Syngas contains a variety of contaminants produced from impurities present in the feed material
gasified. Syngas produced from biomass contains acid gases including HCl, HCN, and H2S. It also
contains NH3 and COS. All of these components must be removed to avoid poisoning of catalysts used in downstream upgrading processes.
Syngas made from biomass contains much larger amounts of CO2 than syngas derived from natural gas or other high heating value feedstock. The CO2 content of the syngas produced from biomass depends on the thermal efficiency and operating conditions of the gasifier and can be as much as 40 vol%. As CO2 content increases, so does the COS content of the syngas produced due to equilibrium of the reaction:
HS + CO2 ↔ COS + H2O
High CO2 content makes it more difficult and costly to remove other contaminants. Acid gases are typically removed contacting with water. Carbon dioxide is also removed by this process. The extent of removal depends on the pH of the water and the relative amount of water and syngas.
Physical absorption methods are also effective means to remove CO2, COS, and H2S from syngas. These systems use amines or methanol as the absorbent. The choice depends on the availability or cost of process steam compared to refrigeration, respectively. These systems are parasitic in nature, and comprise the bulk of the cost associated with syngas cleanup. The high CO2 content of syngas produced from biomass further increases the demand on these systems.
Syngas produced from biomass can also contain significant amounts of tar and soot, especially when produced at low gasifier temperatures (ca. <650 C). Syngas from these systems also contains considerable amounts of light hydrocarbons, including aromatic species. The aromatic components must be removed to prevent poisoning of downstream adsorbents in guard beds used to protect catalysts in the upgrading processes.
SynGas Technologys gasifier technology has been developed to maximize CO selectivity and minimize CO2 yield. Our proprietary gasifier design also reduces the amount of tar and soot in syngas derived from biomass. These benefits of SGTs process technology over competing technology reduce the cost of syngas cleanup and contribute improvement of overall bio‐refinery economics.