We’ve increased the opportunity crude content of our feed and are experiencing high calcium issues. How can we best address this?Jun-2021
Chris Claesen, Nalco Water, Chris.Claesen@ecolab.com
Increased levels of calcium due to opportunity crude processing can be effectively handled in the desalters as described in articles in the PTQ Q3 2017 and PTQ Q1 2018, Opening the crude flexibility window. The calcium that can create problems in downstream processes is in the form of a calcium naphthenate salt that is oil soluble.
Using a suited calcium removal programme consisting of an acidification additive and an efficient corrosion inhibitor, combined with a high-performance emulsion breaker the calcium can be extracted to the desalter brine with a high efficiency while minimising potential downstream impacts of the treatment. Key is to have real-time control of the washwater and brine pH and quality, this can be the best achieved by an automation system such as Nalco Water`s 3DT for brine.
Marcel Foet, KBC, Marcel.Foet@kbc.global
When calcium is present as inorganic salt in crude oil, typically 10% is from calcium. The majority is sodium and the rest is magnesium. Salts of chlorides hydrolyse to evolve HCl when exposed to high temperatures in crude units. The HCl condenses with water in the crude unit overhead and can cause severe corrosion. The main source of chlorides in a crude top system is coming from magnesium chloride and some from calcium chloride. Sodium chloride leaves the crude tower with the bottom stream. Essential in removing chlorides is the efficiency of the desalter and if necessary, by polishing with caustic soda downstream the desalter. Other control strategies are the addition of neutraliser and filming agent, an overhead water wash and overhead temperature (at least 10°C higher than the water dew point). With a good desalting system more than 95% of calcium, magnesium and sodium should leave the desalter with the brine.
Calcium can also be present as an organometallic component in the form of a soap. Problems for refiners associated with high calcium (> 100 ppm) include exceeding metal specs for fuels oils that have resids blended in, poisoning catalysts for residual catalytic crackers, adversely affecting coke specs for metals, and contributing to crude unit fouling and delayed coker furnace fouling. Several methods are available for the removal of calcium from crude oil, essentially using the desalter. All involve the use of organic carboxylic acids like citric acid. High calcium crude oil is contacted with the acid to form a sequestered calcium containing complex that partitions to the water phase in the resolved emulsion.
Steven Van Vegten, Albemarle, Steven.vanVegten@Albemarle.com
Calcium may be removed through pretreatment of the feed. If such pretreatment is unavailable or insufficient, calcium will irreversibly poison the catalyst when the feed is processed in an FCC unit.
Calcium deposits on the outer surface of FCC catalyst particles, much the same as iron. Calcium is detrimental to FCC catalyst performance as it causes sintering of the surface, reducing the accessibility of the catalyst. With reduced catalyst accessibility, it is more difficult for feed molecules to reach actives sites, hampering conversion, particularly in bottoms upgrading.
Because calcium and iron contamination hardly affect Ecat activity, surface area, and pore volume, it may be overlooked. As these lab tests employ long contact/diffusion times, they do not capture the dynamic nature of diffusion. To compensate for these oversights, Albemarle developed a lab test to measure the accessibility of FCC catalysts by allowing large probe molecules to diffuse into the catalyst. The test result is known as the AAI (Albemarle Accessibility Index). A diffusion limited catalyst has a low AAI, while a catalyst whose structure allows easy rapid diffusion has a high AAI.
As calcium poisoning is irreversible, a refiner may choose to increase catalyst additions, perhaps with the use of purchased Ecat, flushing the contaminants from the unit inventory and reducing calcium contamination to a level the catalyst can cope with. Alternatively, employing a high accessibility catalyst with intrinsic tolerance to calcium may provide for a more cost-effective option, allowing for lower catalyst addition rates while maintaining conversion. Albemarle offers a suite of catalysts with high accessibility, such as ACTION for maximising butylenes and AFX for maximising propylene.