Information for Encyclopedia of Chemical Processing and Design
Publication Date: 2012-Sep-15
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Page 01 of 9
MULTI ZONE FURNACE DESIGN
During the past fifteen to twenty years, improvements in pyrolysis furnace design have been necessitated by the trend toward higher selectivity in the form of lower contact t~mes and higher severity cracking. Also accompanying this trend has been the use of heavier feedstocks such as light and heavy gas oils. The Kellogg-HRC furnace design has incorporated separate, independent zones of firing in the radiant section. This furnace design allows dlstlnct9 positive control of the entire tube length in which the pyrolysis reactions take place. With a multlzoned furnace design positive control of the heat in- put or flux in the various zones of the furnace provides maximum tube utiliza- tion of the pyrolysis coil with resulting improved operating flexibility and run lengths.
The Kellogg '~lilllsecond" pyrolysis process was developed to opt~mlze de- sirable olefinlc product yields from a wide range of feedstocks including the heavier gas oils.
Over the past 20 years, with improvements in pyrolysis furnace design and tube metallurgy, contact time for reaction has gradually decreased while oper- atlng temperatures have gradually increased. Design technology has kept pace with available materials to allow improved yields to be realized from shorter contact time and higher temperature operation. During the past 10-15 years, design contact times have been reduced progressively from 2 to 0.25 sec; design outlet.temperatures have increased from 1450 to over 1600°F. Each step has brought an increase in ethylene yields and a decrease in relative tall gas.
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CHEMICAL PROCESSING AND DESIGN
Page 02 of 9
In the late sixties it became apparent that distinct yield advantages could be real~zed by increasing temperature and reducing contact time even further. This idea lead to development of the Millisecond Pyrolysis Furnace which achieves improvement in yields by incorporating a reaction temperature of 1600-1700°F and contact time of less than 0.i second. Single-pass ethy- lene yields over 33 wt% easily can be achieved from naphtha, while methane yield remains below that of conventional heaters. (See Table I) The Milli- second Furnace probably represents the last important step that can be taken with respect to this critical pyrolysis variable because the higher tempera- tures required at contact times below the 0.01 second range lead to the pro- duction of acetylenes in large quantities.
In 1970, Idemtlsu Petrochemical Co. (IPC) and Kellogg agreed on a joint development effort to construct and test a Millisecond Furnace in a full-slze co-=.ercial installation. Final details were worked out and a nominal 25,000 Mt/hr ethylene furnace was constructed and started up on naphtha feed stock in 1972. Operation has continued successfully on kerosine, rafflnate, mixed pentanes and gas oll feedstocks, as well as the co.non naphtha feed.