美国焦化文章.pdfVIP

Refining Overview - Part 3 Processing Chapter 22 Delayed Coking CHAPTER 22 DELAYED COKING OF THE VACUUM RESIDUUM The Essence of Delayed Coking The purpose of Delayed Coking is to process heavy residuum to produce distillates (naphtha and gas oils) that may be catalytically upgraded. Upgrading is by hydrotreating, catalytic cracking or hydrocracking. Delayed coking is especially attractive for heavy residuum that are not suitable for catalytic processes due to large concentrations of resins, asphaltenes, and heteroatom compounds (sulfur, nitrogen, oxygen, metals). Metals, sulfur and other compounds that can poison downstream process catalysts are generally eliminated from the distillates, along with carbon, in the form of coke that may be sold for fuel and other purposes. The Development of Coking Coking evolved from the Dubbs cracker with its tubes and provision for soaking time. Coking received a stimulus when the railroads shifted from steam locomotives to diesel locomotives after World War II causing the demand for heavy fuel oil to sharply decline. Coking offered a method to increase distillate production and minimizes heavy fuel oil. Delayed Coking is one of several resid conversion processes that minimize the yields of heavy fuel oils. Between 1950 and 1970 coking capacity increased five fold, more than twice the rate of increase in crude distillation capacity. The increase in heavy high sulfur crude, together with the decrease in fuel oil, accelerated the use of coking. In 1998, delayed coking capacity amounts to some 12% of crude capacity or 27% of vacuum distillation capacity. Coking capacity is measured in terms of bo