(66c) Improvement of Ethylene Plant Performance Using High-Cr, High-Ni Weld Overlaid Furnace Tubes

High-Cr, high-Ni PPW (Plasma Powder Weld) overlaid furnace tubes have been evaluated in several commercial ethylene pyrolysis furnaces. In addition to extremely high carburization resistance due to the ?dam effect? of the PPW layer, which leads to longer tube life, these tubes demonstrated significant improvements in the operational performance of the pyrolysis furnaces, especially when ethane feed was used. The lower TMT (Tube Metal Temperature) and lower rise of coil pressure indicate a reduction or slowdown of coke formation and as a result, run length was extended to twice or longer in the case of ethane feed and approximately 30% longer for naphtha feed. These effects are brought about by the chemistry of the internal surface of the tube. A high chromium weld overlay creates and maintains a tight chromium oxide layer without iron, nickel, or their oxides which act as catalysts for the coke formation. It was also found that conversion and ethylene yield were improved by 1 - 3%. Combined with higher furnace availability and higher robustness against unplanned shutdowns, the benefits of ROA (Return of Asset) improvement can far outweigh the initial cost penalty of using these tubes.