Modeling, simulation and techno-economic evaluation of a micro-grid system based on steam gasification of organic municipal solid waste

Abstract

The annual increase in population has led to rapid industrialization, urbanization, and economic growth over the years, becoming the lead cause of increased municipal solid waste (MSW) generation worldwide. In this study, MSW of 50 kg sampled by quartering method from Dandora dumpsite in Nairobi, Kenya is physically characterized and a sample of organic waste taken through proximate and ultimate analyses. Data obtained is used as input to a gasification model developed using advanced simulation and process engineering (Aspen) Plus software to provide characteristics of the yielded syngas. The obtained results are used to design a real gasification system and evaluate its techno-economic performance using HOMER® Pro as the tool for analysis. The techno-economic feasibility of the designed 60 kW gasification system is assessed considering a 165.59 kWh/day community-based load demand, with 11.5 % self-electricity consumption and 88.5 % grid feed. Results show organic and inorganic waste contents of 64.2 % and 35.8 %, respectively. The proximate and ultimate analyses reveal a high volatile matter content of 76.10 %, as well as fixed carbon content of 17.03 % in the biomass- rich-organic MSW. The simulated results show good agreement with experimental data and other simulation findings in literature. The study’s simulation output reveals 61.15 % H2, 1.42 % CH4, 24.12 % CO, 13.30 % CO2 contents following steam gasification at 700 °C. At 100 kg/h waste charge rate, a syngas yield of 2.39 m3/kg, gasification ratio of 2.2705 kg/kg and a lower heating value of 10,150 kJ/Nm3 (24.26 MJ/kg) are obtained. The sensitivity analysis results show increasing trend in CO2 and H2 syngas constituents from 0.4 to 1.0 steam-to-biomass ratio increase at 900 °C constant temperature: CO decrease is observed while CH4 values remain negligible and unaffected. The techno-economic findings reveal that the grid sales serve to offset the system’s annual costs by 39.34 %, obtaining a net present value (NPV) of $1.43 M, levelized cost of electricity (LCoE) of 0.155 $/kWh and 93.5 kg/yr. CO2 carbon footprint. An Organic MSW steam gasification micro grid is thus financially feasible in grid connected mode and is 99 % more carbon neutral compared to the Kenyan grid.