Here's why:
* Purpose of Stripping Steam: Stripping steam is primarily used in the bottom section of a distillation column, specifically to remove any trapped lighter components that might be dissolved in the heavier, bottom product (like residuum). This ensures a cleaner, more valuable heavier product.
* Initial Crude Distillation: During the initial heating and separation of crude oil, the goal is to separate components based on their boiling points. The heavier components (residuum) are left behind in the bottom of the column, while lighter fractions (like gasoline, kerosene, etc.) vaporize and are collected higher up. Stripping steam isn't needed in this stage.
* Why it's not used:
* Unnecessary: The initial stages of distillation already separate components effectively based on their boiling points.
* Potential issues: Introducing steam at the bottom of the column during initial distillation could:
* Dilute the heavier fraction: This would affect the quality and yield of the bottom product.
* Increase energy consumption: Heating and vaporizing steam requires additional energy.
* Create safety concerns: Steam can react with some components in crude oil, potentially leading to unwanted byproducts.
In summary: Stripping steam is a valuable tool in the later stages of distillation to ensure high-quality heavier products but is not necessary during the initial separation of crude oil into its various fractions.
