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Developing More Stable Metal Alloy Tubes for Use in High Temperature Processes

Description:

Recently it has been found that metal alloy tubes used in industrial processes that operate at high temperatures can degrade and emit toxic metals.

As a case in point, ethylene (C2H4) is widely used in the chemical industry as a feedstock in the production of industrial chemicals and consumer goods—e.g., plastics, antifreeze, solvents, and detergents. Ethylene is produced in furnaces by “cracking”—i.e., breaking apart—simpler hydrocarbons.

The hydrocarbons to be cracked are mixed with steam and quickly run through tubes that are inside the furnace, which operates at about 850 degrees Centigrade. The combination of high temperature and steam “steam cracks” the hydrocarbons inside the tubes. The tubes are made of an alloy consisting of the toxic metals Nickel (Ni) and Chromium (Cr) mixed with Iron (Fe).

Recent stack testing on cracking furnaces has revealed higher than expected emissions of Ni and Cr. This is probably due to the severe conditions in the furnaces degrading the Fe-Ni-Cr alloy tubes used in the furnaces.

The recent stack testing also found high Ni and Cr emissions during de-coking operations. De-coking is necessary because over time coke will build up inside the tubes, causing facilities to operate less and less efficiently until they reach a point of needing to remove the coke (via burning it off through the injection of steam and air into the tubes) before returning to normal cracking operations.

There are 400-500 ethylene cracking furnaces in the US. Due to the availability of cheap feedstocks from fracking and shale gas, the industry is undergoing rapid growth with new facilities being built.

There may be other industrial processes that use metal alloy tubes in a high temperature environment. Those tubes could also be degrading and emitting toxic metals. With this in mind, EPA is interested in supporting the development and commercialization of innovative technologies that address the following topic:

Topic Code 2D: Developing More Stable Metal Alloy Tubes for Use in High Temperature Processes. Innovative degradation-resistant tubes for use in ethylene cracking furnaces and other high temperature processes to replace tubes that are made with toxic metals. The tubes could be made of alternative metals, different percentages of the currently-used metals and/or other compounds, or non-metals. Compared with the currently-used tubes, the new tubes should produce lower or no Ni, Cr, and/or other toxic emissions during operation, last longer before needing to be replaced, reduce the down time necessary for de-coking and other intra-tube treatments, and cost less.

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