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04/09/2007
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Paez Raul, Baker Energy de Venezuela, rpaez@bakerenergy.com.ve
To upgrade heavy and extra-heavy crude oils, 2 basic technological routes are known.
The criteria to select one of these routes as an upgrading option depends on several factors which must be analyzed in detail when it comes to consider a project of this nature. The technology of Hydrogen Addition produces a high yield of products and upgraded crudes with a commercial value larger than that of the carbon rejection technology, but requires a larger investment and more natural gas availability to produce the amounts of Hydrogen and steam required for these processes.
The upgrading process at the Orinoco Belt is based on the use of Delayed Coking as the principal technology. Nevertheless, since this situation takes place at the upgrading complexes in 4 out of the 5 joint-venture companies currently operating in Jose, with a yield of 16,000 daily tons, the high coke production makes necessary to analyze and develop a very serious consideration of other upgrading options, different from Carbon Rejection, such as Hydrogen Addition and other new technological upgrading proposals.
Along with their technological innovations, these new proposals offer a greater yield of products with a larger commercial value for the refining customers, reduce the energy consumption and minimize the generation of non-desirable byproducts like coke, whose restricted use makes it difficult to commercialize, whilst the production level keeps going up. In this sense, the technology of Hydrogen Addition is a great advance.
One of the more important problems to solve in the hydrocarbon upgrading programme of the Orinoco Belt is the ecological issue. Those hydrocarbons contain high concentrations of Sulphur and metals, particularly Nickel and Vanadium. Their processing implies a coke and Sulphur generation greater than that of the light and medium crudes, as well as a larger amount of effluents and emissions to the atmosphere. A high level of consciousness must be developed about the environmental impact of the extraction, transportation, upgrading, processing and consumption of hydrocarbons with these characteristics, and technological solutions to preserve the ecological and environmental equilibrium of the affected area must be proposed and implemented as well.
Another option under study for the processing of these crudes is Biological Upgrading, using fungus and bacteriae selected and gathered in field operations and reproduced in the laboratory. There have been studies to characterize metabolic routes associated to the desulphurisation and the elimination of other type of contaminants.
Several institutions have identified microorganisms that work between 50 and 65 ºC to degrade crude at atmospheric pressure, whilst the conventional processes require elevated temperatures and pressures. This technology has been widely used in the bio-remediation, but, in the case of upgrading, it is still necessary to go deeper in research and extra-lab test performance. It is expected that the use of bio-technological methods will bring a great impact in the development of crude upgrading.
There are several proved technologies used worldwide in refineries and upgrading complexes for natural bitumen, heavy and extra-heavy crudes. A descriptive summary of the most representative is as follows:
CARBON REJECTION TECHNOLOGIES
There are 2 main technologies of carbon rejection, namely, the Thermal Cracking and Solvent Extraction.
I. Thermal Cracking
Thermal Cracking is one of the first conversion processes used in the oil industry, and has been used since 1913, when different fuels and heavy hydrocarbons were heated under pressure in large drums until reaching their thermal fracture into lower molecular size products with a lower boiling point; at the same time, some of those molecules reacted amongst themselves to form others even larger than the original ones, giving origin to what came to be coke. Without any doubt, the best reference for Thermal Cracking in the last years within the oil industry has been the Delayed Coking process.
I.1 Delayed Coking
This is one of the technologies with greater use to upgrade heavy fractions, since almost 30% of this type of installations uses this process. It started to be used in the 20s, with the necessity to increase the yield of light oil products, and there since it has been the preferred option at many refineries, because it permits to handle heavier fractions containing impurities.
It is a semi-continuous process based on the alternate use of the drums in filling, coking and emptying cycles, due to which heavy hydrocarbons with low commercial value, coming mainly from the bottom of atmospheric distillation towers or vacuum columns, are converted into lighter hydrocarbons of higher value and a solid byproduct known as coke, whose value will depend on its properties, such as Sulphur and metal content.
Top vapors of drums are taken to the separating column, where they are split into wet gas, non-stabilized naphtha, light and heavy gasoil and recycle oil. Wet gas is processed in gas plants, whilst liquids must be hydro-treated to reduce its reactivity and improve their quality.
Once it has been cooled down, coke is hydraulically cut and then handled for disposal, whether mine storage (Canadian case) or commercialization (Venezuelan case). Product yield is in the range of 65 to 70%, whereas the balance stays as coke.
