Quality of gaseous biofuels: Statistical assessment and guidance on production technologies

The wide variation in the properties of gaseous biofuels pose a major challenge to the practical application. This study focused on composition-related qualities of various purified gaseous biofuels excluding the effects of residual impurities. It built an informative compositional database of 20 types of existing and predicted gaseous biofuels. The ranges of the major constituent gases are as follows, CH4: 0.01–98.00 vol%, H2: 0.01–72.74 vol%, CO: 0–56.84 vol%, C2H4: 0–8.89 vol%, C2H6: 0–2.78 vol%, CO2: 0.01–87.40 vol%, N2: 0.01–94.98 vol%, O2: 0–6.53 vol%. The quality indicators, such as heating values, explosive limits, toxicity, and interchangeability, were statistically investigated. Subsequently, two methods for classifying gaseous biofuels regarding heating value and toxicity were proposed. The results show that synthetic natural gas, biogas, and methanation products of producer gases from gasification with steam, high-purity O2 (nearly 100%), and O2-enriched air (50–70% purity) are the preferred gaseous biofuels for different application scenarios. The CO and H2 contents are recommended to be limited to 2 vol% and 5 vol%, respectively. Then, suitable source and upgrading technologies are selected based on the quality results. Furthermore, the concept of electrification of biomass conversion including electricity-driven gasification and synthesis technologies was proposed. Diverse electricity-driven gasification technologies were analyzed with their applications and limitations. The results point out that the biomass and power-to-X pathway provides promising solutions for biomass and organic waste management, grid stability, sustainable fuel production, and decarbonization.