ECC - Ethylene Cracking Heaters
Ethylene is an important chemical widely used in the production of plastics for products such as PVC, packaging, and window frames, among others. The product is obtained by the pyrolysis of naphtha, ethane or propane. Currently there are 45 ethylene plants in the United States, 90% of which use gaseous feedstock. Due to expanded world demand, it has also experienced rapid growth.
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An ethylene cracking furnace is a tall and narrow ...
An ethylene cracking furnace is a tall and narrow box — typically 40ft+ high — with vertical process tubes on one side and a combustion wall’ on the other. They use burners of two types: The first, ‘hearth’ burners are rectangular, floor mounted, vertical-firing against the combustion wall to radiate heat into the tubes on the opposite wall. The second, ‘radiant wall’ burners are installed in one to four rows at various furnace heights and fire radially onto the combustion wall to heat up the refractory surface and radiate energy to the process tubes. These two burner types are designed and installed to try to maintain a uniform heat flux profile to the process tubes.
The Problem
The Problem
Limitations in the ability to optimize burner performance (i.e., meeting NOx objectives while optimizing flame geometry) create challenges in delivering uniform heat flux profiles. Most heaters experience higher heat flux profiles near the bottom of the furnace with fluxes gradually decreasing with furnace height. Delivering a more uniform heat flux profile is desirable because it has the potential to 1) improve energy exchange and 2) lengthen the de-coking cycle.
The ECC Solution
By controlling flame shape on both the hearth burner and radiant wall burners, enhanced tailoring of the heat flux profile should be achieved. Lengthening the de-coking cycle will bring substantial economic benefits to operators of ethylene cracking furnaces. The period of a de-coking cycle varies depending on the process and technology. Under the worst-case scenario, de-coking must be performed after as little as less than 20 days, while under the best-case scenario, de-coking occurs every six months. Improvements in de-coking cycles represents less downtime and more revenue. Additionally, by improving flame luminosity, ECC may provide far greater control (a new degree of freedom) for operators to significantly increase heat flux transfer to the process tubes while still maintaining optimal uniformity.
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