Ethane Cracking in Existing Liquid Crackers - Effects on CGC, Cold Fractionation and Refrigeration

With the availability of low cost ethane feedstock, it may be advantageous to replace a certain portion of the liquid feedstock with ethane feed. Ethane cracking in a liquids cracker results in better ethylene yield; however, there are certain challenges associated with this shift. The amount of ethane which can be cracked in a liquids cracker depends on many factors including:

• Price gap between liquid feedstock and ethane
• Plant configuration
• Desired capacity increase
• Available margins in the existing equipment
• Product shifts and effect on local market economics

Shifting from liquid feed to ethane feed changes plant traffic patterns, decreasing plant loads for systems that handle C3+ components but burdening systems that handle the lighter C2- fractions. The extent of change in traffic patterns and resulting challenges depends on the portion of the liquid feed replaced by the ethane feed. In this paper, the discussion will be focused on the effects of ethane feed cracking on cracked gas compression, cold fractionation and refrigeration areas. Key discussion items will include:

• Reduction in cracked gas molecular weight and resulting impact on the cracked gas compressor performance
• Shift in H2 and methane yields with traffic pattern changes in cold fractionation areas; effects on H2/residue production, chilling train pressure drop, expander performance and ethylene loss
• Performance of C2 Splitter and handling of increased ethane throughput and recycle
• Performance of C2R and C3R compressors and potential refrigeration recovery of fresh ethane feed.