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Roberto Amadei (Chemical & Energy Development srl)

The naphtha catalytic reforming unit can be partially unloaded, by subtracting from its traditional feedstock the higher-boiling C6 hydrocarbons, including naphthenes, benzene and hexane.

Typically, the optimum allocation of this material unloaded from reforming is the isomerization unit. The deriving set-up of reforming and isomerization has the potential of generating value in several ways and in no way destroys any value. However, also in case of an allocation of the above material different from the isomerization, its unloading from reforming keeps a significant value generation potential.

The main components of the optimum reforming + isomerization set-up generated value are the following:

-hydrogen net production gain,

-gasoline yield gain,

-gasoline octane number gain, changeable at will into an additional gasoline yield gain,

-compliance, with margin, with the most severe limits of gasoline benzene content in the world, such as the 0.62 vol% content required by the United States Environmental Protection Agency, in the US resulting in saleable benzene content credits, significant energy savings, besides the hydrogen net availability gain one, emissions reduction of all of the pollutants and greenhouse gases types, in addition to the above, both in the gasoline production and consumption segments, also carrying out a gasoline lifecycle emission reduction of a few percent of CO2 equivalent,

-higher octane gasoline production capacity increase,

-improvement of the engine operation and maintenance.

The case study experimental results pointing out the above and the relevant theoretical explanation can for instance be seen in PTQ and Digital Refining 2013 Q1, article “Improved hydrogen yield in catalytic reforming”, or in “Gasoline Processes”, 2011 NPRA Q&A and Technology Forum.  With that said, a more detailed analysis of the generated value inherent to hydrogen net production gain looks to be useful. While it is clearly apparent the worldwide great value of hydrogen net production gain, a particular case instead has to be attentively examined: the case of North America. The reason for a particular attention is the North America availability of the very cheap shale gas.

Referring to the particular North America case, we premise that the optimum set-up of reforming and isomerization carries out the production of gasoline and hydrogen in lieu of fuel gas. With this due premise, we can conclusively deduce that the above hydrogen gain is much more convenient than the hydrogen production carried out by means of special units consuming the cheap shale gas (SMR). Precisely, neglecting here the gasoline-fuel gas replacement value, said hydrogen production gain is over three times cheaper, as far as the variable (operating) costs alone are concerned. In fact, in the case of the optimum reforming-isomerization set-up, the shale gas should be used, for combustion in the furnaces, in order to replace the fuel gas not produced anymore by reforming. In such a way the rate of substitution of fuel gas by shale gas is 1:1. On the contrary, any use of shale gas for producing hydrogen would require the consumption of more than 3 units of shale gas (taking into account all the energy flows, both consumed and produced by the SMR unit) per each unit of produced hydrogen (rate of substitution: >3:1). Moreover, depending on the specific refineries, the relevant hydrogen gain can even avoid the capital costs of either installations or revamps or even duplications of the special, highly energy consuming,hydrogen generation units.

On top of the value generation potential of the feedstock transfer interplay between isomerization andreforming, an interplay also exists between the whole of these two processes and FCC-gasoline post-treating.

The FCC-gasoline post-treating consumes hydrogen and energy and causes reduction of the FCC-gasoline octane number and yield, due to saturation of high-octane olefins. It is apparent that the above-described optimum set-up of reforming and isomerization, as it provides hydrogen gain, reduction of energy consumption and gasoline octane plus yield gain, counteracts the FCC-gasoline PT negative effects. Plus, it provides additional very low sulfur combined reformate-isomerate gasoline blending component, due to its yield gain, thus allowing a higher sulfur content of the post-treat FCC-gasoline for a given full gasoline sulfur content: this allows further reduction of the FCC-gasoline PT negative effects.

The two last paragraphs outline the qualitative aspect of the matter. As far as the quantities in play are concerned, HOP (Hydrogen-Optimization) analyzes and optimizes the operation and any asset of the specific refinery as a function of the specific refinery plant structure, supply slate and predicted FCC-gasoline PT upcoming additional needs of hydrogen, energy, gasoline octane and gasoline yield, also providing alternative cases results.

Here we owe an explanation: HOP is an Alliance established between Chemical & Energy Development and Prometheus, rendered very suitable by the worldwide hydrogen thirst that deserves the maximum operational efficiency. Chemical & Energy Development brings to the new Alliance its deep knowledge and practice of the specific, above indicated, technology and Prometheus brings to the new Alliance its deep knowledge and practice of planning and optimization procedures and of refinery engineering design. The provided gains, of hydrogen, energy, gasoline octane, gasoline yield and FCC-gasoline sulfur content, can be higher than the predicted FCC-gasoline PT upcoming additional needs and remain partially available for other foreseeable needs deriving from the

-existing or to be installed FCC pre-treats,

-heavy and sour crudes,

-medium-heavy products quality requirements; and

-tight oil.

Jocelyn Daguio (UOP)

CCR Platforming Unit Customers report 3.2 years on average between turnarounds. And 10 % of the units exceed 5 years. Although, catalyst change-out frequently determined this time previously, the ability to change out “on the-fly” while maintaining operations has removed this constraint.

Applying best practice in turnaround planning can extend future turnaround interval. Close monitoring both process and equipment performance is an enabler for exercising best practice during the turnaround.

For examples, evaluation of the combined feed exchanger, stabilizer column performance, fired heater efficiency, equipment pressure, compressor vibration and catalyst health conditions allow timely operation adjustment to prolong turnaround interval. Catalyst fines monitoring and fines control are essential to avoid unnecessary unscheduled turnaround due to fouling of equipment. For fixed bed reforming units, proper procedure of catalyst dump and screen and corrosion control during catalyst regeneration can reduce turnaround frequency or/and avoid unscheduled unit shutdown and turnaround.