I.2 Fluid Coking
This is a continuous coking process developed by Exxon, now ExxonMobil, which converts heavy flows, such as residuals of atmospheric or vacuum distillation, bottoms of desasphaltation and catalytic cracking units, and bitumens of oil sands, into light products. Distillation residual at an average temperature of 1050 ºF goes into the scrubbing section, where it exchanges heat with the vapors coming out from the reaction step. The condensing fraction is recycled and blended with new feed, whereas the vapors are sent to the fractionation tower. At the reaction section, feed is thermally cracked into light products and coke; this is sent to the burner, where air and heat are provided to burn between 15 to 25% of the total; the balance is sent back to the reactor to maintain the reaction temperature. The product yield of the process is in the range of 70 to 75% per load weight, whereas the balance is coke.
Since 1954, 7 units have been put in service worldwide, with an accumulated capacity of 350,000 daily barrels. At the beginning it was said that Fluid Coking would replace Delayed Coking in the market, but it has not taken place so far.
I.3 Flexi-coking
This is a Carbon Rejection process developed by Exxon as a modification to Fluid Coking, adding a step for coke gasifying to produce flexi-gas, a coke gas with a low heating power (80 to 100 BTU / cf), reducing considerably the coke production. Product yield is similar to that of Fluid Coking, but coke production is reduced from 24 to 4%, converting it into flexi-gas. The first Flexi-coking unit was put in service in Japan in 1976, and in the 80s another unit was developed in Venezuela at the Amuay Refinery, within the Paraguaná Refining Center, with a capacity of 55,000 daily barrels.
I.4 Visco-reduction
This is another Carbon Rejection technology that is widely known, and consists of a Thermal Cracking process to produce gasolines and other distillates, with a residual product that is visco-reduced (less viscous than the initial load). In 1993, Foster Wheeler (FW) and Universal Oil Products (UOP) made an agreement to combine their technical experiences, knowledge and resources in the visco-reduction area to impulse the use of the first known Visco-reduction model, referred as Coil type. In total, these companies have developed over 50 Visco-reduction plants, 20 after the agreement.
In this process, the key parameter of the load is product viscosity. Following a preheating step, the load is sent to an oven where the cracking temperature is reached. Although the cracking process starts in the oven, the major part of it takes place within a reaction chamber located immediately after it. The cracked material is cool down to avoid excessive formation of coke, and then is sent to a fractionation unit for product separation, in an operation whose residual is less viscous than the load.
Same as FW and UOP in this case, Shell and ABB-Lummus have been dedicated to the development and commercialization of a drum type application, namely, Reaction Chamber (Soaker), with over 80 projects based on this process, many of them already in service.
I.5 Aqua-conversion
This technology was developed in Venezuela at PDVSA-Intevep, along with FW and UOP, and consists of an improved version of the Visco-reduction process to decrease both the viscosity and the density of heavy crude fractions, achieving a conversion much larger than that of the conventional Visco-reduction technology processes. However, so far it has not been proved at commercial facilities.
In the traditional Visco-reduction units, under severe conditions, the resulting reactions of polymerization decrease the distillate yield and increase that of asphaltenes, generating an unstable residual fuel component and limiting the conversion for the involved load. The crude upgrading achieved with the Visco-reduction conventional technology is in the level of 2 ºAPI, which corresponds to stable synthetic crudes.
In this process, the upgrading goes up to 7 ºAPI, with a conversion level of 40% per residual weight for the 500-ºC+ fraction, due to the use of a homogeneous catalyzer system (catalyzers A and B), which permits Hydrogen transfer from water to residual, in presence of steam.
This technology offers 2 essential applications. The first one –main objective- is the production of a synthetic crude between 14 and 16 ºAPI, lighter and less viscous, easier to transport, out of a base load of natural bitumen and extra-heavies of 8 to 9 ºAPI, like those of the Orinoco Belt. The second application is the processing of atmospheric and vacuum residuals of the refineries, in order to reduce the generation of residual fuel. It is economically attractive, since it permits the conversion of residuals into higher value products, like gasolines and combustibles (jet kerosene and diesel gasoil).
This process offers a low cost option to upgrade heavy crudes, as compared with others commonly used, since it can generate synthetic crudes under operating conditions not that severe. Besides permitting the above mentioned conversion level, preserving the stability, it is regarded as simple enough to be located nearby the production field. The required equipment and operating conditions are similar to those of the Visco-reduction processes, so with some adjustments it is possible to adapt the plant units.
