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I am currently working in the Hydrotreater. My question is if recycle gas compressor trips and our feed pumps remain running due to faulty logic, what will happen to reactor? And can we run the feed pump for cooling of reactor without recycle gas?
 
Answers
01/09/2012 A: Kavittam Patel, Bahrain Petroleum Company, kavittampatel@yahoo.co.in
In this case if you have product recycle facility to the feed pump suction, you can route hydrotreated product to cool down the reactors avoiding fresh feed to the unit. Already hyrotreated product will not result in temperature excursion in reactors even if there will be channeling.
25/10/2011 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Hydrotreating reactions are exothermic. Failure of RG means quenching has failed which could lead to higher temperature shoot up problems. Possibilities of catalyst coking may be appreciably enhanced. Chances of channeling increase leading to further enhancement of temperature at some locations. Instead of cooling there may be possibilities of localized hot spot formation. With the cracked feed stocks as component of feed, delta P problem is observed due to preferential gum / polymeric / condensed coke precursor formation due to non available hydrogen. Catalyst vendor and process licensor are very particular about such events and deal it appropriately in the manuals
24/10/2011 A: Randy Alexander, EURECAT, randy.alexander@eurecat.com
You can also experience heavy coking of the catalyst bed if feed continues to be pumped into the unit without the presence of hydrogen. This coking will affect catalyst performance as well as flow distribution.
24/10/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Unfortunately, hydrocarbon without hydrogen gas will cause excessive hydrocracking and high bed temperature, resulting in damage to the catalyst and possibly exceeding the temperature rating of the vessel. It is important to stop the oil feed flow. If you can, depressure the reactor section and sweep the reactor with makeup hydrogen until the recycle compressor is running again. I agree with Mr. Bowers, who covered the subject well: if it is a licensed unit, the question should be directed to them as well.
24/10/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Your question should be directed to your Process Licensor and/or Catalyst Vendor for their recommendations.
There is no single answer to your question. Several factors must be considered--such as a) catalyst activity at the time, b) hottest operating temperature in the reactor at the time , c) level of heat-of-reaction production at the time, d) amount of quench being used to control catalyst bed and reactor exit temperatures, e) hydrogen to oil ratio in the reactor at the time of the incident ... and so on.
Since a temperature excursion (to higher temperature) is the dangerous condition to avoid, the best method of preventing this differs for each reactor/catalyst/feedstock situation. Modest (<100F) temperature excursion would not normally be worrisome if reactor flow patterns were uniform (no hot spots.)
Hydro-cracking reactions are the heat generators, while thermal cracking ones are heat consumers. Hydro-treating reactions may be either or neutral, but generally not a significant source of additional heat.
The quantity of hydrogen present in the reactor at the time of recycle gas failure limits the amount of hydro-cracking that may take place. If one assumes all that hydrogen is consumed in hydro-cracking reactions--that heat liberation and a simple static energy balance will establish the maximum AVERAGE reactor temperature at equilibrium. However, that DOES NOT give the information needed to judge the risk of a damaging temperature excursion.
The reason this 'Average Maximum Temperature Excursion' does not provide a safe answer is because a small portion of the catalyst mass may react strongly and consume most of the total available hydrogen, leading to local temperatures MUCH higher than average reactor temperature. The potential for very high local temperature development (and lowered reactor pressure containing capability) is why hydro-cracking Licensors often recommend rapid depressuring on recycle gas (or quench ) failure.
Generally, The higher the pressure, higher the heat of reaction generation, the higher the hydrogen to oil ratio---the higher the risk of damaging hot spot development.