Tight Oil Distillate in ULSD Production, What To Expect?

Transcription

1 Tight Oil Distillate in ULSD Production, What To Expect? Greg Rosinski Hydrotreating Technical Service Engineer Brian Watkins Manager, Hydrotreating Pilot Plant and Technical Service Engineer Charles Olsen Director, Distillate R&D and Technical Service Advanced Refining Technologies Chicago, IL, USA Global growth in distillate demand has driven refiners to maximize their middle distillate yield while trying to manage final product properties such as cold flow properties, color, and cetane. This has been coupled with the availability of new domestic and unconventional crude oil sources and the global disparity in hydrogen cost and availability. This has given some refiners a unique opportunity to exploit different catalytic routes to maximizing middle distillate production. Catalytic solutions to increase middle distillate yield while controlling final product properties include hydrotreating, hydrocracking, and hydrodewaxing. Each of these routes present challenges in terms of hydrogen consumption, yield shifts, changes in cycle life, and the chemistry involved. In addition to new sources of crude, the price of natural gas in the North America has decreased and is significantly lower than the rest of the world (Figure 1). This has given North American refiners an incentive to pursue volume gain due to the reduced cost of hydrogen derived from natural gas. Furthermore, worldwide demand for distillates has grown, and the U.S., while still a net importer of crude oil, has become a net exporter of refined products due in part to a competitive cost advantage in hydrogen (Figure 2). ULSD comprises the largest amount of net exports, with most of the balance being gasoline and jet fuel. Thus, U.S. Refiners have been utilizing their competitive advantage in fuels production as the relative price of natural gas has fallen. In the last decade new sources of crude have also come on the market (Figure 3). Most of the increase has come from bitumen derived synthetic crudes from Canada or more recently from shale oil formations, principally Bakken and Eagle Ford. Since 27 almost one million barrels of new synthetic crude from Canada has become available and shale formations have provided over two million barrels of additional crude to the North American market. Almost all of the new crude to come to market is captive to North America. Refiners have eagerly tried to utilize these new sources of crude due to pricing and availability, which has lead to enhanced profitability for refiners who have access to these new crude sources. Grace Catalysts Technologies Catalagram 23

2 USB/MMBTU /1/24 7/1/24 1/1/25 7/1/25 1/1/26 7/1/26 1/1/27 7/1/27 1/1/28 7/1/28 1/1/29 7/1/29 1/1/21 7/1/21 1/1/211 7/1/211 1/1/212 7/1/212 1/1/213 Germany, NG Japan, LNG United States, NG FIGURE 1: World Natural Spot Natural Gas Prices Jan-4 Jul-4 Jan-5 Jul-5 Jan-6 Jul-6 Jan-7 Jul-7 Jan-8 Jul-8 Net Crude Oil Imports Jan-9 Jul-9 Jan-1 Jul-1 Jan-11 Jul-11 Jan-12 Jul-12 Jan-13 Jul-13 7/1/213 Net Refined Product Imports FIGURE 2: Net US Imports of Crude Oil and Refined Petroleum Products Mbbls/Day 1,6 1,4 1,2 1, May-5 Bakken Eagle Ford Jan-14 1/1/214 Oct-6 Feb-8 Jul-9 Nov-1 Apr-12 Aug-13 Dec-14 Lt. Synthetic Oil Sands Heavy FIGURE 3: Canadian Synthetic Crude Supply and U.S. Tight Oil Production The rapidly increasing availability of tight oils like Bakken and Eagle Ford have given rise to questions about the impact these crudes may have on processing units in the refinery. The questions include concerns regarding the cold flow properties, ease of processing and hydrogen consumption implications. With these questions in mind, Advanced Refining Technologies completed a study which investigated the effects of tight oil compared to a conventional crude diesel cut. The study also included LCO blends, to gain an understanding of the differences this would have on distillate hydrotreater performance. Table I summarizes the properties of the various feeds used in the study. Notice that the cloud point of the Bakken feed is not very different from other light sweet crude blends in the mid-continent region of the U.S. Also, note that the aromatics content is similar to other straight run (SR) material with similar gravity. This would indicate that the heat release should be similar to other light sweet crudes such as WTI or Brent (Table II). The sulfur content of the Bakken feed is low, and the fraction of hard sulfur is higher than expected. Furthermore, the cetane index is similar to the reference SR which is expected from similarities in API gravity and aromatics content. The analytical testing showed trace amounts of silicon in the Bakken diesel; all other contaminants were below the detection limit. ART used its newest high activity nickel molybdenum (NiMo) catalyst, 545DX for this study. 545DX is made using a new proprietary alumina technology which enhances the activity derived from ART s DX metals technology platform. This has resulted in a substantial increase in HDS, HDN, and aromatic saturation, over the previous generation of NiMo catalysts. NiMo was chosen for this study as many refiners have shown a preference for volume swell over the concern of increased hydrogen cost. The test was conducted at 15 psi hydrogen partial pressure and 1.1 LHSV with 28 scfb H 2 /Oil. The LCO used in both blends was from the same source. The Bakken diesel cut was from a refiner who was processing a high percentage of Bakken crude in the refinery. The straight run (SR) and LCO both came from a midcontinent refiner processing crudes from Canada. Figure 4 shows the HDS activity for each feed. At these conditions, both the SR and Bakken SR met the 1 ppm product sulfur specification at relatively low temperatures. Notice that the SR is significantly more difficult to treat requiring 2-3 F higher WABT compared to the Bakken diesel. Interestingly, the addition of LCO to the Bakken SR had a much greater impact on HDS catalyst performance than the LCO addition to the reference SR. The difference in required temperature narrows substantially to only about 2-25 F with the addition of 3%LCO. The reference SR/LCO blend required about 3 F higher temperature to achieve 1 ppm sulfur compared to the SR alone, while the Bakken/LCO blend required about 5 F higher temperature compared to the Bakken SR. As typical for many ultra low sulfur diesel (ULSD) 24 Issue No. 114 / 214

