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We use straight run Heavy Naphtha from Tank which has floating roof. Now, my question is what should be the limit of moisture or water content in wt ppm level before entering Naphtha Hydro Treating Catalyst bed. Currently, we have 104 wt ppm moisture in HN feed can this quantity could be the cause to increase the pressure at the inlet of Reactor suddenly to create a peak of DP across the reactor bed? Currently, DP across the catalyst bed is 3 and it has reached gradually after the 3 years of operation cycle but become confuse about the sudden peak. So, please help.
 
Answers
12/02/2017 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
My guess is that the naphtha is contaminated by air. This would account for increase pressure drop by gum formation. Furthermore, gums are severely accelerated by olefinic species in the naphtha. Note that gums can occur in heat exchangers and the fired heater tubes. A careful inspection of tube hot spots is warranted.
Some refiners use the following countermeasures:
1. blanketed tankage
2. chemical additives
3. Avoid olefinic naphtha mixing with air contaminated naphtha. Olefinic naphtha originates in FCC or Coker, as well as "cracked slop".
Note that water saturated naphtha is > 104 ppm.
11/02/2017 A: Ganesh Maturu, Self, maturu.ganesh@gmail.com
There is no relation between moisture and pressure drop in reactor system. If the naphtha from tank is floated to atmosphere, there is a possibility of gum formation at the upstream of reactor and inside reactor which causes pressure drop in reactors.
10/02/2017 A: Patrick Bullen, UOP, patrick.bullen@uop.com
There are two general sources of particulates that cause pressure drop in hydrotreater reactors, suspended solids, and reacted solids. Suspended solids can come from the sides of the floating roof tank as the roof moves up and down. This is typically a fine iron based scale. A sudden increase in scale can occur if the tank level is low and the solids that settled in the bottoms get stirred up. Another source of solids is the scale on inside of the NHT fired heater tubes. A sudden unit shutdown can sometime cause the release of this scale. It is theorized that a sudden change temperature/pressure can cause the scale to come off the pipe.
Solids can form if contaminants in the feed become reactive under a certain set of conditions. Contaminants such as ppm levels of dissolved oxygen and olefinic hydrocarbons can react easily in the NHT combined feed exchanger causing fouling from the exchange through to the NHT catalyst bed. One can eliminate the oxygen by using an internal floating roof tank with a nitrogen blanket that prevents oxygen ingress. Another method is to use an oxygen stripper column to remove the oxygen before the feed enters the NHT unit.
For more information, you can contact your local UOP representative or you can access the UOP portal via www.AccessUOP.com. Registration is required to access the UOP Portal.
09/02/2017 A: NS Murthy, Suez, murthy.ns.ext@suez.com
Typically, such HT feed tanks to be fixed cum floating roof as rain water can seep inside a floating roof tank. Other issues could for sudden dP rise can be: - check upstream unit (CDU & other HTs from where wild naphtha gets reprocessed in crude unit) for any disturbance which coincides with the sudden such rise in cat bed dP.
08/02/2017 A: Muhammad Akhtar, Orpic, mbadgk@gmail.com
Following are some inputs from my side,
1) Normally the reactor pressure drop increases exponentially when the void space at catalyst bed top reduces. Is this the first cycle of operation after commissioning?
2) Check for any temperature upset / thermal shock occurred at the preheat train which changed the Temperature drastically for 15 minutes to 1 hour or any feed upset/shutdown happened?
3) Can you share more details of you system like wash water system and it flow and frequency of cleaning? Do you have grading layer on top of the reactor? Is this the first cycle of operation?
4) What about the efficiency of preheat train, is it same since start of run of the unit?
These answers can help us in finding the better answer.