Ethylene compression plant

Figure 31. Example of ethylene compression and reaction plant.

In the LDPE autoclave process, the general process design (e.g., ethylene compression, high and low pressure product separation and ethylene recycling) is very similar to the LDPE tubular process. Instead of the jacketed tube reactor, however, the autoclave process employs a high-pressure stirred tank reactor. The reactor is designed to allow a residence time of 30-60 s (typical reactor volumes are around 1 m for large plants). The autoclave is usually operated in an adiabatic manner the reaction heat is removed by the fresh ethylene... 

Ethylene Stripping. The acetylene absorber bottom product is routed to the ethylene stripper, which operates at low pressure. In the bottom part of this tower the loaded solvent is stripped by heat input according to the purity specifications of the acetylene product. A lean DMF fraction is routed to the top of the upper part for selective absorption of acetylene. This feature reduces the acetylene content in the recycle gas to its minimum (typically 1%). The overhead gas fraction is recycled to the cracked gas compression of the olefin plant for the recovery of the ethylene. 

Most ethylene plants operate continuously with the expander functioning at or near design point. However, by using inlet guide vanes, the expander can still provide optimum performance at off-design conditions. Also, the expansion process generates power, which is used by the compressor. The ethylene enters the expanders at approximately 26 bar (377 psia) and exits at approximately 6 bar (87 psia). The expanders generate over 2,000 hp for gas compression. 

The Sabic acetic acid technology is characterized by a novel catalyst (a Mo-V-Nb mixed oxide [335]) and a novel oxidation reactor design, which is different from the conventional methanol-based technology. In the process ethane is mixed with oxygen and compressed, then passed over the catalyst to produce acetic acid and some ethylene, which is then separated and purified for use as a feedstock in other associated plants. 

As the plant name implies, the primary product of interest is ethylene however, it is not the only compound produced. A large number of products are produced, ranging from methane to gasoline. When produced, the products must be cooled and the gaseous components compressed to a liquid for separation. After the furnace, the rest of the plant is devoted to this operation. 

Figure 12. Ethylene plant schematic showing the furnace, quench section and compression section.

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