Raschig rings are cylinders used to increase efficiency in gas, oil and chemical refinery towers. They were invented by Friedrich Raschig in 1880 and revolutionized the chemical industry. The rings increase surface area for chemical reactions and are made of ceramic, metal or plastic. They are randomly packed into the tower to create thousands of channels for reactions. Manufacturers provide tables showing packing characteristics for various ring sizes. Raschig rings are still in widespread use due to their simple design and reasonable price compared to other designs.
Raschig rings are cylinders made of ceramic, metal or plastic and are used to increase efficiency in gas, oil and chemical refinery towers. The rings are randomly packed into the tower to increase the surface area available for chemical reactions. They are typically shaped like hollow cylinders, with a diameter equal to the length of the cylinder.
Friedrich Raschig invented rings in 1880 but didn’t patent them until 1910. He also invented or perfected several key processes for making various organic chemicals. Lui Raschig’s rings would revolutionize the chemical industry, because packaging greatly improved the efficiency of existing manufacturing processes. Before his invention, early chemists filled their tanks with broken glass bottles, pottery and even rocks to gain surface area.
Surface area for chemical processes is important, because without adequate mixing of gases and liquids, very little reaction will occur. If gas is bubbled into a tank of liquid, some mixing may occur, but a reaction can occur only where the gas and liquid meet, resulting in low efficiency. Horizontal plates with holes can be installed in a vertical tower, with liquid flowing from top to bottom and gas from bottom to top. The tower trays will help, but the reaction efficiency is only partially improved.
Filling a tower with randomly placed Raschig rings creates a very large surface area for reactions. This occurs because the liquid will move in the thousands of channels formed by the rings, coating the inner and outer surfaces and eventually flowing down. The gas entering from the bottom will flow through the same paths formed by the rings, and will have time to contact and react with the liquid.
There are several ring materials available, the first of which is a ceramic or fired pottery material. The ceramics were resistant to high temperatures, but were brittle and could break easily during tower loading or if a pressure event caused the packed ceramic rings to rise and fall. In the 20th century, manufacturers developed Raschig rings made from metal, plastic, and even carbon graphite for high-temperature applications.
Manufacturers provide tables showing packing characteristics for various ring sizes. Raschig rings contain an average surface area for a given tower volume, and the tables show these values for different ring diameters and thicknesses. If weight is an issue, the loaded ring weight can be determined from the table and tower volume.
Raschig rings are considered to be the first generation of engineered tower gaskets and, due to a relatively simple design, were still in widespread use into the 21st century. Other packing designs were developed in the 20th century, including shapes such as saddles, coil springs, and cylinders with many holes or perforations. These forms were all attempts to improve reaction times or reduce weight, and were useful for some types of chemical processes. Despite these improvements, a simple Raschig ring design provided excellent reaction efficiency at a reasonable price compared to more exotic designs.
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