A Solution for Solving the Long Term Supply of High-Quality Petroleum Coke

Transcription

1 A Solution for Solving the Long Term Supply of High-Quality Petroleum Coke Dr. Ulrich Mannweiler, Mannweiler Consulting, Zürich, Switzerland Raymond C. Perruchoud, R&D Carbon. Ltd., Sierre, Switzerland Robert Tufts, BRSI, Cocrane, Alberta, Canada Abstract With the constantly growing aluminum industry the requirement for anode grade petroleum coke is rising. The sulfur and metal content in crude oil is increasing in most oil producing areas. Brazil is an exception, where new large low sulfur oil deposits have been detected. In China, where local crude oils typically are of rather low sulfur contents, the demand for refined products is growing sharply with the fast industrialization and motorization of the country. As a consequence new refineries are importing crude oil from abroad mostly with high sulfur contents. By 2020 China will produce 50 % of the World Aluminum Production requiring large quantities of anode grade coke. One approach to reduce metals and sulphur contents during the refining process is to treat the residiuum with hydrogen at high operating pressures. This technology is well known but it is expensive in turns of investment and operating costs. In this paper we are presenting several alternatives to this process and are providing corresponding cost figures. The Middle East Aluminum Industry is growing constantly and needs more and more quality calcined coke which has to be imported. By 2015 over 1 million tons of anode grade coke will be required. The Middle East, especially Saudi Arabia possesses large crude oil deposits but all of them are sour crudes with high sulfur contents. As new refineries are built it might be attractive for the Gulf Aluminum Industry to invest in desulfurization units and coke calcining facilities that could produce and supply on the long term an acceptable aluminum grade coke to the Middle East Aluminum Industry The Growing Aluminum Industry Since decades the World wide aluminum industry is growing constantly. In the year 2000 China contributed 12 % only of the total production. By 2020 seventy million tons of primary aluminum will be produced in the World of which 50 % will come from China. 1) Figure 1: World Primary Aluminum Production Petroleum Coke an Important Raw Material To produce one ton of aluminum approximately 360 kg of calcined petroleum coke are required, a material, that must have acceptable physical and chemical properties. Especially the sulfur content and metal impurities are of importance. In the electrolytic process anodes are consumed and sulfur is emitted to the atmosphere, while metal impurities are transferred fully into the aluminum metal. Petroleum coke is produced as by-product in the refining of crude oil. As shown in Figure 2, Delayed Coking is a thermal cracking process in which the residual oil after atmospheric and vacuum distillation is converted into valuable distillate products and offgases, leaving behind a lower value green petroleum coke containing sulfur and metals contents 2). This process is widely applied in the World wide refining industry to produce mainly diesel oil. Green Coke Capacities 1) In 2010 the World wide Delayed Coking capacity was approximately 125 million tons of crude oil about 25 % of which was aluminum grade which is used to produce a calcined coke for smelters. Delayed Cokers operate typically at a 90 % capacity rate which brings the actual green coke production in 2010 to about 110 million tons of which 27 million are of aluminum grade

2 In the next five years new cokers are added in all areas of the World, raising the coking capacity to 170 million tons. Table 1: World wide Coking Capacity (million tons) To our knowledge, in Latin America those cokers will produce mainly a coke that can be used by the aluminum industry. In China many of the new cokers will use crude oil from abroad with higher sulfur levels and only few new aluminum grade coke capacities will be added. By 2015, therefore, the World wide aluminum grade coke level is expected to increase only slightly. Calcined Coke Production and Consumption Calcined coke is produced in Western countries in rotary kilns, while in China more than 50 % are produced in the so called shaft kilns 3). This technology is well adapted to green coke, that typically is fine and has a higher Volatile Maters Content VCM (10 12%). In Table 2 the total consumption of CPC for smelters (~ 85 %), as well as other consumers such as needle coke, recarburizers and TiO 2 production is listed in the different World regions 1). Table 2: Calcined Coke Production, Consumption & Balance In 2010 the World wide production and consumption was practically balanced with North America and China being an exporter of CPC. The picture changes in 2015 as to our knowledge not many new calciner projects are coming on stream except for two projects in Brazil and a shaft kiln project in India. Also new shaft and rotary kilns in China are planned. The negative balance in Europe eases a little bit as several smelters will shut down their operation, due to high operating and power cost. For the Middle East the situation remains critical as nearly one million of CPC needs to be imported. It has to be expected that this situation will even deteriorate in the years to come. Therefore, a new solution is proposed for producing quality CPC from crude oils, by applying partial desulfurization of the crude oil, as described in the chapter below: Residue desulfurization history Already in the sixties for meeting low Sulfur Fuel oil production Cities Service Research Inc. developed a residual desulfurization technology named H-oil 4) that was industrially validated at their Lake Charles refinery fed with West Texas Atmospheric Residuum. Several different oil atmospheric and vacuum residuals (from Venezuelan, Khafji Saudi and Kuwait crudes) were used to demonstrate that their process using Hydrogen and catalysts was efficient for reaching a level of 1 % S (LSFO) in the treated product at a cost below 1 USD/bbl. This H-oil process has been licensed in the seventies to Kuwait KNPC, to Humble Oil Refining Company, today EXXON in the USA, and to Mexicanos Petroleos. This RDS technology was further developed by Chevron 5) in the seventies and the Pascagoula Mississippi Texaco s refinery has installed in 1983 a large RDS unit having a capacity of 100,000bbl/day with significant economic benefits. The residuum hydrotreaters can also be used for preparing the feeds of other conversion units like the Residuum Fluid Catalytic Unit. The first unit of Chevron was installed at Phillips Borger,Texas with bbl/d capacity and reached a Hydro Desulfurization (HDS) and Hydro Demetallization (HDM) levels above 90 %, which is a must for the economics of the FCC unit, as it increases the distillate conversion dramatically and maintains catalyst consumption and cost to a low level 5). Today many hydrocracking technologies are available and the fabrication and utilization of Hydrogen in refineries is very common 6). Contrary to the expectations in the eighties the decrease in fuel oil demand and the low differential value of anode grade to fuel coke has mitigated the interest of refiners for residuum desulfurization when delayed coking in their scheme was considered 7). However in some cases, like for the Canadian refineries Husky and Consumers Co-op built in the nineties, the RDS process was installed and run with economical success. In the Middle-East the reference remains the Mina Abdullah Kuwaiti s refinery, which is processing bbl/d of heavy Kuwaiti crudes. A bbl/d RDS unit prepares the feed to the a coker unit of bbl/d capacity producing - 2 -

