Furnace revamps provide opportunities to enhance new technologies, add feedstock flexibility, increase production capacity, improve efficiency and meet more stringent environmental regulations. With the current economic situation and anticipated environmental requirements, construction of grassroots plants is slowing down, and ethylene producers are leaning towards low-cost renovations to modernize their furnaces and optimize ethylene production. More than one-third of US/EU cracking furnaces are more than 30 years old, and technology has advanced significantly since the 1970s.
Earlier furnace revamp projects focused principally on increasing capacity and/or selectivity. Today's US/EU furnace revamp key objectives are increased feedstock flexibility, improved energy and operational efficiencies plus reduced emissions, all of which have to be achieved at the lowest possible cost with minimal impact on plant production rates. In many cases, adding selective catalytic reduction (SCR) to an existing furnace is necessary to comply with new NOx emissions limits.
In order to minimize furnace shut-down time to accommodate turnaround windows, it is necessary to modularize the new parts of the furnace to the maximum possible extent. Modularization retrofit concepts can be implemented into furnace revamp applications even when the furnace was not originally constructed this way. As each revamp project is unique, involving key specialists and equipment manufacturers in the early planning stages is important to promote innovative solutions to typical revamp challenges.
Key recent revamps (original design of various licensors) that will be described are listed below: • Korea - Fresh feed furnace capacity increases up to ~40 percent; recycle furnace capacities up to 80 percent; linked gas turbine integration. • S. Africa - Significant radiant/convection section modifications to improve capacity by ~70 percent together with other associated improvements. • Thailand - Similar radiant coil improvements ~25 percent together with convection upgrades and significantly improved low emission burners. • EU - Modified radiant coils to improve capacity by 20 percent; increased cracking severity; upgraded convection section including super high pressure steam superheater coils; replaced quench exchangers with compact, lower cost type (USX-MI). • EU/US - Relocated furnaces from original site to new expanding site incorporating selectivity, alternative feedstock and improved efficiency.
Keys to success in the examples that will be presented are the following: • Evaluating existing facilities • Minimizing shut-down time and overall schedule • Maximizing the use of existing material • Ensuring the objectives of the revamp are consistent with the client's business case • Recognizing constraints that limit the revamp (such as firebox size and maximum heat release) • Selecting modifications that meet operational, constructability and safety targets
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