Although distillation is normally generally known as the first process in petroleum refineries, in many instances, desalting should happen before distillation (Figure 3.1). Salt dissolved in water (brine) enters the crude stream as a contaminant throughout the manufacturing or transportation of oil to refineries. If salt is just not removed from crude oil, severe damage can result, especially within the heater tubes, on account of corrosion attributable to the presence of Cl. Salt in crude oil additionally causes discount in heat switch rates in heat exchangers and furnaces.
The three stages of desalting are:
1. adding dilution water to crude;
2. mixing dilution water with crude by a mixer;
Three. dehydration of crude in a settling tank to separate crude and sediment and water (S&W).
Desalting could be carried out in a single-stage or two-stage items. Amount of water wash and temperature of the mixing course of rely mainly on the crude API gravity [2].
Distillation separates hydrocarbon compounds into distillate fractions based mostly on their boiling factors or volatility. Extra volatile compounds (with low boiling points) tend to vaporize extra readily than heavy compounds, and this varieties the idea of separation by means of distillation. In a distillation column, mild parts are removed from the highest of the column, and the heavier part of the mixture appears in the bottom. For a crude that could be a mixture of hundreds of hydrocarbons, some very mild compounds corresponding to ethane and propane solely seem in the top product, while extremely heavy and non-unstable compounds reminiscent of asphalts only seem in the underside. Figure 2 exhibits a simple diagram of atmospheric and vacuum distillation units and the fractional separation of the crude oil into totally different boiling fractions with the indicated boiling ranges. The lightest compounds present in crude oil come out from the top of the distillation column (known as overhead distillate, or full-vary naphtha) and are despatched to the light Ends Unit (LEU) for additional separation into LPG and naphtha, as mentioned later. The side streams separated within the atmospheric distillation column give fractions that include the “straight-runproducts known as kerosene, and gentle and heavy gas oils. The residue from the atmospheric distillation column generates two aspect streams, gentle and heavy vacuum gas oils, and vacuum residue from the bottom. All of these distillation products are subjected to subsequent processing to produce light and middle distillate fuels and non-gas products, as described in the following sections starting with LEU.
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