Review of Biomass Gasification Technologies with a Particular Focus on a Downdraft Gasifier

The utilization of biomass as a renewable energy source has the potential to play a role in mitigating climate change. Furthermore, biomass gasification represents a sustainable solution for the management of lignocellulosic waste. Topics related to the different types of gasification reactors, biomass, and economic feasibility, along with tar formation and its removal in the product gas, are discussed as general aspects in the gasification. A detailed analysis of capital and operational expenditures, the net present value, the payback period, and the internal rate of return of downdraft gasifiers has been conducted. A bibliometric analysis has been conducted; the results are presented in the form of visual maps based on keywords, and likely future trends in gasification modeling were identified. Since modeling is crucial to optimize the production or quality of the syngas, this paper discloses some important aspects related to biomass gasification carried out on downdraft gasifiers. The modeling section encompasses a range of approaches, including those based on chemical equilibrium, both stoichiometric and non-stoichiometric, kinetic models, and computational fluid dynamics. A substantial section is devoted to the modeling of the downdraft reactor, incorporating the primary conservation equations for mass, energy, and momentum. The modeling framework aims to provide a comprehensive overview for researchers seeking to simulate downdraft gasifiers. This enables researchers to utilize a summary of equations and conditions that are pertinent to their own modeling and simulations.