Q & A > Question Details
I am process engineer of Naphta Hydrotreating units in a Refinery with capacity of 350000 bbls/day. In this moment the refinery it has in storage tanks gasoline with higher weight percent in MTBE above 2 % weight. However this gasoline will be send to co-processing in VGO Hydrotreating unit (FCC Pretreatment) where according with our evaluation it is possible co-processing this naphta by dilution in the reactors taking in account because HDO reactions, will have more heat release, hydrogen consumption and water generating.
So we could hydrotreated this naphta in VGO hydrotreating unit, however the quantity of oxygen compounds like MTBE was about 20-40 ppm. This naphta is send to the naphta fractionator and will be separate in Light naphta (LVN) and heavy naphta (HVN), and the HVN stream is send to NHT unit. But the problem is, according with opinion of process engineer of NHT unit, the feedstock to NHT should not have oxygen compounds (0 ppm) in order to avoid fouling in the preheat train by gum formation, but the catalytic scheme installed in the reactor of NHT there are CoMo and according with my evaluation, after dilution of this naphta previous introduce to the NHT, the concentration of ppm in MTBE will be lower and i have read and studied, that in NHT units, the most of oxygen compounds are converted around 90 %, so in my oppinion would have not problems in send this feedstock to NHT unit.
My question is, does it exist a maximum concentration in ppm of oxygen compounds like MTBE in feedstock to naphta hydrotreating units? and which will be the main impacts in point of view catalytic and heat transer in the preheat train?
15/05/2017 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Normally molecular oxygen is the concern for fouling in hydrotreaters. The oxygen can react with olefins/diolefins/nitrogen compounds to form polymers. The oxygen normally comes from the naphtha passing through storage tanks before going to the NHT and coming into contact with air in the tank. Organically bound O is simply converted to water in the hydrotreater, which releases some extra heat and consumes additional hydrogen. Your NHT probably already has some oxygenates present and you may not even know it. These oxygenates would be naphthenic acids because they are present at some level in pretty much all crude oil, and they process with no problem in a hydrotreater.
15/05/2017 A: NS Murthy, GE, murthy.ns@ge.com
Given an option to liquidate the MTBE contaminated gasoline, I will go by the following options.
1. Check the quality of contaminated gasoline and try to blend in finished gasoline directly rather than reprocessing and wasting both capacity and energy.
2. In case the option 1 is not feasible, the best way to process such contaminated gasoline will be either in NHT or in DHT rather than VGO HT. The hydrogen PP requirements are lower as move lower on HC mol wt. Hence, with the inputs from process licensor one can co-process such contaminated gasoline in NHT and or DHT. Pl note it will be easier to manage fouling (if at all an issue) in heat exchangers rather than reactors (from lower H2 pp).
3. Typically fouling is mostly associated with LTMD, velocity, dienes & moisture content in feed. As long as hydrogen is premixed with feed hydrocarbon and heated in exchangers the fouling will be least. I do not see any limits of oxygenates in NT feed. However, check Cl content in feed so that there is no HCl formation unduly while processing such MTBE laden naphtha.
4. Last but not the least, it is common to see every process engineer in hydrotreaters not allowing feed outside design. In refining world, I see Crude unit process engineers are truly brave to accept all types of crude cock tail and yet see a successful processing.
Good luck.