What are the key differences in the operational parameters and product yields between processing a light sweet crude versus a heavy sour crude in an atmospheric distillation unit?

Processing a light sweet crude versus a heavy sour crude in an atmospheric distillation unit involves significant differences in operational parameters and product yields. A light crude oil has a high API gravity (above 31.1°), indicating it is less dense and flows more easily, while a heavy crude oil has a low API gravity (below 31.1°), meaning it is denser and more viscous. A sweet crude oil has a low sulfur content (typically less than 0.5%), whereas a sour crude oil has a high sulfur content (greater than 0.5%). When processing a light sweet crude, the atmospheric distillation unit generally requires lower furnace outlet temperatures because light crudes vaporize more readily. This results in lower energy consumption. Also, the product yields are higher for lighter fractions like naphtha and gasoline, and lower for heavier fractions like gas oil and residue. Since the sulfur content is low, corrosion concerns and the need for extensive desulfurization are reduced, leading to lower operational costs. In contrast, processing a heavy sour crude requires higher furnace outlet temperatures to vaporize the heavier hydrocarbons, leading to higher energy consumption. The product yields favor heavier fractions like vacuum gas oil and residue, and the yields of lighter fractions are lower. Due to the high sulfur content, there's a greater risk of corrosion throughout the distillation unit, requiring the use of corrosion inhibitors and more frequent inspections. The products derived from heavy sour crudes require extensive desulfurization in downstream units to meet product specifications and environmental regulations. Therefore, additional processing steps and equipment are needed, increasing both capital and operating costs. For example, processing a light sweet crude like West Texas Intermediate (WTI) yields a higher percentage of gasoline with minimal sulfur, whereas processing a heavy sour crude like Maya results in a lower gasoline yield and requires significant desulfurization due to its high sulfur content. In summary, the selection of operational parameters and the expected product yields in an atmospheric distillation unit are heavily influenced by the API gravity and sulfur content of the crude oil being processed.