Options for Resid Conversion

Transcription

1 Options for Resid Conversion C. Plain, J. Duddy, S. Kressmann, O. Le Coz, K. Tasker Axens 89, bd Franklin Roosevelt - BP Rueil Malmaison Cedex -France Tel.: Fax: Axens North America, Inc 650 College Road East, Suite 1200 Princeton, NJ USA Tel.: Fax:

2 Options for Resid Conversion C. Plain, O. Le Coz, Axens; K. Tasker, J. Duddy, Axens NA; S. Kressmann, IFP Introduction Market demand for residue upgrading upgrading is of increased interest among refiners due to a continued strong decrease in demand for high sulfur fuel oil (HSFO) and a robust demand for higher volumes and quality of middle distillates (Figure 1). Figure 1: Increased world demand for lighter products Light products 34% 37% 38% Middle distillates 34% 38% 41% Heavy products 32% 25% 21% Refiners can purchase low sulfur crudes (LSC) to reduce the amount of HSFO produced, but the price differential between high sulfur crude (HSC) and LSC is substantial and not the most economic solution in the mid-to-long term. Although contracting for a supply of HSC requires significant investments in desulfurization or conversion units, it enables the refiner to market low sulfur fuel oil (LSFO) or ultra-low sulfur fuel oil (ULSFO) which attract a market premium, as shown in Figure 2. This crude price difference offers an incentive to invest in deep conversion units that also produce high value added middle distillates. Figure 2: HSFO differential price, $/t jan-97 jun-97 nov-97 apr-98 sep-98 feb-99 jul-99 dec-99 may-00 oct-00 mar-01 aug-01 jan-02 jun-02 Diesel Ultra Low sulfur fuel Low sulfur Fuel

3 upgrading options The technology options available for residue upgrading depend on the difficulty of the feed to be processed, whether it is atmospheric (AR) or vacuum residue (VR), the metal contents and the level of conversion desired. Fixed bed ARDS and VRDS technologies, such as Axens Hyvahl TM process, associated with the R2R TM, a residue fluidized catalytic cracker (RFCC) are employed to afford high conversions to middle distillates and gasoline having attractive sulfur levels and cetane numbers. Ebullated bed technologies, such as H-Oil R, are more suitable for feeds with high metals contents and when moderates to high conversions are desired. Figure 3 presents how to select the technology versus the objectives and quality of the feed. 400 Figure 3: Technology selection Metals 300 in Feed 200 (wt ppm ) 100 Hyvahl H-Oil Conversion (wt%) These options are able to cover the entire range of residue feeds by employing unique combinations of commercially proven operating modes and well-adapted graded catalyst systems while maintaining constant product quality. The ebullated bed technologies offer the added advantage of not having the run length limits that conventional fixed-bed reactors have. This is because catalyst is continuously withdrawn from and added to the unit. The cycle length becomes the periods between refinery turnarounds. But the level of desulfurization of ebullated bed technology is a little bit lower (70 to 85 wt%) compared to fixed bed (85 to 95 wt%). This article presents two commercial cases of residue conversion as a function of the crude type. Case 1: A combination of the Hyvahl and R2R technologies processing Arabian Light Vacuum (VR). The vacuum residue desulfurization unit (VRDS) employs a graded combination of HMC 841, HT 318 and HT 328 catalysts with the objective of either producing ultra-low-sulfur fuel oil (ULSFO) having a sulfur content of 0.3 to 0.5 wt% or pretreating the R2R feed, producing zero fuel oil. Case 2: Application of the H-Oil technology on Ural vacuum residue for over 50% feed conversion to higher value middle distillates and production of a low-sulfur fuel oil (LSFO), containing less than 1 wt% sulfur, for utilization in a power station. 2

