Frank J. Elvin, Stephen K. Pavel
Coastal Catalyst Technology Inc.
Houston
A metals removal system for fluid catalytic cracking (FCC) catalysts has proved successful in two commercial test runs and is being installed in a refinery.
The process, called Demet, significantly reduces both fresh catalyst addition and spent catalyst disposal when used with any FCC catalyst. Some results with commercial runs to date are summarized in the accompanying box.
DEMET PROCESS
Demet controls FCC catalyst equilibrium metals concentration by recycling a slip stream of catalyst through an inexpensive, efficient, environmentally safe metals removal system.
All metals in the FCCU feed that have been deposited on the catalyst are removed by the process, The equilibrium catalyst metals concentration is controlled at the level at which the fresh catalyst required to maintain activity and selectivity equals catalyst losses.
The amount of fresh catalyst required to maintain activity and selectivity in a fluid catalytic cracking unit (FCCU) using the Demet process is 0.08 lb/bbl of FCCU feed. This is similar to the fresh catalyst required for FCCUs processing low metals, hydrotreated gas oil, where the fresh catalyst makeup rate also equals catalyst losses.
Demet allows the refiner to process high metals gas oil or residue in an FCCU, while operating at the equilibrium catalyst metals levels and catalyst makeup rates required while processing low metals hydrotreated gas oils.
Demet also virtually eliminates spent catalyst disposal.
Other results of using the catalyst rejuvenation process can be:
- Reduced catalyst consumption. The use of Demet to reduce fresh catalyst consumption is easy to quantify. The analyses presented in Table 1 assume that fresh catalyst costs $1,675/ton. All benefits are shown in terms of $/bbl of FCCU feed.
- Improved yields and increased ability to process residue. Demet improves yields by lowering equilibrium catalyst metals, and can allow additional residue to be processed. Additionally, yield selectivity can be improved by the replacement of fresh catalyst with demetallized catalyst.
Both of these factors will improve FCCU profitability, but exact benefits will vary from refinery to refinery, and are difficult to quantify. However, a refiner can always use more fresh catalyst, instead of Demet, to either reduce catalyst metals or to process more residue.
The cost of any metals removal method (such as Demet, hydrodemetallization of feed, or age separation) should be compared with the cost of the competitive alternative, increased fresh catalyst addition.
Demet achieves the profit improvements resulting from lower metals and/or increased residue processing at as little as one tenth of the cost of fresh catalyst.
Table 1 shows a cost comparison of Demet vs. fresh catalyst addition for three scenarios of varying feed characteristics and equilibrium catalyst metals concentrations. This comparison shows that Demet's benefits increase markedly with higher equilibrium catalyst metals concentration.
COMMERCIAL RESULTS
Two commercial runs have been completed: one of 4 months and one of 9 months. The 4-month test run at the Coastal Eagle Point Oil Co. refinery in Westville, N.J., confirmed that demetallized catalyst can be reused without loss of FCCU activity or selectivity.
The 9-month test run, for a major oil company, has confirmed the effectiveness of the catalyst on high metals catalyst, with over 3,000 ppm vanadium.
EAGLE POINT
Details of the Eagle Point operation have been previously published.1 The fresh catalyst makeup rate was reduced from 15 tons/day to 8.5 tons/day by recycling 10 tons/day through ChemCat's Demet unit in Meraux, La. This was accomplished by continually running truckloads of catalyst between the two locations.
All product yields and catalyst properties were maintained at this lower fresh catalyst makeup rate. The main effect of reducing fresh catalyst by using recycled demetallized catalyst was to increase the average catalyst age from 30 days to 53 days (the catalyst inventory of the Eagle Point unit is about 450 tons).
This increase in catalyst age did not adversely affect FCCU yields (Fig. 1). In fact, the absorber offgas yield decreased by 10% at the higher catalyst age.
The data plotted in Fig. 1 represent average yields for the two distinct periods of operation.
Points labeled "A" are average yields for the 5-month period of 15 tons/day fresh catalyst makeup, and points labeled "B" are average yields for the 4-month period of 8.5 tons/day fresh catalyst makeup and 10 tons/day Demet recycle.
Average metals levels for both periods of operation were 2,000 ppm Ni and 450 ppm V.
The catalyst microactivity and surface area are plotted in Fig. 2. The activity increased by two numbers at the high catalyst age, and the surface area increased by 2 sq m/g.
Because of the large number of catalyst samples tested (20 during the 5-month period and 15 during the 4-month high age period), these increases are considered significant and suggest that demetallized catalyst has a much lower deactivation rate than fresh catalyst.
Further laboratory and commercial testing is in progress to confirm this.
AGE DISTRIBUTION
Using Demet to reduce the fresh catalyst usage from 15 tons/day to 8.5 tons/day changed the average catalyst age from 30 to 53 days. The age distribution changed as shown in Fig. 3. Note that as the catalyst ages, it is subject to attrition through FCC operations.
NICKEL DISTRIBUTION
Because nickel is not mobile, it builds up on the catalyst as it ages. This is illustrated in Fig. 4.
For the Demet case, the catalyst nickel content is lower at any given age. However, this is offset by the fact that the catalyst is older. The average nickel in both cases is 2,000 ppm.
Although the nickel concentration increases as the catalyst ages, the percentage of total nickel on catalyst of a given age reaches a maximum at the average catalyst age, as shown in Fig. 5. The percentage of total nickel on catalyst then decreases because there are fewer and fewer catalyst particles of the higher ages.
