QUESTIONS & ANSW
Previous successes: revamping the unit to DMHC mode
applicable, should be considered as well. Excess air may be increased to generate more thermal mass, but doing so will also increase NOx emissions and reduce efficiency. Furthermore, it may not be practical to completely restore the flue gas mass flow rate by increasing excess air alone. In a recent study, Wood found that the excess air of a coker heater firing 21 vol% H₂ would need to be increased from 15% to approximately 40% excess air to maintain the flue gas mass flow rate. This approach was not recommended. Impact on radiant heat transfer in the firebox In the firebox (radiant section), heat is transferred to the process tubes by three main methods of radiation: 2 • Direct radiant from the flame (such as flame burst) • Reradiation from flue gases • Reradiation from refractory surfaces. The radiation from the flame is related to its luminosity and may impact heat transfer. Luminous radiation is the radiation from solid particles suspended in the flame.⁶ For example, an oil flame has three to four times more flame radiation due to increased luminosity created by soot con- tent.² For a flame from pure H₂, luminosity is reduced to virtually zero, which may decrease radiant heat transfer slightly. However, the contribution from direct flame radia - tion is typically low compared to other forms of radiation in the firebox, as evidenced by the combination of oil and gas burners that have been successfully used in operation with little change in performance noted between fuels fired.² Reradiation from flue gases occurs primarily from CO₂, H₂O, and SO₂ molecules.⁷ Symmetrical molecules (N₂, O₂, and CO) are considered ‘transparent’ and do not reradiate heat.⁷ An all-H₂ flame produces significantly more H₂O, which has higher emissivity than CO₂. Since CO₂ is elimi - nated from the flue gas and essentially replaced with H₂O, this will have the tendency to increase radiant heat transfer. As mentioned previously, an H₂ flame has a higher tem - perature than a CH₄ flame, which may increase the surface temperature of the refractory in close proximity to the flame. This may also increase heat transfer in the radiant section. While a reduction in luminosity may reduce direct radi- ation from the flame, increased emissivity of flue gas mol - ecules and increased refractory temperatures will likely offset this effect, suggesting that current methods for radiant heat transfer calculation are adequate for H₂ firing. Wood recently performed a study of a petrochemical heater designed for and operating with up to 90 vol% H₂ fuel. The study found that the predicted firebox and field-measured temperatures matched very closely (within 5°F). Potential corrosion mechanisms The industry standard for corrosion mechanisms, API 571 – ‘Damage Mechanisms Affecting Fixed Equipment in the Refining Industry’, mentions three major corrosion mecha - nisms involving H²8 : • Hydrogen embrittlement (HE) • Hydrogen stress cracking from exposure to hydrofluoric acid (HSCHF) • High-temperature H₂ attack (HTHA). HSCHF can be ruled out, under the assumption that no Elif Kızlap is Process Superintendent at Tüpraş Kırıkkale Refinery and responsible for hydroprocessing units. Her role involves increasing unit profitability, adopting new technologies and optimisation. She holds bachelor’s and master’s degrees in chemical engineering from Hacettepe University, Turkey. She has published an article in the Jour- nal of Materials Science: Materials in Medicine (2019) and authored a Turkish patent related to her master’s degree topic. Enes Cındır is Chief Process Engineer in the hydroprocessing team at Tüpraş Kırıkkale Refinery, where he is responsible for hydrocracking units, hydrogen manufacturing units, sour water stripping, and sulphur recovery units. He has operational experience in refinery operation, dis - tributed control systems, staff management, process products quality monitoring, and catalyst performance monitoring. He holds a bach- elor’s degree in chemical engineering from Ankara University, Turkey. suboptimal catalyst utilisation and poor vapour–liquid dis- tribution throughout the cracking bed, which would reduce diesel yield and threaten cycle length. Standout performance has been delivered as a result of the new reactor internals and a leading-edge catalyst system. Tüpraş reports enhanced gas–liquid distribution over the catalyst beds. With lower operating temperatures and reduced radial temperature spreads, it has been able to: • Increase throughput by 5% • Process heavier feeds • Extend the cycle length from three to four years. Crucially, increasing the cycle length has enabled the planned distillate hydroprocessing catalyst changeout to fall within a major inspection turnaround, thereby saving Tüpraş the trouble and cost of a catalyst swap outside this period. This is not the first time Tüpraş has demonstrated a will - ingness to think outside the box with this unit. Several years ago, when it was running as a high-pressure distil- late dewaxing unit, Tüpraş revamped it to run as a distil - late mild hydrocracker (DMHC) and became one of only a few refiners worldwide to benefit from this mode of operation. The objective was principally to enable the upgrading of two high-margin streams that are particu- larly challenging, namely the heavy gas oil (HGO) and light vacuum gas oil (LVGO) fractions. In distillate dewaxing service, the unit was process- ing HGO and meeting the T95 ultra-low-sulphur-diesel specification of 360°C. A DMHC can handle much greater quantities of HGO, and LVGO can also be added up to cold-flow property limits. Compared with a conventional distillate dewaxing unit, a DMHC delivers a step change in T90+ shift with benefits to density, cetane, and distil - late recovery. Cracking the heavy tail in a DMHC requires a highly customised catalyst solution that promotes ring CatCheck is a mark of Shell Catalysts and Technologies. Ersev Dağ is Process Control Superintendent at Tüpraş Kırıkkale Re - finery, where he is responsible for the distributed control system and advanced process control environment. He holds a bachelor’s degree in chemical engineering from Gazi University, Turkey.
