(226h) Techno-Economic Analysis of IGCC for the High Ash Indian Coal Using Bubbling Fluidized Bed Gasifier

Energy is the basis for running the economy. Every decade energy demand is increasing. In the last decade, it has grown by 21.54% [1]. Among the various energy sources, coal contributes 26 % of the world’s energy consumption which is significant after oil. However, coal consumption leads to negative environmental impacts such as carbon emissions during burning and soil & air pollution during mining, transport and storage. The world is moving towards renewable energy sources that are cleaner than carbon; however, current renewable technology is expensive and yet to overcome the problem of intermittency. Thus, coal is still the only option to meet the significant energy demand, especially in countries like India where there are large reserves of coal. It also provides energy security. The total amount of coal in the world is 1033.71 billion tons, and 36% of the world’s electricity was produced by coal in 2021 [2]. India has around 11% of the world’s coal reserves [3]. Therefore, a substantial research effort is going on to make coal technology cleaner. However, the challenges include reduction of 9.7 Gt of carbon emitted from the coal-fired power plant in 2021[4]. To overcome some of these challenges, developing countries should adopt clean coal technologies such as integrated gasification combined cycle (IG-CC), chemical looping combustion power generation (CLC-CC) or underground coal gasification coupled with combined cycle (UCG-CC). Among all these options, IGCC not only reduces carbon emission but also increases plant efficiency, and is a more mature technology than UCG.

IGCC incorporates different units such as air separation, gasification, syngas cleaning and power island. This work focuses on gasification which can be performed in a fixed bed, fluidized bed, or entrained flow gasifier. The entrained flow gasifier has limitation in the formation of ash agglomeration for high ash coal because it works above the ash-fusion temperature. Among the other two gasifier types, the fluidized bed gasifier is more efficient. It decreases char production by properly mixing coal particles and gasifying medium, and it works below ash-fusion temperature.

India has a vast amount of Bituminous low-rank coal, which typically has low carbon (60%-80%) and high ash (20%-45%) content [5]. Due to technological constraints and experimental repeatability issues, India still lacks a commercial gasification plant for high-ash coal. The development of fluidized bed gasification technology for high ash coals could provide a cleaner technology from an Indian perspective. Therefore, this study aims to investigate the feasibility of IGCC for high-ash Indian coals using a fluidized bed gasifier. An integrated gasification combined cycle (IGCC) model is developed in Aspen plus for the high ash coal and validated with the experimental data. The validation is done for the following parameters: steam/coal ratio, air (O₂)/coal ratio, and operating temperature. The models are based on the equilibrium approach where Gibb’s free energy minimization has been performed to find the syngas composition. In addition, the temperature approach is used for the water gas shift and methane-steam reforming reactions.

The results suggest an increase in equivalence ratio (ER) from 0.19 to 0.28, increases the carbon conversion efficiency (CC) from 39.42% to 61.04% and cold gas efficiency (CGE) from 20.11% to 26.11%. Further, during air-steam gasification, keeping ER the same and increasing steam/coal ratio from 0.06 to 0.26 results in an increase in CC from 58.06% to 72% and CGE% from 29.03% to 46.18%. The model gave a syngas heating value between 1-2 MJ/m³ during air-assisted gasification and ~3 MJ/m³ during air-steam gasification.

In continuation of previous work, the study also focuses on (i) syngas cleaning and electricity production and (ii) economic analysis of the IGCC plant. However, this work is in progress. The process methodology for the syngas cleaning contains a single-stage Rectisol method with methanol taken as the physical solvent [6]. The low temperature (- 40) operation helps to increase the absorption of corrosive gases like carbon dioxide and hydrogen sulfide gases in the methanol. The model includes a corrosive gas absorber and solvent recovery column. Carbon capture is not considered in the methodology. The power island for the electricity production uses a combined cycle operation. Finally, the economic analysis of IGCC will be done to find the levelized cost of electricity (LCOE). The LCOE will contain the sensitivity analysis with respect to the discount rate, raw material and capital cost.

Overall, the study investigates fluidized bed gasification as cleaner technology for high-ash coal which suits the Indian scenario. In addition, a methodology has been developed to evaluate power production and economic analysis of the IGCC.

Keywords: Efficiency (Energy), Fossil fuels, IGCC, Fluidised bed gasifier

References:

[1] Electricity consumption, Web Link: https://www.iea.org/reports/electricity-information-overview/electricity-consumption, Accessed on 03-April-2023

[2] Proven coal reserves worldwide in 2020, by country Web link: https://www.statista.com/statistics/237096/proven-coal-reserves-of-the-top-ten-countries, Accessed on 03-April-2023

[3] Statistical Review of World Energy (70^th edition), 2021, bp,Web link: https://www.bp.com/content/dam/bp/business-sites/en/global/corporate/pdfs/energy-economics/statistical-review/bp-stats-review-2021-full-report.pdf

[4] How much coal is left, Web link: How much coal is left - U.S. Energy Information Administration (EIA), Accessed on 03-April-2023

[5] Power Sector at a Glance – All India, Web link: https://powermin.gov.in/en/content/power-sector-glance-all-india, Accessed on 03-April-2023

[6] Sun, L. and Smith, R., 2013. Rectisol wash process simulation and analysis. Journal of Cleaner Production, 39, pp.321-328.