Critical reviews of hydrothermal gasification for poultry litter valorization: Process yield, economic viability, environmental sustainability and safety

Poultry litter can be converted into thermal or chemical energy which can assist in meeting the energy needs. The current study focuses on a critical review of the cause-and-effect analysis of hydrothermal gasification (HTG) process yield, safety, and economic analysis. HTG batch and continuous technologies have been investigated, each with its own set of constraints. For example, resident time in a continuous reactor ranges from a few seconds to minutes, whereas it ranges from several min to hours in a batch reactor. Process parameters temperature, pressure, resident time, and solid content also contribute to the syngas quality, but temperature has the most significant effect among all. Syngas quality can be improved by managing process parameters such as 500–550 °C, 25–28 MPa, 120–150 min resident time, and 10–20% of the solid biomass content. Catalyst application in HTG promotes more hydrogen production. HTG is environmentally sustainable as compared to direct land disposal of biomass. H ₂ production costs range from $ 1.94 to 7.0 per kg and an investment payback period of 3.3–5.16 years. Process safety approaches that are appropriate to conduct HTG safety analysis have been investigated, and some control measures have been proposed which can be applied to make the HTG process safer. Finally, HTG future perspective and recommendations have been given based on current work.