How to handle catalyst desulfurization
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This post was last edited by wangdu*ng on 2017-1-5 08:04. The cobalt-molybdenum low-temperature catalyst has been desulfurized; can its activity be restored through re-sulfurization?
Are there any empirical values for the time required for re-sulfurization and the amount of carbon disulfide to use?
Is there any difference in control between re-vulcanization and the vulcanization step with a new catalyst?
Just add some sulfur to the raw coal – it’s the simplest and most effective method.
Our unit uses carbon disulfide for resulfurization, which is effective, but the activity is not as good as it was before desulfurization.
Certainly. First, the sulfidation reaction is a reversible one. Second, after the catalyst has been in use for some time, its activity declines due to various factors; re-sulfidation can restore the catalyst’s activity to at most the level it had before use, but generally this is not the case. Third, even after re-sulfidation, the H2S content in the raw gas remains at the same level as before, so this does not solve the problem fundamentally – it only provides a temporary solution. The root of the issue lies in the low H2S content in the raw gas; when using water-coal slurry for gasification, it is advisable to add sulfur to address this problem, and the same approach should work for pulverized coal as well.
It seems crucial to monitor the gas composition before the transformation; what is the minimum amount required by the catalyst depending on the hydrogen sulfide level?
Generally speaking, the higher the temperature, the lower the hydrogen sulfide content and the greater the water vapor ratio, making desulfurization easier. For transformations at wide temperature and water-vapor ratio ranges (where the water-vapor ratio is 1.0 or higher), our company requires a minimum sulfur content of 200 ppm in the catalyst used for such transformations; whereas for water-vapor ratios below 0.5, the minimum sulfur content is generally above 100 ppm.
How did desulfurization occur in your unit?
It seems to be caused by an excessive amount of water vapor.