In our DHDS unit we recently we noticed product colour changed after the reactors. After some days product colour reverted to normal. Can anybody please explain this colour changing mechanism?
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02/11/2014
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Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
The color forming bodies are organic nitrogen compounds, intermediate coke forming polyaromatics, high EOR temperatures, lower partial pressure of hydrogen due to low RG flow, lower purity of RG and make up gas, larger percentage of CGO or LCO blend feedstock, residence time in reactor and state of catalyst.
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28/10/2014
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Ganesh Maturu, Self, maturu.ganesh@gmail.com
There are different reasons for color problems in Diesel product
1. If feed is highly aromatic compared to design (processing more LCO), it may give color problems because of low H2 partial pressure at the reactor inlet.
2. Low purity makeup hydrogen may also reduces the H2 partial pressure at the reactor inlet which circulate the accumulated C1 and C2 in recycle gas circuit and result in low H2 partial pressure at inlet of reactor. Once the purity is increased, its partial pressure might have increased and no issue was observed.
3. If catalyst activity is not maintained uniformly throughout the cycle by adjusting Normalized WABT based on Sulfur target in the product, it may see color problems.
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07/10/2014
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Satyalal Chakravorty, Sr Consultant, satya1354@yahoo.co.in
Similar phenomena was noticed in one of the hydroprocessing units at our refinery. Increase in partial pressure of H2 and marginal increase in system pressure made the product colour normal. Subsequently it was observed that the catalyst lost its crushing strength and activity. You may review in this line.
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04/10/2014
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Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
It depends upon the colour type for product , also intensity of hydrotreating . The more intense the hydrotreating more refined the colour. ASTM colour of the hydrotreated product is very less and also the product can sometimes become transparent . Monitor the crude oil changes for the particular period it can provide answer for the colour changes of DHDS product.
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03/10/2014
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
From my course manual:
"Cracked and aromatic feedstocks may develop color problems near the end of the cycle when
producing ULSD. For a 900 psig (62.1 barg) reactor, for example, the problem will occur at approximately 382 ºC [720 ºF]. However, a decline in aromatics saturation may limit the run at 371-388 ºC [700-730 ºF], depending on operating pressure. Bypassing the feed tanks with the low quality feed streams can mitigate a color problem. Reference: Lee, C.K., S.J. McGovern, and J.A Zagorski, NPRA Annual Meeting AM-06-08, 'Converting High-aro matic Streams into ULSD', Mar. 19-21, 2006."
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