November 10, 2017 at 11:34 am #27618
We had a Consulting service that analyse our FCCU (we have two) and recommends that we done some test in our site in order to increase unit profit.
They want to increase/decrease some process variables up to:
-TRX (Reaction temperature) : 555 Celsius
-TCC (Feed Temperature) : 180 Celsius
– Main tower bottom temperature : 365 Celsius (maximum LCO recovery)
Is it common these targets in the FCCU ? What about Fuel Gás production in these conditions ?
What is it the typical conditions in the FCCU for these variables ?
November 10, 2017 at 1:11 pm #27619
Alan R. EnglishMember
The process conditions you mention are within the range of normal FCC. It is not possible to comment on if these conditions are right for your unit with studying your constraints and feed/product pricing. 550 C reactor temperature is fairly high. This is justified when conversion, olefinic LPG and/or octane have high value. Gas yield will be high which typically means feed rate must be reduced. Also, expect high gasoline diolefins (potential gum). You must determine if the advantages outweigh the costs. 180 C preheat is on the low end of the typical range. Low preheat is used to increase catalyst/oil ratio and conversion as well as to lower regenerator temperature. Going much lower may adversely affect how well your feed injectors work due to increased feed viscosity. 365 C fractionator bottom temperature is reasonable but keep in mind that this temperature does not determine LCO cut point or recovery. Typically, the bottom pool temperature can be controlled separatly from the flash zone temperature by diverting cool slurry pumparound directly to the fractionator bottom. Adjust slurry pumparound to the shed deck and LCO draw rate to optimize fractionation but be certain to maintain sufficient rate to assure that all surfaces in this section remain wet to prevent coking.
December 10, 2017 at 8:02 pm #27732
The riser temp does seem a bit high, increase riser increase dry gas production. Bottom temp could increase coke in the bottom of the tower by the time you are at the end of run. The preheat that low, I’ve seen lower, could cause you to reach max cat circulation.
December 10, 2017 at 8:02 pm #27733
Reactor temperature is indeed very high so if there is capacity on gascon section that’s a positive. We operate at 515degC at low rates and are typically constrained on butadiene quality (max of 0.5 for Alkylation unit) and Dry gas make(285tpd). Feed temperature is very low so monitor riser coking and mix zone temperature to ensure feed is fully vaporized. Suggest you also review catalyst formulation or use of additives to maximize margin on FCC.
Also monitor tray loading on Gascon columns(do you have a simsci model for this?) in order to simulate how the operate will operate at these conditions suggest you run the specific feed quality at these conditions on an FCC model and check what constraint you reach based on your unit configuration and downstream unit capacities
December 10, 2017 at 8:03 pm #27734
With a 180C preheat temperature, you are also in danger of condensing the feed atomization steam, potentially causing poor atomization (in addition to the comments regarding viscosity).
December 10, 2017 at 8:03 pm #27735
No offense to anyone. Without any information about the current limits on unit, the catalyst (or additives, if used), the goals (max olefins, max conversion, max gasoline and/or octane) this is nonsense. That aside, if they are at wet gas limit, of course reduce RTT (RxT), and allow either more conversion or more feed (the latter being generally more profit). If at coke limit, push up feed preheat to allow more feed rate. Rule of thumb, more feed is more money. If at high RTT because gasoline octane, use additives and reduce RxT. Simple steps. But without details of the situation, rest is pure BS.
December 11, 2017 at 2:07 pm #27736
And I concur with Mike too. Directionally, we can understand and explain the benefits of increasing the ROT, decreasing the Feed Temperature and so on. Does that make sense? Impossible to tell as there are as many situations as there are FCC units…
In case a 555°C ROT makes sense (hum… unless you are targeting real high amounts of light olefins, I doubt it), we, licensors, have process solutions to mitigate the formation of diolefins. Similarly, in order to boost the C/O, there are other solutions which do not come at the expense of feed vaportisation (beware of too low temperatures!).
December 11, 2017 at 2:07 pm #27737
I am retired and have no skin in this game. So what I am writing is I hope to help improve the area of FCC knowledge. It is cynical but unfortunately true.
Most refineries buy or change catalyst based on marketing hype and simplistic technical evaluations provided by suppliers. Yet, suppliers tell FCC operators that each FCC is unique.
