Sunaryo Electrical Engineering Universitas Islam Sultan Agung Semarang, Indonesia sunaryo@std.unissula.ac.id Arinan Najah Putra Electrical Engineering Universitas Islam Sultan Agung Semarang, Indonesia arinannp@std.unissula.ac.id Arief Marwanto Electrical Engineering Universitas Islam Sultan Agung Semarang, Indonesia ariefmarwanto@gmail.com Muhamad Haddin Electrical Engineering Universitas Islam Sultan Agung Semarang, Indonesia haddin@unissula.ac.id Abstract— The consumption of electricity that increase anytime also increases CO2 emissions in the air as a result of coal combustion flue gas at the power plant. The operation of supercritical boilers on the power plant will lead to higher thermal efficiency compared to subcritical boilers. Higher steam pressure boiler will increase the thermal efficiency and automatically reduce CO2 emissions due to a reduction in fuel consumption at the same boiler efficiency and heating value of coal. At 166.9 bar subcritical steam boiler thermal efficiency was 45.47 % and CO2 emissions were 602.2 tons while at supercritical pressure 240 bar, efficiency increased to 47.12 % with a reduction in CO2 emissions of 20.9 tons to 581.3 tons. Keywords—subcritical, supercritical, CO2 emission. I. INTRODUCTION Electricity demand continues to increase anytime, it requires an adequate electricity supply. Coal fired steam power plant is one with the largest supply, more than 50 %. Most power plants in Indonesia still use coal fuel because economically it is the cheapest. The International Energy Agency (IEA) (2009) estimates that CO2 emissions from energy use in cities will grow by 1.8% per year between 2006 and 2030 [1]. However, the use of coal fuel will cause carbon emissions, especially CO2 which is very large, and become one of the biggest contributors to Greenhouse Gases. Each electricity production with coal fuel every 1 kWh produces an average CO2 gas emissions of 1.05 kg [2], while in [3] CO2 emissions are 964 gr / kWh. This value is higher than in diesel power plants with emissions of 541 g per kWh [3]. The emissions per unit of electricity are estimated to be in the range of 0.91 to 0.95 kg/kWh for CO2[4]. Although the use of coal is sensitive to environmental issues, its use is massive in more than 100 countries due to reasons of supply, ease of transportation, and relatively cheaper prices than other fuels [5]. An accurate calculation of CO2 emissions from coal fired power plant is one of the prerequisites for the realization of carbon emission reduction [6]. In this study, analyzing the thermodynamic flow in a reference power plant, and calculating CO2 emissions. Power plant that already have fuel consumption data and have measured fuel quality (proximate analysis or carbon content) can use method-2 [7]. The actual power plant which is still working in subcritical conditions, is simulated into supercritical conditions, and calculated the potential for fuel savings and CO2 emissions reduction. Power plants with supercritical boilers operating above critical points for water 22.12 MPa and 647.14 K pressure and temperature respectively [8]. Operation of the plant with supercritical boilers will result in higher thermal efficiency compared to the use of subcritical boilers. Higher thermal efficiency will lead to smaller CO2 emissions, for example in subcritical generators CO2 emissions of 850 kg / MWh, whereas in supercritical plants smaller emissions are 800 kg / MWh [9] . Simulations by [10] and empirical studies of 600 MW capacity plants in China [11] also showed smaller CO2 production in power plants with supercritical technology. Research on reducing CO2 emmisions in power plant has been done, mitigation to reduce emissions, using CCS (Carbon Capture and Storage) technology, will unfortunately increase the cost of generating 30-70% and reduce efficiency up to 14% [12]. One of CCS applications is oxy-fuel combustion, where coal is burned in a mixture of pure oxygen and recycled exhaust gas with a high content of CO2 gas [13]. Another method is post combustion technology, namely by mounting the membrane captures <90% CO2 [14]. Pre combustion method requires 75-125% higher generation costs than not using CCS technology [15]. Efforts to reduce CO2 emissions are also carried out by increasing the storage capacity of CO2 using CO2-foam[16] and modifications for a CO2 capture process using amine scrubbing [17]. II. RESEARCH METHOD A. Thermodynamic Analysis of Power Plants The principle of the Rankine Cycle working is to combine heat transfer between the components of the plant with the surrounding conditions. So the kinetic and potential energy can be ignored. Work analysis of Rankine cycles operates in steady state. The principle of conservation of mass and energy can be used to calculate the energy transfer from each component of the plant [18]. At a volume set in a steady state, the identity of the essence changes continuously, but the total amount that is there is constant at any time, so that the mass at the volume is set [18]: ௗ௠ ೎ೡ ௗ௧ =0,……………….……………..……………(1) Likewise the rate of energy transfer by heat and work which remains constant with time, so [18]: ௗா ೎ೡ ௗ௧ =0,……………………………….….……….(2) Because kinetic energy and potential energy are ignored [18]: ௐ ௠ሶ = (ℎ ௢௨௧ −ℎ ௜௡ ) ………..……………..…………..(3) with, W= energy produced (kJ) ሶ = mass flow rate (kg / s) ℎ ௢௨௧ = enthalpy of outlet (kJ / kg) ℎ ௜௡ = enthalpy of inlet side (kJ / kg) Proc. EECSI 2020 - 1-2 October 2020 Potential for Reducing CO 2 Emissions in the Operation of Subcritical Power Plants into Supercritical 100