Residue hydrocracking for value addition
Chevron Lummus Global worked closely with a private refiner in China to define a processing scheme that would upgrade low value, opportunistic feedstocks such as Merey 16 crude or high sulphur fuel oil streams to high value, all-liquid products; the refiner did not want to produce petcoke because of current oversupply and low pricing of even anode grade coke in China.
Chevron Lummus Global
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The most important technology selection criteria were robustness proven through commercial experience and the ability of the licensor to deliver finished products from residue hydrocracking through integration of appropriate technologies. Utilising the company’s process planning modelling capabilities, CLG quickly evaluated multiple potential technologies and technology platforms after pinpointing the exact nature of the feedstocks and product demand pattern and narrowed down the processing route as shown in Figure 1.
The LC-Max reaction platform (see Figure 2), built on the proven LC-Fining technology platform, is based on the philosophy that eliminating the heaviest asphaltenes from the conversion process effectively eliminates the most common and persistent fouling issues related to residue hydrocracking while at the same time significantly reducing hydrogen consumption (not wasted in heavy asphaltenes saturation and hydrocracking), reactor volume, and catalyst addition rate.
The vacuum gas oils from the LC-Max unit are sent to an Isocracking unit for conversion to heavy naphtha and diesel. The catalyst system in the two-stage hydrocracking unit is designed for maximum conversion to heavy naphtha while still retaining the capability to produce a significant quantity of diesel. Integrated within the same high pressure loop as the Isocracking unit is an Isotreating unit that utilises the excess hydrogen available in the hydrocracker circuit and the available high hydrogen partial pressure to hydrotreat the naphtha and diesel range material from the crude distillation section and residue hydrocracking. Integration saves at least 30% of the capital compared to a standalone distillates hydrotreating unit.
Natural gas is very expensive in China and, in particular, at this refiner’s location. Many of the recent projects have a natural gas price of $16-18/MMBtu. At these prices, gasification to produce hydrogen starts becoming economically attractive and is an excellent outlet for the pitch from the LC-Max unit. The gasifier will process a blend of pitch and coal. CLG is working with a third party to produce the pitch in a form that is suited to most gasifiers. In addition to hydrogen from gasification, hydrogen is recovered from the catalytic reforming and propane dehydrogenation units that also form part of the refinery complex.
The refiner is driven to complete the detailed engineering on the entire project within 24 months and to start up the unit within 36 months. To this end, long-lead items such as reactors and compressors were ordered very soon after project kick-off.
Since licensing this unit in late 2013, CLG has seen a spate of inquiries from other refiners for both grassroots and revamp options utilising LC-Max. For those refineries with existing delayed coking units or those that are contemplating producing anode grade coke for use in aluminum smelters, incorporating a LC-Fining unit upstream of a delayed coking unit will be the most attractive option, especially for those refiners processing mostly Middle Eastern crudes. CLG has demonstrated that anode grade coke can be produced from unconverted oil derived from a high conversion LC-Fining unit by coking the unconverted residue and then subjecting the coke through calcination and rigorous testing to prove its suitability for use as anode coke.
For more information: BSRI@chevron.com
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