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PRODUCT TREATING AND BLENDING
Publication date:2Q 2019
Product Treating and Blending
Regulatory specifications for the acceptable levels of various compounds (e.g., sulfur, benzene, aromatics, etc.) in transportation fuels have been put in place in many regions around the world. Additionally, legislation regarding more stringent specifications in many countries and first-time regulations in developing nations are imminent. To deal with this situation, refiners spend a great deal of time and capital modifying distilled products before sending them to the marketplace. Hydrotreating is the dominant technology used to remove undesirable compounds from end products, but it is often not ideal.
Non-hydrogen product treating technologies for sulfur removal can be separated into three general categories: (1) mercaptan sweetening/extraction, (2) bulk sulfur removal, and (3) selective removal of refractory sulfur for polishing and niche treating applications. Besides sulfur removal, gasoline benzene reduction is also a critical treatment requirement as benzene is known to be a carcinogen. Refiners have four primary options: (1) benzene saturation with hydrogen, (2) benzene alkylation, (3) benzene extraction, and (4) removal of benzene precursors from the catalytic reformer feed.
Many refiners have already committed large capital investments to hydroprocessing technologies to meet current and future specs. However, the combined implementation of non-hydrogen product treating technologies can still be useful in the current market place for "niche application" (e.g., treating diesel streams with a high concentration of DBT) and for easing the burden of HDS in a hydrogen-constrained refinery. Additionally, the use of these technologies for product polishing to meet current and future "near-zero" sulfur specifications for transportation fuels remains an attractive area.
Mercaptan sweetening/extraction techniques have been commercially available for quite some time, and have proven to be advantageous over hydrotreating technologies when treating mercaptans. The removal or conversion of the odorous organic sulfur compounds via product treatment technologies will help to avoid mercaptan recombination that can occur in hydrotreating schemes. Other commercial product treating technologies utilize oxidative desulfurization, adsorption, emulsification and electric field separation, membrane desulfurization, and olefin alkylation.
Product blending is also important as refiners attempt to meet fuel specifications and remain economically competitive. This is particularly the case for marine fuels as the implementation of the International Maritime Organization (IMO)'s 2020 0.5%-sulfur spec looms closer. One option to meet this requirement is to use a custom fuel oil blended from various refining streams such as low-sulfur straight-run, residue, cutter stock, treated light distillate, unconverted hydrotreated oil, and even a small amount of kerosene.
In regards to gasoline, many countries are utilizing ethanol as a blending component as a way to cut dependence on imported oil and lower CO2 emissions. The inclusion of additional quantities of ethanol into the gasoline supplies around the world is, however, not without its challenges, most notably in relation to the negative impact that ethanol blending has on the gasoline pool's RVP value. Thus, to offset the increase in fuel volatility that occurs when ethanol is added to the gasoline pool, refiners and fuel blenders must increase the use of expensive, low-RVP components (e.g., alkylate).
Also, the ongoing shale boom in the US has created abundant stocks of cheap butane. Profit increases can be realized through gasoline blending when a cheaper blending component like butane is utilized. While butane can increase the knock resistance of gasoline, it also has a significant impact on the vapor pressure of the fuel and its use is therefore limited by RVP specifications.
A number of companies offer automated equipment for monitoring and controlling refinery blending plants to improve economics and enhance efficiency of product blending applications. The technologies incorporate modeling programs, tank monitors, blend analyzers, and comprehensive oil movement systems that will provide efficient planning and scheduling and ensure consistent operations in the blending plant. These systems minimize giveaway and the need to reblend by continuously analyzing the properties of blendstocks and controlling the flow of every component into each batch of product. The control units of today make extensive use of non-linear programming to meet the constraints of the models (e.g. created by the US EPA) with the least costly blending components. The technology offered by commercial companies has evolved in response to tighter fuel specifications around the world.
Additionally, the product treating and blending section features the latest trends and technology offerings, including:
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Keywords: sulfur specification, benzene limits, aromatics specification, light distillate, middle distillate, fuel oil, non-hydrogen desulfurization, mercaptan sweetening, extraction, sulfur adsorption, refractory sulfur, benzene alkylation, caustic treatment, pervaporation membrane, oxidative desulfurization, bio-desulfurization, olefin alkylation, automated blending, color degradation, biofuels, ethanol blending, IMO 2020, bunker fuel, bunker blends