Hydrocarbon streams feeding ethylene steam cracking furnaces often contain significant levels of corrosion products, water, and salts. This is especially true when naphtha is supplied by marine vessels. In these cases, high efficiency liquid-liquid coalescers and filters are recommended to condition the inlet feed stream. Contaminants in the inlet hydrocarbons can adversely affect ethylene production in a number of ways. Sodium and iron oxides are known to be coke promoters, and their presence can reduce the run time of the ethylene furnaces before decoking is required, and in some instances reduce the life of the furnace tubes by as much as one third. Unscheduled or frequent decoking cycles lead to a loss in ethylene production, shortened furnace tube life, and create higher maintenance costs. Frequent decoking will also result in increased particulate release to the atmosphere and can create environmental concerns over excessive emissions. Fouling of flow meters and control valves can lead to difficulty in maintaining the optimum furnace temperature and steam/hydrocarbon feed ratio. This can lead to poor yield of ethylene by the cracker and undesirable by-products. Installation experience at The Dow Chemical Company (Dow) in Freeport, Texas is presented for the use of high efficiency liquid-liquid coalescers and filters to extend the steam cracker service life between decokings. The naphtha feed was supplied by marine transport and contained significant salt water contamination. An economic evaluation of the savings due to improved operation efficiency and the payback period for the coalescer system is provided. The installation of the high efficiency coaiescer -filtration system was found to have a payback of less than ten months based on extended furnace run times alone, assuming that ethylene production is limited by furnace availability.
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