COTE070 - Sair 6 Conferncia sobre Tecnologia de...

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WET H 2 S AND CN - CORROSION CONTROL THROUGH ON-SITE POLYSULFIDE GENERATION Luiz Augusto Correa METALDATA – Rua José Mendes Sobrinho 511 CEP 81350 320 – Curitiba – PR Email : lcorrea@tecpar.br Walmar Baptista PETROBRAS/CENPES Email: walmar@cenpes.petrobras.com.br Luiz Antonio Ferreira PETROBRAS/REPAR 6 COTEQ Conferência sobre Tecnologia de Equipamentos 22 CONBRASCORR – Congresso Brasileiro de Corrosão Salvador-Bahia 19 a 21 de agosto de 2002 As informações e opiniões contidas neste trabalho são de exclusiva responsabilidade dos autores.
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ABSTRACT A new process for controlling corrosion caused by hydrogen sulfide and cyanide ion in sour water, in refinery plants, like catalytic cracking, hydrocracking and coking is presented. The process is featured by profiting the high H 2 S and NH 3 content in the wastewater, typical of high nitrogen oil processing, and its high pH, to produce polysulfide in-situ . Polysulfide is injected into the plant as a cyanide (CN - ) scavenger and corrosion inhibiting agent . Key Words: Cyanide, H 2 S, Corrosion Control, Sour Water, Wastewater, Hydrogen Peroxide, Catalytic Cracking.
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1- INTRODUCTION Wet H 2 S and CN - corrosion process can occurs in plants processing crudes as low as 500 ppm in organic nitrogen content. Up to 1000 ppm, corrosion is small and control can be reached by injecting water for washing the gases. Suitable wash water flow can held the contaminants H 2 S and CN - , by means of dilution the sour water, below the level required for corrosion to present a kinetics that might be harmful to the steel. Ever since the oil crisis of the 70s, the search for new reserves has led to crudes as high as 2000 ppm in organic nitrogen content. These crudes have caused serious damage to several catalytic-cracking and other refinery plants which CN - is generated from organic nitrogen compounds in their gas oil. Research carried out by several oil companies to develop systems to control the corrosive process in these units has been intense in the last few years 1,2,3,4,5,6,7 . Corrosion inhibitors, neutralizers, scavengers and other systems have been presented as alternatives to control this corrosive process. Nonetheless, these techniques present some form of limitation, either technical or economic impracticality. Mainly in terms of effectiveness when processing crudes with organic nitrogen content higher than 2000 ppm. Steels with controlled structural morphology and inclusions, more resistant to hydrogen and cracking, have likewise been developed. However, even these materials are not immune to damage when large amount of Hydrogen is produced by high CN - content in the sour water. In addition, these steels are only applicable to new equipment or plants. The development of an effective and economically feasible system to control corrosion
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COTE070 - Sair 6 Conferncia sobre Tecnologia de...

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