Propylene/ethylene cascaded systems

The following information was used in olefin plant case studies to determine if the ethylene/propylene cascaded refrigeration systems had enough horsepower for various plant operations. The propylene was condensed against cooling water at 110°F and the ethylene was condensed against propylene at -20°F. For comparison, the horsepower requirements for each refrigerant alone are also shown. 

C4 and heavier byproducts are further separated in a sequence of distillation steps. Ethane and propane are typically recycled to pyrolysis. Refrigeration is typically supplied by a cascade ethylene/propylene refrigeration system. 

Heat Pumps. Because of added capital and complexity, heat pumps are rarely economical, although they were formerly commonly used in ethylene/ethane and propylene/propane spHtters. Generally, the former spHtters are integrated into the refrigeration system the latter are driven by low level waste heat, cascading to cooling water. 

Figure 8.26. A cascade refrigeration system employing ethylene and propylene for condensing the overhead of a demethanizer at — 145°F. The diagram is somewhat simplified.

Gas expansion (heat recovery) and external cascade using ethylene and propylene systems supply refrigeration. The main features of Tech-nip s patented technology are ... 

The methyl-acetylene and propadiene in the C3 cut are hydrogenated to propylene in a liquid-phase reactor. Polymer-grade propylene is separated from propane in a C3- splitter. The residual propane is either recycled for further cracking, or exported. C4s and hght gasoline are separated in a debutanizer. Gas expansion (heat recovery) and external cascade using ethylene and propylene systems supply refrigeration. 

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