Amine Sulphate incident
A mixer was used to prepare an amine sulphate prior to further processing. This involved feeding the molten amine to 70% sulphuric acid. The temperature was allowed to rise to around 95°C during the amine feed to maintain a mobile slurry. At several points the batch sheet requires the operator to visually check that the agitator is running.
On one occasion it was noted that agitation had stopped after around 90% of the feed. The operator was certain that there was agitation at the start of the feed. The temperature profile up to this point had appeared normal but was now getting higher than expected. For this reason a waterhose was applied first to the outside of the vessel and then to the contents.This solidified the vessel contents.
An instruction was given to leave steam on the vessel jacket overnight.It was hoped that this would restore mobility and allow the batch to be transferred. This did not work and a decision was made to agitate using a steam lance. Around one tonne of material was immediately ejected from the vessel. Fortunately the operator was unharmed. Clearly there was layering and a significant quantity of amine and sulphuric acid must have remained unreacted prior to agitating with the steam lance.
The mistakes are quite obvious in hindsight but there are reasons why the wrong conclusions were drawn. The amine sulphate slurry is normally held at 95°C prior to transfer to the next stage of the process. Sometimes,if the batch is held up for any length of time, water is lost by evaporation.This can result in the batch going solid. The situation is usually recovered by adding water and heating.
The main cause of the incident was that the agitator was rotating the wrong way and unscrewed itself. This is of enamelled metal construction supplied by Balfour. Unfortunately Balfour manufacture to two standards,DIN and Imperial, which have opposite handed threads.