To produce polymer-grade ethylene and propylene by thermal cracking of hydrocarbon fractions — from ethane through naphtha up to hydrocracker residue. Byproducts are a butadiene-rich C4 stream, a C6 – C8 gasoline stream rich in aromatics and fuel oil.
Fresh feedstock and recycle streams are preheated and cracked in the presence of dilution steam in highly selective PyroCrack furnaces (1). PyroCrack furnaces are optimized with respect to residence time, temperature and pressure profiles for the actual feedstock and the required feedstock flexibility, thus achieving the highest olefin yields. Furnace effluent is cooled in transfer line exchangers (2), generating HP steam, and by direct quenching with oil for liquid feedstocks.
The cracked gas stream is cooled and purified in the primary fractionator (3) and quench water tower (5). Waste heat is recovered by a circulating oil cycle, generating dilution steam (4) and by a water cycle (5) to provide heat to reboilers and process heaters. The cracked gas from the quench tower is compressed (6) in a 4- or 5-stage compressor and dried in gas and liquid adsorbers (8). CO2 and H2S are removed in a caustic-wash system located before the final compressor stage.
The compressed cracked gas is further cooled (9) and fed to the recovery section: front-end deethanizer (10), isothermal front-end C2 hydrogenation (11), cold train (12), demethanizer (13) and the heatpumped low-pressure ethylene fractionatior (14), which is integrated with the ethylene refrigeration cycle. This well-proven Linde process is highly optimized, resulting in high flexibility, easy operation, low energy consumption, low investment costs and long intervals between major turnarounds (typically five years).
The C3 from the deethanizer bottoms (10) is depropanized (15), hydrogenated (16) to remove methyl acetylene and propadiene (16) and fractionated to recover polymer grade propylene. C4 components are separated from heavier components in the debutanizer (18) to recover a C4 product and a C5 stream. The C5, together with the hydrocarbon condensates from the hot section, forms an aromatic rich gasoline product.
Licensor: Linde AG