3 about tpy green coke that is calcined in the nearby PCIC kilns and also exported as anode grade coke of good quality (3 % S, 300 ppm V) with excellent consistency. The present and future of RDS In the Middle-East the low prices of gasoline for transport can not allow massive additional investments related to RDS and other sophisticated processes, for maximizing the distillate fractions in the refineries for the market. With the increased need in diesel the delayed coking option becomes more attractive and for refineries the production of fuel grade coke is practically a reality, like it is the case for the Jubail and Yanbu 2 export refineries project. Both refineries will be on stream in As no RDS was considered in their design the green coke produced in both refineries will be fuel grade (~ 6 % S and 600 ppm V). For such bbl/d refinery processing a blend of 50/50 Arab heavy and Arab light fuel grade coke will represent 9 %wt of the incoming crude i.e. about 1.8 MM tpy. activity is too low. The H 2 S present in the product gas phase is treated in classical Sulfur removal units. The vapor phase, therefore, is not only leaner in S and metals but also converted to lower boiling point hydrocarbons that are ending-up in the distillate fuel pool. The conversion in 350 C - valuable liquid fraction is increased by 25 to 30 % wt. The residuum percentage is massively reduced, but its lower S and metal content allows the production of anode-grade coke that is reduced by a factor of 3 as shown in Figure 3. The resulting coke has 2.5 % S and < 100 ppm V content. This corresponds to a premium purity anode grade coke comparable to the purest high price European cokes that are representing today a tiny 5 % portion of the anodegrade coke market. Figure 2. Middle East Refinery for domestic fuels. As much higher export prices of distillates as well as higher recent prices for anode-grade coke are expected, the RDS process is a real option for the export refineries planned in the future. This is especially valid for the Middle-East region, where Aluminum production is booming, and as shown above, a negative coke balance of over 1 million ton has to be expected by The RDS unit can easily achieve a reduction of 90 % of the Sulfur in the resid and 50 % for Nitrogen and 30 % in asphaltenes that are responsible of poor coke isotropy (shot coke). Large scale Hydrogen production is made in the refineries for other hydroprocesses on distillates by steam-methane gas reforming at 800 C. By the hydrogen injection of typically 200 m 3 /t feed, cracking of heavy molecules in reactors with catalysts will significantly increase the high value distillates. V and Ni impurities remain on the catalyst surface that will be replaced when its catalytic Figure 3. Complete resid desulfurization for export fuels and premium anode coke. The option of complete desulfurization of the resid is probably a costly overkill solution, as the high investment and operational cost are basically not needed for a production of regular anode grade green coke that is today over the 3% S and 300 ppm V thresholds. Therefore, a partial desulfurization and demetallization of the resid as shown in Figure 4 is probably more appropriate. In this example we consider a refinery of bbl/d or 20 million tons of crude oil as feed stock. Figure 4. Partial resid desulfurization for export fuels and regular anode coke

