Hydrogen is a key component in petroleum-refining operations. It is consumed in a variety of hydrodesulfurization and hydrocracking operations. Hydrogen is a by-product from the catalytic reforming operations in the refinery, but typically it cannot supply all of the required hydrogen for the refinery. Hydrogen is a difficult commodity to store and transport, so it is usually more economical to manufacture on site. The most common technology used to produce hydrogen in a traditional refinery is the use of the steam methane reformer with feedstocks consisting of natural gas or other light hydrocarbons. The produced hydrogen is typically at a pressure of 200-400 psig, generally requiring compression before being fed to the consumer units.
Hydrodesulfurization units remove organic sulfur, nitrogen, and metal compounds from different petroleum fractions, and saturates olefins. These contaminants, if not removed, contribute to increased levels of air pollution and equipment corrosion and, in some cases, would cause difficulties in the further processing of the products. Hydrotreating is a catalytic hydrogenation process that decomposes the contaminants with a negligible effect on the boiling range of the feed, by processing the feedstock over a fixed catalyst bed in the presence of large amounts of hydrogen at a specific temperature and pressure. The decomposed contaminants can then be stripped out as a sour gas to be cleaned up and used as fuel.
The primary hydrotreating units in a traditional refinery are:
- Naphtha Hydrotreater – Processes straight run, condensate, and cracked naphthas to reduce sulfur dioxide emissions when burned, and to prevent catalyst poisoning in downstream octane improving units.
- Kerosene Hydrotreater – Removes sulfur and reduces aromatics to improve the product smoke point for jet fuel production.
- Diesel Hydrotreater – Removes sulfur and nitrogen compounds from various diesel feedstocks, to meet ultra-low sulfur diesel product specifications.
- Gas Oil Hydrotreater – Removes sulfur and nitrogen compounds from various heavier gas oil feedstocks, primarily to prepare the feed for units like FCCUs and hydrocrackers.
Hydrocracking units crack heavier petroleum fractions into more valuable, lower boiling range fuel products, such as naphtha, kerosene, and diesel. Associated with the cracking reactions is the addition of hydrogen to saturate the hydrocracked fuel compounds, reducing the aromatic content. The cracked products are virtually contaminant free, as the sulfur, nitrogen, oxygen, and unsaturates are almost completely converted, making them excellent blending components.