COMPONENTS FOR STEAM CRACKER
The production of ethylene and propylene from liquid and/or gaseous raw material feedstocks is carried out in Pyrolysis Furnaces. Feedstock is supplied to the inside of the Convection Coil Tube Bundles, mixed with steam and in the Radiant Section is broken down to ethylene, propylene and valuable co-products. A product of the pyrolysis reaction is the deposition of coke on the bore surface of the centrispun tubes, which, as its builds up reduce the effective cross-sectional area. Due to the thermal insulating properties of coke formation an increase in Furnace Tube Temperature becomes necessary to maintain the cracking efficiency. Periodically it is required to de-coke the Radiant Coil by application of an oxidising air-steam mixture.
The formation of coke in a typical Steam Cracker environment is inevitable and is a complex phenomenon, however, it can be reduced by selecting the proper tube metallurgy, such as Centralloy® ET-45 Micro or Centralloy® HT-E. These alloys are the universally preferred choice especially for “hot” outlet passes and with their carefully controlled specific additions can produce a dense and ”self-healing” oxide layer. This is especially effective in limiting coke formation and subsequent carburisation thereby increasing the overall Furnace performance and extending the Radiant Coil life.
To improve the availability of Steam Cracker Furnaces, it is essential for operating and management personnel to have an understanding of the most common causes of failure in Pyrolysis Coils, Cross-overs, Transfer Lines etc. , relevant to their own plant and mode of operation. In addition, it is vital for plant personnel to be fully aware of inspection techniques currently available that will allow meaningful evaluation of tubing, including identification of service related deterioration and, also assist in providing a realistic assessment of the high temperature tube materials. In this manner, maintenance shut-downs can be planned and scheduled in the most time and cost effective way. Operating and management personnel should be also have a working knowledge of repair and replacement options currently available. This will allow for further reduction in costs associated with maintaining Steam Cracker Furnaces.