3 SR SR + 3% LCO Bakken Bakken + 3% LCO Gravity, API Sulfur, wt.% Nitrogen, wppm Total Aromatics, vol.% PNA (2 + ring), vol.% Cloud Point, F Cetane Index (D976) ASTM Color L1 L5 L5 L3 Distillation (ASTM D86) IBP, F , F , F , F , F , F FBP, F Sulfur Speculation Gasoline Range Sulfur, wppm Benzothiophene, wppm C 1 -Benzothiophene, wppm C 2 -Benzothiophene, wppm C 3 -Benzothiophene, wppm C 4 +Benzothiophene, wppm Dibenzothiophene, wppm C 1 -Dibenzothiophene, wppm C 2 -Dibenzothiophene, wppm ,6-Dibenzothiophene, wppm C 3 +Dibenzothiophene, wppm % Hard Sulfur TABLE I: Feedstock Properties Product Sulfur, wppm Bakken Brent Cut Range See Table API Sulfur, wt.% TABLE II: Properties of Brent and Bakken Diesel FIGURE 4: Comparison of HDS Activity Grace Catalysts Technologies Catalagram 25

4 units, the product nitrogen was low. Even at modest temperatures, all the feeds were below 1 wppm nitrogen, and once the 1 wppm sulfur specification was met, all were <.5 wppm nitrogen. Figure 5 compares the total aromatic saturation of the Bakken feeds. The temperature for maximum aromatic saturation of the straight run Bakken is slightly lower compared to the Bakken/LCO blend, and the conversion is significantly higher. As shown in Table I, the nitrogen content of the LCO blend is nearly three times higher than the SR Bakken which inhibits aromatic saturation reactions. Also, the LCO blend has a higher aromatics content, which reduces the outlet H 2 partial pressure due to the higher hydrogen consumption, which affects equilibrium and limits conversion. The overall effect is the maximum saturation conversion occurs at 1-15 F lower temperature and is almost twice as high with the SR Bakken. Figure 6 compares the aromatics saturation on all the feed blends. The reference SR and Bakken SR both exhibit similar aromatics saturation curves as temperature is increased. The Bakken SR appears to have higher conversion in the kinetically controlled regime, probably due to the lower nitrogen and sulfur content n the feed. The SR/LCO blend behaves similar to the Bakken/LCO blend in terms of aromatic saturation although there are some differences at higher temperature perhaps indicative of different aromatic species. Figure 7 compares the PNA saturation in the Bakken feeds. The PNA conversion on the SR Bakken is nearly 1% until thermodynamic equilibrium is reached and limits conversion. The PNA conversion on the Bakken/LCO is always lower and reaches a maximum of about 94%. Once the aromatic conversion thermodynamic equilibrium is reached, there is a fairly rapid drop off in conversion as temperature is increased. This is what is expected near the end of run in a commercial ULSD unit, and often leads to product color problems. Total Aromatic Conversion, vol.% 7.% 6.% 5.% 4.% 3.% 2.% 1.%.% -1.% -2.% Bakken Bakken + LCO FIGURE 5: Total Aromatics Saturation on Bakken Diesel Total Aromatic Conversion, vol.% 7.% 6.% 5.% 4.% 3.% 2.% 1.%.% -1.% -2.% FIGURE 6: Total Aromatic Saturation for All Feeds Figure 8 compares the PNA conversion on all the feeds tested. It is interesting to note that the PNA conversion when processing the Bakken feeds decreases more rapidly and approaches equilibrium sooner than the other feeds. This is likely due to a difference in the PNA distribution in the Bakken crude. It is generally accepted that PNA conversion has an influence on product color, and in particular, three ring aromatics have been shown to significantly impact product color 1. Since the PNA conversion decreases faster with increasing temperature when processing the Bakken blends, the product color achieved from each of the blends was also investigated. Figure 9 summarizes the product color for each of the feeds that were tested. As observed with the PNA conversion, both the Bakken straight run and the reference SR show a similar change in product color with increasing reactor temperature. However, the Bakken SR product PNA Conversion, vol.% 11% 1% 9% 8% 7% 6% 5% Bakken Bakken + LCO FIGURE 7: PNA Conversion on Bakken Diesel 26 Issue No. 114 / 214

