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ADVANCES IN FCCU TECHNOLOGY FOR THE PRODUCTION OF OLEFINSBlock 2, Forum 10 paper

ADVANCES IN FCCU TECHNOLOGY FOR THE PRODUCTIONOF OLEFINSDerek Lawler, Stone & WebsterWarren Letzsch, Stone & WebsterFakhri Dhaidan, Stone & Webster

Abstract:

Ethylene (20 Wt%) and Propylene (25 wt%) from Fuel Oil is now a reality using advancedFluid Catalytic Cracking Unit (FCCU) technology. Integrated sites with FCCU and SteamCracking maximise the conversion of crude oil to petrochemicals.

This paper describes the advances made in:

FCCU, (Fluid Catalytic Cracking Unit)

Steam Cracking,

Site Integration,

Types of feed that are suitable for this process,

Preparation of feedsShaw Stone & Webster in combination with Total, Axens and Sinopec have developed worldleading technology for the production of Olefins

Introduction

Ethylene and Propylene are light olefins that form the primary building blocks for manymodern plastic materials including polymers such as Polyethylene and Polypropylene. Themarket for plastics and polymers is forecast to grow at or ahead of world GDP. Oil and Gasare the primary raw materials to make olefins and converting them into plastics is aneconomic alternative to producing road fuels. Natural gas contains Ethane and a number ofcompanies, particularly in the Middle East, are currently investing in significant additional

capacity to convert Ethane to Ethylene. Crude Oil and Condensate are the primary sources ofNaphtha that is a traditional feed for conversion to Ethylene and Propylene. Fuel Oil in oilrefineries is converted into Propylene using Fluid Catalytic Cracking Units (FCCU). There is atrend to use lower cost Ethane and Fuel Oil as feeds to produce olefins as Naphtha isincreasingly expensive. The continued growth in the production of olefins and thediversification of feedstocks is supported by technology advances in Fluid Catalytic CrackingUnits (FCCU) and Steam Cracking (SC).

Background

Currently the most widespread method of producing olefins uses Steam Cracker technologywhere paraffins are heated inside tubes in a furnace to above 800 deg C in the presence ofsteam where they thermally crack.

There are two main types of Steam Cracker, Naphtha and Ethane:

Naphtha is a mixture of hydrocarbons in the C3 to C10 range and is a by-product ofoil refining or is sourced from Condensate from gas and oil fields. Naphtha cracks toproduce olefins and aromatics. Naphtha is also in demand to produce Gasoline andthe price of Naphtha is closely linked to that of Gasoline. There are times when it isnot economic to crack Naphtha.

Ethane is co-produced with LNG and as such its availability is growing. ConvertingEthane to Ethylene is a cost effective upgrade route that is being adopted in theMiddle East where several new large Ethane Steam Cracker projects are beingimplemented. The product of cracking Ethane is predominantly Ethylene notPropylene

yright World Petroleum Congress all rights reserved

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Increased Ethylene demand is forecast to be met from cracking Ethane, but this will not meetthe forecast demand for Propylene. There are several technologies other than Naphthacracking for producing Propylene including Propane De-hydrogenation but the most commonproduction route is Fluid Catalytic Cracking.

Approximately one third of the worlds propylene for chemicals is currently produced as a by-product in Fluid Catalytic Cracking (FCC) units in oil refineries. In this process heavy fuel oil issuitably prepared and cracked on a circulating catalyst at above 520 degC. This produces a

range of cracked components including Gasoline and Propylene. Advances in FCCtechnology have allowed greater flexibility to make increased quantities of Propylene. Recentadvances allow FCC Units to be designed and built to produce 25% Propylene from suitablefeeds. Further advances show that the technology can produce both Propylene and 20%Ethylene from Fuel Oil.

