How it works

The first step is to hydrotreat the naphtha feed to remove impurities such as sulfur, nitrogen, and oxygen that would be harmful for the reformer's platinum catalysts.

The naphtha is separated into light naphtha (C5-C6) and heavy naphtha (C7-C10) in a naphtha splitter. This can occur before or after hydrotreating. Only the heavy naphtha goes to the reformer.

Next, the heavy naphtha feed is mixed with recycled hydrogen, heated to about 900 F and sent through a series of 3-4 reactor vessels (either in line, or stacked vertically). Each reactor vessel contains a platinum and alumina catalyst to drive the reaction.

In a CCR process reactors are stacked, allowing the catalyst to gradually flow downward through all the reactors. Small amounts of catalyst are continuously removed from the bottom (last) reactor, regenerated, and returned to the top (first) reactor.

Reforming reactions are highly endothermic, resulting in a lower temperature at the outlet of each reactor and requiring a furnace for reheating of output product before it flows into the next reactor. With each successive reactor reaction rate decreases, heat requirement declines, and reactor vessel size increases.

The product from the last reactor is cooled and separated into liquid and gas streams. Some of the hydrogen rich gas stream is recycled back to the feed to the reformer to maintain optimal hydrogen/hydrocarbon ratio. The liquid product is stabilized in a debutanizer (removing C1-C4s).

Feeds

The input to the reformer is a hydrotreated, high N+A heavy naphtha (C7-C10). This can come from several sources:

• Straight run heavy naphtha - produced in the atmospheric distillation of crude and sent through a naphtha hydrotreater

• Hydrotreated cracked naphtha - from the coker or visbreaker, and sent through a naphtha hydrotreater

• Heavy hydrocracked naphtha - taken directly from the hydrocracker, no need to hydrotreat

Products

The major products from the reformer are:

• reformate - This is naphtha rich in aromatics and iso-paraffins that is either blended into gasoline or separated into component aromatic streams that are used as petrochemicals feed stocks.

• hydrogen - purified and used as feed to hydrotreaters or hydrocracker

• reformer gas - a mixture of refinery gas and light liquids (LPGs). This is sent to the gas plant for separation.

A number of operational levers are used to optimize performance of a reformer:

• Feed N+2A - feeds with higher content of naphthenes and aromatics will yield higher reformate volumes and higher octane.

• Feed C6 - Any hexane in feed naphtha ends up as benzene in the reformate, which is undesirable if blending into gasoline. This is addressed by setting the initial boiling point to cut only C7 and heavier (above 180 F), and/or by extracting benzene from the reformate on the back end

• Temperature - higher temperature increases reformate yield and octane

• Pressure- lower pressure shifts equilibrium toward more reformate yield

• Space velocity - lower space velocity favors higher reformate yield

• Hydrogen - lower hydrogen/hydrocarbon ratios (low hydrogen partial pressure) pushes the reaction toward higher reformate yield. However, low hydrogen ratio also favor coke formation resulting in catalyst deactivation

• Catalyst type - The basic catalyst is a Platinum (Pt) and chlorinate alumina catalyst. Rhenium (Re) is added to the platinum catalyst to support operation at lower pressures, especially in semi-regen units. Tin (Sn) is added to platinum to improve yield at low pressures, especially in CCR units.

• Catalyst activity - Semiregen units will see catalyst activity drop as coke deposits develop between regenerations.

Technology types and licensors

Reformers are split into three main types of technologies:

• Semi-regen (SR) - older units mostly have fixed beds of catalyst that need to be regenerated every few months by burning off the coke that forms on the catalyst during normal operation. These semi-regen (SR) reformers typically operate at relatively high reactor circuit pressures to minimize the amount of coke formation and keep the periods between regeneration shutdowns as long as possible, but as a result only achieve octane numbers of 95-98 in the reformate product.

• Cyclic - this design employs a series of fixed bed reactors with an extra "swing" reactor allowing for regeneration of the reactors one at a time without shutting down the entire process.

• Continuous (CCR) - Newer reformers are built with continuous catalyst regeneration (CCR) capability so they can operate at lower reactor circuit pressures without catalyst deactivation. Coke make is high, but catalyst is moved continuously to a regenerator section where the coke is burned off before the catalyst is returned to the reactor section. This effectively keeps all of the catalyst at full activation through an entire run. CCR reformers can often operate for three or more years continuously between turnarounds and can produce reformate product with octane numbers of 101-103.

Most new units employ either the UOP or Axens CCR technologies. However there are a number of existing older units employing other technologies. Major reforming technologies include:

• UOP - Platforming semiregen and CCR technology

• Axens/IFP - Octanizing semiregen and CCR technology

• ExxonMobil - Powerforming semiregen and cyclic reforming technology

• BP/Amoco - Ultraforming semi-regen and cyclic technology

• Chevron - Rheniforming semi-regen technology

• Englehard/ARCO - Magnaforming semiregen technology

• Houdry - Houdryforming semiregen technology