Abstract.

The Mexican refining industry is facing the challenge of producing ultra-clean fuels, while processing increasingly proportions of heavy and sour crude oil. Of particular relevance in the strategies devised for optimising the overall domestic petroleum industry, are the actions for assuring the supply of low sulphur diesel within a schedule that considers different stages for achieving reductions from 500 to 300 ppm in the near future, to 50 ppm for the year 2006. Other specifications considered are cetane, aromatics, density and distillation points.

The Mexican Refining System includes 6 refineries with a total processing of 8,140.6 m3/h. Diesel feedstock is mainly constituted by atmospheric gasoil; all streams are hydrotreated in 14 units operating in average at 52.6 × 105 N/m2 g. that produce diesel fuel with less than 500 ppm sulphur. Future streams to be incorporated, resulting from ongoing projects, include cracked products from coking and FCC plants. Additionally the refinery reconfiguration in progress will permit the processing of a higher proportion of heavy crude oil, representing a movement from 2.2% to 2.6% sulphur in the crude blend.

The reported strategies in this paper are based on a formal mathematical model and an optimisation exercise, considering operating condition adjustments, catalyst replacement, revamp and new installations. Technology projects for process and catalyst development were considered as scenarios for the decision taking process.

Introduction

The environmental legislation that affects fuel specifications vary from country to country and even (Diesel specification in the same country may be different for particular regions or jurisdictions. In any case, the overall scenarios). trend is towards a severe reduction of sulphur content, with limits that will surely evolve in response to the combination of the economies and environmental problems of each region and the progress in process and catalyst technologies. In particular for diesel, an ultra-low sulphur product is foreseen, looking for a drastic reduction of SO2 emissions and the possibility of applying advanced catalytic converter technologies for NOx reduction in the exhaust gases. There are some other diesel specifications which future is more difficult to predict.

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OPTIMISATION OF THE MEXICAN REFINING SYSTEM FOR LOW SULPHUR DIESEL PRODUCTION

Region USA European Union Sweden Mexico EPA California (1) Year 1994 2006 1993 2006 2000 2005 1991 2000 2006 Sp. gr. min. 0.83 0.83 0.8 Sp. gr. max. 0.876 0.876 0.86 0.86 0.845 0.825 - 0.82 0.85 0.845 Sulphur, ppm max 500 15 500 15 350 50 10 500 50 Cetane Index min. 40 40 50 Cetane Number min. 48 48 51 54 - 58 48 48 Aromat, vol% max. 35 35 10 10 5 30 20 PNA, wt. max. 1.4 1.4 11 1-6 0.02 vol. 11 5 T90, K max. 611.15

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