Refinery

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A refinery is a facility that uses a series of chemical processes to turn raw materials into valuable products. There are many types of refineries.

Oil refineries use many steps to turn crude oil into fuels and other finished products. A schematic flow shows how raw oil moves through different processes to end products. Real refineries vary, and they also include utilities, storage tanks, and power systems that aren’t shown in simple diagrams.

Natural gas processing plants also convert raw natural gas into pipeline gas and byproducts such as sulfur, ethane, and natural gas liquids like propane, butanes, and natural gasoline.

Sugar refining starts with extracting sugar from sugarcane or beets, with sugarcane being the focus here. The process happens in two stages.

Stage 1: Milling and juice treatment
- Cane is washed, chopped, shredded, then crushed to extract juice containing about 10–15% sucrose.
- The juice is mixed with lime to raise the pH to about 7 and remove impurities.
- Impurities settle out, and the juice is concentrated in evaporators to a syrup around 60% sucrose.
- The syrup is further concentrated under vacuum until it becomes supersaturated and crystals begin to form.
- Crystals are separated from the liquid by centrifuging, producing raw sugar that is yellow to brown in color.

Stage 2: Purification and whitening (done in many regions)
- Raw sugar can be purified further by crystallization to increase purity.
- Sulfur dioxide may be bubbled through the juice after crystallization to prevent color formation and produce a whiter sugar (often called mill white or plantation white).
- The fibrous residue left after crushing, called bagasse, can be burned for energy to power the mill. Excess bagasse can be used as animal feed or for other products, like paper, or to generate electricity.

In many industrial regions, the process continues to produce very white sugar, with purity above 99%, through additional purification steps such as fractional crystallization.