(124d) New Furnace Sections - Energy Improvement of Cracking Furnaces of the 1960's and 1970's

During the period from the late 1960s through the 1970s the petrochemical industry has built a generation of new steam cracker plants with a total ethylene production capacity of several million tons per year. Most of these plants have been modified and revamped since their inception. The plant capacity of these older plants is in the range of 400 500 kta ethylene at present.

The furnace sections of those plants consist of typically 10 - 17 small furnaces which feature, for instance: - radiant coils with about 0.4 - 0.6 sec residence time, - thermal efficiency below 90%, typical 87-88%, - central waste heat recovery, - NOx emissions of about 75 - 100 ppmvol (ref. to dry flue gas with 3 vol% O2).

In the light of these technical aspects, replacement of the complete furnace section can be attractive in order to respond to several requirements at once: Enhance ethylene selectivity, increase energy efficiency, and improve HSE by incorporating today's emission and safety standards.

In addition these plants face competition from new cracker capacities in the Middle East based on latest technology. Due to the age of the plants and especially the furnaces (~ 30 years) intensive maintenance is required to guarantee high availability.

This paper will illustrate the improvements made in two recent projects in Europe. Special attention will be paid to the savings and optimisation potential in terms of energy. Both new furnace sections provide somewhat more than 500 kta of ethylene capacity and consist of five cracking heaters which have replaced 16 and, respectively, 17 smaller original units.