II. Solvent Extraction
This is a physical separation process where the vacuum residual is divided into its components by means of a solvent used as an absorption medium. It is going to be used in the Optix-Nexus upgrading project carried out in Canada for its oil sands. Likewise, PDVSA-Intevep has performed pilot tests at some wells in the Orinoco Belt, seeking to extract part of their asphaltenes to obtain higher quality crudes. It is a separating process based on specific gravity (molecular weight), as opposed to the boiling point distillation. Its products are a desasphalted hydrocarbon, commercially known as DAO, and a residual rich in aromatics with high concentrations of contaminants like metals, asphaltenes and Conradson carbon. DAO can be used as a base for the preparation of finished lubricants, as well as feed load of Catalytic Cracking units or Hydro-cracking plants, whereas the residual is used to prepare asphalts and also as feed load of Thermal Cracking processes.
This process offers the additional option of producing a low cost feed load for Hydrogen and electricity generation using the gasification process.
Solvent Desasphalting is an advantageous process because of its relatively low costs and the implicit possibility of obtaining a wide variety of desasphalted oils. It also offers a high selectivity for asphaltenes, a considerable metal rejection, a certain selectivity to reject Carbon and minor selectivity for Sulphur and Nitrogen. Better results are obtained with paraffin vacuum residuals than for those with a high content of asphaltenes, Carbon and metals. Its disadvantages are the lack of residual conversion and the high viscosity of the asphalt produced. Nevertheless, this technology is attractive because of the economical benefits associated to asphalt production. There are currently more than 50 operating units, based on the FW-UOP technology.
The solvent extraction processes are classified into 2 groups, the conventional ones and those used in super-critical conditions. The operational sequence in both cases is the same, and the only difference is referred to the conditions of the involved processes, which are set to optimize the solvent handling and the operation efficiency, as shown in the Demex and Rose processes.
There are currently 36 units in continuous operation, with a combined capacity of over 600,000 daily barrels, under license of Kellogg, Brown & Roots.
HYDROGEN ADDITION TECHNOLOGY
There are several commercial technologies worldwide that compete with Thermal Cracking in the barrel bottom conversion of heavy and extra-heavy crudes, identified as LC Fining, HDH Plus, H-Oil, CanMet, and Shell HyCon, amongst others. All of them are based on the Hydrogen addition in order to increase production and quality of liquid products, as well as reduce the coke generation in the process. A summary of the 2 main technologies is presented below.
LC Fining
This process consists of the addition of catalytic Hydrogen and is used for the conversion of atmospheric and vacuum residuals. The final product contains approximately 25% of non-converted residual and can be commercialized as upgraded or reprocessed crude for Deep Conversion units handling Delayed Coking, Visco-reduction or Solvent Desasphaltation. This technology is preferably used for atmospheric residuals, due to the low capacity to handle flows with high metal content, like in the case or those of the Orinoco Belt, so nowadays it is not a viable option to process these crudes. However, there has been good commercial experience with Arabian and Canadian light and heavy crudes.
HDH Plus
This is a new generation technology developed in the 80s at PDVSA-Intevep for the treatment, conversion and valorization of the Orinoco Belt heavy crudes. It took more than 20 years of research and development, including scaling tests and evaluation of different crudes, and consists of a high conversion process of heavy crudes and refinery residuals via Hydro-conversion, with indexes of 90 to 95%, versus the 70% level of the Delayed Coking case. There are 2 semicommercial-scale plants under construction at the refineries of El Palito and Puerto La Cruz in Venezuela, projected with a capacity enough to convert 25,000 daily barrels of vacuum residuals each, and it has been frequently mentioned by PDVSA top authorities that this technology will be used the future upgrading complexes of the Orinoco Belt new projects .
This technology generates a considerable yield in liquids (115%), renders high quality products and is flexible enough to process different loads with high sulphur and metal contents. Additionally, it noticeably minimizes the handling of solids and refinery byproducts, and is environmentally friendly.
For the time being, it is a technology economically attractive worldwide, since it competes with all of the latest technologies for crude upgrading, with the advantage of rendering a greater yield in high commercial value, like gasoline, medium distillates and fueloil, and much less residual generation than the Thermal Cracking technologies.......
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