5 PNA Conversion, vol.% 11% 1% 9% 8% 7% 6% 5% FIGURE 8: PNA Conversion on all Four Feed Blends ASTM Product Color FIGURE 9: Comparison of Product Color Processing Various Feed Blends API Gain color begins to increase at a lower temperature compared to the reference SR. This is consistent with the PNA conversion shown in Figure 8. Adding LCO to the SR feeds results in higher product colors even for lower temperatures. The temperature at which the product color begins to degrade further is also lower for the LCO blends consistent with the behavior described for PNA conversion. Figures 1 and 11 show the API gain and the cetane lift respectively. As might be expected, the Bakken SR shows the lowest API and cetane lift, which is due in part to the lower sulfur level which is about 1% of that in the reference SR. Even though the total aromatic content of the Bakken feedstock is similar to that of the reference SR feed, the lower feed sulfur is a driving force for lower API upgrade and volume swell. Interestingly, the API increase and cetane lift of the reference SR and the Bakken/LCO blend are almost the same. This is due in part to a greater shift in distillation shift caused by the LCO, as cetane is a function of both API and distillation. The LCO blend also has much higher PNA content which plays a role in API and cetane improvement as well. For the most part, hydrotreating does not change the cloud point substantially. This testing confirms that over the typical operating range, the cloud point stays within a fairly narrow window of +/- 5 F of the feed. Both LCO blends have products with cloud points a few degrees above the feed. The LCO blends must contain naphthenic type species that have a higher cloud point than the feed. All the feed blends show a decrease in cloud point as the temperature increases substantially from start of run. This may be indicative of some cracking that occurs at high temperatures converting molecules with higher cloud points to molecules with lower cloud points. This data does show that the cold flow properties of Bakken are not significantly different than the other feeds in this study. With the concern over the cold flow properties of tight oils it is worthwhile to examine how they compare to other crudes, including some synthetic crudes (Table III). Looking at the assays of several well known crudes, the cloud points of the diesel fractions vary between 15-3 F depending on the source, and the Bakken appears to be no different. The interesting thing to note is the low cloud points of the Canadian synthetic crudes. Canadian synthetic crudes are typically produced with some form of hydroprocessing and or coking so they have higher amounts of naphthenes; thus, these crudes have lower cloud points, compared to conventional crudes. If it made sense for the refiner and they were cloud point constrained, then switching to some synthetic crude may be a sound choice, as opposed to using a dewaxing catalyst which will increase naphtha yield at the expense of distillate yield 3. This would have to be balanced against the economics of the refinery as a whole. FIGURE 1: Difference in API Increase Grace Catalysts Technologies Catalagram 27

