficiency (%) The calculation was carried out under three conditions: baseline ( 2011), business as usual ( 2030) and after implementing control technology scenarios.In baseline conditions, several coal-fired power plants have used Flue Gas Desulfurization (FGD) and Atmospheric Fluidized Bed Combustion (AFBC) control technology.In 2011 (baseline), as many as 28 coal-fired power plants used AFBC to reduce NOx gas emissions.In reducing SO2, as many as 15 coal-fired power plants use AFBC and as many as 13 coalfired power plants use FGD to reduce SO2 gas emissions.In BaU calculation, the fuel consumption used is the projected fuel consumption.The emission factor and supporting data used in this calculation are determined based on the type of coal used in each coal-fired power plant unit.The data used in this study can be seen in Table 1.

Emission load reduction scenarios
The calculation of the emission load with control technology is carried out as an effort to reduce the load of pollutants emitted by coal-fired power plants.This is because with the emergence of Ministry of Environment and Forestry (MoEF) regulation No. 15 of 2019, where the emission standards are getting stricter hence every plant must have control technology to control their air pollutant emissions [5].The control technology used is Flue Gas Desulfurization (FGD) to reduce sulfur dioxide (SO2) gas emissions and Atmospheric Fluidized Bed Combustion (AFBC) to reduce nitrogen oxide (NOx) gas emissions.This is because FGD can reduce SO2 emissions by as much as 90% [9], while AFBC can reduce NOx emissions by as much as 70% [10].After the implementation of control technology in 2030, the calculation results will be compared with the emission load in 2030 (BAU).The reduction in emission load can be calculated using the formula: Where, A = Total emission gas BAU (2030) B = Total emission gas with control technology (2030)

Results and discussion
The calculation results obtained in this study were obtained by calculating the emission load on 147unit coal-fired power plants in Indonesia for.2011 (baseline), emission load in 2030 (business as usual) and emission load in 2030 when the control technology reduction scenario is applied.

Projected coal fuel consumption
Projected fuel consumption was calculated using the ratio between total fuel consumption in 2011 and 2030.The ratio obtained was multiplied by fuel consumption in 2011 to determine, the fuel consumption is obtained in 2030.Total coal fuel consumption in 2011 amounted to 1,079,045 Tj/year [11].Based on the calculation of the ratio of coal fuel consumption in Indonesia in 2011 and 2030 which is 3.841, after projecting the total fuel consumption in Indonesia in 2030 is 4,144,932 Tj/year.Coal fuel consumption in Indonesia has increased by 3,065,887 Tj/year.This is because the increasing industrial activities and population demand for electricity have increased [12], so that coal fuel consumption will consequently increase.Increased coal fuel consumption will also cause emissions such as NOx and SO2 to increase.Increased NOx and SO2 emissions will impact the environment, human health, global warming and ecosystem damage [13].

Calculation of nitrogen oxide (NOx) and sulfur dioxide (SO2) gas emission load
Data on the calculation of NOx and SO2 gas emission loads at baseline conditions can be seen in Figure 2.
Figure Figure 4 shows, the results of emission load calculation in 2030 after all plants applying the control technology.NOx gas emissions produced using AFBC control technology with 70% efficiency accounted for 579,610 tons/year, meanwhile the emitted SO2 gas when the FGD technology is applied with 90% efficiency is to 77,920 tons/year.Based on the results of comparisons on baseline conditions (2011), BaU (2030), and control technology scenarios (2030).NOx gas emissions contribute the most to air pollution around coal-fired power plants in Indonesia.This can be caused by burning coal fuel with high temperatures supporting NOx formation [14].In addition, it can be caused by the content of the coal used, where the nitrogen contained in coal is an organic compound formed from plant material proteins with an amount of about 0.55% to 3%.Usually, bituminous coal contains more nitrogen [15].This aligns with the dominant type of coal used in Indonesia, where as many as 94 units of coal-fired power plants use sub-bituminous coal types and 6 units of coal-fired power plants use bituminous coal types.NOx formation can be minimized by reducing the amount of oxygen and combustion temperature [16].
Most coal-fired power plants in Indonesia use low-sulfur-coal so this can be the cause of SO2 gas emissions produced by coal combustion that tend to be lower than NOx.Because the high emission load of SO2 gas can be caused by high sulfur levels contained in coal so that during the combustion process produces SO2 gas [17].NOx and SO2 emissions are significant contributors to acid rain [18].The impact of acid rain is forest destruction, rice yields that decrease by 30%, damage to aquatic ecosystems such as declining populations of fish and aquatic plants [19].In addition to acid rain, NOx and SO2 also impact health.According to research, SO2 can cause throat irritation [18].Other health impacts caused by NOx and SO2 are respiratory disorders, headaches, and nervous disorders [3].The impact of NOx with exposure to high doses of animals shows symptoms of nervous system paralysis [20].

