Strategies for improved naphtha processing
To take advantage of dilbit from Alberta and light oils from shale formations, refiners must develop a strategy for processing additional naphthas and light components
MIKE ARMSTRONG and MARTIN BRANDT
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Changes to the crude oil supply coupled with changes in gasoline demand and new gasoline regulations mean that US refiners must re-examine naphtha processing throughout the refinery. Many refiners will have access to opportunity crudes, including light, tight oils from shale formations in North Dakota, and Texas and Canadian bitumens that contain lighter diluents. This article argues that refiners will need to upgrade their naphtha processing trains to better handle the added light material, comply with gasoline regulations, and adjust to changes in demand for gasoline and distillate.
Refiners in the Midwest have been revamping their facilities over the past 20 years to process Canadian bitumens and heavy crude oils. These refiners largely targeted improved bottoms upgrading and gas oil cracking to accommodate heavier crude oils. In addition, many upgraded their naphtha processing facilities to accommodate the naphtha-based diluents used to transport bitumen via pipeline to their refineries. These naphtha-based diluents used to transport bitumen are becoming lighter.
More recently, the success of gas field fracturing (or “fracking”) is being replicated in the production of “tight oil” from the hydraulic fracturing of shale formations. Crude oils from these formations are lighter than traditional crude oils and have API gravities ranging from 40–70°API.
This article seeks to:
• Describe the trends in crude oil production, in new regulations affecting fuel production, and in product demand that will increase pressure on the naphtha train
• Define a strategy to take advantage of lower-cost crude oils containing lighter components by identifying naphtha processing bottlenecks in the refinery
• Outline the technologies and configuration changes that should be considered as part of a strategy to process opportunity crude oils
• Propose a methodology to evaluate and rank the various options for improving naphtha processing to take advantage of low-cost crude oils containing light components.
Canadian bitumen and diluent availability
To meet pipeline viscosity and density specifications, bitumen is blended with either light naphtha, which historically has been a natural gas condensate, or synthetic crude oil (SCO) from Alberta-based upgraders. If bitumen is blended with diluents, it is called dilbit; if blended with SCO, it is called synbit. Dilbits contain large amounts of resid, heavy gas oil and naphtha with almost no kerosene or diesel range material. Processing the diluent contained in dilbit and processing the light material in tight crude oils may stress the naphtha and light ends processing portions of the refinery compared to processing other crude oils.
Growth in bitumen production is expected to significantly outstrip SCO production from Alberta-based upgraders as well as the availability of natural gas condensates used as diluent in shipping bitumen. As a result, bitumen shippers will need to import increasing amounts of naphtha diluents, which will provide US refiners a means to send diluent recovered from bitumen together with refined naphtha back to the bitumen production sites in Alberta via recently commissioned pipelines built for this purpose. We anticipate that this returned diluent will become lighter as refiners seek an outlet for their least valuable light products: typically, butanes, pentanes and hexanes. The result will be that US refiners must be prepared to process dilbit containing lighter diluent.
Tight oils tend to be high in API gravity. Processing these crude oils rather than heavier crude oils may mean that refineries will need additional naphtha and distillate processing capabilities.
External factors affecting naphtha processing
There are a number of other external factors that affect naphtha processing capabilities in refineries and drive investment in naphtha processing. These factors are environmental specifications affecting fuel quality, vehicle efficiency standards and increased use of renewable fuels to supply US transportation fuels.
Control of hazardous air pollutants from mobile sources (MSAT2)
We have evaluated the impact of MSAT2 regulations for a number of US refiners and helped define their investment strategies for dealing with the required reduction in gasoline benzene. Our observation is that the options selected for benzene removal — whether extraction, saturation or sales of heart-cut naphtha — offer significant opportunities for process optimisation. For example, small changes in reformer feed composition and severity can create large benefits in terms of pool octane, gasoline yield and benzene saturation hydrogen consumption.
Changes in crude oil composition resulting from changes in diluent composition in dilbit and from increased processing of light, tight crude oil are likely to result in greater naphtha production at the refinery and will require a specialised review of the full naphtha chain to achieve the following goals:
• Ensure benzene removal facilities are still adequate to meet gasoline specifications
• Leverage opportunities to improve benzene removal processes
• Optimise naphtha reformer performance in line with refinery octane, benzene and hydrogen requirements.
Tier 3 gasoline regulations
The EPA’s Tier 3 gasoline regulations will require reducing gasoline sulphur levels to an average of 10 ppm. Although it is possible to independently meet the challenges of Tier 3 regulations and take advantage of the opportunities from processing dilbit and lighter crude oils, a combined strategy that addresses Tier 3 and crude slate changes will reveal synergistic solutions that minimise total investment and increase overall naphtha processing and gasoline production flexibility. The design basis for new and/or revamp scopes of work to accommodate the lighter diluent in Canadian dilbit and the light tight oils should consider the following points:
• Tier 3 regulations will require additional desulphurisation of FCC gasoline, particularly light FCC naphtha that has typically by-passed FCC naphtha hydrotreaters under current regulations
• Lower sulphur blending components such as light, straight-run naphtha and alkylate will require closer attention and possibly additional treatment to reduce their sulphur levels
• The isopentane value will decrease further if RVP specifications are reduced, which will require refiners to remove high- vapour-pressure components from gasoline blends.
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