Tuesday, August 22, 2017

Isomerization (Axens Process Licensing)



From once-through to advanced recycle isomerization processes, we offer the complete line of isomerization solutions that, by increasing C5/C6 naphtha cut octane numbers up to 92, go far to meet tighter gasoline pool specifications. The isomerate product is free of sulfur, aromatics and olefins, making it an excellent gasoline pool component. Isomerization fits well with the trend to remove benzene precursors from reformer feedstock, and possible co-processing of light reformate fractions can resolve benzene content constraints. The question of which process to select will depend on a number of criteria such as feed composition and desired octane number. We have achieved a significant market penetration since the 90’s through the implementation of innovative process schemes combined with state-ofthe-art chlorinated alumina catalysts.


Chlorinated alumina is the best catalyst to meet the need for today’s high octane requirements. Its high activity permits operation at the lower reactor temperatures that enable higher product RON and favor superior yields. The use of molecular sieve adsorbents on the feed and hydrogen make-up streams ensures the removal of feed contaminants and long catalyst lifetimes. Chlorinated alumina-based catalysts are also ideal for retrofitting idle units such as reformers or hydrotreaters with implementation of feed pretreatment and off-gas neutralization packages.  The substantial octane gain and reduced catalyst cost account for the short pay-back time, usually less than a year.

Our isomerization technologies employ ATIS-2L catalyst which provides an unsurpassed combination of high activity low cost and low platinum content.


This least-cost path to moderate octane gain can provide, in some cases, a sufficient boost to the gasoline pool octane. Typically, the octane for a feed having a C5 to C6 ratio of 40:60 will have an increase in RON from 70 to 83-84 after isomerization. We employ a permutable reactor design; that is, either reactor can be used in the lead or lag position or it can be operated independently during catalyst servicing. This assures ultra-high on-stream service.


The maximum octane number available from a oncethrough system is limited by the thermodynamic equilibrium of the C5/C6 mixture. Distillation is one way to achieve octane improvement by either allowing isomers to bypass the reactor (DIP) or by recycling normal paraffins to the reactor (DIH, shown hereafter). However, these approaches still leave normal paraffins in the product.



Ipsorb is the most economic path available to convert all normal paraffins to their iso-paraffins. A vapor phase mole sieve section is used to adsorb normal paraffins for recycle to the reactor.


The Hexorb process also completely adsorbs and converts all normal paraffins to isomers. The difference is that methyl pentanes (RON 74) are also converted, affording the highest possible octane for a C5-C6 feed (up to RON 92).


Our isomerization technologies are ready to help meet a refinery's octane objectives, whether it is for a new unit or debottlenecking and revamping of oncethrough and deisohexanizer units. Relative differences between the isomerization schemes with regard to investment cost, operating cost and product revenue, are shown in the table below. Our isomerization technologies are also well suited for stepwise installation of octane improvement projects. Typical payout times are on the order of a year.


We entered the C5-C6 isomerization field late, in the 90’s, with a powerful R&D support at both lab and pilot scale sizes. Nevertheless, more than 50 isomerization units have been licensed by Axens, and since the marketing of ATIS-2L catalyst in 2003, more than 30 new units have been designed.

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Cryogenic nitrogen plant

From Wikipedia, the free encyclopedia
Nitrogen, as an element of great technical importance, can be produced in a cryogenic nitrogen plant with a purity of more than 99.9999%. Air inside a distillation column is separated at cryogenic temperatures (about 100K/-173°C) to produce high purity nitrogen with 1ppm of impurities. The process is based on the air separation, which was invented by Dr. Carl von Linde in 1895.

Gaseous Nitrogen (GAN) plant with production rate of 800 Nm3/hour
The main purpose of a cryogenic nitrogen plant is to provide a customer with high purity gaseous nitrogen (GAN). In addition liquid nitrogen (LIN) is produced simultaneously and is typically 10% of the gas production. High purity liquid nitrogen produced by cryogenic plants is stored in a local tank and used as a strategic reserve. This liquid can be vaporised to cover peaks in demand or for use when the nitrogen plant is offline. Typical cryogenic nitrogen plants range from 250 Nm3/hour to very large range plants with a daily capacity of 63.000 tonnes of nitrogen a day (as the Cantarell Field plant in Mexico).

Plant Modules
A cryogenic nitrogen plant comprises:
Warm End (W/E) Container
·         Air receiver
·         Chiller (Heat exchanger)
·         Pre-filter
·         Air purification unit (APU)
·         Main heat exchanger
·         Distillation Column
·         Condenser
·         Expansion brake turbine
Storage and Backup System
·         Liquid nitrogen tank
·         Vapouriser

How the plant works

Flowsheet GAN Plant Linde Cryoplants Ltd.

