High sulfur diesel

Hydrofining is employed to desulfurize high sulfur diesel stocks, both virgin and cracked. The stability of cracked diesel stocks is also improved. In the diesel range, operating conditions become more severe. Compared to naphthas, temperatures are increased from the 550-600°F level to 700°F. 

The present infrastructure fuel for heavy vehicles is high sulfur diesel (-300 ppm sulfur by weight) but this may change to a nearly sulfur-free diesel as proposed by the EPA (15 ppm... 

The military will continue with its fuel infrastructure of high sulfur diesel (up to 1,000 ppm sulfur by weight) and jet fuel (JP-8). Sulfur specification will remain high because the military has to consider worldwide fuel sources. High sulfur diesel and JP-8 are close in characteristics so no fuel flexibility is required. However, there is a possibility that some parts of the military or the Coast Guard (a military service within the DOT) could use fuels more compatible to the fuel cell in limited applications. 

In the United States and other parts of the world, both low-sulfur diesel fuel and high-sulfur diesel fuel are being refined. Because fuel sulfur level has been identified as the primary component of fuel emission particulates and acid rain, sulfur reduction has been mandated and implemented. 

Hydroprocessing is utilized to reduce fuel sulfur concentrations. Fuels classed as high-sulfur diesel typically contain up to 5000 ppm of sulfur. Fuels classed as low-sulfur diesel typically contain up to 500 ppm of sulfur. Ultra-low sulfur or sulfur-free fuels typically have sulfur values of 15 ppm or less. 

Since the introduction of low-sulfur diesel fuel, much study has been completed to determine the lubricity properties of this fuel. Comparison of low-sulfur diesel with high-sulfur diesel has clearly revealed that fuel sulfur has a dramatic impact on the ability of fuel to provide a higher level of lubricity performance. A comparison of the lubricity performance of a typical high-sulfur diesel low-sulfur diesel and low-aromatic, low-sulfur diesel is shown in FIGURE 5-3. 

FIGURE 5-3. Comparison of the Lubricity Performance of Typical High-Sulfur Diesel Low-Sulfur Diesel and Low-Aromatic, Low-Sulfur Diesel Fuel... 

How are corrosion rates measured and what rate is too high Corrosion rales are reported in mil/year. A mil is /looo of an inch. For example, a section of carbon steel piping handling 500 F high-sulfur diesel oil may corrode at a uniform rate of 10 mil/yr. If the pipe s wall thickness is A in. (250 mil), the average wall thickness would be reduced to Ve in. after 12 years of service. 

The present infrastructure fuel for heavy vehicles is high sulfur diesel (now -500 ppm sulfur by weight) but this may change to a nearly sulfur-free diesel as proposed by the EPA. Beginning June 1, 2006, refiners must produce a diesel containing a maximum of 15 ppm sulfur (3). The fuel for this sector could also be a gasoline if such a fuel cell system could compete. 

Heavy residue conversion is linked to the demand for high quality diesel motor fuel (aromatics content 10%, cetane number 55) as well as to the demand for production of light fuel-oil having very low sulfur, nitrogen and metal contents. 

Another Pseudomonas strain P. delafieldii R-8 was reported to remove 90.5% sulfur from highly desulfurized diesel oil [259], The biocatalyst achieved desulfurization via a pathway similar to the 4S pathway. The rate of desulfurization was reported to be 11.25 mmol sulfur/kg dcw/h, with the sulfur being reduced from 591 to 56 mg/L. This was achieved via two biocatalyst treatments lasting 20 hours each, although the biocatalyst was active only for first 6h in each treatment. Up to C4-DBTs were reported to be removed. Almost 100% of Q and C2 DBTs were removed and about 94% C3 DBTs and 97% C4 DBTs were removed. This strain of Pseudomonas thus appears to have a mechanism to uptake up to C4 DBTs through its cell membrane. 

McDermott has operated non-catalytic POX reformers as large as 35 kWe and catalytic autothermal reformers as large as 30 kWe, the latter on high-sulfur marine diesel. McDermott has over 1,000 hours experience utilizing a POX reactor and about 400 hours on the autothermal unit. The longest continuous run of the autothermal reformer has been 175 hours (30,31). 

Shell Gas B.V. constructed a 1987 mVd (12,500 bbl/d) F-T plant in Malaysia that started operations in 1994. The Shell Middle Distillate Synthesis (SMDS) process uses natural gas as the feedstock to fixed-bed reactors containing cobalt-based catalyst. The heavy hydrocarbons from the F-T reactors are converted to distillate fuels by hydrocracking and hydroisomerization. The quality of the products is very high, the diesel fuel having a cetane number in excess of 75 with no sulfur. 

If a diesel fuel is low in viscosity due to kerosene dilution or solvent dilution, its lubricity is probably poor. The possibility of wear of the high-pressure fuel injection pump parts will increase. The effect of kerosene dilution on the lubricity of a typical low sulfur diesel fuel is shown in FIGURE 5-2. 

Because of the low-sulfur, -nitrogen, and -aromatic content of Fischer-Tropsch fuels, there is renewed interest in these products. In two recent studies, Fischer-Tropsch diesel was evaluated and compared to an ultra-low sulfur California diesel and to a 49 cetane number, low-sulfur diesel. In the two studies, carbon monoxide, nitrogen oxide, hydrocarbon, particulate, and carbon dioxide emissions were reduced in vehicles fuels by Fischer-Tropsch diesel. The fuel economy, however, was also reduced. The low aromatic content and high concentration of waxlike hydrocarbons in Fischer-Tropsch diesel can lead to the need for special handling and treatment of the fuel to prevent gelling when used in cold-temperature conditions. 

It is in the field of middle distillates and fuel oils that sulfur may confront some refiners with major problems that will grow as the production of higher sulfur crudes increases. It may be worth while to consider in some detail the case of high speed Diesel oil, for which discussion about sulfur content is controversial. Curiously enough it is in the United States, where low-sulfur material has been in relatively plentiful supply, that... 

Time will show if there is need for desulfurization of high speed Diesel fuels. There is no doubt that many companies are actively studying desulfurization processes so as to be in a position to make the best choice. Of those for which published information is available for full scale operation, the most attractive seemed to be sulfur dioxide and furfural extraction, the latter having merit because it has successfully handled high sulfur catalytically cracked recycle stocks. The previously mentioned extraction process using anhydrous hydrogen fluoride also seems attractive because of the low treatment and high yield of refined product, but, until the results of commercial operation are fully known its merits cannot be established. 

Presently, there is an ample supply of low-sulfur crudes. The price spread between low- and high-sulfur crudes is also low. With these low-sulfur crudes, the present specifications for diesel fuels can be met by the developed countries that have imposed the new low-sulfur restrictions without straining the supply. However, as the competitive demand for these low-sulfur crudes increases in the future, their value will escalate and higher sulfur crude supplies will have to be considered even though processing will be much more difficult. 

However, high U.S. diesel fuel prices may put a spoke in marketing efforts. Adding insult to injury is the added costs of transitioning to low-sulfur diesel fuel and a higher federal excise tax (24.4 cents per... 

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