Abstract
There is a worldwide trend towards the production of cleaner gasoline and diesel. Legislation is placing increasingly tight limits on the sulphur content of fuels. There is also a worldwide trend towards processing heavier crude oils This requires increased levels of hydroprocessing, which places increased demands on hydrogen supply in refineries. At the same time, reduction in the aromatics content of fuels in constraining catalytic reformer operation and removing some of the traditional sources of hydrogen available to refineries. In addition, there is also a worldwide trend towards processing heavier crude oils that contain more long chain hydrocarbons and organic sulphur. To obtain the best value from these heavy crudes, refiners must be able to convert heavy end compounds to lighter fractions that can be blended with gasoline or diesel. All these trends point in the same direction of placing increasing demands on the hydrogen systems of refineries. Meeting the increased demands for hydrogen can require significant investment in, for example, steam reformers and compression equipment. Yet, most refinery hydrogen systems are inefficient and have significant room for improvement. By modifying the hydrogen network, perhaps with recovery of hydrogen from tail gas, refiners can often satisfy the increased demands for hydrogen with much significantly reduced operating cost and investment. In recent years, systematic methods for the analysis of hydrogen systems have been developed and are now practiced worldwide. The assessment of hydrogen processes can be presented in a simple, graphical manner, which gives the engineer insight into process design, sensitivity analysis and operations planning. Targets can be set for hydrogen recovery and hydrogen plant production. Targets also give insights into the effective use of hydrogen purification units. However, these simple methods that are now widely practiced neglect many issues that can be important in the study of the hydrogen network. Importantly, impurities in the hydrogen are all lumped together as methane. However, small amounts of certain impurities can prevent what would otherwise be very useful recovery. In addition, pressure constraints need to be considered explicitly. These cannot be included in the targeting methods. Other issues that need to be considered are recycle of hydrogen to steam reformers. Recent developments in the field have allowed systematic ways to address these complexities. This paper will review the background and recent developments and present an industrial case study.
