Feed & Byproduct Flexibility for New and Existing Crackers

The shale gas revolution has significantly increased the percentage of ethylene produced from ethane feed while reducing the amount produced from heavier feeds, particularly naphtha. However, with falling oil prices, naphtha feed prices have dropped and the operating margin of naphtha feed units has improved. In addition, in some regions the availability of ethane feed has dropped and the conversion of ethane feed plants to naphtha feed units is being studied. Many new plants are being designed for a range of feeds from ethane through naphtha and are identified as mixed feed crackers. To address these issues the paper will examine the design considerations of several cases including adding ethane flexibility to an existing liquid feed plant and naphtha flexibility to an existing ethane feed plant. In addition, adding propane and butane flexibility to an ethane cracker will also be examined. In addition to presenting material and energy balance information, the paper will also present the impact on various plant systems feed flexibility has and examine the modifications required to achieve various levels of feed flexibility. Finally, the paper will examine the impact on the byproducts slates the various feed combination has and will examine alternate technologies that can help meet the byproduct demand of existing downstream units in the complex.