In our Flare Gas Recovery Unit, the liquid ring compressors suction check valve and coolers shell tubes side (cone seal water) get covered with deposits that contain 95%wt elemental sulfur plus iron and carbon. Our question is: How elemental sulfur forms from H2S or other sulfur compounds in this water system? I have always heard that elemental sulfur indicates that oxygen was present. I have no independent basis to know whether this is true. Assuming that it is true, then logic would suggest that there must have been some H2S or a similar compound present along with oxygen (in the water that was non-de-aerated, so I suppose that water could have been a source of oxygen). The refinery flare gases contain some H2S, and some minor amount of oxygen. Initially we used to use reject water from an RO unit as the main water source. That water is no longer used, since it has been change to Stripped Sour water. Water system pH is controlled between 7.3 and 8.3.