4 In this 60 % ARDS case, the S in the green coke is still below 4 % so that after calcining, we can expect a coke with a 3.5 % S and 350 ppm V contentl. This intermediate option will significantly reduce the investment cost (down-sizing of all RDS units) and will reduce proportionally the catalyst and H 2 costs as well. The produced coke is a regular green coke material and the available quantity rises to 1.1MM tpy of green coke and 0.9 MM tpy of calcined material, which is good news for the Al industry but also for the refineries, as a partnership venture can be imagined for this scenario. Coke Calcination The green coke produced in the refinery has to be calcined to obtain a material that can be used by the aluminum industry for anode manufacturing. There exist two calcining technologies 2), i.e. the Rotary Kiln process with typical capacities of about ½ million tons and the Shaft Kiln technology with capacities of tons per kiln where multiple kilns are built in series. Both technologies are widely applied with Rotary Kilns mainly built in the Western World and Shaft Kilns in China. Depending on the refinery regarding delayed coking operation, a green coke may have properties (Volatile Combustible Matters, VCM) and Fines Content that are better suited for Rotary Kilns (VCM < 10 % and relatively coarse material) and Shaft Kilns (VCM > 10 % and high amount of Fines). Therefore, at this time it can not be decided which calcining technology will be applied prior to the refinery has made a decision on how to operate the Delayed Coker. For both technologies the waste heat energy generated during the calcination process can be recuperated. Rotary kilns produces 25 % more energy than shaft kilns, due to the fact, that it needs fuel for the calcination process and burns more entrained fine coke dust in the incinerator. The energy can be used in the refinery either in form of steam ore electric power, depending on the refineries needs. If a project will be realized, a detailed feasibility study together with the refinery and the consumers of the calcined coke has to be conducted to determine the most cost effective operation. Investment and Operating Cost for ARDS. A refinery as described above treating 20 MM tpy of crude oil has a typical investment cost of 500 USD per ton or 10 billion USD. Residual desulfurization is an expensive process. For an ARDS of 100 % the investment is MM USD has to be anticipated. If only 60 % of the resid is desulfurized, the investment cost lowers to 700 MM USD. The total production cost including capital cost, hydrogen generation, manpower etc. amounts to 600 MM USD per year. However, an additional revenue of 700 MM USD can be created due to the higher yields of refined products (gas and liquid fuels) as well as the anode grade coke produced resulting in a positive desulfurization level of 100 MM USD per year. Above figures do not include the coke calcining facility which typically cost USD per ton of calcined coke. The justification for this investment, however, is to supply on long terms a consistent quality product to the Middle East Aluminum Industry that otherwise needs to be imported from sources that are not secure anymore. A Solution for the Middle East Aluminum Industry? As mentioned above the Middle East Aluminum Industry grows since its start in the mid seventies. Low energy cost and cheap qualified labor are the main advantages of this industry. Table 3: Middle East Smelting Capacity and CPC Requirement and Balance As shown in Table 3 between 2010 and 2015 the smelting capacity will double. For the time being only one potential new calciner is expected, i.e. the PCIC Calciner in Kuwait, which may add a second calciner to use in full KNPC refineries green coke production. By 2015, therefore, the import needs rises to 0.9 MM tpy. However, the World wide demand on quality calcined coke with acceptable sulfur and metal levels will increase drastically, This will have an impact on coke prices that will rise. Therefore, our proposition to produce locally green coke and to calcine it in one of the refineries makes great sense. The technology of Reisd Desulfurization exists as shown above. With its abundant oil sources the Middle East is well placed for that. Therefore, a Joint venture between the Refining and Aluminum Industry may be the Solution for Solving the Long Term Supply of High Quality Petroleum Coke to the Middle East Aluminum Industry

5 1) CRU Analysis, The Five Year Outlook for Carbon Products ,. Some of the 2015 data have been adjusted to latest industry developments. 2) Mirta Mortaghi, Kanu Shree, Sujatha Krisnamurthy, Anode grade coke from traditional crudes, PTQ Q ( 3) U.Mannweiler, W.Fischer, R.Perruchoud, A. devries, Profitable Calcining of Non-Calcinable Petroleum Coke, 9 th Jacobs Pet Coke Conference, Seattle, ) A.A.Gregoli, G. R. Artos, Hydrodesulfurization of Residuals, 27 th Conference on P and energy Need solution Control, pp.98ff., August ) D.N. Brossard, Chevron Lummus Global RDS/VRDS Hydrotreating, Transportation Fuels from the Bottom of the Barrel, Handbook of Petroleum Refining Processes by Robert A. Meyers, edited in 2003 by Mc Grw-Hill, ISBN , Chapter ) James H. Gary and Glenn E. Handwerk, Petroleum Refining, Technology and Economics, Chapter 7 on Catalytic Cracking,pp.142, edited in 2001 by Marcel Dekker Inc., ISBN: ) R. De Biase and J.D. Elliott, Coking Process Reflects Trend, Innovations, Foster Wheeler Energy Corp., Oil & Gas Journal Technology, pp April