Emission load reduction scenarios
The emission load reduction scenario applied is the control technology scenario.This control technology is used for new coal-fired power plants that do not yet have emission control devices.In baseline conditions (2011), some coal-fired power plants already have control tools such as FGD and AFBC to reduce the load of SO2 emissions and AFBC to reduce the load of NOx emissions.The FGD control technology scenario will be applied to reduce SO2 emission load, where FGD has an efficiency of 90% [9] and AFBC reduces NOx emission load with an efficiency of 70% [10] emissions will certainly reduce the potential for acid rain and the potential for health problems such as respiratory problems, nervous disorders to the community around the PLTU.

Conclusion
The coal fuel consumption from 2011 to 2030 increased by 3,065,887 Tj/year, attributable to the population and industrial activities increment during the time.

Fuel
in the projection year Total fuel consumption a = total fuel consumption in the projection year Fuel consumption b = fuel consumption in the baseline year Total fuel consumption b = total fuel consumption in the baseline year 2.3 Calculation of nitrogen oxide (NOx) and sulfur dioxide (SO2) gas emission load Coal-fired power plants can produce polluting gases such as SO2 and NOx [7].This study calculated NOx and SO2 pollution loads based on procedures in the Atmospheric Brown Clouds-Emissions Inventory Manual (ABC-EIM) [8].The equation used to calculate the exhaust emission load as follows:

Table 1 .
Emission factors for NOx and SO2 Source: ABC-EIM . The results of the comparison Comparison of projected emission load for NOx and SO2 based on BAU Emissions and Control Technology scenario for the year 2030Figure5shows, the NOx emission load after applying the scenario with AFBC control technology is 579,610 tons/year, while the SO2 emission load after using the scenario with FGD control technology is 77,920 tons/year.Based on the results of a comparison between the emission load of NOx and SO2 gas in BAU conditions (2030) and after applying the technology scenario, this scenario can reduce the load of NOx and SO2 emissions resulting from combustion at coal-fired power plants in Indonesia.The NOx emission load between BAU conditions and after applying AFBC control technology can reduce the emission load by 860,582 tons/year.The SO2 emission load between BAU conditions and FGD technology can reduce the emission load by 535,201 tons/year.This is because FGD can reduce the load of SO2 emissions by binding sulfur using a binder in the form of lime so that the sulfur content produced is low [6], while AFBC can reduce NOx by burning at low temperatures so that the NOx produced is lower[21].The reduction in emission load after applying control technology occurs because in this scenario all coal-fired power plants are considered to have control technology for NOx and SO2 parameters, while in BAU conditions (2030) only a few coal-fired power plants already have control technology.Reducing the emission load after implementing this control technology scenario certainly positively impacts the surrounding environment and human health.The reduced load of NOx and SO2 Based on the BaU condition, the NOx emission load produced from coal-fired power plants in 2011 (baseline) accounted of 374,923 tons/year and increase by 1,440,192 tons/year in 2030.In 2030 the NOx emissions decrease to 579,610 tons/year when the AFBC control technology is implemented, resulting a 60% (860,582 tons/year) reduction of the NOx emission load in 2030.The SO2 emission load produced from coal-fired power plants in 2011 (baseline) amounted to 159,613 tons/year and is projected to increase to 613,121 tons/year in 2030 during the BaU condition.In 2030, the implementation of control technology FGD is able to decrease the SO2 emissions load to 77,920 tons/year, resulting a 535,201 tons/year or 87% SO2 reduction in the targeted year.