Tougher regulations are challenging refi ners to produce higher quality products while trying to maximize effi ciency. The

U.S. Environmental Protection Agency (EPA) is enacting Tier 3 requirements that will begin in 2017 requiring sulfur levels in gasoline to be 10 ppm or lower. Increased Hydrotreating and modifying crude slate are some of the levers that can be pulled to help lower sulfur levels in fi nished products.

Hydrotreating catalyst life depends on the feed and operation of the unit. Increased monitoring will be critical in meeting these requirements and maximizing effi ciency. WDXRF has

proven to be a fast, easy, and precise method to measure sulfur in hydrocarbon streams.

Beginning in 2017, the EPA will begin enforcement of the Tier 3 Regulations on Gasoline. Current Tier 2 regulations allow an annual average standard of 30 ppm sulfur in gasoline which will be lowered to 10 ppm on January 1st, 2017. In order to meet these lower sulfur levels, refi neries must invest in new or upgraded equipment, modify operations or a combination of both. Regardless, it will increase the cost of producing gasoline.

US refi ners have had more choices of crude types in recent years. Heavy, sour crude provided cost advantages as these were

priced lower. Refi ners modifi ed equipment and operations to accommodate the cheaper crude. Figure 1, illustrates the trend of US sulfur content and API Gravity from 1985 through 2015. Crude trended heavier and sulfur content increased as technology improvements were made to suit these cost-effective feedstocks. Advances in drilling techniques led to readily available Light Tight Oils to serve the refi ning market and lessen dependence on less stable crude sources. Although these feeds were lighter and had little sulfur, they pose other challenges to refi ners. Specifi cally, they tend to be high in waxes and are prone to fouling.

As crude sulfur levels increased, refi ners invested heavily in sulfur

removal. This was done to capitalize on the cheaper high sulfur crude as well as meet increasingly stringent sulfur specifi cations on fi nished products. Between 1985 and 2015, desulfurization capacity nearly doubled from 8.9 Million Barrels per Stream Day to over 17.3 Million Barrels per Stream Day. Figure 2, shows the relationship between US crude sulfur levels and US refi nery desulfurization capacity.

For the implementation of Tier 3 regulations, refi ners are looking at increasing desulfurization at the fl uid catalytic cracking unit (FCCU). The entire feed can be pre-treated or the gasoline can be post- treated or a combination of both. Careful consideration must be given to factors such as hydrogen availability, heat balance, catalyst type, incoming sulfur content, feed nitrogen content, and planned cycle life. Pre-treating feed provides several advantages for sulfur removal. Pre-treating will remove metals and nitrogen, which are poisons to the FCCU catalyst. Additional hydrogenation from pre- treating will increase conversion in the FCC process. Conversely, pre-treating can be very expensive and may not be possible due to heat or hydrogen limitations. Post-treating the gasoline stream may be an easier option, although there is signifi cant reduction of octane in the process. FCCU gasoline contains valuable olefi ns that contribute to the octane. Post-treatment will reduce the octane number of the gasoline by conversion of valuable olefi ns, which must be supplemented by reformate.

For every part per million of sulfur removed, a refi nery spends signifi cant money on capital, hydrogen, catalyst, and energy. The related downtime to catalyst change out must also be factored into the equation. Catalyst has a fi nite life, and that length of time is dictated by how the Hydrotreater is operated. By varying temperature, space velocity, and hydrogen partial pressure, sulfur removal and catalyst life are impacted. Crude slate can be modifi ed to reduce total sulfur content and reduce strain on sulfur removal equipment. Crude swaps come at a cost, either in the form of higher purchase price, creating problems on other refi nery units, or product yield.

Regardless of what method is utilized to produce gasoline at these lower sulfur levels, monitoring sulfur levels will be critical in controlling costs. Optimization is dependent on knowing the sulfur levels at all times, accurately and reliably.

Figure 1. US Crude Quality (Sulfur Content and API Gravity) – EIA.GOV.

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