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Aug-2018

Increasing resid processing flexibility

A resid processing technology converts low value refinery streams to full range refinery products.

RUNPU ZHAO Beijing CUP-Qiantai, Supercritical Extraction Technology Company
WARREN CHUNG, Well Resources Inc
ZHIFANG TANG and BO YUAN, North Huajin Chemicals Industries Group
ZHIMING XU and SUOQI ZHAO, China University of Petroleum
KENG H CHUNG, Chinese Academy of Sciences
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Article Summary
Refiners face increasing economic and stringent regulatory pressures both upstream and downstream in their operations. These external pressures translate to a real risk for a refiner’s bottom line. The key to maintaining a refiner’s competitiveness in this market is to adopt technologies or an operating configuration that allows for flexibility in handling variable feedstocks while producing desirable end products.

External pressures
Many refiners in the US Gulf Coast and Midwest are configured with cokers specifically to handle ultra heavy crudes originating from Canada and South America. In Venezuela, recent political instability has led to a significant decline in heavy oil production. In Canada, regulatory uncertainty has led to an inability to expedite and expand diluted bitumen pipeline carrying capacity. Also, the emergence of horizontal multistage fracturing technology has led to the exploitation of large volumes of light crude from shale reservoirs in the continental US, which further impacts the market share of heavy crudes. Refiners are consequently left questioning the long term economy and viability of processing heavy feedstocks. Similar sentiments are being observed globally.

Environmental regulations such as bunker fuel sulphur content limits imposed by the International Maritime Organisation (IMO) present an additional risk to a refiner’s bottom line. In 2012, the IMO imposed a 3.5% m/m sulphur content limit for bunker fuel oils. This regulation led many refiners to reconsider end uses for vacuum residue (VR). In one case, a European refiner retrofitted its visbreaker with an ebullated bed hydrocracking process to produce distillates and fuel oil that met 3.5% sulphur IMO specifications.

Recently, the IMO announced additional regulation, taking effect in 2020, which prescribes the bunker fuel sulphur content limit to further drop to 0.5% m/m. Refiners that already invested capital in response to the 2012 regulation are once again faced with making additional investment decisions. While some refiners are looking to move away from processing sour feedstock altogether, other refiners are looking to make process changes.

Market disruptions both upstream and downstream of the refiner’s operations will significantly impact the medium-heavy sour feedstock processing space.

Building an economic and flexible case
Refiners are currently assessing the implementation of novel technologies, or reconfiguring their operations to best position themselves in the changing market. A careful approach is being taken which assesses both economics and risk.

When it comes to reconfigurations, it is often difficult for a refiner to build an economic case for implementing traditional technologies. The limitations and shortcomings associated with conventional technologies are already well understood, and many technologies do not economically address the underlying problems associated with heavy feedstock processing.

From a risk perspective, a refiner must not only consider the technical risk associated with implementing novel technologies, but also risks associated with future market disruptions. With regard to bunker fuel sulphur specifications for example, there exists a future risk that the IMO could one day impose a stricter mandate of less than 0.5% m/m, sending refiners back to the drawing board.

Accordingly, refiners will benefit most from commercially proven technologies that offer maximum processing flexibility. This is a crucial consideration which can mark a step-wise change in a refiner’s ability to remain competitive.

Selective extraction of asphaltenes (Selex-Asp)
Selex-Asp is one of the emerging resid processing technologies. Five commercial units have been built in Asia for a combined processing capacity of 36500 b/d. The largest operating Selex-Asp unit has a capacity of 20000 b/d. Another commercial scale unit has been licensed in North America for bitumen processing.

Selex-Asp is a low cost, low complexity, and environmentally friendly process. The novelty of the technology lies in its ability, cleanly and with a high degree specificity, to reject asphaltenes from heavy petroleum fractions under moderate operating conditions; in the extreme case, in the form of solid granules.1-2 By doing so, it maximises the yield and economics of producing deasphalted oil (DAO), which can then be sent to conventional refining processes to produce clean transportation fuels.

The following cases illustrate the use of Selex-Asp for resid processing flexibility, which allows refiners not only to reduce their environmental footprints but also to add value to their byproduct streams.

Low sulphur IMO fuel
Figure 1 shows a 20 000 b/d Selex-Asp operation for producing low sulphur fuel product from oil sands bitumen derived VR, which is among the highest sulphur-containing asphaltenic heavy feedstocks.2 The operating configuration is presented in Figure 2. A previous study indicated that sulphur species in asphaltenes are refractory to commercial desulphurisation treatment.3 Hence, asphaltenes (in the form of solid granules) were selectively removed from the VR and the remaining oil fraction was subjected to packed bed mild hydrocracking. Table 1 shows the properties of the VR and DAO before and after hydrotreating. The results show that the hydrotreated product of DAO is less than 0.5 wt% sulphur, which can be sold as IMO fuel.

Alternatively, if Selex-Asp is a component of a sophisticated refinery process scheme, the hydrotreated DAO product can be fractionated and processed in various existing refinery processes into gasoline and diesel. 

The rejected asphaltenes granules can either be used as feedstock for making carbon products or disposed of in an environmentally friendly manner without the need for secondary treatment. Selex-Asp replaces the need for operating high energy and capital intensive processes, such as coking, visbreaking, ebullated bed hydrocracking, or conventional solvent deasphalting technologies which require secondary processing to reclaim the value of the pitch.

Depending on the nature of the feedstock, the process operating conditions can also be adjusted to produce a pitch type co-product.

Hydrotreating feedstock and asphalt blending stock
A greenfield, 4000 b/d Selex-Asp unit was commissioned in China by Shandong Yida Petrochemical Ltd in May 2014. Figure 3 shows a process flow diagram of the commercial operation from May 2014 to August 2017. Under this simple process scheme, the operator purchased VR feedstock from nearby refineries and processed it in Selex-Asp to produce a DAO product which was then sold as a hydrotreating feedstock. The pitch co-product was sold as an asphalt blending stock to service the local asphalt market.4 The properties of VR, DAO, and pitch for this operation are shown in Table 2. The VR was formerly sold to asphalt makers as asphalt air-blower feedstock. Using Selex-Asp, half of the VR was extracted as a premium DAO refinery feedstock while producing a pitch which had superior properties to VR for making asphalt. More importantly, the derived pitch does not require air-blowing. Payback from this operation occurred within a year.
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