From sludge to fuel: 4E evaluation of a solar-powered tri-generation process producing methanol, freshwater, and electricity

• New multigeneration: power, water & methanol via solar, MED and refinery wastewater. • System delivers GOR of 5.1 for freshwater production efficiency • Production costs: $0.0438/kWh electricity & $1.6/m³ freshwater • Energy and exergy efficiencies are 67.28% and 59.16%, respectively • Strong profitability: NPV of $198M and IRR of 17.24% over project life This study offers a complete techno-economic and environmental evaluation of a new integrated system designed to simultaneously produce electricity, freshwater, and methanol. By combining refinery sludge combustion, biomass pyrolysis-gasification, and solar thermal energy alongside a Rankine power cycle, multi-effect distillation (MED), and methanol synthesis, the system ensures effective energy integration between all of its subsystems. The 67.28% energy efficiency and 59.16% exergy efficiency suggest effective use of the energy provided. Featuring a net present value (NPV) of $198 million, an internal rate of return (IRR) of 17.24%, and a payback period (PBP) of 5.8 years, the project exhibits robust economic results. The projected cost of freshwater is $1.62 per cubic meter, and power production is estimated to cost $0.0438 per kilowatt-hour. At just 0.38 tons per megawatt of electricity, the environmental assessment indicates CO₂ emissions are far lower than those of standard fossil-fuel systems. Furthermore, the system yields 34,494.2 kg/h of methanol as a valuable secondary product. The sensitivity analysis showed that greater solar radiation, higher gasifier outlet temperatures, and MED effects improve performance, whereas profitability is most affected by steam and interest rate costs. The innovative aspect of this research is the integration of waste sludge combustion, biomass gasification, and solar energy, leading to improvements in energy and exergy efficiencies, a reduction in production expenses, and better economic performance than existing multi-generation systems.