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Challenges and opportunities of an FCC revamp

An FCC revamp for enhanced refinery performance and profitability called for close coordination with the technology licensor and contractors.

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Article Summary
To improve refinery performance by reducing fuel oil make, an FCC revamp was envisaged to process heavier feeds and maximise unit conversion and utilisation. One of the key objectives of the FCC revamp was enhancing the safety and reliability of the unit to achieve a cycle length of four years. KNPC scouted several of the latest available technological options and selected UOP technology including VSS, Elevated Optimix feed distributors and the Advanced Fluidized (AF) stripper for the reactor revamp. Following unit commissioning, the technology has performed successfully. Heavier feed was processed and met unit objectives in terms of yields as UOP and KNPC have jointly conducted optimisation tests

Project background
KNPC operates three refineries in Kuwait. They have a combined processing capacity of 460000 b/d of crude oil to produce primary products like petrol (gasoline), diesel fuel, kerosene, liquefied petroleum gas (LPG), heating oils and bitumen.

KNPC Mina Al-Ahmadi (MAA) refinery (see Figure 1) has a UOP FCC unit which was designed in 1984 for a feed rate of 30000 b/d of vacuum gas oil (VGO). The unit started up in 1987 and consists of a high efficiency style combustor regenerator, a downturn arm riser termination system in the reactor, and feed injected into the riser Wye. It has since been revamped once by UOP in 1997, to increase the capacity to 40000 b/d with a feed of either VGO or HVGO and some coker 
gas oil.

Propylene recovery, MTBE and alky units were added in the same revamp. With changing market demand for fuel quantity and quality, KNPC continued exploring the possibilities to further increase the unit’s capacity, and possibly to upgrade the technology to process heavier feeds and improve yields. The Clean Fuels Project (CFP) 2020 provided the opportunity to achieve this objective.
KNPC’s CFP 2020 vision
As a part of the CFP 2020 project, KNPC set out the following project objectives:
•    Develop KNPC refineries into integrated merchant refining complexes to meet diversified market needs
•    Meet future market demand and specifications for fuels for local and international markets
•    Enhance the environmental and safety performance of KNPC refineries
•    Execute a major upgrade of 
the MAA and Mina Abdullah (MAB) refineries to convert high sulphur fuel oil to higher value products
•    Respond effectively to KPC/KNPC strategic directives for expanding refining capacity in Kuwait
•    Provide new employment opportunities for Kuwaitis in the refining sector.

FCC project objectives
The CFP 2020 vision was incorporated into the FCC project’s objectives as follows:
•    An additional 6% increase in unit capacity (42 500 b/d)
•    Improve unit reliability and on-stream factor
•    Process difficult feedstocks and optimise conversion
•    Meet local gasoline and propylene commitments
•    Extend operational run length
•    Sustain operation at higher capacity
•    Improve environmental performance (flare less during start-up, control particulate emissions and SOx).

To meet all of these objectives, the FCC unit was successfully revamped in 2014. The revamp 
was to process more difficult feeds while updating the reactor side technology. Table 1 shows typical feed qualities processed by the FCC unit.

Technology selection
To meet KNPC’s objectives for the FCC revamp, UOP proposed that the following technologies be incorporated:

FCC reactor
•    VSS technology
•    AF stripper internals
•    Optimix feed distributors.

Air and flue gas circuit equipment
•    Additional auxiliary air blower
•    Change from hot wall to cold wall regenerated catalyst stand pipe, flue gas piping, and new cold wall orifice chamber
•    Modify regenerator cyclones.

Main fractionator
•    Replace trays in the top four sections (LCN/HCN fractionation, HCN pumparound, HCN/distillate fractionation, distillate pumparound) with random packing to save expensive wet gas compressor modifications.

Gas concentration columns
•    Replace internals in different sections with high capacity trays
•    Lines added to aid in flareless start-up.

The three key reactor technologies to enable profitability and reliability improvements are the VSS riser termination device (RTD), UOP AF stripper internals, and UOP Optimix feed distributors. Each of these technologies has been extensively commercialised for proven results.

The VSS RTD greatly improves gasoline selectivity through superior vapour catalyst separation, minimising post riser cracking. Similarly, delta coke and dry gas will be reduced along with the regenerator temperature. Some 77 of these devices have been commissioned since commercialisation in 1995.

AF stripper internals represent the latest FCC stripper technology, reducing delta coke through improved stripping efficiency, leading to a conversion increase from the boost in catalyst to oil ratio. These internals have been demonstrated at very high flux rates and have minimal maintenance issues. Some 89 of these have been commissioned since commercialisation in 2004.

Optimix feed distributors are elevated in the FCC riser which allows a lower density and even catalyst regime for feed injection. Through pressure drop control and three stage atomisation, Optimix distributors minimise droplet size and steam rates, leading to improvements in conversion, selectivity and dry gas. They are reliable and can save on maintenance costs through easy outer tip replacements. Some 110 of these have been commissioned since commercialisation in 1994.
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