There has been growing debate about the use of biomass for various reasons, including food, feed, energy, heating, and cooling, and most crucially, as a feedstock for biorefineries.
By 1798, the technique of biomass gasification had been independently identified in France and England. 60 years later, the technology gained prominence. The gasification technique flourished for another 30 years until natural gas was discovered in oil fields. Until 1970, natural gas was replaced with liquid fuels for cooking and lighting due to the discovery of oil. In general, biomass gasification is an endothermic thermochemical conversion of solid biomass fuels utilizing gasifying agents such as air, steam, or CO2 to produce a combination of combustible gases, including H2, CH4, CO, and CO2. The procedure takes place at temperatures ranging from 800 to 1300°C. Nowadays, the versatility of the gasification technique, together with the variety of applications for the generated syngas, enables the integration of biomass gasification with a wide variety of industrial processes and power generation systems.
Particle size, moisture content, shape, heating value, carbon content, and ash content of biomass feedstock all substantially affect gasifier performance. However, understand feedstock factors such as volatility, elemental analysis, heat content, and biomass fouling or slagging potential for gasification process evaluation. As a result, feedstocks with low volatile content are preferable for partial oxidation gasification, whereas feedstocks with a high volatile content are better suited for indirect gasification.
Biomass gasification feedstocks come in a variety of forms, each with its own set of difficulties. As a result, it is critical to anticipate the optimal biomass type for a specific gasifier type under specified parameters. Although the characteristics of particular biomass feedstock species are identical, the shape and size of the feedstock particles help determine potential challenges during transportation, delivery, and feedstock behavior in the gasifier. The feedstock's size and size distribution affect the thickness of the gasification zone, the pressure drop in the bed, and the maximum hearth load. To address some of these issues, uniform-sized biomass feedstock was used.
The operation of the gasifier is dependent on the moisture content of the biomass feedstock. The use of feedstock with a high moisture content decreases biomass conversion efficiency and the production rate. This is because the process consumes additional fuel or generates additional heat to vaporize the extra moisture to the temperature of the syngas.
Water requires approximately 2.3 MJ/kg to vaporize and 1.5 MJ/kg to reach 700°C during the pyrolysis/gasification. Additionally, biomass with a high moisture content decreases the temperature obtained in the oxidation zone, resulting in inadequate cracking of the products generated in the pyrolysis zone. As a result, the excessive moisture content in the biomass feedstock affects the composition or quality of the syngas, as CO2 is produced as a result of the moisture reaction. Additionally, high-moisture feedstock produces syngas with high moisture content, putting additional strain on downstream cooling and filtering equipment.