6 Crude Cutpoints ( F) Cloudpoint ( F) Conventional Bonny Light Brent Dubai Forties Ural Southern Green Canyon Blend Maya Canadian Synthetic Cold Lake Kearl Western Canadian Select Blend Synbit SHB (Surmont Heavy Blend) TABLE III: Cloud Point of the Diesel Fractions of Various Crudes SR SR/LCO Bakken Bakken/LCO WABT Base +33 F -41 F +1 F API Change Sulfur, wppm Nitrogen, wppm Total Aromatics, vol.% PNA, vol.% Cetane Lift Delta Cloud H 2 Consumption, SCFB TABLE IV: Comparison of Product Properties at 1 wppm Sulfur Table IV compares the product properties from all the feeds at a product sulfur of 1 wppm. As expected, the Bakken diesel has a very low temperature for 1 wppm product sulfur. This is primarly due to the low feed sulfur, which is approximately.1 wt.%, whereas the other feeds have sulfur levels closer to 1 wt.% or greater. The cetane lift and API gain of the Bakken are also noticeably lower compared to the other feeds. All of these indicate lower hydrogen consumption for the Bakken SR compared to the other feeds. A breakdown of the hydrogen consumption at constant product sulfur by compound type is shown in Figure 13. The lower required temperatures shown in Table III result in much lower total aromatic and PNA saturation for the Bakken SR feed. This, combined with the very low sulfur conversion required to achieve 1 ppm product sulfur, contributes to the lower overall hydrogen consumption. It is expected that most refiners will be blending in LCO and/or light coker gas oil which will increase the hydrogen consumption over the Bakken SR feed. The Bakken/LCO blend appears to behave API Gain FIGURE 11: PNA Comparison of Cetane Uplift Issue No. 114 / 214

7 Cloud Point Change (Product - Feed), F FIGURE 12: Change in Cloud Point of the Various Feed Blends Estimated Hydrogen Consumption, SCFB SR Sulfur SR/LCO Bakken Bakken/LCO Nitrogen Total Aromatics PNA FIGURE 13: Comparison of Hydrogen Consumption at 1 ppm Sulfur 16 much like the reference SR feed in terms of SOR temperature and hydrogen consumption. The lower hydrogen consumption with the Bakken SR feed may cause a heat balance issue if the unit was originally designed for processing feed from a heavier crude slate, and the Bakken displaced some of the heavy crude. Figure 14 compares the heat release for the different feeds. Consistent with the hydrogen consumption just discussed, the heat release from the Bakken is significantly lower than that for the other feeds, and the Bakken/LCO looks similar to the reference SR feed. As with any crude change, Bakken can present some challenges depending on the refinery configuration. However, diesel derived from Bakken crude appears from this analysis, to be similar to other light sweet crudes in terms of feed characteristics and its behavior during hydrotreating. If the refiner is prepared for crudes similar to Bakken, then there should be minimal problems in processing Bakken crude. There may be opportunities for catalyst selection to help maximize performance when processing this or other opportunity crudes. Advanced Refining Technologies LLC has the ability to conduct detailed customer-specific pilot plant testing to provide the refiner the confidence and understanding of the various options available when considering a catalyst change. Both the hydrotreating catalyst system and the operating strategy for the ULSD unit are critical for providing the highest quality products. Use of tailored catalyst systems can optimize the ULSD hydrotreater in order to produce higher quality products while utilizing the greatest flexibility of feedstocks. The complex relationship between hydrotreater operation and catalyst kinetics underscores the importance of working with a catalyst technology supplier that can tailor product offerings for each refiner s unique operating conditions. This knowledge enables ART to meet the refiner s objectives and maximize revenue. Estimated Heat Release, BTU/bbl References 1. Rosinski, G., C. Olsen and B. Watkins, Factors Influencing ULSD Product Color, Advanced Refining Technologies ; Catalagram 15, Watkins, B., Olsen, C., Custom Catalyst Systems for Higher Yields of Diesel AFPM Annual Meeting, Paper AM Watkins, B., Lansdown, M., Understanding Cloud Point and Hydrotreating Relationships Catalagram 112, 212 SR Sulfur SR/LCO Bakken Bakken/LCO Nitrogen Total Aromatics PNA FIGURE 14: Heat Release at 1 ppm Sulfur Grace Catalysts Technologies Catalagram 29