Michael Crocker and Ka Lok (UOP)

For Isom units, the typical run length between maintenance turnarounds is approximately between two to five years, depending on naphtha complex flow schemes. Process evaluations include determination of catalyst activity and unit performance. Also included in the evaluation is the identification of any unit constraints during the run, which would include normal monitoring of process equipment. Traditionally, most ISOM units are corrosion-free due to the nature of the design of the unit (i.e., water is a poison to the catalysts), but where high HCl can possibly meet with free water (such as in the case of the Net Gas Scrubber in Penex and Butamer process units), online routine non-destructive testing techniques and monitoring of pipe wall thicknesses, where applicable, should be conducted.

Kurt Detrick (UOP)

Typical run lengths for HF Alkylation units have been increasing over the past couple of decades. The HF Alky run is typically tied to the FCC run length and the majority of units are planning for either 4 or 5 year run lengths. Some units plan for 3-year runs, and a very few are trying for 6-year runs.

A prolonged interval is not always the most profitable choice. Things that make longer runs less profitable are:

 - Higher probability of unplanned shutdowns. An unplanned shutdown almost always has a higher Lost Profit Opportunity (LPO) than a planned shutdown.

- Piping and Equipment inspection and replacement must be done more aggressively. The general guideline is that the inspection interval should not exceed ½ the estimated remaining life of the piping or equipment. Things that cannot be replaced without a shutdown (such as key valves, exchangers, piping and vessels) must be renewed more frequently (it is a lot easier to get a valve to seal properly for 4 years than 6 years).

- The longer the run length, the less meaningful a 1-year extension of run length becomes (diminishing returns). A 6-week planned shutdown is 5.8% of a 2-year run, 3.8% of a 3-year run, 2.9% of a 4-year run and 2.3% of a 5-year run. So, you don’t gain a lot by extending from a 4-year run to a 5-year run (but you do increase the risk of an unplanned shutdown).

Kurt Detrick (UOP)

One metallurgy issue that has been a hot topic in recent years is the specification for low Residual Elements (RE) in carbon steel for HF service. Based on recommendations made in NACE paper 03651, ASTM developed Supplemental Specifications for carbon steel that can be called out in purchase orders for steel that is to be used in HF Alky service. However, steel that meets those Supplemental Specifications has sometimes been difficult and/or expensive to procure. Recently, there have been one or two suppliers that have made a commitment to maintaining a supply of steel that meets the low RE spec, but price and availability are still a bit of a concern.

Normalization of the steel is one of the requirements listed in the ASTM Supplemental Specifications mentioned above. Many prominent metallurgists agree that Normalization of the steel is not beneficial toward resistance to corrosion from HF and it has been suggested that the requirement for Normalization be dropped from the ASTM Supplemental Specs for carbon steel in HF service.

The use of Hastelloy C-276 in HF service has increased significantly in recent years. In most cases, it does not appear to be significantly better or worse than Monel from a corrosion standpoint, but it is a much harder material than Monel and it is often easier to cast, so it is an attractive alternative to Monel in some specific cases even though the material cost is typically somewhat higher than Monel. Hastelloy C22 and C-2000 has also been successfully used in HF service on a very limited scale.

Kurt Detrick (UOP)

The n-butane stream from an alkylation unit contains some organic fluorides. The fluoride must be removed in alumina treaters before being fed to an isomerization unit because the fluoride is a catalyst poison. When the fluoride is removed from the organic fluoride molecule, an olefin is formed. There should not be any olefins in the n-butane going into the alumina treaters, so the only olefins in the product are those created from the organic fluorides. So, the key to preventing excessive olefins in the n-butane product from the HF Alkylation unit is to prevent formation of an excessive number of organic fluorides in the n-butane going to the alumina treaters. This can be done by:

- Avoiding excessively low acid purity. Organic Fluoride production can increase significantly bat acid purity below about 85% HF.

- Avoiding excessively low reactor temperature. Organic Fluoride production can increase significantly bat acid purity below about 80 °F (27 °C).

- Avoiding excessively high concentration of iso-butane in the n-butane product. The iso-butane fraction from the main fractionator in the HF Alkylation unit typically has a higher concentration of organic fluorides than the n-butane fraction. (The organic fluorides in the iso-butane stream should be kept in the recycle isobutane stream to the reactor where the organic fluorides can be converted back to HF).

Kurt Detrick (UOP)

Some advantages to alkylating amylenes are:

- It helps reduce the RVP of the FCC gasoline

- It helps reduce the RVP of the entire gasoline pool (although not as much as it might appear on the surface due to the Hydrogen Transfer Reaction)

- It reduces the total olefin content of the gasoline pool.

- It increases the volume of gasoline produced from the amylenes (or another way to look at it is that it allows the refiner to convert some iso-butane into gasoline)

Some challenges are:

- Dealing with the increased amount and type of feed contaminants (sulfur and diolefins)

- Increased ASO production – difficulty maintaining acid purity

- More olefin feed means lower iso-butane/olefin ratio for most units

- Increased iC5 production in the Alky (due to the Hydrogen Transfer Reaction). This can cause higherRVP of the alkylate or more iC5 in the n-butane produc

Jason Noe (UOP)

Normally clay downstream of extraction lasts a long time. Units utilizing glycol can damage the clay easily if there is any glycol carry over. SulfolaneTM generally does not damage clay. For the glycol processes, it is possible to use a scrubber to reduce glycol carry over to the clay. This is a standard requirement of UOP’s CaromTM units but the older UdexTM and Union Carbide TetraTM units could benefit if this is a problem for them.