Warm end process
Atmospheric air is roughly filtered and pressurised by a compressor, which provides the product pressure to deliver to the customer. The amount of air sucked in depends on the customer’s nitrogen demand.
The Air Receiver collects condensate and minimises pressure drop. The dry and compressed air leaves the air to refrigerant heat exchanger at about 10°C.
To clean the process air further, there are different stages of filtration. First of all, more condensate is removed, this removes some hydrocarbons.
The last unit process in the warm end container is the thermal swing adsorber (TSA). The Air purification unit cleans the compressed process air by removing any residual water vapour, carbon dioxide and hydrocarbons. It comprises two vessels, valves and exhaust to allow the changeover of vessels. While one of the TSA beds is on stream the second one is regenerated by the oxygen rich waste flow, which is vented through a silencer into the ambient environment.
Coldbox process
After leaving the air purification unit, the process air enters the main heat exchanger, where it is rapidly cooled down to -165°C. All residual impurities (e.g. CO2) freeze out, and the process air enters at the bottom of the distillation column partially liquefied.
Back up process
Liquid Nitrogen produced from the cold box transfers into the liquid storage tank. An ambient air vaporiser is used to vaporise stored liquid during peak demand. A pressure control panel senses the demand for gaseous nitrogen and regulates the gas flow into the end-users pipeline to maintain line pressure.
Applications for high purity nitrogen production
§  Ammonia production for the fertilizer industry
§  Float glass manufacture
§  Petrochemical
§  Purge gas
§  Blanketing/Inerting gas for tanks and reactor vessels
§  Amine gas treatment
§  Bearing seal gas
§  Polyester manufacture
§  Semiconductor manufacture
§  Photovoltaic manufacture
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Monday, January 16, 2017

Pilot-Operated Relief Valve

Like other pressure relief valves (PRV), pilot operated relief valves (PORV) are used for emergency relief during overpressure events (e.g., a tank gets too hot and the expanding fluid increases the pressure to dangerous levels). The difference between PORV and conventional PRV is that pilot valves use system pressure to seal the valve. A PRV typically uses a spring to hold the disc or piston on seat. The essential parts of a PORV are a pilot valve (or control pilot), a main valve, a pitot tube, the dome, a disc or piston, and a seat. The volume above the piston is called the dome.

PORV are also called pilot-operated safety valve (POSV), pilot-operated pressure relief valve (POPRV), or pilot-operated safety relief valve (POSRV), depending on the manufacturer and the application. Technically POPRV is the most generic term, but PORV is often used generically (as in this article) even though it should refer to valves in liquid service.

Mode of functioning
The pressure is supplied from the upstream side (the system being protected) to the dome often by a small pilot tube. The downstream side is the pipe or open air where the PORV directs its exhaust. The outlet pipe is typically larger than the inlet. 2 in × 3 in (51 mm × 76 mm), 3 in × 4 in (76 mm × 102 mm), 4 in × 6 in (100 mm × 150 mm), 6 in × 8 in (150 mm × 200 mm), 8 in × 10 in (200 mm × 250 mm) are some common sizes.
The upstream pressure tries to push the piston open but it is opposed by that same pressure because the pressure is routed around to the dome above the piston. The area of the piston on which fluid force is acting is larger in the dome than it is on the upstream side; the result is a larger force on the dome side than the upstream side. This produces a net sealing force.
The pressure from the pilot tube to the dome is routed through the actual control pilot valve. There are many designs but the control pilot is essentially a conventional PRV with the special job of controlling pressure to the main valve dome. The pressure at which the control pilot relieves at is the functional set pressure of the PORV. When the pilot valve reaches set pressure it opens and releases the pressure from the dome. The piston is then free to open and the main valve exhausts the system fluid. The control pilot opens either to the main valve exhaust pipe or to atmosphere.

Snap acting
At set pressure the valve snaps to full lift, it can be quite violent on large pipes with significant pressure. The pressure has to drop below the set pressure in order for the piston to reseat (see blowdown in relief valve article).

The pilot is designed to open gradually, so that less of the system fluid is lost during each relief event. The piston lifts in proportion to the overpressure. Blowdown is typically short.

Comparison to non piloted pressure relief valves
  • Smaller package on the larger pipe sizes.
  • More options for control.   
  • Seals more tightly as the system pressure approaches but does not reach set pressure.
  • Control pilot can be mounted remotely.
  • Some designs allow for changes in orifice size within the main valve.
  • can be used in engines
  • More complex, resulting in various fail-open failure modes.
  • More expensive at smaller sizes (starts to even out as pipe size increases).
  • Small parts in pilot valve are sensitive to contaminant particles.
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