1. FCCU ADVANCES

1.1 OVERVIEW OF FLUID CATALYTIC CRACKING

FCC Flow Scheme

Hot Catalyst Flows under gravity from the Regenerator to the Riser

Feed and Steam are Injected in the Riser

Feed Vaporizes and Cracks and Lifts Catalyst Into the Reactor Separator

At the Top of the Riser the Products and Catalyst are Separated

Product Vapours go to a Fractionator

Catalyst Falls into a Steam Stripper

Spent Catalyst Returns to the Regenerator

Regenerator Burns Coke on Catalyst and Heats it to approximately 720C

Catalyst Re-circulates at 30 to 100 Tonnes per Minute


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FCCU Schematic

FCCU was developed in the 1930s and 40s to produce high octane aviation gasoline and isnow a standard process in oil refineries with over three hundred units throughout the world.The primary product from FCC is gasoline but the FCC is used to make a range of productsfrom Diesel to Ethylene. The process uses a circulating catalyst that is fine enough to befluidized. The catalyst particle sizes in an FCCU are like a very fine sand and typically rangefrom 20 to 100 microns with an average size around 70 microns. FCCUs have been built witha capacity range from 60 to 600 M3/H. The process is continuous with the catalyst beingregenerated as part of the process. The feed for most FCC units is Vacuum Gasoil that isproduced from Fuel Oil by Vacuum Distillation. Recently the trend is to crack whole Fuel Oilsin Residue FCC Units to convert the bottom of the barrel into higher value components.

Developments in these technologies by the licensors and catalyst companies make this aneconomic way to upgrade fuel oil residues.


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1.2 FEED INJECTION

Feed for the FCCU is pumped to the feed injectors, atomised with steam and injected into thehot catalyst. The Feed is typically at 200 deg C and the catalyst is typically at 720 deg C.Good contact between the feed and the catalyst in the mix-zone is essential for efficientcracking. The feed vaporizes and cracks on the hot catalyst. The steam and vaporized feedlift the catalyst up the riser. Residence time in the riser is 1 3 seconds.

There are a number of different technologies for Feed Injection that aim to provide goodmixing with the catalyst to vaporize the feed. One of the most effective technologies uses awell developed design that is more commonly applied to make artificial snow. In the snow-maker, water is injected through a shaped orifice onto a target bolt where it splashes; airunder pressure is blown across the bolt and shears the water into very fine filaments that areatomised by the tip to form a fine mist that blows into the cold atmosphere to make artificialsnow. The droplet size is determined by the ratio of water to air, the velocity of the water andair, the angle of incidence and by the physical properties, density, surface tension andviscosity. The relationship is described by Mugele and Evans

1and applied extensively by

Spray Systems Inc. For the FCCU the liquid is oil and the gas is steam.

Stone & Webster Feed Injector

There are over seventy FCCUs using these feed nozzles in operation throughout the worldgiving trouble free operation. Several nozzles have been in service for ten years withoutreplacement or loss of performance.

FCC catalyst is highly porous with a large surface area. Only vapour molecules are able toenter the pores of the catalyst to crack on the active sites. Fuel Oil requires high temperatureand low partial pressure to vaporize the heavy molecules in it. The excellent performance ofthe S&W feed injector is because the droplet size of the oil is very small, similar to the particlesize of the catalyst giving excellent heat and mass transfer and the steam lowers the partialpressure.

FCC licensors continue to develop Feed Injection technology because it is the heart of theFCC process. Recent developments for the highly successful S&W Feed Injectors are toimprove the shape of the slot and to reduce fabrication costs.


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1.4 RISER TERMINATION

When the feed meets the catalyst it vaporizes and the cracking reactions are fast, producingintermediate cracked compounds in the vapour phase. These intermediate compounds enterthe pores of the catalyst and are further cracked to Gasoline and Propylene. If the vapourremains in contact with the catalyst it is further cracked to coke and fuel gas.

In a modern FCCU all the valuable cracking reactions take place in the riser and it is

important to rapidly separate the products from the catalyst at the end of the riser. Theprinciple separating mechanism used to disengage the solid catalyst from the vapour productuses some form of ballistic or centrifugal force such as a cyclone. The product vapours andsteam leave the reactor through second stage cyclones that remove the remaining catalyst.The catalyst drops to the bottom of the reactor into the stripper.

