DOI: 10.22146/ajche.16677 ASEAN Journal of Chemical Engineering 2025, Vol. 25, No. 1, 87 – 96 Techno-economic Analysis of Biomass Co-firing Application on Indonesia 660 MW Class Subcritical Coal-Fired Power Plant Alfian Muhammad Reza* ,1 Muhammad Royan Alfi Rosyidin 1,2 Imam Hambali Supardi 1,2 Ari Hindarto 1 Hengky Setiawan 1 Winny Wulandari 2 1 PT PLN Enjiniring, Jakarta, Indonesia 2 Institut Teknologi Bandung, Bandung, Indonesia * e-mail: alfianreza17@pln.co.id Abstract. Following the publication of the Ministerial of Energy and Mineral Resources of Indonesia Decree number 14.K/TL.04/MEM.L/2023 regarding the greenhouse gas (GHG) emission cap for coal-fired power plant (CFPP), PLN, the electricity company owned by Indonesia, is attempting the GHG reduction of its CFPPs at certain levels through several decarbonization programs, with biomass co-firing on its existing CFPP as the first step. The CFPP that becomes the object of this study is 660 MW class subcritical, Suralaya units 5-7, with a net capacity of 643.09 MW per unit. The biomass used is sawdust that was taken from local suppliers. The existing power plant has a carbon emission intensity of 1.03 Ton/MWh, higher than that of the carbon cap (0.911 Ton/MWh). Therefore, it should pay a carbon tax at a certain value. The biomass co-firing implementation can reduce its intensity depending on the ratio. The biomass implementation would probably require an upgrade investment. The other cost-effect factors are fuel cost and carbon tax. The degradation of CFPP performance can impact on fuel costs. Then, the biomass co-firing implementation can reduce or even prevent a power plant from paying the carbon tax. The best option regarding the financial calculation result is a 5% ratio. It potentially reduces the levelized cost of electricity (LCOE) by 0.36 IDR/kWh. However, a higher biomass ratio will probably increase the power plant LCOE. Implementing a higher biomass co-firing ratio does not always result in better financial aspects. The decision to implement shall consider the valid regulation comprehensively. Keywords: Biomass, Co-firing, Carbon Cap, Carbon Tax, Renewable Energy. INTRODUCTION The Indonesian government released several laws, including a maximum greenhouse gas (GHG) cap for coal-fired power plants (Natalia et al., 2022), to speed up the proportion of renewable energy in the country's electricity system. Early in 2023, Indonesia's Minister of Energy and Mineral Resources (MEMR) issued Decree Number 14.K/TL.04/MEM.L (Ministerial of Energy and Mineral Resources Decree, n.d.). Additionally, it denotes implementing the carbon tax legislation indicated in Undang-undang No. 7 Submitted 27 September 2024 Revised 4 March 2025 Accepted 10 March 2025