What is the reason behind DMDS injection in CCR Platforming Unit ?
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04/10/2016
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Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Reason behind injecting DMDS in CCR Platforming Unit is to activate the catalyst , since it may be in form of oxide. DMDS on injection converts the oxide form to sulfide form.
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04/10/2016
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Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Furnaces in CCR operate at high temperatures. Such high temperatures in presence of hydrogen cause corrosion and damage to metallurgy of tubes by precipitation of carbon formation of lumps of carbon has been observed in the process. This damage can be prevented by injecting DMDS in very low ppm may be 0.2 or of the order specified by licensor. It forms protective layer of sulfide on the skin preventing damage to metallurgy of tubes.
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04/10/2016
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
From my Workshop manual: "Coke formed in the furnace tubes can migrate to the reactors and lodge behind the scallops or baskets. The coke deposits can grow until the scallops or baskets are deformed, affecting catalyst circulation. Carburization of the furnace tubes can result as well, a mechanism by which carbon atoms diffuse through the matrix of a metal and crystalizes. This phenomenon results in loss of malleability during thermal stress, leading to tube failure. A solution to both the coke formation and the carburization phenomena is to maintain a trace of sulfur in the feed by injecting dimethyl di-sulfide (DMDS). A target of 0.3-0.5 wppm in the feed is often used."
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03/10/2016
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Patrick Bullen, UOP, patrick.bullen@uop.com
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03/10/2016
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Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
Organic sulphiding agents are typically injected into CCR Platforming Unit feed to mitigate metal-catalysed coking (MCC) which can result in mechanical failure of reactor internals leading to internal loss of catalyst containment and an unplanned shutdown. MCC reactions are favoured by low pressures, high temperatures and low hydrogen partial pressures so low pressure units operating at high severity are at greatest risk. Organic sulphiding agent injection rates are highest for these units (target injection rates may be equivalent to 0.5 ppmwt total sulphur in feed or higher).
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