Riser Termination Devices have evolved from a basic tee to more sophisticated proprietarydisengaging devices that all try to achieve the following:

Rapid Separation of Products and Catalyst

Compact Design

Easy Start-up and Operation

Efficient Catalyst Removal

Reduces Dry Gas

Reduces Coke

Sealed or Open Operation

Stone & Webster RS2 Separator


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1.5 PACKED STRIPPER

The stripper removes hydrocarbons from the catalyst by stripping it with steam before itreturns to the Regenerator. In the reactor stripper the ratio of catalyst to oil is very high andprolonged contact results in all the hydrocarbons cracking to coke and gas. FCC Cokeconsists of heavy aromatic and multi ring compounds. A measure of the effectiveness of astripper is the Hydrogen on Coke and this is reduced by good stripping or by excessivecontact time.

To be effective in stripping hydrocarbons from the catalyst, the steam has to be well

dispersed. A steam ring with nozzles jets the steam into the catalyst and is very effective instripping. Within 0.5m of the steam ring the steam velocity reduces and bubbles of steam andhydrocarbon form. These bubbles have to rise against the catalyst descending. The larger thebubble the faster it ascends and the less effective it is in stripping. In traditional disc anddonut or shed deck stripper designs, part of the available cross section is blocked. At theseconstrictions the velocity of the descending catalyst increases and the size of steam bubbleable to flow against it has to increase.

Total of France developed the use of packing in strippers in the 1990s. Koch-Glitsch furtherdeveloped the materials and design and its use has been widely licensed for use in revampsand new FCC units. In a Packed Stripper 95% the whole area is open to flow and thestripping is more effective. Increasing the flow area is particularly valuable in revampingexisting units to increase catalyst circulation and capacity.

Total / Stone & Webster / Koch-Glitsch Stripper Packing

.

1.6 COLD WALL CONSTRUCTION

Cold Wall construction allows the use of Carbon Steel for the construction of the FCC. Theinternals of the vessels and transfer lines are covered in insulating and abrasion resistantrefractory. Advances in refractory and anchoring technologies have made this design veryreliable. The move to Cold Wall design removes metallurgical limits from the operatingwindow of the FCC and it is these advances that Stone & Webster has developed to makehigh temperature, high Olefins FCC a reality.

Robust Construction

Improved Operation

Reduces Coke to the

Regenerator Good Start-up Characteristics

Minimises Steam Usage


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High Olefins FCC Technology increases the yields of Propylene and Ethylene from FCCs.These valuable products are then recovered and purified using the techniques developed inSteam Cracking.

2.0 HIGH OLEFINS FCC

FCCUs currently produce approximately 30% of the Propylene used in the Chemical Industry.This figure is likely to increase as Refiners with FCCUs recover more Propylene from their

existing units and build new FCCU that maximise Propylene production. FCC producesPropylene by cracking heavy molecules to light gasoline molecules and then cracking thesemolecules further to Propylene.

Conventional FCC catalyst produces Propylene rather than Ethylene because the activecatalyst sites are Bronsted Acid sites that promote proton addition reactions resulting in

carbenium ions and Beta Scission. The fundamental mechanism of catalytic cracking, -scission, leads to high yields of C3and C4olefins. This is because the hydrocarbon moleculein the presence of an acid site tends to form a carbenium ion at the secondary or tertiary

carbon atom. The cracking actually occurs at the position relative to the carbenium ion.This type of a reaction mechanism always results in the production of a C3or C4 olefin. Inaddition the process is operated such as to minimize secondary hydrogen transfer reactionswhich compromise the olefin yield.

RIPP in China has recently developed catalysts that produce Ethylene. These catalysts haveactive Lewis acid sites that promote electron removal and the formation of free radicals.Details of the catalyst development are given by Wang Xieqing et al

2.

By utilising the properties of these catalysts and the advances in FCC design S&W can offermore opportunities to produce light olefins from heavy feeds.

