Selective catalytic reduction, SCR, is the best proven technology to achieve maximum NOx reduction and SCR units for NOx abatement can be designed to meet today’s stringent requirements by offering 95%+ NOx reduction. SCR units have successfully been installed on ethylene cracking furnaces and steam methane reformers. Deactivation of the SCR catalyst as a result of chromium accumulation has to be taken into consideration in the SCR design. The deactivation from chromium masking can be minimised by using an SCR catalyst with a high porosity diverse pore structure which offers less susceptibility to poisoning. One of the largest NOx emission sources in a refinery is the flue gas coming from the regenerator in the fluid catalytic cracking unit. It can be the source of 50% of the total NOx emitted from the refinery. The high sulphur oxides concentration and carry-over of FCC fines in the flue gas represent a challenge. With the use of a properly designed SCR reactor and catalyst, experience shows that very low levels of NOx emissions can be achieved from FCC units that have high NOx, Sox and particulates in the flue gas. Installations at shell and Citgo are described.

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• Citgo Petroleum

• Haldor Topsoe

• Shell

• Catalyst

• NoXn-electrode

• SCR

• Article