Digest feedback may help explain INEOS Bio’s high levels of HCN gas

Last week, we reported that excessive levels of hydrogen cyanide gas have been resulting in low ethanol output at the INEOS Bio plant in Vero Beach — and that a scrubber is being installed and will be commissioned that is expected to alleviate the problem.

Leaving the question of how a gas, at deadly levels to the core microorganism, could have gone undetected for so long. (Note to readers: yes, we did ask INEOS Bio about this, in late August, but have not yet heard back on this one).

According to the state of Florida’s report, at the INEOS plant, “the gasification of vegetative matter produces low levels of hydrogen cyanide (HCN) in the syngas of between 15 and 200 parts per million (ppm) depending on the operating conditions in the gasifier. In general, a higher gasifier temperature is required to achieve a lower HCN concentration. However, operating the gasifier at a very high temperature may lead to equipment unreliability, poor availability and high maintenance costs.”

Florida adds: “The HCN in the syngas is toxic to the bio-organisms in the fermentation process and INPB has determined through pilot scale testing that HCN at a level of 15 ppm is too high for the bio-organisms in the fermentation process to survive. It has been determined that the maximum HCN concentration for bio-organisms survival is less than 10 ppm with levels of less than 1 ppm of HCN required for the fermentation bio-organisms to survive and to reliably meet the project design targets.”

By way of a follow-up comment, however, we did hear from Iowa State professor Robert Brown, who helpfully advises:

“Because of systematic errors in measuring HCN, many researchers assume it is present in negligible amounts in biomass-derived syngas.  In fact, as one of my students has documented in a soon to be published paper, HCN can easily exceed 10 ppm.  Another misperception is that it can be destroyed by operating at higher temperatures.  We have found that it actually increases due to release of nitrogen as tar and char are consumed at higher temperatures (another paper soon to be published).”

The good news? Dr. Brown advises, “Fortunately HCN can easily be removed from gas streams, which is the reason why it has been under reported so frequently.”

To read last week’s report.