4 Case 1: Zero Fuel Refinery with R2R and Hyvahl VRDS This scheme provides a further step towards the near-zero fuel production by adding a Hyvahl unit to pretreat the R2R feedstock. Hyvahl process description: This unit consists of a Permutable Reactor System (PRS), based on two permutable hydrodemetallization reactors, followed by four single bed hydrodemetallizationhydrodesulfurization-hdm-hds reactors (Figure 4). Figure 4: Hyvahl process flow diagram This arrangement facilitates reaction section temperature control as well as the loading and unloading catalyst from the reactors. During the run, both the pressure drop and the quantity of metals removed in the lead (permutable) reactor increase. When one of these reaches its threshold value, a switch occurs. With the PRS technology, the HDS catalyst is well protected from premature deactivation because the PRS ensures a reduced and constant level of contaminants throughout the cycle. This refinery scheme as shown in Figure 5 is a good example of residue upgrading via the Axens technology portfolio: high pressure hydrocracking (HP HDC), mild hydrocracking (MHDC), Hyvahl and fluidized bed residue catalytic cracking (R2R). The Hyvahl unit was put on stream in 1995 using Arabian Light residue (Vacuum or blended with atmospheric residue) feedstock. The hydrotreated residue was mixed with the MHDC residue as feed for the R2R unit. The level of conversion to 565 C - distillates was varied over a large range throughout the catalyst cycle: from 25% at the start-of-run (SOR) to 55% at the end-of-run (EOR). In this scheme, the C VGO cut is not separated from the 565 C + vacuum residue and the entire 370 C + cut is sent to RFCC. The RFCC therefore processes both hydrotreated VGO from the MHDC unit and hydrotreated vacuum residue. The only product used as fuel is the clarified oil obtained by filtration of the RFCC slurry. This can be completely consumed as refinery fuel. Representing less than 3.5% of the crude, it has a moderate sulfur content of around 0.5 to 0.8 wt%. Minor amounts of LCO make up the balance of the refinery fuel requirement. 3

5 Figure 5: Refinery block flow diagram GO 8000 bpsd S < 400 wppm bpsd HP HDC GO+Jet bpsd S < 5 wppm VDU bpsd S=2.6% MHDC HR400 Series bpsd S=0.08% Gasoline bpsd S < 60 wppm bpsd S=4.4% Hyvahl VRDS HMC/HT GO 5000 bpsd S < 350 wppm bpsd S=0.5% bpsd S=0.3% R2R LCO 7000 bpsd S <0.5 % Slurry to refinery FO 3500 bpsd S < 0.8% The concluding advantage of the Hyvahl unit is that its high flexibility and PRS system enable the refiner to produce three different kinds of fuel oil which greatly assists in meeting market needs for a period of at least 11 months of continuous operation on 100% VR feed. The fuels are produced by the following HDS operating modes: 100% vacuum residue, BPSD, that produces wt% sulfur feedstocks for the RFCC unit at moderate conversion and efficient removal of metals and Conradson Carbon (Cycle 4 on Figure 6). 50% vacuum 50% atmospheric residue to increase the capacity to BPSD, that performs HDS to produce 0.5 wt% sulfur LSFO (Cycle 5 on Figure 6). 35% vacuum 65% atmospheric residue desulfurization unit, BPSD, that performs HDS to produce ULSFO at 0.3 wt% sulfur (Cycle 6 on Figure 6). The characteristics of the three feedstocks are presented in Table 1. Table 2 shows the main 370 C + product qualities. Table 1. Typical characteristics of Hyvahl unit feedstocks Middle East Blend 100 % Vacuum Blend Atmospheric / Vacuum Blend Atmospheric / Vacuum Specific Gravity C, cst Sulfur, wt% Nitrogen, wt ppm Conradson Carbon, wt% Asphaltenes, wt% Metals (Ni+V), wt ppm

6 Table 2. Typical characteristics of Hyvahl unit 370 C + effluent Middle East Blend 100 % Vacuum Blend Atmospheric / Vacuum Blend Atmospheric / Vacuum 100 C, cst Sulfur, wt% Conradson Carbon, wt% Metals (Ni+V), wt ppm The results of the last four cycles of this unit are compared based on a given VR feedstock. Cycle 3 employed a conventional HDS catalyst while the last three cycles (Cycles 4 to 6) used a catalytic system composed of Axens HT 318 and HT 328 catalysts. The excellent stability of the HT series catalytic system is apparent (Figure 6). Figure 6: Comparison of HDS catalyst activity for cycles 3 to 6 - Normalized for 100% VR Cycle 6 with Axens catalytic system Cycle 5 with Axens catalytic system Cycle 4 with Axens catalytic system HDS Catalyst Activity Cycle 3 with Conventional HDS catalyst Months On-Stream The catalyst stability is greatly improved for the last three cycles in comparison with the conventional catalyst whose activity dropped dramatically at mid-of-run and, as a result, the operators had to relax the sulfur specification while processing lighter feedstock. Catalyst stability expressed as the temperature required for constant product sulfur (0.5 S % wt) is illustrated in Figure 7. Figure 7: HDS catalyst stability - Aging curve for constant 0.5% sulfur in product EOR Temp. Delta = 25 C SOR Temp. HDS: HT318/HT328 Conventional HDS Catalyst Axens Catalyst Run with 100% VR Months on Stream 5