The effect of the Demet process is that the nickel is more heavily distributed over the older particles. This results in the lower dry gas and hydrogen yields at constant average metals that were observed at the Eagle Point refinery.
VANADIUM DISTRIBUTION
Vanadium is mobile and relatively constant at all ages. Therefore, Demet does not change the vanadium content of catalyst particles of a given age. This is shown in Fig. 6.
Because of the mobility of vanadium, the vanadium distribution follows the catalyst age distribution. This means that only a small percentage of the total vanadium in the catalyst inventory is on the older catalyst, as shown in Fig. 7.
The fact that vanadium is mobile makes vanadium removal by methods other than Demet, including catalyst age separation, impossible.
TECHNICAL IMPROVEMENTS
Design constraints have limited the Meraux Demet unit to a maximum of 92% nickel removal and 60% vanadium removal. Process improvements have enabled tests units in the laboratory to achieve 99.9% nickel removal, 80% vanadium removal, and 80% sodium removal.
Iron and copper removals are now more than 90%.
The Meraux unit constraints also limited the reductions in fresh catalyst addition and spent catalyst disposal to the commercial achievement values outlined in the accompanying box. These design improvements will enable a new Demet unit to reduce fresh catalyst addition to 0.08 lb/bbl feed and spent catalyst disposal by 87%.
These improvements are being incorporated into new commercial unit designs.
DERBY DEMET UNIT
A new Demet unit is being built at Coastal Refining & Marketing's Derby refinery in Wichita, Kan. The unit consists of two main sections for demetallization of the spent catalyst: the reactor section, followed by the filtration and drying section.
The simplified process flow diagram is shown in Fig. 8.
In the reactor section, the metals on the catalyst are oxidized, sulfided, and chlorinated. The volatile iron and vanadium chlorides are vaporized from the catalyst, and the nickel and sodium chlorides are washed from the catalyst.
The process begins with the routing of spent catalyst from the FCCU regenerator to the Demet calciner reactor, where the residual carbon is removed from the catalyst. The oxidized catalyst flows by gravity to the sulfiding reactor, where it is sulfided with refinery-provided H2S.
Here the metal oxides produced in the calciner are converted to metal sulfides. The sulfided catalyst then flows by gravity to the sulfided catalyst cooler where it is cooled with nitrogen.
The cooled catalyst mixture flows to the chlorinator reactor where the metal sulfides are converted to metal chlorides by the injection of chlorine. The catalyst is cooled before flowing to the wash vessel.
At this point, the filtration and drying section begins.
The catalyst slurry flows to the catalyst belt filter where it is sprayed with water. The resulting filtered catalyst cake is sent to the flash drier.
The dried demetallized catalyst is then sent to either Demet catalyst storage or to the FCCU through the existing regenerator catalyst make-up system.
The calciner flue gas, together with quench air from the process air compressor and FCCU flue gas from the orifice chamber inlet, is sent to the flash drier cage mill for use as the catalyst drying medium.
The sulfider overhead offgas is sent to the amine scrubber. The H2S-rich amine is sent to the refinery sulfur recovery unit in a closed piping system.
The chlorinator overhead scrubber bottoms solution is routed to the metals recovery reaction tank for pH control of the metal hydroxides. The combined solution is mixed in the concentration tank mixer, where the metals precipitate from the excess caustic.
The metal hydroxides are dried in the spray drier and sent to storage. The metal hydroxides will be sold to a metal reclaimer.
UTILITIES AND CHEMICALS
The new Demet unit will require electric power and natural gas. Adequate capacity has been arranged for the supply and distribution of all other utilities.
Stripped sour water will be used for all process applications. Fresh water will be used as a backup to the stripped sour water system. Process and instrument air will be supplied by a new air compressor dedicated to this unit.
Chemicals required for the process are hydrogen sulfide, caustic, chlorine, and nitrogen.
Hydrogen sulfide will be supplied from the existing amine regenerator. Caustic (50 Baume NAOH) and chlorine will be supplied from an outside source.
A 60 scfm pressure swing absorption (PSA) nitrogen system will be used to supply the required nitrogen for cooling and purging purposes. The PSA system will provide 99.5 wt % nitrogen.
A small liquid nitrogen tank will be used as a backup.
OPERATING COSTS
Table 2 presents estimated operating costs for the Demet unit at the Derby refinery.
Variable operating costs for the unit are based on the following:
- The normal total electric power requirement for the Demet unit is 300 kw.
- Fuel requirements for natural gas are 1.00 MMBTU/hr.
- Hydrogen sulfide feed to the sulfider reactor is 23.33 scfm with composition by weight of 85.8% H2S.
- Caustic soda (NaOH), 50 Baume requirement is 104 lb/hr.
- Chlorine requirement is 62.5 lb/hr.
- Nitrogen requirement will be provided by an on site 60 scfm PSA system. The PSA system requires electricity only and is included in the total power requirement of the unit.
Fixed costs for the unit are based on the following:
- Manpower for the operation of the unit consists of one operator per shift plus one breaker, for a total of five operators.
- Miscellaneous operating supplies and maintenance are estimated at $107,000/year. Ad valorem tax and insurance are estimated at $75,000/year.
ENGINEERING/CONSTRUCTION COSTS
The engineering for the Derby plant has been performed by Talbert & Associates, and the construction cost, including escalation and contingencies, is $6-7 million.
REFERENCE
- Elvin, Frank J., "Long Term Effects of FCCU Catalyst Demetallization," American Institute of Chemical Engineers summer national meeting, Aug. 19-22, 1990, San Diego.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.
