Naptha cracking streamlined

New anti-coking and carburisation-resistant tubes for cracking furnaces, jointly developed by Shell Global Solutions International BV and Daido Steel Corporation, are increasing the run length between decoking operations by 50% to 70%.

This translates into savings of up to US$1.5 million per year for a typical 100,000T/Y capacity furnace through increased operational availability. In addition, tube life is extended through the reduced carburisation of the base material and process yields can be higher due to reduced coke. In naphtha cracking furnace trials, the tubes were found to greatly reduced coke lay down and carburisation. Additional studies revealed that the decreased carburisation of the new tubes increases their lifetime by about 2 to 3 times compared with standard tubes and that this is governed by creep and not by carburisation. The tube construction is based on a standard centricast alloy with an internal overlay weld that has similar mechanical and thermal properties to the base tube material. It is the composition of the overlay weld that provides the enhanced properties. The overlay is applied by a plasma-powder-welding (PPW) technique developed by Daido. The tubes were developed as a result of Shell Global Solutions' coke lay down studies and laboratory tests. These demonstrated the coking tendency of alloys with a wide range of chemical compositions. Shell Global Solutions and Daido Steel are seeing keen interest in the anti-coking tubes from the petrochemical industry. Production of complete furnace coils is being stepped up to meet market demand. Globally, about $300 million a year is expected to be spent on existing furnace tubes replacement and on new projects to meet the rising demand for ethylene. Development work is starting on further improvements in the overlay weld layer in terms of coking and carburisation properties, and features to optimise the cost-effectiveness of the product.

Further process and equipment applications are also being investigated.

For more information contact: Shell Global Solutions:

Tel: +31 20 630 2366Fax:+31 20 630 8004

or Daido Steel

Tel: +81 52 201 9358Fax: +81 52 211 1664