capital one of t alysts d Nobel a phur re abatem platinu capabil ❝ H w techno molecu ing fac Goelze between respect oppose sented) few alte From plier or lar and feeds an problem and gua Refin method under-a or in oi gy/cata toleran Som for adv and mo or via m ry analy cated a For FCC/RF ern flu reactor pilot pl A nu or week tion an high te sophist tion an with RV for dist ucts an dard fo D-1160 employ Berth for dire key m (FCC/R diesel hydrog been sl tions an gen as k
hydrofluoric acid is involved in this application. That leaves HTHA and HE: • HTHA typically occurs at high temperature and pressure (Refer to API 941 for temperature and pressure limits for various materials). • HE typically occurs at a lower temperature (<300°F) and pressure at or near atmospheric. In both mechanisms, atomic H₂ (as opposed to molecular H₂) forms and diffuses into steel. Once inside the steel, it Mbugua Gitau is Senior Technical Service Engineer – Hydroprocessing at Shell Catalysts & Technologies, where he engages with refining cus - tomers, helping to unlock potential from their hydroprocessing units with a focus on value-adding catalyst solutions. He holds a master’s degree in chemical engineering from the University of Bath, UK. Email: mbugua.gitau@shell.com Increased ability of the FCC catalysts system to make lower sulphur-containing products is necessary for an overall more profitable refining operation. Reduced NO x and SO x emissions from the FCC stack are also required. The introduction of new FCC catalyst additives as Figure 5 Flue gas flow rate vs vol% H₂ in the fuel for a 100 MMBtu/hr (fired duty) heater. Assumes balance of fuel is methane and 15% excess air The solution they devised was a customised catalyst system. No hardware changes were necessary. It fea- tured a latest-generation, high-activity NiMo catalyst and a zeolite cracking catalyst to crack the heavy tail. As the latter catalyst also had a tendency for dewaxing, the win- ter diesel specifications were also met. With respect to the processing of residual feedstock in FCC, perhaps the most important change in modern FCC catalyst design is the quantification and subsequent optimisation of catalyst accessibility. Data from about 20 commercial experiences show that when contaminants like iron, vanadium, calcium and sodium increase, cata- lyst accessibility decreases rapidly. When catalysts with high accessibility (as measured by the AAI – Akzo Acces- sibility Index) are used, very marked improvements in activity and selectivity are achieved. 100 60 70 80 90 30 40 50 0 10 20 Vol% H in fuel 75,000 80,000 90,000 To evaluate revamping the unit into a DMHC, Tüpraş worked with Shell Catalysts & Technologies. This work included dedicated pilot plant testing and thermal stabil- ity reviews. 95,000 opening, an advanced chemical upgrading technique. Such a solution, capturing a substantial margin, does not come off the shelf. upgrading process for the oil refining industry, producing vast quantities of transportation fuels. It is also expected that it will gain importance as supplier of propylene worldwide and occasionally ethylene. The FCC process and the products it produces will have to meet strict emission standards. 85,000 100,000 The revamp achieved a significant increase in T95 shift of 16°C, compared to the average of the origi - nal cycle when the unit was just in distillate dewaxing service. Additional benefits included a large density improvement, and therefore volume gain, and high die- sel recovery. High accessibility and accessibility retention are required the make the processing of even more contam- inated residual feedstock possible. Akzo Nobel has intro- duced the Opal, Sapphire and Coral catalysts line featuring enhanced accessibility. To enhance the production of light olefins, especially propylene, in the FCCU stable narrow pore zeolites, eg ZSM-5, are required. This has to be combined with a host FCC catalyst featuring high propensity to produce olefinic precursors, which are subsequently cracked to light olefins.
Kidextractor Quarter page
After you have used it the first time, the Kid Extractor will become your trusty hydraulic-tube- bundle-extractor
KIDExtractor Ltd. P.O. Box 11, Zebbug MALTA
Tel. 00356-21-462891 Fax. 00356-21-462755 MOBILE: 00356-94-20596 E-mail: idrojet@videobank.it Website: www.kidextractor.com
Do y
panel
85
PTQ Q2 2023
www.digitalrefining.com
PTQ AUTUMN 2002 18 15/03/2023 17:03:58 51
ENQUIRY NO 314 www. ptq enquiry.com
PTQ Q3 2023
www.digitalrefining.com
q2 shell tupras.indd 85
Powered by FlippingBook