ANALYSIS OF COKE PRODUCED IN ETHYLENE FURNACES - INSIGHTS ON PROCESS IMPROVEMENTS

Six industrial coke samples were analyzed by using a scanning-electron microscope and EDAX. These samples were from the pyrolysis coils, transfer lines, and inlet cones of transfer-line exchangers of the ethylene units. All coke samples contained iron, nickel, and chromium that had been abstracted from a metal wall or had been transferred through the coil and then incorporated in the coke. The coke which was formed catalytically contained metals and served as a collection site of noncatalytic coke. The catalytic coke was most prevalent on and near stainless steel surfaces. The coke near these surfaces was porous and obviously had high resistances to heat transfer. Methods of reducing coke formation are proposed.