7 During the previous run the deactivation rate of the conventional HDS catalyst was over 5 C per month. When the temperature necessary to maintain 0.5% wt sulfur in the residue exceeded the reasonable EOR temperature (around Base + 40 C), the product could no longer be kept on-specification, the unit entered the "Off-Spec Product Zone" and the resultant product properties started to change. During this period, the run continued with a off-spec product. Figure 7 shows how the deactivation rate was reduced significantly by the use of the Axens catalytic system. In Cycle 4, the monthly temperature increment was only 3 to 3.5 C (from SOR until EOR). The lower industrial deactivation rate confirms on commercial scale the results of the intensive pilot tests made on the same feed in IFP pilot center at Solaize. Axens has the tools to accurately predict catalyst-aging rates in an industrial context. Figure 8 compares pilot temperatures with those observed in this commercial unit. Figure 8: Comparison between pilot tests and commercial results EOR 3.5 C / month SOR Commerciall results Pilot tests on Axens HDS catalytic system Catalyst Age, hrs At the time of this writing, Cycle 6 achieved 12 months of continuous operation, meeting product sulfur specifications that alternated from 0.3 to 0.6 wt% according to the refiner s market requirements with no catalyst over-deactivation due to the different severities employed. The next new cycle will commence with the same Axens catalytic system (HMC 841, HT 318, HT 328). A new Hyvahl unit, similar to this one, will be started up on the same site at the end of 2002 using the same catalytic system. In Hyvahl units, owing to a constant performance of the HDM section (using the Permutable Reactor System), the run duration is only limited by the HDS section. The good stability of Axens HDS catalysts enables the unit run length to be increased by two to three months compared to conventional HDS catalytic systems on the market. It thus becomes possible to achieve 12 to 13 month cycles using heavy feeds (100% vacuum residue) with at least 11 months at constant product quality. In the case of low severity objectives (0.8 to 1.0% wt. sulfur in the residue) as well as in the case of atmospheric resid processing, cycles of 15 months are now possible. The Hyvahl process has demonstrated through ten years of cumulated operation its capacity to upgrade atmospheric and vacuum residues successfully. Significant benefits are achievable in terms of cycle length and catalyst consumption using the new HDS catalytic system. Furthermore, newly developed catalysts of the Axens 400 series are undergoing testing and show promising results. 6

8 Case 2: Hydrotreating and conversion of difficult feedstocks H-Oil - PKN Orlen Refinery scheme Needing to convert residue and remove sulfur, refiners are turning to residue hydroprocessing, especially ebullated beds for difficult feedstock such as Ural vacuum residue, as shown in Table 3. Table 3: Typical characteristics of Ural H-Oil unit feedstock URAL CRUDE 100 % Vacuum Specific Gravity Sulfur, wt% C, cst Nitrogen, wt ppm Conradson Carbon, wt% Asphaltenes, wt% 6 9 Metals (Ni+V), wt ppm The H-Oil ebullated bed process can operate over a wide range of conversion levels and is particularly adapted to heavy vacuum residues with high metals and Conradson Carbon. Another major advantage of H-Oil is the maintaining of constant product properties during long cycles, the objective being to fit with the FCC operation periods. The latest H-Oil unit to start up was at the PKN Orlen s Plock refinery in Poland. This BPSD refinery is located about 100 km north of Warsaw. PKN Orlen was required to meet new sulfur emissions standards in its 250 MW power plant by This power plant provides steam and electricity for the refinery and steam for the town of Plock in the winter. As a consequence the power plant fuel oil demand is seasonal (Figure 9). Figure 9: Refinery block flow diagram at high conversion level VDU SRVGO HP HDC GO to pool FCC Gasoline LCO HCO to HOil GO bpsd S< 1000 ppm bpsd S=2.8% H-Oil Conversion 66% Vol LVGO+HVGO 12000bpsd S # 3900 ppm VR bpsd S <1 % POWER PLANT 7

9 The H-Oil unit designed by Axens for PKN Orlen is a single train, two-stage plant with a catalyst rejuvenation unit planned for the future. This unit will allows the fresh catalyst makeup rate to be reduced by 45% with a corresponding reduction in the spent catalyst produced by the plant. The spent catalyst will ultimately have a higher metal loading making it more desirable for a metal reclaimer. H-Oil process description: Figure 10: Two-stage H-Oil process The conversion level of the 538 C + residue into distillates varies from 52% to 68 vol% to meet seasonal fuel oil demand. The main difficulty with this feed is to reach the conversion and product quality levels while maintaining product stability by minimizing sedimentation. Various process and design solutions are available in the H-Oil unit including catalyst and operating conditions. The use of the second generation high-conversion catalyst provides improved product qualities; the sulfur content in the residue is maintained below 1.0 wt% for both conversion levels and sediment formation and fouling are reduced. One process step to increase the conversion level at a given fresh feed rate and given temperature level involves to recycle the vacuum tower bottoms stream (VBR). This reduces both light gas yield and sediment formation. Another process solution is to inject FCC slurry oil at a key point in the process. This highly aromatic oil peptizes the otherwise unconverted asphaltenes resulting in reduced fouling rates that are characteristic of high conversions. In this way, the refiner is able to upgrade low valuable slurry oil into high quality distillate. The PKN Orlen H-Oil plant started up in October 1999 and within a few weeks processed the design feedrate at approximately 50-55% conversion. Overall performances (HDS, HDN, etc.) have been achieved at or better than design. All H-Oil process guarantees were achieved for both the summer (52% conversion) and the winter (66% conversion) operations. A summary of the operating conditions, process performance, yields and product qualities is shown in tables 4 and 5. 8