2.1 ZSM-5 FCC ADDITIVE

A form of zeolite, named ZSM-5 by its licensors at Mobil, is the most widely used technologyto increase the yield of Propylene from existing FCC units. When molecules of FCC Naphthaenter the zeolite structure they are preferentially cracked to Propylene and Butylene by acatalytic action initiated the Bronsted Acid sites. Because Paraffins are cracked by ZSM-5 it

also has an advantage as it increases the Octane of FCC Gasoline.

The normal yield of Propylene in FCCs is approximately 3% Using ZSM-5 and temperaturesup to 540 C and can increase Propylene yield to approximately 6%.

2.2 DEEP CATALYTIC CRACKING (DCC)

RIPP in China produce an FCC catalyst that contains a Pentasil zeolite they have developed.This catalyst operates up to temperatures up to 565 C and can produce a yield of Propyleneof 15% to 20%. This catalyst is used in a successful development of the FCC called DCC.DCC uses well proven FCC technology and applies it to the different operating conditionsrequired for the production of Propylene. This includes more steam and lower operatingpressures. DCC has been in successful operation for several years at units in China and in

Thailand. A new 92,000 Barrel Per Day DCC unit is licensed for construction in Saudi Arabiaand will produce approximately 900,000 Tonnes per year of Propylene.

2.3 CATALYTIC PYROLYSIS (CPP)

RIPP has developed a new catalyst and demonstrated it in a unit that operates at up to 650C. A new commercial unit for his process is under construction in China. As well as Bronsted

Acid sites, the new catalyst contains Lewis Acid sites that produce Ethylene. The CPP canproduce a mix of Ethylene and Propylene and this provides a route to produce light olefinsfrom Fuel Oil. The production from a CPP unit compares well to that of a Steam Cracker.


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CPP is essentially a Chemicals Unit because the recovery systems required to purify thePropylene and Ethylene are those required on a Steam Cracker. The light olefins are madeby cracking the Gasoline components in the FCC. The paraffins and olefins crack and leave aNaphtha that is highly aromatic.

Table 2.1 Comparative Yields

Cracking to produce light olefins requires higher temperatures, lower pressures and moresteam.

Reactor Temp. CReactor Pressure, Bar GaugeResidence Time, SecsCatalyst to Oil Ratio, wt/wtDispersion Steam, wt% FeedCracking Environment

FCC

500 - 5501-31-54-81-3Riser

DCC

530 - 5901-21-1010-155-30Riser & Bed

CPP

560 - 67011-315-2530-50Riser

SC

760 - 87010.1 0.2-30 - 80Coil


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Significant advances have been made to improve the performance, reliability andenvironmental impact of Steam Crackers. There are now single furnaces producing 250,000TPA of Ethylene and furnaces 50% larger are being planned. Furnace designers continue toseek improved coil designs to minimize coking and enhance run lengths using advancedtubing materials including current trials using ceramic tubes. Advanced burner designsincrease efficiency and reduce NOx emissions.

4 SITE INTEGRATIONIntegrating an oil refinery with petrochemicals is a proven way to optimize the return oninvestment and many of the major oil companies follow this strategy. Integration reducesoverall investment costs because infrastructure and utilities are shared, tankage and transportare minimized and units are sized to be complementary. Low value streams from thepetrochemical plant such as fuel gas and C4 olefins are valuable intermediates in the refineryto provide Hydrogen and Alkylate. Low value streams from the refinery such as FCC off-gasand propylene are suitable as feed streams in the petrochemical plant. Integration can includea cogeneration facility to generate electricity using low value fuel and co-product streams andto reduce energy costs.

S&W has evaluated many scenarios and has seen repeatedly that integration of refining andpetrochemicals shows a good return. As well as integrating the refinery and olefins

production, integrating olefin production and the first line derivative products can achieveoptimum recovery, minimise investment costs and achieve high returns. In most scenariosintegrated sites are more profitable than merchant facilities producing polymer grademonomers for sale.

4.1 Refinery/Olefins Plant Integration

A simple integrated refinery/olefins plant utilises Naphtha from the Crude Distillation Unit asfeed to a Steam Cracker. This configuration is used successfully in North Africa where aHydroskimming refinery processes light sweet crude oil to produce Naphtha, Kero, Diesel andFuel Oil. In the case of North African crude the Fuel Oil is a Low Sulphur Waxy Residue andis sold at a premium as a supplementary feed for FCCU. The Naphtha is converted toEthylene and Propylene. The Ethylene is converted to Polyethylene and the Propylene isexported.

