Question: We operate a direct-fired (multiple burner) belt oven to perform drying and calcining operations with a catalyst product. During a recent trial, HCN was a suspect process contaminant, which led to the assessment of levels generated vs. baseline with natural gas burners operating but no materials present in the oven. Surprisingly, the assessment of baseline HCN showed values at 6 ppmv generated from the burner. In researching the matter, it was found that HCN can be formed as a byproduct of incomplete combustion of methane. In the chemistry, a rich mixture produces ammonia that, when reacted with unburned methane at high temperatures, forms HCN. Little information is available on the contaminant gases (NOX, HCN, NH3, etc.) generated through efficient vs. inefficient combustion processes (methane). Is anyone aware of research data on the topic? - G.H.
Answer: Editor's Note: I asked columnist Dick Bennett for his expert help on this technical question. Here's his answer.
I've checked with some people closer to the fundamentals of combustion than I am, and their response is that natural gas combustion produces such low levels of HCN that they'd be virtually impossible to measure. Levels of 6 ppm are way higher than anyone would expect. They suggested two possibilities:
1. Something else is getting into the combustion chamber during combustion, introducing a wild card ingredient.
2. The measuring instrument is giving an incorrect reading. I don't know what you're taking your measurements with, but my contacts said getting a reliable measurement would probably require taking a bottle or bag sample and sending it to an analytical laboratory. - Dick Bennett, Janus Technology Group, (815) 282-8044 or e-mail firstname.lastname@example.org.