Feasibility study of green ammonia and electricity production via an innovative wind-solar-biomass polygeneration system

Abstract

The increase in greenhouse gases in the world due to the use of fossil fuels and the risk of losing non-renewable resources are important factors in the expansion of renewable polygeneration systems. The current research focuses on integrating solar-biomass-wind renewable energies to produce power, process steam, and ammonia simultaneously. The general operation of the proposed system is that a syngas-solar hybrid boiler is used to produce steam at two low-pressure and medium-pressure levels. Medium-pressure steam has been used as the feed of gasification process unit along with air and municipal solid waste. The syngas produced from the gasification unit is used to supply boiler fuel and ammonia unit feed. Before the ammonia synthesis process, it is necessary to purify the feed syngas. In this regard, water gas shifting and CO₂ capture units have been used for purification. Next, the purified syngas with nitrogen in the presence of ammonia synthesis reactors are converted to ammonia. The nitrogen feed needed by the unit is created through a cryogenic air separation unit that supplies its electricity from wind turbines. A part of the ammonia produced has been used to fuel the downstream power generation unit. The Brayton open cycle based on ammonia-hydrogen hybrid fuel uses the described ammonia stream. The hydrogen required by this unit is supplied from the wind PEM electrolyzer. Finally, supercritical carbon dioxide cycles and organic Rankine cycle have been used to recover heat output from the Brayton cycle. Geothermal energy has also been used to preheat the organic fluid entering the turbine to increase power. Energy, exergy, exergeoeconomic, and exergoenvironmental (4E) analyses, along with sensitivity analysis and multi-objective optimization using the dragonfly algorithm, were performed. The overall energy efficiency, exergy efficiency, total cost rate, and environmental impact rate were 31.33 %, 38.53 %, 1.56 $/s, and 14.77 mPts/s, respectively. Three-objective optimization improved energy efficiency by 1.72 % and reduced the total cost rate by 15.86 %. In optimal operation, the system produces 275.44 tons/day of ammonia, 3.17 kg/s of steam, and 18.51 MW of power. The payback period was calculated to be 3.29 years, but in real-world scenarios, it may be longer, so the result should be interpreted cautiously.