Trace-Metal Scavenging from Biomass Syngas with Novel High-Temperature Sorbents

Abstract

EXECUTIVE SUMMARYEffective syngas cleanup is one of the remaining major technical challenges yet to be resolved and one that will provide the most benefit to the suite of bio-thermochemical process technologies. Beyond tars and acid gases, which are themselves a significant detriment to reforming catalysts and associated equipment, semi-volatile metals can also damage cleanup systems, catalysts, and contaminate the fungible products. Metals are a difficult challenge to deal with whether using hot-gas filtration or low-temperature processing. Even though most of the metal tends to condense before the barrier filter of hot-gas cleanup systems, some small percentage of the metal (large enough to damage syngas-reforming catalysts, the candle filters themselves, and gas turbine blades) does pass through these barrier filters along with the clean syngas. Low-temperature processing requires expensive measures to remove metals from the process stream. Significant costs are required to remove these metals and if they are not removed before contacting the catalyst, they will significantly reduce the life of the catalyst.One approach to solving the metals problem is to use high-temperature sorbents to capture all of the semi-volatile metals upstream of the barrier filter, which would prevent even small amounts of metal from passing through the filter with the clean syngas. High Temperature sorbents have already been developed that have been shown to be effective at capturing semi-volatile metals from vitiated combustion effluent, i.e., high-temperature flue gas. The objective on this project was to evaluate these same sorbents for their ability to scavenge metals from inert, reducing, and real syngas environments. Subsequently, it was the objective of this project to develop designer sorbents and an injection technology that would optimize the effectiveness of these sorbents at capturing metals from syngas, protecting the barrier filters from damage, and protecting the catalysts and other downstream equipment from damage. Finally, the high-temperature sorbent technology would be expanded to look at the role that these sorbents play in relation to tars and acid gases, which are the other significant pollutants within syngas. In addition to the technology development work described above, all of the information obtained in this work was to be incorporated into a syngas speciation model, which would allow direct prediction of transformations that occur in syngas as it passes from the gasifier and the sorbent-injection section and through the barrier filters.Unfortunately, Congressional budget cuts prevented most of this work from being accomplished. Hopefully, additional funds will be provided to this work in the future, which will allow its completion. However, at the halting point of this project, the following has been accomplished.A major initial objective of the project was accomplished, which was to determine whether or not high-temperature sorbents found to work within vitiated air might also work in an inert environme...