A more complex integrated refinery/olefins plant incorporates an FCC that converts part of theFuel Oil to Gasoline and Propylene. This configuration is used in Middle Europe. TheEthylene is converted to Polyethylene and other derivatives such as Ethyl Benzene.Propylene is typically converted to Polypropylene or Cumene. FCCU gases that contain C2sand C3s are used to supplement the feed to Steam Crackers. A Spanish refinery hasintegrated a Hydrocracker with Naphtha Steam Cracking to produce high quality Diesel andChemicals.

In the USA and Europe there are several complexes that are highly integrated and convertcrude oil into range of high value products including Polymers, Chemicals, road fuels andLube Oils. Typically these facilities have no fuel oil production because they either convert thefinal residue to Coke or to Electricity.

4.2 Revamp of Existing Facil it ies

There is currently more activity in revamping existing refineries and olefins plants to increasecapacity and yields than there is building grass root units. In developed countries it is easierto obtain permission to expand and existing facility than it is to build on a new site.

Due to advances in Steam Cracker technology the economics are attractive to replace oldSteam Cracking furnaces with fewer, larger new furnaces capable of cracking a wider rangeof liquids. An alternative option that some companies are looking at is the DCC/CPP process


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to replace old furnaces and take advantage of lower cost feeds. A DCC/CPP unit occupiesapproximately the same plot space as two furnaces and utilises the same recovery facilities.

An FCCU is typically a refinery unit that produces Propylene and some Ethylene that can beconverted to polymers and chemicals. There are many existing locations where Refineries,Petrochemical and Chemical plants are adjacent to each other. Often they are integrated byinterchanging products and the trend is towards more integration.

FCCUs are producing more C2s and C3s.

In countries that are developing their Petrochemical industries the infrastructure and expertiseis often centred on existing refinery facilities.

There is a trend towards mega sites to take advantage of the economies of scale and thereare a series of investment currently taking place to install the largest capacity Steam Crackersand largest capacity High-Olefin FCCU. As well as separate recent development

Many medium sized refinery/petrochemical sites are looking at modernising and improvingtheir profitability by processing lower cost feeds.

An ultimate configuration is for a design where Crude Oil is converted completely intoPlastics, Chemicals and Energy.

Light Crude Oil Petrochemical Refinery

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FEEDSTOCKS

FCCU is a very versatile technology for producing Olefins as it accommodates a wide rangeof feeds. As is shown in the Crude to Chemicals refinery, potentially all the Crude Oil isconverted to Chemicals and power.

The FCCU process obtains the heat it requires for the heat of cracking by burning the coke on

the re-circulating catalyst. Feed to the FCCU has to contain material that will form coke andthis is mostly found in heavy residue feeds. It is feasible to process whole crudes through theFCCU but more typically the residue from the atmospheric crude distillation unit is used asfeed to the FCCU either directly or after being further processed. Crude distillation residue istraditionally sold as Fuel Oil and so has a relatively low cost as a feedstock.

Traditional FCCUs convert Fuel Oil to gasoline and the technology is well proven. Fuel Oil is alow cost feedstock and is available in many forms and qualities. The desirable properties forFCCU are that the Fuel Oil contains a high level of paraffinic compounds that crack and that itis low in contaminants. Residue from crude oil that is low in metals and contaminants isused directly as feed for the FCCU. Residues containing high metals are further processed asdescribed in the next section of this paper.

FCCU concentrates any non-volatile or non-crackable components in the feed on the catalyst.Contaminants such as metals build up on the catalyst. To keep the catalyst active a portion ofthe catalyst is replaced on a continuous basis by purging. An FCCU on low metals feedtypically uses 1-4 Tonne of catalyst a day. An FCCU on high metals feed can use up to 30Tonnes a day. The spent catalyst is usually returned to the supplier for re-use or safedisposal. Feedstocks that are high in metals (above 20ppm) use more catalyst to purge themetals from the system. At levels above 50ppm metals in feed it is no longer economic toreplace so much catalyst.

