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07/01/2020
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Ganesh Maturu, Self, maturu.ganesh@gmail.com
Following are the main reasons for typical increase in Naphtha Hydrotreater Reactor delta pressure-
1. NHTs are typically gas phase reactors and hence no inlet tray distributor required. Feed directly enters on the catalyst from inlet diffuser. If we maintain the reactor inlet temperature near to dew point temperature, there is a possibility of liquid in Reactor which creates mal-distribution/channeling in the Reactor catalyst system and creates pressure drop in long run.
2. Especially during startup, it may be possible that Reactor inlet temperature should be maintained high enough to have feed in to the reactor to avoid liquid phase in reactors. This is the main reason, we generally feed in to NHT reactors at low pressures and then increase temperature and pressure to normal operation conditions.
3. It may be possible that some diolefins present in Feed which causes polymerization and hence increases Reactor DP. Hence typcal guideline of Diene number <1-2 maintained in NHT feed. If high Dienes present, Diolefin reactor is required to convert Diolefins to Mono olefins
4. It may be possible that Feed filter leakage and obviously cause any reactor pressure drop. Especially in NHT, there is no grading material available which increases pressure drop immediately if we don't take care of Feed filter healthiness.
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19/12/2019
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Ed Ouwerkerk, Catalyst Intelligence Sarl, ouwerkerk@catalyst-intelligence.com
When the dP goes up at constant intake, the catalyst bed is fouling up. Most often this is due to corrosion products (FeS) from upstream piping. Sometimes an upset causes these corrosion products to be released and dumped on the bed. Crushing of catalyst itself is a seldom cause. A simple top tray and/or top bed grading can take out these particulates before they clog up the bed. Sampling the bed before the next reload can confirm the source of fouling as well as guide the best abatement.
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17/12/2019
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Dipankar Phukan, Indian Oil Corporation, dipankarphukan79@yahoo.com
Naphtha hydrotreaters normally utilise makeup hydrogen from the Reformer. If you do not have a chloride gaurd in the makeup hydrogen then chances are that the delta P is because of the iron dust carried over from the pipe and fittings and getting deposited over the catalyst bed. Another reason is carry over of olefinic material in feed if your NHT catalyst is not designed to handle olefins. In one of the NHTs I have worked, the root cause of delta P increase could be tracked to oxygen ingress in the feed tank as the feed tank did'nt have Nitrogen blanketing and feed had around 1% olefin as per design., The problem was partially resolved after tank was operated at high level, so that the level never comes below the floating roof support leg. In another NHT, we had issues of high delta P due to carry over of sludge from feed tank. Whatever be the reason a significant amount of iron rust is always found whenever, I have seen a Naphtha hydrotreater reactor opened for catalyst replacement. and getting rid of that always helps reduce the delta P. A lot of chemical dosing vendors provide online chemicals to dissolve this iron rust over the catalyst bed thus reducing the delta P
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16/12/2019
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Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
HDT reactor dP increase is often due to fixed bed catalyst fouling by particulate matter (largely corrosion products plus sometimes gums). This can gradually increase reactor dP, and result in liquid maldistribution and shorter HDT campaign length.
Pall 10um absolute rated external feed filter (Beta >5000 or 99.98% efficiency) has been proven to remove the majority of particulate contamination from the HDT feed and can increase campaign length due to reactor dP increase. If feed / effluent exchanger dP is increasing also, a Pall feed filter can reduce exchanger fouling and improve heat recovery also. A different grade if media maybe required for that as a significant amount of corrosion products can be <5um in size and while that size range is not necessarily detrimental to the fixed bed reactor this can foul the feed heat exchanger in 20-30% of cases when short HDT run time is experienced.
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16/12/2019
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Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Normal culprits in a NHT are coke build up on catalyst or corrosion products in the feed.
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16/12/2019
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keith bowers, B and B Consulting, kebowers47@gmail.com
there are two possible reasons for a 'pressure drop increase' across a Cat Reforming reactor, assuming the indication is true and accurate.
Reason No 1, which is by far more common, is mechanical plugging by particulates in the feed to the reactor. Reason No 2 is formation of particulates 'in-situ' caused by the on-going reactions.
External particulates in the feed to the unit may cause plugging of the catalyst beds resulting in additional measured pressure drop across the catalyst bed(s). Said particles may be iron oxidation (rust) particles from feed storage tanks or other steel/iron surfaces anywhere in the system contacted by the feedstock, or even in the crude oil as produced from the formation. Of course, other particles may be "picked up'' anywhere the feedstock is stored, moved through, or mixed with something. Fine feed filters may be the best solution to protect from catalyst plugging, though particulate contamination prevention is preferred by economic and entropy conservation measures.
'Soluble iron' chemically dissolved in the naphtha feedstock is also possible if there are organic acids present in the crude oil or naphtha feedstock. The 'hydrotreating' reactions on-going in the reforming process reduce the organic acids causing iron (or other minerals) to 'un-dissolve' precipitate out of solution and lead to catalyst pore and bulk plugging. This situation is both more difficult to detect and analyze and to alleviate bad impacts from.
Bench scale/pilot plant experiments may be able to determine when/where in the reforming process the insoluble materials (in-situ particle formation) are being formed. Once such a determination is made, a thorough study must be conducted to evaluate how best to prevent reactor plugging since presumably the fundamental reforming process must be continued. There are several potential methods for preventing catalyst pore and bulk plugging, but all involve mechanical redesign to 'filter out' the offending particles. Discussion of the several mechanical means is beyond the scope of this answer.
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16/12/2019
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Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com
There are multiple possibilities, but the most common are:
1. Contamination of the feed with solids, e.g. sediment from the feed tank or corrosion products from an upstream unit.
2. Foulants that had built up in the feed exchangers moving forward into the reactor. Trend the reactor pressure drop and heat exchanger fouling factor on the same graph.
3. Gums developed from highly olefinic or diolefinic feed. Coker / visbreaker and FCC naphtha streams are the worst offenders.
4. If any of the feedstocks come from a tank they will have some oxygen content. This oxygen makes the gum formation from olefinic feeds even worse.
5. Corrosion deposits from the furnace tubes. Even if the corrosion rate is low enough to be acceptable for the integrity of the tubes, the small amount of corrosion product can cause steady increase in reactor DP. Upgrading the tubes to 347 might be justified when the existing tubes reach end-of-life.
At the next catalyst change or skim, collecting samples from the top catalyst layers of the reactor can be useful to understand the chemistry and particle size of the foulants. This information can be used to develop the solution.
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