10 Table 4 - PKN Orlen H-Oil plant operating conditions and process performance Yields on feed 52% vol conversion 68% vol conversion Feedrate, BPSD Catalyst Addition Rate C 0.7C Temperature, C T T+8 Hydrodesulfurisation, wt% Nitrogen removal, wt% CCR Conversion Demetallisation, wt% Table 5 - PKN Orlen H-Oil Plant yields and key product qualities Diesel ( C), wt% Sulfur, wppm VGO ( C), wt% Sulfur, wppm Nitrogen, wppm Vac Res (538 C + ) Sulfur, wt% CCR, wt% 52 vol % Conversion 68 vol % Conversion The 68% conversion operation was conducted at a lower catalyst usage rate since the required product quality, specifically vacuum residue product sulfur, was less severe. Over 80 wt% HDS was achieved for both the summer and winter operations. The H-Oil process results in a high selectivity towards diesel product. In this case, the diesel yield is in the range of 25 to 29 wt% and increases with the conversion level. The quality of the distillates and unconverted residue are excellent considering the difficult nature of the Ural vacuum residue and the relatively high conversion attained. During periods of low fuel oil demand, the refinery will operate at the higher conversion mode and produce greater quantities of high value diesel oil. This matches the transportation demand, which is typically the highest in the summer months. In the future, sulfur specifications are expected to tighten but the H-Oil unit will have the flexibility to produce 0.6% sulfur in the residue fuel oil through adjustments in operating conditions. Effluents post- treatments The tightening sulfur specifications, especially in Europe and the United States, and also the high cetane specification in Europe, will likely create a need to upgrade the converted gas oil (GO) into valuable "High Speed Diesel" (HSD) fuel. Such upgrades are challenging as GO streams from MHDC, Hyvahl or H-Oil are characterized by complex naphtheno-aromatic structures with unfavorable hydrodesulfurization kinetics. Based on long-term pilot studies and on solid experience in this field, Axens is in a position to offer tailor made solutions via 9

11 its Prime-D TM toolbox: new proprietary reactor internals -EquiFlow TM - which design enables optimized catalyst use, feedstock sulfur species, analysis kinetic modeling and advanced control. Axens was awarded four cetane-boosting units that achieve a cetane improvements between 8 and 14 numbers, and twenty-two ULSD units (50 to 10 wppm) worldwide over the last two years. All of these units will process blends of SRGO, LCO, and various diesel cuts from MHDC, VRDS or H-Oil units. Economics The following table illustrates typical inside battery limit investment for a 30,000 bpsd capacity unit. Total Pressure, bar SRVGO HDT Converted Effluent HDT Hyvahl ARDS Hyvahl VRDS / H-Oil LHSV, h -1 Base Base/1.6 Base/3 Base/6 ISBL Investment Cost, million Euros Conclusions The need for converting heavier crude oils to valuable lighter products and for producing low sulfur fuel oil will continue to encourage refiners to evaluate proven residue conversion process options. conversion and hydrotreatment units such as H-Oil or Hyvahl VRDS and FCC pretreatment (MHDC) are powerful tools that refiners can use to meet future market demands and product specifications. These tools offer solutions to address major challenges such as the decreasing heavy fuel demand, the need for low sulfur heavy fuels, reduced sulfur emissions, reduced sulfur content in gasoline, and the increasing diesel-to-gasoline ratio. Years of research and development in the field of residue hydrotreating catalysis for both ebullated and fixed bed processes allow Axens to create a real breakthrough and to bring forward a new best-in-class HDS catalytic system that pushes back the limitations of residue desulfurization processes. Moreover, the Axens catalyst and process portfolio allows refiners to meet the most stringent motor fuel specifications by its combination of conversion schemes with Prime-D hydrotreating technology. 10