Many African crude oils such as those from Algeria, Libya and Angola are low enough inmetals to be attractive as feeds for RFCC.

The quantity of metals in the feed determines the feasibility to process the residue withoutfurther processing. The Paraffinicity of the feed determines how much of it will crack to lightolefins. Paraffins and Naphthenes in crude oil will crack to form light Olefins but Aromaticsand Asphaltenes will not crack.

In many cases the crude oils that are low in metals are also low in aromatics and are the mostsuitable feeds for RFCC.

Steam Cracker feed has to be low in residue components to minimise coking, Coke is formedduring Steam Cracking but it is not a useful by-product and has to be removed from theprocess. A particular advantage of the FCCU is its capability to process heavier feeds thanSteam Cracking and these are typically less expensive.

6 PREPARATION OF FEEDS

Low metal paraffinic residues are ideal feeds for FCCU to produce Olefins. Crude Oils fromAlgeria, Angola and Libya as well as China and Vietnam meet these requirements. Other

crude oils such as Arab Light and Arab Heavy are paraffinic but contain too manycontaminants to be economically cracked directly. To process feeds that contain a lot ofmetals and asphaltenes the feed has to be treated to remove the contaminants. The primarytechnologies used are Atmospheric Reside Hydrotreating, Vacuum Distillation and SolventDe-Asphalting.


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Integrated Fuels / Petrochemical Refinery

Atmospher ic Residue Hydrotreat ing

This process takes the residue from the atmospheric distillation and processes it in thepresence of Hydrogen over a series of catalysts that remove the contaminant metals andcoke precursors as well as Sulphur and Nitrogen that are other contaminants. The resultantresidue product is an excellent feed for the FCCU. The main disadvantage of this process isthat has a relatively high capital cost.

Vacuum Distillation

The most widely used process to prepare FCCU feed is by Vacuum distilling the fuel oilresidue formed during atmospheric distillation of Crude Oil to produce Vacuum Gasoil Oil(VGO). Vacuum distillation concentrates the Asphaltenes and metals in the Vacuum Residueand the VGO distillate is relatively free of them. Between 60 and 70 percent of the

Atmospheric residue is recovered as VGO. The remaining vacuum residue is either burnt asfuel or further processed. Coking converts the vacuum residue to lighter hydrocarbons andcoke. Solvent De-asphalting of the residue extracts more feed for the FCCU.

Solvent De-Asphalting

Heavy paraffin components in residue will dissolve in light paraffin liquids such as Propaneand Butane. This solvent action is used in Solvent De-Asphalting (SDA) to separate out morefeed for the FCCU. SDA recovers material from the vacuum residue that can be cracked inthe FCC. The FCCU feed is De-Asphalted Oil (DAO) and is low in metals and asphaltenes.

The quantity and quality of the DAO is determined by the residue feed and the solvent.Propane extracts less DAO than Butane but it is higher quality. Butane extraction typicallyextracts 60 percent of the Vacuum residue. The SDA residue is very heavy and contains mostof the metals that were in the crude oil. While disposal of this material is troublesome, itmakes a good feedstock for gasification.

Recovering the solvent in SDA is usually achieved by heating the solvent under pressure toits supercritical phase where the heavy oils are no longer soluble. Solvent in the residue isrecovered by distillation.

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References1. Mugele, R. and Evans, H. D., Droplet Size Distributions in Sprays, Ind. Eng. Chem.,Vol. 43, No. 6,

pp. 1317-1324, 19512. Wang Xieqing, Shi Wenyuan, Xie Chaogang, Li Zaiting Research Institute of Petroleum Processing,

SINOPEC, Catalytic Pyrolysis Process (CPP)-An Upswing of RFCC for Ethylene and PropyleneProduction, AIChE National Spring Meeting, session T5a01 Advances in Catalytic Cracking, March10 to 14 2002,New Orlean, LA

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