Simple questions regarding asymmetry of information are often not raised.
An ISO 9000 certificate of catalyst quality supplied to the refinery is generally not asked. Nor are third party evaluations carried out.
Many refineries are charged highly specialized catalyst prices for formulations which are in fact commodities. Catalyst performances should not be based on lunches/ superficial technical presentations in fancy hotels but hard technical evaluations.
A more discerning critical supply chain/technical expertise can increase FCC profitability and throw light of areas which really need focus.
December 11, 2017 at 2:08 pm #27738
We need more info: type of feedstock, product targets, type of unit. If the feed has a low UOP K Factor (very hard to crack) and unit targets are max gasoline/max octane barrel and LPG, and the reactor cyclones system is a short contact time, the multi-feed atomizing system is very well performing (properly steam/feed ratio, good pressure drop, nozzles tips in good shape…), the cat/oil presumably high (high mix zone temp/high feed percent vaporization=avoid coke formation) and the main fractionator bottom residence time short, the said parameters appears adequate. But if the feedstock has a high UOP Kfactor (very crackable), operating the unit with the above parameters, likely, everything is converted: bottom product probably disappear, gasoline decrease dramatically/LPG increase consequently, coke and gas increase significantly.
Maybe your situation is similar to not equal to the first, so I agree with your consultant: run tests to optimize your unit, according to your objectives.
December 13, 2017 at 9:17 am #27753
Salvatore, While you make an excellent point, UOP K also has its limitations. The 90% point is very important. It only shows up indirectly in the UOP K factor. In fact most heavy feed stocks do not vaporise and that s why all the Ni is deposited on the outside edge of the catalyst.
Catalyst companies use smoke and mirrors techniques by telling refineries they have large pore which allows the heavy portion to diffuse into the interior. Then why is all the nickel deposit on the outside edges. The liquid portion of heavy is drawn into only a short distance into the catalyst by capillary action.
I agree the UOP is important but so is the 90% point.
The ultimate driver of catalytic cracking in FCC is the hydrogen content in the feed. High UOP K means higher higher hydrogen. Higher hydrogen is found in paraffinic stocks. These are easily crackable. The worst is aromatics. Aromatics stocks are very stable and do not crack under FCC conditions. They need high H2 partial pressure.
For straight run Vacuum Gasoil or HDT feed, density and UOP K tell just enough for the first approach to a FCC feed quality. If in the feed mix there is also some Residue, the simulated distillation is more suitable for the VABP (and CABP) calculation in the UOP K: refineries now have this approach, being D-86 and D-1160 distillation not always applicable, as Solly said. Aniline point analysis is good, fast and reliable, for feed characterization, but for dark feeds, sample needs dilution and operator high attention; nowadays some refineries don’t run any more. Refractive index is among the most used for FCC feed characterizations: needs four decimal digits. There are also other indirect indications: hydrogen content is one, and it is excellent; it is very good to trend in an every single refinery, unless we are in agreement on the calculation method (Total?).
Talking about FCC unit optimization first we need at least this information: feed quality, objectives and unit type hardware.
Excellent Salvatore! You have nailed it. The most important by far for optimizing the FCC unit is unit is the Feed Quality. Then comes operation conditions and lastly catalyst selection.
While catalyst selection is important, make no mistake, it is more important what is going into the unit, than from whom it is supplied. Catalyst quality supplied to refineries varies greatly and quality supplied is not always what was initially agreed on. For example, there was long standing anecdote, that FCC catalyst supplied by the Chinese was inferior. Then during the Rare Earth Crises during 2010 to 2012 , several refineries bought catalyst from the Chinese. When we analyzed the FCC catalyst from the Chinese was excellent! It had low attrition, comparable selectivity, and much lower cost.
Catalyst suppliers often say each FCC is unique and then go on to say how good their catalyst in other refineries, meaning that it will just as well (FCC unique!) in yours.
Does anyone know of objective technical analysis provided by catalyst company A which states that FCC catalyst from company B is better suited for the given unique operation?
Hoekstra Trading offers independent catalyst testing according to this presentation: https://refiningcommunity.com/presentation/pushing-the-limits-of-fcc-gasoline-desulfurization/. For more FCCU presentations on catalyst go here https://refiningcommunity.com/past-presentations/ and type in catalyst
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