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28/04/2014
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Vishnu Ram A S, RIL, vishnu.selvaraj@ril.com
The Color deterioration is due to the following reasons:
1. Crude processed containing more Nitrogen content. Mostly it will be reflecting up to Kerosene section. In worst case Naphtha section too will be affected.
2. Flooding in the section beneath your Gas oil section. This may be reflected in the pressure drop measurement. Reason shall be, more partial pressure of Gas oil in the flash zone which is a reflection of improper crude blending containing higher gas oil content or stretching the throughput beyond the design.
3. Very high sensitive Crudes which can crack in the Crude Heaters can contribute to this cause.
4. Heavy cut of gas oil at considerably lower temperature of Draw off may absorb moisture and it may turn bright(not black).
In all cases, we need to scrutinize the position and try to solve it as soon as possible. The best safe solution would be change the successful crude blend composition and run to retrieve the position.
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27/02/2014
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Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Brown/Black coloration of gas oil is a problem frequently observed in CDU and can be resolved easily with proper efforts. Such coloration may be accompanied with increase in metal contents too like V or Ni in the gas oil. Care may be taken for the reason that the contaminated stream with increased metals may have adverse effect on downstream Hydrotreating or conversion catalysts.
The coloration may be due to poor fractionation with improper split of the cuts. The reasons for poor fractionation may be flooding, dumping at specific locations particularly wash zone region. The problem could crop up due to mal-operation, improper design of internals leading to residue entrainment in gas oil.
The tests like delta P survey in the zone, gamma scanning can throw light on the roots of the problem. I agree with other respondents stating the probable causes like bottom stripping steam rate, damage to wash zone, distributor issues for wash bed, wash bed coking etc. I know of published case where the coloration was caused due to an issue in the downcomer clearance after a revamp.
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24/02/2014
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Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com
As mentioned it is a common problem due to residue entrainment with the Gas Oil, it can be caused ether by low liquid rate going to the wash section or high vapor coming from the feed, also flooding in the stripping section or damage in the wash zone internals (cause by operational upset) can deteriorate the color of Gas Oil
You will need to performed a series of tests to determine what is affecting the Gas oil color, some tests are:
Reduce Gas Oil draw
Reduce bottom stripping steam rate
Reduce Fired Heater outlet temperature
Based on your unit configuration you may try other tests that will help you to improve the Gas Oil color
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24/02/2014
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Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
Is this colour issue due to haze? Steam stripping of AGO saturates AGO and can then can form haze due to condensation of water after the cooler on the rundown. Its a pretty stable emulsion with an IFT usually lower than 10 dynes/cm however a high efficiency Liquid Liquid coalescer can break the emulsion and prevent the need for tank settling. It's possible to get < 15 ppmv free water after the coalescer which will be C&B provided the rundown temperature is not too high.
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23/02/2014
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S Banik, Centre for High Technology, sbdr@rediffmail.com
Gas oil colouration is normally due to entrainment of residue from the wash bed which may be malfunctioning or the stages provided in the bed are insufficient or the distributor (normally spray type) is maldistributing. If the column loads and internals details are available better analysis of the causes can be made. In fact we have carried out gamma ray scanning of the wash bed and the distributor to find out exact cause.
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22/02/2014
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Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
It is likely either entrainment or a leaking gas oil vs crude heat exchanger that is leaking crude oil into the gas oil stream. A number of things can cause entrainment - increasing rate, change in feed stock to one with a higher gas oil yield, an increase in vacuum, coking of the wash bed or inadequate wash oil rate.
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21/02/2014
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keith bowers, B and B Consulting, kebowers47@gmail.com
It may be either poor distillation internals allowing entrainment of jet spraying OR it may be a leaking heat exchanger. Check the heat exchangers first.
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21/02/2014
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Keng Chung, Well Resources Inc., kengchung@hotmail.com
Very common problem due to entrainment. Did you increase the cut point? The tray efficiency? If the gas oil is fed to hydrotreater, you may see quicker catalyst deactivation.
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