(35c) An Overview of Recycle Streams As a Source of Contamination

To minimize waste, steam crackers tend to feature a range of recycle streams, either internally within the plant, or externally from neighboring units. These recycles can contain compounds that can adversely affect olefin operation. Examples of these factors include: a component returns to its place of origin and results in an increase in concentration e.g. MAPD contaminant ion of recycled propane increases MAPD from furnaces, a component is made and goes to a place upstream of where it is produced e.g. caustic red oil being routed to a primary fractionator a component is added for a specific function but can create a problem elsewhere, an additive in a recycle stream decomposes and produces a new contaminant upstream e.g. nitroxides in light ends fractionators can produce NOx in furnaces which could be a cold box problem,. With these factors in mind, an assessment has been made regarding the origin and impact of a number of common compounds. The effect of recycle streams will vary from site to site. However, there are some common themes and thus a mitigation strategy outline is included